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PGE geochemistry of Jiding ophiolite in Tibet and its constraint on mantle processes
Authors:XIA Bin  CHEN Genwen  MEI Houjun  GUO Lingzhi  XIAO Xuchang  YU Hengxiang  QI Liang  WANG Guoqiang  Zhong Zhihong
Affiliation:1. Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China;Open Laboratory of Ore Deposit Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550002, China;
2. Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China;
3. Department of Geosciences, Nanjing University, Nanjing 210093, China;
4. Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China
5. Open Laboratory of Ore Deposit Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550002, China;
Abstract:
The total PGE amount (σPGE) of mantle peridotite in the Jiding ophiolite is slightly higher than that of the primitive mantle, but the PGE contents of basalt are higher than those of the mid-ocean ridge basalt (MORB), with obviously lower Pd/Ir ratios. The accumulates, dyke swarm and basalts show remarkable negative Pt and positive Rh anomalies, resulting in the special N-type PGE patterns. Mantle peridotite and crustal rocks have similar distribution patterns. It is proposed that the PGE distribution patterns in the Jiding ophiolite are closely related with a higher degree of partial melting of the mantle in this region. Magmatic crystallization-differentiation led to PGE fractionation, thus making the contents of PGE in the accumulates decrease in the ascending direction. The higher content of Au in the Jiding ophiolite is the result of metasomatic alteration at later stages. Pt-Pd fractionation indicates that both the PGEs are controlled by their alloy and sulfide phases. Positive Rh anomalies seem to be related with higher oxygen fugacity in the melts.
Keywords:platinum group element (PGE)  geochemistry  ophiolite  upper mantle  Jiding of Tibet
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