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引用本文:张林奎,李光明,曹华文,张志,付建刚,夏祥标,董随亮,梁维,黄勇. 藏南错那洞花岗质片麻岩锆石年龄、Hf同位素及其对原特提斯洋演化的启示[J]. 中国地质, 2019, 46(6): 1312-1335.
ZHANG Linkui,LI Guangming,CAO Huawen,ZHANG Zhi,FU Jiangang,XIA Xiangbiao,DONG Suiliang,LIANG Wei,HUANG Yong. Zircon geochronology and Hf isotope compositions of the granitic gneiss from Cuonadong in South Tibet and its insights for the evolution of the Proto-Tethys[J]. Geology in China, 2019, 46(6): 1312-1335(in Chinese with English abstract).
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藏南错那洞花岗质片麻岩锆石年龄、Hf同位素及其对原特提斯洋演化的启示
张林奎, 李光明, 曹华文, 张志, 付建刚, 夏祥标, 董随亮, 梁维, 黄勇
中国地质调查局成都地质调查中心, 四川 成都 610081
摘要:
错那洞穹隆是藏南特提斯喜马拉雅地区新发现的一个片麻岩穹隆构造。穹隆核部发育一套早古生代眼球状片麻岩。本文在野外地质调查的基础上,利用LA-(MC)-ICP-MS对花岗质片麻岩2个样品的锆石开展U-Pb年代学和Lu-Hf同位素分析。片麻岩中的锆石发育核-幔-边结构,核部为具溶蚀港湾结构的继承锆石,幔部为具韵律(震荡)环带的岩浆锆石,边部(增生边)为重熔变质成因的黑锆石。岩浆锆石幔部的206Pb/238U年龄加权平均值为(500.6±2.6)Ma~(501.1±2.5)Ma,代表该片麻岩的早古生代岩浆结晶年龄。边部变质锆石的新生代重熔年龄为(37.7±0.5)Ma,可能代表藏南拆离系的启动时间。早古生代岩浆锆石幔部的εHft)值为-2.1~+5.3(平均值为+2.2),Hf同位素两阶段模式年龄(TDM2)为1.1~1.6 Ga(平均值为1.3 Ga),表明其源岩起源于高喜马拉雅元古宙地层的部分熔融。结合区域内早古生代岩浆活动和新生代穹隆构造变质事件,本文认为错那洞花岗质片麻岩的形成受控于早古生代原特提斯洋壳板片向冈瓦纳大陆下俯冲的造山作用,同时记录了新生代印度—欧亚大陆碰撞造山后的变质和深熔事件。
关键词:  花岗质片麻岩  锆石U-Pb  Lu-Hf同位素  错那洞  穹隆  特提斯喜马拉雅  地质调查工程
DOI:10.12029/gc20190606
分类号:
基金项目:国家重点研发计划项目(2018YFC0604100,2016YFC0600308)及中国地质调查局项目(DD20190147)联合资助。
Zircon geochronology and Hf isotope compositions of the granitic gneiss from Cuonadong in South Tibet and its insights for the evolution of the Proto-Tethys
ZHANG Linkui, LI Guangming, CAO Huawen, ZHANG Zhi, FU Jiangang, XIA Xiangbiao, DONG Suiliang, LIANG Wei, HUANG Yong
Chengdu Center, China Geological Survey, Chengdu 610081, Sichuan, China
Abstract:
The Cuonadong dome is a newly discovered gneiss dome in the Tethys-Himalaya area of southern Tibet. Early Paleozoic augen gneiss is developed in the core of the dome. Based on field investigation, the authors conducted LA-(MC)-ICP-MS U-Pb dating and Lu-Hf isotopic analysis for two samples from the granitic gneiss. Core-mantle-rim texture is well developed in the zircons from the gneiss in CL images:the core is the inherited zircon with erosion embayed texture, the mantle is the igneous zircon with oscillatory zone, and the rim is the black zircon with re-melting metamorphic genesis. The weighted mean 206Pb/238U age of igneous zircon varies in the range of (500.6±2.6) Ma-(501.1±2.5) Ma, which represents the Early Paleozoic magmatic crystallized age, whereas the Cenozoic re-melting age of margin metamorphic zircon is (37.7±0.5) Ma, which represents the onset of the southern-Tibet detachment. The εHf(t) values and two-stage model ages (TDM2) of mantle Paleozoic igneous zircons range from -2.1 to +5.3 (averagely +2.2) and from 1.1 to 1.6 Ga (averagely 1.3 Ga), respectively, indicating that the source was derived from the partial melting of the High Himalaya Paleoproterozoic strata. Considering the regional Early Paleozoic magmatism and Cenozoic metamorphic event, the authors hold that the Cuonadong granitic gneiss was formed in the orogeny triggered by the Early Paleozoic Proto-Tethyan Oceanic subduction beneath the Gondwana continent, and recorded the Cenozoic post-collisional metamorphic and anatexis events.
Key words:  granitic gneiss  zircon U-Pb  Lu-Hf isotope  Cuonadong  dome  Tethys Himalaya  geological survey engineering