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. To download the pdf files of our articles you can register <a href="https://www.ofioliti.it/index.php/ofioliti/user/register" target="_blank" rel="noopener">here</a>. </p> <p><em>2019 Impact Factor: 0.941</em></p> <p><em>5-year Impact Factor: 1.41</em></p> <p> </p> en-US editor@ofioliti.it (Alessandra Montanini) frankycalo@gmail.com (Francesco Calò) Sat, 26 Sep 2020 11:55:46 +0200 OJS 3.2.1.1 http://blogs.law.harvard.edu/tech/rss 60 METASOMATIC HORIZON SEALING SERPENTINITE-METASEDIMENTS PAIR IN THE ZERMATT-SAAS METAOPHIOLITE (NORTHWESTERN ALPS): RECORD OF A CHANNEL FOR FOCUSSED FLUID FLOW DURING SUBDUCTION https://www.ofioliti.it/index.php/ofioliti/article/view/583 <p>A metasomatic horizon (MH) occurs between the metaophiolite (serpentinite and metaophicarbonates) basement and metasedimentary sequence (chaotic rocks and calcschists) of the Lake Miserin Ophiolite, in the high pressure Zermatt-Saas Zone of the Northwestern Alps. Macro- and microstructural analyses combined with petrological and geochemical investigations of the MH and surrounding lithologies unravelled a polyphase blastesis-deformation history, which led to the formation of a complex fabric and minero-chemical alteration of the serpentinite basement-metasediments interface. Dehydration, decarbonation and carbonation interplayed from early Alpine subduction up to HP-LT metamorphic peak (T=550-630 °C, P=1.8-2.5 GPa), to produce a distinctive, pervasive amphibole (tremolite/actinolite) replacement both in carbonate-rich and serpentinite-rich domains pertaining to the MH protoliths, i.e. serpentinite and carbonate-bearing metabreccia of the chaotic rock unit. This characteristic amphibole metasomatism is more pronounced toward the contact with the metaophicarbonates, and the average δ<sup>18</sup>O<sub>VSMOW</sub> and δ<sup>13</sup>C<sub>VPDB</sub> values of dolomite within the MH (+14.4‰ and +0.7‰ respectively) lie between those of the metaophicarbonates and of calcschist. These results suggest that Mg- H<sub>2</sub>O-rich fluids from the dehydrating slab, CO<sub>2</sub> released by decarbonation and SiO<sub>2</sub>-rich fluids evolved in calcschists mixed together and circulated mostly along the metaophiolite basement/metasediments interface, where the MH developed and recorded a preferential channel for mixed metamorphic fluid flow. These findings highlight and confirm that the study of metasomatic rocks in convergent systems is crucial to comprehend the behaviour of different fluids circulating, mixing and interacting with lithologies along slab-parallel discontinuities, which act as major fluid conduits for deep volatile recycling.</p> Francesca Claudia Rotondo, Paola Tartarotti, Sara Guerini, Giovanna Della Porta, Nicola Campomenosi Copyright (c) 2020 Ofioliti https://www.ofioliti.it/index.php/ofioliti/article/view/583 Sat, 26 Sep 2020 00:00:00 +0200