气候变化领域集成服务门户(CCPortal): Melt/mantle mixing produces podiform chromite deposits in ophiolites: Implications of Re-Os systematics in the Dongqiao Neo-tethyan ophiolite, northern Tibet

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DOI	10.1016/j.gr.2011.05.011
	Melt/mantle mixing produces podiform chromite deposits in ophiolites: Implications of Re-Os systematics in the Dongqiao Neo-tethyan ophiolite, northern Tibet
	Shi, Rendeng; Griffin, William L.; O'Reilly, Suzanne Y.; Huang, Qishuai; Zhang, Xiaoran; Liu, Deliang; Zhi, Xiachen; Xia, Qiongxia; Ding, Lin
通讯作者	Shi, RD (通讯作者)
发表日期	2012
ISSN	1342-937X
EISSN	1878-0571
起始页码	194
结束页码	206
卷号	21 期号:1
英文摘要	Podiform chromite deposits occur in the mantle sequences of many ophiolites that were formed in suprasubduction zone (SSZ) settings. We have measured the Re-Os isotopic compositions of the major chromite deposits and associated mantle peridotites of the Dongqiao Ophiolite in the Bangong-Nujiang suture, Tibet, to investigate the petrogenesis of these rocks and their genetic relationships. The Os-187/Os-188 ratios of the chromite separates define a narrow range from 0.12318 to 0.12354, less variable than those of the associated peridotites. Previously-reported Os-187/Os-188 ratios of the Os-rich alloys enclosed in the chromitites define two clusters: 0.12645 +/- 0.00004 (2 s; n = 145) and 0.12003 to 0.12194. The ultra-depleted dunites have much lower Os-187/Os-188 (0.11754, 0.11815). and the harzburgites show a wider range from 0.12107 to 0.12612. The average isotopic composition of the chromitites (Os-187/Os-188: 0.12337 +/- 0.00001) is low compared with the carbonaceous chondrite value (Os-187/Os-188: 0.1260 +/- 0.0013) and lower than the average value measured for podiform chromitites worldwide (0.12809 +/- 0.00085). In contrast, the basalts have higher Os-187/Os-188, ranging from 0.20414 to 0.38067, while the plagioclase-bearing harzburgite and cumulates show intermediate values of Os-187/Os-188 (0.12979 similar to 0.14206). Correspondingly, the basalts have the highest Re-187/Os-188 ratios, up to 45.4 +/- 3.2, and the chromites have the lowest Re-187/Os-188 ratios, down to 0.00113 +/- 0.00008. We suggest that melts/fluids, derived from the subducting slab, triggered partial melting in the overlying mantle wedge and added significant amounts of radiogenic Os to the peridotites. Mass-balance calculations indicate that a melt/mantle ratio of approximately 15:1 (melt: Re-187/Os-188: 45.4, Os-187/Os-188: 0.34484; mantle peridotite: Re-187/Os-188: 0.0029, Os-187/Os-188: 0.11754) is necessary to increase the Os isotopic composition of the chromitite deposits to its observed average value. This value implies a surprisingly low average melt/mantle ratio during the formation of the chromitite deposits. The percolating melts probably were of variable isotopic composition. However, in the chromitite pods the Os from many melts was pooled and homogenized, which is why the chromitite deposits show such a small variation in their Os isotopic composition. The results of this study suggest that the Os-187/Os-188 ratios of chromitites may not be representative of the DMM, but only reflect an upper limit. Importantly, the Os-isotope compositions of chromitites strongly suggest that such deposits can be formed by melt/mantle mixing processes. (C) 2011 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.
关键词	SPINEL PERIDOTITE XENOLITHS WESTERN GNEISS REGION LITHOSPHERIC MANTLE LUOBUSA OPHIOLITE ISOTOPIC COMPOSITIONS TECTONIC ENVIRONMENT SIDEROPHILE ELEMENTS GEOCHEMICAL EVIDENCE DONQIAO OPHIOLITE MIDOCEAN RIDGE
英文关键词	Chromite deposit; Melt/mantle mixing; Geochemistry; Os isotope; Dongqiao ophiolite; Tibet
语种	英语
WOS研究方向	Geology
WOS类目	Geosciences, Multidisciplinary
WOS记录号	WOS:000300204400015
来源期刊	GONDWANA RESEARCH
来源机构	中国科学院青藏高原研究所
文献类型	期刊论文
条目标识符	http://gcip.llas.ac.cn/handle/2XKMVOVA/258033
推荐引用方式 GB/T 7714	Shi, Rendeng,Griffin, William L.,O'Reilly, Suzanne Y.,et al. Melt/mantle mixing produces podiform chromite deposits in ophiolites: Implications of Re-Os systematics in the Dongqiao Neo-tethyan ophiolite, northern Tibet[J]. 中国科学院青藏高原研究所,2012,21(1).
APA	Shi, Rendeng.,Griffin, William L..,O'Reilly, Suzanne Y..,Huang, Qishuai.,Zhang, Xiaoran.,...&Ding, Lin.(2012).Melt/mantle mixing produces podiform chromite deposits in ophiolites: Implications of Re-Os systematics in the Dongqiao Neo-tethyan ophiolite, northern Tibet.GONDWANA RESEARCH,21(1).
MLA	Shi, Rendeng,et al."Melt/mantle mixing produces podiform chromite deposits in ophiolites: Implications of Re-Os systematics in the Dongqiao Neo-tethyan ophiolite, northern Tibet".GONDWANA RESEARCH 21.1(2012).