龙门山南段盐井-五龙断裂磁组构特征及其对几何学、运动学的制约  

Kinematics and Geometry of the Yanjing-Wulong Fault in the Southern Section of Longmenshan Tectonic Belt: Constraints from Magnetic Fabrics

作　　者：陈应涛[1] 张国伟[2] 鲁如魁[2] 郭安林[2] 谢晋强 朱伟 CHEN Yingtao;ZHANG Guowei;LU Rukui;GUO Anlin;XIE Jinqiang;ZHU Wei(College of Geology and Environment,Xi’an University of Science and Technology,Xi’an 710054,Shaanxi,China;State Key Laboratory of Continental Dynamics,Department of Geology,Northwest University,Xi’an 710069,Shaanxi,China;College of Mining Engineering of Taiyuan University of Technology,Taiyuan 030024,Shanxi,China;Shaanxi Center of Geological Survey,Xi’an 710068,Shaanxi,China)

机构地区：[1]西安科技大学地质与环境学院,陕西西安710054 [2]西北大学地质学系/大陆动力学国家重点实验室,陕西西安710069 [3]太原理工大学矿业工程学院,山西太原030024 [4]陕西省地质调查中心,陕西西安710068

出　　处：《大地构造与成矿学》2019年第2期199-212,共14页Geotectonica et Metallogenia

基　　金：国家自然科学基金项目(41602212;41072159);国土资源部煤炭资源勘查与综合利用重点实验室开放课题项目(ZKF2018-1;ZP2018-2)联合资助

摘　　要：盐井?五龙断裂是龙门山中央断裂北川?映秀断裂的南延部分,也是龙门山南段的三大控制性主干断裂之一。为了详细认识盐井?五龙断裂的构造几何学、运动学特征,在野外构造研究的基础上,运用磁组构方法对盐井?五龙断裂105块构造岩定向样品进行深入研究。野外构造解析表明断裂至少发生了韧性挤压剪切、脆?韧性逆冲和脆性挤压碎裂三期构造变形。磁组构研究显示构造岩磁组构样品的平均磁化率k_m值具有强磁化率和弱磁化率两种特征。磁组构形状参数T、磁面理F值、磁线理L值和T-P_J图解显示磁化率椭球体主要为压扁型,磁面理较磁线理发育,局部发育较强磁线理,进一步表明盐井?五龙断裂以挤压、剪切为主,伴有拉伸变形的整体特征,样品的P_J整体较大,显示出构造强变形磁组构特征。最小磁化率主轴K_(min)方位表明盐井?五龙断裂北段和南段分别受到了NW-SE向和NEE-SWW向的挤压作用;K_(min)方位和倾伏角表明北段晚一期的脆韧性变形主体为自NW向SE的较高角度的挤压逆冲剪切变形,局部伴有极小量的左行走滑特征。断裂南段早期韧性变形整体以自SWW向NEE的挤压逆冲剪切变形为主,上盘(西盘)远离主干断裂表现为左行走滑兼逆冲的运动学特征,下盘变形主要以逆冲剪切变形为主,走滑分量极小,并且自西向东韧性剪切变形具有相对强弱相间的特征。The Yanjing-Wulong Fault is the southern extension of the Beichuan-Yingxiu Fault,which is also one of the three main faults in the southern segment of the Longmenshan Tectonic Belt.In order to decipher the structural geometry and kinematics of the Yanjing-Wulong Fault,magnetic fabrics of 105 oriented samples were carried out on the basis of field structural investigation.Field structural analysis shows that the fault underwent at least three episodes of deformation,which include(1)ductile deformation with mylonitized zones developed between the crystalline basement and cover;(2)brittle-ductile deformation with intensive cleavage belt in the Maoxian Group(SM)and the Shimenkan Formation(Z1sm)in the middle level;(3)crushed zone and shallow-surface brittle deformation dominated by fault-block structure superimposed on the two early stages of deformation.The tectonites can be divided into two groups,with strong and weak average susceptibility,respectively.The overall shape parameter(T),corrected anisotropy of magnetic susceptibility(PJ),magnetic foliation(F),magnetic lineation(L)and T-PJ diagram suggest an oblated magnetic susceptibility ellipsoid.The magnetic foliation prevails over magnetic lineation,but with intensive magnetic lineation in local places.These characteristics indicate that the Yanjing-Wulong Fault experienced mainly compression and shearing with accompanying stretching deformation.The high PJ values are consistent with the strong structural deformation.The orientations of minimum principal axes(Kmin)reflect that the northern and southern sections of the Yanjing-Wulong Fault experienced NW-SE and NEE-SWW compressions,respectively.The orientation and plunge angles of Kmin indicate that the brittle-ductile deformation of the northern section is mainly with high-angle NW to SE compressional thrust,accompanied with minimum left-lateral deformation in areas.The early ductile deformation of the southern section is mainly SWW to NEE compressional thrust.The hanging wall(W wall)that is away from the major fau

关 键 词：龙门山构造带 盐井.五龙断裂 磁组构 构造变形 AMS 

分 类 号：P542[天文地球—构造地质学]