Petrology and Geochemistry of Cretaceous Ultramafic Volcanics from Eastern Kamchatka |
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Authors: | KAMENETSKY V S; SOBOLEV A V; JORON J-L; SEMET M P |
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Institution: | 1VERNADSKY INSTITUTE OF GEOCHEMISTRY, RUSSIAN ACADEMY OF SCIENCES KOSYGIN STR. 19, MOSCOW 117975, RUSSIA
2GROUPE DES SCIENCES DE LA TERRE, LABORATOIRE PIERRE SE, CEN SACLAY 91191 GIF SUR YVETTE CDEX, FRANCE
3LABORATOIRE DE GOCHIMIE COMPARE ET SYSTEMATIQUE URA X-01758 CNRS, 75252 PARIS CDEX 05, FRANCE |
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Abstract: | The origin, evolution and primary melt compositions of lateCretaceous high-K ultramafic volcanics and associated basaltsof Eastern Kamchatka are discussed on the basis of a study ofthe mineralogy and geochemistry of the rocks and magmatic inclusionsin phenocrysts. The exceptionally primitive composition of thephenocryst assemblage olivineFo;8895, Cr-spinelCr/(Cr + Al) up to 85] provides direct evidence of the mantleorigin of primary melts, which were highly magnesian compositions(MgO 1924 wt%). The rocks and meltsare characterizedby strong high field strength element (HFSE) depletion in comparisonwith rare earth elements, and high and variable levels of enrichmentin large ion lithophile elements (LILE), P, K and H2O (0.612wt % in picritic to basaltic melts). Nd values lie in a narrowrange (+107 to +91), typical of N-MORB (mid-ocean ridge basalt),but 87Sr/86Sr (0.703160.70358) is slightly displacedfrom the mantle array. High-K ultramafic melts from Kamchatkaare considered as a new magma type within the island-arc magmaticspectrum; basaltic members of the suite resemble arc shoshonites.The primary melts were produced under high-pressure (3050kbar) and high-temperature(15001700C) conditions bypartial melting of a refractory peridotitic mantle. KEY WORDS: Kamchatka; Late Cretaceous magmatism; ultramafic volcanics; shoshonites
*Corresponding author. Present address: Department of Geology, University of Tasmania, GPO Box 252C, Hobart, Tas., Australia |
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