Trace elements geochemistry and origin of volcanic units from the San /XLV

Two main volcanic fields separated by a volcano-tectonic structure were emplaced in the southern part of San Luis Potosi state during the Cenozoic peak of continental extension in the SE portion of the Sierra Madre Occidental. The Eocene to Quaternary volcanic rocks associated to these structures range in composition either from subalkaline basalts to basanites or from basaltic andesite to rhyolites, and were emplaced during five magmatic events. New trace element analyses obtained by the ICP-QMS method show that the three oldest ones, ranging in age from middle Eocene to late Oligocene, emplaced potassic calc-alkaline intermediate to evolved lavas. These originated from subduction-related mafic magmas through open-system fractional cristallization coupled with assimilation and possibly melting of the continental crust. The two youngest volcanic phases (Miocene and Quaternary) emplaced intraplate subalkaline to alkaline basalt and basanites derived from variable melting degrees of enriched mantle.