To be or not to be Alpine: New petrological constraints on the metamorphism of the Chenaillet Ophiolite (Western Alps)

The Chenaillet Ophiolite represents a very well-preserved portion of Ligurian-Piedmont ocean in the Western Alps. It is formed from an oceanic lithospheric succession comprising exhumed mantle, various mafic intrusives (i.e., gabbro sensu lato), and world-renowned sequence pillow basalts. Apart scarce breccias closely related to lithosphere, no sedimentary cover exposed. Historically, has been known for its low temperature–low pressure Alpine metamorphism, ascribed obduction processes. However, studies aimed at constraining peak pressure–temperature (P–T) conditions metamorphism are virtually lacking, general focus having so far on high temperature geochemical features. In this paper, we investigate two kinds rocks: albitite/alkali syenite, whose petrographic features shed light complex metamorphic history Ophiolite. Detailed analyses mineral assemblages, blastesis/deformation relationships, chemical data allow events be distinguished: earlier, event (already reported literature) second, later temperature, event, recognized here first time. strikingly testified by occurrence lawsonite relicts interstitial omphacite albitite. Thermodynamic modelling via isochemical phase diagrams) performed sample suggests unit minimum 9 kbar 300°C maximum 15 450°C. Overlapping these P–T with those inferred albitite based observed assemblage allows constrained 10–11 340–360°C. These suggest thickness overlying nappe stack about 35–40 km, which incompatible or burial processes, instead consistent subduction processes orogeny. We argue that, opposite common belief that escaped our new strongly support idea it experienced temperature-blueschist-facies evidence can still tracked (few) rocks better recorded preserved it. This finding generates challenging questions regarding both exhumation orogens such as