Phonolitic origin of Roque-Nublo ignimbrites of Gran-Canaria (Canary-Islands, Spain) from clinopyroxene melt inclusion studies

Abstract

The Roque Nublo non-welded ignimbrites - which are Pliocene in age (5-3.5 Ma.) - are characteristic deposits of the second magmatic cycle on Gran Canaria. They are very heterogeneous, with 30-50 % volume lithic fragments, 15-20 % mildly vesiculated pumice, 5-10 % phenocrysts and 30-40 % ash matrix. The juvenile materials (pumice fragments and ash matrix) are largely altered to zeolites. A melt inclusion study using microthermometric and electron-microprobe analyses was carried out on clinopyroxenes from Roque Nublo ignimbrites. The chemical composition of melt inclusions indicates that the original melt prior to the eruptions that formed the ignimbritic Roque Nublo deposits was phonolitic in composition.