Geochemical and isotope data from the Acatlán Volcanic Field, western Trans-Mexican Volcanic Belt: Origin and evolution

Abstract

The Quaternary Acatlán Volcanic Field (AVF) is located at the western edge of the Trans-Mexican Volcanic Belt (TMVB). This region is related to the subduction of the Pacific Cocos and Rivera plates beneath the North American plate since the late Miocene. AVF rocks are products of Pleistocene volcanic activity and include lava flows, domes, erupted basaltic andesite, trachyandesite, trachydacite, and rhyolite of calc–alkaline affinity. Most rocks show depletion in high field-strength elements and enrichment in large ion lithophile elements and light rare earth elements as is typical for magmas in subduction-related volcanic arcs. 87Sr/ 86Sr values range from 0.70361 to 0.70412, while ɛNd values vary from +2.3 to +5.2. Sr–Nd isotopic data plot along the mantle array. On the other hand, lead isotope compositions ( 206Pb/ 204Pb=18.62–18.75, 207Pb/ 204Pb=15.57–15.64, and 208Pb/ 204Pb=38.37–38.67) give evidence for combined influences of the upper mantle, fluxes derived from subducted sediments, and the upper continental crust involved in magma genesis at AVF. Additionally δ 18O whole rock analyses range from +6.35‰ in black pumice to +10.9‰ in white pumice of the Acatlán Ignimbrite. A fairly good correlation is displayed between Sr as well as O isotopes and SiO 2 emphasizing the effects of crustal contamination. Compositional and isotopic data suggest that the different AVF series derived from distinct parental magmas, which were generated by partial melting of a heterogeneous mantle source.