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闫国川,王保弟,刘函,王立全,周放.西藏洞错埃达克质火山岩LA-ICP-MS锆石U-Pb年龄及其构造意义[J].地质通报,2017,(10):1772-1782.
西藏洞错埃达克质火山岩LA-ICP-MS锆石U-Pb年龄及其构造意义    点此下载全文
闫国川1  2  王保弟2  刘函2  王立全2  周放1  2
1. 中国地质大学, 北京 100083;
2. 中国地质调查局成都地质调查中心, 四川 成都 610081
基金项目:中国地质调查局项目《西南三江有色金属资源基地调查》(编号:DD20160016)和国家自然科学基金项目《羌塘中部泥盆纪—石炭纪岩浆作用对古特提斯洋构造演化的制约》(批准号:41773026)、《藏南仲巴地区始新世花岗质岩石成因及其对拉萨地壳加厚的启示》(批准号:41603038)
DOI:
摘要:
      班公湖-怒江缝合带是青藏高原的主要缝合带之一,其闭合时限还存在争议,制约了班公湖-怒江特提斯洋演化历史的研究。在班公湖-怒江缝合带洞错地区新识别出一套早白垩世晚期的粗安岩,LA-ICP-MS测得其锆石206Pb/238U年龄为102.0±1.9Ma,岩石高SiO2、Al2O3、富Na及高的Sr/Y值(25.2~42.2),贫Nb(11.1×10-6~16.6×10-6)、Y(11.7×10-6~18.3×10-6)和Yb(1.06×10-6~1.77×10-6),轻、重稀土元素分异明显,具有与埃达克质岩相似的地球化学特征,同时具有高Mg#的特点(Mg#=50.0~54.1)。认为洞错高Mg#埃达克质岩很可能是残留洋壳部分熔融上升过程中交代地幔的产物,形成于板内构造环境。由此推测,洞错早白垩世晚期埃达克质岩的形成与班公湖-怒江洋盆闭合后拉萨地块与羌塘地块碰撞有关,结合区域地质资料,认为班公湖-怒江特提斯洋闭合时限应该在102Ma之前。
关键词:西藏洞错  班公湖-怒江特提斯洋  粗安岩  埃达克质岩  LA-ICP-MS锆石U-Pb年龄  残余洋壳熔融
LA-ICP-MS zircon U-Pb ages of adakitic rocks in Dongco area, Tibet, and their tectonic implications    Download Fulltext
YAN Guochuan1  2  WANG Baodi2  LIU Han2  WANG Liquan2  ZHOU Fang1  2
1. China University of Geosciences, Beijing 100083, China;
2. Chengdu Center of Geological Survey, CGS, Chengdu 610081, Sichuan, China
Fund Project:
Abstract:
      The Ban'gong Co-Nujiang suture zone is one of the main suture zones in the Tibetan Plateau. Its closure time has been controversial, which causes some restrictions to the study of the evolution of the Tibetan Plateau. This paper deals with the discov-ered trachyandesite which occurs in Bangong Co-Nujiang suture zone. LA-ICP-MS zircon U-Pb analyses suggest that the trachy-andesite was formed at 102±1.9Ma, and that the volcanic rocks were formed in late Early Cretaceous. They are characterized by ada-kite-like rock:high Na content, SiO2, Al2O3, Mg# and high Sr/Y values(25.2~42.2), and low Nb(11.1×10-6~16.6×10-6), Y (11.7×10-6~18.3×10-6)and Yb(1.06×10-6~1.77×10-6) values. The differentiation between HREE and LREE is obvious. The authors hold that high Mg# adakite-like rock(Mg#=(50.0~54.1) resulted from the reaction between the rising melt of remnant oceanic crust and the mantle wedge. Therefore, the origin of Dongcuo adakitic-like rocks may be related to the collision between Lasha and Qiang-tang blocks after the closure of the Bangong Co-Nujiang Ocean. Based on these data, the authors consider that Bangong Co-Nuji-ang Ocean had been closed before 102Ma.
Keywords:Dongco area  Bangong Co-Nujiang Ocean  trachyandesite  adakitic rock  LA-ICP-MS zircon U-Pb ages  remnant oceanic crust
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