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This contribution analyses the structural architecture and tectono-metamorphic evolution of Briançonnais units in the southern French-Italian Western Alps. The studied area extends from a virtually non-metamorphic area adjacent to the Helvetic-Dauphinois External Domain in the west to the Monviso-Queyras ocean-derived units in the east, where metamorphism increases up to eclogite-facies. Mapping at the scale 1:10.000 of a mountainous part of the Ubaye-Maira transect was performed, which portrays in detail the Briançonnais units over ~ 100 km2. The lithologies include meta-andesite, meta-siliciclastics, marbles, turbiditic calcschists and flysch whose age spans from Late Carboniferous to Eocene. Metamorphism is low-grade greenschist-facies in the west but reaches the blueschist-facies to the east. Structures related to four phases of deformation are identified. The first two generations of structures (D1–D2), related to the original top-to-the-west nappe stacking, are associated with conditions close to the peak of Alpine metamorphism. Previous tectonic surfaces are transposed by the dominant deformation structures (D3), developed under retrograde/decompression conditions. This D3 corresponds to a backfolding and back-thrusting event with a top-to-the-E transport. A fourth phase (D4) developed during late low-grade metamorphic conditions and deforms the previous surfaces by locally developing a crenulation cleavage, followed by brittle tectonics. An updated metamorphic map is presented, backed on published estimates and new thermometric data obtained by Raman Spectroscopy of Carbonaceous Material (RSCM). The TRSCM values range from ~ 295 °C to > 350 °C, moving from the most external Briançonnais unit to the internal Queyras "Schistes Lustrés" units. Suspected Upper Cretaceous palaeofaults have been documented, allowing us to group the classic Aiguille de Mary and Ceillac (sub-) units into a single tectonic unit, here referred to as Maurin unit. The palaeogeographical reconstruction of the evolution of the studied transect highlights the importance of the Marinet and Maurin axial units in the feeding of the Late Cretaceous-Eocene breccias deposited on the more internal Acceglio-type units. [ABSTRACT FROM AUTHOR]

Near the eastern end of the Tonale fault zone, a segment of the Periadriatic fault system in the Italian Alps, the Adamello intrusion produced a syn-kinematic contact aureole. A temperature gradient from ∼250 to ∼700 °C was determined across the Tonale fault zone using critical syn-kinematic mineral assemblages from the metasedimentary host rocks surrounding deformed quartz veins. Deformed quartz veins sampled along this temperature gradient display a transition from cataclasites to mylonites (frictional–viscous transition) at 280±30 °C. Within the mylonites, zones characterized by different dynamic recrystallization mechanisms were defined: Bulging recrystallization (BLG) was dominant between ∼280 and ∼400 °C, subgrain rotation recrystallization (SGR) in the ∼400–500 °C interval, and the transition to dominant grain boundary migration recrystallization (GBM) occurred at ∼500 °C. The microstructures associated with the three recrystallization mechanisms and the transitions between them can be correlated with experimentally derived dislocation creep regimes. Bulk texture X-ray goniometry and computer-automated analysis of preferred [c]-axis orientations of porphyroclasts and recrystallized grains are used to quantify textural differences that correspond to the observed microstructural changes. Within the BLG- and SGR zones, porphyroclasts show predominantly single [c]-axis maxima. At the transition from the SGR- to the GBM zone, the texture of recrystallized grains indicates a change from [c]-axis girdles, diagnostic of multiple slip systems, to a single maximum in Y. Within the GBM zone, above 630±30 °C, the textures also include submaxima, which are indicative of combined basal 〈a〉- and prism [c] slip. [Copyright &y& Elsevier]