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

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.

Fossils are rare in metamorphic rocks due to recrystallization and deformation, especially under high-pressure metamorphic conditions. Here, we report the discovery of exceptionally preserved Paleozoic palynofloras in ten graphite-rich samples collected from the Dora-Maira Massif (Western Alps), which underwent blueschist-facies to ultra-high-pressure (UHP) metamorphism (~ 28 kbar, 520 °C). These findings challenge the assumption that fossils cannot survive such conditions, offering a new biostratigraphic tool for reconstructing the geological and tectonic history of metamorphic basement in collisional orogens worldwide.

Despite the fact that rock textures depend on the 3D spatial distribution of minerals, our tectono-metamorphic reconstructions are mostly based on a 2D visualisation (i.e. thin sections). This work compares 2D and 3D investigations of petrography and microstructures, modal abundances, and local bulk rock composition and their implication for P–T estimates, showing the pros and cons and reliability of 2D analysis. For this purpose, a chloritoid–garnet-bearing mica schist from the Dora-Maira Massif in the Western Alps has been chosen. In particular, for 2D a thin section scan has been combined with chemical X-ray maps, whereas for 3D the X-ray computerised axial microtomography (µCT) has been applied. Two-dimensional investigations are readily accessible and straightforward but do not consider the entire rock volume features. Conversely, the rise of 3D techniques offers a more comprehensive and realistic representation of metamorphic features in the 3D space. However, they are computationally intensive, requiring specialised tools and expertise. The choice between these approaches should be based on the research aims, available resources, and the level of detail needed to address specific scientific questions. Nevertheless, despite differences in the modal distribution, the estimated bulk rock compositions and relative thermodynamic modelled phase fields show similarities when comparing the 2D and 3D results. Also, since different thin section cut orientations may influence the results and consequent interpretations, three different cuts from the 3D model have been extrapolated and discussed (i.e. XZ, YZ, and XY planes of the finite-strain ellipsoid). This study quantitatively corroborates the reliability of the thin section approach for tectono-metamorphic reconstructions, still emphasising that 3D visualisation can help understand rock textures.

The Dora-Maira Massif offers a unique window into the pre-Alpine and Alpine tectonic history of continental crust involved in the collision that formed the Western Alps. Whereas high-pressure Alpine metamorphism has strongly affected the rocks, zircon crystals still retain age domains from earlier magmatic events, offering a reliable tool for reconstructing the evolution of the continental basement. Combining new U–Pb LA-ICP-MS zircon geochronology with whole-rock geochemistry, this study unveils a more complex magmatic and tectonic evolution than previously recognized. New findings reveal that the Dora-Maira basement preserves three distinct magmatic cycles: Ediacaran–Early Cambrian ( c . 550–530 Ma), Ordovician–Silurian ( c . 460–440 Ma) and Permian ( c . 280–260 Ma). These results challenge the overestimated presence of Permian intrusions in the Massif, instead highlighting a significant Lower Paleozoic magmatic component that was previously overlooked. We document the oldest magmatic suite recognized to date in the area (540.0 ± 5.4 and 548.0 ± 5.5 Ma), which sheds light on the Cambrian-to-Precambrian tectonic history of the northern margin of Gondwana. This contribution refines the geodynamic framework of the Dora-Maira Massif. It demonstrates that its polycyclic basement was assembled through successive crust-forming events during the Ediacaran–Early Paleozoic and subsequently reworked during the Variscan and Alpine orogenies. This underlines the key role of Lower Paleozoic tectono-magmatic processes in shaping the continental crust of the Western Alps.