High-alumina pyroxenite xenoliths from Quaternary basalts of NW Spitsbergen - evidence of continental crust delamination

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Abstract

The origin of spinel-garnet pyroxenite from xenoliths in Quaternary basaltoids of Spitsbergen Island (Svalbard Archipelago) is discussed. The rocks have a high concentration of Al2O3 and MgO and low Cr. The primary magmatic association Spl-Opx-Cpx and the high Al content in pyroxenes provide evidence for the formation of these rocks as cumulates of hydrous basaltic melts in the lower crust at a pressure of ~1.2 GPa. Transformation of the texture from the magmatic hypidiomorphic to the metamorphic granoblastic and growth of garnet at the expense of spinel and high-alumina pyroxenes indicate transport of rocks to a depth below the spinel/garnet phase transition boundary in the Cr2O3-free CaO-MgO-Al2O3-SiO2 system. The parameters of the Grt-Opx equilibrium range within 1060-1120 °C and 2.2-2.6 GPa. Thus, magmatic pyroxenite was transported to a great depth into the mantle, which provides evidence for delamination in the region of the lower continental crust containing ultramafic cumulates.

About the authors

M. Yu. Koreshkova

Institute of Еarth Science of Saint-Petersburg State University

Author for correspondence.
Email: m.koreshkova@spbu.ru
Russian Federation, 33-35, 10 th line, Vasilevsky Ostrov, Saint-Petersburg, 199178

Yu. B. Marin

Saint-Petersburg Mining University

Email: m.koreshkova@spbu.ru

Corresponding Member of the Russian Academy of Sciences

Russian Federation, 2, 21st line, Vasilevsky Ostrov, Saint-Petersburg, 199106

L. P. Nikitina

Institute of Precambrian Geology and Geochronology of the Russian Academy of Sciences

Email: m.koreshkova@spbu.ru
Russian Federation, 2, Makarova embankment, St.Petersburg, 199034

H. Downes

Birkbeck University of London

Email: m.koreshkova@spbu.ru
United Kingdom, WC1E 7HX, Malet Street, Bloomsbury, London

A. A. Tokusheva

Institute of Еarth Science of Saint Petersburg State University

Email: m.koreshkova@spbu.ru
Russian Federation, 33-35, 10 th line, Vasilevsky Ostrov, Saint-Petersburg, 199178

A. G. Goncharov

Institute of Еarth Science of Saint Petersburg State University

Email: m.koreshkova@spbu.ru
Russian Federation, 33-35, 10 th line, Vasilevsky Ostrov, Saint-Petersburg, 199178

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