Rare-earth and other element distribution in some ophiolitic metabasalts of Corsica, Western Mediterranean

Abstract

The NE part of Corsica, which is intersected by the Alpine orogeny, is mostly formed of tectonic units containing abundant ophiolitic slices of Jurassic age. In the Balagne region an interesting ophiolite sequence occurs showing petrographic and geological characteristics similar to those of the outcrops widespread in the Northern Apennines. The most abundant rocks occurring in the Balagne region are basaltic pillow lavas which underwent both oceanic alteration and regional low-grade metamorphism (to the prehnite-pumpellyite facies) during the Alpine orogenesis. Despite this metamorphism, clinopyroxenes survived virtually unaltered. Their composition is characterised by high Ca ( Fe+Mg) ratios, and the TiO 2 and Na 2O contents differ from those of most ocean-floor basalts. The Balagne metabasalts constitute a differentiation series characterised by the increase of REE, Zr, Y, P, Fe, V and Zn during magmatic evolution. The REE patterns show Ce N Sm N ∼ 1 and Ce N Yb N > 1 , they thus differ from many of the Eastern Mediterranean ophiolites and from many other ophiolitic and ocean-floor basaltic rocks. The geochemistry of the Balagne metabasalts excludes formation in environments similar to the present-day “normal ridge” segments. They have probably been formed by partial melting of a more clinopyroxene-rich source and/or of a more light-REE enriched source.