【摘要】 2008年汶川地震(MW7.9)发生在青藏高原东缘龙门山断裂带上,并沿映秀-北川断裂和灌县-安县断裂分别产生约270km和80km的不同性质的地表破裂带。断裂岩是断裂活动的产物,是断裂带的物质组成,其结构特征记录了断裂活动演化的历史。本文以汶川地震发震断裂映秀-北川断裂带中虹口八角庙地区地表露头和汶川地震科学钻探一号孔(WFSD-1)岩心为主要研究对象,通过详细的野外调研、显微结构及XRD分析等,识别出映秀-北川断裂带由五个次级单元组成,分别为:碎裂岩带、黑色断层泥和角砾岩带、灰色断层角砾岩带、深灰色断层角砾岩带以及断层泥和角砾岩带。断裂岩组合显示映秀-北川断裂带具有多核断裂结构特征。映秀-北川断裂带在地表出露的宽度约为240m,岩心中厚度约为105m,碎裂岩、断层角砾岩、断层泥在地表及岩心中均发育,而假玄武玻璃仅在地表碎裂岩部分出现。汶川地震主滑移带斜切了映秀-北川断裂带,不完全沿袭古地震滑移带,暗示汶川地震断裂带与映秀-北川断裂带可能不是同一个断裂体系。通过断裂岩的研究确定了映秀-北川断裂带存在着摩擦熔融、热增压、动态润滑和机械润滑等多种断裂滑移机制。低温热年代学的研究推断映秀-北川断裂带的形成时代为15～10Ma,自形成以来,映秀-北川断裂带的长期活动控制着龙门山的快速隆升。断裂带五个不同断裂岩组合的内部结构带,可能与龙门山不同的隆升速率期有着一定的联系。更多还原

【Abstract】 The 2008 Wenchuan earthquake ( M W 7. 9)occurred at the eastern margin of the Tibetan Plateau,producing 270km and 80km-long co-seismic surface ruptures with different kinematics features,along the Yingxiu-Beichuan and Guanxian-Anxian faults, respectively. Fault rocks are the products of fault activities. The characteristics of fault rocks provide information on fault activities and their evolution history. Here,we focus on the outcrop of the Yingxiu-Beichuan fault in Bajiaomiao village,Hongkou town and results from WFSD-1drill cores. Based on field survey,X-raydiffraction analysis,microstructure and drill cores analysis,a ～240m-wide fault zonewas confirmed as the Yingxiu-Beichuan fault zone from the outcrop,corresponding to the～105m-wide fault zone at depth, as determined from the WFSD-1 drill cores,which presents the characteristics of a multiple cores model. Fault rocks,including fault breccia,fault gouge and cataclasite were identified in both the outcrop and drill cores,while pseudotachylyte was only visible at the outcrop. The location of the Principal Slip Zone of the Wenchuan earthquake,which does not entirely follow the ancient fault zone, obliquely crossing the Yingxiu-Beichuan fault zone,might indicate that the Wenchuan earthquake fault and Yingxiu-Beichuan faultdo not belong to the same fault system. Based on fault rocks studies,there are four kinds of fault mechanisms along the Yingxiu-Beichuan fault zone, such as frictional melting, thermal pressurization, mechanical lubrication and elasto-hydrodynamic lubrication. Thermochronometry research indicates that the Yingxiu-Beichuan fault activity has controlled the rapid uplift of the Longmenshan since it formed at 15～10Ma ago. The fact that the internal structure shows five different fault rock units in the fault zone may be related to the different episodes of the Longmenshan uplift.更多还原