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Journal of Petrology Advance Access published online on March 24, 2008
Journal of Petrology, doi:10.1093/petrology/egn010
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© The Author 2008. Published by Oxford University Press. All rights reserved. For Permissions, please e-mail: journals.permissions@oxfordjournals.org

Petrogenesis of Ultramafic Rocks from the Ultrahigh-pressure Metamorphic Kimi Complex in Eastern Rhodope (NE Greece)

I. Baziotis1, E. Mposkos1 and P. D. Asimow2,*

1National Technical University of Athens, Department of Mining and Metallurgical Engineering, Section of Geological Sciences, Heroon Polytechniou 9, 15780, Athens, Greece
2California Institute of Technology, Division of Geological and Planetary Sciences, Pasadena, CA 91125, USA

Received January 25, 2007; Revised typescript accepted February 13, 2008


  Abstract

Widespread bodies of garnet–spinel metaperidotites with pyroxenitic layers occur in the ultrahigh-pressure metamorphic Kimi Complex. In this study we address the origin of such peridotite–pyroxenite associations in the context of polybaric melting regimes. We conduct a detailed geochemical investigation of major and trace element relations and compare them with a range of major element modelling scenarios. With increasing bulk-rock MgO content, the garnet–spinel metaperidotites exhibit decreasing CaO, Al2O3, TiO2, and Na2O along with increasing Ni and a gradually increasing Zr/Zr* anomaly, consistent with an origin as residues after variable degrees of melt extraction. The major element modelling further suggests a polybaric adiabatic decompression melting regime beginning at high to ultrahigh pressure, with an intermediate character between pure batch and fractional melting and a mean extent of melting of 9–11%. The pyroxenites exhibit major element compositions that cannot be reproduced by experimental or calculated melts of peridotite. Moreover, the Kimi pyroxenites have highly variable Ni and Sc contents and a wide range of Mg-number (0· 76–0· 89), inconsistent with an origin as frozen melts or the products of melt–peridotite interaction. However, both the major element systematics and the observed rare earth element patterns, with both convex and concave shapes, can be explained by an origin as clinopyroxene-rich, high-pressure cumulates involving garnet and/or Cr-spinel.

KEY WORDS: peridotite; pyroxenite; partial melting; UHP metamorphism; cumulate

*Corresponding author. Telephone: + 1-626-395-4133. Fax: + 1-626-568-0935. E-mail: asimow{at}gps.caltech.edu


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