Middle-Late Ordovician magmatism and Late Cretaceous collision in ...

IN PRESS

Middle-Late Ordovician magmatism and Late Cretaceous collision in the southern Maya block, Rabinal-Salamá area, central Guatemala: Implications for North America–Caribbean plate tectonics C. Ortega-Obregón Instituto de Geología, Universidad Nacional Autónoma de México, 04510 México D.F., México

L.A. Solari† Centro de Geociencias, Universidad Nacional Autónoma de México, 76001 Campus Juriquilla, Querétaro, México

J. D. Keppie F. Ortega-Gutiérrez J. Solé Instituto de Geología, Universidad Nacional Autónoma de México, 04510 México D.F., México

Sergio Morán-Ical Universidad de San Carlos, Centro Universitario del Norte, Cobán, Guatemala

ABSTRACT The Rabinal-Salamá area in central Guatemala provides critical data bearing on the relationships between the North American and Caribbean plates because it lies within the Polochic-Motagua fault zone that separates the two plates. The cumulative Cenozoic sinistral displacement across this zone that separates the Maya and Chortís terranes has been variously estimated to be ~125 km or ~1100 km, evidence for which should be recorded in the rocks of the studied area. The Rabinal-Salamá area lies between two of the east-west faults within the Motagua fault zone, the Polochic fault, and the Baja Verapaz shear zone. The shear zone separates the Maya block from eclogitic rocks of the Chuacús Complex that pass southward into ophiolitic rocks and mélanges that define a suture between the Chuacús Complex and the Chortís block. The following sequence of events is recorded in the Rabinal-Salamá area: (1) lowgrade, pre-Silurian siliciclastic metasedimentary rocks (San Gabriel unit), that are intruded by (2) ca. 462–453 Ma calc-alkaline, peraluminous, S-type Rabinal granite suite, and unconformably overlain by (3) very low grade clastic and calcareous metasedimentary rocks (Santa Rosa Group) contain†

E-mail: [email protected]

ing Mississippian conodonts and pebbles of granite, sandstone, and phyllite derived from the older units. The Rabinal granite suite is inferred to be rift related, inheriting its calc-alkaline signature from its source, along with the ca. 1 Ga xenocrystic zircons (upper intercept U-Pb data). Deformation in all these Paleozoic rocks produced a steeply south-southwest–dipping cleavage (chlorite and sericite) and a stretched quartz lineation. These fabrics become more intense adjacent to the Baja Verapaz shear zone, where C-S fabrics and rotated porphyroclasts indicate a reverse sense of motion with a sinistral component. White mica in the shear zone yields 74–65 Ma K-Ar ages, which are inferred to closely postdate the time of crystallization. Thus, although evidence for major sinistral displacement is absent, the kinematics are consistent with uplift and exhumation of the Chuacús Complex during obduction of the Baja Verapaz ophiolite onto the Paleozoic rocks of the Rabinal-Salamá area in latest Mesozoic-Paleocene. This is inferred to have been produced during collision of the Cuban arc and Chortís block with the southern Maya block. Restoration of the Early Mesozoic ~70° anticlockwise rotation of the Maya block places the Rabinal-Salamá area adjacent to northeastern Mexico, where comparable continental-shallow marine, Paleozoic rocks occur near Ciudad Victoria overlying the ca. 1 Ga Oaxaquia basement.

Keywords: Guatemala, Maya block, Chortís block, Caribbean tectonics, Motagua, Paleozoic, Rabinal granite. INTRODUCTION The tectonic boundary between the North America and Caribbean plates in Guatemala consists of a complex system of large-scale faults that separate blocks with contrasting geologic features (Donnelly et al., 1990; Giunta et al., 2002a; Rogers, 2003; Ortega-Gutiérrez et al., 2007). The Maya block of southeastern Mexico, Belize, and Guatemala is the southernmost continental assemblage of the North America plate, whereas the Chortís block in Guatemala, Honduras, and the Nicaragua rise is the northernmost part of the Caribbean plate (e.g., McBirney, 1963; Weyl, 1980; Donnelly et al., 1990; OrtegaGutiérrez et al., 1995; Keppie, 2004) (Fig. 1). The Sierra de Chuacús eclogitic rocks were traditionally included in the Maya block (e.g., McBirney, 1963; Weyl, 1980; Donnelly et al., 1990); however, Ortega-Gutiérrez et al. (2007) consider it to be a separate block and/or terrane of uncertain affinity. These blocks constitute two major continental terranes with ca. 1 Ga and Neoproterozoic basement overlain by Paleozoic rocks that are separated by the Motagua fault zone. Estimates of Cenozoic displacements along the Motagua fault system vary from ~170 km (Donnelly et al., 1990) to ~1200 km (Pindell et al., 1988). This zone is made up of

GSA Bulletin; Month/Month 2008; v. 120; no. X/X; p. 000–000; doi: 10.1130/B26238.1; 9 figures; 3 tables.

For permission to copy, contact [email protected] © 2008 Geological Society of America

1

IN PRESS Ortega-Obregón et al.

Figure 1. (A) Main tectonic subdivision of southern Mexico and Central America in crustal blocks. N—Náhuatl-Guerrero terrane; TMVB— Trans Mexican Volcanic Belt; M—Mixteco terrane; CH—Chatino terrane; Z—Zapoteco terrane; CU—Cuicateco terrane; MAYA—Maya block; CHORTIS—Chortís block. Nomenclature after Sedlock et al. (1993). PMFZ—main (simplified) trace of the Polochic-Motagua fault zone. (B) Schematic geological map showing basement rocks of central Guatemala, southeasternmost Mexico, and northwestern Honduras. Geology is recompiled from Kesler et al. (1970); Anderson et al. (1973); Steiner and Walker (1996); Weber et al. (2005; 2006a); and unpublished data of the authors. PFZ—Polochic fault zone; MFZ—Motagua fault zone; BVFZ—Baja Verapaz fault zone; JChFZ—Jocotán-Chamelecón fault zone; LCF—La Ceiba fault. Main ophiolitic bodies are also shown in black: SSC—Sierra de Santa Cruz; BVP—Baja Verapaz; SJP—San Juán de Paz; NM—north Motagua unit, ophiolite and mélange; SM—south Motagua unit, ophiolite and mélange. Modified from Solari et al., 2008.

several east-west faults and contains abundant tectonized mafic-ultramafic complexes, eclogites, blueschists, and tectonic mélange. This assemblage is interpreted as an oceanic suture between the two continental blocks that formed during collision associated with the eastward migration of the Antillean arcs during the Late Cretaceous (Anderson et al., 1985; Donnelly et al., 1990; Fourcade et al., 1994; Giunta et al., 2002a, 2002b; Harlow et al., 2004). How, where,

2

and when these blocks stitched together has been a matter of intense debate, and the tectonic history of the involved continental margins is far from being understood (e.g., Ross and Scotese, 1988; Pindell et al., 1988; Meschede and Frisch, 1998; Pindell et al., 2006). Several models have been proposed for the genesis of the Motagua fault zone. Some authors consider the Polochic-Motagua-Cayman to be the boundary along which the Chortís

block moved in Cenozoic times from a location off southern Mexico to its present position (e.g., Burkart, 1983; Ross and Scotese, 1988; Schaaf et al., 1995; Meschede and Frisch, 1998; Pindell et al., 2006; Cerca et al., 2007; Rogers, 2007; see also diagram in Fig. 2A). Other models suggest that Chortís block collided with southern Maya block during the Late Cretaceous (Fig. 2B), leading to obduction of ophiolites (El Tambor sequence) and exhumation of high-pressure

Geological Society of America Bulletin, Month/Month 2008

IN PRESS Ordovician magmatism and Cretaceous collision, Maya-Chortís, Guatemala

A

USA

M

S SMEXICO Z G

*

U E R R E R O

** * * *Z+ J + M A Y A * ** 40

Y CA

*

CHO

0 R T 20 at 8 IS BL OCK 0 or 45 M a

MEXICO

M

T AN

R

OU

TR GH

500

Sutures

CK

O BL NT + R T I SE S E t en O PR rpm CH at ca s E ss He NICARAGUA

CHORTIS

rib

be

an

Cu

ba

ar

c

CLIP

*

RISE

Ca

*

S ANFORM

Farallón plate

SOUTH AMERICA

Late Cretaceous

C

Salamá

* Present subduction zone

B

Salamá

arc *+ Permian ~1 Ga

Salamá

+

60 TRIPLE POINT at various times

GULF OF MEXICO

* +

80Ma

km

0

MEXICO

Chortís at present

Figure 2. Paleocene reconstructions showing the possible location of the Rabinal-Salamá area through time: (A) according to Ross and Scotese (1988); (B) according to Kerr et al. (1999), Pindell et al. (2005), and Mann et al. (2006); (C) according to Keppie and Morán-Zenteno (2005).

SOUTH AMERICA

Chortís at 45 Ma

Subduction zone at 45 Ma

rocks (e.g., Anderson et al., 1985; Fourcade et al., 1994; Harlow et al., 2004; Giunta et al., 2002a, 2002b; Solari et al., 2007). Alternatively, Keppie and Morán-Zenteno (2005; Fig. 2C), citing the fact that the late Mesozoic-Holocene sediments in the Gulf of Tehuatepec, which straddles the western projection of the Motagua fault zone, are undeformed, place the Chortís block ~1100 km west-southwest of its present position in the early Cenozoic. During the Cenozoic, Keppie and Morán-Zenteno (2005) move the Chortís block to its present location along a west-southwest–trending paleotransform concealed under the Central American Volcanic Arc. Correlations between the Maya and Chortís blocks have suggested close connections. For instance, Mesozoic platformal carbonates occur in both blocks (Anderson and Schmidt, 1983; Mills, 1998), and Grenvillian gneisses occur in both southeastern Mexico and Honduras (cf. Manton, 1996; Weber and Köhler, 1999). On the other hand, the Paleozoic record in the Chortís block is unknown, in contrast to that in southern Mexico where sedimentary rocks of Cambrian to Permian age are common (e.g., Sánchez-Zavala et al., 2004). For these reasons, the geological

record of the Rabinal-Salamá area will help to elucidate the complex and protracted geologic makeup of the Chortís-Maya boundary. This paper presents results from structural, geochronological, and geochemical work performed north of Guatemala City and south of the Polochic fault, between the northernmost Sierra de Chuacús and the Baja Verapaz region in the vicinity of Rabinal and Salamá towns (Figs. 1B and 3). Results presented below suggest that: (a) the rocks originated adjacent to northeastern Mexico as part of Pangea; (b) the area rotated passively through ~60° anticlockwise with the Maya block during Jurassic opening of the Gulf of Mexico; (c) the rocks were deformed in the latest Mesozoic–earliest Cenozoic associated with northward obduction of ophiolitic rocks; and (d) there is no evidence for major sinistral displacements during the Cenozoic. GEOLOGICAL SETTING The regional geology of Central Guatemala has recently been synthesized by Donnelly et al. (1990), Martens et al. (2006), and OrtegaGutiérrez et al. (2007), and therefore only a

brief summary is presented in this paper. Initial work in the Rabinal-Salamá area concluded that it was characterized by sheared, low-grade Paleozoic sedimentary rocks (assigned to the Santa Rosa Group) and poorly dated, Early Permian to Mesoproterozoic intrusive granitic rocks (McBirney, 1963; Gomberg et al., 1968; van der Boom, 1972). Such rock assemblages contrast with the high-grade gneisses and eclogites, recently reported by Ortega-Gutiérrez et al. (2004) in the Sierra de Chuacús immediately north of the Motagua ophiolites, and south of the studied area. Ortega-Gutiérrez et al. (2007) recognized several fault blocks within the E-W trending Motagua fault zone, which can be synthesized as follows (Fig. 1): (1) The Chortís block (s.s.) lies to the south of the Jocotán-Chamelecón fault and includes a ca. 1 Ga gneissic basement overlain unconformably by platformal Early Paleozoic, Mesozoic, and Cenozoic rocks (Donnelly et al., 1990; Solari et al., 2008). Ortega-Gutiérrez et al. (2007) and Rogers (2007) suggested a further subdivision of crustal blocks south of the Jocotán-Chamelecón fault, based upon their (poorly studied) contrasting geological features.

Geological Society of America Bulletin, Month/Month 2008

3

4

Geological Society of America Bulletin, Month/Month 2008

RABINAL

Gt0340

90°30′

5

0m

500

1000

1500

2000

B3

Cerro Mamús

Las Minas

Figure 3. Geological map of the Rabinal-Salamá quadrangle, showing structural data and location of dated samples. The geological section shows the structural relationships of the Chuacús Complex metasediments, which are thrust over the San Gabriel sequence along the Baja Verapaz shear zone (BVSZ).

15°00′

15°05′

15°10′

PEG

Chixolop

B3

B1

Gt03115

Gt0357b

San Gabriel

90°25′

B2

San Miguel Chichaj

5

San Francisco

Río Salamá

B2

El Tempisque

?

eb

Qu

?

Section line

Secondary roads

0

S. GABRIEL SANTA ROSA CHUACÚS COMPLEX GROUP UNIT

e qu yá Pa

1

VPEG3

Gt03122

12

Río

SALAMÁ

BVSZ

?

Main faults Inferred contacts

Dated samples

Main trace of the Sa “Baja Verapaz la mshear zone” á

n atá

Rí o

Or

?

a rad

B3

Main roads

Towns

LEGEND

Gt03122

B1

90°20′

Río

17

im o

rón

5 Km

La E stan cia

Je

Río

Sa n

Metasediments (undifferend.)

Rabinal granite

Metaconglomerate

Metalimestones Metasandstone phyllite, shale

B1

Orthogneiss Augen gneiss, Bt-Pl gneiss Muscovite and garnet schist

Volcanic and fluvial deposits undifferentiated

IN PRESS

Ortega-Obregón et al.

IN PRESS Ordovician magmatism and Cretaceous collision, Maya-Chortís, Guatemala (2) Between the Jocotán-Chamelecón and Motagua faults are Mesozoic ophiolites and ultramafic mélange (El Tambor Group; McBirney, 1963; Donnelly et al., 1990; Lewis et al., 2006), unconformably overlain by Cenozoic sediments, inferred to represent obducted paleo-Caribbean oceanic floor (Weyl, 1980; Donnelly et al., 1990; Giunta et al., 2002a, 2002b; Chiari et al., 2006; Lewis et al., 2006). These rocks are in tectonic contact with the underlying Las Ovejas metamorphic rocks (Schwartz, 1977), which are considered to be the northernmost exposure of basement rocks belonging to the Chortís block. (3) Between the Motagua fault and Baja Verapaz shear zone lie the eclogitic rocks and gneisses of the Chuacús Complex (OrtegaGutiérrez et al., 2004). (4) Between the Baja Verapaz shear zone and the Polochic fault, a pre-Silurian sequence is cut by Ordovician-Silurian granites and overlain by Carboniferous platformal sedimentary rocks (this paper). The Baja Verapaz Mesozoic ophiolite has been thrust over these rocks (Giunta et al., 2002a). (5) North of the Polochic fault is the Maya block (s.s.), which consists of ca. 1 Ga granulites cropping out in southern Mexico (Guichicovi Complex; Weber and Köhler, 1999), unconformably overlain by Late Paleozoic platformal sequence (Santa Rosa Group; Bohnenberger, 1966; Anderson et al., 1973; Weber et al., 2006a, and references therein). These rocks disconformably overlie Silurian-Devonian plutons in Belize (Steiner and Walker, 1996; Martens et al., 2006) and in the Altos Cuchumatanes (Solari et al., 2008). The Santa Rosa Group was intruded by Permo-Triassic plutons that were syntectonically deformed (e.g., Chiapas batholith; Weber et al., 2005, 2006b). Paleozoic plutons have also been reported elsewhere in southern Mexico: (a) in the Mixteca terrane (Fig. 1A), both Ordovician and Permian granites crop out (Elías-Herrera and Ortega-Gutiérrez, 2002; Talavera-Mendoza et al., 2005; Nance et al., 2006; Keppie et al., 2006; Elías-Herrera et al., 2007; Miller et al., 2007); (b) in the Maya terrane, Permian plutons are exposed in La Mixtequita and Chiapas massifs (Weber et al., 2006b) and in western Guatemala (Solari et al., 2008); and (c) in the Xolapa Complex (a Mesozoic metamorphic belt fringing the Guerrero, Mixteca, and Oaxaquia terranes along the Pacific coast), a Permian granite has been reported (e.g., Ducea et al., 2004). These Permian plutons form part of an extensive magmatic arc that extends along the backbone of Mexico (Torres et al., 1999). These Paleozoic rocks are overlain by a Mesozoic platformal sequence (Todos Santos, Ixcoy, and Sepur Formations; Bonis, 1967; Blount, 1967; Blount and Moore, 1969; Anderson et al., 1973). These

Mesozoic rocks are structurally overlain by a Late Cretaceous ophiolitic allochthon (Sierra de Santa Cruz; Rosenfeld, 1981; San Juán de Paz; Giunta et al., 2002a). GEOLOGY AND GEOCHRONOLOGY OF THE RABINAL-SALAMÁ AREA Mapping of the Rabinal-Salamá area revealed the presence of three units (Fig. 3): (1) the San Gabriel unit (Salamá sequence of van der Boom, 1972, redefined), which is intruded by (2) the Rabinal granite suite (Gomberg et al., 1968 calculated U-Pb discordant ages for this granite using very large zircon fractions, with intercepts of 1075 ± 25 Ma and 345 ± 20 Ma, interpreted as either inheritance and intrusion, respectively, or as crystallization of hosting gneisses and metamorphism); and (3) the Santa Rosa Group unit (Sacapulas formation of van der Boom, 1972). A fourth unit, the Baja Verapaz island arc ophiolite, occurs just to the north of the mapped area, where it has been thrust over the three previously mentioned units (Giunta et al., 2002a).The protolith age of the ophiolite is unknown and is presumed to be Cretaceous to Jurassic based on radiolarian mainly found in the El Tambor Group (Lewis et al., 2006; Chiari et al., 2006). On the other hand, the time of overthrusting is recorded by the latest Cretaceous and Paleocene foreland basin turbidites of the Sepur Formation (Bonis, 1967; Rosenfeld, 1981; Giunta et al., 2002b). New age constraints and geochronological results will be presented in the following geological description of each unit. San Gabriel Unit The San Gabriel unit consists of low-grade, interbedded sandstone, arkose, graywacke, phyllite, slate, and mafic-felsic lavas and tuffs (Figs. 4A–4C). These lithologies indicate a continental, possibly shallow marine, environment of deposition. Petrographically, the metasedimentary rocks contain quartz, feldspar, muscovite, epidote, chlorite as well as scarce biotite, and clay minerals. The mafic volcanic rocks are made up of albite-oligoclase, green amphibole (rare hornblende and, more often, tremolite), epidote, and chlorite set in a cryptocrystalline matrix. The felsic rocks contain feldspar and quartz. The mineral associations found in metasediments and metabasites suggest that the rocks were metamorphosed under greenschist facies conditions. There are no continuous sections across the unit, and this, combined with the folding and discontinuous outcrop, makes it impossible to measure a type section. Although it is difficult to estimate the real thickness of the San Gabriel unit, it is at least 200 m thick based

on the continuous and undeformed section cropping out along the San Miguel–Rabinal road. The best exposures are on the roads between San Miguel Chichaj and San Gabriel and Rabinal (Figs. 3 and 4A–4C). No independent age constraints are available for this unit; however, an Ordovician upper limit is provided by the age of the Rabinal granite suite, which intrudes the unit (see below). The San Gabriel unit shows striking similarities with low-grade metasediments cropping out south of Huehuetenango, in western Guatemala (Fig. 1), where detrital zircon geochronology yielded Precambrian ages bracketed between ca. 920 and ca. 1000 Ma (Solari et al., 2008). Rabinal Granite Suite The coarse- to medium-grained Rabinal granite, and its associated minor intrusions and pegmatites, intrudes the San Gabriel unit. The San Gabriel unit locally preserves primary sedimentary features, such as graded and/or cross stratification. It is locally weakly foliated, and composed of K-feldspar (orthoclase and rare perthite), plagioclase (oligoclase), quartz, muscovite, accessory apatite, zircon, titanite, and opaque minerals, and secondary sericite and chlorite, replacing biotite. Modal analyses show a range from granite to granodiorite (Figs. 5A and 5B). The felsic dikes contain quartz, microcline, and biotite, whereas the pegmatites are made up of quartz, K-feldspar, and muscovite. The lack of contact metamorphism suggests that intrusion occurred into sediments at shallow depths with crystallization of magmatic muscovite occurring at a minimum depth of ~10 km (Chatterjee and Johannes, 1974; Wyllie, 1977). Chemically the granite has a SiO2 content of 72%–76%, and a high-K, calc-alkaline, peraluminous affinity (Table 1 and Fig. 5C). Normalized against primitive mantle, the analyzed trace elements show enrichment in high field strength elements; low Nb, P, and Ti anomalies; and high K and Pb (Fig. 5D). Normalized against chondrites, the rare earth element (REE) pattern is slightly enriched in light rare earth elements (Fig. 5E). On discriminant diagrams, they plot in the volcanic arc field, straddling the within plate and syncollisional granite fields (Figs. 5F–5G). Three granite samples and three pegmatite samples were collected for U-Pb zircon and KAr geochronology using methods described in Solari et al. (2007) and Ortega-Gutiérrez et al. (2004), respectively (sample locations are shown in Fig. 3). All of the zircons yielded discordant analyses, and chords through analyses from each sample yielded lower intercepts of 496 ± 26 Ma, 462 ± 11 Ma, and 417 ± 23 Ma and an upper intercept of 483 ± 7 Ma (Fig. 6). The best-fit chord is

Geological Society of America Bulletin, Month/Month 2008

5

IN PRESS Ortega-Obregón et al.

A

D

Rabinal granite

1m

E B

SanGabriel sequence SW

NE

F

Rabinal granite

S

C

C’ Pegmatite

SW

G

500 µm

NE 1 mm

Figure 4. (A) Intrusive relationships between the Rabinal granite and the San Gabriel sequence. The scale bar corresponds to 1 m. (B) Detail of the intrusive relationships, showing the foliation in both units. Note the absence of contact metamorphism. The pen is 14 cm long. (C) Dated sample PEG (Table 2) related to the Rabinal granite suite and cutting an arkose of the San Gabriel sequence. The pen is 15 cm long. (D) Granite and metasediments pebbles in deformed conglomerate assigned to the Sacapulas Formation, base of the Santa Rosa Group. The pen is 14 cm long. (E) Kinematic indicators in the Rabinal granite suite, indicating a top-to-the-northeast sense of shearing. (F) Photomicrography of S–C′ shear bands in metasediments of the San Gabriel sequence, indicating a top-to-the-northeast sense of shearing. Plane polarizers. The scale bar corresponds to 500 μm. (G) Strain fringes around a pyrite crystal in pelitic schists of the San Gabriel sequence, indicating a top-to-the-northeast sense of shearing. Crossed polarizers. The scale bar corresponds to 1 mm.

6

Geological Society of America Bulletin, Month/Month 2008

Geological Society of America Bulletin, Month/Month 2008

1

10

100

1000

0.1

1

10

100

1000

1

PEG

P

PEG

Gt0375

10

Gt03115

Gr02

VAG + syn-COLG

WPG

Gt0369

Gt0457B

GT0340

100

Y (ppm)

ORG

1000

Cs Rb Ba Th U Nb K La Ce Pb Pr Sr

Gt0357c Gt0115

Granite

e

F

D

A

SAMPLE / PRIMITIVE MANTLE

GT0340 Gr02

G

1

10

100

1000

10

VAG

Gt03115

PEG

Gt0375

Gt0369

Gr02

syn-COLG

ORG

La

1000

Ce

PEG

Gt0375

Or

Y+Nb (ppm) 100

Gt0457B

WPG

10

100

E

GT0340

Granite

Gt0457B PEG Gt0375

Gt03115

P Nd Zr Sm Eu Ti Dy Y Yb Lu

Ab

Gt0369

Tonalite

Trondhjemite

B

An

ior ite od

A

lite

Nb (ppm)

orit

i nod Gr an

Gra na

Rb (ppm)

To

SAMPLE / CHONDRITE

Q

Pr

C

45

Pm

Sm

50

Eu

55

65

Tb

Dy

Ho

Er

70

Tholeitic

SiO2 (wt%)

60

lkaline Calk a

hK Hig

itic on osh Sh

Gd

K2O (wt%)

Gt0457B

Tm

75

Yb

Gt0369

Gt03115

Gr02

GT0340

Gt0375

PEG

Lu

80

Figure 5. Some geochemical and tectonic discrimination diagrams used to describe the analyzed samples of the Rabinal granite suite. (A) Quartz-feldspar-plagioclase modal mineralogical composition (from Streckeisen [1976]). (B) Ab-An-Or triangle. (C) K2O versus SiO2 Harker diagram, showing the subalkaline fields subdivision. (D) Trace-element geochemical composition of selected samples, normalized to the primitive mantle values of McDonough and Sun (1995). (E) Rare-earth patterns of Rabinal granite suite, normalized to the chondrite values of McDonough and Sun (1995). (F) and (G) Tectonic discrimination diagrams for granitic rocks (from Pearce et al. [1984]). Labels indicate the analyzed samples as reported in Table 1. WPG—within-plate granitoids; VAG—volcanic-arc granitoids; syn-COLG— syn-colliisonal granitoids; ORG—orogenic granitoids.

Nd

1

2

3

4

5

6

IN PRESS

Ordovician magmatism and Cretaceous collision, Maya-Chortís, Guatemala

7

IN PRESS Ortega-Obregón et al.

Sample SiO2 (wt%) Al2O3 Fe2O3 MnO MgO CaO Na2O K2O TiO2 P2O5 LOI* TOTAL ACNK**

TABLE 1. GEOCHEMISTRY OF SELECTED SAMPLES OF RABINAL GRANITE SUITE, GUATEMALA Gt0457B Gt0369 Gt0375 Gt03115 Gr02 GT0340 75.11 74.40 76.00 72.51 74.32 73.45 13.68 13.44 13.62 14.59 14.32 13.05 1.13 1.66 0.50 1.77 2.01 1.87 0.033 0.078 0.014 0.050 0.027 0.062 0.30 0.53 0.15 0.35 0.56 0.34 0.19 1.42 0.12 1.63 0.25 0.83 3.36 4.88 2.76 4.14 2.51 3.45 4.20 1.49 5.86 3.33 4.29 4.97 0.12 0.25 0.05 0.18 0.19 0.271 0.10 0.06 0.07 0.06 0.03 0.07 1.33 1.18 1.05 0.97 1.66 0.58 99.6 99.4 100.2 99.6 100.2 98.95 1.31

1.10

1.23

Sr (ppm) 159 290 70 Y 26.0 23.9 8.3 Sc 4 4 3 Be 3 2 2 V 7 16