Compositional signatures of SSZ-type peridotites from the northern Vourinos ultra-depleted upper mantle suite,NW Greece |
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| Institution: | 1. Department of Geology, University of Patras, Panepistimiopolis of Rion, Patras 265 04, Greece;2. School of Earth Sciences and Geological Engineering, Sun Yat-sen University, Guangzhou 510275, PR China;1. Department of Mineralogy, Petrology and Economic Geology, School of Geology, Aristotle University of Thessaloniki, 54124 Thessaloniki, Greece;2. Laboratory of Nuclear Physics, Aristotle University of Thessaloniki, 54124 Thessaloniki, Greece;1. Geochemistry Department of Chengdu University of Technology, Sichuan Province 610059, China;2. Key Laboratory of Nuclear Techniques in Geosciences, Sichuan Province 610059, China;1. Laboratoire d’Hydrologie et de Géochimie de Strasbourg, UMR 7517, 1 rue Blessig, 67084 Strasbourg Cedex, France;2. 4, rue de Marlenheim, 67000 Strasbourg, France;3. SQU, College of Science, Oman;4. Università degli Studi di Messina, Dipartimento di Fisica e di Scienze della Terra Viale F, Stagno d’Alcontres 31, 98100 Messina, Italy |
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| Abstract: | The northern Vourinos massif, located in the Dinarides-Hellenides mountain belt in the Balkan Peninsula, forms a section of the so-called Neotethyan ophiolitic belt in the Alpine-Himalayan orogenic system. It is comprised mainly of a well-preserved mantle sequence, dominated by voluminous massive harzburgite with variable clinopyroxene and olivine modal abundances, accompanied by subordinate coarse- and fine-grained dunite. The harzburgite rock varieties are characterized by high Cr# Cr/(Cr + Al)] values in Cr-spinel (0.47–0.74), elevated Mg# Mg/(Mg + Fe2+)] in olivine (0.90–0.93), low Al2O3 content in clinopyroxene (≤1.82 wt.%) and low average bulk-rock concentrations of CaO (0.52 wt.%) and Al2O3 (0.40 wt.%), which are indicative of their refractory nature. In addition, dunite-type rocks display even more depleted compositions, containing Cr-spinel and olivine with higher Cr# (0.76–0.84) and Mg# (0.91–0.94), respectively. They also display extremely low average abundances of CaO (0.13 wt.%) and Al2O3 (0.15 wt.%). The vast majority of the studied peridotites are also strongly depleted in REE. Simple batch and fractional melting models are not sufficient to explain their ultra-depleted composition. Whole-rock trace element abundances of the northern Vourinos mantle rocks can be modeled by up to 22–31% closed-system non-modal dynamic melting of an assumed primitive mantle (PM) source having spinel lherzolite composition. The highly depleted compositional signatures of the investigated peridotites indicate that they have experienced hydrous melting in the fore-arc mantle region above a SSZ. This intense melting event was responsible for the release of arc-related melts from the mantle. These melts reacted with the studied peridotites causing incongruent melting of pyroxenes followed by considerable olivine and Cr-spinel addition in terms of cryptic metasomatism. This later metasomatic episode has obscured any geochemical fingerprints indicative of an early mantle melting event in a MOR setting. The lack of any MOR-type peridotites in the northern Vourinos depleted mantle suite is quite uncommon for SSZ-type Neotethyan ophiolites. |
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| Keywords: | Partial melting Depletion Metasomatism Peridotites Ophiolites |
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