PERMIAN BASIC VOLCANISM ON THE NW MARGIN OF GONDWANA IN THE GUACAMAYA FORMATION, CIUDAD VICTORIA BLOCK, TAMAULIPAS, MEXICO

The Huizachal-Peregrina Anticlinorium represents an important regional Laramide structure, located west of Ciudad Victoria, Tamaulipas, Mexico. It displays an NNW-SSE axis. Its eroded core forms a geological window, comprising a wide variety of Precambrian and Paleozoic basement units. The present work focuses on the top of the recently described Devonian-Permian Tamatán Group. This group has been interpreted as deposited in a back-arc basin located between Oaxaquia and the Maya Block along the northwestern Gondwanan margin during the closure of the Rheic Ocean, before completing the assemblage of Pangea.The Tamatán Grpoup includes the following formations: Cañón de Caballeros, Vicente Guerrero, Del Monte and Guacamaya. The latter is the object of this study.

The main objective is the petrographic and geochemical characterization of the epiclasts in the Permian Guacamaya Formation's turbiditic units to propose a geodynamic model and correlation with other contemporary volcanic units. The Tuzancoa Formation (Huayacocotla Anticlinorium) stands out, potentially correlatable with the Permian volcano-sedimentary sequence.

The lithic-quartz-feldspathic sandstones of the Guacamaya Formation display a clastic fabric containing carbonate clasts (extra- and intrabasinal) and Permian-aged bioclast, too. The grains are mainly sub-rounded to sub-angular, showing point compaction between them. The epiclasts contain glass shards and spherulitic textures.

The major- and trace element concentrations of the selected epiclasts of the Guacamaya Formation indicate an affinity to a basic to an intermediate continental magmatic arc that shows a tendency towards the field of compositional variation, without relative concentration of zircon, suggesting a hydraulic sorting and minimal weathering. According to these data, the source was close to the depocenter, and the transport was relatively short.