Mineralogical Characteristics of the Dong Tso Ophiolite and Its Tectonic Implications
详细信息
- 责任者：Li Jianfeng (State Key Laboratory of Isotope Geochemistry ; Guangzhou Institute of Geochemistry ; Chinese Academy of Sciences ; Guangzhou 510640 ; China) ; Xia Bin
- 刊名：Geotectonica et Metallogenia
- 出版年：2013
- 卷期：37(2)
- 关键词：橄榄岩 ; peridotites ; 辉长岩 ; gabbros ; 青藏高原 ; Qinghai-Tibetan Plateau
- 页码：p.308-319
- 图表：illus., 2 tables, 21 refs.
- 分类号：0801
- issnNo：ISSN1001-1552
- isbnNo：CN44-1595/P
摘要
The Dong Tso ophiolite,with a wedge exposure shapeis,is located at 20 km north of Dong Tso,Gertse county. The ophiolite emplaced in the Jurassic strata of the Mugagangri Group,and was overlain unconformably by the Cretaceous strata of the Langshan Group. The Dong Tso ophiolite consists of all common units,such as the mantle peridotite of lherzolite and harzburgite,cumulate rocks,diabase dyke,and basaltic lavas. The spinel and pyroxene in the mantle peridotite and massive gabbro of the Dong Tso ophiolite were analyzed using EMPA and EDS methods. The spinel from the Dong Tso spinel lherzolite plots in the region of abyssal peridotite on the tectonic discrimination diagrams. Chemical compositions of the spinels show that the spinel iherzolite experienced < 10% melt extraction while the harzburgites experienced about 13% to 30% melt extraction,which are much lower than that of the typical mantle peridotite of island arc affinity. The mineral composition of the gabbro is similar to those of the typical mafic intrusions. Combined with the reported data,we conclude that the Dong Tso ophiolite was developed mainly in a normal oceanic ridge and experienced gradual melt extraction. The geothermomal calculation results show that the orthopyroxene and clinopyroxene crystallized at 900 ～ 1000 ℃ and < 500 ～ 600 ℃,respectively. The former should be the formation temperature of the host rock,while the latter may represent the equilibrium temperature of the metamorphism or re-crystallization.
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