https://www.ofioliti.it/index.php/ofioliti/issue/feed Ofioliti 2021-04-18T23:07:16+02:00 Alessandra Montanini editor@ofioliti.it Open Journal Systems <p>Since 1976, <em>Ofioliti</em> provides an international forum for original contributions and reviews in the field of the geodynamics, petrology, geochemistry, biostratigraphy, stratigraphy, tectonics and paleogeography applied to ophiolitic terrains and modern oceanic lithosphere, including their sedimentary cover. Studies of topics such as geodynamics of the mantle, the evolution of orogens including ophiolites and paleoceanography are also welcome.</p> <p>Ofioliti is a FREE ACCESS journal with low </p> <p><a href="https://www.ofioliti.it/index.php/ofioliti/about"><strong>Read more..</strong></a></p> https://www.ofioliti.it/index.php/ofioliti/article/view/630 Corundum-bearing veins in chloritite from the Etirol-Levaz Austroalpine continental slice (Valtournenche, Aosta, Italy) 2021-02-21T11:52:02+01:00 Roberto Cossio roberto.cossio@unito.it Roberto Compagnoni roberto.compagnoni@unito.it Daniele Regis daniele.regis@canada.ca <p>The high-pressure (<em>HP</em>) continental Etirol-Levaz slice (ELS) is exposed on the right side of the Valtournenche (Aosta) at the contact between the overlying blueschist-facies Combin Zone and the underlying eclogite-facies Zermatt-Saas Zone. The ELS contains a layered metagabbro showing a complex evolution, which includes a pre-Alpine high-temperature (H<em>T</em>) recrystallization of the igneous mineralogy, a polyphase Alpine high-pressure (H<em>P</em>) quartz eclogite-facies and a late greenschist-facies (GS) retrogression.</p> <p>In this paper, an unusual corundum-bearing ultramafic rock associated with the metagabbro is described. The studied sample is a Mg-chloritite with relict green spinel partly replaced by corundum, Mg-beltrandoite-2<em>N</em>3<em>S</em> (a new mineral of the högbomite supergroup), Mg-chlorite and dolomite. The rock is cut by mm- to cm-thick veins composed of coarse-grained corundum + Mg-chlorite + dolomite. <em>P-T</em> phase-diagram projections indicate that the corundum-bearing assemblages formed in the presence of a water-rich fluid (X<sub>(CO2)</sub> ≤ 0.04), during a retrograde decompressional evolution in continuity with the prograde to H<em>P</em>-peak path estimated from the associated eclogites. The new estimated prograde-to-retrograde <em>P-T</em> path suggests that the ELS and the underlying Zermatt-Saas Zone shared a common Alpine metamorphic evolution.</p> <p>A detailed study of the relict minerals preserved in the chloritite allowed to infer its pre-Alpine protolith, a green spinel websterite, and evolution, characterized by a high-<em>T</em> recrystallization of the original igneous minerals. During the Alpine orogeny, the spinel websterite experienced a metasomatic process that converted the original igneous rock into a chloritite.</p> 2021-04-18T00:00:00+02:00 Copyright (c) 2021 Roberto Cossio, Roberto Compagnoni, Daniele Regis