Petrogenesis and geodynamic implications of Oligocene A-type granite in the Guadalcazar area, San Luis Potosi, central Mexico

Abstract

The Guadalcazar is located in the Mesa Central (MC) province, which is mainly composed of granitic rocks and is known for its metallogenetic. The granitic rocks contain complex Sn-Hg-Ag-F mineralization and were emplaced during Eocene to Oligocene. However, the source, origin, and evolution of magma and the tectonic setting of this magmatic area have never been explained. In this study, we have conducted petrology, whole-rock geochemistry, and U–Pb zircon geochronology on granitic rocks from the Guadalcazar to constrain the petrogenesis and tectonic environment. LA-ICP-SF-MS zircon U–Pb dating shows that the Guadalcazar granite was emplaced ca. 31 Ma. These rocks are characterized by high (SiO2) contents (64–75 wt%), low CaO (0.28–1.78 wt%), with relatively high (FeOt)adj/(FeOt + MgO) values ranging from 0.90 to 0.98. The geochemical diagrams of SiO2 vs [(FeOt)/(FeOt + MgO)] and SiO2 vs [(Na2O + K2O) − CaO] show the ferroan and mostly alkali-calcic nature of these rocks. The granite shows an A2-type affinity and is strongly peraluminous, with ASI (molar Al2O3/[CaO + Na2O + K2O]) values of 1.13 to 2.60. These granitic rocks are characterized by enrichments in rare earth elements (REE) and high field strength elements (HFSE), and depletion in Ba, Nb, Sr, Ti, and Eu. These features suggest that these A-type granites were derived from the metasedimentary rocks and evolved through extensive fractional crystallization. The multidimensional discrimination diagrams showed a continental rift or within-plate setting. By combining previous and new data, we proposed a new magmatic evolution model that supports an extension during ca. 34–28 Ma in the Guadalcazar, central Mexico.