Geochemical modeling of acid–basic magma interaction in theSardinia–Corsica Batholith: the case study of Sarrabus,southeastern Sardinia, Italy

The Hercynian intrusive rocks outcropping in the Sarrabus area, southeastern Sardinia, Italy, consist of microgranular mafic enclave (MME)-bearing granites (>95%) associated with coeval stratified gabbroic complexes and basic septa (BS) (<5%). The coexistence of partially molten magmas of contrasting composition offers the opportunity to study interaction processes in intrusive environments and the geochemical characteristics of hybrid products. In this paper we present a petrogenetic model for the differentiation of basic magmas injected into coeval, partially molten, granite magmas, on the basis of field, petrographic and geochemical data. Samples from the stratified basic complex of Capo Carbonara (CCB) and BS were grouped into outer and inner facies based upon the sampling sites close to, or far away (a few meters) the host granite contact. MME were grouped according to their composition: gabbro-diorites and tonalites. The inner facies of the basic complex and BS represent cumulus of amphibole+clinopyroxene+plagioclase with trapped intercumulus liquid. The calculated chemical composition of the parental magma is well within those calculated for the Hercynian basic magmas of the Sardinia–Corsica Batholith. The geochemical features of the MME and the outer facies of the basic complex and BS establish an origin by mixing/mingling mechanisms controlled by fractional crystallisation and contamination (CFC) of the parental magma of the inner gabbroic facies. Additional refinements of the model, addressed in this paper, establish the occurrence of a filter pressing process operating during the CFC evolution of the basic magma injected into the acid magma.