INTERNAL ARCHITECTURE AND TECTONO-SEDIMENTARY EVOLUTION OF THE TLAXIACO BASIN, SOUTHERN MEXICO: A SEDIMENTOLOGICAL APPROACH FOR RECONSTRUCTING THE EARLY–MIDDLE JURASSIC CONTINENTAL ATTENUATION HISTORY OF WESTERN EQUATORIAL PANGEA

By early Mesozoic time, continental rifting of Pangea began in its western margin developing several basins. The basin boundaries were major faults that accommodated the continental extension. However, the tectonic evolution of the Pangea breakup is still poorly understood in some places, as in the case of continental Mexico, which was located in western equatorial Pangea during this global tectonic event. In the last years, the Jurassic tectonic evolution of Mexico has been the focus of debate in regional-scale reconstructions. The main challenges in identifying the faults that accommodated the continental attenuation in Mexico are due to the complex overprinting of post-Jurassic deformation events that obliterate the Jurassic faulting evidence, and the sedimentary and volcanic successions that cover these faults. Therefore, a sedimentological approach of the Jurassic basins can help to identify faults that accommodated continental extension during Pangea breakup.

In the PAPIIT IN104018 project framework, we integrated new sedimentologic, petrologic, and U-Pb geochronologic data to reconstruct the internal architecture and sediment routing of the Tlaxiaco Basin (TB), one of the largest rift basins associated with the Pangea breakup exposed in southern Mexico. Two different drainage systems characterized the internal architecture of the TB: 1) an axial fluvial system located in the central part of the basin, sourced by the Proterozoic, granulite-facies metamorphic rocks from the Oaxacan Complex; and 2) a transverse system represented by a set of alluvial fans that interacted in their distal part with the axial fluvial system, fed by the Paleozoic, greenschist-facies metamorphic rocks from the Acatlán Complex. Our data allowed to track the northern boundary of the TB, a regional-scale WNW-trending fault that controlled the sedimentary architecture and evolution of this basin. This work documents the first major WNW-trending fault involved in the crustal thinning of Pangea in southern Mexico during Early-Middle Jurassic, which acted contemporaneously to NNW-trending system faults. The discovery of this fault suggests that previous models assuming that the Jurassic tectonic evolution of Mexico was entirely influenced by NNW-trending faults related to the Gulf of Mexico opening must be refined.