SINISTRAL NORMAL BLOCK MOTION OF CRUSTAL BLOCKS IN SOUTHERN MEXICO DURING PANGEA BREAKUP: NEW EVIDENCE FROM SANDSTONE PROVENANCE ANALYSIS OF THE TEZOATLÁN BASIN

The structural evolution that accompanied the breakup of Pangea during Jurassic time has been constrained in Mexico only at the regional scale on the basis of global plate tectonics and geometric considerations. According to available regional-scale reconstructions, the Jurassic tectonic evolution of Mexico was characterized by 1) anticlockwise rotation of the Yucatán block along NNW-trending dextral faults and 2) sinistral block motions along W- to WNW-trending faults, which are geometrically needed to avoid the overlap between North and South America in the reconstruction of Pangea. Reports of W- to WNW-trending sinistral faults that were active in Mexico during Jurassic time are presently few, and the existence, extension, and age of some of these structures have been questioned by many authors.

In this work, we present the provenance analysis from a Jurassic clastic succession deposited within the Tezoatlán Basin in southern Mexico. Whole-rock sandstone petrography integrated with chemical analysis of detrital tourmaline and U–Pb detrital zircon geochronology documents that the analyzed stratigraphic record was in part deposited during rapid exhumation of the Paleozoic metamorphic rocks of the Acatlán Complex along the Río Salado fault, which is a WNW-trending sinistral normal fault that extends along the northern boundary of the Tezoatlán Basin. U–Pb zircon ages and biostratigraphic data bracket the age of the Río Salado fault between 179 and 170 Ma. This indicates that the Río Salado fault was involved in the crustal attenuation that accompanied breakup of Pangea and that sinistral motion of continental blocks along WNW-trending structures was taking place in southern Mexico as predicted by global plate tectonic reconstructions.