Eclogitic metamorphism in the Alpine far-west: petrological constraints on the Banchetta-Rognosa tectonic unit (Val Troncea, Western Alps)

Abstract The Banchetta-Rognosa tectonic unit (BRU), covering an area of 10 km 2 in the upper Chisone valley, consists two successions referred to a continental margin (Monte Banchetta succession) and proximal oceanic domain (Punta Rognosa respectively. In both successions, Mesozoic meta-sedimentary covers discordantly lie on their basement. This paper presents new data lithostratigraphy metamorphic evolution basement Monte succession. It comprises sequences with minor meta-intrusive bodies preserving original lithostratigraphic configuration, despite intense Alpine deformation re-equilibration. Phase equilibrium modeling points eclogitic peak (D1 event) 20–23 kbar 440–500 °C, consistent among three different samples, analyzed from suitable lithologies. exhumation P–T path is characterized by first decompression at least kbar, leading development main regional foliation (i.e. tectono-metamorphic event D2). subsequent stage (D3 marked further almost 7–8 associated significant temperature decrease (cooling down 350–400 °C), implying geothermal gradient compatible collision regime. These infer for this higher conditions than previously estimated conventional thermobarometry. comparison our results registered other neighboring units allows interpret BRU as one westernmost eclogite-facies Alps.