Inherited structures controlling the development of the Arista-Ahualulco graben in the Mesa Central, Mexico

The reactivation of inherited structures is of utmost importance in extensional regions such as rifts and basins. We have investigated the possibility that normal faults found in the NNW Arista-Ahualulco graben may have formed due to an inversion of previous NNW trending contractile structures. Available geological information consistently suggests that the Arista-Ahualulco graben has experienced repeated phases of post-Laramide extension, starting with extensional reactivation of the basal Mexican Orogen structures. Our data in the studied area indicate inheritance of Mexican Orogen structures in the following aspects: (a) The Cenozoic normal faults are nearly parallel to the Mesozoic fold and thrust structures; (b) Preexisting faults controlled Cenozoic magmatism. In the preexisting contractile structures, three types of normal faults are observed: newly-formed, reactivated from the reverse faults and reactivated by bed-parallel slip. Based on the above observations, we proposed a two-stage model to explain the Cenozoic gravitation collapse: a late-orogen stage (late Paleogene-Eocene) with a collapse coeval to shortening and post-orogen stage (late Eocene-Miocene) under extensional regime).