Along-arc variation of Sr-isotope composition in volcanic rocks from the Southern Andes (33°S-55°S)

Abstract

Strontium isotopic compositions were determined in thirty-two volcanic rock samples collected in thirteen volcanic centers of the 41°30′ - 46°S region of the Southern Volcanic Zone (SVZ) of the Andes. This region is just north of the Chilean triple junction, where the Chile Rise subducts under the South American plate. The along-arc variation of ⁸⁷Sr/⁸⁶Sr ratios of volcanic rocks from the SVZ (33°S-46°S) is complex and shows a wave-like pattern, which does not correlate either with the age pattern of the subducted Nazca plate or with the thickness of the continental crust. Furthermore, the variation of the Sr-isotope composition in along-arc direction does not seem to correspond to those of other geochemical parameters examined up to now of SVZ rocks. We interpret this Sr-isotopic variation in terms of either locally different crust-magma interactions or heterogeneities in the mantle wedge. Effects of subduction of the Chile Rise on the ⁸⁷Sr/⁸⁶Sr ratios are not obvious.