Mineralogy, Geochemistry and Tectonic Setting of the Raobazhai Ultramafic Complex, North Dabie
Fangchao Yan; Qing Liu; Quanlin Hou; Miao He
The Raobazhai ultramafic complex is located in the north of the Dabie Mountains and is composed of spinel peridotites accompanied by a few lenticular mafic metamorphic rocks. The spinel peridotites are mostly harzburgite, along with minor dunite and lherzolite. This study reports the petrological, geochemical, and Re-Os isotopic data of spinel and chromite harzburgites from Raobazhai. The major and trace whole-rock geochemistry characteristics indicate that the rocks are remnants of partial melting to different degrees (6&ndash:17%). Both mineral and whole-rock geochemistry showed typical abyssal peridotite affinity. Due to the presence of water-bearing minerals, the Sr, Ba, and U were enriched, and the Nb, Zr, and Hf were depleted, which can be attributed to the strong metasomatism of the boninitic melting/fluid in the fore-arc domain. The flat distribution of platinum group elements (PGE) and the decoupling of Pt-Pd were also the result of the fore-arc melting/fluid interaction. The 187Os/188Os ratios (0.1149&ndash:0.1266) were generally lower than the recommended value of the primitive mantle and fell within the abyssal peridotite isotope range. This indicated that the Raobazhai harzburgites were likely mantle peridotites with oceanic characteristics that underwent a fore-arc boninitic melting/fluid transformation event.
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