Ofioliti https://www.ofioliti.it/index.php/ofioliti <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> en-US editor@ofioliti.it (Alessandra Montanini) journals@edizioniets.com (Giovanni Campolo) Wed, 02 Jun 2021 14:16:49 +0200 OJS http://blogs.law.harvard.edu/tech/rss 60 Corundum-bearing veins in chloritite from the Etirol-Levaz Austroalpine continental slice (Valtournenche, Aosta, Italy) https://www.ofioliti.it/index.php/ofioliti/article/view/630 <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. 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. 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> Roberto Compagnoni, Roberto Cossio, Daniele Regis Copyright (c) 2021 Roberto Cossio, Roberto Compagnoni, Daniele Regis https://www.ofioliti.it/index.php/ofioliti/article/view/630 Wed, 02 Jun 2021 00:00:00 +0200 U-Pb dating and geochemical constraints to Early Cretaceous hydrothermal dolomitization in the Provençal Domain (Maritime Alps, NW Italy–SE France) https://www.ofioliti.it/index.php/ofioliti/article/view/631 <p>In the Maritime Alps (NW Italy - SE France), the Middle Triassic-Berriasian platform carbonates of the Provençal Domain are locally affected by an intense hydrothermal dolomitization. This dolomitization resulted from a large-scale hydrothermal circulation related to deep-rooted faults, and is indirect evidence of a significant earliest Cretaceous fault activity in this part of the Alpine Tethys European palaeomargin. New carbonate U-Pb dating and geochemical (stable isotope and noble gases on inclusion-hosted water, <sup>87</sup>Sr/<sup>86</sup>Sr, clumped isotopes) data allowed a better understanding of the timing and mechanisms of the hydrothermal circulation. Hydrothermal fluids probably originated from seawater, which was involved in a deep circulation within the underlying crystalline basement, undergoing heating to more than 200°C and substantial compositional modification by prolonged interaction with basement rocks. Thin cement rims rich in carbonaceous material, locally alternated with hydrothermal dolomite cements, are interpreted as remnants of ephemeral microbial communities that could colonize the upper part of hydrothermal conduits, during periods of reduced hot fluid flow and contemporaneous downward seawater infiltration.</p> Luca Barale, Carlo Bertok, Anna d'Atri, Fabrizio Piana, Stefano Bernasconi, György Czuppon, László Palcsu, Axel Gerdes, Daniel Birgel, Luca Martire Copyright (c) 2021 Luca Barale, Carlo Bertok, Anna d'Atri, Fabrizio Piana, Stefano Bernasconi, György Czuppon, László Palcsu, Axel Gerdes, Daniel Birgel, Luca Martire https://www.ofioliti.it/index.php/ofioliti/article/view/631 Wed, 02 Jun 2021 00:00:00 +0200