Melts and residua geochemistry in a low-to-mid crustal section (Central Spain)

Abstract

Granulite terranes from Central Spain are Hercynian anatectic areas of mid-crustal levels (P-T conditions: 750–800° C and 4–6 kb). The granulite xenolith suite of the same sector comes from the lower crust as deduced from their P-T estimates (850–950° C and 8–11 kb). Chemical differences between granulites from terranes and those from xenoliths are less marked in Central Spain than in other places as this xenolith suite lack mafic lithologies. Granulitic xenoliths show U and Rb depletion, and occasionally a subtle enrichment in Ba, Fe, Mg, Ti, (V) and HREE. Contents in Zr, Th, Y, and REE in both granulite types might be explained as a consequence of the minor role of accessory phases in controlling the geochemistry of the residual rocks in the lower crust. Migmatitic leucosomes and other felsic anatectic melts show the same trend of Rb and K enrichment and Fe, Mg, Ti, Cr, Ni, V and Th, Y, Zr, Nb, REE impoverishment (compared to protoliths) than granitic plutons. Although plutonic granites show higher Ca (Na), Fe and Mg contents a genetic link with anatectic melts is suggested. Isotopic differences (Sr, O) between granitic plutons and anatectic melts might be a reflection of their derivation from a different crustal level in an isotopically stratified crust.