Tectonic implications of alternative Cenozoic reconstructions for southern Mexico and the Chortis block

Most Current Eocene reconstructions juxtapose the Chortis block of northern Central America against Southern Mexico, and invoke similar to 1100 km Cenozoic sinistral displacement on the Acapulco-Motagua-Cayman fault zone, the inferred northern margin of the Caribbean plate. Such a hypothesis is incompatible with the presence of undeformed Upper Cretaceous-Recent sediments that cross the projected it-ace of the Motagua fault zone in the Gulf of Tehuantepec, minimal offset of the Permian Chiapas batholith, and the absence in Honduras of several major features in southern Mexico. These problems may be overcome if the Chortis block is back-rotated anticlockwise about a pole near Santiago, Chile, i.e. similar to 1100 km along the Cayman transform faults during the Cenozoic. Such a reconstruction when combined with reconstructions of features in the Pacific Ocean, suggests that Middle Miocene collision of the Tehuantepec aseismie ridge with the Acapulco Trench led to: (1) asymmetric flattening of the subduction zone; (2) an anticlockwise rotation of the Mexican magmatic are to its present location by the Middle Miocene; (3) the development of a volcanic are gap in southeastern Mexico, in which the late Middle Miocene Chiapas fold-and-thrust belt developed: as the Tehuantepec Ridge swept westward, are volcanism was re-established in the gap. Eocene collision of the Chumbia Seamount Ridge (inferred mirror image of the Moonless Mountains-unnamed seamount ridge between the Molokai and Clarion fracture zones) with the Acapulco Trench followed by its ESE migration during the Oligocene led to: (a) flattening of the subducting slab inducing subduction erosion and exhumation of the southern Mexican margin, (b) anticlockwise rotation of the volcanic are; and (e) sinistral strike-slip faulting in the Sierra Madre del Sur. This contrasts with the region north of the projected Molokai fracture zone where the dip of the subduction zone appears to have steepened, producing extension. Eocene(-Late Cretaceous) subduction along the southern coast of Mexico explains the remnants of a Late Cretaceous are in the Gulf of Tehuantepec and neighboring Guatemala.