GAO Tian-shan^1,2, CHEN Jiang-feng², XIE Zhi²

1. Nanjing Institute of Geology and Mineral Resources, Nanjing 210016, China;
2. School of Earth and Space Sciences, University of Science and Technology of China, Hefei 230026, China

Abstract: The ultramafic body at Hujialin consists of two parts. The southern part, which is the Huashishan body, consists mainly of serpentinite and serpentinized peridotite with thin layers of garnet olivine pyroxenite and (garnet) clinopyroxenite. The northern part consists mainly of clinopyroxenite with thick layer of serpentinite. Serpentinite and serpentinized peridotite are low in Al2O3 and CaO and high in MgO. These rocks are low in REE, but slightly enrich in LREE. The garnet olivine pyroxenite and (garnet) clinopyroxenite are low in MgO and high in CaO and total REE contents. Primitive mantle-normalized trace element patterns for all types of mafic-ultramafic rocks show positive Pb anomaly and weak negative Nb and Ta anomalies, suggesting metasomatism of crustally derived fluid/melt. The Sr, Nd and Pb isotopic compositions of these ultramafic rocks can be explained by mixing between the depleted mantle and the crust at 216 Ma. The serpentinized garnet olivine pyroxenite exhibits the lowest concentrations of lithophile elements, suggesting significant contributions from the metasomatic fluid/melt. The garnet olivine pyroxenite and (garnet) clinopyroxenite were metasomatised by hydrous melt. Therefore, the ultramafic rocks were metasomatised by different compositions of crustal material.

Keywords: element geochemistry radiogenic isotopes mafic-ultramafic rock Sulu metamorphic zone

E-Mail: tsgao@ustc.edu.cn

Bulletin of Mineralogy, Petrology and Geochemistry Vol. 34, No.3, 2015, page 601-618