Journal of the Virtual Explorer

The Monviso ophiolitic massif in the Western Alps is one of the best exposed serpenite subduction channels. As has been suggested for over 30 years, metamorphosed mafic igneous rocks in the Monviso ophiolite were originally oceanic basalts formed at a slow spreading ridge on the western Tethys ocean floor. The origin of the serpentinites remains partly unclear, but the majority of serpentinites are likely derived from oceanic lherzolites. Some refractory harzburgites at the basal unit may have derived from the mantle wedge overlying the subduction plate, as observed in the Himalaya and presently observed along Pacific subduction zones. The serpentinites are completely recrystallized under HP conditions as only the high grade antigorite specimen of serpentine is observed. The low viscosity of serpentinites favours the formation of a low viscosity subduction channel (10¹⁹-10²⁰ Pa.s) where cm to kilometric blocs of eclogitized oceanic crust are incorporated at different depths and exhumed together to blueschist facies conditions along a 40-50 km long subduction channel with a width of 4 to 10 km. The time difference between the different units of 5 to 15 Ma may reflect the minimum life span of serpentinite subduction channel. Finally we propose that this serpentinite subduction channel ended when continental subduction started at about 45-40 Ma.