Geochemistry and petrology of lavas from San Jose volcano, Southern Andes (33.DEG.45'S).
1985; The Geochemical Society of Japan; Volume: 19; Issue: 4 Linguagem: Inglês
10.2343/geochemj.19.209
ISSN1880-5973
AutoresLeopoldo López‐Escobar, Hugo Moreno, Michio Tagiri, Kenji Notsu, Naoki Onuma,
Tópico(s)earthquake and tectonic studies
ResumoSan José volcano, one of the northernmost volcanoes of the Southern Andes, is composed of calc-alkaline rocks with SiO2 in the 56–63 wt% range. These rocks have some major-element, trace-element and Sr isotope compositions (0.70513–0.70551) that are intermediate between those of the Central and 37°–46°S Southern Andes andesites. The REE patterns of these rocks exhibit relatively high La/Yb normalized ratios (∼10) with La about 80 times as much as in chondrites and Yb ranging from 6 to 9 times as much as in chondrites. The trace element abundances and SB systematics are consistent with a derivation of the most basic San José andesite from primary magmas, generated by relatively low degrees of partial melting of a garnet-peridotite source, through a crystal fractionation process dominated by olivine, clinopyroxene and plagioclase. The trace element composition of this sample is also consistent with the derivation from a source modified by subduction-related fluids. The relatively high Sr isotopic ratios of the samples suggest that mantle derived magmas are contaminated during their passage through the continental crust.
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