Regional tectonics of western Mexico and its implications for the northern boundary of the Jalisco block

Abstract

The Tepic-Zacoalco rift of western Mexico had been considered the result of right-lateral and normal faulting of Plio-Quaternary age produced along the northern boundary of the Jalisco Block by its rifting away from the North America plate. Geologic and structural field studies in the States of Nayarit and Jalisco revealed that the boundary is wider than previously reported and that since late Miocene no major strike-slip deformation has been occurring along it.
The structure of the boundary consists of a system of half-grabens and grabens which formed at different times after a transpressional phase of middle Miocene age. Part of these structures formed in connection with the separation of Baja California from mainland Mexico in late Miocene-early Pliocene. The late Pliocene and Quaternary extensional tectonics is mainly concentrated in the southern part of the boundary and according to microtectonic data is characterized by an average NNE-SSW trending minimum stress axis. These data, combined with the direction of extension in the Colima graben, indicate a possible trenchward displacement of the Jalisco Block. Our results, together with seismological and plate motion studies raise doubts about the models which hypothesise a Pilo-Quaternary active rifting of the Jalisco Block. We suggest instead that the late Pliocene to Quaternary extensional tectonics along the Jalisco Block boundaries could be a passive feature induced by the differential motion of the Rivera plate with respect to the adjacent Cocos and Pacific plates.