Delineation of Middle Neoproterozoic Ophiolite Mélange in the Northern Lhasa Terrane, South Tibet and Its Significance
详细信息
- 责任者：Zhang Xiuzheng (Research Center for Tibetan Plateau ; Jilin University ; Changchun 130061 ; China) ; Dong Yongsheng
- 刊名：Acta Petrologica Sinica
- 出版年：2013
- 卷期：29(2)
- 关键词：蛇绿混杂堆积 ; ophiolite complexes ; 青藏高原 ; Qinghai-Tibetan Plateau
- 页码：p.698-722
- 图表：illus., 3 tables, 87 refs.
- 分类号：0300
- issnNo：ISSN1000-0569
- isbnNo：CN11-1922/P
摘要
The amphibolite-facies and granulite-facies metamorphic rocks from the Lhasa terrane, South Tibet, have been traditionally grouped as the Precambrian metamorphic basement, but related research is still in the initial stages, particularly the study on geochronological and tectonic attribute. This paper reports petrological and geochemical features and zircon U-Pb age of typical ortho-metamorphic rocks, including garnet-bearing amphibolite, plagioclase gneiss and felsic veins from Nyainqentanglha Group in Yongzhu area, northern part of Lhasa terrane. We report for the first time Late Neoproterozoic metamorphic and magmatic events from the Lhasa terrane and provide important data for study on origin and Paleozoic tectonic evolution of the Lhasa Terrane. Geochemical data indicate that the garnet-bearing amphibolite (Sample TQ18 and Sample Q11T15), originated in both E-MORB and island-arc tectonic settings, and that the plagioclase gneiss (Sample TQ19) are of similar geochemical feature to plagiogranites which are interpreted to have derived from anatexis of hydrated amphibolites by ductile shearing during transports of the oceanic crust. In situ zircon U-Pb LA-ICP-MS dating on the zircons possess residual magmatic cores yielded an protolith age of the 758.3±6.1Ma, 730.8±6.9Ma and 742.1±8.3Ma, representing the age of Neoproterozoic ocean basin formation, metamorphism and melting process during transports of the oceanic crust and island arc magmatism. Zircons from garnet-bearing amphibolite (Sample Q11T15) show typical features of metamorphic origin, and yield peak-metamorphic ages of 665.7±6.5Ma, probably representing the age of continent collision during the oceanclosing. Geochemical evidence indicated that felsic veins (Sample Q11T16) are similar to adakite. Zircon rim from felsic veins record ages of 660.1±4.2Ma, slight later the peak-metamorphic ages of sample (Q11T15), which are preliminary explained as the age of anatexis during initial extensional collapse or exhumation processes of the high-pressure rocks.
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