龙门山地震断裂带的热年代结果及其对断裂活动的指示  

Thermochronology of the Longmen Shan seismic fault and its implications for faulting activities

作　　者：郑勇 李海兵[1,2,3] 王焕 司家亮[1,2,3] 张蕾 李成龙[1,2,3] 张佳佳 ZHENG Yong;LI HaiBing;WANG Huan;SI JiaLiang;ZHANG Lei;LI ChengLong;ZHANG JiaJia(Key Laboratory of Deep-Earth Dynamics of Ministry of Natural Resources,Institute of Geology,Chinese Academy of Geological Sciences,Beijing 100037,China;Southern Marine Science and Engineering Guangdong Laboratory(Guangzhou),Guangzhou 511458,China;Jiangsu Donghai Continental Deep Hole Crustal Activity National Observation and Research Station,Donghai 222300,China;Institute of Exploration Technology,China Geological Survey,Chengdu 611734,China)

机构地区：[1]中国地质科学院地质研究所,自然资源部深地动力学重点实验室,北京100037 [2]南方海洋科学与工程广东省实验室(广州),广州511458 [3]江苏东海大陆深孔地壳活动国家野外观测研究站,东海222300 [4]中国地质调查局探矿工艺研究所,成都611734

出　　处：《岩石学报》2022年第11期3542-3558,共17页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(42072240、41602218);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);自然资源部深地动力学重点实验室自主研究课题(J1901-30);中国地质调查局地质调查项目(DD20221630)联合资助.

摘　　要：中生代和新生代多期次的新老构造活动叠加造成了龙门山现今地震频发和复杂的构造格局。沿2008年汶川地震断裂带出露有多种断裂岩组合,为直接开展断裂带热年代学研究提供了重要素材。本研究首次尝试针对映秀-北川断裂带出露的假玄武玻璃开展^(40)Ar/^(39)Ar年龄的多重扩散域(MDD)模拟研究。与钾长石相似的阶梯状上升的年龄谱图表明假玄武玻璃同样具有开展MDD模拟的应用潜力。模拟结果显示,映秀-北川断裂带分别经历了~230Ma和~180Ma起始的构造热事件,对应青藏高原东缘中-晚三叠世统一的挤压造山运动和造山后的伸展垮塌。断裂带内新获得的断层角砾岩磷灰石裂变径迹(AFT)结果与上、下盘已有结果共同组成了较为完整的年龄-高程剖面,揭示出年龄拐点出现在~13Ma,位于~1100m的海拔高度,与热历史反演结果一致,对应映秀-北川断裂带的出露位置,直接证实断裂活动在中中新世以来龙门山的隆升过程中发挥了重要作用。进入中中新世以来,龙门山断裂带的快速剥蚀和地温梯度的显著降低很可能暗示了构造活动机制上的重要转变。Multiple-phase superposition tectonic events occurring in Mesozoic and Cenozoic causes the present-day earthquake-prone and complicated tectonic framework of the Longmen Shan.Multi-combination of fault rocks has been discovered along the seismic fault of the 2008 Wenchuan earthquake,which therefore provides new objectives allowing study of low-temperature thermochronology.This study first attempts to perform multiple-diffusion domain(MDD)modelling of the pseudotachylyte^(40)Ar-^(39)Ar ages along the Yingxiu-Beichuan fault.The staircase rise spectrum similar to the K-feldspar indicates that pseudotachylyte is most likely a potential objective which is suitable for MDD modelling.The modelling results show that the Yingxiu-Beichuan fault at least experienced twice tectonic thermal events in~230Ma and~180Ma,corresponding to the wide compressional orogeny and post-orogeny extensional collapse during mid-late Triassic,respectively,along the eastern margin of Tibetan Plateau.The new obtained apatite fission track data of the fault breccia,together with the previous data of the hanging wall and footwall,constitute a relatively completed age-elevation profile and reveal a slope-break point at~13Ma.This break point is located at~1100m asl,consistent with the reverse-modelling of thermal history,and corresponds to the location of the Yingxiu-Beichuan fault,confirming the important role of the fault activity in uplifting of the Longmen Shan since Mid-Miocene.Since Mid-Miocene,the rapid exhumation and significant reduction in thermal gradient of the Longmen Shan fault belt most likely imply a key transition in tectonic activity mechanism.

关 键 词：断裂岩 热年代学 假玄武玻璃 多重扩散域 磷灰石裂变径迹 

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