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Paleogeographic reconstructions show that the Ligurian‐Piedmont Ocean (LPO) was a relatively narrow oceanic basin but the actual amount of oceanic lithosphere generated and the timing of magmatic accretion are still subjects of debate. New U–Pb dating of zircon from two pairs of FeTi‐oxide metagabbro and metaplagiogranite s.l. of the Susa and Lanzo Valleys Ophiolites (Western Alps) yields Late Jurassic magmatic ages (~150 Ma), 10–15 Ma younger than most of the magmatism in the LPO. The potential significance of the geochronological data presented are discussed in relation to the structural architecture of the LPO, emphasizing that the investigated ophiolites represent the youngest oceanic lithosphere accreted in the Western Alps. [ABSTRACT FROM AUTHOR]

New petrologic data from meta‐ophiolites exposed in a relatively poorly known sector of the Western Alps (i.e. Susa Valley, Internal Piedmont Zone) are reported. Garnet+chloritoid‐bearing phengitic micaschist and Fe–Ti metagabbro preserving eclogite facies assemblages have been investigated in detail to constrain the HP tectono‐metamorphic evolution of meta‐ophiolites in the study area. Microstructural investigations allowed to identify different assemblages related to different tectono‐metamorphic stages, whose pressure–temperature (P–T) conditions of the HP stages were constrained using the pseudosection modelling approach combined with multi‐equilibrium thermobarometry. Four main metamorphic stages have been recognized: (a) an Alpine peak‐P stage (M1a), which reached the HP–UHP eclogite facies boundary (P = 25–29 kbar, T = 460–510°C); (b) a slightly prograde decompression stage (M1b), still under eclogite facies conditions (P = 21–25 kbar, T = 500–530°C); (c) a greenschist facies re‐equilibration stage (M2); (d) a nearly isobaric late heating stage (M3), developed at the boundary between greenschist‐ and amphibolite facies conditions. The new P–T path inferred for the HP phases recorded by the studied meta‐ophiolites is compatible with that reported from other meta‐ophiolite units in the Western Alps, that is, the Zermatt–Saas ophiolite to the north and the Monviso ophiolite to the south, confirming that subduction of the Tethys oceanic lithosphere occurred at similar P–T regimes all along its length. The comparison with the tectonic evolution of the adjacent Dora Maira continental crustal unit suggest that the early exhumation of eclogitized oceanic crust likely occurred along the plate interface in the subduction channel, without the buoyancy contribution of continental crust. [ABSTRACT FROM AUTHOR]

The 1:10,000 scale geological map of the Susa Shear Zone (SSZ) in the inner sector of the Western Alps, aims to describe the geological setting and tectonic evolution of a first-order Alpine shear zone, which drove exhumation and juxtaposition of different oceanic and continental margin units (i.e. the blueschist-facies External Piedmont Zone in its hanging wall and the eclogite-facies Internal Piedmont Zone and Dora Maira Massif in its footwall). The SSZ corresponds to a tectonic mélange showing a block-in-matrix structure, wherein mylonitic calcschists embed blocks of different rock units. Geological mapping and structural analysis investigated overprinting relationships among shear planes and structures related to different deformation phases: they show that the SSZ evolved through two tectonic events, during which apparent reverse top-to-E shear planes were superposed by extensional top-to-W ones. [ABSTRACT FROM AUTHOR]