Metamorphic peak estimates of the Marguareis Unit (Briançonnais Domain): New constrains for the tectonic evolution of the south-western Alps

Abstract

In the Western Alps, while many P–T constraints are available for the high-grade units, the dataset for the low-grade units located along the westernmost edge of the belt remains scarcer and incomplete. To face these uncertainties, we quantify for the first time the metamorphic peak conditions of the Marguareis Unit, a fragment of European margin (Briançonnais Domain) regarded till now as very-low-grade unit, exposed along the boundary between Maritime and Ligurian Alps (South-Western Alps), whose deformation history is well constrained. The Marguareis Unit is regarded as a thinned portion of the European continental margin involved in the Alpine collision. Metamorphic peak conditions reconstructed using the chlorite–phengite multi-equilibrium approach on the Eocene siliciclastic deposits indicate that the Marguareis Unit recorded high-pressure and low-temperature conditions during its subduction, accretion and subsequent exhumation into the Alpine wedge.