内蒙古呼和浩特变质核杂岩韧性拆离带^40Ar-^39Ar定年及其构造含义  

^(40)Ar-^(39)Ar dating of the detachment fault of the Hohhot metamorphic core complex,Inner Mongolia,China

作　　者：刘江[1,2,3] 张进江[1] 郭磊[2] 戚国伟[1] 

机构地区：[1]造山带与地壳演化教育部重点实验室、北京大学地球与空间科学学院,北京100871 [2]中国地质科学院地质研究所,北京100037 [3]大陆构造与动力学国家重点实验室,北京100037

出　　处：《岩石学报》2014年第7期1899-1908,共10页Acta Petrologica Sinica

基　　金：973项目(2013CB429804);国家自然科学基金项目(91214301)联合资助

摘　　要：晚中生代,内蒙古大青山依次经历晚侏罗世盘羊山逆冲推覆、早白垩世呼和浩特变质核杂岩伸展、早白垩世大青山逆冲推覆断层及早白垩世以来高角度正断层复杂构造演化。其中,呼和浩特变质核杂岩韧性剪切带的冷却时间和抬升机制的制约尚不明确。本文在野外考察和显微构造分析基础上,采用逐步加热40Ar-39Ar定年法对韧性剪切带内不同单矿物的冷却年龄进行了测定。角闪石、白云母、黑云母和钾长石单矿物40Ar-39Ar冷却年龄处于120~116Ma之间。结合已有年龄数据及单矿物封闭温度,构建了韧性剪切带的冷却曲线。结果表明,韧性剪切带在122~115Ma期间存在一个明显的快速冷却过程。这一阶段快速冷却是与变质核杂岩拆离断层相关核部杂岩拆离折返作为大青山逆冲推覆断层上盘抬升的结果。Daqing Shan in central Inner Mongolia had experienced a complex structural evolution during the Late Mesozoic. The Panyang Shan Thrust （P ST）, the Hohhot metamorphic core eomplex （Hohhot MCC）, the Daqing Shan thrust-nappe system （DST） and high angle normal faults are the major structures formed during this stage. However, the temporal and special relationships among these events are still not clear. Based on field observations, we give a chronologieal sequenee on them. Then we measured the 40Ar-39Ar ages of different minerals from the detaehment fault zone of the Hohhot MCC and explain the tectonic implications of these ages based on the newly constructed structural evolution of the Daqing Shan area. The south-directed PST overlay pre-Cambrian rocks on Late Paleozoic-to-Mesozoie rocks. The PST was active at roughly the same time as the deposition of the Daqingshan Formation during the time from Late Jurassic to Early Cretaceous. The Hohhot MCC eonsists of metamorphic core complex, hanging wall unites and detachment faults. The metamorphic core complex is composed of pre-Mesozoic metamorphie rocks and Late Mesozoic granitoids. The hanging wall is made of pre-Cambrian low grade metamorphic rocks and syn-extensional sediments. There ate three detachment faults outcropped representing different evolutionary phases of the detachment fault. The detachment faults from south to north are Hohhot fault zone, Xiaojing fault zone and Deshengying fault zone, whieh are the master detaehment fault, early and deep detachment fault, and late and shallow fault, respectively. Lineation and fabrics of all these ductile shear zones indicate a common top-to-southeast shear in the detaehment faults zone. Zircon ages of granitoids which intruded into the detaehment fault zones indicate that the deformation of ductile shear zone had ended before - 131Ma, much earlier than the 40Ar-39Ar ages of the detachment fault zones. The DST is made up of a series of top-to-the-north or to-the-northwest reverse faults. These faults moved

关 键 词：呼和浩特变质核杂岩 韧性剪切带 40Ar-39Ar定年 大青山 

分 类 号：P542[天文地球—构造地质学] P597.3[天文地球—地质学]