塔吉克斯坦南帕米尔阿里秋(Alichur)穹隆花岗岩锆石U-Pb定年、Hf同位素特征及地质意义

U-Pb Dating,Hf-isotopic Characteristics and Tectonic Implications of Granite,Alichur Dome,Southern Pamir,Tajikistan

南帕米尔地区分布一系列受拆离断层控制,于印度–欧亚大陆碰撞过程中形成的穹隆构造,穹隆核部以晚中生代花岗岩和高级变质岩为主,并有少量新生代花岗质侵入岩。为阐明穹隆有关花岗岩的侵位背景和构造意义,笔者通过LA-MC-ICP锆石U-Pb定年测试获得侵位到穹隆拆离断层韧性剪切带中的花岗岩和占穹隆体积主体的核部白垩纪花岗岩年龄,分别为(19.3±0.4)Ma和(111.7±0.8)Ma。结合帕米尔地区和南帕米尔穹隆构造已有研究成果,笔者认为锆石Hf同位素特征反映南帕米尔地区晚中生代花岗岩是含有亏损地壳熔融作用的结果。新生代花岗岩形成于构造减压导致的中下地壳部分熔融作用,宏观上可能形成于印度板块碰撞俯冲过程中的减速调整阶段。

Cenozoic domes separated by detachments and formed during the India-Eurasian collision,are commonly distributed in the southern Pamir.The core complex of these domes are made up of high-grade metamorphic rocks and granite.The granite mainly formed during the Late Mesozoic and minor of them formed during the Cenozoic.The granite samples gathered along the detachments and from the granite comprising the bulk Alichur dome are measured by on the LA-MC-ICP U-Pb zircon dating.The formation times of the granite are(19.30±0.36)Ma and(111.7±0.8)Ma.Hf-isotopic characteristics of zircon demonstrate the granite formed by partial melting of crust.The Cenozoic granite is probably closely associated with the structural decompression caused by the extensional decollement of the domes.