Petrology of some amphibole-bearing volcanics of the pre-Ellittico period (102-80 ka)

Abstract

We present here petrological and geochemical data on volcanics cropping out in southern and north-eastern walls of the Valle del Bove (Mt. Etna), belonging to the the Rocche, Serra Giannicola Grande and Canalone della Montagnola Units. These units constitute the remnants of several volcanoes which were active in the time span 102 - 80 ka, i.e. before the growth of the Ellittico-Mongibello strato-volcano. Their products (Na-alkaline in serial affinity), range in composition from hawaiites to benmoreites. Amphibole (kaersutite) is present as phenocryst in all the studied rocks, and commonly show breakdown coronas of rhönite +/- clinopyroxene, formed during magma ascent. Nevertheless, in mafic rocks, amphibole occurs as an early liquidus-phase enclosed in a Ca-rich plagioclase (up to An87). We propose that early cotectic crystallization of amphibole and Ca-plagioclase may reflect H2O-rich melts. Variations in major and trace elements among lavas erupted from coeval centers, suggest that fractional crystallization was the principal evolutionary process but at the same time magmas feeding the various volcanoes belonging to the Rocche Unit were more heterogenous with respect to the younger Units studied here.