龙门山中、新生界软沉积物变形及构造演化  

Soft-sediment deformation structures and their implications for tectonic evolution from Mesozoic to Cenozoic in the Longmen Shan

作　　者：乔秀夫[1] 姜枚[1,2,3] 李海兵[1,2] 郭宪璞[1,2] 苏德辰[1,2] 许乐红[1,2] 

机构地区：[1]国土资源部大陆动力学重点实验室,北京100037 [2]中国地质科学院地质研究所,北京100037 [3]中国地质科学院矿产资源研究所,北京100037

出　　处：《地学前缘》2016年第6期80-106,共27页Earth Science Frontiers

基　　金：国土资源部大陆构造与动力学国家重点实验室自主基金项目(Z1301-a3);科学技术部汶川地震断裂带与科学钻探项目所属课题"穿越龙门山断裂带的反射地震探测及深部构造地质解释";中国地质调查局项目"青藏高原东北缘和东缘的隆升时限;过程及前陆盆地形成的动力学机制"(1212011121268);科学技术部汶川地震断裂科学钻探WFSD项目

摘　　要：龙门山是由三条主要断裂组成的山体。汶川—茂县断裂,也称后山断裂,构成龙门山的西部边界;映秀—北川断裂为龙门山的中央断裂;灌县—安县断裂为龙门山的东部边界,也称前山断裂。龙门山断裂带以东为始自晚三叠世末的不同时期的前陆盆地。前陆盆地中从晚三叠世至2008年5月12日汶川地震(MS8.0),在不同年代地层中均有丰富的软沉积物变形构造(SSDS)记录,包括液化变形、重力作用变形、水塑性变形及其他相关的变形。这些变形层的地点紧邻龙门山的三条断裂,这些断裂在不同时期的活动诱发不同时期的强地震,导致当时尚未固结的沉积物变形(震积岩)。上三叠统小塘子组的软沉积的变形构造有液化角砾岩、液化滴状体、液化底辟、触变底辟、卷曲变形、拉伸布丁、负载、球-枕构造、枕状层及粒序断层等。侏罗系、白垩系主要为粗粒沉积物,除少数层位发现有液化变形外,主要的软沉积变形类型为各种形态、大尺度的砾岩负载构造。古近系为湖相沉积,沉积物粒度较细,软沉积物变形又出现大量液化变形构造,如液化混插、液化角砾岩等。2008年5月12日汶川地震(MS8.0)诱发大规模地表以下沙层液化,形成一系列液化变形构造与微地貌:液化沙堆、液化席状沙、沙火山、液化丘、坑状地形与混杂堆积。应用龙门山反射地震成果、古地震记录,结合区域构造可以给出龙门山断裂带发生的时间顺序与地震造山时期:(1)松潘—甘孜造山带与扬子板块的碰撞发生于晚三叠世早期,二者的边界即现在的汶川—茂县断裂;汶川—茂县断裂于晚三叠世末逆冲推覆造山,三叠纪末龙门山地区的山地可称松潘-甘孜山,在其东侧形成前陆盆地;晚三叠世印支造山旋回的大陆动力作用是龙门山诞生与孕育的阶段。(2)映秀—北川断裂与灌县—安县断裂的逆冲活动时间为侏罗纪—早白�The Longmen Shan is a mountain body composed of three main faults.The Wenchuan-Maoxian fault,also called the range-back fault,constitutes the western boundary of the Longmen Shan;the YingxiuBeichuan fault is the central fault of the Longmen Shan;and the Guanxian-Anxian fault,also called the rangefront fault,is the eastern boundary of the Longmen Shan.On the east of the Longmen Shan fault belt,there is a foreland basin which has been experienced different periods since the terminal of the Late Triassic.There had been rich soft-sediment deformation structures（SSDS）in the strata of different ages in the foreland basin from the Late Triassic to the May 12,2008 Wenchuan earthquake（MS8.0）,including liquefaction deformation,gravitational deformation,hydroplastic deformation,and other related deformations.These deformation strata were located immediately near the three faults of the Longmen Shan,and the activities of these faults in different periods induced strong earthquakes in different periods,leading to the deformation of the sediments that had not consolidated then（seismites）.The SSDS in the Upper Triassic Xiaotangzi Formation included liquefied breccia,liquefied droplet,liquefied diapir,thixotropic diapir,convolute deformation,stretched pudding,load,ball-and-pillow structure,pillow beds,and graded fault.In the Jurassic and Cretaceous,there were mainly coarse-grained sediments,and the main soft sediment deformation types were large-scale conglomerate load structures with various shapes except liquefaction deformation found in a few horizons.In the Paleogene,there was lacustrine sediments,with fine grains,and there were large quantities of liquefaction deformation structures in the soft sediment,e.g.,plunged sediment mixtures,liquefied breccia,and pillow beds.The May12,2008 Wenchuan earthquake（MS8.0）induced large scale liquefaction of underground sand bed,forming a series of liquefaction deformation structures and microfeatures,e.g.,liquefied dune,liquefied sheet sand,sand volcano,liquefied mound,pit

关 键 词：龙门山 龙门山断裂带 古地震 软沉积物变形构造 构造演化 

分 类 号：P315.5[天文地球—地震学]