青藏高原东缘汶川-茂县断裂韧性变形对龙门山早期隆升的制约

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青藏高原东缘汶川-茂县断裂韧性变形对龙门山早期隆升的制约
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作者单位:1.中国地质科学院地质研究所;2.法国里昂大学地学实验室,里昂;3.中国地质科学院地质力学研究所;4.北京大学地球与空间科学学院
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基金项目:国家自然科学基金项目（面上项目，重点项目，重大项目）

Ductile deformation of Wenchuan-Maoxian fault constrain the early uplift of Longmen Shan

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1.Institute of Geology,Chinese Academy of Geological Sciences,Beijing;2.Laboratoire de Gé3.ologie de Lyon,Villeurbanne,France;4.institute of geomechanics Chinese academy of geological sciences, Beijing, 100089, China;5.ologie de Lyon, Villeurbanne, 69622, France;6.School of Earth and Space Sciences,Peking University,Beijing

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摘要:

青藏高原东缘的汶川-茂县断裂是龙门山构造带中发育有深层次韧性变形的断裂，对于揭示龙门山隆升中的深部过程有着重要的意义。本文通过断裂带物质组成、宏观/微观构造变形和石英组构的分析，对断裂带内韧性变形的运动学、流变特征和变形条件进行了约束。结果表明：（1）断裂带内存在宽约3 km、向北西陡倾的韧性剪切带；（2）在剪切带内部识别出两期剪切变形：早期北西向正断剪切和晚期东向逆冲剪切；（3）石英晶格组构特征显示逆冲韧性变形以石英底面滑移为主，伴随膨凸重结晶作用，指示变形温度为300 - 400℃；正断韧性变形以石英柱面滑移为主，伴随亚颗粒旋转重结晶作用，对应温度为350 - 650℃。结合已发表的地质年代学和低温热年代学数据，我们认为汶川-茂县断裂带在渐新世发生了北西向的正断韧性剪切，在中新世发生东向的逆冲韧性变形。汶川-茂县断裂在中晚新生代期间的强烈活动导致了龙门山后缘大量深部物质的抬升，最终形成了现今构造地貌雏形。

Wenchuan-Maoxian fault in the eastern margin of the Tibetan Plateau (Longmen Shan) is the major fault that has developed deep ductile deformation and played an important role in controlling the early uplift of the Longmen Shan. By using the field survey, macro/micro structure analysis, and crystal fabric analysis, we have constrained the kinematic and rheological characteristics and deformation conditions of ductile deformation of the Wenchuan-Maoxian fault. The results show that (1) ductile shear zone approximately 3 km wide and steeply dipping to the north west exists within the fault; (2) two phases of deformation are identified within the shear zone: early Top-to-NW normal shearing and late Top-to-E reverse shearing; (3) The quartz CPO results show that the reverse ductile deformation is dominated by basal slip, accompanied by bulging recrystallization, with an indicated deformation temperature of 300 - 400℃. The normal ductile deformation is dominated by prism slip, accompanied by subgrain rotation recrystallization, with a corresponding temperature of 350 - 650℃. Combining with published geochronological and thermochronological data, we suggest that the Wenchuan-Maoxian fault underwent Top-to-NW normal ductile faulting in the Oligocene and Top-to-E reverse ductile deformation in the Miocene, which resulted in the uplift and exhumation of large amounts of deep material in the hinterland region of Longmen Shan.

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收稿日期:2023-01-14
最后修改日期:2023-04-13
录用日期:2023-04-15
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