Noble gases and deformation history of Finero phlogopite peridotite massif, northern Italy

Abstract

The Finero phlogopite peridotite in Northern Italy is an alpine-type peridotite and it had been metazomatized by slab dehydration in the mantle wedge from Palezoic to Mesozoic time. We focused on the effect of water in mantle region on the deformation characteristics. In order to reveal the water-rock interaction and the deformation history, we performed microstructural observation mainly using electron microscopies and noble gases analysis of the fluid/melt inclusions in mineral grains that provide information of the origin of them.In field research, we found the stress concentration zone in the phlogopite peridotite unit. With an optical microscope, it was found that the rock of the stress concentration zone may have been deformed with forming microcracks under hydrous condition and subsequently being trapped the fluid/melt inclusions. No such characteristic was observed in the samples away from the stress concentration zone.The results of the olivine slip systems suggest that fluid may have penetrated the rock of the stress concentration zone during brittle-ductile deformation. On the other hand, noble gases analysis of the fluid/melt inclusions in all samples (He, Ar and Ne isotopic and elemental ratios) show three component mixture of atmosphere, crust and mantle. To identify whether the fluid/melt with such noble gases components are related to the deformation structure, we need to additional measurements of each separate minerals.