Geochemistry of the Catalonian Volcanics, Spain

Abstract

On the basis of twenty-nine new bulk analyses and several microprobe determinations the geochemistry and mineral composition of catalonian volcanics have been investigated. The lavas form a sequence of trachybasalts and leucite basanites. The fractionation trends may be explained by an olivine-clinopyroxene crystallization (ankaramtic type) with some significant variations in alkalies. These variations may be due to localisation within flows of residual alkalies during the initial cooling of lava flows as well as to leachining or hydrothermal processes. The K/Rb ratio is calculated to be about 290 for lavas with more than 2.5 % KzO wlhile those with 1.5 % 'o0 have a K/Rb ratio of 490. Then mean K/Rb ratio of 350 differs considerably f r m that of 53 for the most altered basalts. There is a rather minor variation in Ni (10-200 ppm) and MgO (7.3-10 '$o) contents. Acll clinopyroxenes shaw a relatively high Alzo8 (6.0-9.0 %) concentration. The composition range for plagioclase is Anri- Anea. Olivine composition varies as a function of grain size: 16.0 % Fe0 in phenocrysts increases to 26.0 % in the groundmass olivine. Spinel corresponds to some intermediate compositions between the two end members of the ulvospinel-magnetite series.