Heterogeneous refertilization of the upper mantle beneath the Azorean volcanoes. Evidence from mantle xenoliths

Several mantle xenoliths from the island of Sao Miguel (Azores, Portugal) have been studied to investigate the nature of the mantle beneath the Azorean archipelago. Ultramafic xenoliths are porphyroclastic spinel harzburgite and subordinate clinopyroxene-poor lherzolite, range between 3 and 10 cm in size and show clear signs of plastic deformation. In harzburgites, olivine porphyroclasts have Fo89-91, while in neoblasts it ranges between 80 and 87. Mg# in orthopyroxene and clinopyroxene spans between 85-91 and 84-92 respectively, while spinel is characterized by Cr# between 64 and 78. Two harzburgites show phlogopite. In lherzolite, olivine porphyroclasts show Fo89-91, orthopyroxenes and clinopyroxenes have Mg# 91-92 and 90-92 respectively, and spinel has Cr# 76-84. Abundant silica- and alkali-rich glass is present as intergranular micro-veins, and as primary melt inclusions in both porphyroclasts and neoblasts. Orthopyroxene porphyroclasts (1 - 6 mm) have exsolution-free rims, stro...