Geoquímica elemental e isotópica (Sr, Nd) del vulcanismo Cámbrico en la Zona de Ossa-Morena (SO Macizo Ibérico)

Resumen

The results of an elemental and isotope (Sr, Nd) geochemical study on volcanic to subvolcanic rocks intercalated or intrusive into Cambrian sediments of the Ossa-Morena Zone are reported. The analysed rocks define a mildly sodic alkaline series of Coombs type integrated mainly by transitional basalts, hawaiites, mugearites, benmoreites, trachytes and rhyolites. The basic rocks are moderately enriched in incompatible elements and show geochemical affinities with ocean island basalts (OIB), whereas in the tectonomagmatic discrimination diagrams the whole series have typical intraplate features. eNd510 values for the basic rocks: +0.9 to +5.9 are comprised between those of mantle reservoirs OIB-HIMU and the BSE (Bulk Silicate Earth). The basaltic rocks could have formed by partial melting of sublithospheric mantle through adiabatic decompression during the rising of mantle plume, with melt segregation at the spinel-garnet transition zone (ca. 75-90 km deep). The intermediate and acid rocks have similar eNd510 values to those of the basic rocks and might be produced from the basic melts by fractional crystallization. The intracontinental rift process could be related to the impact of a deep mantle plume in the preexisting lithosphere.