EVIDENCES OF AN ORDOVICIAN MAGMATIC ARC IN THE BASEMENT OF THE SIERRA MADRE ORIENTAL: A NEW PIECE OF THE GEOLOGICAL PUZZLE IN NE MEXICO

The core of the Huizachal-Peregrina Anticlinorium (HPA), located W of Cd. Victoria, Tamaulipas, displays a wide variety of Precambrian and Paleozoic lithologies. Before this work, tectonic implications of the Paleozoic magmatic units had not been deeply studied, generating inconsistencies in preexisting models. The igneous units set key points for the understanding of geodynamic conditions during the evolution of NE Mexico through Paleozoic times.

The HPA core comprises two felsic bodies, which prior of this work had been associated to a magmatic arc along NW Gondwana margin during Carboniferous times. The first unit, Peregrina Tonalite, is tectonically emplaced between the Precambrian Novillo Gneiss and Carboniferous Granjeno Schist. The second unit, referred as Aserradero Rhyolite, is interbedded in the strongly deformed Paleozoic Sedimentary Sequence.

Petrographic analysis shows a modal composition of plagioclase, quartz, ortopyroxene, muscovite and chlorite, with calcite, orthoclase, zircon and titanite as accessory minerals for the Peregrina Tonalite, while plagioclase, quartz, sanidine, biotite in a microcrystalline matrix with chlorite and sericite as secondary minerals, as well as disseminated pyrite, for the Aserradero Rhyolite. Chemical composition confirms the lack of genetic relationships between both acid units, while trace element point out to a magmatic arc setting for the origin of both units.

New U-Pb LA-ICP-MS data obtained from zircons from Peregrina Tonalite shows several populations, the oldest from Grenvillian and Panafrican ages, while the younger, interpreted as crystallization age, is 449.2 ± 2.9 Ma (Katien, Upper Ordovician). Aserradero Rhyolite results were inconclusive because of the limited population of zircon crystals in the rock, but the younger age (331.9 ± 5.2 Ma, Middle Pennsylvanian) is congruent with its stratigraphic position in the Paleozoic Sedimentary Sequence, and radiometric ages previously reported on literature.

With this new information, a new tectonic model is proposed. Peregrina Tonalite is generated as part of a magmatic arc developed during Upper Ordovician in Oaxaquia, which has not been reported yet in NE Mexico. Aserradero Rhyolite is still considered as a product associated to the Permo-Carboniferous magmatic arc along Western Pangea.