HP tectono‐metamorphic evolution of the Internal Piedmont Zone in Susa Valley (Western Alps): New petrologic insight from garnet+chloritoid‐bearing micaschists and Fe–Ti metagabbro

A new study reveals that the subduction of the Tethys oceanic lithosphere in the Western Alps occurred under similar high-pressure (HP) and ultra-high-pressure (UHP) conditions, as evidenced by garnet+chloritoid-bearing micaschists and Fe–Ti metagabbro from Susa Valley. The research identifies four distinct metamorphic stages, including an Alpine peak-P stage reaching HP-UHP eclogite facies boundary (25–29 kbar, 460–510°C), followed by decompression under eclogite facies conditions and later greenschist facies re-equilibration. The inferred P–T path aligns with other Western Alpine meta-ophiolites, suggesting a consistent subduction regime along the Tethys lithosphere's length. Comparison with adjacent Dora Maira continental crustal units indicates early exhumation likely occurred within the subduction channel without continental crust buoyancy contribution.

Ghignone, S., Borghi, A., Balestro, G., Castelli, D., Gattiglio, M., & Groppo, C. (2020). HP tectono‐metamorphic evolution of the Internal Piedmont Zone in Susa Valley (Western Alps): New petrologic insight from garnet+chloritoid‐bearing micaschists and Fe–Ti metagabbro. Journal of Metamorphic Geology, 39(4), 391–416. Portico. https://doi.org/10.1111/jmg.12574