IN PRESS Tectonic signifi cance of Cretaceous–Tertiary magmatic and structural evolution of the northern margin of the Xolapa Complex, Tierra Colorada area, southern Mexico L.A. Solari† R. Torres de León G. Hernández Pineda J. Solé G. Solís-Pichardo Instituto de Geología, Universidad Nacional Autónoma de México, 04510 Mexico City, Mexico T. Hernández-Treviño Instituto de Geofísica, Universidad Nacional Autónoma de México, 04510 Mexico City, Mexico ABSTRACT volcanic rocks, and open folding during D4. have markedly different basement characteris- These four pulses of subduction-related mag- tics, including metamorphic grade, composition, The Tierra Colorada area sits along the matism in the Tierra Colorada area indicate ages, and tectonic histories. According to Campa northern limit of the Xolapa Complex, where a regular northeastward subduction at the and Coney (1983), and as modifi ed by Sedlock et it is juxtaposed against the Mixteco (Paleo- Mesoamerican trench since Jurassic time, al. (1993), these terranes are: (1) the Guerrero ter- zoic) and Guerrero (Mesozoic) terranes of and alternate with contractile and/or exten- rane, mainly composed of Mesozoic arc-related southern Mexico, just north of Acapulco. sional tectonic events. The gap in magmatic rocks (Centeno-García et al., 1993; Elías-Herrera This paper presents combined structural and activity ca. 90–100 Ma roughly coincides et al., 2000); (2) the Mixteco terrane, consist- geochronological data from Tierra Colorada with deposition of platformal limestones of ing of the Paleozoic Acatlán Complex, which is area that show evidence of four deformational the Morelos Formation during the middle characterized by an assemblage of high-grade events and several episodes of arc magmatism Cretaceous. The stable conditions during oceanic and continental rocks faulted against during Mesozoic and Cenozoic time. The old- deposition of the Morelos Formation may low-grade pelites and psammites, and covered est magmatism is represented by ca. 165 Ma have resulted from a combination of back- by late Paleozoic–Jurassic continental sediments granitoids and was followed by intrusion of arc extension and development of a passive (Ortega-Gutiérrez et al., 1999; Keppie et al., the foliated El Pozuelo granite (129 ± 0.5 Ma; margin during the Early–middle Cretaceous, 2004; Talavera-Mendoza et al., 2005; Nance et concordant U-Pb zircon analysis). This which postdated the accretion of an exotic al., 2006); (3) the Oaxaca terrane, the Grenvillian intrusion postdates D1 metamorphism and block, either the Guerrero terrane or the Oaxacan Complex basement of which comprises migmatization in the Xolapa Complex. The Chortís block. Following the Laramide orog- rift-related anorthosite- mangerite- charnockite- next magmatic episode is represented by eny in southern Mexico (roughly during the granite, paragneiss, volcanic-arc rocks, and the peraluminous, foliated El Salitre granite Late Cretaceous) the Paleocene–Miocene tec- calcsilicates metamorphosed to granulite facies (55.3 ± 3.3 Ma; mineral–whole-rock Rb-Sr tonic evolution in the Tierra Colorada area (Keppie et al., 2003; Solari et al., 2003); and isochron) and the protomylonitic Las Piñas involved an alternation of magmatic pulses (4) the ~600 × 50–80 km Xolapa terrane, which I-type granite (54.2 ± 5.8 Ma; lower intercept with extensional and contractile events. This bounds the other three terranes on the south (e.g., U-Pb zircon). Las Piñas granite is character- was the result of a combination of several fac- Herrmann et al., 1994; Corona-Chávez, 1997; ized by D2 ductile fabric with normal, top-to- tors, including the geometry of the subducted Werre-Keeman and Bustos-Díaz, 2001; Ducea et the north-northwest sense of shear, deformed slab, convergence rate, stress transmission al., 2004; Corona-Chávez et al., 2006). at 45–50 Ma (Rb-Sr and K-Ar ages). The between the subducting and overlying plates, The Xolapa Complex, the basement of the ca. 34 Ma undeformed granites correspond and the rate of subduction erosion. Xolapa terrane, has been interpreted as an to the last intrusive pulse in the area, postdat- allochthonous, Jurassic–Cretaceous, deformed ing both D3 south-southwest–verging thrust- Keywords: southern Mexico, U-Pb geochro- magmatic arc terrane (Ortega-Gutiérrez et al., ing of the Cretaceous Morelos Formation nology, Xolapa Complex, Cenozoic tectonics, 1995; Morán-Zenteno et al., 1996; Dickinson over sheared granites and Lower Cretaceous arc magmatism. and Lawton, 2001; Schaaf et al., 2002; Corona- Chávez et al., 2006), or an autochthonous mag- INTRODUCTION matic arc (Herrmann et al., 1994; Meschede et †Present address: Centro de Geociencias, Uni- versidad Nacional Autónoma de México, Campus al., 1996; Ducea et al., 2004; Keppie, 2004). Juriquilla, 76230 Querétaro, Querétaro, México; so- Southern Mexico is composed of a mosaic of The boundaries between terranes in southern [email protected]. at least four different crustal terranes (Fig. 1) that Mexico are generally marked by regional shear GSA Bulletin; Month/Month 2007; v. 119; no. X/X; p. XXX–XXX; doi: 10.1130B26023.1; 7 fi gures; 2 tables. For permission to copy, contact [email protected] 1 © 2007 Geological Society of America IN PRESS Solari et al. Mesozoic Xolapa Complex A Mexico City Oaxaca fault Paleozoic-Mesozoic (?) Mazatlán Complex 050100 km Puebla Sierra de Juarez Mylonitic Complex Permian Caltepec fault Paleozoic Acatlán Complex Cuernavaca Mid-Jurassic Precambrian Oaxacan Complex (right lateral) Laramide Precambrian Guichicovi Complex rePapalutla n fault Acatlan ?Triassic Gue r ro terra e (thrust) Major shear zones 18° At ne Zpo Maya terra oterra at ne Chilpancingo c Cu ca ec ter Laramide (thrust) La Venta shear zone Mixte eco terrane ito (Early Eocene) Studied area (Fig. 2) XT Oaxaca Matías Romero TC rane 17° Acapulco Xolap t r ane Tertiary (thrust, Laramide 97°00' USA normal, Oligocene/Miocene) aer Tehuantepec 30° Chacalapa shear zone (Oligocene) MEX Salina Cruz 16° IC Pacific Ocean Pacif O Huatulco Gulf of Mexico ic Oc 98° Puerto Ángel 96° MEXICO CITY B ean Zihuat. Aca. Huat. 16° Fig. 1a 110° 100° 90° Figure 1. (A) Terrane map of southern Mexico (modifi ed after Campa and Coney, 1983; Sedlock et al., 1993; Kep- pie, 2004). The square indicates the studied area as depicted in Figure 2. Position of the terrane map is marked by a rectangle in the inset of B. Locations in italics in B: Zihuat.—Zihuatanejo; Aca.—Acapulco; Huat.—Huatulco. zones or faults (Fig. 1). (1) The Caltepec fault during the Early Cretaceous by the subduc- about a pole near Santiago, Chile (Keppie and zone is a Permian dextral shear zone between tion of the Mezcalera plate and closure of the Morán-Zenteno, 2005). the Mixteco and Oaxaca terranes (Elías-Herrera Arperos basin (e.g., Dickinson and Lawton, The southern Mexico structural pattern was and Ortega-Gutiérrez, 2002). (2) The Tertiary 2001, and references therein), or a continental revised by Nieto-Samaniego et al. (2006), who Laramide Papalutla fault forms the boundary fringing arc (e.g., Elías-Herrera and Ortega- proposed grouping deformation structures into between the Guerrero and Mixteco terranes Gutiérrez, 1998). The Chortís block currently three events (shortening, strike slip, and nor- (e.g., Cerca et al., 2004). (3) The Chacalapa–La constitutes the basement of the northern part of mal faulting), from the Late Cretaceous to the Venta shear system is an Eocene–Oligocene Central America. Two alternative models have Miocene, progressively younging toward the sinistral strike fault along the northern border of been proposed for the southern Mexico-Chortís east. Detailed structural observations and geo- the Xolapa Complex (Ratschbacher et al., 1991; connections. (1) The Chortís block was adja- chronology of the Tierra Colorada area bear Riller et al., 1992; Tolson, 2005; this paper). cent to southwestern Mexico until the middle on the tectonic evolution of southern Mexico. Mesozoic and Cenozoic reconstructions of Tertiary, when it started to move toward its Combining the new data presented here with southern Mexico need to be based upon the current position along a transform fault paral- those previously published (e.g., Riller et al., correct time assignment of signifi cant geologic lel to the Middle America trench; this fault is 1992; Herrmann et al., 1994; Meschede et al., events, such Laramide shortening and Paleo- now represented by the Acapulco trench and 1996; Ducea et al., 2004; Nieto-Samaniego et cene–Oligocene arc magmatism (e.g., Cerca the Polochic-Motagua fault zone in Guatemala al., 2006) provides a wider database for testing et al., 2004; Morán-Zenteno et al., 2005; this (Anderson and Schmidt, 1983; Pindell et al., some of the previous models, such as the age of study), the time of migmatization in the Xolapa 1988; Ross and Scotese, 1988; Herrmann et al., migmatization, the migration of structural pat- Complex (66–46 Ma according to Herrmann 1994; Schaaf et al., 1995; Morán Zenteno et al., terns, and pulses of magmatism. et al., 1994; Jurassic–Cretaceous according to 1996; Meschede et al., 1996). (2) Keppie (2004) Ducea et al., 2004), and possible interactions also placed the Chortís block adjacent to south- LITHOLOGICAL UNITS between southern Mexico with the Guerrero ern Mexico in the Pangean reconstruction, but terrane and the Chortís block. The Guerrero by Eocene time it was southwest of its current In the fairly well exposed geologic record of terrane occupies most of western Mexico, and position. The Chortís block would have reached the Tierra Colorada area (Fig. 2), the southern- has been interpreted as either an exotic intraoce- its present position rotating clockwise, covering most unit is represented by the Xolapa Complex, anic terrane accreted to southwestern Mexico a distance of ~1100 km during the Cenozoic which is composed of high-grade orthogneiss 2 Geological Society of America Bulletin, Month/Month 2007 America Bulletin, Geological Societyof MEX E P Xolapa NW 95 R ER MEX N A IO EPOCH D Alluvial S poles N QUATER- HOLOCENE 95 1 NARY PLEISTOCENE 0.01 1.8 PLIOCENE deposits ¿J?Gn 17° 10´ Tierra 5.3 Colorada 54 Xolapa NE S1 poles N EOGENE N Xolapa MIOCENE Papagayo Fm.