Mineralogía de las rocas intrusivas sálicas del sur de la isla de Tenerife

Resumo

At the south of Tenerife island on the Miocene Roque del Conde Old Edifice emerge various domed structures that form singular morphologies of “roques”. They are trachyandesites, trachytes and phonolites composed by phenocrysts of feldspars and clinopyroxenes , occasionally with amphiboles and feldspathoids in a groundmass of similar composition. Feldspars are essentially sodium-rich sanidine and anorthoclase. Plagioclase is restricted to trachyandesitic rocks. Clinopyroxenes have a strong variation in their composition and can be observed an enrichment in the FeO content with the most evolved rocks. Generally, clinopyroxenes are diopside and augite, whereas hedenbergites appear in trachytic rocks. In some of the roques clinopyroxenes are egirinic. Amphiboles are frequently transformed to anhydrous minerals and have a broad compositional range: magnesium-hastingsites, pargasites, ferropargasites and kaersutites. Feldspathoids are restricted to phonolites and are nephelines and sodalites. It has been determined the formation conditions of mafic minerals: temperatures around 1000ºC for amphiboles and 870ºC for clinopyroxenes with similar pressure for both (around 3kbar) , which indicate that these rocks could have been formed in low deep crust levels of the island.