摘要
断裂带的岩石组成、内部结构和地球化学特征是认识断裂活动性质和变形行为的关键,而断层泥作为断裂带核部的重要物质,不仅影响断裂带强度,而且控制断裂的滑移机制。本文以汶川地震的发震断裂龙门山映秀-北川断裂带北川段沙坝探槽中的断层泥为研究对象,通过对断层泥进行宏观与显微构造观察、粉末X射线衍射分析(XRD)、矿物自动化定量分析(TIMA)和薄片微区X射线荧光光谱分析(μXRF)等多种分析,探讨了其所蕴含的断裂变形行为和滑移机制。研究表明:北川段断裂带NW盘主要为寒武纪碳质泥页岩和板岩,SE盘由半固结的黄色砂质黏土层组成。断裂带核部由面理发育的黑色断层角砾岩和面理化的断层泥组成,断层泥厚约25cm,分为黄色断层泥、灰色断层泥和黑色断层泥,汶川地震滑移带沿灰色断层泥和黑色断层泥边界分布,在滑移带附近可见明显的拖曳构造与R1次级剪切破裂,指示了逆冲滑动的性质。断层泥中的碎块呈棱角状大小不均一,显示出地震快速滑动特征,表现为粘滑行为。黄色和灰色断层泥中黏土矿物含量(42%~52%)远高于黑色断层泥(19%~29%),前者石英(36%~47%)、伊利石(18%~32%)和绿泥石(7%~15%)含量整体略高于后者中的含量,而长石含量整体低于后者,表明黄色和灰色断层泥中水-岩作用较强于黑色断层泥,推测前者断层泥的孔隙度高于后者;断层泥中含有较多的伊蒙混层,靠近滑移带Fe元素呈明显增加趋势,暗示了摩擦产生了大量的热,同时,黑色断层泥中发育有石墨,说明断层滑移具有热增压弱化机制。龙门山映秀-北川断裂带北段北川断裂在岩石组成和规模上与南段映秀断裂虹口段断裂带有着明显差异,但均存在断裂滑移的石墨化作用,这些研究对认识映秀-北川断裂带南北段的滑移行为具有重要的指示意义。
Rock composition,internal structures and geochemical properties of a fault zone are three critical aspects for the understanding of its nature of fault activities and deformation behaviors.Fault gouge,as a key component of a fault zone,not only determines the strength of a fault zone,but also controls its slip mechanism.In this study,we focused on the fault gouge in the Shaba trench in the Beichuan section of the Yingxiu-Beichuan fault zone.Based on macroscopic and microstructural observation,X-ray diffraction(XRD),TESCAN Integrated Mineral Analyzer(TIMA)and micro X-ray fluorescence(μXRF)analyses,we systemically dissected the nature of fault gouge,and discussed its deformation behaviors and faulting mechanisms related to the fault zone.Our research results show that the fault core in Beichuan section consist of foliated black fault breccia and fault gouge.Among which,a 25-cm-thick fault gouge belt is layered by yellow,gray and black fault gouges.The Wenchuan earthquake slipping zone was lying in the border of the gray and black fault gouges,where drag structures and R1 secondary shear fractures are visible around the slip zone,indicating a characteristic of thrust slipping.The clasts in the fault gouge are angular with varying sizes,showing the characteristics of rapid seismic sliding.The yellow and gray fault gouges contained much more clay minerals(42%~52%)than the black one(19%~29%),and their quartz(36%~47%),illite(18%~32%)and chlorite(7%~15%)contents are also higher,while the feldspar content is lower than that of the latter.These may indicate that water-rock interaction in yellow and gray fault gouge was stronger than in the black fault gouge,suggesting that the porosity of the former gouge is higher than that of the latter.Highly enriched illite/smectite formation and Fe element in the slip zone imply friction heat was generated during the slip.Meanwhile,graphite was emerged in the black fault gouge,which indicates that thermal pressurization occurred as a weakening mechanism during the fault sliding.In the Yingxiu-Beichuan fault zone,obvious differences in rock compositions and fault zone scales were observed between the southern segment in the Hongkou area and the northern segment in the Beichuan section.However,fault gouge graphitization exists in both sections.Together,the systemic investigations have important implications for understanding the faulting behavior of the northern and southern segments of the Yingxiu-Beichuan fault zone.
作者
李成龙
李海兵
王焕
张进江
LI ChengLong;LI HaiBing;WANG Huan;ZHANG JinJiang(MNR Key Laboratory of Deep-Earth Dynamics,Institute of Geology,Chinese Academy of Geological Sciences,Beijing 100037,China;School of Earth and Space Sciences,Peking University,Beijing 100871,China;Southern Marine Science and Engineering Guangdong Laboratory(Guangzhou),Guangzhou 511458,China)
出处
《岩石学报》
SCIE
EI
CAS
CSCD
北大核心
2021年第10期3145-3166,共22页
Acta Petrologica Sinica
基金
国家自然科学基金项目(41830217,41972229)
南方海洋科学与工程广东省实验室(广州)人才团队引进重大专项(GML2019ZD0201)
中国地质调查项目(DD20190059)联合资助.
关键词
汶川地震
断裂泥
变形行为
北川断裂带
龙门山
Wenchuan earthquake
Fault gouge
Deformation behavior
Beichuan fault zone
Longmen Shan
