Geochemical characteristics and tectonic significance of the Paleocene-Eocene felsic diques and dome complex of La Tesorera, Zacatecas, Mesa Central, México
Keywords: felsic dikes and domes, Tesorera Granodiorite, Mesa Central volcanism, igneous complex, K-Ar ages
AbstractThe Tesorera igneous complex (CIT) is composed of Mesozoic sedimentary and volcano-sedimentary sequences belonging to the Guerrero terrane (TG) and Early Cretaceous calcareous sediments, deformed by the shortening of the Laramide orogeny and the intrusion of the Tesorera granodiorite around 74 Ma. During Paleogene, dacitic lava domes were emplaced on the granodioritic rock, and were followed by the extrusion of rhyolitic dikes and volcanic domes between 44 to 50 Ma. The Upper Cretaceous volcano-sedimentary sequence was deposited in an intra- or back-arc setting. The development of the Sierra Madre Occidental volcanic arc during the Late Cretaceous is contemporary to the Laramide orogeny and is associated with the folds and thrusts belt of the Sierra Madre terrane. The Tesorera Granodiorite pluton, dykes and felsic domes associated with the development of the Sierra Madre Occidental arc were settled along faults and fractures with variable widths up to 500 m and lengths of ~5 km. They were emplaced on the volcano-sedimentary units that form the Asientos-La Tesorera volcanic arc (referred with this name in this work). The granodioritic plutons of this southern part of the Mesa Central do not show laramidic contractile deformation and were emplaced where the San Luis-Tepehuanes Faults System (SLTFS) and the eastern shoulder of the Aguascalientes graben intersect. Structural data of dykes have an average direction N60°W and a dip between 45° and 85° SW, suggesting an extension direction ~ NE-SW. In accordance with the age of the volcanic rocks of the study, the deformation that caused these faults belongs to the initial stages of the extensional tectonics that formed the Basin and Range Province. The orientation of the dykes coincides with the orientation of the SLTFS, mainly at the San Luis de la Paz-Salinas de Hidalgo stretch, whose main activity occurred during the Paleogene time. The geochemical characteristics, like major and trace elements, for the igneous rocks that make up the volcanic complex indicate that they are sub-alkaline to alkaline rocks, and peraluminous with an alumina saturation index >1, [Al2O3 /(CaO+Na2O+K2O) > 1]. The lavas evolved from a volcanic arc tectonic environment into an intrapalte volcanism. They were associated with mantle-derived magmas and fractional crystallization processes, and resulted in intrusive rocks of granodioritic composition and extrusive rock of rhyolitic composition that formed dikes and volcanic domes.