Seismic properties of lower crustal xenoliths from El Hoyazo (SE Spain): Experimental evidence up to partial melting |
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| Institution: | 1. UMR CNRS 6118, Géosciences Rennes, OSUR, Université, Rennes 1, 35042 Rennes Cedex, France;2. Planetary and Space Sciences, The Open University, Walton Hall, Milton Keynes MK7 6AA, UK;3. GeoRessources UMR 7359, CREGU, Campus Sciences-Aiguillettes, BP 70239, 54506 Vandoeuvre-lès-Nancy, France;1. Université de Lyon, Université Jean Monnet, UMR CNRS IRD 6524, Laboratoire Magmas et Volcans, 42023 Saint Etienne, France;2. Microstructures and Processing Department, Ecole nationale supérieure des mines de Saint-Etienne, 158 cours Fauriel, 42023 Saint-Etienne, France;3. Department of Earth Sciences, Durham University, Science Labs, Durham DH1 3LE, England, United Kingdom;1. Géosciences Rennes, UMR CNRS 6118, Université de Rennes 1, Campus de Beaulieu, 35042 Rennes Cedex, France;2. Queen''s University, Kingston, Ontario, Canada;3. UMR GEORESOURCES 7539 CNRS-UL, BP 239, 54506 Vandoeuvre-lès-Nancy, France;4. Université de Lorraine, ENSG, INP, Rue Doyen Marcel Roubault, Vandoeuvre-les-Nancy, France;5. CRPG UMR 7358 CNRS-UL, 15 Rue Notre Dame des Pauvres, Vandoeuvre les Nancy, France;1. V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia;2. Far Eastern Geological Institute, Far Eastern Branch of the Russian Academy of Sciences, pr. 100-letiya Vladivostoka 159, Vladivostok, 690022, Russia;3. Institute of Precambrian Geology and Geochronology, Russian Academy of Sciences, nab. Makarova 2, St. Petersburg, 199034, Russia;4. Geological Institute of the Kola Research Center, ul. Fersmana 14, Apatity, Murmansk Region, 184209, Russia;5. Zavaritsky Institute of Geology and Geochemistry, Ural Branch of the Russian Academy of Sciences, Pochtovyi per. 7, Yekaterinburg, 620151, Russia;1. Departamento de Geología, Facultad de Ciencias, Universidad de Salamanca, Spain;2. Departamento de Matemáticas, Facultad de Ciencias y Tecnologías Químicas, Universidad de Castilla-La Mancha, Ciudad Real, Spain;3. Department of Geology, Naturalis Biodiversity Center, Leiden, The Netherlands;4. Group of Volcanology, SIMGEO (UB-CSIC), Institute of Earth Sciences Jaume Almera, ICTJA-CSIC, Lluis Sole i Sabaris s/n, 08028 Barcelona Spain |
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| Abstract: | Seismic techniques provide unique tools to investigate the structure and, in combination with petrological, geochemical and petrophysical study, the composition of the lower crust. Controversies can be solved with comparative study of metamorphic terrains or xenoliths that occur adjacent to areas where seismic refraction/reflection data are available. Xenoliths represent a direct sampling of the inaccessible lower crust at the time of the volcanism, whilst exposed crustal sections can only be used as analogue of present day lower crust.The present study is focused on the measurements of compressional wave velocities up to conditions exceeding the beginning of melting (950 °C at 500 MPa confining pressure) on three garnet–biotite–sillimanite metapelitic xenoliths recovered from the Neogene dacites of El Hoyazo (SE Spain). They preserve widespread interstitial rhyolitic glass as evidence of primary melt extraction and represent the best example of partially molten lower crust in the Alborán Domain. The influence of glass on Vp is primarily reflected by anomalous positive dVp/dT while heating with velocity increasing at 500 MPa from 4.98 to 5.50 km s? 1 at room temperature to 5.85–6.79 km s? 1 at 650–700 °C. This corresponds to the glass transition where all the grain boundaries and most of the pores within the glass are closed. After this point, the velocity decreases to 6.2–6.5 km s? 1 at 950 °C where re-melting of the glass is achieved and additional partial melt produced. On cooling, the behavior is normal with negative dVp/dT. After the thermal treatment velocities are 30% higher (6.07–7.21 km s? 1) and reveal that in the presence of intergranular melt velocity measurements at room temperature cannot be extrapolated to high temperatures.P-waves measured at melting conditions are in agreement with deep seismic refraction data and tomography in the area and corroborate the hypothesis that partial melts are actually present in Alborán lower crust. |
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