摘要
活动断裂出露于浅层或地表,其变形条件具有低温、低围压、高应变速率的特点,对于调节地壳变形具有重要意义。断裂带的结构与变形特征反映了岩石对脆性破裂的力学响应,这对于评价断裂活动性,揭示断裂带的形成与演化过程具有重要意义。本文以滇西地区地震活动频繁的曲江断裂为研究对象,通过露头尺度、微观尺度的构造解析并结合有限元模拟,探究该活动断裂的结构特征及变形演化机制。野外观测表明基岩区发育的活动断层一般由断层核和破碎带组成,断层核内可见未固结或弱固结的断层泥和断层角砾,吸收和容纳了绝大多数应变;破碎带内广泛发育裂隙以及次级断裂。微观变形组构揭示基岩断裂形成过程中岩石矿物发生显著碎裂作用、细粒化和碎屑流动,导致岩石强度显著降低。本次研究使用有限元方法,采用理想弹塑性模型和库仑屈服准则,通过杨氏模量表征断层破裂程度,模拟了含断层岩体在固定的位移约束条件下应变分布情况。模拟结果结合不同尺度的构造观察指示,断裂带中杨氏模量相对较小的先存破裂会吸收较多的应变,进而发育成断层核;周缘的次级断裂和裂隙构成破碎带,起到调节应变的作用。断裂带在演化过程中经历了由应变分散向应变集中的转变。
Deformation of active faults outcropped on earth’s surface is characterized by low temperature,low confining pressure,and high strain rate.Active faults are the most important structures regulating crustal deformation.The architecture and deformation patterns of bedrock fault zones reflect the mechanical response of rock to brittle fractures,and are of great significance for revealing fault activity and its evolution.In this study,we focused on the Qujiang fault,which is one of the most seismically active faults in Western Yunnan,China.We conducted structural analyses at outcrop and microscales,combined with FEM simulation,to study the architecture and mechanism of active fault zones.Active faults in bedrock are generally composed of a fault core and damage zone,according to field observations.The core zone generally consists of an unconsolidated or weakly consolidated fault gouge and fault breccia,which absorb most of the strain.Fractures and secondary faults are widespread in the damage zone.The micro-deformation fabric revealed cataclastic flow and fine-grained rock minerals,resulting in a significant decrease in rock strength.We calculated the strain distribution within fault zones under fixed displacement constraints using the FEM,which is based on the ideal elastic-plastic model and Coulomb yield criterion.We used Young’s modulus to characterize the degree of brittle rupture.Structural analysis at different scales and FEM results indicated that pre-existing structures with the lower Young’s modulus absorb most displacements,forming fault cores.In contrast,the damage zone adjusts less strains.The fault zone experienced a transition from relative diffuse deformation to strain localization.
作者
林浩
汪意
刘金锋
崔亚
王洋
LIN Hao;WANG Yi;LIU Jinfeng;CUI Ya;WANG Yang(Guangdong Provincial Key Laboratoty of Geodynamics and Geohazards,School of Earth Sciences and Engineering,Sun Yat-sen University,Zhuhai 519082,Guangdong,China;Southern Marine Science and Engineering Guangdong Laboratory(Zhuhai),Zhuhai 519082,Guangdong,China)
出处
《大地构造与成矿学》
EI
CAS
CSCD
北大核心
2024年第3期446-459,共14页
Geotectonica et Metallogenia
基金
国家重点研发计划项目(2023YFC3007301)
国家自然科学基金项目(U2344212、42272247)联合资助。
关键词
曲江断裂
断层结构
变形机制
构造解析
有限元模拟
杨氏模量
Qujiang fault
fault structure
deformation mechanism
structural analysis
FEM
Young’s modulus
