CAJ | 학술논문

西秦岭北缘断裂带是青藏高原东北缘主要构造边界断裂带之一,其构造变形历史和运动学特征研究可以为西秦岭中新生代构造过程和印度—亚洲板块碰撞动力学的远程构造响应提供约束.漳县—车厂断层是西秦岭北缘断裂带的重要组成部分,通过对工程开挖所揭露的断层带内丰富构造现象的观测与分析,至少可以辨别出3期性质、规模、运动学特征各异的构造变形事件.第一期为向北北东陡倾的伸展正断层作用;第二期为向南南西倾的由南向北的逆冲断层作用;第三期为沿近直立断面左旋走滑作用.尽管每期变形的时代尚缺乏构造物质测年的约束,但根据其与白垩系、新近系的空间关系以及已有第四纪以来沿断层地貌位错和相关沉积物测年以及地震活动历史研究对断层左旋走滑作用的时代约束,认为第一期伸展正断层作用起始于早白垩纪,可能持续到渐新世;第二期向北逆冲断层作用起始于渐新世初,可能持续到早第四纪;第三期左旋走滑断层作用起始于晚第四纪,持续至今.漳县—车厂断层是一条典型的多期变形的脆性断层,其变形特征与历史,如果代表了西秦岭北缘断裂带特征与构造变形过程,那么现今西秦岭北缘断裂带仅是起始于早白垩纪、新生的脆性断裂带,并非是印支主造山期大规模韧性逆冲推覆作用的边界断层.
서진령북연단렬대시청장고원동북연주요구조변계단렬대지일,기구조변형역사화운동학특정연구가이위서진령중신생대구조과정화인도—아주판괴팽당동역학적원정구조향응제공약속.장현—차엄단층시서진령북연단렬대적중요조성부분,통과대공정개알소게로적단층대내봉부구조현상적관측여분석,지소가이변별출3기성질、규모、운동학특정각이적구조변형사건.제일기위향북북동두경적신전정단층작용;제이기위향남남서경적유남향북적역충단층작용;제삼기위연근직립단면좌선주활작용.진관매기변형적시대상결핍구조물질측년적약속,단근거기여백성계、신근계적공간관계이급이유제사기이래연단층지모위착화상관침적물측년이급지진활동역사연구대단층좌선주활작용적시대약속,인위제일기신전정단층작용기시우조백성기,가능지속도점신세;제이기향북역충단층작용기시우점신세초,가능지속도조제사기;제삼기좌선주활단층작용기시우만제사기,지속지금.장현—차엄단층시일조전형적다기변형적취성단층,기변형특정여역사,여과대표료서진령북연단렬대특정여구조변형과정,나요현금서진령북연단렬대부시기시우조백성기、신생적취성단렬대,병비시인지주조산기대규모인성역충추복작용적변계단층.
@@@@The north margin fault zone of West Qinling is one of the tectonic boundary faults and earthquake faults in the northeast margin of Tibetan plateau. Its structural characteristics and deformation history can provide important constraints on the Mesozoic-Cenozoic tectonic processes of West Qinling and the remote tectonic responses to the Indian-Europe plate collisions. Based upon the tectonic observation and analysis of Zhangxian-Chechang fault zone which was uncovered by engineering construction and is located in the central segment of the north margin faults of West Qinling, the authors identified three phases of deformation events with different properties, scales, and kinematics. The first event is characterized by steep NNE-dipping extensional normal faulting. According to the relationship between Cretaceous red bed basin and the fault, it is suggested that this normal faulting event documented the Cretaceous regional crustal extension and development of the red bed basin. The fault gouge with a lot of grinding gravels and well-developed faulting foliations indicates its long duration, probably lasting to the Late Oligocene, i.e., 29 Ma when Linxia basin began developing. The second event is characterized by south-dipping inverse faulting, which led to the folding and thrusting of the Cretaceous red bed strata, possibly indicating the transition from crustal extension to contraction. This tectonic transition probably suggests that the India-Europe plate collision might have been spread to West Qinling, and strong thrusting should have occurred at 3.6 Ma when Jishishan and Wuquanshan conglomerates occurred. The third event is characterized by sinistral strike-slipping along the nearly vertical NNW-striking fault plane, which began in Late Quaternary and has continued up till now. Zhangxian-Chechang fault as one of the north margin faults of West Qinling is a typical brittle fault, which failed to document the large-scale ductile shearing in Indochina orogeny. Therefore it is held that the north margin fault zone of West Qinling, which has been generally believed to be the tectonic boundary fault between the Central Qinling and North Qinling or Central Qilian Block, is a newly generated fault from the Cretaceous instead of the boundary fault in the Indochina orogeny.