Geochemical, Sr-Nd Isotopic, and P-T Data on a Central Mexican Xenolith Suite: Evidence for Upper Mantle and Lower Crust Compositions

Abstract

Northeast of San Luis Potosi (Central Mexico, 22~ 101~ Quaternary basanites and tuff breccias have sampled a suite of ultramafic upper mantle to lower crustal xenoliths, associated with seven phreatomagmatic maars. Xenolith distribution range from spinel lherzolites (55%), spinel pyroxenites (10%), hornblende pyroxenites (18%) to metaigneous and metapelitic granulites (17%). The SLP volcanic field is located in the back-arc region of two major volcanic belts along the southwestern border of the North American craton (Fig.l): The Oligocene calc-alkaline volcanics from the Sierra Madre Occidental in the east and the late Miocene to recent basaltic to rhyolitic volcanics f rom the Transmexican Volcanic Belt. Analysis of the geochemical and Sr-Nd isotopic data together with p-T-conditions of the xenolith profile gives hints for the thermal evolution and composition of the upper mantle segment and lower crust in Central Mexico. The latter is of