Constraining the Late Mesozoic and Early Tertiary Tectonic Evolution of Southern Mexico: Structure and Deformation History of the Tierra Caliente Region.

Abstract

We analyze the structure and assess the deformation history of the Tierra Caliente Metamorphic Complex (TCMC) of southern Mexico, where Laramide accretion of exotic terranes is in debate. The TCMC consists of a south-plunging antiform fault that is bounded on both its eastern and western flanks. Tierra Caliente Metamorphic Complex rocks show at least two phases of compressional deformation. The first and most prominent records a mean tectonic transport direction of 068 degrees. This phase is responsible for east-verging asymmetrical folding and thrusting of both metamorphic and superjacent sedimentary rocks. The second phase has an average transport direction of 232 degrees and is restricted to the western portion of the TCMC. A third phase is responsible for normal faulting. Lack of discernible deformation before Late Cretaceous time indicates that the main deformation phase is coincident with Laramide orogenesis elsewhere in the North American Cordillera. The stratigraphy, structure, and deformational history of the TCMC do not require accretion of exotic terranes. We explain the Mesozoic tectonostratigraphic evolution of the TCMC in terms of deposition and deformation of Mesozoic volcanic and sedimentary strata over the attenuated continental crust of the North American plate.