摘要
高喜马拉雅结晶岩系由中-高级变质岩和淡色花岗岩组成,是研究喜马拉雅造山带形成与演化的天然实验室.高喜马拉雅结晶岩系混合岩和淡色花岗岩中锆石和独居石的定年结果往往是分散的,对这些定年结果的解释还存在争议,严重制约了对高喜马拉雅结晶岩系变质、部分熔融作用的起始时间和持续过程的理解.对造山带中段亚东地区高喜马拉雅结晶岩系上部构造层位的乃堆拉混合岩进行了锆石U-Pb年代学研究.研究结果显示,乃堆拉混合岩暗色体给出了29.1~24.7 Ma的进变质和部分熔融的时间,混合岩浅色体获得了25.0~13.7 Ma的退变质和熔体结晶的时间,表明亚东地区高喜马拉雅结晶岩系的部分熔融作用大约开始于30 Ma并持续到13 Ma,暗示它是一个长期、持续的过程.亚东地区高喜马拉雅结晶岩系发生部分熔融的时间明显早于藏南拆离系和主中央断裂开始活动的时间,部分熔融可能在高喜马拉雅结晶岩系俯冲过程中就已经发生了.相关成果为建立造山带构造演化模型提供了新信息.
The Higher Himalayan Crystalline Sequence is composed mainly of middle-high grade metamorphic rocks and leucogranites,forming a natural laboratory for studying the formation and evolution of the Himalayan orogen.However,the geological significance of the U-Pb ages remains controversial because zircons and monazites of the migmatites and leucogranites from the Higher Himalayan Crystalline Sequence commonly have yielded variable U-Pb ages,which significantly restricts our understanding of timing and duration of metamorphism,partial melting and melt crystallization of the orogen.Here it presents zircon U-Pb geochronological study of the Naiduila migmatites in Yadong region from the upper structural level of the Higher Himalayan Crystalline Sequence,middle Himalaya.The results show that zircons from the melanosomes of the migmatites in Naiduila area have variable U-Pb ages ranging from 29.1 to 24.7 Ma,and zircons from the leucosomes of the migmatites yield various U-Pb ages of 25.0-13.7 Ma.The former may be interpreted as the timing and duration of prograde metamorphism and partial melting,and the latter represents timescales of retrogressive metamorphism and melt crystallization.Therefore,it is proposed that the partial melting of the Higher Himalayan Crystalline Sequence in the Yadong region initiated at ca.30 Ma and lasted to ca.13 Ma,indicating that it is a long-term and sustained process.The study also indicates that the timing of partial melting of the Higher Himalayan Crystalline Sequence is earlier than the starting activation of the South Tibetan detachment and the Main Central Thrust.This may further indicates that the partial melting occurred during subduction.The study provides new information on the structural evolution model of the orogen.
作者
苟正彬
刘函
段瑶瑶
李俊
张士贞
Gou Zhengbin;Liu Han;Duan Yaoyao;LiJun;Zhang Shizhen(Chengdu Center of China Geological Survey,Chengdu 610081,China)
出处
《地球科学》
EI
CAS
CSCD
北大核心
2020年第8期2894-2904,共11页
Earth Science
基金
国家自然科学基金项目(Nos.41802071,41773026)
中国地质调查局项目(No.DD20190053)。
