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> Edizioni ETS - Pisa en-US Ofioliti 0391-2612 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 2020-10-24 2020-10-24 46 1 SUBDUCTED BASALTS AND SEDIMENTS AS SOURCES FOR FELSIC DYKES IN THE MAWAT OPHIOLITE, NE IRAQ https://www.ofioliti.it/index.php/ofioliti/article/view/610 <p>The Mawat ophiolite is a fragment from the Neo-Tethyan oceanic lithosphere and is regarded as the largest and best-exposed ophiolite within the Zagros Suture Zone, northeast Iraq. Field work, petrology, and geochemical data of felsic intrusive rocks in Mawat ophiolite are investigated. The felsic dykes are classified into two types: oceanic plagiogranites in western (Mirza and Ismail, 2007), and leucogranites in central (Mohammad et al. 2014) Mawat ophiolite, here called tonalites and granites, respectively. Both types, but variously mixed, occur in the eastern felsic dykes. The tonalites are weakly peraluminous to metaluminous and are low in K<sub>2</sub>O and TiO<sub>2</sub> and high in Na<sub>2</sub>O. The granites are strongly peraluminous, moderate to high in K<sub>2</sub>O and Na<sub>2</sub>O, and very low in TiO<sub>2</sub>. The western tonalites are similar to adakites and are interpreted to have derived from melts from subducted oceanic slab interacted with the mantle. The eastern tonalites have gone through hornblende and plagioclase fractionation in a shallow-level magma chamber modifying their original compositions. The granites are interpreted to have derived from the melted psammitic sediments on top of the subducted slab. The tonalitic and granitic melts were partially mixed and fractionated in shallow level in eastern Mawat.&nbsp;</p> Heider Sabri Al Humadi Markku Väisänen Sabah Ismail A. Marja Lehtonen Bo Johanson Copyright (c) 2020 Ofioliti 2020-10-24 2020-10-24 46 1