Isótopos de oxígeno en rocas granulíticas hercínicas de la Región Central Española

Abstract

O-isotope measurements have beeen made on different types of granulitic rocks from Central Spain (two groups from granulite-migmatite terranes of mid-crustal conditions, a third group from granulitic xenoliths from lower crustal levels). O-isotope fractionations define equilibrium temperatures significatively lesser than metamorphic peak estimates. This is explained as a consequence of fluid-rock interaction during cooling of granulitic terranes, being more resetted in the case of the Guadarrama sector. Major O-isotope homogeneity combined with a lowering in the IH0 / I('0 ratios is defined by granulitic xenoliths. We propose homogenization and lowering of oxygen isotopic ratios in the lower crust to be related to the dehydration and partial melting suffered by these crustal protoliths with minor influx of external fluids. O-isotopes also corroborate the petrogenetical link between these granulitic xenoliths and the huge granitic batholith of the Spanish Central System.