Open AccessEclogitic metamorphism in the Alpine far-west: petrological constraints on the Banchetta-Rognosa tectonic unit (Val Troncea, Western Alps)
Author(s) -
Alberto Corno,
Chiara Groppo,
Pietro Mosca,
Alessandro Borghi,
Marco Gattiglio
Publication year - 2021
Publication title -
swiss journal of geosciences
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.665
H-Index - 34
eISSN - 1661-8734
pISSN - 1661-8726
DOI - 10.1186/s00015-021-00393-7
Subject(s) - geology , eclogite , metamorphism , metamorphic rock , metamorphic facies , basement , continental collision , tectonics , sedimentary rock , thermochronology , tectonic phase , facies , lithology , paleontology , petrology , geochemistry , subduction , structural basin , civil engineering , engineering
The Banchetta-Rognosa tectonic unit (BRU), covering an area of 10 km 2 in the upper Chisone valley, consists of two successions referred to a continental margin (Monte Banchetta succession) and a proximal oceanic domain (Punta Rognosa succession) respectively. In both successions, Mesozoic meta-sedimentary covers discordantly lie on their basement. This paper presents new data on the lithostratigraphy and the metamorphic evolution of the continental basement of the Monte Banchetta succession. It comprises two meta-sedimentary sequences with minor meta-intrusive bodies preserving their original lithostratigraphic configuration, despite the intense Alpine deformation and metamorphic re-equilibration. Phase equilibrium modeling points to a metamorphic eclogitic peak (D1 event) of 20–23 kbar and 440–500 °C, consistent among three different samples, analyzed from suitable lithologies. The exhumation P–T path is characterized by a first decompression of at least 10 kbar, leading to the development of the main regional foliation (i.e. tectono-metamorphic event D2). The subsequent exhumation stage (D3 event) is marked by a further decompression of almost 7–8 kbar associated with a significant temperature decrease (cooling down to 350–400 °C), implying a geothermal gradient compatible with a continental collision regime. These data infer for this unit higher peak P–T conditions than previously estimated with conventional thermobarometry. The comparison of our results with the peak P–T conditions registered by other neighboring tectonic units allows to interpret the BRU as one of the westernmost eclogite-facies unit in the Alps.