| 念青唐古拉花岗岩热演化历史和山脉隆升过程的热年代学分析 |
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| 关键词:uplift process of mountain range granite thermal event thermo-chronological analysis Nyainqentanglha Range |
| 基金项目:西藏当雄幅1：25万区域地质调查与科技部资助青藏高原深部过程与地表效应课题 |
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| Chronological Analyses of the Thermal Evolution of Granite and the Uplift Process of the Nyainqentanglha Range in Central Tibet |
| As an important mountain range in central Tibetan plateau, the Nyainqentanglha Range is world-famous. It is mainly composed of biotite-plagioclase-K-feldspar granite (NG) containing a variety of enclaves such as Lgn and Ygn gneiss and Pt metamorphic rocks. Huge ductile shear zones (NSZ) consisting of extensional mylonite were discovered on both sides of the Nyainqentanglha granite. They gradually change into schistosity belts in the north. SHRIMP U-Pb dating of zircons from Lgn gneiss enclave and NG granite yielded ages of 65.0～55.0 Ma and 18.3～11.1 Ma, representing periods of granitic magma crystallization in Palaeocene and Miocene respectively. Rb-Sr isochronic dating of biotite and K-feldspar from NG granite, K-Ar dating of samples from NG granite and NSZ mylonite and fission-track dating of apatite from NG granite gave time constraints for thermo-tectonic events after the emplacement of the NG granite. Thermal-chronological analyses show that the Nyainqentanglha granite (NG) was emplaced and crystallized during 18.3～11.1 Ma beneath Lgn and Ygn gneiss at an average depth of 11 km, followed by rapid uplift (cooling) processes at the rate of 5.56 mm/a (222.2 ℃/Ma), 3.57 mm/a (142.8 ℃/Ma), 3.50 mm/a, 2.31 mm/a (92.3 ℃/Ma) and 0.68 mm/a (27 ℃/Ma) in 11.1～9.3 Ma, 9.3～8.6 Ma, 8.0～5.0 Ma, 5.0～3.7 Ma and 3.7 Ma to the present respectively. Rapid uplif- ting (cooling) in 8.0～5.0 Ma was caused by extensional ductile shearing of NSZ, and extensional faulting contributed to the uplif- ting of the Nyainqentanglha Range since 3.7 Ma. Magma accumulation and NG granite emplacement related geodynamically to partial melting of the crust detected by INDEPTH-II seismic bright-spots at the depth of 13～20 km caused the upper crust extension of central Tibet, the gradual cooling of NG and the rapid uplift of the Nyainqentanglha Range. |
| WU Zhen-han,HU Dao-gong,LIU Qi-sheng,YE Pei-sheng,WU Zhong-hai.2005.Chronological Analyses of the Thermal Evolution of Granite and the Uplift Process of the Nyainqentanglha Range in Central Tibet[J].Acta Geoscientica Sinica,26(6):505-512. |
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