Petrogenesis of the Solanas gabbro-granodiorite intrusion, Sàrrabus (southeastern Sardinia, Italy): implications for Late Variscan magmatism

Abstract

The igneous complex of Solanas is a small, composite calc-alkaline intrusion emplaced at ~ 300 Ma in the Sarrabus region (southeastern Sardinia), and consists of olivine gabbronorites, amphibole gabbros, microgabbros, quartz diorites, tonalites, amphibole granodiorites, and biotite granodiorites. Thermobarometry calculations indicate that the Solanas rocks were emplaced at mid-to-upper crustal levels (0.6–4.0 kbar). The intermediate and silicic rocks are metaluminous to weakly peraluminous and are enriched in large ion lithophile elements. The range in the initial Sr and Nd isotopic compositions is small throughout the intrusion despite a large range in silica contents (46.3–73.6 wt% SiO2). The isotopic signatures, mineralogy, and geochemistry suggest that the quartz diorites, tonalites, and granodiorites derived from fractional crystallisation and crustal contamination processes starting from different mafic parental magmas. The origin of tonalites and granodiorites is compatible with removal of plagioclase, hornblende, biotite, apatite and zircon starting from a quartz dioritic magma. The mafic rocks range in composition from primitive to relatively evolved (Mg# 49–70). The olivine gabbronorites and amphibole gabbros have petrographic and geochemical features of arc cumulates derived from different basaltic magmas. The microgabbros have geochemical characteristics similar to high-alumina basalts with fractionated rare-earth element patterns (LaN/YbN = 4.3–6.0), enrichment in large ion lithophile elements (e.g., Rb, Ba, U, and K) and depletion in Nb and Ta compared with the primitive mantle. These characteristics are consistent with partial melting of a mantle source that was enriched by subduction-related fluids.