Stratigraphic Assessment of the Arcelia±Teloloapan Area, Southern Mexico: Implications for Southern Mexico's Post-Neocomian Tectonic Evolution
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Journal of South American Earth Sciences 13 (2000) 443±457 www.elsevier.nl/locate/jsames Stratigraphic assessment of the Arcelia±Teloloapan area, southern Mexico: implications for southern Mexico's post-Neocomian tectonic evolution E. Cabral-Canoa,*, H.R. Langb, C.G.A. Harrisonc aInstituto de GeofõÂsica, Universidad Nacional AutoÂnoma de MeÂxico, Ciudad Universitaria, MeÂxico , DF 04510, Mexico bJet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109, USA cMarine Geology and Geophysics, Rosenstiel School of Marine and Atmospheric Science, University of Miami, 4600 Rickenbacker Cswy, Miami, FL 33149, USA Abstract Stratigraphic assessment of the ªTierra Caliente Metamorphic Complexº (TCMC) between Arcelia and Teloloapan in southern Mexico, based on photo interpretation of Landsat Thematic Mapper images and ®eld mapping at the 1:100,000 scale, tests different tectonic evolution scenarios that bear directly on the evolution of the southern North American plate margin. The regional geology, emphasizing the strati- graphy of a portion of the TCMC within the area between Arcelia and Teloloapan is presented. Stratigraphic relationships with units in adjacent areas are also described. The base of the stratigraphic section is a chlorite grade metamorphic sequence that includes the Taxco Schist, the Roca Verde Taxco Viejo Formation, and the Almoloya Phyllite Formation. These metamorphic units, as thick as 2.7 km, are covered disconformably by a sedimentary sequence, 2.9 km thick, composed of the Cretaceous marine Pochote, Morelos, and Mexcala Formations, as well as undifferentiated Tertiary continental red beds and volcanic rocks. The geology may be explained as the evolution of Mesozoic volcanic and sedimentary environments developed upon attenuated continental crust. Our results do not support accretion of the Guerrero terrane during Laramide (Late Cretaceous±Paleogene) time. q 2000 Elsevier Science Ltd. All rights reserved. Keywords: Tectonic evolution; Arcelia; Teloloapan; Stratigraphy 1. Introduction a tectonostratigraphic analysis carried out in the surround- ings of the proposed tectonostratigraphic terrane boundary. The location of the study area between two extensive Ortega-Gutierrez (1981, p. 194) considered the TCMC in carbonate platforms (Huetamo area and the Guerrero± southern Mexico to be a provisional designation, ªuntil Morelos platform located between Mexico City and Chil- better geochronology and mapping establish their true pancingo; Fig. 1) of similar mid-Cretaceous age and deposi- geological relationships.º A compilation and comparison tional environment has resulted in the formulation of of published maps (Cabral-Cano, 1995) reveals contradic- contrasting evolutionary schemes for southern Mexico. tory stratigraphic af®nity. This is a direct consequence of the Some interpretations explain the non-continuity of the two diverse criteria used to de®ne mapping units and the lack of carbonate platforms as the result of deposition controlled by clear contact de®nitions and lithologic characterizations. topography (e.g. de Cserna et al., 1978). Others assert that A tectonostratigraphic assessment on the metamorphic the metamorphic rocks of the ªTierra Caliente Metamorphic rocks of the Tierra Caliente complex in the vicinity of the Complexº (TCMC), upon which the carbonates sit, are alleged terrane boundary was precluded by the absence of a allochthonous, resulting from the tectonic accretion of an reliable cartographic base. Thus, new mapping and strati- island arc (e.g. Campa and Ramirez, 1979; Tardy et al., graphic analyses serve as the basis to test opposing tectonic 1991), with consequent dissimilar stratigraphic records scenarios and derive important constraints on the tectonic and geologic evolution from the rest of cratonic Mexico. evolution of the southern North American plate margin. These contrasting tectonic scenarios can only be tested by 2. Approach * Corresponding author. Tel.: 152-5-622-4027; fax: 152-5-550-2486. The approach used for this study was that described by E-mail address: [email protected] (E. Cabral-Cano). Lang et al. (1987) and Lang and Paylor (1994) in which 0895-9811/00/$ - see front matter q 2000 Elsevier Science Ltd. All rights reserved. PII: S0895-9811(00)00035-3 444 E. Cabral-Cano et al. / Journal of South American Earth Sciences 13 (2000) 443±457 Fig. 1. Location of the Tierra Caliente Metamorphic Complex (TCMC) and other metamorphic complexes in southern Mexico, and Cretaceous carbonate deposits. Study area is boxed. Modi®ed from Ortega-Gutierrez et al. (1992). Fig. 2. Location of the Teloloapan±Arcelia study area in southern Mexico (boxed). Major roads and towns in the region are shown for reference. Landsat Thematic Mapper satellite imagery was used for photointerpretion of the area. The background is a greyscale version of a principal component image (RGB PC1, PC2, and PC3) generated from a Landsat TM Image which shows an example of digital enhancement of the imagery to better discriminate lithologies due to contrasting spectral characteristics of the different rock units, which are expressed as different shades of grey on this image. Compare with Fig. 3 for correspondence to lithostratigraphic units. E. Cabral-Cano et al. / Journal of South American Earth Sciences 13 (2000) 443±457 445 geologic mapping and structural/stratigraphic analyses ®ne- and coarse-grained mica and/or chlorite pelitic schists using photogeology and spectral interpretations of Landsat and phyllites (Fries, 1960). Outcrops are restricted to the Thematic Mapper (TM) images are guided by published lowermost topographic areas, in the north-central portion mapping and ®eld work. This approach makes ®eld work of the study area (Fig. 3). The schists have a well-developed more ef®cient by remotely identifying localities where key cleavage, which is folded to centimeter-scale chevron folds, stratigraphic and structural relationships are well exposed and crenulation cleavage in the case of the ®ne-grained and are most accessible. Three digital TM scenes acquired rocks. in the winter of 1985±1986 under essentially cloud-free The base of the Taxco Schist is not exposed in the study conditions provided image base maps. Color composites area, but near Zacazonapan (90 km northwest of the study using different band combinations, principal component, area) it rests in a fault contact with Permian±Early Triassic decorrelation stretch and edge enhanced images (Moik, mylonitic granite of continental af®nity (Elias-Herrera and 1980; Gillespie et al., 1986) were registered to Universal Sanchez-Zavala, 1990). The upper contact with the Roca Transverse Mercator (UTM) geographical coordinates and Verde Taxco Viejo is poorly exposed near La Parota Lidice photographically enlarged to 1:250,000; 1:100,000, and (Fig. 3). All outcrops of the Taxco Schist we visited are 1:50,000 scales. Fig. 2 is an example of the images used. deeply weathered and thus inappropriate for radiometric dating. The age can be constrained only as pre-Aptian± Albian Ð that is, older than the base of the overlying 3. Results Roca Verde Taxco Viejo (94.4±82.8 my; Fig. 5) and More- los Formations. 3.1. Overview The Roca Verde Taxco Viejo and the Taxco Schist Formations are composed of distinct lithostratigraphic The study area in Guerrero State, Mexico (Fig. 1), encom- units (Fig. 3). Besides their lithological differences, the passes approximately 1600 km2 of greenschist facies meta- Taxco Schist presents high drainage density and a low resis- morphic rocks known as the TCMC. In 1981, Ortega- tance to erosion, in contrast with the more resistant Gutierrez de®ned the TCMC as a complex of low-grade geomorphic expression of the Roca Verde Taxco Viejo. metamorphic rocks, including calc-alkaline andesites, Within the study area, the Taxco Schist outcrops are consis- ignimbrites, tuffaceous shales, sandstones, and limestones tently topographically below outcrops of the Roca Verde exposed ªmainly in the southern slopes of the Balsas River Taxco Viejo, suggesting a lower stratigraphic position for Basin and beyond the southern limits of the Transmexican the former. The minimum exposed thickness of the Taxco Volcanic Beltº (1981, p. 194) (see Fig. 1). The earliest Schist in the study area is approximately 900 m. This was formal lithostratigraphic description in the study area was calculated in the vicinity of La Parota Lidice by measuring that of Fries (1960), with complementary work by de Cserna the relief between the lowest part of the schist exposure (1965). In a later stratigraphic review, Ontiveros-Tarango along the Sultepec River and the highest point of the (1973) reported a thrust of Roca Verde Taxco Viejo green- upper contact with the Roca Verde Taxco Viejo. This esti- stone over mid-Cretaceous Morelos limestone west of Telo- mate is crude, because it is likely that this sequence is loapan. This fault was later interpreted by Campa and Coney duplicated by small thrust faults that are dif®cult to detect (1983) and Centeno-GarcõÂa et al. (1993) as a tectonostrati- at the 1:50,000 scale mapping. graphic terrane boundary. Mapping of this area has also We correlated rocks that we mapped as the Taxco Schist been published by Campa et al. (1974), de Cserna (1978), with rocks mapped by Fries (1960) in the Taxco type area, Campa and Ramirez (1979) and INEGI (1981a,b). 33 km northeast of the study area, and with the metamorphic Lithostratigraphic units used here are summarized in the sequence mapped by Elias-Herrera