Sr, Nd, and Pb isotopic evidence for the origin and evolution of the Cántaro–Colima volcanic chain, Western Mexican Volcanic Belt

Abstract

We report new geochemical and Sr, Nd, and Pb radiogenic isotope data on Pleistocene to Recent subalkaline, basanite–minette, and mixed alkaline magmas from the Cántaro–Colima volcanic chain in the western part of the Mexican Volcanic Belt (MVB). All rocks from this area, including the basanites and minettes, show enrichment in LILE (e.g., Cs, Ba, and Sr) and depletion in HFSE (e.g., Ta and Ti), generally considered to be a characteristic of subduction-related magmas. The isotopic ratios of Cántaro–Colima rocks show the following ranges: 87Sr/ 86Sr 0.70282–0.70395, 143Nd/ 144Nd 0.51282–0.51305, 206Pb/ 204Pb 18.54–18.70, 207Pb/ 204Pb 15.53–15.61, and 208Pb/ 204Pb 38.09–38.52. The most mafic basaltic andesite from Volcán Cántaro is isotopically the most depleted rock, similar to MORB and oceanic basalts from seamounts in the adjacent oceanic basins. It has the least radiogenic Sr and Pb and the most radiogenic Nd yet measured from any locality in the MVB. The combined geochemical and isotopic evidence is compatible with the generation of both alkaline and subalkaline magmas of the Cántaro–Colima volcanic chain in the mantle wedge by fluid-transport to the mantle from the subducted plate. The isotopic data are also generally consistent with the actual physical mixing of subalkaline and alkaline basanite–minette magmas to generate intermediate alkaline magmas. The geochemical and isotopic data from the western part of the MVB, including the Cántaro–Colima volcanic chain, however, also reflect the tectonic complexity of simultaneously ongoing subduction and rifting, requiring more complex petrogenetic processes and a chemically and isotopically heterogeneous mantle.