Abstract

The San Pedro – Linzor volcanic chain located in the Central Andean volcanic zone runs along the western border of the Altiplano-Puna magma body (APMB). The APMB corresponds to a partially molten upper crustal (<25km depth) MASH-type zone, now thought to be a crystalmush, related to the eruption of ignimbrites and dacitic domes of the Altiplano-Puna Volcanic Complex. Eruption of the San Pedro – Linzor volcanic chain started 2 Ma ago, generating the NW-SE trending volcanic edifices observed within the chain. This volcanic chain shows a decrease in 87Sr/86Sr isotope ratios in the orientation of the volcanic chain, from Toconce (>0.7075) to San Pedro (<0.7070) volcanoes. Changes in the isotopic ratios would be associated with different extends of interaction between mantle-derived magmas and the APMB. Thus, erupted lavas in the SE would have assimilated more crustal material than those that evolved in the NW-most part of the volcanic chain.