Stratigraphy, geochronology, and geochemistry of the Laramide magmatic arc in north-central Sonora, Mexico Carlos M. González-León1, Luigi Solari2, Jesús Solé3, Mihai N. Ducea4, Timothy F. Lawton5, Juan Pablo Bernal2, Elizard González Becuar6, Floyd Gray7, Margarita López Martínez8, and Rufino Lozano Santacruz3 1
Instituto de Geología, Estación Regional del Noroeste, Universidad Nacional Autónoma de México, Apartado Postal 1039, Hermosillo, Sonora, México 83000 2 Centro de Geociencias, Universidad Nacional Autónoma de México, Campus Juriquilla, Querétaro, QRO, México 76001 3 Instituto de Geología, Ciudad Universitaria, Universidad Nacional Autónoma de México, México, Distrito Federal 04510 4 Geosciences Department, University of Arizona, Tucson, Arizona 85721, USA 5 Department of Geological Sciences, New Mexico State University, Las Cruces, New Mexico 88003, USA 6 Departamento de Geología, Universidad de Sonora, Hermosillo, Sonora, México 83000 7 U.S. Geological Survey, Geology–Ecosystem Analysis, 520 North Park Avenue, Suite 355, Tucson, Arizona 85719, USA 8 Departamento de Geología, Centro de Investigación Científica y de Educación Superior de Ensenada (CICESE), Km 107 Carretera Ensenada-Tijuana No. 3918, 22860 Ensenada, Baja California, México ABSTRACT The Laramide magmatic arc in the Arizpe-Mazocahui quadrangle of northcentral Sonora, Mexico, is composed of volcanic rocks assigned to the Tarahumara Formation and several granitic plutons that intrude it. The arc was built over juxtaposed crustal basements of the Caborca and Mazatzal provinces. A basal conglomerate of the >4-km-thick Tarahumara Formation overlies deformed Proterozoic igneous rocks and Neoproterozoic to Early Cretaceous strata, thus constraining the age of a contractional tectonic event that occurred between Cenomanian and early Campanian time. The lower part of the Tarahumara Formation is composed of rhyolitic ignimbrite and ash-fall tuffs, andesite flows, and interbedded volcaniclastic strata, and its upper part consists of rhyolitic to dacitic ignimbrites, ash-fall tuffs, and volcaniclastic rocks. The Tarahumara Formation shows marked lateral facies change within the study area, and further to the north it grades into the coeval fluvial and lacustrine Cabullona Group. The age of the Tarahumara Formation is between ca. 79 and 59 Ma; the monzonitic to granitic plutons have ages of ca. 71–50 Ma. The informally named El Babizo and Huépac granites, La Aurora and La Alamedita tonalities, and the Puerta del Sol granodiorite compose the El Jaralito batholith in the southern part of the area. Major and trace element composition of the Laramide igneous rocks shows calc-alkaline
differentiation trends typical of continental magmatic arcs, and the isotope geochemistry indicates strong contribution from a mature continental crust. Initial 87Sr/ 86Sr values range from 0.70589 to 0.71369, and εNd values range from –6.2 to –13.6, except for the El Gueriguito quartz monzonite value, –0.5. The Nd, Sr, and Pb isotopic values of the studied Laramide rocks permit comparison with the previously defined Laramide isotopic provinces of Sonora and Arizona. The El Gueriguito pluton and Bella Esperanza granodiorite in the northeastern part of the study area along with plutons and mineralization of neighboring northern Sonora have isotopic values that correspond with those of the southeastern Arizona province formed over the Mazatzal basement (Lang and Titley, 1998; Bouse et al., 1999). Isotopic values of the other Laramide rocks throughout the study area are similar to values of provinces A and B of Sonora (Housh and McDowell, 2005) and to those of the Laramide Pb boundary zone of western Arizona, while the Rancho Vaquería and La Cubana plutons in the northernmost part of the area have the isotopic composition of the Proterozoic Mojave province of the southwestern United States. These data permit us to infer that a covered crustal boundary, between the Caborca block with a basement of the Mojave or boundary zone and the Mazatzal province, crosses through the northeastern part of the area. The boundary may be placed between outcrops of the El Gueriguito and Rancho Vaquería plutons, probably following a reactivated Cretaceous
thrust fault located north of the hypothesized Mojave-Sonora megashear, proposed to cross through the central part of the area. INTRODUCTION The Late Cretaceous–early Cenozoic Laramide magmatic arc of Sonora, Mexico (Damon et al., 1983a, 1983b; McDowell et al., 2001), is composed of a thick and geographically extensive volcanic succession and nearly contemporaneous, mostly granitic, plutons that are part of the Sonoran batholith (Damon et al., 1983a) (Fig. 1). These rocks formed in a continental, Andean-type magmatic arc related to subduction of the Farallon plate beneath North America during Late Cretaceous and early Cenozoic time (Coney and Reynolds, 1977; Dickinson, 1981, 1989; Damon et al., 1983a; Engebretsen et al., 1985; Stock and Molnar, 1988). Based mostly on their own data set of predominantly K-Ar ages of plutonic rocks, Damon et al. (1983a) proposed that the Laramide arc in Sonora spanned 90–40 Ma, a range mostly accepted by others and broadly supported by subsequent geochronologic studies (Anderson and Silver, 1977; Anderson et al., 1980; Valencia-Moreno et al., 2001, 2003, 2006; McDowell et al., 2001; Housh and McDowell, 2005; Pérez-Segura et al., 2009; Roldán-Quintana et al., 2009). In contrast, the study of the arc’s cogenetic volcanic succession has long been neglected despite extensive exposures, although some ages were published from northern and central Sonora (Supplemental Table 11). The name Mesa formation (Valentine,
Geosphere; December 2011; v. 7; no. 6; p. 1392–1418; doi: 10.1130/GES00679.1; 14 figures; 2 tables; 5 supplemental tables.
1392
For permission to copy, contact
[email protected] © 2011 Geological Society of America
Laramide magmatic arc in northern Sonora
109°00′
112°00′
Sonoita
AR IZ SO NO ONA RA Nogales
+
Puerto Penasco Santa Ana
Caborca
A
G ulf
Nacozari
C Cucurpe
CABORCA BLOCK
31° 00′
MAZATZAL PROVINCE
Bacoachi B
+
Arizpe
D
Study quadrangle Figure 2 Moctezuma
Mazocáhui
Ures
of
S ierra Los Ajos La Lámina Cerro Prieto El Crestón Trace of MojaveSonora megashear
Agua Prieta
Cananea
31°00′ 114°00′
A B C D
N
HERMOSILLO
Sahuaripa
Cabullona Group
Mazatán
Laramide volcanic rocks (Tarahumara Formation)
Tecoripa
Yécora
Laramide plutonic rocks (Sonoran batholith of Damon et al., 1983a) 28° 00′
al if
OR A
or
SO N
Guaymas
C
U S A
ni
C. Obregon
a
MEXICO
Navojoa
27°00′ 111°00′
100 km
Figure 1. Map outcrop distribution of plutonic and volcanic rocks of the Laramide magmatic arc in Sonora. The distribution of outcrops of the Late Cretaceous Cabullona Group, localities mentioned in the text, and inset map for location of Figure 2 are shown. The boundary between the Mazatzal province and Caborca blocks is indicated by the trace of the hypothetical Mojave-Sonora megashear as presented by Anderson and Silver (2005, their fig. 4).
1936) was first assigned to outcrops of this succession near the town of Cananea (Fig. 1), where it consists of a basal conglomerate and overlying bedded tuffs, andesite flows, agglomerates, and subordinate rhyolite flows >1600 m thick. Wilson and Rocha (1949) applied the term Tarahumara Formation to the Laramide volcanic succession and it became a commonly used name for extensive volcanic and volcani1 Supplemental Table 1. Bibliographic compilation of geochronologic ages of Laramide volcanic and plutonic rocks of Sonora between isochrones of 70 and 50 Ma, as indicated in Figure 14. Histogram of plutonic ages in Figure 13 was drawn with this information. If you are viewing the PDF of this paper or reading it offline, please visit http://dx.doi .org/10.1130/GES00679.S1 or the full-text article on www.gsapubs.org to view Supplemental Table 1.
clastic outcrops in Sonora; they described it as consisting of highly altered, aphanitic intermediate volcanic rocks unconformably overlying Triassic strata in its type section near the town of Tecoripa, in central Sonora (Fig. 1). From that locality, McDowell et al. (2001) reported an age range of 90–70 Ma for an ~2.5-km-thick rhyolitic, dacitic, andesitic, and volcaniclastic succession. Other studies of partial sections of these rocks in northern Sonora assigned local informal names, including Alcaparros formation and Arroyo Alcaparros andesitic rocks (GonzálezLeón et al., 2000) and El Tuli formation (Rodríguez-Castañeda, 1994). To avoid confusion and to provide uniformity in the terminology, we follow other authors in applying the formal, more commonly used name Tarahumara Forma-
Geosphere, December 2011
tion to this succession throughout its region of exposure (McDowell et al., 2001). In this paper we provide new constraints on the stratigraphy and geochronology of the Tarahumara volcanic succession and the petrology and geochronology of associated plutonic bodies that represent the Laramide magmatic arc within the Arizpe-Mazocahui area in northcentral Sonora (Fig. 1). The area is located in a position that is transitional between the classic localities of the Tarahumara Formation to the south, and the Mesa formation to the north. It includes the 15′ × 20′, 1:50,000 scale topographic quadrangles named Arizpe, Nacozari (part), Santa Ana (part), Banámichi, Agua Caliente, Aconchi, Cumpas, Baviácora, and El Rodeo (part) (Fig. 2), published by Instituto Nacional de Estadística, Geografía e Informática of the Mexican government. Our work is based on geologic mapping conducted at that scale and illustrated here by a generalized geologic map (Fig. 2). This cartography improves and in many instances corrects some of the previous geologic maps of the Arizpe, Banámichi, Baviácora, and Santa Ana quadrangles (González Gallegos et al., 2003; Quevedo León and Ramírez López, 2008; Servicios Geológicos y Cartográficos del Noroeste, S.A. de C.V., 1999; Corral Gastelum and Hernández Morales, 2008, respectively). Six measured stratigraphic columns and seven accompanying structural sections are included to illustrate the stratigraphic and tectonic relationships of the Laramide rocks with older and younger geologic units. The ages of the Laramide volcanic succession and the plutonic bodies are constrained by 28 U-Pb dates, one 40Ar/39Ar date, and 9 K/Ar dates, none of which have been reported previously. Another new 40Ar/39Ar date reported here helps to constrain the age of the younger unit of the basement over which the Laramide succession was deposited as well as the age of the younger tectonic event that deformed that basement in the region. We also dated detrital zircons from four sandstone units to constrain their maximum deposition ages. Two of these come from the Proterozoic basement and two others are from sandstone beds within the Laramide succession. The study also incorporates 35 whole rockgeochemical analyses and 12 isotope analyses of Sm/Nd, Rb/Sr, and Pb/Pb of the Laramide plutonic and volcanic rocks, and 2 from the Proterozoic plutons. All of the analyzed samples have age and stratigraphic control. The field and analytical data help to document the stratigraphic, tectonic, and temporal framework of the Laramide magmatic arc for this part of the Cordillera, and the new cartography
1393
González-León et al. Arizpe quadrangle
35
C
27
El Tuli
Aconchi quadrangle
R.Viejo 26
28
30
U/Pb age (detrital zircons) U/Pb age (igneous rocks) Ranch K-Ar age Mine Ar-Ar age Town
lt fau chi
20
30
38
6 35
Baviácora quadrangle
70 Ma 48 Ma 71 Ma
Bacachi
El Rodeo 15 quadrangle
Baviácora
24 15 31
35 39
35 33
22 27
G′
72 Ma 22 22 36
76 Ma 33
25
78.7 Ma
El Rodeo 16
Moctezuma
18
Arroyo Seco
42
31
31
65
57 Ma
55 Ma 29 Ma 23 Ma
d appe Unm ea ar
Cumobabi mine
56Ma
61 Ma
60 Ma 69 Ma
G
31
28 Ma 47 Ma 49 Ma
Strike and dip Normal fault
Mazocáhui
29°30′
12
42
F′
F
89
B′ Cross section
37
14 12
28
Cumpas
14
20
68.5 Ma
n Aco
batholith
58 Ma
Sierra
Proterozoic?-Paleozoic?strata - schist Proterozoic Las Víboras Group Santa Margarita granite (1.1 Ga) El Jacalón diorite (1.7 Ga)
29 36
27
Aconchi
Jaralito
Paleozoic strata
51 Ma
El
Tarahumara Formation Middle Cretaceous Cocóspera Fm Lower Cretaceous Bisbee Group Upper Jurassic Cucurpe Fm Middle Jurassic Lily formation
de Sierra hi Aconc
22
Cumpas quadrangle
a
Washington mine
30°00′
24
zum
12
El Pajarito
cte
8
18
Plutonic rocks Rhyolitic dome
20
24
Huépac
San Felipe mine
33
15 22
28 27 25
6
10
12
39
29
59 Ma
12
15
69 Ma
29
22
17
15
Mo
10
10 24
28
28 26
29
25
20
24
Río
LARAMIDE MAGMATIC ARC
73.8 Ma Santa Elena
Banámichi Río Sonora
20
Oligocene-Holocene volcanic, sedimentary rocks Oligocene rhyolitic domes Oligocene volcanic rocks
110°20′
35
74 Ma El Sa 25 fau ucito lt
Los Hoyos
27
10
o Os
38
26
23
36
El
DE
67.7 Ma
5
60
55
rra
El J
f.
E′
25
33 35
16 15
Los Toros
Sie
l cara
74.8
26
16 10
Sierra La Huerta
76 Ma 34 20 75 Ma 48
32
Agua 32 Caliente
19
70 Ma 38
12
53
34
26
12
u
B
C′
32
26
09 09
Sinoquipe
42
25
Range Front fault
B
75
23 45
3 58 Ma 34
38 11
Agua Caliente quadrangle
15 38
D′
32
57 Ma
15
25
Los Alisos fault
27
35
20
4 62 Ma
35 33 27 34
Banámichi quadrangle
45
9
39
28
S. La Cieneguita
76 Ma
10 22
El Rodeo fault
25
25
28
45 12
Sierra Las Palomas
18
24 19
23
73.8 Ma
Nacozari
Jesus Maria
28
Arizpe
27
33
12
A
33
Teguachi
22
47
18
Huepac 8 Rancho Viejo 9 Bella Esperanza 20 10 San Felipe porphyry 30 28 Santa Ana B′ 73 Ma quadrangle El 55 32
38
109°40′
35
30°30′N
Unmap ped are a
A′ Picacho de Arizpe 27 75.7 Ma
1
55.8 Ma 2 Ta hu ich fau op a lt
El Jaralito batholith
El Babizo
110°00′W
52.7 Ma
Nacozari quadrangle
riza Cob rra Sie
PLUTONS 1 La Cubana 2 Rancho Vaquería 3 El Gueriguito 4 Los Alisos 5 San Antonio 6 Las Cabecitas 7 Mazocahui Puerta del Sol La Alamedita La Aurora
7
49 Ma
20 km
Thrust fault Syncline
Figure 2. Geologic map of the study area that includes the 15′ × 20′ Arizpe, Nacozari, Banámichi, Santa Ana (part), Aconchi, Agua Caliente, Baviácora and El Rodeo quadrangles. Geology is simplified from our detailed geologic mapping (scale 1:50,000). Location and ages of all the dated samples are indicated. All 40Ar/ 39Ar and K-Ar ages were done on biotite.
1394
Geosphere, December 2011
Laramide magmatic arc in northern Sonora and isotope data place constraints on possible delimitations of the Caborca and Mazatzal crustal blocks.
concentrations were determined at the Isotopic Laboratory of the Geosciences Department of the University of Arizona following procedures reported in Appendix 4.
ANALYTICAL METHODS REGIONAL GEOLOGIC SETTING U-Pb ages by laser ablation–multicollector– inductively coupled plasma–mass spectrometry (LA-MC-ICP-MS) were determined at the Arizona Laser ChronCenter of the Geosciences Department of the University of Arizona (results are reported in Supplemental Table 22) and at Centro de Geociencias, Universidad Nacional Autónoma de México (UNAM) (Supplemental Table 33) (procedures are described in Appendices 1 and 2, respectively). K-Ar analyses on biotites from igneous rocks were conducted at the Instituto de Geología, UNAM. Procedures are described in Appendix 3 and results are in Supplemental Table 44. The 40Ar/39Ar dating was performed at the Geochronology Laboratory of the Departmento de Geología, Centro de Investigación Científica y de Educación Superior de Ensenada (CICESE), and procedures were described in González-León et al. (2010). A hornblende separate from sample 04ES-8 was analyzed by the resistance-furnace incremental-heating age spectrum method at the New Mexico Geochronology Research Laboratory. (Details of the method and overall operation of the laboratory are provided at http://www.ees.nmt.edu/Geol/labs/Argon_Lab /Methods/Methods.) Geochemical analyses for major and trace elements were done by X-ray fluorescence and with a SIEMENS SRS 3000 spectrometer in the Laboratorio Universitario de Geoquímica Isotópica, UNAM, and by high resolution ICP-MS at the Department of Geology, University of Wisconsin–Eau Claire, USA. Radiogenic isotopic and select trace element 2 Supplemental Table 2. U-Pb data of detrital zircon from sandstone and tuffaceous sandstone samples, and Laramide volcanic and plutonic rocks of the study area. Analyses were done at the Arizona Laser Chron Center of the University of Arizona by LAICP-MS method. If you are viewing the PDF of this paper or reading it offline, please visit http://dx.doi .org/10.1130/GES00679.S2 or the full-text article on www.gsapubs.org to view Supplemental Table 2. 3 Supplemental Table 3. U-Pb data for volcanic and plutonic rocks of the study area done at the Centro de Geociencias, Universidad Nacional Autónoma de México by the LA-ICP-MS method. If you are viewing the PDF of this paper or reading it offline, please visit http://dx.doi.org/10.1130/GES00679.S3 or the full-text article on www.gsapubs.org to view Supplemental Table 3. 4 Supplemental Table 4. K-Ar age data of dated samples of the study area. If you are viewing the PDF of this paper or reading it offline, please visit http:// dx.doi.org/10.1130/GES00679.S4 or the full-text article on www.gsapubs.org to view Supplemental Table 4.
The Proterozoic basement of Sonora was recognized as part of crustal southwestern North America by Damon et al. (1962) on the basis of geochronology data. Silver and Anderson (1974) noted that it could be divided into a northern block with ages between 1.7 and 1.6 Ga and a southern block with ages from 1.8 to 1.7 Ga that were later assigned to the North America (or Mazatzal) and Caborca terranes, respectively (Campa and Coney, 1983) (Fig. 1). However, the nature, age, and location of the crustal boundary are debatable. On one side, the Caborca block is interpreted as a piece of crustal southwestern USA translated to its present position by a major left-lateral fault assigned either to the Jurassic Mojave-Sonora megashear (Silver and Anderson, 1974; Anderson and Silver, 2005) (Fig. 1) or to the Permian–Triassic California-Coahuila transform fault (Dickinson and Lawton, 2001). On the contrary, Poole et al. (2005) argued that the Mojave basement and its Neoproterozoic sedimentary cover wrap around the Laurentian margin in the southwestern USA to continue southeast into the Caborca block, without major structural displacement. Similarly, Arvizu et al. (2009) depicted the Mojave and Mazatzal blocks in Sonora separated by a Nd isotope Yavapai crustal province. The Pinal Schist, the basement of the Mazatzal province, crops out in Sierra Los Ajos (Fig. 1) and nearby areas of northern Sonora, where it is dated as 1.69 Ga (Anderson and Silver, 2005) and 1.64 Ga (U-Pb, zircon) (Page et al., 2010). Proterozoic granites with ages near 1.4 Ga intrude the Pinal Schist (Anderson and Silver, 2005), and the nearest outcrop of this granite to the study area is in the town of Bacoachi (Fig. 1; our own observations). Other granites and gabbros that are assigned to the basement of the Caborca block because of their isotopic signatures and ages of ca. 1.7 Ga crop out in near localities of Cerro Prieto (Anderson and Silver, 2005), Rancho La Lámina (Amato et al., 2009), and El Crestón (Valenzuela-Navarro et al., 2005) (Fig. 1). Based on the occurrence of Caborcan Proterozoic granites in Rancho La Lámina, Amato et al. (2009) inferred that if present, the trace of the hypothetical MojaveSonora megashear might be located north of that locality (Fig. 1). Proterozoic, mostly clastic, strata assigned to the Las Víboras and El Aguila Groups by Stewart et al. (2002) crop out within a few kilometers to
Geosphere, December 2011
the west of the study area. These units exceed a combined thickness of 3.5 km and overlie the igneous basement of the Caborca block. Superjacent Paleozoic clastic and carbonate strata (Stewart et al., 1997, 1999) are >4 km thick. This Proterozoic–Paleozoic succession of the Caborca block is lithologically different from the Cambrian–Permian sedimentary succession that unconformably overlies the basement of the Mazatzal province and that correlates with and resembles the Paleozoic formations of southeastern Arizona (e.g., Hayes and Landis, 1965). The nearby outcrops of this Paleozoic succession occur in the town of Bacoachi (Stewart and Poole, 2002) and in the vicinity of Cananea, where the successtion is 1.2 km thick (GonzálezLeón, 1986; Page et al., 2010). Mesozoic rocks of the neighboring region to the north in Sonora include the Lower Jurassic Basomarí Formation (Legget et al., 2007) and the Middle Jurassic Rancho San Martín (Mauel, 2008), Elenita (Valentine, 1936; Wodzicki, 1994), and Lily (McAnulty, 1970, GonzálezLeón et al., 2009) Formations, and a few dated Middle Jurassic granites (Anderson et al., 2005). These formations make up a clastic and volcanic succession that was deposited within a continental magmatic arc that developed in northern Sonora (Riggs et al., 1993, Anderson et al., 2005). Marine strata of the Upper Jurassic Cucurpe Formation (Villaseñor et al., 2005; Mauel et al., 2011) overlie the Basomari and Rancho San Martín successions near the town of Cucurpe. The combined thickness of the Jurassic formations is at least 3.5 km, and they are unconformably overlain by strata of the Bisbee Group, which in this region is documented to be Early Cretaceous in age and ~3 km thick (Peryam, 2006; Peryam et al., 2011). A major Middle to Late Jurassic tectonic event of extensional deformation formed a rift basin, termed the Altar-Cucurpe Basin, where the Cucurpe Formation was deposited (Peryam, 2006; Mauel, 2008; Mauel et al., 2011). Alternatively, formation of this basin has been assigned to development of the left-lateral displacement of the Mojave-Sonora megashear (Anderson and Nourse, 2005; Anderson and Silver, 2005). A younger, contractional tectonic event affected the Bisbee Group and older strata during early Late Cretaceous time (Rangin, 1986). The age of the clastic continental succession of the Cocóspera Formation (Gilmont, 1978) deposited during this tectonic event (González-León et al., 2000) is constrained by a 40Ar/39Ar age of 93.3 ± 0.7 Ma (Fig. 3) obtained from an interbedded andesite in outcrops ~2 km northwest of the study area (Lawton et al., 2009). Following a period of uplift and erosion, deposition of the Laramide volcanic arc succession commenced.
1395
80
L# 55854: 04ES-8, Hornblende
40
1
0
0.1 120
0.01
965 B
110
93.3 ± 0.7 Ma (MSWD = 1.7)
100 90 1050 C
80
1080 D
1105 E
1125 F
1155 G
1200 H
70
1300 I
1700 J
Apparent age (Ma)
K/Ca
% Radiogenic
González-León et al.
60 A
Integrated age = 90.9 ± 0.7
50 0
10 20
30 40
50 60
70 80
90 100
39
Cumulative % Ark released Figure 3. 40Ar/39Ar age spectrum of hornblende separate of sample 04ES-8 from an andesite interbedded with conglomerate of the Cocóspera Formation. This sample was collected near Rancho San Antonio, ~2 km northwest of the study quadrangle (Universal Transverse Mercator locality 12R 562410E 3382580N). MSWD—mean square of weighted deviates.
Regionally, the Laramide magmatic arc of Sonora has been documented mostly through a large geochronology database and geochemical and isotopic studies of the plutonic rocks (Anderson and Silver, 1977; Anderson et al., 1980; Damon et al., 1983a, 1983b; Wodzicki, 1994; McDowell et al., 2001; Valencia-Moreno et al., 2001, 2003, 2006; Valencia et al., 2005; Roldán-Quintana et al., 2009; Pérez-Segura et al., 2009; Pérez-Segura and González-Partida, 2010), but far fewer data are available for the volcanic rocks (McDowell et al., 2001). Some ages are published for the Laramide volcanic rocks north of the study area, in the CananeaNacozari region (Wodzicki, 1994; Valencia et al., 2005; Cox et al., 2006; Page et al., 2010), and 6 40 Ar/39Ar ages between 73 and 66 Ma are listed in Supplemental Table 1 (see footnote 1). Based on Sr and Nd isotopic variations and trace element compositions, Laramide granites of northern and central Sonora with ages between 57 and 68 Ma were assigned to northern and central granites by Valencia-Moreno et al. (2001). On the basis of Sr, Nd, and Pb isotope geochemistry, other granites with ages between 59 and 67 Ma were considered as belonging to provinces A
1396
and B by Housh and McDowell (2005), who also included isotopic characteristics of Oligocene and Miocene volcanic rocks to define their provinces. Geographically, the Laramide granites of provinces A and B roughly occupy the same region as the northern and central granites of Valencia-Moreno et al. (2001), while rocks of the study area are within the geographic domains of the northern granites and province A. Younger regional events consist of Late Oligocene–Miocene magmatism, core complex formation, and basin-fill continental sedimentation of the Báucarit Formation that occurred associated with Basin and Range extensional deformation. Basin and Range deformation structurally dismembered the Laramide arc and older basement (Nourse et al., 1994; Wong and Gans, 2008; González-León et al., 2010; Wong et al., 2010). GEOLOGY OF THE STUDY AREA AND PREVIOUS STUDIES Within the study area the older rocks are El Jacalón diorite and the Santa Margarita granite (Rodríguez-Castañeda, 1994) that crop
Geosphere, December 2011
out in the Santa Ana quadrangle (Fig. 2). The diorite and granite have U-Pb (zircon) ages of 1702 Ma and 1104 Ma, respectively (Anderson and Silver, 2005). A gneissic zone developed in the El Jacalón diorite is spatially associated with the El Jucaral normal fault of post–Early Cretaceous age (Fig. 2) and is not a separate Proterozoic lithostratigraphic unit, as previously interpreted (the El Alamito unit of RodríguezCastañeda, 1994). A thick Proterozoic succession (>1 km thick) of mostly sandstone that locally overlies the igneous basement crops out in the Banámichi and Santa Ana quadrangles. It was named the Los Changos orthoquarzite, of supposed Paleozoic age by Rodríguez-Castañeda (1994) and later reassigned to the Proterozoic Las Víboras Group by Stewart et al. (2002) (Fig. 2). Detrital zircons from a sample of the middle part of this succession in the Banámichi quadrangle yielded U-Pb peak ages at 1.2, 1.47, 1.67, and 1.87 Ga (Figs. 2 and 4A) (Plascencia Corrales, 2008), similar to a sample collected from this succession that unconformably overlies the El Jacalón granodiorite in the Santa Ana quadrangle (Figs. 2 and 4B). Isolated outcrops of schist, recrystallized limestone, and quartz-rich sandstone that occur as roof pendants in the Laramide plutons in the Sierra El Jaralito may be Proterozoic and/or Paleozoic in age (Peabody, 1979, in RoldánQuintana, 1989; Mead et al., 1988) (Fig. 2). Cambrian to Permian formations in the Nacozari and Agua Caliente quadrangles (Fig. 2) are typical of Paleozoic strata that overlie the Mazatzal basement in northeastern Sonora. The Mesozoic rocks in the study area include incomplete sedimentary successions of the Lily (González-León et al., 2009) and Cucurpe Formations of Jurassic age, the Morita, Mural and Cintura Formations of the Early Cretaceous Bisbee Group, and the previously undated Cocóspera Formation (Fig. 2). Assignment of a Jurassic age by Rodríguez-Castañeda (1994) and Corral Gastélum and Hernández Morales (2008) to widespread outcrops of the Bisbee Group and the Tarahumara Formation in the Santa Ana quadrangle are herein corrected on the basis of our geochronology. However, most of the area is occupied by outcrops of the volcanic and plutonic rocks of the Laramide magmatic arc; volcanic rocks, sedimentary strata, and a few rhyolitic domes of Oligocene–Miocene age; and by younger alluvial deposits (Fig. 2). Previously published geochronologic information of the Laramide volcanic rocks in the study area include a U-Pb (zircon) age of 76 Ma from the Santa Ana quadrangle (McDowell et al., 2001), a 40Ar/39Ar (biotite) age of 58.67 ± 0.17 Ma from the Arizpe quadrangle (González-
Laramide magmatic arc in northern Sonora data-point error ellipses are 2σ
A
data-point error ellipses are 2σ
0.65
11-22-07-1
B
3-25-09-4
2200
0.4
0.55
2600 0.45
1800
2200
Pb/ 238U
14
~1670 Ma
Number
206
0.2
1000
Relative probability
10
8
~1470 Ma 6
~1218 Ma
1800
~1460 Ma 4
1400
0.25
0.15
~1870 Ma
2
0 0
2
1000
1500
Age, Ma
2000
0
2500
6
Pb/235U
8
4
1500
2000
2500
3000
0.8
12
Pb/235U
0.05
D
11-21-07-1
82
1000
8
207
data-point error ellipses are 2σ
0.0126
500
Age, Ma
0.05 0
data-point error ellipses are 2
0.0130
C
500
4 207
~1870 Ma
1
0
0.1 0
~1670 Ma
3
2
1000
~1260 Ma
4
5
Relative probability
1400
6
0.35
206
12
Number
Pb/ 238U
0.3
12-5-08-3
300 260
0.04
16
data-point error ellipses are 2σ
220
0.6
0.0122
78 0.03
180
0.0118 0.092
140
74
0.02 0.088
0.0110
100
2500
Concordia Age = 76.39 ±0.67 Ma (2σ, decay-constant errors included) MSWD (of concordance) = 2.5,
70
0.0106 0.064
0.068
0.072
0.076
206
206
25
Number
15
10
0.2
0.00 0.0
0.1
2500 14
0.4
~152 Ma
12
10
Relative probability
20
0.2
20
Relative probability
1500
60
0.01
Pb/ 238U
Pb/ 238U
0.4
0.3
0.6
Probability (of concordance) = 0.11
Number
0.0114
1500
8
~78 Ma 6
0.2
~192 Ma
~1060 Ma
4
~1744 Ma
500
5
0
0.0 0
4
2
0 0
500
1000
8 207
1500
Age, Ma
12
2000
2500
3000
16
0.0
0
500
1000
1500
2000
2500
3000
Age, Ma
0
10
20
30
207
Pb/235U
Pb/235U
Figure 4. Detrital zircon age distribution for sandstone and tuffaceous sandstone samples of the Arizpe-Mazocahui quadrangle. (A) Sample 11-22-07-1 from the Proterozoic Las Víboras Group, Banámichi quadrangle. (B) Proterozoic sandstone from the Las Víboras Group in the Santa Ana quadrangle. (C) Tuffaceous sandstone from the lower part of the Tarahumara Formation in structural section D–D′. (D) Tuffaceous sandstone from the Tarahumara Formation in the Santa Ana quadrangle. Approximate locations of these samples are indicated in Figure 2. MSWD—mean square of weighted deviates.
León et al., 2000), and a K-Ar (whole rock) age of 40.6 ± 1.1 Ma from the El Rodeo quadrangle (Damon et al., 1983a). Freshwater, non-age-diagnostic fossils including plants (Hernández-Castillo and Cevallos-Ferriz, 1999), algae (Beraldi-Campesi et al., 2004), diatoms (Chacón-Baca et al., 2002), and other microfossils (Beraldi-Campesi and Cevallos-Ferriz, 2005) were reported from local, interbedded lacustrine strata of the Tarahumara Formation in the Aconchi quadrangle. Ages reported for the plutonic rocks include a 40Ar/ 39Ar (biotite) age of 56.7 Ma for the
Rancho Vaquería pluton (pluton names derive from our informal terminology described in the following; Fig. 2) (González-León et al., 2000), a K-Ar (biotite) age of 56.4 Ma (Mead et al., 1988), and a 40Ar/39Ar (biotite) age of 57.3 Ma (Zuñiga Hernández, 2010) for the Las Cabecitas granodiorite (Fig. 2), and K-Ar ages reported by Damon et al. (1983b) of 51 Ma (orthoclase) for the San Felipe porphyry and 55.9 Ma (biotite) for the Bella Esperanza granodiorite (Fig. 2). The Bella Esperanza granodiorite was also dated as 56.9 Ma (K-Ar, whole rock) by Housh and McDowell (2005). Stocks of monzonite
Geosphere, December 2011
and diorite in the Cumobabi Mine (Fig. 2) yielded K-Ar ages between 63 and 56 Ma on biotite (Scherkenbach et al., 1985) and 51 Ma (40Ar/39Ar; Zuñiga Hernández, 2010). Mead et al. (1988) first reported 40Ar/39Ar ages of 46.6 Ma (hornblende) and ca. 37.1 Ma (biotite), and a K-Ar age of ca. 39.5 Ma (biotite) for a granodiorite pluton in the Sierra El Jaralito. The El Jaralito and the Aconchi batholiths are names assigned by Roldán-Quintana (1991) to plutonic rocks that crop out in the Sierra El Jaralito and the Sierra de Aconchi, respectively (Fig. 2). Roldán-Quintana (1991)
1397
González-León et al. noted that the El Jaralito batholith is composed of granitic, granodioritic, quartz dioritic, and quartz monzonite facies with ages between ca. 69 and ca. 51 Ma, whereas he referred to the Aconchi batholith as a two-mica, alkaline granite with red garnet with an age of 35.96 ± 0.7 Ma. Radelli et al. (1991) and Macias Valdéz (1992) later renamed this two-mica pluton the Huépac granite. In this work we follow the subsequent authors to include the Aconchi batholith as part of the El Jaralito batholith and based on our geochronology identify granite outcrops to the south in the Sierra El Jaralito as the Huépac granite. Furthermore, in this work and based mostly on geochronology and geochemistry, we recognize the El Jaralito batholith as a plutonic suite that includes previously unrecognized plutons (Fig. 2) (described herein). Abundant centimeter- to meter-thick pegmatite dikes composed of K-feldspar, quartz, plagioclase, muscovite, biotite, garnet, and accessory minerals that cut through the El Jaralito batholith were studied in detail by Roldán-Quintana et al. (1989) and MaciasValdez (1992). Several published K-Ar and 40 Ar/39Ar ages obtained from K-feldspar, hornblende, muscovite, and biotite from the twomica Huépac granite, from pegmatite dikes, and from skarn rocks range from 41.6 Ma to ca. 18 Ma. The older ages are interpreted as cooling ages of the plutons (Mead et al., 1988), while ages between ca. 28 to ca. 18 Ma were interpreted by Lugo Zazueta (2006) and Wong et al. (2010) as cooling ages of the exhumed footwall of the core complex that forms the Sierra de Aconchi (Fig. 2). The Laramide and older rocks of the study area are intruded by rhyolitic and dacitic domes with ages between 23 and 25 Ma (Fig. 2; González-León et al., 2010; our data) and by basaltic dikes with ages near 23 Ma (Wong and Gans, 2008). These rocks are deformed by normal faults of the Basin and Range extensional event that formed the north-south elongated basins of the Sonora and Moctezuma Rivers, where thick, Late Oligocene to Miocene volcanic and terrigenous strata of the Báucarit Formation accumulated (González-León et al., 2010) (Fig. 2). Stratigraphy and Structural Relationship of the Tarahumara Formation Structural relationships of the Tarahumara Formation with older and younger units are illustrated along seven cross sections (Figs. 2 and 5). Tarahumara Formation stratigraphy is described by means of six measured columns (Fig. 6) and from its estimated thickness along structural sections F-F′ and G-G′ (Fig. 5). Sam-
1398
ples from different stratigraphic levels of the Tarahumara sections were collected during field work for petrographic, geochronologic, and geochemical studies. A summary of the U-Pb, K-Ar, and 40Ar/39Ar geochronology is presented in Table 1. Geochemical and isotope analyses were performed from samples collected at same stratigraphic levels of the dated samples and results are presented in Supplemental Table 55 and Table 2, respectively. The main structural and the stratigraphy characteristics of the Tarahumara Formation along the cross sections are described next. Cross-section A-A′ located in the Arizpe quadrangle crosses through the Picacho de Arizpe peak (Figs. 2 and 5). On the eastern flank of the Picacho, the Tarahumara Formation unconformably overlies deformed strata of the tectonically juxtaposed Mural and Cocóspera Formations. It dips homoclinally to the northeast and is unconformably overlain by Oligocene volcanic rocks (González-León et al., 2000). In the western flank of the Picacho de Arizpe, the Mural Formation is part of a block of Bisbee Group strata that thrusts over the deformed Cocóspera Formation. The measured thickness of the Tarahumara is 1260 m (Fig. 6A). Its lowermost part consists of crystal-poor rhyodacitic welded tuff and crystal-rich porphyritic dacite. Zircons from the rhyodacite gave a U-Pb age of 75.70 +0.30/–0.70 Ma (Fig. 7A; mean 206Pb/238U age, 97.3% confidence, n = 21). The remainder of the section is composed of well-bedded rhyolite ash-fall tuff and brown to reddish volcaniclastic sandstone and siltstone. Along cross-section B-B′, the Tarahumara Formation unconformably overlies the deformed Late Jurassic Cucurpe Formation, which crops out in an erosional window of an open anticline of the Tarahumara Formation in the El Teguachi ranch area (Figs. 2 and 5). In the southern part of this section the Cintura and Tarahumara Formations are normally faulted against each other across the Los Alisos fault. Between the El Teguachi ranch and the Sierra El Juparo, the Tarahumara Formation dips to the north and its section is offset by the normal fault of Cañada El Potrerito. The composite stratigraphic column of the Tarahumara starts north of the El Teguachi ranch and ends in Sierra El Juparo (Fig. 6B). It has an incomplete thickness of 1000 m and its lower part is occupied by a basal, 29-m-thick conglomerate that grades 5 Supplemental Table 5. Summary of geochemical analyses for the Laramide rocks and Proterozoic granites of the study area. If you are viewing the PDF of this paper or reading it offline, please visit http:// dx.doi.org/10.1130/GES00679.S5 or the full-text article on www.gsapubs.org to view Supplemental Table 5.
Geosphere, December 2011
upward to interbedded volcaniclastic strata, rhyolitic to dacitic ignimbrite, ash-fall tuff and lacustrine limestone. The overlying unit consists of andesitic breccia, rhyolitic ash-fall tuff, and ignimbrite. A normal fault at the top of this unit omits part of the stratigraphic column, and its upper part was measured in the southern flank of Sierra Los Juparos. It is composed of bedded ash-fall tuff, rhyolitic breccias, sandstone, and conglomerate, and its upper part is composed of ignimbritic rhyolite and subordinate interbedded rhyolitic ash-fall tuff. Zircons from the upper ignimbritic rhyolite gave a U-Pb age of 71.7 ± 1.7 Ma (Fig. 7B; mean 206 Pb/ 238U age, n = 16). In cross-section C-C′ (Fig. 5) the Tarahumara Formation unconformably overlies the El Jacalón diorite and the Morita Formation of the Bisbee Group, both of which are juxtaposed across the El Jucaral fault (Fig. 2). Tarahumara rocks dip homoclinally 30°NE and at Cañada La Nopalosa are unconformably overlain by Cenozoic dacite, rhyolite, and conglomerate of the Sierra Las Guijas (Fig. 5). The 880-m-thick Cañada Motepori stratigraphic column (Fig. 6C) was measured between the creek of same name and Cañada La Nopalosa. Its basal unit is a 100-m-thick conglomerate with subordinate coarse-grained sandstone and ash-fall tuff beds that grade upward to volcaniclastic sandstone and ash-fall tuffs. Its middle part is composed of dacite to rhyolite ignimbrite and subordinate ash-fall tuffs and its upper part consists of volcaniclastic sandstone, siltstone, andesite breccia, fiamme-rich rhyolite ignimbrite, and dacite ignimbrite. A tuff bed from the lower part of this column did not yield zircons, but McDowell et al. (2001) reported a U-Pb zircon age of 76 Ma for the “volcanic section near El Tuli” ranch (Fig. 2) that we believe probably belongs to our measured section. At cross-section D-D′ (Figs. 2 and 5), the Proterozoic Las Víboras Group thrusts over the Early Cretaceous Mural Formation of the Bisbee Group and the Tarahumara Formation overlies both faulted units. Tarahumara beds homoclinally dip to the northeast with angles as steep as 50°. The 1040-m-thick stratigraphic column El Salmón (Fig. 6D) has in its lower part an 80-m-thick conglomerate that is overlain by conglomerate, sandstone, and siltstone beds arranged in upward-fining successions with intercalations of rhyolitic and andesitic ash-fall tuffs. Concordant detrital zircons separated from a tuffaceous sandstone collected 133 m above the base of the formation yielded a younger U-Pb peak age of 76.39 ± 0.67 Ma, interpreted as the maximum age of deposition (Fig. 4C, inset; concordia age, n = 10), and abundant Proterozoic grains.
Picacho de Arizpe
A Tahuichopa 1300
fault
75.7 Ma
Arroyo El Cumarito
Arroyo La Galera
BAUCARIT Fm (Oligocene/Miocene)
Laramide magmatic arc in northern Sonora
A′
1000
B 1500
Cerro Cajon de Enmedio
Arroyo Los Alisos Los Alisos 62 Ma fault
Puerto El Teguachi
Cañada El Potrerito 73 Ma
El Teguachi ranch
Conglomerate and sandstone Rhyolite,breccia and agglomerate
Dacite flow Sierra El Juparo
B′
Cañada Motepori
76 Ma
Cañada La Nopalosa
Cañada El Picacho
C′
Sierra Las Guijas
1000
Cerro El Vigia
1250
Cañada El Salmón
70 Ma Cañada Cerros El Cuervo El Cuervo
Arroyo El Aliso
Arroyo Las Higueras
D′
750
2 km E 74 Ma
1500
Cerro Colorado
Arroyo Malpaso
Arroyo El Saucito Los Nogales fault 74.8 Ma
Andesite Rhyolitic ignimbrite and ash-fall tuff
Limestone Volcanosedimentary rocks Conglomerate Angular unconformity
Pre-Tarahumara basement
76 Ma
D
Granitic to dioritic plutons Agglomerate and breccia Dacite
Sierra El Oso 75 Ma
Cocospera formation Cintura Formation Mural Formation
Bisbee Group
C
1500
LARAMIDE MAGMATIC ARC Tarahumara Formation
900
Morita Formation Cucurpe Formation Proterozoic sedimentary rocks El Jacalon diorite (1.7 Ga)
E’ 750
F 1500
1 km
59 Ma
68.6 Ma
Las Cabecitas
Cerro El Volantin
63 Ma
Puerto F′ Los Mojones
Mine Unconformity
1000
G
Downthrown block in normal fault Thrust fault
70 Ma
5 km
78.7 Ma El Rodeo fault
Rancho Agua Zarca
Sierra La Front 76 Ma Ranges Cieneguita fault
72 Ma
G′ Moctezuma
1000 500
Figure 5. Structural cross sections from the study quadrangle showing relationships of the Tarahumara Formation with other older and younger lithologic units. Rock ages shown as reported in this contribution, except for cross-section C–C′, taken from McDowell et al. (2001). Locations of cross sections indicated in Figure 2. Vertical scale is in meters. Horizontal scale of 2 km is for cross-sections A–A′ to E–E′.
The middle part of the column is composed of andesite flows and breccia, while the upper part that crops out between Cerros El Cuervo and Cañada El Cuervo (Fig. 5) is composed of rhyolite ignimbrite, ash-fall tuff, and andesitic to dacitic breccia and agglomerate. A rhyolite from
this section yielded a 70.02 ± 1.5 Ma age (Fig. 7C; mean 206Pb/238U age, n = 24). The uppermost part of this section between Cañada El Cuervo and Arroyo El Aliso (Fig. 5) has an estimated thickness of 700 m and is composed in its lower part of bedded dacitic ignimbrite, dacitic
Geosphere, December 2011
agglomerate and subordinate volcaniclastic sandstone with an uppermost quartz porphyritic rhyolite ignimbrite. Cross-section E-E′ preserves the most complete stratigraphic succession of the Tarahumara Formation (Figs. 2 and 5), which unconformably
1399
González-León et al. C. Cañada Motepori
B. Rancho Teguachi
A. Picacho de Arizpe 1260
1000
Middle and upper parts of the column are composed of rhyolitic ash-fall tuff, volcaniclastic sandstone and siltstone. The tuff occurs as bedded intervals up to 58 m thick and typically has quartz, altered feldspar and biotite crystals in a groundmass of devitrified glass shards. The volcaniclastic strata are brown, reddish and green and occur as massive beds up to 5 m thick that become more abundant upwards in the section.
1000
500 500
0
Conglomerate, sandstone, stromatolitic limestone, dacitic to rhyolitic breccia and ash-fall tuff. The tuff contains plagioclase, biotite and pumice fragments altered to chlorite and clay minerals, and the groundmass consists of devitrified microcrystalline quartz and clay material. Crystal-poor rhyodacite with crystals of quartz, feldspar, biotite and volcanic rock fragments in a vitric groundmass. Crystal-rich porphyritic dacite with feldspar and volcanic rock fragments in a fluidal vitric matrix. Early Cretaceous Bisbee Group
0
Crystal-rich ignimbritic rhyolite flows composed of fragmented and partially resorbed quartz phenocrystals, feldspar and altered biotite in a vitric eutaxitic groundmass. Interbedded rhyolitic 880 ash-fall tuff. Ignimbritic rhyolite flows composed of quartz phenocrysts, feldspar and fiamme, with interbedded rhyolitic ash-fall tuff. Lithic, bedded ash-fall rhyolitic tuff, rhyolitic breccia, sandstone, siltstone and subordinate pebble conglomerate lenses. Andesitic breccia and ash-fall tuff, rhyolite ignimbrite flows and 500 rhyolitic ash-fall tuffs.
Massive, clast-supported, angular to sub-rounded, poorly sorted cobble- to pebble-conglomerate with clasts of quartzarenite, andesite, sandstone and siltstone. Interbedded, coarse-grained volcaniclastic sandstone and rhyolite to dacite ignimbrite flows, andesitic ash-fall tuff and medium bedded, dark gray, stromatolitic, oolitic and oncolitic, dolomitized lacustrine limestone. Late Jurassic Cucurpe Formation
Bedded volcaniclastic sandstone, conglomerate, siltstone and andesite breccia in the lower part. A 40-m-thick, fiamme-rich rhyolite ignimbrite in the middle part is overlain by reddish sandstone. The upper part is composed of reddish rhyolitic ignimbrite, subordinate ash-fall tuffs and a top 50-mthick welded dacite tuff composed of feldspar, biotite and altered mafic minerals. Dacite to rhyolite ignimbrite in beds up to 12 m thick, and subordinate, interbedded ash-fall tuffs. Petrographic composition of a dacitic ignimbrite is crystal-rich with altered plagioclase and hornblende in glomeroporphyritic texture, in a hyalopilitic groundmass. Basal, massive to poorly bedded, clastsupported, cobble conglomerate with clasts of subrounded sandstone, quartzarenite, andesite and gneiss. Upper part composed of coarse- to medium-grained volcaniclastic sandstone and bedded ash-fall tuff.
0
Proterozoic El Jacalón diorite
Figure 6 (on this and following page). Measured stratigraphic columns of the Tarahumara Formation in the study area with lithologic description. Thickness is in meters.
overlies the Proterozoic Las Víboras Group and dips homoclinally to the east. In the western foothills of the Sierra El Oso, the Tarahumara is offset by the northwest-southeast El Saucito normal fault that dips steeply to the southwest. In the eastern part of the section the Tarahumara is unconformably overlain by conglomerate and rhyolite of the Báucarit Formation. Because of the El Saucito fault offset, we measured the stratigraphy of the Tarahumara in two columns, named Cerro Colorado and Sierra El Oso, located west and east of the El Saucito fault, respectively. The Cerro Colorado stratigraphic column (Fig. 6E) is 1865 m thick. Its basal unit is a 50-m-thick conglomerate composed of quartzrich sandstone clasts that grades upward to a volcaniclastic succession with interbedded rhyolite and dacite ignimbrite. Zircons from a 20-m-thick, fiamme-rich rhyolite tuff located 120 m above the base of the formation yielded an age of 74.30 ± 1.3 Ma (Fig. 7D; mean 206 Pb/238 age, n = 39). Upward, the succession
1400
is composed of rhyolite ignimbrite and ash and lapilli tuff, whereas its middle part consists of andesite flows and breccia, rhyolitic and dacitic ignimbrite, volcaniclastic sandstone, and wellbedded ash-fall tuff. Its upper part is composed of rhyolitic and dacitic ignimbrite, interbedded volcaniclastic sandstone, conglomerate, and andesite ash-fall tuff. The lower part of this column located between the measured section and the Santa Elena Mine (Fig. 2) is intruded by a quartz phenocryst–bearing rhyolite dome that we dated as 73.56 ± 1.3 Ma (Figs. 6E and 7E; mean 206Pb/238U age, n = 59). The exposed lower part of the 930-m-thick Sierra El Oso stratigraphic column (Fig. 6F) is a rhyolitic ignimbrite flow that was dated as 74.64 ± 1.5 Ma (Fig. 7F; mean 206Pb/238U age, n = 43). Most of the lower part of this succession is composed of rhyolitic to dacitic ignimbrite and interbedded ash-fall tuffs, whereas its middle part consists of volcaniclastic strata, minor ash-fall tuffs, dacite, and andesitic breccia. Its upper part is andesitic and rhyolitic
Geosphere, December 2011
ash-fall tuff, trachyandesite flows, and rhyolite. Zircons from a rhyolitic tuff of this upper part yielded a U-Pb age of 75.10 ± 1.2 Ma (Fig. 7G; mean 206Pb/238U age, n = 41). Structural cross-sections F-F′ and G-G′ in the southern part of the area traverse thick successions of the upper Tarahumara Formation as its lower part is offset by normal faults and cut by plutonic intrusions (Figs. 2 and 5). Its estimated thickness along section F-F′ is more than 2 km dipping homoclinally to the northeast, except in its upper part where it forms an open syncline, the northwest-southeast axis of which follows the upper part of the Sierra Las Palomas (Fig. 2). Outcrops of its exposed lower part are interbedded andesitic volcaniclastic sandstone, conglomerate, and andesite flows that are overlain by crystal- and lithic-rhyolite ignimbrite and an interbedded porphyritic dacite that was dated as 68.50 ± 2.0 Ma (Fig. 7H; mean 206Pb/238U age, n = 14). The middle part of the Tarahumara Formation is occupied by andesitic flows and its upper part is composed of stratified, crystal- to
Laramide magmatic arc in northern Sonora
1800
1040 Lithic-, and crystal-rhyolite ignimbrite in beds up to 50 m thick, subordinate interbeds of ash-fall tuff, dacite 1000 ignimbrite and andesitic to dacitic breccia and agglomerate. A typical, crystal-rich rhyolite tuff from this interval is composed of fragmented and resorbed phenocrysts of quartz, feldspar, biotite and fiamme fragments in a fluidal vitric matrix.
500
Massive, light gray porphyritic hornblende andesite and andesitic breccia. Reddish brown to purple volcaniclastic, lenticular, pebble conglomerate, sandstone and siltstone forming upward-fining cycles up to 45 m thick. Interbedded yellow rhyolitic ash-fall tuff beds and subordinate andesite tuffs.
0
Massive, clast-supported, poorly sorted cobble conglomerate with clasts of quartzarenite. It fines upwards to pebble-conglomerate. Proterozoic Las Víboras Group.
F. Sierra El Oso
E. Cerro Colorado
D. El Salmon
200
0
Rhyolite and crystal-rich dacite ignimbrite in units up to 50 m thick, sandstone, pebble conglomerate and andesitic tuff. Typically rhyolite has abundant fiamme, up to 25% volume of feldspar and biotite crystals in a vitric mesostasis. Dacite consists of up to 35% crystals of feldspar, andesite lithic fragments, and biotite in a eutaxitic vitric matrix. Porphyritic dacite ignimbrite, hornblende andesite, breccia, and volcaniclastic sandstone. Dacite in cooling units up to 40 m thick is crystal-rich with plagioclase, hornblende, andesite lithics and fiamme fragments in a hyalopilitic mesotasis. Andesite has hyalopilitic texture, phenocrysts of plagioclase and hornblende. Volcanic breccia in massive units up to 50 m thick with blocks of andesite and rhyolite. Fiamme-rich rhyolite ignimbrite. Crystals are fragmented and resorbed quartz crystals, feldspar and biotite set in a eutaxitic, vitric mesostasis.
Rhyolite ignimbrite
Limestone Ash-fall tuff Andesitic tuff Andesite flows
Proterozoic Las Víboras Group.
Andesitic breccia and agglomerate Volcaniclastic rocks Rhyolitic breccia and agglomerate Rhyolitic dome
Dacite
Pre-Tarahumara basement rocks
Covered
Unconformity
930 Andesitic and rhyolitic ash-fall tuff and trachyandesite flows.
Aphanitic andesite flows, well-bedded ashfall tuff and minor volcaniclastic sandstone. The upper part of this interval is massive, aphanitic andesite flows and beds up to 5 m thick of andesite and rhyolite breccias. Crystal- and lithic-rich rhyolite ignimbrite and interbedded ash- and lapilli-tuff beds. Crystals in rhyolite are feldspar, quartz and biotite; lithic grains are altered volcanic rocks. Mesostasis is vitric and eutaxitic. Flat fiamme fragments are common. Bedded, arkosic to lithic sandstone, siltstone and interbedded ash-fall tuff beds, pebble-conglomerate and rhyolitic to dacitic ash-flow tuffs. Intruded by a quartz phenocryst-bearing rhyolite dome. Massive, poorly sorted, clast-supported, pebble- to cobble-conglomerate.
Conglomerate
500
Stratified, fine- to coarsegrained, thin- to mediumbedded volcaniclastic litharenite, ash-fall tuffs, lenses of pebble conglomerate with clasts of volcanic rocks, dacite and andesitic breccia. Crystal-rich rhyolitic, dacitic and rhyodacitic ignimbrite and interbedded dacitic to rhyolitic ash-fall tuff.
0
Rhyolite ignimbrite with plagioclase, sanidine, biotite and rock fragments in a vitric and eutaxitic groundmass with fiamme fragments. Base faulted
Figure 6 (continued).
lithic-rich rhyolite ignimbrite with subordinate rhyolitic and andesitic ash-fall tuff and breccias. A rhyolite from the uppermost part of this succession was dated as 63.5 ± 1.4 (Fig. 7I; mean 206 Pb/238U age, n = 19). Along section G-G′ the Tarahumara Formation dips homoclinally to the east and is offset by normal faults that bound north-trending Cenozoic basins (Fig. 5). At the southwestern end of this section, the Tarahumara Formation is intruded by the La Aurora tonalite (discussed in the following). The faulted section of the Tarahumara Formation between the El Rodeo ranch and the Range Front fault (Deen and Atkinson, 1988) (Figs. 2 and 5) is ~1 km thick and composed of interbedded rhyolitic ignimbrite and pebble-cobble conglomerate, and its upper part is composed of stratified ash-fall tuff, rhyolitic ignimbrite, conglomerate, and sandstone. A rhyolite from the lower part of this succession was dated as 78.7 ± 1.3 (K-Ar, biotite, sample 11–26–09–4; Table 1). The normal-faulted Tarahumara succession that crops out from Sierra La Cieneguita to the town of Moctezuma (Figs.
2 and 5) consists in its lower part of interbedded rhyolitic and dacitic flows and subordinate ash-fall tuff, volcaniclastic sandstone, and conglomerate; the upper part, near Moctezuma, it is composed of stratified red ignimbrite rhyolite. A dacitic ignimbrite from the lower part of this section yielded an age of 75.75 ± 0.55 Ma (Fig. 8A; mean 206Pb/238U age, 94.3% confidence, n = 14) and a rhyolite from its upper part yielded an age of 72.20 ± 1.6 Ma (Fig. 8B; mean 206Pb/238U age, 96.1% confidence, n = 12). The thickness of the Tarahumara Formation in this section may be >1.5 km. Other U-Pb ages of the Tarahumara succession in the study area come from samples that are not located on a measured section. From the Santa Ana quadrangle (Fig. 2) we dated detrital zircons from a volcaniclastic sandstone (Fig. 4D, n = 85) that yielded a dominant age peak of 152 Ma and subordinate peaks of 78, 192, 1060, and 1700 Ma, and two other rhyolites that yielded ages of 76.0 ± 2.7 Ma (Fig. 8C; mean 206 Pb/238U age, n = 13) and 73.8 ± 1.6 Ma (Fig. 8D; mean 206Pb/238U age, n = 23). A reworked,
Geosphere, December 2011
tuffaceous rhyolite from the Aconchi quadrangle (Fig. 2) yielded an age of 69.1 ± 2.4 Ma (Fig. 8E; mean 206Pb/238U age, n = 17). Laramide Plutonic Rocks Laramide plutons in the northern part of the study area crop out as small exposures of a few square kilometers, but they form larger outcrops in Sierra El Jaralito batholith in the southern part (Roldán-Quintana, 1989). Based on field observation of well-exposed outcrops, most of the plutons are apparently fresh and homogeneous in texture and mineralogy, although detailed examination could reveal subtle variations in these characteristics. As also observed by other authors from the Laramide plutons of Sonora (Richard et al., 1989; Roldán-Quintana, 1991), mineralogy of the study plutons is simple with varying proportions of plagioclase, alkali feldspar, quartz, biotite, scarce amphibole and pyroxene, and accessory minerals including titanite, opaque minerals, and zircon. Feldspar, biotite, and hornblende may present slight to moderate
1401
González-León et al. TABLE 1. SUMMARY OF U-Pb, K-Ar AND 39Ar/40Ar GEOCHRONOLOGY FOR THE LARAMIDE ROCKS IN THE STUDY AREA Age Age Age (Ma) (Ma) (Ma) U-Pb (zr) K-Ar (bi) Sample Ar/Ar (bi) UTM location, altitude Observations Porphyritic rhyolite with quartz, sodic plagioclase, and 4-23-09-5 63.5 ± 1.4 12R 597200E 3305069N, 1477 m chloritized grains of biotite in a eutaxitic vitric mesostasis moderately altered to sericite. Crystal-rich, porphyritic dacite with plagioclase, biotite, 4-23-09-12 68.5 ± 2 12R 593822E 3298900N, 1218 m and hornblende strongly altered to chlorite. Hyalopilitic mesostasis recrystallized to microcrystalline quartz, chlorite, and iron oxides. 12R 577038E 3333810N, 869 m Porphyritic rhyolite with resorbed and fragmented quartz 3-5-08-2 70.02 ± 1.5 crystals to 3 mm long, broken plagioclase crystals, biotite altered to chlorite and scarce volcanic rock fragments. Hyalopilitic mesostasis and glass shards. 1-28-09-2 71.7 ± 1.7 12R 561534E 3345455N, 1304 m Crystal-rich rhyolitic ignimbrite with corroded and fragmented quartz crystals to 3 mm long, K-feldspar and sodic plagioclase and subordinate biotite in a hyalopilitic mesostasis with glass shards. 11-25-09-6 72.20 +1.60/–1.20 12R 625743E 3295070N, 684 m Rhyodacite with altered crystals of feldspar up to 2 mm long, quartz and subordinate laths of biotite altered to chlorite. Groundmass is vitric and fluidal with fragments of fiamme recrystallized to quartz and calcite. 11-16-07-4 73.56 ± 1.3 12R 581246E 3322656N, 907 m Porphyritic rhyolite with resorbed quartz grains to 2 mm long, sodic plagioclase and orthoclase and subordinate chloritized biotite. Vitric mesostasis with incipient recrystallization. 12-5-08-2 73.8 ± 1.6 12R 553442E 3338772N, 1220 m Rhyolitic tuff with crystals of quartz, plagioclase, subordinate lithic fragments, and biotite. Crystals are broken and angular. Quartz is locally resorbed and plagioclase is altered to calcite. Matrix recrystallized to microcrystalline quartz. 9-18-07-2 74.30 ± 1.3 12R 580721E 3327213N, 1146 m Crystal-poor (2 km for its younger, upper part at cross-section F-F′, we infer that the volcanic pile might exceed 4 km in the study area. The Tarahumara succession is mostly rhyolitic, volcaniclastic, and andesitic, with subordinate lacustrine limestone in its lowermost 2 km, and rhyolitic to dacitic in its upper
Figure 10. U-Pb data for Laramide plutonic rocks of the study area. MSWD—mean square of weighted deviates. (A) Sample 3-4-08-2 from the Rancho Vaquería granodiorite. (B) Sample 1-30-09-1 from the San Antonio granodiorite. (C) Sample 3–31–09–2 from the Las Cabecitas granodiorite. (D) Sample 4-23-09-13 from the Las Cabecitas granodiorite. (E) Sample 3-5-08-4 from the Puerta del Sol granodiorite. (F) Sample 3-5-08-3 from the Puerta del Sol granodiorite. (G) Sample 10-1-09-4 from the El Babizo granite. (H) Sample 10-2-09-8 from the El Babizo granite. (I) Sample 11-27-09-5 from the Huépac granite.
Geosphere, December 2011
0.08
0.08
0.09
0.04 10
0.05
0.06
0.07
Pb/206Pb
207
0.07
0.04 74
0.05
0.06
66
D
30
Mean = 55.8 ± 0.9 Ma
70
62
66
70
74
78
80
82
86
238
90
U/206Pb
box heights are 2σ
TuffZirc Age = 71.50 +0.20 -0.70 Ma
(94.3% confidence, coherent group of 14)
130
150
70
150
94
98
102
10-1-09-4 El Babizo Mean 206Pb/238U at 71.50 + 0.20/ -0.70 Ma MSWD= 7.1
data-point error ellipses are 2σ
130
4-23-09-13 Las Cabecitas Mean 206Pb/238U at 56.3 ± 1.2 Ma MSWD (concordance)= 0.62
data-point error ellipses are 2σ
110
3-4-08-2 Rancho Vaquería Mean 206Pb/238U at 55.8 ± 0.9 Ma MSWD (concordance)= 0.52
90 U/206Pb
238
110 U/206Pb
238
78
90
60
MSWD = 0.62 (95% confidence) (error bars are 2σ)
Mean = 56.3 ± 1.2 Ma
50
80
MSWD = 0.52 (95% confidence) (error bars are 2σ)
82
80
44
48
52
56
60
64
68
72
240
400
42
46
50
54
58
G
0.04 70
0.05
0.06
0.07
Pb/206Pb
207
Pb/206Pb
207
62
Age
0
92
80
E
B
36
40
44
48
52
56
60
64
68
52
56
60
64
68
72
76
80
84
88
100
140
64
68
72
76
80
84
88
H
0.040 40
0.044
0.048
0.052
0.056
0.060
0.064
0.04 70
0.06
0.08
0.10
0.04
0.05
0.06
0.07
0.08
0.09
Pb/206Pb 207
Pb/206Pb 207
A
207
Pb/206Pb
90
60 110
80
238
160
U/206Pb
Figure 10.
120
box heights are 2σ
100
120
140
150
200
240
10-2-09-8 El Babizo Mean 206Pb/238U at 70.50 +0.20/ -0.70 Ma MSWD= 4.5
data-point error ellipses are 2σ
40 170
data-point error ellipses are 2σ
3-5-08-4 Puerta del Sol Mean 206Pb/238U at 51.26 ± 1.0 Ma MSWD (concordance)= 0.28
U/206Pb 130
238
(97.7% confidence, coherent group of 24)
60
80 U/206Pb
238
60
MSWD = 0.28 (95% confidence) (error bars are 2σ)
Mean = 51.26 ± 1.0 Ma
40
TuffZirc Age = 70.50 +0.30 -0.60 Ma
20
200
MSWD = 0.40 (95% confidence) (error bars are 2σ)
Mean = 67.7 ± 1.6 Ma
1-30-09-1 San Antonio Intercepts at 63.7 ± 6.3 & 1101 ± 58 Ma MSWD = 0.58
data-point error ellipses are 2σ
0.08
0.10
0.07
0.08
0.040 85
0.044
0.048
0.052
0.056
0.060
0.064
0.068
0.04 70
0.05
0.06
I
50
54
58
62
66
70
74
78
80
35
45
55
65
75
80
42
46
50
54
58
62
66
70
74
F
C
0.04 0.0970
0.06
Pb/206Pb 207
Pb/206Pb 207
data-point error ellipses are 2σ
Age
Geosphere, December 2011 207
Pb/206Pb
70
Age
0.09
70
Mean = 59.1±1.6 Ma
o
110
238
95
105
60
U/206Pb
238
box heights are 2σ
(93.5% confidence, coherent group of 11)
TuffZirc Age = 58.00 +0.60 -0.90 Ma
90
60
(error bars are 2σ)
(95% confidence, coherent group of 26)
U/206Pb
110 U/206Pb 238
TuffZirc Age = 49.95 +1.05/ -0.45 Ma
90
60
MSWD = 1.5 (95% confidence) (error bars are 2σ)
150
150
115
11-27-09-5 Huépac granite Mean 206Pb/238U at 58.00 +0.60/ -0.90 Ma MSWD= 7.7
125
data-point error ellipses are 2σ
130
3-5-08-3 Puerta del Sol Mean 206Pb/238U at 49.95 ± 0.80 Ma MSWD=5.4
data-point error ellipses are 2σ
130
3-31-09-2 Las Cabecitas Mean 206Pb/238U at 59.1 ± 1.6 Ma MSWD (concordance)= 1.5
data-point error ellipses are 2σ
Laramide magmatic arc in northern Sonora
1409
González-León et al. 100 Los Alisos granodiorite 11-28-08-2 biotite
Age in Ma
80 60
tp = 61.76 ± 0.81 Ma
40 20 0
39 37
Figure 11. 40Ar/39Ar plateau age (tp) in biotite for sample 11–28– 08–2 from the El Aliso granodiorite.
ArCa / ArK
0.6 0.4
0.2
0 0.2
0
40 Ar/ Ar
0.8
1.0
a
0.003
36
0.6 0.4 39 Fraction of Ar released
b
tc = 61.58 ± 1.15 Ma 0.002 40
36
( Ar / Ar)i = 319 ± 11 0.001
SumS / (n-2) = 0.88, n = 6
c g
0 0
0.02
0.01
dF e
0.03
39
Ar/ 40Ar
part, with subordinate andesite and volcaniclastic strata. The most conspicuous stratigraphic characteristic of the formation is its regionally extensive basal conglomerate. Overlying lithologies in the succession show marked lateral facies changes, mainly a gradation from mostly volcanic in the Banámichi quadrangle to more volcaniclastic and tuffaceous lithologies toward the northern part of the Arizpe quadrangle. Further to the north, between the study area and the city of Cananea, several 40Ar/30Ar dates indicate that the Tarahumara succession has ages as old as ca. 73 Ma and as young as ca. 64 Ma (Cox et al., 2006; Supplemental Table 1 [see footnote 1]). Northward and east of Cananea, the Tarahumara Formation grades laterally into the Cabullona Group, a mostly fluviolacustrine sedimentary succession that was deposited in the Laramide Cabullona basin (Taliaferro, 1933; González-León and Lawton, 1995). Ashfall tuffs in the lower strata of the Cabullona Group yielded late Campanian U-Pb ages (López-Higuera et al., 2008) that corroborate its equivalence with the Tarahumara Formation. At Sierra Los Ajos, an intermediate area between the main outcrops of the Cabullona Group to the north and the Tarahumara Formation to the south, there is an incomplete basal succession of detrital and volcanic rocks that is correlative with the Cabullona Group (Page et al., 2010).
1410
The 40Ar/39Ar ages between ca. 80 and 74 Ma obtained by Page et al. (2010) from volcanic rocks of this succession are similar to the ages we report here, supporting the inference of a transitional facies relationship between the mostly volcanic Tarahumara Formation to the south and the mostly sedimentary Cabullona Group to the north. In southern Sonora, strata assigned to the Tarahumara Formation are >2.5 km thick and composed of dacite and andesite flows, volcaniclastic strata, and felsic tuffs (McDowell et al., 2001); the 1.4-km-thick lower member of the formation here has U-Pb ages from 89 to 70 Ma (McDowell et al., 2001) and ages as old as ca. 90 Ma have also been reported for plutonic rocks of the region (Pérez-Segura et al., 2009). The geochronological results indicate that the Tarahumara Formation ranges from 80 to 59 Ma in the study area. The older age is based on a dated rhyolite (sample 11–26–09–4) from the El Rodeo quadrangle and from young detrital grains in a volcaniclastic sandstone (sample 12–5-08–3, Fig. 4D) of the Santa Ana quadrangle. Although the base of the formation is not exposed at these places, the ages of the basal Tarahumara where it unconformably overlies basement are consistently ca. 76 Ma (Fig. 5). The proposed maximum age for the Tarahumara is also supported by ages reported by Page et al.
Geosphere, December 2011
(2010) from Sierra Los Ajos. The younger U-Pb age that we obtained for the Tarahumara is ca. 63 Ma from a rhyolite in the upper part of section F-F′, but a 40Ar/39Ar age of ca. 59 Ma was previously reported for a Tarahumara dacite from the Arizpe quadrangle (González-León et al., 2000). Similarly, according to our U-Pb ages, pluton emplacement in the study area occurred ca. 70–50 Ma. This indicates that Tarahumara volcanism is ~10 m.y. older than plutonism and it continued after volcanic activity ended. On the basis of these data, we infer that Laramide magmatism in the study area took place between 80 and 50 Ma (Fig. 13). Damon et al. (1983a, 1983b), taking into consideration that plutons as old as 90 Ma are present in coastal Sonora, proposed that Laramide arc development in Sonora occurred between 90 and 40 Ma; McDowell et al. (2001) and Valencia-Moreno et al. (2006) noted that eastward migration of the arc plutonism resulted in ages arranged in approximately north-south isochronous belts (Fig. 14). Our study area is within the 70 Ma isochron of McDowell et al. (2001) and the 60 Ma isochron of Valencia-Moreno et al. (2006, their Fig. 6), but we modify this eastern isochron line to a 50 Ma age based on a regional age compilation and our new ages (Figs. 13 and 14; Supplemental Table 1 [see footnote 1]), although relatively minor magmatic activity reached central Chihuahua to the east ca. 68 Ma (McDowell and Mauger, 1994). Compilation of somewhat varied and limited Laramide volcanic and plutonic ages within the 70–50 Ma isochronous belt (Fig. 13) confirms that regional Laramide volcanism began near 80 Ma, ended ca. 55 Ma, and had a peak age of activity near 73 Ma, apparently predating local plutonism. The compilation is also consistent with U-Pb ages in our study area suggesting that Laramide plutonism occupied central Sonora for at least 20 m.y., from the Maastrichtian to early Eocene, with an apparent peak of activity ca. 56 Ma. Protracted magmatic activity may have contributed to the evident resetting of ages of the plutonic bodies, as indicated by discordant U-Pb and K-Ar ages. For example, La Aurora tonalite (ca. 70 Ma U-Pb) yielded K-Ar ages of ca. 60, 57, and 49 Ma in three different parts of its regionally extensive outcrop and a ca. 49 Ma K-Ar age was obtained from an El Babizo granite sample dated as ca. 70 Ma (U-Pb). We consider the K-Ar age of the Mazocahui monzodiorite, ca. 48 Ma, as a result of the ca. 49 Ma resetting event that coincided with ending of important plutonic activity. Two other apparently separate pulses of magmatism in the age compilation of central Sonora (Fig. 13) are supported by scarce data. These episodes include an older one centered near
Laramide magmatic arc in northern Sonora
16.0
Pb/ 204Pb
o aM
G
e
jav
Mo
42
15.6
na
o
riz
–10
NW Province
1.7
15.4
208
207
εNdi
46
Pb/ 204Pb
1.7
15.8
South Province
ve
ja
0
SE Province
C
B
A
8
A Ga
pai Yava rizona)
38
al A
r (cent
Laramide rocks of the study area
–20 0.700
0.705
0.710 87 86 Sr/ Sri
El Gueriguito quartz monzonite (EG) Rancho Vaquería granodiorite Huepac granite El Babizo granite La Cubana monzonite Other plutonic and volcanic rocks Laramide plutons of the Cananea-Nacozari region
0.715
15.2 17
19 206
Oposura granodiorite Northern and central Laramide granites of Sonora (ValenciaMoreno et al., 2001) Laramide granites of Sonoran provinces A and B (Housh and McDowell, 2005) El Jacalón diorite (1.7 Ga) Santa Margarita granite (1.1 Ga) Laramide granites (ca. 73 Ma) of northwesternmost Sonora (Nourse et al., 2005)
Pb/
204
21 Pb
23
17
19 206
EG, BE and sulfide mineralization in the Cananea Mine Laramide granite and volcanic rocks of the study area, except for the EG and BE granites Laramide granites of the Pb southern subprovince of the southeastern Arizona province (Bouse et al., 1999) Laramide granites of the Pb boundary zone of Arizona (Bouse et al., 1999)
21 Pb/ 204 Pb
23
Proterozoic granites of the Caborca block (Iriondo et al., 2004) Granites ca. 1.1 Ga of NW Sonora (Iriondo et al., 2004), including the Aibo granite (thick square) from Farmer et al., (2005) 1.7–1.8 Ga granite and gneiss of the Caborca block (Farmer et al., 2005)
Figure 12. Regional comparison of isotopic data of the Laramide and Proterozoic igneous rocks of the study area. (A) Plot of initial εNd versus 87Sr/ 86Sr values of the Laramide igneous rocks of the study area compared with granite provinces of Sonora; Nd and Sr values from south-central Sonora, reported by Roldán-Quintana et al. (2009), overlap with values of central granites. Thick black line indicates fields of Laramide Nd-Sr provinces of Arizona (Lang and Titley, 1998). El Gueriguito (EG) and granites from the Cananea-Nacozari region plot apart within field of the Arizona south province. The Cananea-Nacozari granites (Fig. 14) include the ca. 64 Ma Cuitaca granodiorite (Anderson and Silver, 1977), a ca. 59 Ma quartz-feldspar porphyry and the poorly dated Tinaja monzodiorite and El Torre syenite (from Wodzicki, 1994), the ca. 68 Ma El Manzanal granodiorite (Valencia-Moreno et al., 2001), the ca. 64 Ma sample CH-98–17 of Housh and McDowell (2005) that we call the Oposura granodiorite, and a ca. 60 Ma quartz-feldspar porphyry (Rascón Heimpel et al., 2010). Value for the Proterozoic El Jacalón diorite is indicated. (B) Uranogenic diagram comparing values of the Laramide studied rocks, the Bella Esperanza granodiorite (BE) (data from Housh and McDowell, 2005), and sulfide mineralization of the Cananea Mine (from Bouse et al., 1999) with granites of provinces A and B of Sonora and Laramide Pb provinces of Arizona of Bouse et al. (1999). The EG and BE of the northeastern part of the study area along with mineralization of the Cananea Mine compare better with Laramide granites of the south-southeastern Arizona Pb isotope province. Also indicated are values for El Jacalón diorite, Santa Margarita granite, and Proterozoic granites and gneiss of the Caborca block (from Farmer et al., 2005). (C) Thorogenic diagram indicating that our Laramide rocks compare with granites from provinces A and B and partly overlap with those of the Pb boundary zone of Arizona (Bouse et al., 1999). The EG, BE, the Oposura plutons, and mineralization from the Cananea Mine district compare better with the field of the south-southeastern Pb isotope province of Arizona. Also shown are values of the Proterozoic plutons of the study area and others reported from the Caborca block by Iriondo et al. (2004) and Farmer et al. (2005).
90 Ma and a younger one near 43 Ma. Based on their age compilation for a quadrangle in southcentral Sonora, McDowell et al. (2001) considered that arc development occurred between 90 and 55 Ma, although they noted a gap of magmatism between 90 and 74 Ma (their Fig. 5) and the long duration of the Laramide event. Because the same gap of magmatism is indicated in the study quadrangle between 93 Ma, the age of the Cocóspera Formation, and the 80 Ma maximum age of the Tarahumara Formation, we regard the ca. 90 Ma magmatic event as syndeformational with earliest Late Cretaceous shortening, an idea that might be tested by future
work. The younger magmatism with ages near 43 Ma is rare in Sonora. For example, a 42 Ma (U-Pb) two-mica granite (González Becuar, 2011) and upper Eocene volcanic rocks (Supplemental Table 1 [see footnote 1]) with poor stratigraphic control are present in this region. This event corresponds to sporadic igneous activity that, according to Damon et al. (1983a), postdates the Laramide arc, which by 46 Ma had migrated, with abundant magmatism, to central Chihuahua (McDowell and Mauger, 1994). Younger K-Ar ages of ca. 30 and 24 Ma that we obtained from the Huépac granite and the Puerta del Sol granodiorite are similar to
Geosphere, December 2011
40 Ar/39Ar ages obtained from these same plutons by Lugo Zazueta (2006), Wong and Gans (2008), and Wong et al. (2010), that they interpreted as cooling ages related to metamorphic core complex denudation of this region.
Geochemistry and Isotope Interpretation The Laramide volcanic and plutonic rocks of the study quadrangle show LREE enrichment relative to HREE, a typical distinctive character of arc-related magmas, and they plot within that field in the diagram Rb versus Y + Nb of Pearce et al. (1984) (Fig. 9E). Notable differences in the
1411
González-León et al. 14 Plutonic rocks Volcanic rocks
11
New ages of plutonic rocks in the study area
6
4
2
40
REE characteristics of the Laramide rocks are associated with variations in rock types within the study area. The intermediate plutonic rocks (diorite to granodiorite) have a similar, consistent steep-sloped fractionation pattern with enrichment of LREE, lower HREE, and minor to negligible negative Eu anomalies. The volcanic rocks have patterns similar to those of these plutons, but show a more notable negative Eu anomaly. The REE pattern of El Babizo granite is similar to that of the volcanic rocks and intermediate plutonic rocks, but REEs of the Huépac granite are fractionated, depleted with respect to the other rocks, and have an important negative Eu anomaly. The REE pattern of the Laramide rocks of the study area is similar to the REE patterns reported by Valencia-Moreno et al. (2001) for granites of central and northern Sonora, except for the Huépac granite (Fig. 9C). The Nd and Sr isotope data of these rocks have consistent narrow ranges, except for the El Gueriguito, Rancho Vaquería, Huépac, and El Babizo granites (Fig. 12A). The εNdi value of –0.5 for the El Gueriguito granite is the least negative, while the Huépac and the Rancho Vaquería granites have the most negative values. All the other rocks have εNdi values that range from –6.2 to –9.3. The El Babizo granite has the most radiogenic initial Sr value (0.71369); an initial Sr value of 0.70900 reported by Mead et al. (1988) for the Huépac granite is more radiogenic than the two values we obtained for this pluton. The Huépac and probably El Babizo granites have characteristics of S-type granites; they are both peraluminous, two-mica leucocratic granites with low εNdi values and metersized enclaves of metasedimentary rocks. The Huépac granite contains garnet and El Babizo has the higher initial Sr value. As a whole, the
1412
New ages of the Tarahumara Formation reported in this paper
8
Number
Figure 13. Histogram of age compilation of Laramide volcanic (n = 51) and plutonic (n = 78) rocks of Sonora located within isochrones of 70–50 Ma (Fig. 14), including our new ages (reported herein). Data ages from other authors and references are listed in Supplemental Table 1 (see footnote 1). The oldest volcanic age corresponds to the herein reported ca. 93 Ma that we obtained from the Cocóspera Formation.
50
70 60 Age (Ma)
80
90
isotope geochemistry is indicative of a strong crustal contribution to an arc built over mature continental crust; this is supported by highly radiogenic 87Sr/86Sr initial ratios, negative εNdi ratios, and highly radiogenic common Pb. In Figure 12 we compare our isotope data with others few published from Sonora, although those of Pb isotopes are scarcer. The data are also compared with provinces of Arizona recognized from Laramide magmatic complexes to try to find isotopic affinities within the neighboring regions. Lang and Titley (1998) defined the northwest, southeast, and south provinces according to Nd and Sr isotope variations, and Bouse et al. (1999) defined the Mojave, boundary zone, central, and southeast Arizona provinces (Fig. 14) according to Pb isotope compositions of Laramide plutons and sulfide mineralization. Bouse et al. (1999) further divided the southeast province into northern and southern subprovinces (Fig. 14) and suggested that the lead isotope compositions of the Laramide rocks of these provinces reflect the Pb isotope compositions of their Paleoproterozoic basement rocks. Our initial Nd versus Sr values are more similar to the values of provinces A and B of Sonora defined by Housh and McDowell (2005) and south and southeast provinces of Arizona, but the Huépac, Rancho Vaquería, and one Tarahumara rhyolite from near Moctezuma plot within the northwest province (Fig. 12A). Nevertheless, the El Gueriguito granite and granites of the Cananea-Nacozari region (Figs. 12B and 14) plot apart, with values that are clearly restricted to the geographically neighboring south province of Arizona (Fig. 12A), as are the northern and central granites of Valencia-Moreno et al. (2001). Two data from ca. 73 Ma Laramide gran-
Geosphere, December 2011
ites were reported by Nourse et al. (2005) from northwesternmost Sonora. One of them, interpreted by Nourse et al. (2005) to be in the Mazatzal block, plots within the southeastern province of Arizona, and the other, assigned to the Yavapai province, plots within the northwestern province of Lang and Titley (1998) (Fig. 12A). In the western part of the study area, the Proterozoic El Jacalón diorite (1.7 Ga) and the Santa Margarita granite (1.1 Ga) have εNdi values of 0.56 and 4.58 and depleted mantle model ages (TDM) of 2.23 Ga and 1.34 Ga, respectively (Table 2). The initial Nd and TDM values of the El Jacalón correspond to values of the Proterozoic Mojave isotopic province of southwestern North America (Bennett and DePaolo, 1987) and are similar to values of Proterozoic granites from La Lámina (Amato et al., 2009), El Crestón (Valenzuela-Navarro, 2005), and other granite and metamorphic rocks of the Caborca block (Farmer et al., 2005) (Fig. 1). Iriondo et al. (2004) reported other Proterozoic granites of the Caborca block with εNdi values between 0.6 and 2.6 and Nd model ages between 2.07 and 1.8 Ga, and considered them to have affinity either to the Yavapai or the Mojave-Yavapai boundary zone provinces. Pb isotope data indicate that the El Jacalón pluton plots within the trend of the 1.7 Ga Mojave basement in the uranogenic diagrams of Wooden et al. (1988) and Wooden and DeWitt (1991), and the Santa Margarita granite plots in the 1.7 Ga central Arizona trend (Fig. 12B). These data plots are similar to those reported by Farmer et al. (2005) for the 1.7 and 1.1 Ga metamorphic and plutonic basement rocks of the Caborca region (Fig. 12B). The Laramide rocks of the study area and the Oposura granodiorite located east of the study area (Fig. 14) show transitional 207Pb/204Pb versus 206Pb/204Pb isotope compositions between the Mojave and Arizona trends and have values that overlap with Sonoran provinces A and B and with the Laramide Pb boundary zone of Arizona (Bouse et al., 1999). However, the El Gueriguito, the Bella Esperanza granodiorite, and sulfur mineralization of the Cananea district (Fig. 12B) are within the south-southeastern subprovince of Arizona (Bouse et al., 1999). Bouse et al. (1999) recognized that sulfur mineralization of the Cananea Mine district belongs to that subprovince. La Cubana and Vaquería plutons have the higher 207Pb/204Pb isotope values and plot in the Mojave province (Fig. 12B). In a thorogenic diagram, the Pb values of the El Jacalón and Santa Margarita plutons plot intermediate between the Mojave and central Arizona Pb isotope provinces (Wooden and Miller, 1990; Wooden and DeWitt, 1991), similar to most of the scattered field of the Proterozoic
Laramide magmatic arc in northern Sonora
Mojave province
Mojave
Northern granites of Valencia-Moreno et al. (2001) Central granites of Valencia-Moreno et al. (2001)
te as he ona t u iz So Ar
ARI
JA
s u S ou bp th ro ern v in ce
BA
ZON A
OR
A
Al
lc v
to
IA
i is
N OR LIF
sm M
CA
la
Sa
s ar c
km
Caborca
Southeast South Laramide provinces of Arizona defined by Pb isotope compositions (from Bouse et al., 1999) (blue letters)
N be eg o
Az
A
30°
Boundary of Pb isotope provinces A and B in Sonora (Housh and McDowell, 2005)
M Ma
70
B
H
200
Northwest
Mazatzal
f
80
0
Provinces of Arizona defined according to Nd-Sr isotope composition by Lang and Titley (1998)
CA
C
Eastward migration of arc 105-90 Ma
n er e th vinc r No pro b su
rn
CALIFORNIA SON
Granites of Provinces A and B of Housh and McDowell (2005)
110°
C Ar entr izo al na
Bound ary zone
Yavapai
70
50 70
Isochron of eastward migration of Laramide plutonism (age in Ma) (modified from Valencia-Moreno et al., 2006) El Gueriguito (eg), Rancho Vaquería (v), La Cubana (lc), Oposura (o) and Bella Esperanza (be) plutons Paleoproterozoic crustal provinces, inferred from Pb isotopes (Wooden and DeWitt, 1991) Granites of the Cananea-Nacozari region referred to in Figure 12
Figure 14. Map showing distribution of Proterozoic crustal provinces inferred from Pb isotopes in southwestern USA (from Wooden and Miller, 1990; Wooden and DeWitt, 1991), Nd-Sr and Pb-Pb isotope provinces of Arizona and southeastern California (Lang and Titley, 1998; Bouse et al., 1999), and boundaries of provinces A and B in Sonora (Housh and McDowell, 2005). Locations of samples that define provinces A and B and northern and central granites (Valencia-Moreno et al., 2001) are shown. Isochrones of eastward migration of the plutonic arc in Sonora are modified from McDowell et al. (2001) and Valencia-Moreno et al. (2006), and accreted Alisitos arc position is from Asleben et al. (2008). Our inferred boundary (thick black line) between the Mazatzal and Caborca crustal blocks crosses through the northeastern part of the study quadrangle between El Gueriguito and Rancho Vaquería and La Cubana plutons and continues northwest to join the San Antonio fault (Saf) of Rodríguez-Castañeda (2000). Trace of the Mojave-Sonora megashear (Msm) as drawn by Anderson and Silver (2005). Towns: Az—Arizpe; C—Caborca; CA—Cananea; H—Hermosillo; N—Nacozari; M—Moctezuma; Ma—Mazocahui; la—Rancho La Lámina.
granites and so-called Grenvillian granites reported by Iriondo et al. (2004) and Farmer et al. (2005) from the Caborca block (Fig. 12C). As noted by Bouse et al. (1999) for Arizona, the Pb isotope compositions of the Laramide granites of Sonora show a restricted range of values compared with the wider values of the Proterozoic rocks. In this diagram, our Laramide rocks overlap with the Sonoran provinces A and B and partially overlap with the Pb boundary zone of Bouse et al. (1999). Nevertheless, the El Gueriguito, Bella Esperanza granodiorite, Laramide
mineralization of the Cananea district, and probably the Oposura granodiorite cluster within the south-southeastern Arizona subprovince. Although the database is limited, isotope data of the El Gueriguito and Bella Esperanza granodiorite of the northeastern part of the study quadrangle, along with granite and mineralization of the Cananea-Nacozari region (Fig. 14), indicate isotopic affinity with the Nd, Sr, and Pb Laramide isotope province of south-southeastern Arizona located within the Mazatzal province. In contrast, data from the other Laramide
Geosphere, December 2011
rocks (including the northernmost La Cubana and Rancho Vaquería plutons; Fig. 14) of the study area, which are similar to isotope data from Laramide provinces A and B, show isotopic affinity with the Laramide Pb boundary zone of Arizona that is located with the Proterozoic boundary zone of Arizona. These isotopic affinities support the hypothesis that a crustal boundary between the Caborca block with an affinity either to Proterozoic Mojave or boundary zone provinces, and the Mazatzal province, may cross through the area.
1413
González-León et al. This boundary may occur between outcrops of the El Gueriguito and Rancho Vaquería plutons (Fig. 14), probably coincident with the thrust fault at Picacho de Arizpe that places the Bisbee Group over the Cocóspera Formation. To the northwest, this boundary may extend and continue as the San Antonio fault (RodríguezCastañeda, 2000), which also emplaces Bisbee Group strata over the Cocóspera Formation, interpreted as having formed during the early Late Cretaceous deformation. Nevertheless, the crustal boundary is not observable and its precise age is not herein constrained because the San Antonio fault may be a reactivated transtensional fault of Jurassic age (Anderson and Nourse, 2005). In any case, our inferred crustal boundary is north of the proposed trace of the MojaveSonora megashear suggested by Anderson and Silver (2005) within the study quadrangle, and also north of the Proterozoic granites of Rancho La Lámina as previously proposed by Amato et al. (2009) (Fig. 14). CONCLUSIONS Rocks of the Laramide magmatic arc of Sonora are well exposed in north-central Sonora, where the Tarahumara Formation unconformably overlaps basement rocks of Paleoproterozoic to Cenomanian age. This basement records several deformational events, the youngest of which is an early Late Cretaceous shortening that led to deposition of the clastic Cocóspera Formation, thus indicating that the volcanic arc might have been deposited over a tectonically thickened basement. The ca. 93 Ma age of the Cocóspera Formation and the ca. 80 Ma maximum age of the Tarahumara Formation constrain the duration of the shortening event from Cenomanian to early Campanian, and its inception may be related to accretion of the Alisitos arc to adjacent Baja California. The >4-km-thick Tarahumara Formation consists of a basal conglomerate overlain by dominant rhyolitic to dacitic ignimbrite, rhyolitic to andesitic ash-fall tuffs, andesite flows and breccia, interbedded volcaniclastic fluvial strata, and lacustrine limestone. The upper part of the formation consists of dacitic to rhyolitic ignimbrite and tuffs with subordinate volcaniclastic strata. Lateral facies changes are present within the study area, and further into northern Sonora it grades to the contemporaneous fluvial and lacustrine Cabullona Group. Widespread outcrops of the Tarahumara Formation extend into southern Sonora, where they are also composed of rhyolitic, dacitic, and andesitic tuffs (McDowell et al., 2001). Laramide plutons that intrude the Tarahumara Formation comprise dioritic, monzonitic, and granodioritic to
1414
granitic plutons that are given informal names. The Proterozoic El Jacalón diorite (1.7 Ga) and the Santa Margarita granite (1.1 Ga) that crop out in the western part of the study area have implications for identification of a Proterozoic crustal boundary in this part of Sonora. Geochemical data of the Laramide arc indicate that both volcanic and plutonic rocks are calc-alkaline, pertaining to Cordilleran magmatism. The age of the Tarahumara Formation in the study area ranges from ca. 80 to ca. 59 Ma, while the ages of the plutons range from 71 Ma to ca. 50 Ma. The study area was thus within isochrons 70–50 Ma, defined by the eastwardmigrating plutonism of the Laramide arc in Sonora (Valencia-Moreno et al., 2006), and a compilation of available published ages between them indicates that volcanism started near 80 Ma and ended ca. 54 Ma. Similarly, regional plutonism started ca. 72 Ma and ended at 50 Ma. These ages agree with our data obtained from the study quadrangle and indicate that regionally, magmatism lasted nearly 30 m.y., ages of volcanism are nearly 10 m.y. older than plutonism, and there were apparent major peak ages of volcanism ca. 73 Ma and a peak age of plutonism ca. 56 Ma. Magmatism as old as ca. 90 Ma in southern Sonora might be syntectonic with the early Late Cretaceous deformation event, while scarcer magmatism as young as 40 Ma corresponds to waning activity of the Laramide arc. Although structural attitudes of the Tarahumara Formation in the study area range from homoclinal to open folds apparently related to strong dissection of Cenozoic normal faulting, compressive deformation by basementcored uplift thrusting is recorded for the origin of the Cabullona basin in northeastern Sonora (González-León and Lawton, 1995). Nd and Sr isotope data of the studied Laramide rocks compare more with values of Laramide provinces A and B of Sonora (Housh and McDowell, 2005) and with those of the northwest and southeast isotopic provinces of Arizona (Lang and Titley, 1998). However, the El Gueriguito pluton in the northern part of the area has the less negative εNdi value and, along with granites of the Cananea-Nacozari region, can be compared with the neighboring south Laramide province of Arizona (Lang and Titley, 1998) (Figs. 12 and 14) that is in the Proterozoic Mazatzal province. Similarly, when Pb isotope data of the El Gueriguito quartz monzonite, Bella Esperanza granodiorite, and ore minerals from the Cananea Mine district are plotted in a uranogenic diagram (Wooden et al., 1988; Wooden and DeWitt, 1991), they show values similar to the south-southeastern province of Arizona (Bouse et al., 1999), while the other Laramide rocks plot within the field of the Pb
Geosphere, December 2011
boundary zone of Arizona (Bouse et al., 1999), but the northernmost La Cubana and Rancho Vaquería plutons plot within values of the Mojave province. The isotope affinities of the Laramide rocks indicate that a crustal boundary between the Caborca block that has an affinity to the Mojave or boundary provinces and the Mazatzal province is present in the area. This inference is supported by outcrops of the Proterozoic El Jacalón diorite, which has Mojave isotopic affinity, in the western part of the quadrangle and outcrops of Paleozoic strata belonging to the Mazatzal province in the northeastern part of the quadrangle. The boundary may be south and west of the Paleozoic outcrops and between the El Gueriguito and the Rancho Vaquería plutons, most probably following the early Late Cretaceous thrust fault at Picacho de Arizpe. The nature and age of this boundary, however, cannot be precisely determined because outcrops are covered, although it is located well to the north of the proposed trace of the Mojave-Sonora megashear in the area (Anderson and Silver, 2005). APPENDIX 1. U-Pb AGE DETERMINATION PROCEDURES AT ARIZONA LASERCHRON CENTER, GEOSCIENCES DEPARTMENT, UNIVERSITY OF ARIZONA, TUCSON Zircon crystals were extracted from samples by traditional methods of crushing and grinding, followed by separation with a Wilfley table, heavy liquids, and a Frantz magnetic separator. Samples were processed such that all zircons were retained in the final heavy mineral fraction. A large split of these grains (generally 1000–2000 grains) was incorporated into an epoxy mount together with fragments of our Sri Lanka standard zircon. The mounts were sanded down to a depth of ~20 μm, polished, imaged, and cleaned prior to isotopic analysis. U-Pb geochronology of zircons was conducted by laser ablation–multicollector–inductively coupled plasma–mass spectrometry (LA-MC-ICP-MS) at the Arizona LaserChron Center (Gehrels et al., 2006, 2008). The analyses involved ablation of zircon with a New Wave UP193HE Excimer laser (operating at a wavelength of 193 nm) using a spot diameter of 30 μm. The ablated material is carried in helium into the plasma source of a Nu Plasma high-resolution MCICP-MS, which is equipped with a flight tube of sufficient width that U, Th, and Pb isotopes are measured simultaneously. All measurements were made in static mode, using Faraday detector with 10-E11 ohm resistors for 238U, 232Th, 208Pb-206Pb, and discrete dynode ion counters for 204Pb and 202Hg. Ion yields are ~0.8 mv/ppm. Each analysis consisted of one 15 s integration on peaks with the laser off (for backgrounds), 15 1 s integrations with the laser firing, and a 30 s delay to purge the previous sample and prepare for the next analysis. The ablation pit is ~15 μm deep. For each analysis, the errors in determining 206Pb/238U and 206 Pb/204Pb resulted in a measurement error of ~1%– 2% (at 2σ level) in the 206Pb/238U age. The errors in measurement of 206Pb/207Pb and 206Pb/204Pb also result in ~1%–2% (at 2σ level) uncertainty in age for grains that are older than 1.0 Ga, but are substantially larger for younger grains due to low intensity of the 207Pb
Laramide magmatic arc in northern Sonora signal. For most analyses, the crossover in precision of 206Pb/238U and 206Pb/207Pb ages occurs at ~1.0 Ga. The 204Hg interference with 204Pb was accounted for in measurement of 202Hg during laser ablation and subtraction of 204Hg according to the natural 202Hg/204Hg of 4.35. This Hg correction is not significant for most analyses because our Hg backgrounds were low (generally ~150 cps at mass 204). Common Pb correction was accomplished by using the Hg-corrected 204Pb and assuming an initial Pb composition from Stacey and Kramers (1975). Uncertainties of 1.5 for 206Pb/204Pb and 0.3 for 207Pb/204Pb were applied to these compositional values based on the variation in Pb isotopic composition in modern crustal rocks. Interelement fractionation of Pb/U is generally ~5%, whereas apparent fractionation of Pb isotopes is generally 20% discordant (by comparison of 206Pb/238U and 206Pb/207Pb ages) or >5% reverse discordant were not considered further. The resulting interpreted ages are shown on Pb*/U concordia diagrams (Figs. 3, 7B–7I, 8C–G, and 10A–F) and relative age-probability diagrams using the routines in Isoplot (Ludwig, 2008). The age-probability diagrams show each age and its uncertainty (for measurement error only) as a normal distribution, and sum all ages from a sample into a single curve. Composite age probability plots were made from an in-house Excel program (available from www.geo .arizona.edu/alc) that normalizes each curve according to the number of constituent analyses, such that each curve contains the same area, and then stacks the probability curves. APPENDIX 2. U-Pb AGE METHODOLOGY EMPLOYED AT CENTRO DE GEOCIENCIAS, UNIVERSIDAD NACIONAL AUTÓNOMA DE MÉXICO U-Pb ages on separate zircons were dated by laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) at the Laboratorio de Estudios Isotópicos, Centro de Geociencias, Universidad Nacional Autónoma de México, according to the procedures in Solari et al. (2010). The analytical data are reported in Supplemental Table 3 (see footnote 3). The Plešovice reference zircon (ca. 337 Ma; Sláma et al., 2008) was used in combination with NIST 610 standard glass to correct for instrumental drift and down-hole fractionation and to recalculate elemental concentrations, using UPb.Age software (Solari and Tanner, 2011). Precision on the measured 207Pb/206Pb, 206 Pb/238U, and 208Pb/232Th ratios typically was ~0.8%, 0.7%, and 0.9% 1σ relative standard deviation, respectively. Replicate analyses of the Plešovice zircon indicate an external reproducibility of 0.75%, 0.6%, and 1.6% on the measured 207Pb/206Pb, 206Pb/238U, and 208Pb/232Th ratios, respectively. These errors are quadratically included in the quoted uncertainties for individual analyses of the analyzed zircons. Because its signal is swamped by the 204Hg contained in the
carrier gases, 204Pb was not analyzed during this study. Common Pb correction was thus performed employing the algebraic method of Andersen (2002). A filter was then applied to ensure the quality of selected analyses, consisting in evaluation of the concordance. For grains with ages younger than 1000 Ma, the analysis was considered concordant if the 206Pb/238U and 207Pb/235U ages differed by 2%. Samples weighing between 1 and 2 mg were degassed under high vacuum at ~150 °C for 12 h before analysis in order to reduce atmospheric contamination. Argon was extracted by total sample fusion using a 50W CO2 laser defocused to 1–3 mm diameter. The evolved gasses were mixed with a known amount of 38Ar spike and purified with a cold finger immersed in liquid nitrogen and two SAES getters in a stainless steel extraction line. Measurements were done in static mode with an MM1200B mass spectrometer using electromagnetic peak switching controlled by a Hall probe. Analytical precision on 40 Ar and 38Ar peak heights was >0.2%, and >0.6% on 36 Ar. The data were calibrated with internal standards and the international reference materials LP-6 and HD-B1 biotites. All ages were calculated using the constants recommended by Steiger and Jäger (1977). A detailed description of the procedure and calculations was given in Solé (2009). APPENDIX 4. ISOTOPIC AND SELECT TRACE ELEMENT CONCENTRATION PROCEDURES The isotopic ratios of 87Sr/86Sr, 143Nd/144Nd, and the trace element concentrations of Rb, Sr, Sm, and Nd were measured by thermal ionization mass spectrometry on whole-rock samples. Rock samples were crushed to about one-third of their grain size. Rock powders were put in large Savillex vials and dissolved in mixtures of hot concentrated HF-HNO3 or alternatively, mixtures of cold concentrated HF-HClO4. The dissolved samples were spiked with the Caltech Lunatic Asylum Rb, Sr, and mixed Sm-Nd spikes (Wasserburg et al., 1981; Ducea and Saleeby, 1998) after dissolution. Rb, Sr, and the bulk of the rare earth elements were separated in cation columns containing AG50W-X4 resin, using 1N to 4N HCl. Separation of Sm and Nd was achieved in anion column containing LN Spec resin, using 0.1N to 2.5N HCl. Rb was loaded
Geosphere, December 2011
onto single Re filaments using silica gel and H3PO4. Sr was loaded onto single Ta filaments with Ta2O5 powder. Sm and Nd were loaded onto single Re filaments using platinized carbon, and resin beads, respectively. Mass spectrometric analyses were carried out at the University of Arizona on an automated VG Sector multicollector instrument fitted with adjustable 1011 ohm Faraday collectors and a Daly photomultiplier (Otamendi et al., 2009). Concentrations of Rb, Sr, Sm, Nd were determined by isotope dilution, with isotopic compositions determined on the same spiked runs. An off-line manipulation program was used for isotope dilution calculations. Typical runs consisted of acquisition of 100 isotopic ratios. The mean result of 10 analyses of the standard NRbAAA performed during the course of this study is 85Rb/87Rb = 2.61199 ± 20. Analyses (n = 15) of standard Sr987 yielded mean ratios of 87Sr/86Sr = 0.710285 ± 7 and 84 Sr/86Sr = 0.056316 ± 12. The mean results of 5 analyses of the standard nSmβ performed during the course of this study are 148Sm/147Sm = 0.74880 ± 21, and 148Sm/152Sm = 0.42110 ± 6. Measurements (n = 15) of the LaJolla Nd standard were performed during the course of this study. The standard runs yielded the following isotopic ratios: 142Nd/144Nd = 1.14184 ± 2, 143 Nd /144Nd = 511853 ± 2, 145Nd /144Nd = 0.348390 ± 2, and 150Nd/144Nd = 0.23638 ± 2. The Sr isotopic ratios of standards and samples were normalized to 86 Sr/88Sr = 0.1194, whereas the Nd isotopic ratios were normalized to 146Nd/144Nd = 0.7219. The estimated analytical ±2σ uncertainties for samples analyzed in this study are: 87Rb/86Rb = 0.35%, 87Sr/86Sr = 0.0014%, 147 Sm/144Nd = 0.4%, and 143Nd/144Nd = 0.0012%. Procedural blanks averaged from five determinations were: Rb 10 pg, Sr 150 pg, Sm 2.7 pg, and Nd 5.5 pg. Washes from the cation column separation were used for separating Pb in Sr Spec resin (Eichrom, Darien, Illinois) columns by using protocol developed at the University of Arizona. Samples were loaded in 8M HNO3 in the Sr spec columns. Pb elution was achieved via 8M HCl. Lead isotope analysis was conducted on a GV Instruments (Hudson, New Hampshire) multicollector–inductively coupled plasma–mass spectrometer (MC-ICP-MS) at the University of Arizona (Drew et al., 2009). Samples were introduced into the instrument by free aspiration with a low-flow concentric nebulizer into a water-cooled chamber. A blank, consisting of 2% HNO3, was run before each sample. Before analysis, all samples were spiked with a Tl solution to achieve a Pb/Tl ratio of ≈10. Throughout the experiment, the NBS-981 standard was run to monitor the stability of the instrument. All results were Hg corrected and empirically normalized to Tl by using an exponential law correction. To correct for machine and interlaboratory bias, all results were normalized to values reported by Galer and Abouchami (2004) for the NBS-981 standard (206Pb/204Pb = 16.9405, 207Pb/204Pb = 15.4963, and 208Pb/204Pb = 36.7219). Internal error reflects the reproducibility of the measurements on individual samples, whereas external errors are derived from long-term reproducibility of the NBS-981 Pb standard and result in part from the mass bias effects within the instrument. In all cases, external error exceeded the internal errors: external errors associated with each Pb isotopic ratio were 206Pb/204Pb = 0.028%, 207Pb/204Pb = 0.028%, and 208Pb/204Pb = 0.031%. ACKNOWLEDGMENTS
This contribution was funded by Project 24893, granted by Consejo Nacional de Ciencia y Teconología. We thank George E. Gehrels for use of facilities of the
1415
González-León et al. Arizona LaserChron Center to perform U-Pb geochronologic analyses, and Victor Valencia for assistance with the geochronologic analyses. The Arizona LaserChron Center was supported by National Science Foundation grant EAR-0443387. We also thank Matt Heizler and Lisa Peters of the New Mexico Geochronology Research Laboratory, New Mexico Bureau of Geology & Mineral Resources, for 40Ar/39Ar analysis of the Cocóspera andesite, Elena Lounejeva for analytical support with analyses for trace elements, and Pablo Peñaflor Escárcega in Estación Regional del Noroeste (Universidad Nacional Autónoma de México, UNAM), who prepared samples for geochemical analyses and stained rock thin sections. We thank Carlos Ortega-Obregón and Ofelia PérezArvizu for laboratory assistance at Centro de Geociencias, UNAM. Lawton acknowledges partial support by National Science Foundation grant EAR-0229565. We greatly appreciate thoughtful reviews by Jonathan A. Nourse and Carl Jacobson that helped to improve the manuscript. REFERENCES CITED Alsleben, H., Wetmore, P.H., Schmidt, K.L., Paterson, S.R., and Melis, E.A., 2008, Complex deformation during arc-continent collision: Quantifying finite strain in the accreted Alisitos arc, Peninsular Ranges batholiths, Baja California: Journal of Structural Geology, v. 30, p. 220–236, doi: 10.1016/j.jsg.2007.11.001. Amato, J.M., Lawton, T.F., Mauel, D.J., Leggett, W.J., González-León, C.M., Farmer, G.L., and Wooden, J.L., 2009, Testing the Mojave-Sonora megashear hypothesis: Evidence from Paleoproterozoic igneous rocks and deformed Mesozoic strata in Sonora, Mexico: Geology, v. 37, p. 75–78, doi: 10.1130/G25240A.1. Andersen, T., 2002, Correction of common lead in U-Pb analyses that do not report 204Pb: Chemical Geology, v. 192, p. 59–79, doi: 10.1016/S0009-2541(02)00195-X. Anderson, T.H., and Nourse, J.A., 2005, Pull-apart basins at releasing bends of the sinistral Late Jurassic MojaveSonora fault system, in Anderson, T.H., et al., eds., The Mojave-Sonora megashear hypothesis: Development, assessment, and alternatives: Geological Society of America Special Paper 393, p. 97–122, doi:10.1130 /0-8137-2393-0.97. Anderson, T.H., and Silver, L.T., 1977, U-Pb isotope ages of granitic plutons near Cananea, Sonora: Economic Geology and the Bulletin of the Society of Economic Geologists, v. 72, p. 827–836, doi: 10.2113/gsecongeo .72.5.827. Anderson, T.H., and Silver, L.T., 2005, The Mojave-Sonora megashear—Field and analytical studies leading to the conception and evolution of the hypothesis, in Anderson, T.H., et al., eds., The Mojave-Sonora megashear hypothesis: Development, assessment, and alternatives: Geological Society of America Special Paper 393, p. 1–50, doi: 10.1130/0-8137-2393-0.1. Anderson, T.H., Silver, L.T., and Salas, G.A., 1980, Distribution and U-Pb isotope ages of some lineated plutons, northwestern Mexico, in Crittenden, M.D., Jr., et al., eds., Cordilleran metamorphic core complexes: Geological Society of America Memoir 153, p. 269–283. Anderson, T.H., Rodríguez-Castañeda, J.L., and Silver, L.T., 2005, Jurassic rocks in Sonora, Mexico: Relations to the Mojave-Sonora megashear and its inferred northwestward extension, in Anderson, T.H., et al., eds., The Mojave-Sonora megashear hypothesis: Development, assessment, and alternatives: Geological Society of America Special Paper 393, p. 51–95, doi:10.1130 /0-8137-2393-0.51. Arvizu, H.E., Iriondo, A., Izaguirre, A., Chávez-Cabello, G., Kamenov, G.D., Foster, D.A., Lozano-Santacruz, R., and Solis-Pichardo, G., 2009, Gneisses bandeados paleoproterozoicos (1.76–1.73 Ga) de la zona Canteras-Puerto Peñasco: una nueva ocurrencia de rocas del basamento tipo Yavapai en el NW de Sonora, México: Boletín de la Sociedad Geológica Mexicana, v. 61, p. 375–402.
1416
Bennett, V.C., and DePaolo, D.J., 1987, Proterozoic crustal history of western United States as determined by neodymium isotopic mapping: Geological Society of America Bulletin, v. 99, p. 674–685, doi: 10.1130 /0016-7606(1987)992.0.CO;2. Beraldi-Campesi, H., and Cevallos-Ferriz, S.R.S., 2005, Diversidad de microfósiles en la Formación Tarahumara, Sonora: Revista Mexicana de Ciencias Geológicas, v. 2, p. 261–271. Beraldi-Campesi, H., Cevallos-Ferriz, S.R.S., and ChacónBaca, E., 2004, Microfossil algae associated with Cretaceous stromatolite in the Tarahumara Formation, Sonora, Mexico: Cretaceous Research, v. 25, p. 249– 265, doi: 10.1016/j.cretres.2003.12.002. Bouse, R.M., Ruiz, J., Titley, S.R., Tosdal, R.M., and Wooden, J.L., 1999, Lead isotope compositions of Late Cretaceous and early Tertiary igneous rocks and sulfide minerals in Arizona: Implications for the source of plutons and metals in porphyry copper deposits: Economic Geology and the Bulletin of the Society of Economic Geologists, v. 94, p. 211–244, doi: 10.2113 /gsecongeo.94.2.211. Busby, C., 2004, Continental growth at convergent margins facing large ocean basins: A case study from Mesozoic convergent-margin basins of Baja California, Mexico: Tectonophysics, v. 392, p. 241–277, doi: 10.1016/j.tecto .2004.04.017. Busby-Spera, C.J., 1988, Speculative tectonic model for the early Mesozoic arc of the southwest Cordillera, United States: Geology, v. 16, p. 1121–1125, doi: 10.1130 /0091-7613(1988)0162.3.CO;2. Campa, M.F., and Coney, P.J., 1983, Tectonostratigraphic terranes and mineral resources distribution in Mexico: Canadian Journal of Earth Sciences, v. 20, p. 1040– 1051, doi: 10.1139/e83-094. Centeno-García, E., Busby, C., Busby, M., and Gehrels, G., 2011, Evolution of the Guerrero composite terrane along the Mexican margin, from extensional fringing arc to contractional continental arc: Geological Society of America Bulletin, v. 123, p. 1776–1797, doi: 10.1130/B30057.1. Chacón-Baca, E., Beraldi-Campesi, H., Cevallos-Ferriz, S.R.S., Knoll, A.H., and Golubic, S., 2002, 70 Ma nonmarine diatoms from northern Mexico: Geology, v. 30, p. 279–281, doi: 10.1130/0091-7613(2002)030 2.0.CO;2. Coney, P.J., and Reynolds, S.J., 1977, Cordilleran Benioff zones: Nature, v. 270, p. 403–406, doi: 10.1038 /270403a0. Corral Gastélum, R., and Hernández Morales, P., 2008, Carta Geológico-Minera Santa Ana H12–B82: Servicio Geológico Mexicano, scale 1:50,000. Cox, D.P., Miller, R.J., and Woodburne, K., 2006, The Laramide Mesa Formation and the Ojo de Agua Caldera, southeast of Cananea Copper Mining District, Sonora, Mexico: U.S. Geological Survey Scientific Investigations Report 2006–5022, 7 p. Damon, P.E., Livingston, D.E., Mauger, R.L., Giletti, B.J., and Alor, J.P., 1962, Edad del Precámbrico “Anterior” y de otras rocas del zócalo de la región de CaborcaAltar de la parte noroccidental del estado de Sonora, México: Universidad Nacional Autónoma de México, Instituto de Geología Revista, v. 64, p. 11–44. Damon, P.E., Shafiqullah, M., Roldán-Quintana, J., and Cochemé, J.J., 1983a, El batolito Laramide (90–40 Ma) de Sonora: Asociación de Ingenieros de Minas, Metalugistas y Geólogos de México (AIMMGM), Memoria técnica XV, p. 63–95. Damon, P.E., Clark, K.F., and Shafiqullah, M., 1983b, Geochronology of the porphyry copper deposits and related mineralization of Mexico: Canadian Journal of Earth Sciences, v. 20, p. 1052–1071, doi: 10.1139/e83-095. Deen, J.A., and Atkinson, W.W., Jr., 1988, Volcanic stratigraphy and ore deposits of the Moctezuma District, Sonora, Mexico: Economic Geology and the Bulletin of the Society of Economic Geologists, v. 83, p. 1841– 1855, doi: 10.2113/gsecongeo.83.8.1841. De la Roche, H., Leterrier, J., Grandclaude, P., and Marchal, M., 1980, A classification of volcanic and plutonic rocks using R1R2-diagram and major element analyses: Its relation with current nomenclature: Chemical Geology, v. 29, p. 183–210, doi: 10.1016/0009-2541(80)90020-0.
Geosphere, December 2011
Dickinson, W.R., 1981, Plate tectonic evolution of the southern Cordillera: Arizona Geological Society Digest, v. 14, p. 113–135. Dickinson, W.R., 1989, Tectonic setting of Arizona through time: Arizona Geological Society Digest, v. 17, p. 1–16. Dickinson, W.R., and Lawton, T.F., 2001, Carboniferous to Cretaceous fragmentation and assembly of Mexico: Geological Society of America Bulletin, v. 113, p. 1142–1160, doi: 10.1130/0016-7606(2001)1132.0.CO;2. Dickinson, W.R., Gehrels, G.E., and Stern, R.J., 2010, Late Triassic Texas uplift preceding Jurassic opening of the Gulf of Mexico: Evidence from U-Pb ages of detrital zircons: Geosphere, v. 6, p. 641–662, doi: 10.1130 /GES00532.1. Drew, S.T., Ducea, M.N., and Schoenbohm, L.M., 2009, Mafic volcanism on the Puna Plateau, NW Argentina: Implications for lithospheric composition and evolution with an emphasis on lithospheric foundering: Lithosphere, v. 1, p. 305–318, doi: 10.1130/L54.1. Ducea, M.N., and Saleeby, J.B., 1998, The age and origin of a thick mafic ultramafic root from beneath the Sierra Nevada batholiths: Contributions to Mineralogy and Petrology, v. 133, p. 169–185, doi: 10.1007 /s004100050445. Engebretsen, D.C., Cox, A., and Gordon, R.G., 1985, Relative motions between oceanic and continental plates in the Pacific basin: Geological Society of America Special Paper 206, 59 p. Farmer, G.L., Bowring, S.A., Matzel, J., Espinoza-Maldonado, G., Fedo, C., and Wooden, J., 2005, Paleoproterozoic Mojave province in northwestern Mexico? Iso tope and U-Pb zircon geochronologic studies of Precambrian and Cambrian crystalline and sedimentary rocks, Caborca, Sonora, in Anderson, T.H., et al., eds., The Mojave-Sonora megashear hypothesis: Development, assessment, and alternatives: Geological Society of America Special Paper 393, p. 183–198, doi:10.1130/0-8137-2393-0.183. Frost, B.R., Barnes, C.G., Collins, W.J., Arculus, R.J., Ellis, D.J., and Frost, C.D., 2001, A geochemical classification for granitic rocks: Journal of Petrology, v. 42, p. 2033–2048, doi: 10.1093/petrology/42.11.2033. Galer, S.J.G., and Abouchami, W., 2004, Mass bias correction laws suitable for MC-ICP-MS measurement: Geochimica et Cosmochimica Acta, v. 68, p. A542. Gastil, G., Diamond, J., Knaack, C., Walawender, M., Marshall, M., Boyles, C., Chadwick, B., and Erskine, B., 1990, The problem of the magnetite/ilmenite boundary in southern and Baja California, in Anderson, J.L., ed., The nature and origin of Cordilleran magmatism: Geological Society of America Memoir 174, p. 19–32. Gehrels, G., Valencia, V., and Pullen, A., 2006, Detrital zircon geochronology by laser ablation multicollector ICPMS at the Arizona LaserChron Center, in Olszewski, T., ed., Geochronology: Emerging opportunities: Paleontology Society Papers, v. 12, p. 67–76. Gehrels, G.E., Valencia, V.A., and Ruiz, J., 2008, Enhanced precision, accuracy, efficiency, and spatial resolution of U-Pb ages by laser ablation–multicollector–inductively coupled plasma–mass spectrometry: Geochemistry Geophysics Geosystems, v. 9, Q03017, doi: 10.1029 /2007GC001805. Gilmont, N.L., 1978, Geology of the Puerto La Bandera area, Sonora, Mexico [M.S. thesis]: Flagstaff, University of Northern Arizona, 109 p. González Becuar, E., 2011, Geología, geoquímica y geocronología del área de Puerta del Sol, Sonora central, México [B.S. thesis]: Hermosillo, Universidad de Sonora, 65 p. González Gallegos, A., Morales Morales, H., and Orantes Contreras, V., 2003, Carta geológico-minera Arizpe H12B73: Servicio Geológico Mexicano, scale 1:50,000. González-León, C., 1986, Estratigrafía del Paleozoico de la sierra del Tule, noreste de Sonora: Universidad Nacional Autónoma de México: International Geology Review, v. 6, p. 117–135. González-León, C., and Lawton, T.F., 1995, Stratigraphy, depositional environments, and origin of the Cabullona basin, northeastern Sonora, in Jacques-Ayala, C., et al., eds., Studies on the Mesozoic of Sonora and adjacent
Laramide magmatic arc in northern Sonora areas: Geological Society of America Special Paper 301, p. 121–142, doi: 10.1130/0-8137-2301-9.121. González-León, C., McIntosh, W.C., Lozano-Santacruz, R., Valencia-Moreno, M., Amaya-Martínez, R., and Rodríguez Castañeda, J.L., 2000, Cretaceous and Tertiary sedimentary, magmatic, and tectonics evolution of north-central Sonora (Arizpe and Bacanuchi quadrangles), northwest Mexico: Geological Society of America Bulletin, v. 112, p. 600–611, doi: 10.1130 /0016-7606(2000)1122.0.CO;2. González-León, C.M., Valencia, V.A., Lawton, T.F., Amato, J., Gehrels, G.E., Leggett, W.J., Montijo Contreras, O., and Fernández, M.A., 2009, The lower Mesozoic record of detrital zircon U-Pb geochronology of Sonora, Mexico and its paleogeographic implications: Revista Mexicana de Ciencias Geológicas, v. 26, p. 301–314. González-León, C.M., Valencia, V., López, M., Bellon, H., Valencia Moreno, M.A., and Calmus, T., 2010, The Arizpe sub-basin: Sedimentary and magmatic evolution of the Basin and Range in north-central Sonora, Mexico: Revista Mexicana de Ciencias Geológicas, v. 27, p. 292–312. Hayes, P.T., and Landis, E.R., 1965, Paleozoic stratigraphy of the southern part of the Mule Mountains, Arizona: U.S. Geological Survey Bulletin, v. 1201-F, p. F1–F43. Hernández-Castillo, G.R., and Cevallos-Ferriz, S.R.S., 1999, Reproductive and vegetative organs with affinities to Haloragacea from the Upper Cretaceous Huépac Chert locality of Sonora, Mexico: American Journal of Botany, v. 86, p. 1717–1734, doi: 10.2307/2656670. Housh, T.B., and McDowell, F.W., 2005, Isotope provinces in Laramide and mid-Tertiary igneous rocks of northwestern Mexico (Chihuahua and Sonora) and their relation to basement configuration, in Anderson, T.H., et al., eds., The Mojave-Sonora megashear hypothesis: Development, assessment, and alternatives: Geological Society of America Special Paper 393, p. 671–692, doi: 10.1130/2005.2393(25). Iriondo, A., Premo, W.R., Martínez-Torres, L.M., Budahn, J.R., Atkinson, W.W., Jr., Siems, D.F., and GuarásGonzález, B., 2004, Isotopic, geochemical, and temporal characterization of Proterozoic basement rocks in the Quitovac region, northwestern Sonora, Mexico: Implications for the reconstruction of the southwestern margin of Laurentia: Geological Society of America Bulletin, v. 116, p. 154–170, doi: 10.1130/B25138.1. Johnson, S.E., Tate, M.C., and Fanning, C.M., 1999, New geologic mapping and SHRIMP U-Pb zircon data in the Peninsular Ranges batholith, Baja California, Mexico: Evidence for a suture?: Geology, v. 27, p. 743–746, doi: 10.1130/0091-7613(1999)0272.3.CO;2. Lang, J.R., and Titley, S.R., 1998, Isotopic and geochemical characteristics of Laramide magmatic systems in Arizona and implications for the genesis of porphyry copper deposits: Economic Geology and the Bulletin of the Society of Economic Geologists, v. 93, p. 138–170, doi: 10.2113/gsecongeo.93.2.138. Lawton, T.F., González-León, C.M., Amato, J.M., Iriondo, A., Leggett, W.J., Mauel, D.J., and Peryam, T.C., 2009, Contrasting tectonic regimes recorded by Jurassic and Cretaceous arc-related sedimentary basins, Sonora, Mexico: Geological Society of America Abstracts with Programs, v. 41, no. 7, p. 137. Lawton, T.F., Barboza-Gudiño, R., González-León, C.M., Iriondo, A., Leggett, W.J., Peryam, T.C., and RubioCisneros, I.I., 2010, Latest Triassic–Middle Jurassic age of Cordilleran-Nazas arc in Mexico indicated by U-Pb detrital zircon and volcanic-rock ages: Geological Society of America Abstracts with Programs, v. 42, no. 5, p. 345. Leggett, W.J., Lawton, T.F., Amato, J.M., and GonzálezLeón, C.M., 2007, New age constraints and geochemical data on Early to Middle Jurassic strata near Cucurpe, Sonora, Mexico: A record of the CordilleranNazas arc in north-central Sonora, in Spencer, J.A., ed., Ores and orogenesis: A symposium honoring the career of William R. Dickinson, program with abstracts: Tucson, Arizona Geological Society, p. 148. López-Higuera, A., Martínez-Hernández, E., and GonzálezLeón, C.M., 2008, Upper Cretaceous pollen from the Cabullona basin, northeastern Sonora, Mexico—Pre-
liminary results: 12th International Palynological Congress, 8th International Organisation of Paleobotany Conference, Abstract Volume, Bonn, Germany: Terra Nostra, 2008, no. 2, p. 424. Ludwig, K., 2008, User’s manual for Isoplot 3.6: Geochronological toolkit for Microsoft Excel: Berkeley Geochronology Center Special Publication 4, revised, 77 p. Ludwig, K.L., and Mundil, R., 2002, Extracting reliable U-Pb ages and errors from complex populations of zircons from Phanerozoic tuffs: Conference abstracts, 12th Goldschmidt Conference: Geochimica et Cosmochimica Acta, v. 66, p. A463. Lugo Zazueta, R.E., 2006, Extensión Basin and Range en la Sierra de Aconchi, Sonora, México: análisis termocronológico basado en 40Ar/39Ar y trazas de fisión [M.S. thesis]: Hermosillo, Universidad Nacional Autónoma de México, 77 p. Macias Valdez, G., 1992, Geoquímica (elementos mayores, trazas y tierras raras) del granito de Huépac (Sonora): implicaciones petrogenéticas y tectónicas [B.S. thesis]: Sonora, México, Universidad de Sonora, 152 p. Maniar, P.D., and Piccoli, P.M., 1989, Tectonic discrimination of granitoids: Geological Society of America Bulletin, v. 101, p. 635–643, doi: 10.1130/0016-7606(1989)101 2.3.CO;2. Mauel, D.J., 2008, Stratigraphy, sedimentology, and geochronology of Upper Jurassic rocks of the AltarCucurpe Basin in the vicinity of Cucurpe, north-central Sonora, Mexico [M.S. thesis]: Las Cruces, New Mexico State University, 174 p. Mauel, D.J., Lawton, T.F., González-León, C.M., Iriondo, A., and Amato, J.M., 2011, Stratigraphy and age of Upper Jurassic strata in north-central Sonora, Mexico: Southwestern Laurentian record of crustal extension and tectonic transition: Geosphere, v. 7, p. 390–414, doi: 10.1130/GES00600.1. McAnulty, W., 1970, Geology of the northern Nacozari district, Sonora, Mexico [Ph.D. thesis]: Albuquerque, University of New Mexico, 103 p. McDonough, W.F., and Sun, S.S., 1995, The composition of the Earth: Chemical Geology, v. 120, p. 223–253, doi: 10.1016/0009-2541(94)00140-4. McDowell, F.W., and Mauger, R.L., 1994, K-Ar and U-Pb zircon chronology of Late Cretaceous and Tertiary magmatism in central Chihuahua state, Mexico: Geological Society of America Bulletin, v. 106, p. 118–132, doi: 10.1130/0016-7606(1994)1062.3.CO;2. McDowell, F.W., Roldán-Quintana, J., and Connelly, J.N., 2001, Duration of Late Cretaceous–early Tertiary magmatism in east-central Sonora, Mexico: Geological Society of America Bulletin, v. 113, p. 521–531, doi: 10.1130 /0016-7606(2001)1132.0.CO;2. Mead, R.D., Kesler, S.E., Foland, K.A., and Jones, L.M., 1988, Relationship of Sonora tungsten mineralization to the metallogenic evolution of Mexico: Economic Geology and the Bulletin of the Society of Economic Geologists, v. 83, p. 1943–1965, doi: 10.2113/gsecongeo .83.8.1943. Nourse, J.A., Anderson, T.H., and Silver, L.T., 1994, Tertiary metamorphic core complexes in Sonora, northwest Mexico: Tectonics, v. 13, p. 1161–1182, doi: 10.1029 /93TC03324. Nourse, J.A., Premo, W.R., Iriondo, A., and Stahl, E.R., 2005, Contrasting Proterozoic basement complexes near the truncated margin of Laurentia, northwestern Sonora-Arizona international border, in Anderson, T.H., et al., eds., The Mojave-Sonora megashear hypothesis: Development, assessment, and alternatives: Geological Society of America Special Paper 393, p. 123–182, doi: 10.1130/2005.2393(04). Otamendi, J.E., Ducea, M.N., Tibaldi, A.M., Bergantz, G.W., de la Rosa, J.D., and Vujovich, G.I., 2009, Generation of tonalitic and dioritic magmas by coupled partial melting of gabbroic and metasedimentary rocks within the deep crust of the Famatinian magmatic arc, Argentina: Journal of Petrology, v. 50, p. 841–873, doi: 10.1093/petrology/egp022. Page, W.R., Gray, F., Iriondo, A., Miggins, D., Blodgett, R.B., Maldonado, F., and Miller, R.J., 2010, Stratigraphy and Mesozoic-Cenozoic tectonic history of northern Sierra Los Ajos and adjacent areas, Sonora,
Geosphere, December 2011
Mexico: Journal of South American Earth Sciences, v. 29, p. 557–571, doi: 10.1016/j.jsames.2009.11.008. Pearce, J.A., Harris, N.B.W., and Tindle, A.G., 1984, Trace element discrimination diagrams for the tectonic interpretation of granitic rocks: Journal of Petrology, v. 25, p. 956–983, doi: 10.1093/petrology/25.4.956. Peccerillo, A., and Taylor, S.R., 1976, Geochemistry of Eocene calc-alkaline volcanic rocks from the Kastamonu area, northern Turkey: Contributions to Mineralogy and Petrology, v. 58, p. 63–81, doi: 10.1007/BF00384745. Pérez-Segura, E., González-Partida, E., and Valencia, V.A., 2009, Late Cretaceous adakitic magmatism in eastcentral Sonora, Mexico, and its relation to Cu-ZnNi-Co skarns: Revista Mexicana de Ciencias Geológicas, v. 26, p. 411–427. Pérez-Segura, E., and González-Partida, E., 2010, Mineralogía de skarn y fluidos asociados a los yacimientos de Cu-Zn-Ni-Co de La Esperanza, Sonora, México: Revista Mexicana de Ciencias Geológicas, v. 27, p. 1–17. Peryam, T.C., 2006, Stratigraphy, sedimentology, geochronology, and sediment provenance of Lower Cretaceous strata of the Altar-Cucurpe basin, north-central Sonora, Mexico: Implications for the tectonic evolution of northwestern Mexico [M.S. thesis]: Las Cruces, New Mexico State University, 247 p. Peryam, T.C., Lawton, T.F., Amato, J.M., González-León, C.M., and Mauel, D.J., 2011, Lower Cretaceous strata of the Sonora Bisbee basin: A record of the tectonomagmatic evolution of northwestern Mexico: Geological Society of America Bulletin, doi:10.1130 /B30456.1 (in press). Plascencia Corrales, C.A., 2008, Caracterización estratigráfica y petrográfica de la Formación Tarahumara en el área de Banámichi, Sonora [M.S. thesis]: Hermosillo, Centro de Estudios Superiores del Estado de Sonora, 65 p. Poole, F.G., Perry, W.J., Jr., Madrid, R.J., and AmayaMartínez, R., 2005, Tectonic synthesis of the OuachitaMarathon-Sonora orogenic margin of southern Laurentia: Stratigraphic and structural implications for timing of deformational events and plate-tectonic model, in Anderson, T.H., et al., eds., The MojaveSonora megashear hypothesis: Development, assessment, and alternatives: Geological Society of America Special Paper 393, p. 543–596, doi: 10.1130/2005 .2393(21). Quevedo León, A., and Ramírez López, J., 2008, Carta geológico-minera Banámichi H12B83: Servicio Geológico Mexicano, scale 1:50,000. Radelli, L., Soto-V, I., Urrutia-B., J., and Macias-V., G., 1991, Discovery of Columbite tantalite in Sonora, Mexico: Universidad de Sonora, Departamento de Geología Boletin, v. 8, p. 7–11. Ramos-Velázquez, E., Calmus, T., Valencia, V., Iriondo, A., Valencia-Moreno, M., and Bellon, H., 2008, U-Pb and 40 Ar/39Ar geochronology of the coastal Sonora batholith: New insights on Laramide continental arc magmatism: Revista Mexicana de Ciencias Geológicas, v. 25, p. 314–333. Rangin, C., 1986, Contribution à l’étude géologique form du système Cordillerain mesozoique du nord-ouest du Mexique: Societé Géologique de France, Memoire 148, 136 p. Rascón Heimpel, M., Valencia-Moreno, M., Ochoa Landin, L., Calmus, T., and Martínez Muller, R., 2010, Geología y geoquímica del prospecto pórfido cuprífero Los Alisos, distrito minero de Nacozari, Sonora, México, in Valencia-Moreno, M., and Manea, M., eds., La Orogenia Laramide del SW de Norte América, Simposio GeoLaramide: Universidad Nacional Autónoma de México y Universidad de Sonora, resúmenes, p. 37. Richard, D., Bonin, B., and Monod, O., 1989, Les granites du Sonora (Mexique) et leur contexte géodynamique: Paris, Académie des Sciences Comptes Rendus, v. 308, série II, p. 537–543. Riggs, N.R., Mattinson, J.M., and Busby, C.J., 1993, Correlation of Jurassic eolian strata between the magmatic arc and the Colorado Plateau: New U-Pb geochronologic data from southern Arizona: Geological Society of America Bulletin, v. 105, p. 1231–1246 doi: 10.1130 /0016-7606(1993)1052.3.co;2.
1417
González-León et al. Rodríguez-Castañeda, J.L., 1994, Geología del área El Teguachi, estado de Sonora, México: Revista Mexicana de Ciencias Geológicas, v. 11, p. 11–28. Rodríguez-Castañeda, J.L., 2000, Deformación Sonorense: tectónica extensional en el área rancho San Antonio, Sonora norte-central—sus efectos y características en rocas cretácicas y terciarias [Ph.D. thesis]: México, D.F., Universidad Nacional Autónoma de México, 217 p. Roldán-Quintana, J., 1989, Geología de la Hoja Baviácora, Sonora: Universidad Nacional Autónoma de México, Instituto de Geología Revista, v. 8, p. 1–14. Roldán-Quintana, J., 1991, Geology and chemical composition of El Jaralito and Aconchi batholiths in east-central Sonora, in Pérez-Segura, E., and Jacques-Ayala, C., eds., Studies of Sonoran geology: Geological Society of America Special Paper 254, p. 19–36. Roldán-Quintana, J., Lozano-Santacruz, R., and ArrazoloReyna, S., 1989, Pegmatitas de la sierra El Jaralito al suroeste de Baviácora, Sonora: Universidad Nacional Autónoma de México, Instituto de Geología Revista, v. 8, p. 15–22. Roldán-Quintana, J., McDowell, F.W., Delgado-Granados, H., and Valencia-Moreno, M., 2009, East-west variations in age, chemical and isotopic composition of the Laramide batholith in southern Sonora, Mexico: Revista Mexicana de Ciencias Geológicas, v. 26, p. 543–563. Scherkenbach, D.A., Sawkins, F.J., and Seyfried, W.E., Jr., 1985, Geologic, fluid inclusion, and geochemical studies of the mineralized breccias at Cumobabi, Sonora, Mexico: Economic Geology and the Bulletin of the Society of Economic Geologists, v. 80, p. 1566–1592, doi: 10.2113/gsecongeo.80.6.1566. Servicios Geológicos y Cartográficos del Noroeste, S.A. de C.V., 1999, Carta geológico-minero Baviácora H12D23: Servicio Geológico Mexicano, scale 1:50,000. Silver, L.T., and Anderson, T.H., 1974, Possible left-lateral early to middle Mesozoic disruption of the southwestern North America craton: Geological Society of America Abstracts with Programs, v. 6, p. 955. Silver, L.T., and Chappell, B.W., 1988, The Peninsular Ranges batholith: An insight into the evolution of the Cordilleran batholiths of southwestern North America: Royal Society of Edinburgh Transactions, v. 79, p. 105–121. Sláma, J., Košler, J., Condon, D.J., Crowley, J.L., Gerdes, A., Hanchar, J.M., Horstwood, M.S.A., Morris, G.A., Nasdala, L., Norberg, N., Schaltegger, U., Schoene, B., Tubrett, M.N., and Whitehouse, M.J., 2008, Plešovice zircon—A new natural reference material for U-Pb and Hf isotopic microanalysis: Chemical Geology, v. 249, p. 1–35, doi: 10.1016/j.chemgeo.2007.11.005. Solari, L.A., and Tanner, M., 2011, UPb.age, a fast data reduction script for LA-ICP-MS U-Pb geochronology: Revista Mexicana de Ciencias Geológicas, v. 28, p. 83–91. Solari, L.A., Gómez-Tuena, A., Bernal, J.P., Pérez-Arvizu, O., and Tanner, M., 2010, U-Pb zircon geochronology by an integrated LA-ICPMS microanalytical workstation: Achievements in precision and accuracy: Geostandards and Geoanalytical Research, v. 34, p. 5–18, doi: 10.1111/j.1751-908X.2009.00027.x. Solé, J., 2009, Determination of K-Ar ages in milligram samples using an infrared laser for argon extraction: Rapid Communications in Mass Spectrometry, v. 23, p. 3579–3590, doi: 10.1002/rcm.4280.
1418
Solé, J., and Enrique, P., 2001, X-ray fluorescence analysis for the determination of potassium in small quantities of silicate minerals for K-Ar dating: Analytica Chimica Acta, v. 440, p. 199–205, doi: 10.1016/S0003-2670 (01)01060-1. Stacey, J.S., and Kramers, J.D., 1975, Approximation of terrestrial lead isotope evolution by a two-stage model: Earth and Planetary Science Letters, v. 26, p. 207–221, doi: 10.1016/0012-821X(75)90088-6. Steiger, R.H., and Jäger, E., 1977, Subcommission on geochronology: Convention on the use of decay constants in geo- and cosmochronology: Earth and Planetary Science Letters, v. 36, p. 359–362, doi: 10.1016/0012-821X (77)90060-7. Stewart, J.H., and Poole, F.G., 2002, Inventory of Neoproterozoic and Paleozoic strata in Sonora, Mexico: U.S. Geological Survey Open-File Report 02–97, 49 p. Stewart, J.H., Amaya-Martínez, R., Stamm, R.G., Warldaw, B.R., Stanley, G.D., Jr., and Stevens, C.H., 1997, Stratigraphy and regional significance of Mississippian to Jurassic rocks in sierra Santa Teresa, Sonora, Mexico: Revista Mexicana de Ciencias Geológicas, v. 14, p. 115–135. Stewart, J.H., Poole, F.G., Harris, A.G., Repetski, J.E., Warldaw, B.R., Mamet, B.L., and Morales-Ramírez, J.M., 1999, Neoproterozoic(?) to Pennsylvanian innershelf, miogeoclinal strata in sierra Agua Verde, Sonora, Mexico: Revista Mexicana de Ciencias Geológicas, v. 16, p. 35–62. Stewart, J.H., Amaya-Martínez, R., and Palmer, A.R., 2002, Neoproterozoic and Cambrian strata of Sonora, Mexico: Rodinian supercontinent to Laurentian Cordilleran margin, in Barth, A., ed., Contributions to crustal evolution of the southwestern United States: Geological Society of America Special Paper 365, p. 5–48, doi: 10.1130 /0-8137-2365-5.5. Stock, J., and Molnar, P., 1988, Uncertainties and implications of the Late Cretaceous and Tertiary position of North America relative to the Farallon, Kula and Pacific plates: Tectonics, v. 7, p. 1339–1384, doi: 10.1029 /TC007i006p01339. Taliaferro, N.L., 1933, An occurrence of Upper Cretaceous sediments in northern Sonora, Mexico: Journal of Geology, v. 41, p. 12–37. Valencia, V.A., Ruiz, J., Barra, F., Gehrels, G.E., Ducea, M., Titley, S.R., and Ochoa-Landin, L., 2005, U-Pb zircon and Re-Os molybdenite geochronology from La Caridad porphyry copper deposit: Insights for the duration of magmatism and mineralization in the Nacozari District, Sonora, Mexico: Mineralium Deposita, v. 40, p. 175–191, doi: 10.1007/s00126-005-0480-1. Valencia-Moreno, M., Ruiz, J., Barton, M.D., Patchett, P.J., Zürcher, L., Hodkinson, D.G., and Roldán-Quintana, J., 2001, A chemical and isotopic study of the Laramide granitic belt of northwestern Mexico: Identification of the southern edge of the North American Precambrian basement: Geological Society of America Bulletin, v. 113, p. 1409–1422, doi: 10.1130/0016-7606 (2001)1132.0.CO;2. Valencia-Moreno, M., Ruiz, J., Ochoa-Landín, L., MartínezSerrano, R., and Vargas-Navarro, P., 2003, Geochemistry of the Coastal Sonora batholith, northwestern Mexico: Canadian Journal of Earth Sciences, v. 40, p. 819–831, doi: 10.1139/e03-020. Valencia-Moreno, M.A., Iriondo, A., and González-León, C.M., 2006, Temporal constraints on the eastward migration of the Late Cretaceous–Early Tertiary magmatic
Geosphere, December 2011
arc of NW Mexico based on Ar/Ar hornblende geochronology of granitic rocks: Journal of South American Earth Sciences, v. 22, p. 22–38, doi: 10.1016/j.jsames .2006.08.006. Valentine, W.G., 1936, Geology of the Cananea Mountains, Sonora, Mexico: Geological Society of America Bulletin, v. 47, p. 53–86. Valenzuela Navarro, L.C., Valencia-Moreno, M., Calmus, T., Ochoa-Landín, L., and González-León, C., 2005, Geológico del pórfido de molibdeno El Crestón, Sonora central, México: Revista Mexicana de Ciencias Geológicas, v. 22, p. 345–357. Villaseñor, A.B., González-León, C.M., Lawton, T.F., and Aberhan, M., 2005, Upper Jurassic ammonites and bivalves from the Cucurpe Formation, Sonora, Mexico: Revista Mexicana de Ciencias Geológicas, v. 22, p. 65–87. Wasserburg, G.J., Jacobsen, S.B., DePaolo, D.J., McCulloch, M.T., and Wen, T., 1981, Precise determination of Sm/Nd ratios, Sm and Nd isotopic abundances in standard solutions: Geochimica et Cosmochimica Acta, v. 45, p. 2311–2323, doi: 10.1016/0016-7037(81)90085-5. Wilson, F.I., and Rocha, S.V., 1949, Coal deposits of the Santa Clara district near Tonichı´, Sonora, Mexico: U.S. Geological Survey Bulletin 962A, 80 p. Wodzicki, W.A., 1994, The evolution of Laramide igneous rocks and porphyry copper mineralization in the Cananea district, Sonora, Mexico [Ph.D. thesis]: Tucson, University of Arizona, 181 p. Wong, M.S., and Gans, P.B., 2008, Geologic, structural and thermochronological constraints on the tectonic evolution of the Sierra Mazatán core complex, Sonora, Mexico: New insights into metamorphic core complex formation: Tectonics, v. 27, TC4013, doi: 10.1029 /2007TC002173. Wong, M.S., Gans, P.B., and Scheier, J., 2010, The 40Ar/39Ar thermochronology of core complexes and other basement rocks in Sonora, Mexico: Implications for Cenozoic tectonic evolution of northwestern Mexico: Journal of Geophysical Research, v. 115, B07414, doi: 10.1029 /2009JB007032. Wooden, J.L., and DeWitt, E., 1991, Pb isotopic evidence for the boundary between the Early Proterozoic Mojave and central Arizona crustal provinces in western Arizona, in Karlstrom, K.E., ed., Early Proterozoic geology and ore deposits of Arizona: Arizona Geological Society Digest, v. 19, p. 27–50. Wooden, J.L., and Miller, D.M., 1990, Chronologic and isotopic framework for early Proterozoic crustal evolution in the eastern Mojave Desert region, SE California: Journal of Geophysical Research, v. 95, p. 20133– 20146, doi: 10.1029/JB095iB12p20133. Wooden, J.L., Stacey, J.S., Howard, K.A., Doe, B.R., and Miller, D.M., 1988, Pb isotopic evidence for the formation of Proterozoic crust in the southwestern United States, in Ernst, W.G., ed., Metamorphism and crustal evolution, western conterminous United States: Rubey Volume 7: Englewood Cliffs, New Jersey, PrenticeHall, p. 68–86. Zuñiga Hernández, L.G., 2010, Estudio geológico, geoquímico y metalognético del cuadrángulo HuépacMoctezuma, centro-norte de Sonora, México [M.S. thesis]: Hermosillo, Universidad de Sonora, 126 p. MANUSCRIPT RECEIVED 25 FEBRUARY 2011 REVISED MANUSCRIPT RECEIVED 21 JUNE 2011 MANUSCRIPT ACCEPTED 23 JUNE 2011
