POST-PALEOCENE DEFORMATION IN THE TIQUICHEO REGION, MICHOACAN, CENTRAL MEXICO

We are studying the deformation in the paleogene sequence of the Tiquicheo region in Michoacan State, south of the Mexican Volcanic Belt in southwestern Mexico. The stratigraphy of the area comprises jurassic to cretaceous marine volcaniclastic (interbedded volcanic sandstone, shale and conglomerate) and volcanic (andesitic to rhyolitic flows) rocks of the Guerrero terrane. They are unconformably overlain by paleogene continental sedimentary rocks, which have been grouped in five facies associations (Altamira, 2002): The La Cañita 3 facies consists of sandstones with conglomerate lenses interbedded with tabular conglomerate beds. This facies is in transitional contact with Tzetzenguaro facies that consists of sandstone with conglomeratic lenses interbedded with thickly bedded sandstone. The Tiquicheo 1 facies consists of sandstone and mudstone interbedded with conglomerates. The variation of El Cirian facies is from sandstones to conglomerate rocks. The Los Bonetes facies consists of interbedded sandstones, conglomerates, limestones, and mudstones. In the southwestern part of the field area are exposed volcaniclastic, calcareous rocks, and intrusive bodies. The bedding of the paleogene sedimentary sequence is moderately inclined (~30-40°) to the east and west on either side of the uplifted blocks. The structural grain of the area is north-south and defined by major block uplifts where the mesozoic rocks are exposed. The blocks are bounded by right-stepping right-lateral strike-slip faults, which produce positive flower structures. Another fault system is defined by NW-SE-trending strike-slip faults with less important displacements, which also affect both Paleogene as well as Cretaceous rocks. An E-W-trending fault system is subordinate to the other two and consists of both strike-slip as well as normal faults. Associated with these normal faults is a dike swarm, particularly well exposed in the Tiquicheo region in the northwest of the study area. The dikes are of andesitic composition and are one meter thick on average.