| 龙门山构造带北段构造变形特征——来自汶川科钻四号孔(WFSD-4)的证据 |
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| 引用本文：张佳佳,李海兵,郑勇,王焕,李成龙,张钊荣.2019.龙门山构造带北段构造变形特征——来自汶川科钻四号孔(WFSD-4)的证据[J].地球学报,40(1):93-105. |
| DOI：10.3975/cagsb.2018.111402 |
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| 基金项目:国家自然科学基金项目(编号: 41602226; 41330211; 41620104006);中国地质调查局地质调查项目(编号: DD20160279; DD20190644) |
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| 中文摘要:2008年MW7.9汶川地震在青藏高原东缘龙门山构造带内毫无征兆的情况下发生, 并沿灌县—安县断裂和映秀—北川断裂分别产生了约80 km和275 km的不同性质的地表破裂带, 在世界地震史上实属罕见, 表明龙门山构造带在以往经历了极为复杂的构造演化和运动变形。地震后迅速启动的汶川地震断裂带科学钻探项目, 为我们认识龙门山构造带以往运动和变形本质提供了全新的素材和视角。本文以位于龙门山构造带北段的汶川地震断裂带科学钻探四号孔(WFSD-4)岩心作为主要研究对象, 并结合地表构造变形研究, 对WFSD-4的岩心变形特征和龙门山构造带北段的构造变形序列进行了分析与探讨, 认为: D1变形期以岩心和地表早期面理S1顺成份层发育为特征, 多被同时期长英质脉体填充, 显示伸展机制下的韧性变形, 推测为轿子顶穹隆构造的形成时期; D2变形期为区域主导性面理S2的形成时期, 岩心中劈理面上可见绢云母等矿物, 石香肠构造指示NW–SE的韧性挤压变形特征。岩心和地表均可见S2切割早期面理S1, 错断早期顺S1贯入的长英质脉体; D3变形期以NW–SE向挤压冲断为主, 岩心中面理S2发生褶皱变形, 局部生成间隔劈理S3。地表可见区域主导面理S2变形, 形成平行褶皱, 轴面走向北东, 发育同时期的NW向陡倾的活动断裂, 部分成为汶川地震的发震断裂, 该期对应于龙门山构造带北段的喜山期构造运动, 褶皱强化, 推覆强烈, 也是唐王寨向斜的最终成型时期; 岩心和地表均可见面理S2膝折的构造现象, 为局部地表抬升过程中的重力成因, 构成D4期变形。 |
| 中文关键词:龙门山 汶川地震断裂带科学钻探 岩心特征 变形序列 面理 |
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| Characteristics of Tectonic Deformation in North Longmen Shan Tectonic Belt: Evidence from No. 4 Borehole of the Wenchuan Earthquake Fault Scientific Drilling (WFSD-4) |
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| Abstract:In 2008, the Wenchuan earthquake (MW7.9) struck the Longmen Shan tectonic belt, eastern Tibetan Plateau without warning, which produced surface ruptures 80 km and 275 km long co-seismic with different kinematics features along the Guanxian–Anxian and Yingxiu-Beichuan faults, respectively. The characteristics of Wenchuan earthquake are very rare in the earthquake history all over the world, which indicated that the Longmen Shan tectonic belt has experienced extremely complex tectonic evolution and deformation. As a rapid response to the large earthquake, the Wenchuan earthquake fault scientific drilling project provides new view for studying the essence of the movement and deformation of the Longmen Shan tectonic belt in the past. Bbased on the Wenchuan earthquake Fault Scientific Drilling project, the authors took the cores of the WFSD-4 as the principle study object and, in combination with the research on surface structural deformation, discussed the deformation features of the cores and tectonic deformation history of North Longmen Shan tectonic belt: The first tectonic deformation was characterized by foliation S1, which was developed along the composition layer, and was most injected by felsic veins later, indicating ductile deformation under extensional deformation mechanism, with the period probably in the formative period of Jiaoziding Complex; The second period of tectonic deformation was the time of foliation S2 formation, as shown by the obseration of sericite and other flaky minerals on the foliation S2. The boudinage indicates the ductile NW–SE compression. The phenomenon that S1 is incised by S2 can be seen both in the cores and on the surface; The third tectonic deformation was characterized by compressive thrusting, with local spaced cleavage S3 developed in cores. Cleavage S2 deformed and formed parallel fold whose axial plane trended NW; in addition NW dipping active faults were developed in this region and some became the seismic faults of Wenchuan earthquake. All these phenomena indicate that this activity occurred in the Himalayan period in north Longmen Shan tectonic belt, and also in the ultimate formation period of Tangwangzhai fold. The fourth tectonic deformation was characterized by partial cleavage S2 kinking both in cores and on the surface, and this kind of deformation was brittle. |
| keywords:Longmen Shan Wenchuan earthquake fault scientific drilling (WFSD) features of drilling cores tectonic deformation history foliation |
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