Sierra de Catorce: Remnants of the ancient western

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outcrops from west to east along the Arroyo San Antonio, con- ...... out near El Alamito, west of Rioverde, 200 km SE of Catorce, and with strata of the ...
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The Geological Society of America Field Guide 25 2012

Sierra de Catorce: Remnants of the ancient western equatorial margin of Pangea in central Mexico José Rafael Barboza-Gudiño* Instituto de Geología, Universidad Autónoma de San Luis Potosí, Manuel Nava 5, Zona Universitaria C.P. 78240 San Luis Potosí, S.L.P, México Roberto S. Molina-Garza Centro de Geociencias, Universidad Nacional Autónoma de México, Campus Juriquilla, Querétaro Timothy F. Lawton Department of Geological Sciences, New Mexico State University, Las Cruces, New Mexico 88003, USA

ABSTRACT The Sierra de Catorce in northern San Luis Potosí, Mexico, represents an uplifted block with exposures of the oldest rocks of the region which include Upper Triassic turbidites interpreted as deposits of a submarine fan system (“Potosí Fan”) and overlying Lower Jurassic volcanic and volcaniclastic strata interpreted as a record of the Early-Middle Jurassic volcanic arc (“Nazas Arc”) of western North America. These lower Mesozoic units, recognized in several exposures in the region, are interpreted as remnants of the ancient western margin of Pangea prior to accretion of Late Jurassic–Early Cretaceous magmatic arc complexes and associated marginal basins that constitute the Guerrero composite terrane in western Mexico and that resulted in construction of a new Pacific margin. A field trip in the Sierra de Catorce and surrounding exposures of the Upper Triassic–Lower Jurassic succession allows observation and discussion of key features that demonstrate the sedimentary and tectonic history of the western equatorial margin of Pangea. INTRODUCTION

faults, which are cut also by west-northwest–striking normal faults. The Sierra de Catorce is reached by an ~200 km freeway from San Luis Potosí to Matehuala and then to Cedral, along the northern side of the Sierra. The village of Real de Catorce, in the internal part of the sierra is reached by a 14 km long road, and the ~2.7 km long “Tunel de Ogarrio,” constructed in 1800 as the access to the old mining district located at an altitude of 2700 m (Fig. 1).

The Sierra de Catorce, located at the eastern edge of the Mesa Central Province, directly west of the Sierra Madre Oriental, in northern San Luis Potosí, Mexico, represents an uplifted block with an internal folded structure and exposures of the oldest rocks of the region. The current horst structure of the sierra is delimited by “basin and range” north-south–striking normal

*[email protected] Barboza-Gudiño, J.R., Molina-Garza, R.S., and Lawton, T.F., 2012, Sierra de Catorce: Remnants of the ancient western equatorial margin of Pangea in central Mexico, in Aranda-Gómez, J.J., and Tolson, G., eds., [[space for volume title space for volume title space for volume title space for volume title space for volume title]]: Geological Society of America Field Guide 25, p. 1–18, doi:10.1130/2012.0025(01). For permission to copy, contact [email protected]. ©2012 The Geological Society of America. All rights reserved.

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Barboza-Gudiño et al.

Discovered before 1773, Real de Catorce was an important mining district during the nineteenth and part of the twentieth centuries. The district attracted the attention of Mexican and foreign miners, as well as geoscientists. For geologists, the district offers an interesting stratigraphic section which records the complex tectonic evolution described in several published works (del Castillo and Aguilera-Serrano, 1895; Baker, 1922; Erben, 1956; Mixon, 1963; Bacon, 1978; Cuevas-Pérez, 1985; Zarate del Valle, 1982; López-Infanzón, 1986; Barboza-Gudiño, 1989; Barboza-Gudiño et al., 1999, 2004; Franco-Rubio, 1999; Hoppe, 2000).

Triassic to Lower Jurassic lithostratigraphic units exposed in the Sierra de Catorce, as well as in several places in the Mesa Central, such as Charcas, Presa de Santa Gertrudis, La Ballena, Zacatecas, and Sierra de Teyra, are closely related to the ancient western equatorial margin of Pangea. After collision and suturing of Laurentia and Gondwana during the Late Paleozoic, the region of what today is central Mexico occupied a remnant basin at the westernmost culmination of the Ouachita-Marathon belt, at the west equatorial margin of Pangea. The earliest deposits in this paleo-pacific sub-basin were Middle to Upper Triassic turbidites

28

To Monterrey

33

To Laredo

38

Estación Vanegas Cedral

ZA C ATE CAS N LU IS P OT OS Í

N

SA

263

N

Real de Catorce La Paz

Estación Catorce

Matehuala Santa Rita

Refugio de Coronados

SAN LUIS POTOSÍ

Villa de Guadalupe

eón vo L Nue í otos is P

Lu San

Guadalupe del Carnicero

258

258

San Francisco Charcas Estación Charcas

San Rafael

Entronque El Huizache

Venado

63

253

Moctezuma

57

To Zacatecas

16

Guadalcázar

Arista

49

La Ballena

Villa Hidalgo slp Ahualulco

La Pendencia Villa Hidalgo zac.

248

Pinos

Potosí

SAN LUIS POTOSÍ

San Luis

Zacatecas

Mexquitic

To Ríoverde

248

70

Key areas

80

243

To Cd. del Maíz

253

57

JA LIS CO

243

km

Ojuelos 23

0

10

20

50

GUANAJUATO GUANAJUATO 28

To Queretaro 33

Figure 1. Locality map and access to the selected areas.

38

fld025-01 1st pgs page 3 Sierra de Catorce

3

In our interpretation, the Potosí Fan was formed in a basinal setting at the western margin of Pangea. As a consequence of latest Triassic–Early Jurassic subduction along this continental margin, the Potosí Fan was deformed and uplifted, so that the first volcanic deposits of the Nazas Formation are subaerial and rest unconformably on the Triassic Zacatecas Formation. The Nazas Formation is unaffected by the intense folding and thrusting registered in the Triassic rocks. Deposits of La Joya Formation represent development of an erosional unconformity following the main period of volcanic activity and erosion of the arc in an extensional setting. The main goal of this excursion is to visit some of the Lower Mesozoic stratigraphic units (Upper Triassic–Middle Jurassic)

known as the Zacatecas Formation and interpreted as deposits of a submarine fan named the Potosí Fan (Silva-Romo et al., 2000). Deposition of the fan was followed by deposition of volcanic and volcaniclastic strata of the Lower Jurassic Nazas Formation, interpreted as remnants of the Early Jurassic continental volcanic arc, known also as “Nazas Arc.” Overlying the Nazas succession, the La Joya Formation, consisting of Middle to Upper Jurassic alluvial to lagoonal and shallow marine deposits, represents a basal transgressive succession in the region (Michalzik, 1988). This unit grades upsection to the Upper Jurassic–Cretaceous carbonate and evaporitic successions of the Gulf Series which are widely distributed from north-central to northeastern Mexico (Figs. 2 and 3).

101°

Monterrey

N

COAHUILA

Juarez

Saltillo ra er Si

NUEVO LEÓN

de co ul m Ji

Si de

Ra m

Rodeo Caopas

S.MARCOS

M

n

de

ire z

Galeana

liá Ju

DURANGO

ra

n Sa S.

er ra

S.

r e ad

a

yr

Te

S i e r r a

Si

er

Aramberri Miquihuana

Catorce

Mesa Central

S Cha. de rcas

Sierra de

Matehuala

ZACATECAS

Charcas

SAN LUIS POTOSÍ

O r i e n t a l

al nt de ci O c

Huizachal Valley alley

TAMAULIPAS 50 km

La Ballena

eS alin as

Zacatecas

S. d

23°

e M a d r

24° 24°

La Boca Canyon

CaAbB aA RaOnSlleLrLoEsC yoCn.

G. Palacio Torreón orreón Villa

San Luis Potosí

Cenozoic (Neogene) cover

Jurassic-Cretaceous volcanosedimentary sequence

Cenozoic volcanics

Pre-Mesozoic rocks and Upper Triassic-Lower Jurassic marine-continental red beds and volcanics

Upper Jurassic-Cretaceous sedimentary cover

Thrust fault

Normal fault

Figure 2. Synthesis of regional geology.

fld025-01 1st pgs page 4 Barboza-Gudiño et al.

QUATER. PALEOGENE NEOGENE

SERIES

Ma STAGE HOLOCENE

PLIOCENE MIOCENE

UPPER

CRETAEOUS

37

EOCENE

55 67

PALEOCENE MAASTRICHTIAN

71.5

CAMPANIAN

83

SANTONIAN

86

CONIACIAN

89

TURONIAN

91 CENOMANIAN

97.5 ALBIAN

108

APTIAN

NEOCOMIAN

LOWER

5.1 23.7

OLIGOCENE

BARREMIAN

114

UPPER

Basalt Quartzmonzonit 53 Ma Mudstone - Sandstone (Caracol Formation) Limestone - Mudstone (Indidura Formation) Limestone (Cuesta del Cura Formation) Limestone - Marl (Formación Tamaulipas Superior Formation) Marl -mudstone (La Peña Formation)

140

Siltstone - Marl (La Caja Formation)

KIMMERIDGIAN

OXFORDIAN

160

CALLOVIAN M IDDLE

Conglomerate

Marl - Mudstone (Taraises Formation)

VALANGINIAN

TITHONIAN

JURASSIC

Alluvium

Limestone (Tamaulipas Inferior Formation)

HAUTERIVIAN

BERRIASIAN

M E S O Z OI C

0.01

PLEISTOCENE 1.68

SENONIAN

TERTIARY

CENOZOIC

ERA System

4

Limestone (Zuloaga Formation) Siltstone-Sandstone Polimictic Conglomeratebreccia Rhyolitic Porphyr (174.7 ± 1.3)

BATHONIAN BAJOCIAN AALENIAN

184 TOARCIAN

Dacit

LOWER

PLIENSBACHIAN

Andesit

SINEMURIAN

HETANGIAN

210

TRIASSIC

UPPER

230 MIDDLE

Volcanic succession (Nazas Formation)

andesíticbasaltic dike Sandstone-mudstone Cerro El Mazo beds siliciclastic succession (”Fm. Zacatecas”)

243 LOWER

CARBON.

PALE O Z O I C

250 PERMIAN

La Joya Formation

290

PENNSYLVANIAN

No deposits MISSISSIPPIAN

360

Figure 3. Stratigraphic column of the Sierra de Catorce.

fld025-01 1st pgs page 5 Sierra de Catorce which crop out in several places of the Mesa Central province, and whose tectonic setting is interpreted as linked to the evolution of the ancient margin of Pangea, prior to opening of the Gulf of Mexico. These units are particularly well preserved in the Sierra de Charcas, and nicely exposed in Cañón General of the Sierra de Catorce. In Cañón General, exposures of the complete stratigraphic column of the region allow unambiguous reconstruction of tectonic setting and, therefore, they are of great interest for understanding the western Pangea and Cordilleran evolution. We will show that the Potosí Fan is a quartz-rich turbidite succession composed of detritus eroded from the East Mexico Arc (Dickinson and Lawton, 2001), as well as from Grenville and Pan African basement sources. This suggests that basement uplifts associated with Triassic rifting existed at that time. Defor23°°10′

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mation of the Potosí Fan is not well understood, but accretionary prism and subduction complex settings have been proposed (Centeno-García, 2005; Anderson et al., 2005). Although this interpretation is somewhat speculative, it is clear that shortening and thrust faulting registered in the Triassic succession, predated less deformed Jurassic arc volcanic rocks. DAY 1 Stop 1.1. Charcas: 200 m Trip along the Arroyo San Rafael (274188 2553577) The Arroyo San Rafael is placed few kilometers west of Charcas, San Luis Potosí (Fig. 4) and drains a large range located in

101°°10′

23°°10′

B

Cenozoic cover oy o Ar r Las m Pal as

Late JurassicCretaceous limestone

LA TRINIDAD

Ar roy

MORELOS oC

ha

rca sV ieja

SAN ANTONIO DE LAS HUERTAS

s

Lower to Middle Jurassic redbeds Figure 4. Geological map of the La Trinidad Anticlinorium, west of Charcas showing the location of Arroyo San Rafael and Arroyo San Antonio.

23°°05′ EL PERDIDO EL LLANO

Lower Jurassic volcanic rocks

SAN RAFAEL

POTRERO EL LLANO

Triassic marine succession Sierra de Catorce

N

C

Matehuala

B Sierra de Charcas Zacatecas

A

Sierra de Salinas 0 50 100

San LuisPotosí Rioverde Valles 200 km

Normal fault

1 2

3

101°°15′

San Luis Potosí

2 km 23°°00′

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Barboza-Gudiño et al.

an uplifted area known as La Trinidad Anticlinorium. It contains the best preserved exposures of Upper Triassic strata (Zacatecas Formation, after Martínez-Pérez, 1972, or La Ballena Formation, following Centeno-García and Silva-Romo, 1997), consisting of massive thick-bedded sandstone, conglomeratic sandstone, and turbidites with partially developed Bouma sequences and interbedded subordinate shales. Some beds contain common graded bedding. Other sedimentary structures include load and groove casts –which constitute the most common sole marks and slump structures. The clastic components of the sandstone are quartz, feldspar, detrital mica, and shale intraclasts in a matrix of detrital and diagenetic quartz, muscovite+illite, and chlorite (Hoppe et al., 2002). The resulting lithofacies assemblage corresponds to “facies A,” “facies B,” and “facies C” of Mutti and Ricci Lucchi (1972), interpreted as channel and channel margin environments (Fig. 5). Subordinate facies “D,” “E,” “F,” and “G” (suprafan lobe, levee, and inter-channel flats), corresponding to a midfan or suprafan zone, are especially well exposed at Arroyo San Rafael. Also interesting are excellent exposures of a wild flysch, consisting of decimeter-sized to several meter–sized intraformational sandstone blocks, embedded in a sandstone-siltstone and mudstone matrix, which correspond to facies “F” of Mutti and Ricci Lucchi (1972). A Late Triassic age for this succession is well established through uncommon ammonites (Early Carnian Juvavites sp. reported by Cantú-Chapa, 1969, as well as Carnian Anatomites aff. herbichi and Aulacoceras sp., reported by Gallo-Padilla et al., 1993), conodonts (Carnian Neogondolella polygnatiformis and Epigondolella primitia, reported by Cuevas-Pérez, 1985), and results of detrital zircon geochronology (Barboza-Gudiño et al., 2010) that yielded an Early Triassic maximal depositional age of ca. 230 Ma for a sample of medium-grained sandstone collected from the Arroyo San Rafael. The main clusters of individual zircon ages reported for this sample (Fig. 6) and their possible

Figure 5. General features of the Triassic turbiditic sequence exposed along the Arroyo San Rafael, west of Charcas.

source are as follows: 290–220 Ma (Permo-Triassic east Mexico magmatic arc); 440–400 Ma (peri-Gondwanan magmatic assemblages); 700–500 Ma (Pan-African-Brasiliano basement); and 1300–900 Ma (Grenvillian basement). The Triassic turbiditic succession exposed west of Charcas is interpreted as part of the “Potosí Fan” (Silva-Romo et al., 2000; Centeno-García, 2005), a submarine fan deposited in a basinal setting during Middle to Late Triassic at the paleo-margin of Pangea or in a remnant basin at the westernmost culmination of the Ouachita-Marathon belt. Stop 1.2. Charcas: 300 m Trip along the Arroyo San Antonio (276995 2555811) West of Charcas, in the Arroyo San Antonio, at the eastern extreme of La Trinidad Anticlinorium, there are exposures of a volcanic succession of Early to Middle Jurassic age. Although the volcanic rocks in Arroyo San Antonio are in tectonic contact with the Triassic Zacatecas Formation, in other sections measured in the region, the volcanic succession rests unconformably on the Triassic rocks. The volcanic rocks, exposed in several isolated outcrops from west to east along the Arroyo San Antonio, consist of rhyodacitic ash flow tuff (ignimbrites), welded basal vitrophyre, distorted spherulites and vapor zones, massive welded zones, volcaniclastic breccias and epiclastic strata (Fig. 7). The most common structures observed in the field are eutaxitic structures, fiamme, the already described spherulites, lithophysae, and collapsed pumice. Petrographic and reconnaissance geochemical studies in several localities of comparable rocks in the region, included rocks of Charcas (Barboza-Gudiño et al., 2008) indicate a continental volcanic arc setting. To the west along the arroyo, basaltic-andesitic lava flows are well exposed; commonly they occur as brecciated lava flows, which contain angular fragments with common puzzle-structure consisting of tightly packed angular clasts. Petrographic examination reveals porphyritic, trachytic, and pilotaxitic textures. Several lithic fragments that occur in the previously described rhyodacitic flows are trachytic andesites, suggesting that the andesitic lava flows are older than the rhyodacitic pyroclastic flows and were incorporated in the rising magmas that erupted to form the pyroclastic succession. The andesitic lava flows unconformably underlie clastic deposits of the Callovian-Oxfordian La Joya Formation. This clastic sequence grades upwards into limestones of the Oxfordian Zuloaga Formation. La Joya consists of sandstone, conglomerate, and mudstones. Conglomerate clasts are dominated by volcanic rocks, which we infer were derived from the Nazas Formation. The age of the volcanic succession is well established by a U-Pb date for a rhyodacitic ignimbrite, 29 concordant zircon ages from the rock yielded a mean age of 176.8 +4.9/–1.7 Ma, a rather Toarcian/Aalenian boundary age (Zavala-Monsiváis et al., 2012). An Early to Middle Jurassic age for the succession is likewise supported by its stratigraphic relations, in which the

fld025-01 1st pgs page 7 Sierra de Catorce

7

166 Ma Middle Jurassic La Joya Formation Miquihuana

210 Ma Lower Jurassic C. El Mazo beds Los Catorce

225 Ma Upper Triassic Charcas

238 Upper Triassic Los Catorce

219

Upper Triassic San Marcos

Figure 6. Plots of Paleozoic to Jurassic published detrital zircon data from northeastern Mexico. The plots are probability curves, showing maximal deposition age of the sediments.

215 Ma Upper Triassic La Boca

530 Ma

Paleozoic Aramberri

Paleozoic Caballeros

458 Ma

0

1.0

Age (Ga)

2.0

volcanic succession overlies the Late Triassic Zacatecas Formation and unconformably underlies the Callovian–early Oxfordian La Joya Formation. The Nazas volcanic succession has been correlated by lithological similarity and stratigraphic position with volcanic successions exposed in Durango, Zacatecas, and Coahuila (Nazas Formation), and with volcanic-volcaniclastic successions exposed in southern Nuevo León, Tamaulipas, and other localities in western

3.0

San Luis Potosí State (Table 1). These volcanic rocks are thus considered part of the Early Jurassic continental volcanic arc, located along the paleo-margin of Pangea, possibly extending from California, through Sonora (Mauel et al., 2011), and into eastern Mexico. DAY 2 Stop 2.1. Real de Catorce (“Mirador”) (310202 2622353)

Figure 7. Outcrops of the Nazas Formation. Arroyo San Antonio, west of Charcas. (A) Pyroclastic flow; (B) vitrophyre at the base of a younger welded ash flow tuff or ignimbrite; (C) spherulitic horizon of the same ash flow tuff; and (D) ignimbrite.

The point known as “Mirador,” at the entrance to the Ogarrio tunnel, offers a good regional overview of the region’s rocks and style of deformation of the Jurassic-Cretaceous succession of the Sierra de Catorce uplift. Cretaceous limestones are well exposed along the road to Real de Catorce, and at this point Upper Jurassic medium-bedded limestone of the upper Oxfordian Zuloaga Formation (Reyeros de Castillo, 1978) and marls of the Kimmeridgian-Berriasian La Caja Formation (Olóriz, et al., 1999) are well exposed. They are intensely deformed by folding and thrusting as a result of Laramide shortening, which also produced uplift of the sierra and detachment of its mostly calcareous cover. The detachment zone is at the contact between shale of the top of La Joya Formation and limestone of the Zuloaga Formation. This weak zone allowed independent deformation of the cover into north-northwest–trending asymmetrical and overturned fold structures. The general asymmetry of these folds is to the east-northeast. The age of folding is constrained between

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Barboza-Gudiño et al. TABLE 1. REPRESENTATIVE ISOTOPIC AGES OF LOWER TO MIDDLE JURASSIC VOLCANIC ROCKS FROM THE NAZAS FORMATION IN NORTH-CENTRAL TO NORTHEASTERN MEXICO Locality State Rock type Method Material dated Age Source (Ma) Caopas Zacatecas Meta-rhyolitic sub-volcanic Rb-Sr Whole rock 195 ± 20 Fries and Rincón-Orta (1965) Caopas Zacatecas Meta-rhyolitic sub-volcanic Rb-Sr Whole rock 156 ± 40 Fries and Rincón-Orta (1965) Caopas Zacatecas Meta-andesite (rodeo formation) K-Ar Hornblende 183 ± 8 López-Infanzón (1986) Caopas Zacatecas Meta-rhyolitic sub-volcanic U-Pb Zircon 158 ± 4 Jones et al. (1995) 40 Villa Juárez Durango Rhyolite Ar/39Ar Plagioclase 195.3 ± 5.5 Bartolini and Spell, (1997) Catorce San Luis Potosí Rhyolite U-Pb Zircon 174.7 ± 1.3 Barboza-Gudiño et al. (2004) Charcas San Luis Potosí Rhyolitic ignimbrite U-Pb Zircon 176.8 +4.9/–1.7 Zavala-Monsiváis et al. (2012) Coherent grains Huizachal Tamaulipas Rhyolitic ash flow U-Pb Zircon 189.0 ± 0.2 Fastovsky et al. (2005) Aramberri Nuevo León Rhyolitic ignimbrite U-Pb Zircon 193.1 ± 0.3 Barboza-Gudiño et al. (2008) Huizachal Tamaulipas Rhyolite U-Pb Zircon 194.1 +4.1/–4.5 Zavala-Monsiváis et al. (2009) Aramberri Nuevo León Rhyolitic ignimbrite U-Pb Zircon 189.5 ± 3.8 Zavala-Monsiváis et al. (2009) Note: See Figure 2 for location of the areas.

the Campanian-Maastrichtian folded successions and the oldest unfolded rocks or structures in the area. Specifically, for the Sierra de Catorce, unfolded rocks are middle Eocene quartzmonzonitie dikes. These dikes also crop out in the “Mirador” point as a porphyritic rock consisting of idiomorphic centimetersized white feldspar and plagioclase crystals and minor quartz in a microcrystalline, gelb to gray and green matrix. Stop 2.2. Real de Catorce (“Puerta del Sol”) (306924 2621952) View of the Cañón General (General Canyon of Sierra de Catorce): Polymictic conglomerate and conglomeratic red sandstones of La Joya Formation (Callovian-Oxfordian) form a prominent cliff west of Real de Catorce, and offer a panoramic view of the stratigraphic units exposed in the Cañón General (Fig. 8). The units include from base to top, marine beds of the Upper Triassic Zacatecas Formation, Lower Jurassic marine marginal facies, and interlayered greenstone informally named “Cerro El Mazo beds,” rhyolitic, dacitic, and andesitic volcanic rocks of the Lower to Middle Jurassic Nazas Formation, continental to shallow marine conglomerate and red sandstone of La Joya Formation, and limestone of the Zuloaga Formation. The basal part of the Zuloaga Formation constitutes an intensely sheared zone, which resulted from Laramide detachment faulting. The La Joya Formation was defined by Mixon et al. (1959) as a Middle to Late Jurassic conglomeratic redbed sequence exposed in the Huizachal-Peregrina Anticlinorium. They proposed a type locality at Rancho La Joya Verde in the Huizachal Valley, Tamaulipas, ~200 km east of Real de Catorce. La Joya Formation consists of an upward fining megasequence composed of a basal polymictic breccia and conglomerate-fanglomerate facies overlain by red sandstone, siltstone, and mudstone. The clastic components of La Joya basal breccia in Real de Catorce are volcanic, sedimentary, and light-colored metamorphic rocks, as well as white hydrothermal quartz. In the Huizachal area, the main detrital components are gneiss, schist or phyllite, and quartz. La Joya Formation varies locally in its thickness, ranging from a few meters to as much as 200–300 m, and is absent in some localities in northeastern Mexico.

The different facies of La Joya Formation record several depositional environments, interpreted by Michalzik (1988) as follows: fanglomerates, channels and distal alluvial fan conglomerates, shallow-marine carbonates and caliche concretions and crusts, fine-grained alluvial plain deposits, and lagoonal to sabkha evaporites. The age of the La Joya Formation is known only from its stratigraphic position, overlying Lower Jurassic volcanic rocks, and underlying Oxfordian limestone of the Zuloaga Formation. Detrital zircon geochronology results yielded a maximal depositional age of ca. 170 Ma, a rather Bajocian age (Table 2; Fig. 9), in agreement with its stratigraphic position and the Early to Middle Jurassic age of volcanic rocks exposed northwest of Real de Catorce and contained as clastic fragments in a basal breccia of La Joya Formation. Rubio-Cisneros and Lawton (2011) reported a single younger grain age of 163.6 ± 2.6 Ma, a rather Callovian age from La Joya Formation in the Huizachal Valley. Stop 2.3. Cañada Ojo de Agua (El Salto) (306272 2625008) About 5 km north-northwest of Real de Catorce, at Cañada Ojo de Agua or El Salto, a conspicuous rhyolitie dike exhibiting steeply dipping banding underlies La Joya Formation. At the same locality, La Joya Formation is composed of conglomerates with a variety of volcanic rocks as angular to subrounded pebbles and cobbles up to several cm in diameter. These include rhyolitic fragments identical to the rhyolite of the dike. The rhyolite has a porphyritic texture, with hypidiomorphic quartz phenocrysts in a groundmass of totally kaolinitized feldspar. The rhyolitic dike is strongly altered and affected by subsequent silicification of the rock. Locally, foliation with lepidoblastic texture results from the occurrence of oriented sericite associated with a dynamic metamorphism. The analysis of three zircon grains from a sample of a rhyolite collected at this point yielded an age of 174 Ma, a rather early Aalenian age on the basis of a single concordant zircon, and

Figure 8. Geological map of the northwestern Sierra de Catorce.

fld025-01 1st pgs page 9 100°5′

Sierra de Catorce

9

Kt Cz-Lu

N

T-Q al

T-Q al

Kace Cz 2200

Kapa Cz-Mg

Kap Mg-Lu T-Q al

Alluvium (silt, sand, gravel) Neogene-Quaternary

Tmi Ba

Basalt, Miocene

Kt Cz-Lu

Limestone-shale Upper Cretaceous (Turonian/Indidura Formation )

Jco Lm-Ar 70

71 23°45′

23 45

73

Khba Cz Pad

C. EL PAISANO

13

C. LA CALABAZA

89

00

Kace Cz 22

Limestone-marl (Upper Aptian-Albian, Tamaulipas Superior Formation)

Kap Mg-Lu

Marl-Shale (Aptian, La Peña Formation )

Khba Cz

Thick bedded limestone, chert nodules (HauterivianBarremian, Tamaulipas Inferior Formation)

KbevMg-Lu

Marl-shale (Berriasian-Valanginian, Taraises Formation)

Jkt Lm-Mg

Siltstone, marl (Kimmeridgian-Tithonian, La Caja Formaction)

C. EL AGUILA

JmRi Kapa Cz-Mg

EL SALTO TR Lu-Ar

Jok Cz 8

KbevMg-Lu

A. El Tunalillo

Kapa Cz-Mg

moncillo

C. LA CAMPANA

Oj od eA gu a

Thin bedded limestone with black chert bands (Albian-Cenomanian, Cuesta del Cura Formation)

00

POBLAZON

Tmi Ba

43

Kace Cz

A. El Ja

28

Ca ña da

C. LA CUEVA DEL SOL

28 00

re

T-Q al

Jbac Cgp

oyote

Jkt Lm-Mg

C A. El

85 Tmi Ba

C. EL INDIO

3000

Kapa Cz-Mg

89

LA BUFA

65

C. PUERTO DEL AIRE

20 TR Lu-Gr

ELMAZO TO DUC E U AC

SANTA CRUZ DE CARRETAS

52 280

88

Ji Ar-Lu

A

A′

Tmi Ba

Ge ner

SOCAVON DE al d e C PURISIMA ato rce

Jok Cz

Jco Lm-Ar

Red siltstone-sandstone (CallovianOxfordian, Upper part of La Joya Formation)

JbacCgp

Polygmictic Conglomerate-breccia (Bathoniano-Calloviano, Lower part of La Joya Formation)

0

65

LOS CATORCE

83

Limestone (Oxfordian-Kimmeridgian, Zuloaga Formation)

C. LA DESCUBRIDORA

Jkt Lm-Mg

Khba Cz

Jok Cz

C. EL ZANJON

Tmi Ba

JmRi

29

Rhyolite (Nazas Formation)

43 REAL

7 A. El Pino

DE CA

T ORCE Jok Cz

85

30 ALAMITOS DEL PALILLO

18

28

00

55

C. LA MISIÓN

Siliciclastic turbiditic succession Upper Triassic (Zacatecas Formation) Dykes, cuarzo-monzonite (Eocene)

00

30

2800

TR Lu-Gr

70 2800

25

Sandstone and shale (Lower Jurassic, Cerro El Mazo beds)

C. EL QUEMADO

50

REGO

23°40′

Ji Ar-Lu

PUERTO DE PALILLO

JbacCgp

A. El Tecolote

Volcanics dacitic-andesitic (Lower Jurassic) (Nazas Formation)

JimA

C. EL RUCIO

CAÑON EL BOR

80

detachment

C, GRANDE

23°40′

Jco Lm-Ar

C. EL ARCO

Normal fault

35

Khba Cz

04

Jco Lm-Ar

2000

62

Inferred normal fault anticline

T-Q al

JimA

JbacCgp

Kt Cz-Lu

100°5′

18

A. M

12

A.

0

zas

atan

LAS ADJUNTAS

0

00

24

syncline

65 SAN JUAN DE MATANZAS Sa

nI

Jok Cz

25

gn ac

io

A′

38

bedding cleavage (S1) frequently subparallel to bedding (S0)

75

2800 A 2600 2400 2200 2000

topography

3

a l Anim A. E

Kapa Cz-Mg

2

23

cleavage (S2)

A

A′ section

1 km

fld025-01 1st pgs page 10 10

Barboza-Gudiño et al.

U ppm

TABLE 2. DETRITAL ZIRCON AGES FOR A SAMPLE FROM LA JOYA FORMATION, REAL DE CATORCE AREA Apparent ages Isotope ratios 206 206 (Ma) Pb/ Pb*/ ± ± Error Best age U/Th 207 204 207 206 207 206 Pb Pb* % (Ma) ± ± ± ± Pb*/ Pb*/ (%) corr. 206Pb*/ Pb*/ Pb*/ 235 238 238 235 207 U* % U U* (Ma) U (Ma) Pb* (Ma) 3.3

1

357

15512

1.5

20.4754

0.0261

1.1

0.32

166.2

1.9

164.5

5.4

140.1

78.6

166.2

2

194

5229

1.8

19.5030 11.7 0.1929 11.9 0.0273

2.4

0.20

173.5

4.1

179.1

19.6

253.2

269.3

173.5

4.1

3

258

10826

2.1

20.5031

1.9

0.48

179.7

3.4

176.7

6.5

136.9

82.2

179.7

3.4

4

132

3724

1.0

17.2239 12.8 0.2267 13.2 0.0283

3.0

0.23

180.0

5.4

207.5

24.7

532.0

281.7

180.0

5.4

5

507

12947

1.8

19.3236

1.0

0.26

195.5

1.9

201.6

7.0

274.4

84.2

195.5

1.9

6

181

10374

2.0

19.9201

3.4

0.2357

3.5

0.0341

1.0

0.29

215.9

2.1

214.9

6.8

204.3

78.3

215.9

2.1

7

254

7721

1.3

18.3306

2.9

0.2877

3.7

0.0383

2.4

0.63

242.0

5.6

256.8

8.4

393.9

64.6

242.0

5.6

8

684

25725

1.1

19.0884

1.8

0.2779

3.7

0.0385

3.3

0.88

243.4

7.8

249.0

8.2

302.4

40.7

243.4

7.8

9

253

4403

0.5

14.9900 18.6 0.3642 18.9 0.0396

2.9

0.16

250.3

7.2

315.3

51.2

828.7

392.0

250.3

7.2

10

207

10826

1.4

19.7918

5.8

0.2761

5.9

0.0396

1.3

0.21

250.5

3.1

247.5

12.9

219.2

133.3

250.5

3.1

11

80

4508

1.5

22.4680

8.3

0.2442

8.4

0.0398

1.4

0.16

251.6

3.4

221.9

16.7

-82.5

202.6

251.6

3.4

12

273

18603

2.0

19.9656

3.6

0.2752

4.1

0.0399

2.1

0.50

251.9

5.1

246.9

9.1

199.0

83.0

251.9

5.1

13

477

26838

1.9

19.3655

3.8

0.2844

4.0

0.0399

1.3

0.32

252.5

3.2

254.1

9.0

269.4

87.3

252.5

3.2

14

166

7756

1.2

19.8495

9.6

0.2783

9.7

0.0401

1.8

0.19

253.2

4.6

249.3

21.5

212.5

222.1

253.2

4.6

15

298

19761

1.1

19.9041

2.5

0.2788

3.5

0.0402

2.4

0.69

254.4

6.0

249.7

7.7

206.1

58.7

254.4

6.0

16

172

9125

0.9

18.9678 13.0 0.2930 14.8 0.0403

7.1

0.48

254.7

17.7

260.9

34.1

316.8

296.6

254.7

17.7 6.1

3.5

3.7

0.1759

0.1901

0.2197

3.5

± Ma

4.0

3.8

0.0283

0.0308

1.9

17

403

26992

1.6

19.6869

1.9

0.2826

3.1

0.0403

2.4

0.79

255.0

6.1

252.7

6.9

231.5

43.9

255.0

18

282

17070

1.0

19.4055

5.3

0.2869

5.4

0.0404

1.3

0.24

255.1

3.3

256.1

12.3

264.7

120.9

255.1

3.3

19

679

16618

0.7

18.7672

1.9

0.3007

2.4

0.0409

1.4

0.57

258.5

3.4

266.9

5.5

340.9

43.6

258.5

3.4

20

174

9559

1.5

19.8414

4.7

0.2886

5.4

0.0415

2.6

0.48

262.3

6.7

257.4

12.3

213.4

110.0

262.3

6.7

21

151

6395

1.1

17.8541

7.6

0.3212

7.7

0.0416

1.2

0.15

262.7

3.0

282.8

19.1

452.7

169.7

262.7

3.0

22

320

15386

1.4

19.4941

6.1

0.2974

6.3

0.0420

1.5

0.24

265.5

3.9

264.3

14.7

254.2

141.3

265.5

3.9

23

336

8666

1.5

18.8629

4.6

0.3083

4.9

0.0422

1.6

0.32

266.3

4.1

272.9

11.7

329.4

105.1

266.3

4.1

24

603

30580

1.3

19.1531

2.0

0.3048

2.2

0.0423

1.0

0.45

267.3

2.6

270.2

5.3

294.6

45.9

267.3

2.6

25

82

5121

1.6

19.4898 10.0 0.3061 10.1 0.0433

1.0

0.10

273.1

2.7

271.2

23.9

254.7

230.6

273.1

2.7

26

484

30114

1.2

18.8660

1.5

0.3215

1.8

0.0440

1.0

0.55

277.5

2.7

283.0

4.5

329.0

34.4

277.5

2.7

27

83

3455

1.4

17.9821

9.5

0.3466

9.9

0.0452

2.7

0.28

285.0

7.6

302.2

25.8

436.8

211.8

285.0

7.6

28

337

21476

4.7

19.7858

3.9

0.3165

4.5

0.0454

2.1

0.48

286.4

6.0

279.2

10.9

219.9

91.3

286.4

6.0

29

954

28868

1.3

19.3410

2.4

0.3243

4.1

0.0455

3.3

0.81

286.8

9.3

285.2

10.2

272.3

54.8

286.8

9.3

30

96

7014

2.3

19.3639 10.3 0.3307 10.4 0.0464

1.5

0.14

292.6

4.3

290.1

26.3

269.6

236.6

292.6

4.3

31

237

16048

1.7

18.2202

6.6

0.3556

6.7

0.0470

1.1

0.16

296.0

3.2

308.9

17.8

407.5

147.8

296.0

3.2

32

137

7032

2.6

18.3147

5.8

0.3628

5.9

0.0482

1.2

0.21

303.4

3.6

314.3

16.0

395.9

130.3

303.4

3.6 3.3

33

38

3563

1.7

17.8392 17.2 0.4110 17.2 0.0532

1.0

0.06

334.0

3.3

349.6

51.0

454.6

384.5

334.0

34

349

57897

3.7

17.1415

2.8

0.6897

3.0

0.0857

1.2

0.40

530.3

6.2

532.6

12.5

542.5

60.2

530.3

6.2

35

625

57313

11.2

17.2178

1.8

0.6920

3.3

0.0864

2.7

0.83

534.3

13.8

534.0

13.5

532.7

39.9

534.3

13.8

36

329

51643

3.7

16.2093

1.8

0.8907

2.1

0.1047

1.0

0.48

642.0

6.1

646.8

10.0

663.5

39.3

642.0

6.1

37

80

10052

1.9

15.6931

2.1

0.9799

2.5

0.1115

1.4

0.55

681.6

9.0

693.5

12.6

732.4

44.3

681.6

9.0

38

148

15071

2.4

13.8840

2.3

1.1450

4.6

0.1153

4.0

0.86

703.4

26.5

774.9

25.0

986.6

47.6

703.4

26.5

39

474

24035

2.9

15.5665

2.7

1.0426

4.2

0.1177

3.3

0.77

717.3

22.1

725.2

21.8

749.5

56.2

717.3

22.1

40

529

76013

7.2

14.5866

2.7

1.2233

5.3

0.1294

4.6

0.86

784.5

34.0

811.3

29.8

885.4

55.4

784.5

34.0

41

369

73931

1.4

14.4126

2.5

1.3920

2.8

0.1455

1.1

0.41

875.7

9.3

885.6

16.3

910.2

51.9

875.7

9.3

42

262

52129

6.6

14.1546

2.5

1.4983

3.7

0.1538

2.7

0.73

922.3

23.5

929.7

22.7

947.2

52.0

922.3

23.5

43

109

33943

1.5

14.2724

2.6

1.5118

3.1

0.1565

1.8

0.56

937.3

15.3

935.2

19.1

930.2

53.1

937.3

15.3

44

41

10409

1.4

14.1585

3.7

1.5547

3.9

0.1597

1.2

0.31

954.8

10.5

952.4

23.9

946.7

75.4

954.8

10.5

45

61

17546

1.2

14.0023

2.9

1.6260

5.3

0.1651

4.5

0.83

985.2

40.7

980.3

33.6

969.3

60.1

969.3

60.1

46

616

154448

4.4

13.9353

1.2

1.6231

1.8

0.1640

1.4

0.75

979.2

12.5

979.2

11.5

979.1

24.5

979.1

24.5

47

692

155309

28.6

13.9340

2.8

1.6200

3.2

0.1637

1.6

0.50

977.4

14.4

978.0

20.2

979.3

56.8

979.3

56.8

(continued)

fld025-01 1st pgs page 11 Sierra de Catorce

11

TABLE 2. DETRITAL ZIRCON AGES FOR A SAMPLE FROM LA JOYA FORMATION, REAL DE CATORCE AREA (continued) Apparent ages Isotope ratios 206 206 (Ma) U ± ± Error Best age Pb/ Pb*/ U/Th 207 204 207 206 206 207 206 ppm Pb Pb* % (Ma) ± ± ± ± Pb*/ Pb*/ (%) corr. Pb*/ Pb*/ Pb*/ 235 238 238 235 207 U* % U U* (Ma) U (Ma) Pb* (Ma) 49

186

34213

50

302

79408

51

229

54282

52

166

47282

53

92

25092

54

153

19016

55

101

56

114

57

1.6

13.7837

2.2

1.6766

2.6

2.5

13.7106

1.9

1.6899

2.2

1.9

13.6443

1.0

1.7970

1.4

8.7

13.5813

2.1

1.8322

3.2

2.7

13.5206

3.0

1.8002

3.3

1.3

13.4709

2.3

1.6292

6.0

19600

2.7

13.4700

1.5

1.7517

20850

7.8

13.4465

3.1

1.6288

290

43337

2.9

13.4290

2.5

58

129

41059

4.7

13.3029

59

198

21725

1.1

13.2460

60

256

31147

1.8

13.1684

61

860

182539

3.1

13.1266

62

356

80693

3.3

13.1198

0.1676

1.4

0.54

998.9

12.9

0.1680

1.1

0.50

1001.3

0.1778

1.0

0.71

1055.1

0.1805

2.4

0.76

1069.6

0.1765

1.3

0.40

1048.0

0.1592

5.5

0.92

952.2

1.9

0.1711

1.2

0.62

4.2

0.1588

2.9

0.69

1.7898

2.8

0.1743

1.2

1.3

1.8636

1.8

0.1798

1.6

1.9416

1.9

0.1865

2.6

1.9299

2.8

0.1843

1.0

0.37

2.3

1.8945

2.9

0.1804

1.9

0.64

4.1

1.7857

4.2

0.1699

1.0

0.24

1011.6

43.9

1001.4

± Ma

999.7

16.4

1001.4

43.9

10.2

1004.7

14.2

1012.2

39.1

1012.2

39.1

9.7

1044.4

9.2

1022.0

20.3

1022.0

20.3

24.0

1057.1

21.1

1031.3

42.1

1031.3

42.1

12.8

1045.5

21.7

1040.4

61.5

1040.4

61.5

48.7

981.6

37.5

1047.8

46.2

1047.8

46.2

1018.3

11.0

1027.8

12.1

1048.0

29.5

1048.0

29.5

950.4

25.6

981.4

26.6

1051.5

62.1

1051.5

62.1

0.42

1035.9

11.3

1041.7

18.2

1054.1

51.2

1054.1

51.2

1.2

0.68

1065.9

11.8

1068.3

11.7

1073.1

26.3

1073.1

26.3

1.0

0.52

1102.6

10.1

1095.6

12.8

1081.7

32.7

1081.7

32.7

1090.5

10.4

1091.5

18.6

1093.4

51.7

1093.4

51.7

1069.0

18.3

1079.2

19.5

1099.8

45.2

1099.8

45.2

9.4

1040.3

27.4

1100.9

81.8

1100.9

81.8

63

30

9716

4.9

13.0294

3.4

1.7347

3.9

0.1639

2.0

0.51

978.6

17.9

1021.5

25.1

1114.7

67.1

1114.7

67.1

64

196

60876

4.8

13.0247

2.1

1.8489

2.6

0.1747

1.5

0.58

1037.7

14.4

1063.0

17.0

1115.4

41.9

1115.4

41.9

65

41

12922

1.4

13.0224

5.2

2.0218

5.9

0.1910

2.8

0.47

1126.6

28.5

1122.9

40.0

1115.7

103.7

1115.7

103.7

66

756

147217

6.1

12.9750

4.4

1.6605

8.6

0.1563

7.5

0.86

936.0

65.0

993.6

54.8

1123.0

87.2

1123.0

87.2

67

312

83167

2.0

12.9050

1.4

1.9861

2.9

0.1859

2.5

0.87

1099.0

25.2

1110.8

19.4

1133.8

28.3

1133.8

28.3

68

415

135513

5.3

12.7241

1.8

2.1584

2.3

0.1992

1.5

0.64

1171.0

15.7

1167.8

16.0

1161.8

35.3

1161.8

35.3

69

180

59269

2.7

12.6976

1.1

2.1804

1.5

0.2008

1.0

0.69

1179.6

10.8

1174.8

10.1

1166.0

20.8

1166.0

20.8

70

145

55307

3.3

12.6870

2.0

2.1627

2.2

0.1990

1.0

0.45

1170.0

10.7

1169.1

15.5

1167.6

39.4

1167.6

39.4

71

95

21378

2.6

12.6815

2.8

2.0719

3.0

0.1906

1.1

0.37

1124.4

11.7

1139.6

20.7

1168.5

55.5

1168.5

55.5

72

433

84991

3.3

12.6709

1.0

2.0006

3.4

0.1839

3.2

0.96

1088.0

32.4

1115.7

23.0

1170.1

19.8

1170.1

19.8

73

65

14067

5.1

12.6044

5.3

2.0460

6.0

0.1870

2.7

0.44

1105.3

26.9

1130.9

40.7

1180.5 105.6

1180.5

105.6

74

116

42693

3.5

12.5895

2.4

2.0647

4.4

0.1885

3.7

0.84

1113.4

37.6

1137.2

30.0

1182.9

47.1

1182.9

47.1

75

221

28805

2.3

12.5892

4.1

1.9521

5.9

0.1782

4.2

0.72

1057.4

41.2

1099.2

39.6

1182.9

81.3

1182.9

81.3

76

534

138404

5.5

12.5053

3.2

1.8247

5.0

0.1655

3.9

0.78

987.3

36.0

1054.4

33.0

1196.1

62.1

1196.1

62.1

77

121

34297

2.7

12.4711

1.3

2.1364

2.3

0.1932

1.9

0.83

1138.9

19.7

1160.7

15.8

1201.5

25.3

1201.5

25.3

78

103

21756

2.8

12.4551

1.8

2.2532

2.3

0.2035

1.4

0.60

1194.3

14.9

1197.8

16.1

1204.1

36.1

1204.1

36.1

79

58

17696

2.3

12.4447

3.9

2.2456

5.1

0.2027

3.3

0.64

1189.7

35.9

1195.4

36.0

1205.7

77.3

1205.7

77.3

80

556

52070

19.3

12.4038

2.6

2.1088

3.2

0.1897

1.9

0.58

1119.8

19.1

1151.7

22.0

1212.2

51.0

1212.2

51.0

81

147

72678

3.6

12.2902

1.1

2.3837

1.5

0.2125

1.0

0.67

1242.0

11.3

1237.7

10.7

1230.3

21.8

1230.3

21.8

82

333

89404

3.3

12.2889

2.3

2.3293

2.8

0.2076

1.6

0.58

1216.0

18.1

1221.3

20.1

1230.5

45.3

1230.5

45.3

83

282

84172

2.7

12.2385

1.7

2.4600

2.7

0.2184

2.1

0.77

1273.2

23.8

1260.4

19.3

1238.6

33.3

1238.6

33.3

84

171

37611

2.1

12.1875

1.1

2.4278

2.6

0.2146

2.3

0.90

1253.3

26.3

1250.9

18.5

1246.7

22.1

1246.7

22.1

85

381

99414

2.6

12.1005

2.2

2.4812

3.6

0.2178

2.9

0.80

1270.0

32.9

1266.6

25.9

1260.7

42.4

1260.7

42.4

86

81

3742

2.5

11.8179

2.4

2.0238

2.9

0.1735

1.6

0.56

1031.2

15.3

1123.5

19.5

1306.8

46.1

1306.8

46.1

87

198

65898

1.3

11.7905

1.9

2.6382

2.3

0.2256

1.2

0.55

1311.4

14.7

1311.4

16.7

1311.3

36.9

1311.3

36.9

88

145

55787

1.8

11.7181

2.1

2.7817

2.4

0.2364

1.2

0.51

1368.0

15.0

1350.6

17.8

1323.2

39.7

1323.2

39.7

89

246

85358

2.6

11.6508

1.3

2.7740

1.8

0.2344

1.3

0.69

1357.5

15.4

1348.6

13.6

1334.4

25.3

1334.4

25.3

90

590

139706

3.0

11.5709

1.6

2.7869

2.1

0.2339

1.3

0.63

1354.8

15.9

1352.0

15.3

1347.7

30.7

1347.7

30.7

91

54

16300

5.4

11.4981

2.8

2.6194

3.2

0.2184

1.5

0.48

1273.6

17.6

1306.1

23.2

1359.8

53.4

1359.8

53.4

92

151

59990

2.6

10.6641

2.3

3.3796

2.6

0.2614

1.2

0.45

1496.9

15.9

1499.7

20.5

1503.5

44.0

1503.5

44.0

93

197

75012

1.9

9.7939

2.1

3.8152

2.6

0.2710

1.6

0.60

1545.9

21.4

1596.0

20.8

1662.7

38.1

1662.7

38.1

94

431

131079

2.3

9.7750

1.0

4.0892

2.5

0.2899

2.3

0.92

1641.0

33.3

1652.2

20.5

1666.3

18.5

1666.3

18.5

95

225

54436

2.4

7.5945

1.5

4.9690

9.6

0.2737

9.4

0.99

1559.5 130.6 1814.1

80.9

2120.4

26.8

2120.4

26.8

Note: Analysis performed in the LaserChron Center, Arizona, following procedures of Gehrels et al. (2006). Coordinates: 306190 2625120.

fld025-01 1st pgs page 12 12

Barboza-Gudiño et al.

16 255 Ma

14

12

10

8

6

1056 Ma 166 Ma 1186 Ma

4

2

0 0

400

800

1200

1600

2000

2400

2800

Ma data-point error ellipses are 68.3% conf ζ

0.4

1800 0.3

238U/206 Pb

1400 0.2

1000

600

0.1

0.0 0

2

4 207

6

8

Pb/235 U

Figure 9. Detrital zircon plots as relative probability curve and histogram (A) and U/Pb concordiadiagrams for the analyzed sample (2σ error ellipses) (B), obtained from a sample from La Joya Formation, collected in the Sierra de Catorce (see data and coordinates in Table 2).

fld025-01 1st pgs page 13 Sierra de Catorce 176 Ma a rather late Toarcian age on the basis of a lower concordia intercept (Barboza-Gudiño et al., 2004). Stop 2.4. Transect along the “Upper” Cañón General (“La Purisima-Real de Catorce”) (306838 2621719) At the point known as La Purisima, on the road from Estación Catorce to Real de Catorce, the base of a sequence of pyroclastic rocks of rhyolitic composition rests on red sandstones to mudstones, greenstones and quarzites of the Lower Jurassic marine marginal facies known as “Cerro El Mazo beds” (Barboza-Gudiño et al., 2004; Venegas-Rodríguez et al., 2009). Maher et al. (1991), Bartolini et al. (1999), and McKee et al. (1999) reported plant fossils from this unit that suggests an Early Jurassic age. The pyroclastic rocks consist of airfall deposits or laminated ash, unwelded tuff with volcanic breccia horizons and marked pseudostratification at the base, grading upsection into massive deposits, showing several intensely sheared zones containing sericite as a result of dynamic metamorphism and associated hydrothermal alteration. Basaltic-andesitic lava also occurs in the volcanic succession exposed in the Sierra de Catorce. The lava contains fluidal porphyritic texture with highly altered, probable hornblende phenocrysts, scarce pyroxene, olivine, and plagioclase in a fine groundmass composed of acicular plagioclase, ferromagnesian minerals, and opaque grains. Some lavas are brecciated. Similar basaltic-andesitic lavas crop out at Sierra de Salinas and Sierra de Charcas. The volcanic units are unconformably overlain by Middle to Upper Jurassic redbeds of La Joya Formation. The exposed succession along this trip forms part of the eastern flank of an uplifted structure known as the “Los Catorce Antiform.” DAY 3 Stop 3.1. Trip along the “Lower” Cañón General (Los Catorce) (303145 2621843) The field trip follows the road from Real de Catorce to Cedral for 14 km and then the highway to Vanegas, where it crosses the Mexico-Laredo railroad; from there, a paved road parallel to the tracks leads to Estacion Catorce, and to the east a dirt road leads into the lower part of Cañon General of Sierra de Catorce. Along this part of the canyon the western flank of the Los Catorce Antiform is exposed, in the northwestern Sierra de Catorce uplift. Along the road to Los Catorce from the small town of Carretas, there are excellent exposures of the mid-Cretaceous (AlbianCenomanian) Cuesta del Cura and Tamaulipas Superior formations. These units are characterized by medium- to thin-bedded limestone with black chert bands and nodules. They were deposited in the Mexican Sea, west of the Valles–San Luis platform. To the west along the same road, the Lower Cretaceous units are also exposed; these occur as thin- to medium-bedded limestone

13

with interbedded thin shale horizons of the Taraises Formation (Berriasian-Valanginian), thick-bedded micritic limestone with brown-gray chert nodules of the Tamaulipas Inferior Formation (Barremian), and thin-bedded limestone and marls of La Peña Formation (Aptian). Figure 3 shows the complete stratigraphic column of Sierra Catorce and a brief lithologic description of the units exposed (after Barboza-Gudiño and Torres-Hernández, 1999, and Barboza-Gudiño et al., 2004). For comparison, Figure 10 shows a general correlation table of the Sierra de Catorce stratigraphy with the Mesozoic stratigraphy of other localities in northern Mexico and southeastern United States. Stop 3.2. Cerro El Mazo (304502 2622356) Two km west of the town of Los Catorce, along the road from this town to Carretas, the Upper Jurassic is represented by marls, shaly limestone, and uncommon interlayered sandstone of the La Caja Formation (Kimmeridgian-Berriasian) overlying thick-bedded limestone of the Zuloaga Formation (Oxfordian). The Zuloaga Formation gradationally overlies redbeds of the La Joya Formation, which constitute an upward-fining succession of more than 250 m that includes breccias and conglomerates at the base, grading upward into red sandstone, with a dominantly fine sequence of siltstone and claystone at the top. The transition between mudstones of La Joya into limestone of the Zuloaga Formation is characterized by thin evaporite interbeds and progressively more abundant limestone. However, this interval contains numerous detachment surfaces where the limestone of the basal Zuloaga Formation is commonly mylonitized. This is expressed as a foliated white fault rock with a very fine SC fabric, which is visible only in thin section. In the west flank of the Los Catorce Antiform, the volcanic succession of the Nazas Formation is markedly diminished to a few meters of red-purple, possibly epiclastic deposits, which are similar to interlayered horizons within the volcanic succession that occur in the eastern flank of the same structure. The Lower Jurassic succession here includes the “Cerro El Mazo beds” unit, consisting of quartzite and litharenite and interlayered red and yellow mudstone (Fig. 11), and containing remains of plants (probably Cycadeoids) as well as basaltic-andesitic greenstones both as dikes or sills and lava flows, the products of synsedimentary volcanic activity. The Cerro El Mazo beds are interpreted as shallow marine and marginal facies. This unit of the Sierra de Catorce is comparable in age with Lower Jurassic strata cropping out near El Alamito, west of Rioverde, 200 km SE of Catorce, and with strata of the Huayacocotla Formation in Hidalgo and Veracruz. Cerro El Mazo beds may be also correlative with Lower Jurassic strata of the Santa Rosa Formation of Sonora (González León et al., 2009). An initial report of the probable existence of Lower Jurassic strata in the Sierra de Catorce, based on the presence of the ammonites Vermiceras sp. and Arnioceras cf. Abjectum Fucini n. subsp., has remained in doubt since 1956 because of uncertainty

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Barboza-Gudiño et al.

Cretaceous

regarding the precise location of the outcrop and a lack of subsequent reports of fossils. However, detrital zircon geochronology on coarse-grained litharenites from the Cerro El Mazo beds (Venegas-Rodríguez et al., 2009) yielded a Late Triassic–Early Jurassic maximum depositional age on the basis of the youngest zircon grains in the sample (age of youngest zircons here), as well as three possible basement sources of zircons that include Grenvillian (ca. 900–1200 Ma), Pan-African (ca. 500–700 Ma) and

Maastrichtian Campanian Santonian Coniacian Turonian Cenomanian Albian Aptian Barremian Hauterivian Valanginian Berriasian Tithonian

Sierra de Catorce

Galeana, N.L.

La Boca canyon

Texas

Caracol/Mendez

Mendez

Mendez

Navarro Taylor

Indidura

San Felipe

San Felipe

Austin

Agua Nueva Agua Nueva Cuesta del Cura Cuesta del Cura Cuesta del Cura Tamaulipas sup. Tamaulipas sup. Tamaulipas sup. La Peña (Otates) La Peña (Otates) La Peña (Otates)

Jurassic

Trinity Pearsall

Tamaulipas inf.

Sligo

Taraises

Taraises

Taraises

Hosston Sycamore

La Caja

La Casita

La Casita

Cotton Valley

Olvido

Buckner Smackover

Zuloaga

Zuloaga Olvido Minas Viejas

Caliza Novillo

La Joya

La Joya

La Joya

Bathonian Bajocian Aalenian Toarcian

Nazas

La Boca

Pliensbachian Sinemurian Hettangian Rhaetian

Triassic

Fredericksburg

Tamaulipas inf.

Callovian

Norian Carnian

Eagle Ford Woodbine-Buda

Tamaulipas inf.

Kimmeridgian Oxfordian

the Permo-Triassic magmatic arc (ca. 245–280 Ma). The interlayered mafic rocks likely record the onset of Jurassic volcanic arc activity, but it is also possible that this earliest Jurassic mafic magmatism is not related to the Nazas arc. This is because there are several differences in the geochemistry of these rocks. The chemistry of Cerro El Mazo volcanic rocks is typical of poorly evolved magmatic rocks, and their petrographic features are more characteristic of spilitic rocks. However, these rocks are indicative

Zacatecas

El Alamar

El Alamar

Ladinian Anisian Scythian Figure 10. Correlation chart for northeastern Mexico and southeastern Texas.

LouannWerner

fld025-01 1st pgs page 15 Sierra de Catorce

15

Figure 11. Aspect of the Lower Jurassic Cerro El Mazo beds, near Los Catorce, Sierra de Catorce. This succession consists of sandstones or litharenites (Sst.) and quarzites (Qz.), red purple to yellow-green siltstone and shale (Sh.), alternating with several basaltic-andesitic lava flows (greenstones, Gst.); sills and dikes also are present in the area.

of subduction volcanism (Rodríguez-Hernández, 2009). On the basis of our observations, we conclude that marginal marine strata of Cerro El Mazo in the Sierra de Catorce (post-Norian to pre-Bajocian?) were probably deposited along the paleo-Pacific margin of Mexico during the Early Jurassic in a forearc setting.

Triassic age of deposition for this succession. The facies associations in Triassic strata in Real de Catorce are comparable with those of the Charcas exposures visited in Day 1, but finer grained rocks dominate the section at Real de Catorce. These are interpreted as inter-channel deposits (lithofaces “D,” “E,” and “G”), and subordinate suprafan, levee, and channel deposits (Fig. 12).

Stop 3.3. Los Catorce: Late Triassic Turbidite Succession (305484 2622469)

DISCUSSION AND CONCLUSIONS

The Zacatecas Formation in Sierra de Catorce consists of finely laminated shale and intercalated thin siltstone and sandstone layers. The exposures at Cañón General, around the village of Los Catorce represent the most extensive exposures of Triassic rocks in the Sierra de Catorce. In addition, there are outcrops of comparable strata in Cañon Ojo de Agua or “El Salto” to the north and the southern Sierra de Catorce in El Astillero canyon. A Late Triassic age for the succession is inferred from lithologic similarities with fossil-bearing strata at other localities and their stratigraphic position; there are no reports of Triassic fossils in this locality. An older age has been suggested by a possible late Paleozoic flora (Franco-Rubio, 1999) and late Paleozoic spores (Bacon, 1978), but recently published detrital zircon geochronology (Fig. 6; Barboza-Gudiño et al., 2010) and geochronological data obtained from Jurassic volcanic rocks in the Sierra de Catorce (Barboza-Gudiño et al., 2004) are consistent with a Late

One of the most relevant aspects of the Mesozoic evolution of the Mexican subcontinent is a continuous stratigraphic record of plate convergence along its Pacific margin (e.g., Dickinson and Lawton, 2001; Sedlock et al., 1993). Convergence has been related to subduction of the Farallon plate. Stratigraphic units in several uplifted structural complexes in north-central and northeastern Mexico indicate repeated tectonic-magmatism cycles from Permian to Cretaceous, corresponding to sedimentation, magmatism and deformation in subduction settings (Fig. 13). The geologic record of subduction in Mexico during that time is complex, but in general there is a westward younging trend in the locus of magmatism. Each cycle of sedimentation, magmatism, and deformation is displaced progressively more than 500 km westward from the Permian paleo-Pacific margin of Pangea, whose remnants are located today in eastern Mexico up to the present Pacific margin.

fld025-01 1st pgs page 16 16

Barboza-Gudiño et al.

Figure 12. Triassic turbiditic sequence exposed by Los Catorce, Cañon general, Sierra de Catorce.

Nascent Guerrero Terrane

subduction Late Jurassic-Cretaceous Nazas Arc

Early to Middle Jurassic Low stress subduction

Deformation of the Potosi Fan

Late Triassic El Alamar Formation

Latest Triassic-Early Jurassic

Figure 13. Model of the tectonic evolution of the ancient western margin of Pangea, during the Late Paleozoic– Early Mesozoic.

high stress subduction Potosi Fan Late Triassic

Permian-Triassic Low stress subduction

Permo-Triassic Arc

WSW

ENE metamorphism of Granjeno shist

Carboniferous-Permian

high stress subduction

Oaxaquia

fld025-01 1st pgs page 17 Sierra de Catorce At several localities of the Mesa Central province, Upper Triassic strata of the Zacatecas Formation and its correlatives, which form the record of the “Potosí submarine Fan,” are strongly deformed and locally exhibit low-grade metamorphism. Lithofacies assemblages have locally been interpreted as the record of a subduction complex (Anderson et al., 2005; Dávila-Alcocer et al., 2008), suggesting that a subduction zone was active in a high-stress stage during the latest Triassic time, producing deformation and uplift of Zacatecas Formation strata. Whereas Centeno-García (2005) suggested that the fan was formerly located to the northwest and was displaced to its present position by the hypothetical Mojave-Sonora megashear, the detrital zircon geochronology of this unit is consistent with an autochthonous or para-autochthonous setting. Widespread arc-volcanism occurred during a subsequent low-stress stage of subduction. Predominantly subaerial volcanic deposits of the Nazas Formation rest on deformed marine Triassic rocks in the states of Zacatecas and San Luis Potosí, and on continental Triassic strata or older rocks in Nuevo León and Tamaulipas (Barboza-Gudiño et al., 2008, 2010; Rubio-Cisneros and Lawton, 2011). Whereas previous authors (e.g., Jones et al., 1995) have suggested that volcanic rocks of the Nazas Arc are a displaced fragment of the Sonora Cordilleran Arc, transported to the southeast by the Mojave-Sonora megashear, the fact that the continuity of outcrops of Jurassic volcanic rocks on both sides of the inferred megashear trace from Sonora (Rancho Basomari Formation of Mauel et al., 2011), through Chihuahua, into San Luis Potosí, Nuevo León, and Tamaulipas suggests that a NW-trending paired arc-trench system was continuous across northern Mexico. The remnants of the Paleozoic Pangean continent located to the east and represented by the Proterozoic Novillo Gneiss and Granjeno Schist that yields late Paleozoic metamorphic ages are exposed in Tamaulipas and Nuevo León. El Alamar Formation (BarbozaGudiño et al., 2010), initially considered as part of La Boca Formation (Mixon et al., 1959), is an Upper Triassic fluvial succession which crops out in El Alamar Canyon and in the San Marcos area, south of Galeana, Nuevo León, as well as in the northern part of the Huizachal Peregrina Anticlinorium in Tamaulipas. These continental strata are interpreted as the headwaters of the Potosí Fan. La Boca Formation, unconformably overlain by the Middle to Upper Jurassic La Joya Formation in the Sierra Madre Oriental, includes interlayered volcanic rocks and epiclastic strata, comparable in age with the Nazas Formation of the Mesa Central, and is now considered part of the Early Jurassic volcanic arc of eastern Mexico (Rubio-Cisneros and Lawton, 2011). GodínezUrban et al. (2011) have suggested that arc volcanism continued east into the Chiapas massif which lay reconstructed east of the Tamaulipas outcrops of La Boca Formation prior to the opening of the Gulf of Mexico (Molina-Garza et al., 1992). Available observations and data from northeastern Mexico, as well the areas to be visited during this field trip, indicate that the Triassic to Lower Jurassic stratigraphic units present in the Sierra de Catorce, and in several localities in western San Luis Potosí and Zacatecas, can be considered remnants of the paleo-

17

Pacific margin of western Pangea during early Mesozoic times. West of this ancient margin, parts of the sedimentary pile of the voluminous Potosí Fan were likely deposited on the continental slope and the adjacent oceanic crust and carried eastward into the active trench. During the Late Jurassic and Early Cretaceous, the intraoceanic volcanic activity of the Guerrero terrane was initiated, followed in the Late Cretaceous by the consolidation of most of the actual Mexican subcontinent. ACKNOWLEDGMENTS We acknowledge constructive reviews and suggestions by Ana Bertha Villaseñor and Federico Olóriz. REFERENCES CITED Anderson, T.H., Jones, N.W., and McKee, J.W., 2005, The Taray Formation: Jurassic(?) mélange in northern Mexico—Tectonic implications, in Anderson T.H., Nourse, J.A., McKee, J.W., and Steiner, M.B., eds., The Mojave-Sonora Megashear hypothesis: Development, assessment and alternatives: Geological Society of America Special Paper 393, p. 427– 455, doi:10.1130/0-8137-2393-0.427. Bacon, R.W., 1978, Geology of the northern Sierra de Catorce, San Luis Potosí, México [master’s thesis]: Arlington, University of Texas, 124 p. Baker, C.L., 1922, General geology of the Catorce mining district: Transactions of the American Institute of Mining and Metallurgical Engineers, v. 66, p. 42–48. Barboza-Gudiño, J.R., 1989, Geologische Kartierung (1:10 000) des Gebietes “Cañón General,” Sierra de Catorce, San Luis Potosí, México—mit besonderer Berücksichtigung des prä-oberjurassichen Gründgebirges (Diplomarbeit): Technische Universität Clausthal, Germany, 107 p. Barboza-Gudiño, J.R., and Torres-Hernández, J.R., 1999, Carta geológicominera Real de Catorce (F14–A24), escala 1:50 000: México, Consejo de Recursos Minerales, SECOFI, 1 mapa y texto explicativo. Barboza-Gudiño, J.R., Tristan-Gónzalez, M., and Torres-Hernández, J.R., 1999, Tectonic setting of pre-Oxfordian units from central and northeastern Mexico: A Review, in Bartolini, C., Wilson, J.L., and Lawton, T.F., eds., Mesozoic Sedimentary and Tectonic History of North-Central Mexico: Geological Society of America Special Paper 340, p. 197–210, doi:10.1130/0-8137-2340-X.197. Barboza-Gudiño, J.R., Hoppe, M., Gómez-Anguiano, M., and Martínez-Macías, P.R., 2004, Aportaciones para la interpretación estratigráfica y estructural de la porción noroccidental de la Sierra de Catorce, San Luis Potosí, México: Revista Mexicana de Ciencias Geológicas, v. 21, p. 299–319. Barboza-Gudiño, J.R., Orozco-Esquivel, M.T., Gómez-Anguiano, M., and Zavala-Monsiváis, A., 2008, The Early Mesozoic volcanic arc of western North America in northeastern Mexico: Journal of South American Earth Sciences, v. 25, p. 49–63, doi:10.1016/j.jsames.2007.08.003. Barboza-Gudiño, J.R., Zavala-Monsiváis, A., Venegas-Rodriguez, G., and Barajas-Nigoche, L.D., 2010, Late Triassic stratigraphy and facies from northeastern Mexico: Tectonic setting and provenance: Geosphere, v. 6, no. 5, p. 621–640, doi:10.1130/GES00545.1. Bartolini, C., and Spell, T., 1997, An Early Jurassic age (40Ar/39Ar) for the Nazas Formation at the Canñada Villa Juárez, northeastern Durango, México: Geological Society of America Abstracts with Programs, v. 29, no. 2, p. 3. Bartolini, C., Lang, H., and Stinnesbeck, W., 1999, Volcanic rock outcrops in Nuevo León, Tamaulipas and San Luis Potosí, México: Remnants of the Permian–Early Triassic magmatic arc? in Bartolini, C., Wilson, J.L., and Lawton, T.F., eds., Mesozoic sedimentary and tectonic history of NorthCentral Mexico: Geological Society of America, Special Paper 340, p. 347–356, doi:10.1130/0-8137-2340-X.347. Cantú-Chapa, A., 1969, Una nueva localidad del Triásico Superior marino en México: Instituto Mexicano del Petróleo, Revista, v. 1, p. 71–72. Castillo, A., del, and Aguilera-Serrano J.G., 1895, Fauna fósil de la Sierra de Catorce, San Luis Potosí: Comisión Geológica de México, Boletín n. 1, 55 p., 24 láminas. Centeno-García, E., 2005, Review of Upper Paleozoic and Mesozoic stratigraphy and depositional environments of central and west Mexico:

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