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Recent advances in the knowledge of the Cenozoic structure and stratigraphy of southern México reveal a geological evolution characterized by Upper Cretaceous orogenic deformation, followed by truncation of the continental margin and gradual extinction of arc magmatism in the Sierra Madre del Sur, prior to the onset of magmatism in the Trans-Mexican Volcanic Belt. Orogenic deformation began in the Late Cretaceous and was coeval with the Laramide orogeny with structures of similar orientation. Deformation consisted of E-W shortening that migrated to the east with time and with a general easterly vergence. Models that relate the Laramide deformation to a decrease in the angle of subduction of the Farallon plate, which was converging in western México, cannot be applied in southern México because Paleocene to upper Eocene arc magmatism occurs near the inferred paleotrench. An alternative possible origin due to collision of an insular arc against the western margin of México suffers from an absence of features and petrogenetic associations indicating the closure of an oceanic basin.

In light of recent geochronological data, the general pattern of magmatic extinction from Upper Cretaceous–Paleocene in Colima and Jalisco to the middle Miocene in central and southeastern Oaxaca presents some variations inconsistent with a simple pattern of extinction toward the E-SE.

Maastrichtian to lower Paleocene plutonism recognized in the Jalisco block and Manzanillo areas is contemporaneous with a magmatic episode that has some documented adakitic 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 the present-day continental margin and extends 200 km inland as a broad band. 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 lower 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 deformational episodes suggests that extensional directions related to lateral faulting changed from NNW-SSE to NE-SW, and locally produced normal displacements on preexisting discontinuities.

Fundamental problems still exist in the interpretation of the plate tectonic processes that produced the stress regimes acting on the different sets of faults, as well as in the determination of the factors influencing the migration of magmatism. Some of the arguments used to postulate the presence of the Chortis block off the southwestern Mexican 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 México—suggest that continental truncation was essentially caused by subduction erosion and leave open the interpretation of the observed magmatic migration.

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