Caracterización geoquímica de las intrusiones sinvolcánicas intercaladas en el Albiense de la cuenca Vasco-Cantábrica

Resumen

The main results of a whole rock chemical study on subvolcanic rocks outcropping as dykes and sills, intruded/interlayered in Albian sediments of the Basque-Cantabrian basin are presented. The rocks studied may be classified as basanites, nephelinites and alkali basalts and are regarded as genetically and temporally related to coetaneous volcanic products. They are ultrabasic to basic in composition and strongly subsaturated in silica, with normative NeCIPW or Hy-OlCIPW. On the normalized multielemental diagrams, the rocks analysed show an enrichment in elements regarded as mobile with respect to the less mobile elements, and Nb/La ratios >> 1. The normalized REE spectra are very homogeneous with marked enrichment in LREE and continuous fractionation from light to heavy rare earths. The overall chemical features thus attest to an alkaline affinity. The plotting on tectonomagmatic diagrams are consistent with these chemical features placing the rocks studied in the fields for alkali basalts from intracontinental rift settings. It is suggested that the precursor magmas were possibly formed during the ascent of a deep mantle sublitospheric plume in Early Cretaceous times