Las rocas volcánicas neógenas de Nuévalos (provincia de Zaragoza)

Abstract

On the basis of petrological data, the ultra-alkaline character of the volcanics from Nuévalos is clearly pointed out. This character rejects any type of relationship with Permian and Mesozoic volcanic events. Furthermore, analogies with plio-quaternary volcanics from Cofrentes suggest a similar episode related to a tensional regime that can be linked to the openning of the Valencia gulf. The volcanics are massive and look a porphyritic crystalline texture. Mineralogical composition define them as olivine-nephelinite rocks. They have a large amount of xenocrysts from mantle spinel-peridotite. The high xenocryst accumulation percentage has modified the original character of the primary melt. The whole geochemical data suggest a parental magma derived by a very low degree of melting (4,3%) from a peridotitic mantle source, strongly enriched in incompatible elements, and from a depth near to 100 km.