Clinopyroxenes From Vulcano (aeolian Islands, Italy) - Crystal-chemistry and Cooling History

Twenty-three clinopyroxene phenocrysts from different rock types with different emplacement mechanisms and cooling histories from Vulcano island (Aeolian Archipelago) were studied by microanalysis and single-crystal X-ray diffraction methods. Their structures were refined by the least-squares method to an average R value of 0.022. From the two techniques, reliable site-occupancy data, as well as accurate lattice and structural parameters, are obtained. The results show that, in spite of the quite large compositional variety of the host rocks, clinopyroxenes from Vulcano have a narrow compositional range. Not-withstanding this, they yield crystal-chemical patterns characterising the different volcanic units and reflecting the evolutionary trends. On the basis of cation partitioning on M1 and M2 sites, the pyroxene quenching temperature has been estimated and related to the cooling history of the rocks.