The Lanzo peridotite massif, Italian Western Alps: Jurassic rifting of the Ligurian Tethys

Abstract

AbstractThe Lanzo Massif in the Western Alps consists of three bodies (North, Central and South) of mantle peridotites that were exhumed from the subcontinental mantle lithosphere to the sea floor during lithosphere extension related to the formation of the Jurassic Ligurian Tethys oceanic basin. The North Lanzo protoliths were located at shallower lithospheric levels than the South Lanzo protoliths. During exhumation, early MORB-type fractional melts from the asthenosphere infiltrated and modified the South Lanzo protoliths. Later on, aggregate MORB melts passed through the South Lanzo peridotites, migrating within replacive peridotite channels, and impregnated the North Lanzo peridotites. Ongoing lithosphere extension and stretching caused break-up of the continental crust and sea-floor exposure of the Lanzo peridotites. The North Lanzo peridotites, deriving from shallower lithospheric levels, were exhumed and exposed at more external ocean–continent transition (OCT) zones of the basin, whereas the South Lanzo peridotites, deriving from deeper lithospheric levels, were exhumed and exposed at more internal oceanic (MIO) settings of the basin. Field, petrographical–structural and petrological–geochemical studies on the Lanzo mantle peridotites provide mantle constraints regarding the geodynamic evolution of the Europe–Adria extensional system during the rifting and opening of the Ligurian Tethys basin.