Articles

 

Boletín de la Sociedad Geológica Mexicana
Volumen Conmemorativo del Centenario
Temas Selectos de la Geología Mexicana


Vol. 57, núm. 3, 2005, p. 319-341

http://dx.doi.org/10.18268/BSGM2005v57n3a4

 La evolución tectónica y magmática cenozoica del suroeste de México: avances y problemas de interpretación

 Dante Jaime Morán-Zenteno1,*, Mariano Cerca1,2, John Duncan Keppie1

1 Instituto de Geología, Universidad Nacional Autónoma de México, Ciudad Universitaria, Delegación Coyoacán, 04510, México D.F.
2 Centro de Geociencias, Universidad Nacional Autónoma de México, Campus Juriquilla, Querétaro, Qro. 76230, México.

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Abstract

Recent advances in the knowledge of the Cenozoic structure and stratigraphy of southern Mexico reveal a geological evolution characterized by Late Cretaceous orogenic deformation, followed by truncation of the continental margin and gradual extinction of arc magmatism in the Sierra Madre del Sur, previous to the onset of magmatism in the Trans- Mexican Volcanic Belt. Orogenic deformation beginning in the Late Cretaceous was coeval with the Laramide orogeny and displays structures with a similar orientation. Deformation consisted of E-W shortening with a general eastward vergence and a well defined migration to the east. Models that associate the origin of Laramide deformation to a decrease in the angle of subduction of the Farallon plate, which was converging in western Mexico, cannot be applied in this region because of the occurrence of Paleocene to early Eocene arc magmatism near the inferred paleotrench. A possible origin related to the collision of an insular arc against the western margin of Mexico does not seem plausible due the absence of features and petrogenetic associations indicating the closure of an oceanic basin. In light of recent geochronological data, the general pattern of magmatism extinction, from Late Cretaceous-Paleocene in Colima and Jalisco to the middle Miocene in central and southeastern Oaxaca, presents variations inconsistent with a simple pattern of extinction toward the east-southeast. Maastrichtian to early Paleocene plutonism recognized in the Jalisco block and Manzanillo areas is contemporaneous with a magmatic episode with some documented adakite affinities in the central part of the Sierra Madre del Sur. Magmatism from the Paleocene to middle Eocene seems to be concentrated in the Presa del Infiernillo area, although isolated centers existed in areas such as Taxco or the eastern Jalisco block. Finally, the main axis of magmatism between the middle Eocene and Oligocene developed along what is now the present day continental margin and also within a band located 200 km inland. In general, the geochemical characteristics of this magmatism indicate a low degree of continental crustal assimilation. Two episodes of principally sinistral lateral faulting that activated NW-SE and later N-S oriented faults, with variations in time and space, have been documented during the Eocene and the beginning of the Oligocene. The N-S set of faults was active only in the north of the Sierra Madre del Sur, whereas the activity of the NW-SE set continued during the Oligocene along the Oaxaca continental margin. The recognition of these deformation episodes suggests that extension directions related to lateral faulting changed from NNW-SSE to NE-SW, and locally activated normal displacements on pre-existing discontinuities. Fundamental problems still exist in the interpretation of the plate tectonic processes that originated the stress regimes acting on the different sets of faults, as well as in the knowledge of the factors influencing the migration of magmatism. Some of the arguments used to postulate the presence of the Chortis block off the southwestern Mexico continental margin during the early Cenozoic are uncertain. On the other hand, models that explain restricted displacements of the Chortis block with respect to the Maya block without juxtaposition with the southwestern margin of Mexico suggest that continental truncation was essentially caused by subduction erosion but leave open the interpretation of the observed magmatic migration.

Keywords: Southern Mexico, arc-magmatism, deformation, tectonics, Cenozoic.