EARLY MISSISIPPIAN, PERI-GONDWANAN ARC VOLCANISM IN NE-MEXICO: ASERRADERO RHYOLITE FROM THE CIUDAD VICTORIA BLOCK

The study of the Paleozoic development of Mexico is greatly hindered by the scarcity and dispersion of outcrops of this age. Thick Mesozoic and Cenozoic sedimentary and volcanic sequences cover these units, which are the product of the processes that occurred in the NW margin of Gondwana, before its collision against Laurentia. The collision is linked to the closure of the Rheic Ocean, during the Late Paleozoic Ouachita-Marathon-Sonora Orogeny.

One of the key locations to study this process is the pre-Mesozoic basement of the Sierra Madre Oriental, which occurs in the eroded core of the Huizachal-Peregrina Anticlinorium, located near Ciudad Victoria, Tamaulipas. We describe it now as “Ciudad Victoria Block”, consisting of the following units: (a) the Neoproterozoic granulitic Novillo Complex, (b) the Ordovician Peregrina Tonalite, (c) the Pennsylvanian greenschist Granjeno Complex, and (d) the sedimentary Silurian – Permian siliciclastic Tamatán Group. The latter includes irregular rhyolitic bodies, which were originally described as Devonian novaculites. However, its volcanic nature and Carboniferous age were later recognized and determined.

In this work we present the results of the geochemical characterization and new geochronological data by LA-ICP-MS U–Pb in zircons of this acidic unit described as Aserradero Rhyolite. These rocks are high-K, low-Sr and correspond to S-type granitoids. The source may have been one like the rocks of the Novillo Complex. The crystallization age of the rhyolites has been better constrained with 347.8 ± 2.7 Ma and 340.7 ± 3.6 Ma, corresponding to Early to Middle Mississippian. These data confirm that their stratigraphic position is original, despite the strong deformation of the Tamatán Group.

According to our model, Aserradero Rhyolite represents a very early pre-collisional stage of a peri-Gondwanan Carboniferous-Permian arc. This arch is also located in Las Delicias, Oaxaca, the Acatlán Complex, the Maya Block, as well as in the buried crystalline basement along the Western Gulf of Mexico.

During the Upper Jurassic opening process of the Gulf of Mexico, the Ciudad Victoria Block was dismembered from Oaxaquia and its peripheral units, as the Yucatán Block migrated to its current position.