Geologic and Geochronologic Data from the Guerrero Terrane in the Tejupilco Area, Southern Mexico: New Constraints on Its Tectonic Interpretation
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Journal of South American Earth Sciences 13 (2000) 355±375 www.elsevier.nl/locate/jsames Geologic and geochronologic data from the Guerrero terrane in the Tejupilco area, southern Mexico: new constraints on its tectonic interpretation M. ElõÂas-Herrera*, J.L. SaÂnchez-Zavala, C. Macias-Romo Instituto de GeologõÂa, Universidad Nacional AutoÂnoma de MeÂxico, Ciudad Universitaria, DelegacioÂn CoyoacaÂn, Mexico DF 04510, Mexico Abstract The eastern part of the Guerrero terrane contains two tectonically juxtaposed metavolcanic-sedimentary sequences with island arc af®nities: the lower, Tejupilco metamorphic suite, is intensely deformed with greenschist facies metamorphism; the upper, Arcelia-Palmar Chico group, is mildly to moderately deformed with prehnite-pumpellyite facies metamorphism. A U±Pb zircon age of 186 Ma for the Tizapa metagranite, and Pb/Pb isotopic model ages of 227 and 188 Ma for the conformable syngenetic Tizapa massive sul®de deposit, suggest a Late Triassic±Early Jurassic age for the Tejupilco metamorphic suite. 40Ar/39Ar and K±Ar age determinations of metamorphic minerals from different units of the Tejupilco metamorphic suite in the Tejupilco area date a local early Eocene thermal event related to the emplacement of the undeformed Temascaltepec granite. The regional metamorphism remains to be dated. 40Ar/39Ar ages of 103 and 93 Ma for submarine volcanics support an Albian±Cenomanian age for the Arcelia-Palmar Chico group, although it may extend to the Berriasian. U±Pb isotopic analyses of zircon from the Tizapa metagranite, together with Nd isotopic data, reveal inherited Precambrian zircon components within units of the Tejupilco metamorphic suite, precluding the generation of Tejupilco metamorphic suite magmas from mantle- or oceanic lithosphere-derived melts, as was previously considered to be the case. Instead, these data, together with high-grade gneiss xenoliths with Grenvillian Nd isotopic af®nity in Oligocene subvolcanics, indicate the presence of pre-Mesozoic continental crust beneath at least the eastern part of the Guerrero terrane. As a Late Triassic±Early Jurassic basement unit in the eastern part of the Guerrero terrane, the Tejupilco metamorphic suite may therefore represent an evolved volcanic arc developed on old crust with assimilated craton-derived sediment. This would imply a tectonic cycle of deformation, metamorphism and erosion during the Middle±early Late Jurassic that was probably related to the accretion and consolidation of part of the Guerrero terrane into the AcatlaÂn Complex, the pre-Mississippian poly- deformed and metamorphosed basement of the Mixteco terrane. q 2000 Elsevier Science Ltd. All rights reserved. Keywords: Guerrero terrane; Tectonic interpretation; Arcelia-Palmer Chico group 1. Introduction and geologic setting and southern Mexico. The same units were subsequently assigned to the Upper Jurassic±Lower Cretaceous Guerrero Greenschist and subgreenschist facies volcanic-sedimen- terrane by Campa and Coney (1983), a composite terrane tary metamorphic rocks are exposed in the Balsas River made up of the Teloloapan-Ixtapan, Zihuatanejo and basin region of southern Mexico (Fig. 1). Because of uncer- Huetamo subterranes. Relations among these subterranes tainties in their geochronologic, stratigraphic and structural have not yet been established; however, according to relations, these rocks were informally grouped into the Campa and Coney (1983), the eastern margin of the Guerrero Tierra Caliente complex (Ortega-GutieÂrrez, 1981). The terrane is thrust against the Cretaceous calcareous Morelos- complex was interpreted to record the tectonic juxtaposition Guerrero platform of the Mixteco terrane (Fig. 1). of two separate terranes, one belonging to an oceanic-trench Additional subdivisions based on geochemical, Sm±Nd setting and the other to a marginal sea-island arc environ- isotopic and limited paleontologic data have also been ment (Ortega-GutieÂrrez, 1981) in a similar fashion to that proposed for the Guerrero terrane (Talavera-Mendoza et proposed previously by de Cserna (1971) for the ªUpper al., 1993; Centeno-GarcõÂa et al., 1993a). The Mesozoic Triassic eugeosynclinal assemblageº in northern, central submarine volcanic and sedimentary sequences of island arc af®nity in southwestern Mexico were regrouped into the Hauterivian (?)±Aptian Teloloapan subterrane, the * Corresponding author. Tel.: 152-5-622-4288/4290; fax: 152-5-550- 6644. Albian±Cenomanian Arcelia-Palmar Chico subterrane, E-mail address: [email protected] (M. ElõÂas-Herrera). and the Ladinian to Albian Zihuatanejo-Huetamo subterrane 0895-9811/00/$ - see front matter q 2000 Elsevier Science Ltd. All rights reserved. PII: S0895-9811(00)00029-8 356 M. ElõÂas-Herrera et al. / Journal of South American Earth Sciences 13 (2000) 355±375 Fig. 1. Simpli®ed geologic map of southwestern Mexico showing the location of the Tejupilco area and the Guerrero (GT), Mixteco (MT), and Xolapa (XT) terrane boundaries: (1) terrane boundary between Guerrero and Mixteco terranes after Campa and Coney (1983); (2) terrane boundary between Guerrero and Mixteco terranes after Sedlock et al. (1993). Division of the Guerrero terrane into subterranes (after Coney and Campa-Uranga, 1987; Talavera-Mendoza et al., 1995): A Arcelia, Ar Arteaga, H Huetamo, I-Z Ixtapa-Zihuatanejo, LO Las Ollas locality, P Palmar Chico, PO Placeres del Oro, Pp Pepechuca locality, SP San Pedro LimoÂn, Tl Teloloapan, Tj Tejupilco, Tx Taxco, VB Valle de Bravo, Zt ZitaÂcuaro. The Index Map shows the Oligocene volcanics of the La Sierra Madre Occidental (SMOCC), the Miocene-Quaternary volcanics of the Transmexican volcanic belt (TMBV), and the terrane bondaries of the southern Mexico: (1) Guerrero terrane (NaÂhuatl, Sedlock et al., 1993), (2) Xolapa terrane (Chatino, Sedlock et al., 1993), (3) Mixteco terrane, (4) Zapoteco terrane. (Fig. 1), with inferred or observed tectonic relationships basin located in the back-arc position (Huetamo sequence) between them (Talavera-Mendoza et al., 1993; Centeno- which also formed on previously deformed ocean-¯oor GarcõÂa et al., 1993a). These subterranes are suggested to (Placeres complex), and a subduction complex (Las Ollas form a Mesozoic multi-arc system accreted to the North complex) (Talavera-Mendoza et al., 1993; Centeno-GarcõÂa American plate. Thus, the Teloloapan subterrane, the east- et al., 1993a). The paleogeographic relations and tectonic ernmost part of the Guerrero terrane (Fig. 1), is thought to evolution of these subterranes, and the relationships with the correspond to an evolved intra-oceanic island-arc system Mixteco terrane are obscure. (Talavera-Mendoza, 1993; Talavera-Mendoza et al., 1995) The Mixteco terrane comprises the AcatlaÂn Complex and and the Arcelia-Palmar Chico subterrane is considered to its cover. The AcatlaÂn Complex is a pre-Mississippian represent a primitive intra-oceanic island-arc (Ortiz- poly-deformed and metamorphosed basement unit HernaÂndez et al., 1991; Talavera-Mendoza, 1993) and an (Ortega-GutieÂrrez, 1978, 1981; Sedlock et al., 1993; oceanic back-arc basin (Talavera-Mendoza et al., 1993; Ortega-GutieÂrrez et al., 1994). The metamorphic basement Centeno-GarcõÂa et al., 1993a). The Zihuatanejo-Huetamo rocks are interpreted to record early Paleozoic subduction subterrane has been interpreted as a complex assemblage and obduction of an ophiolite onto a subduction complex, made up of an island-arc (Zihuatenejo sequence) developed early to middle Paleozoic collision of the oceanic rocks with on previously deformed oceanic crust (Arteaga complex), a continental crust, and middle to late Paleozoic deformation M. ElõÂas-Herrera et al. / Journal of South American Earth Sciences 13 (2000) 355±375 357 Fig. 2. Simpli®ed geologic map of the Tejupilco area showing the localities that were sampled for geochronology. In phyllite and muscovite schist the NW±N- trending regional foliation is generally subhorizontal (5±308) with W±SW- or E±NE-dipping directions. and metamorphism (Sedlock et al., 1993; Ortega-GutieÂrrez 1994) and, according to its geologic relationships, is pre- et al., 1994). The AcatlaÂn Complex is unconformably Late Jurassic in age (Pantoja-Alor, 1990). The Arteaga and covered by unmetamorphosed marine siliciclastic and Placeres complexes are pre-Upper Jurassic basement units carbonate strata of Mississippian±Permian ages, ignimbrite of the Guerrero terrane (Centeno-GarcõÂa, 1994). In Fig. 1, and andesite of apparent Triassic, epicontinental and marine the Placeres complex is not differentiated from the Artega strata of Middle Jurassic and Cretaceous ages, and Cenozoic complex. continental clastic and volcanic rocks (Corona-Esquivel, The existence of deformed Triassic basement introduces 1981/3; VillasenÄor-MartõÂnez, 1987; GonzaÂlez-Arreola et al., a new dimension to those tectonic interpretations (Campa, 1994). The westernmost exposure of the AcatlaÂn Complex is 1978; Campa and RamõÂrez, 1979; Ortiz-HernaÂndez et al., thrust westward over the Cretaceous calcareous Morelos- 1991; Tardy et al., 1991, 1992, 1994; Lapierre et al., 1992) Guerrero platform along the Papalutla fault (de Cserna et for the Guerrero terrane, in which the Upper Jurassic± al., 1980), which has been suggested as the boundary Lower Cretaceous island-arc assemblages were assumed between the Mixteco and NaÂhuatl terranes (Sedlock et al., to be constructed over oceanic lithosphere. However, it is 1993; Ortega-GutieÂrrez et al., 1994) (Fig. 1). The NaÂhuatl consistent with those interpretations