2008 Joint Annual Meeting (5-9 Oct. 2008): Sandstone Provenance and Tectonic Setting of Volcanic and Sedimentary Units of the Mesozoic Zacatecas Volcanic Complex, Sierra De Zacatecas, Mexico

Most of the scarce outcrops of Mesozoic igneous rocks in central México are interpreted to be related to the Triassic-Early Cretaceous Guerrero composite terrane. In the Sierra de Zacatecas, an almost continuous sequence is defined from the older and dominantly sedimentary Zacatecas Fm. (ZF) to the younger Las Pilas Volcanosedimentary Complex (LPC). Contact relationships between the ZF and LPC units are gradual. The ZF is composed by feldespathic wacke, mudstone, chert and discrete limestone lenses. Basaltic lava flows, few dikes and hydrothermal vent-like structures are also identified in the ZF. The LPC is mainly composed of laccolithic intrusions and basaltic lava flows interlayered with feldespathic and lithic wacke, mudstone, chert and rare limestone.

U-Pb ages distribution patterns of detrital zircons from the ZF (n=33) show age peaks at 132-160, 288, 325, 445, 679 and 1020 Ma. Age clusters for the LPC (n=34) are at 133-142, 160, 1150 and 1260 Ma. We propose that the youngest zircon ages can be associated with the Late Jurassic-Early Cretaceous Alisitos-Teloloapan arc; the Paleozoic and Precambrian ages should reflect crustal blocks from the northern North American craton or the northeastern Tampico block, but the Acatlan and Oaxaca complexes should be also potential sources from southern Mexico.

The basaltic lava flows plot in the destructive plate margin field of the Th-Hf-Ta tectonic discrimination diagram, while trace elements signatures and REE patterns are typical of island arc environments.

Based on the combined field and geochemical data, we interpret that the ZF and LPC units are distal and proximal facies related to a ca. 133-132 Ma old Zacatecas volcanic complex of island arc affinity. We also propose that such complex is part of the Guerrero composite terrane.