FROM JURASSIC RIFTING TO CRETACEOUS-PALEOGENE INVERSION IN THE HUAYACOCOTLA AREA OF E MEXICO – INSIGHTS FROM STRUCTURAL GEOLOGY, GEO- AND THERMOCHRONOMETRY, AND STRATIGRAPHY

The Phanerozoic tectonic evolution of eastern Mexico is dominated by the complex interplay of subduction-related magmatism, back-arc extension, and retro-arc shortening as well as the opening of the Gulf of Mexico (GOM) during the break-up of Pangea. The major tectonic episodes that configured the E of Mexico include 1) the late Paleozoic tectonic assembly of Pangea, amalgamating granulitic Proterozoic Oaxaquian basement and early Paleozoic Gondwanan terranes, and associated Permo-Carboniferous arc magmatism. 2) Early Jurassic breakup of Pangea, opening of the GOM, incl. southward translation of the Yucatan block along the East Mexican transform, and formation of fault-bounded extensional basins. 3) Late Cretaceous–Paleogene shortening and associated foreland sedimentary successions associated with the Mexican Orogeny (MO). While early Mesozoic extensional basins exhibit thick fluvial to marine sedimentary successions, organic-rich shales, and evaporites, limited information is available for the syn-rift stratigraphy, facies distribution, provenance, basin thermal history or tectonic context in relation to GOM opening. This study presents new detrital zircon (DZ) U-Pb and (U-Th)/He provenance data integrated with sedimentologic and petrographic observations and regional stratigraphic correlations, to resolve the tectonic evolution from rifting to inversion in the Huayacocotla area, at west GOM. The DZ U-Pb data show that Permian Tuzancoa Fm. was deposited in an extensional basin exclusively sourced from the East Mexican Arc. Subsequent Jurassic syn-rift strata of the Huayacocotla and Cahuasas Fms. record unroofing of Oaxaquian basement and Permian arc and input of Jurassic arc magmatism, with sedimentary facies controlled by proximity to normal faults. Finally, Paleogene Chicontepec samples are characterized by Middle Jurassic and Cretaceous to Paleocene DZ ages derived from both the eroding Mesozoic strata in thin-skinned Mexican fold-and-thrusts belt and contemporaneous volcanism, but prior to inversion of the Jurassic rift basins. These preliminary data paint a clearer picture of late Paleozoic to early Cenozoic tectonic, magmatic, and basin evolution of east-central Mexico in response to Pangea assembly and break up and subsequent shortening and inversion during the MO.