Petrogenesis of ultramafic rocks from the ultrahigh-pressure metamorphic kimi complex in eastern Rhodope (NE Greece)

作者：Baziotis I; Mposkos E; Asimow P D^*

来源：Journal of Petrology, 2008, 49(5): 885-909.

DOI：10.1093/petrology/egn010

• peridotite
• pyroxenite
• partial melting
• UHP metamorphism
• cumulate

Widespread bodies of garnetspinel metaperidotites with pyroxenitic layers occur in the ultrahigh-pressure metamorphic Kimi Complex. In this study we address the origin of such peridotitepyroxenite 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 garnetspinel metaperidotites exhibit decreasing CaO, Al(2)O(3), TiO(2), and Na(2)O 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 meltperidotite 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.

• 出版日期2008-5