| 王世龙,米玛旺久,马文成.西藏拉康地区南部拆离断层构造变形特征[J].甘肃地质,2024,(4):14-25 |
| 西藏拉康地区南部拆离断层构造变形特征 |
| Tectonic Deformation of Detached Fault in Southern Lacang Area of Tibet |
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| DOI： |
| 中文关键词: 西藏 拉康地区 拆离断层 构造特征 活动时代 |
| 英文关键词:detachment fault structural characteristics activity age Lhakang area Tibet |
| 基金项目:中国地质调查局成都地质调查中心地调科研项目（１２１２０１０１００００１５００１４－０１、ＤＤ２０１６００１５－０５） |
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| 中文摘要: |
| 西藏拉康地区发育的拆离断层叠加在先期逆冲推覆构造之上，在持续挤压作用下，大喜马拉雅基底杂岩带相对向南楔形挤出，同时北侧发生拆离效应，形成研究区内规模较大的北倾韧脆性剪切带。本文通过野外地质调查，根据岩石组合、变形变质、构造层次等，将拉康地区南部拆离断层带进一步划分为上拆离面（F18）和下拆离面（F20），厘定出两期主要的构造活动：①D2期韧脆性变形；②D3期脆性变形。二云二长花岗岩中锆石U-Pb年龄为（19. 2 ± 0. 1） Ma，代表D2期构造活动的时间下限；白云母二长花岗岩中锆石U-Pb年龄为（13. 4 ± 0. 1） Ma，代表D3期构造活动发生时间；正断层中石英脉的电子自旋共振（ESR）测年结果：20. 43 ～ 21. 34 Ma和10. 64 ~ 14. 04 Ma，分别与两期构造活动（D2、D3）时代相吻合，说明研究区内主要的两期构造活动时代集中在中新世中晚期。 |
| 英文摘要: |
| The detachment faults developed in the Lhakang area of Tibet are superimposed upon the earlier thrust-nappe structure. Under the continuous compressive effect, the Great Himalayan Basement Complex Zone is extruded relatively southward in a wedge shape, while detachment occurs on the northern side, forming a large-scale north-dipping brittle-ductile shear zone within the investigation area. Through field geological investigations and based on rock assemblages, deformation and metamorphism, and structural hierarchies, the southern detachment fault zone in the Lhakang area is further divided into the upper detachment surface（F18） and the lower detachment surface（F20）, and two phases of tectonic activities are determined: ① D2 phase ductile-brittle deformation; ② D3 phase brittle deformation. The zircon U-Pb age of the two-mica monzogranite is 19. 22 ± 0. 14 Ma, representing the lower limit of the D2 phase tectonic activity; the K-Ar age of the muscovite in the muscovite monzogranite is 11. 6 Ma, representing the occurrence time of the D3 phase tectonic activity; the electron spin resonance （ESR） dating results of quartz veins in the normal faults: 20. 43 ~ 21. 34 Ma and 10.64 ~ 14.04 Ma are consistent with the two phases of tectonic activities（D2，D3）, indicating that the two main phases of tectonic activities （D2，D3） in the study area are concentrated in the middle to late Miocene. |
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