NEW SR-ND-PB-O ISOTOPE DATA FOR COLIMA VOLCANO AND EVIDENCE FOR THE NATURE OF THE LOCAL BASEMENT

Abstract

Colima volcano is situated at the western edge of the Mexican volcanic belt within the Colima rift zone. This contribution presents new geochemical and Sr-Nd-Pb-O isotope data for Colima volcano rocks and plutonic xenoliths found in prehistorical lava flows. Colima volcano magmas display strong subduction signatures (positive peaks of Ba, K, Pb, and Sr, and negative anomalies of Nb and Ti) and were generated in a depleted mantle source and emplaced at crustal levels (garnet-free zone), where they experienced fractional crystallization of plagioclase and pyroxene. Gabbroic and granitoid xenoliths found in prehistorical lava flows show evidence for partial melting and are considered to be representative of the basement beneath Colima volcano. At upper-crustal levels, Colima volcano magmas were contaminated by granitoids, like those of the nearby Cretaceous Manzanillo and Jilotlán Batholiths. Sr-Nd isotope ratios of these intrusives are nearly identical to those of Colima volcano lavas. For that reason assimilation of the granitic crust is not detectable in diagrams of these isotopic systems but can be clearly seen in a εNd versus δ18O plot. In comparison to other large Mexican volcanic belt stratovolcanoes, Colima volcano lavas display the least evolved geochemical and isotopic signatures of this arc. © 2006 Geological Society of America.