阿尔金北缘喀腊大湾地区早古生代岩石变形特征分析

发布时间：2018-03-17 06:41

  本文选题：阿尔金北缘　切入点：磁组构　出处：《中国地质大学(北京)》2017年硕士论文　论文类型：学位论文

【摘要】：阿尔金北缘喀腊大湾地区位于阿尔金走滑断裂与阿尔金北缘断裂所夹持区域的中东段,大地构造位置属于敦煌地块与中阿尔金地块的俯冲-碰撞带,本文着重对其在本区所产生的岩石变形特征进行了详细的研究。为了探究阿尔金北缘喀腊大湾地区的应变型式和变形条件,在野外地质观测的基础上,沿喀腊大湾沟构造观察剖面采集变形岩石定向样品,实验研究本区变形岩石的磁组构特征,并对变形强烈的岩石进行镜下显微构造特征和石英EBSD岩组分析。磁组构结果显示研究区校正磁化率各向异性度P’总体较大,反映出本区岩石变形强烈的特征。此外,而磁化率椭球主轴下半球赤平投影和类弗林图解表明,整个区域受到统一的南北向挤压应力的作用,表现为压扁型的应变,而中部发育陡倾线理的部位呈现出拉长型的应变型式。同时,变形岩石的镜下显微构造特征和石英EBSD岩组,反映出喀腊大湾地区以中温(400~500°C)条件下的柱面(10(?)0)11(?)0滑移变形为主,而研究区南部局部叠加有高温条件(500~600℃)下的(10(?)0)0001滑移变形。此外,局部的地区还叠加有低温条件下(300~400℃)的(0001)11(?)0滑移变形。且叠加型变形的出现,均表现为由高温型的滑移变形,向相对低温型的滑移变形逐渐过渡转变的现象。喀腊大湾沟剖面中段含磁铁矿砾石砾岩LA-ICP-MS锆石U-Pb测年分析表明,其峰值年龄为510.22Ma,而北部砾岩的峰值年龄为456.75Ma,整体呈现出由北向南碎屑锆石的年龄逐渐变老的趋势。前人研究表明,未卷入变形的阿北花岗岩体的锆石U-Pb SHRIMP测年结果为427~417Ma;而南部卷入变形的长英质糜棱岩锆石U-Pb LA-ICP-MS年龄为477.6±4.9Ma,北部糜棱岩化闪长岩的锆石U-Pb LA-ICP-MS年龄为478.1±2.1Ma。这些同位素地质年代学的资料表明本区岩石变形形成于477~427Ma,处在一个由俯冲到碰撞的连续变化的过程中。一系列的证据表明,在477~427Ma阿尔金北缘喀腊大湾地区受到敦煌地块与中阿尔金地块俯冲碰撞的连续影响,在本区形成以压扁型应变为主的中温(400~500℃)柱面(10(?)0)11(?)0滑移变形,而由于俯冲角度的逐渐增大,以及地幔对流产生的拖拽力的作用下,使得研究区中部的岩石,将近于南北向的挤压应力转化为沿板片陡倾的拉伸应力,形成一系列拉长型的应变。
[Abstract]:The Kaladawan area on the northern edge of Altun is located in the middle and east segment of the zone between the Altun strike slip fault and the northern Altun fault. The tectonic location belongs to the subduction-collision zone between the Dunhuang block and the middle Altun block. In this paper, the characteristics of rock deformation produced in this area are studied in detail. In order to explore the strain patterns and deformation conditions in Kaladawan area on the northern edge of Altun, on the basis of field geological observations, Directional samples of deformed rocks were collected along the observation section of Kaladawangou structure, and the magnetic fabric characteristics of deformed rocks in this area were studied experimentally. The microscopic structural characteristics of the strongly deformed rocks and the analysis of quartz EBSD rock formation are also carried out. The results of magnetic fabric show that the corrected anisotropy of magnetic susceptibility in the study area is generally larger, which reflects the strong deformation characteristics of the rocks in this area. On the other hand, the hemispherical plain projection of the magnetic susceptibility ellipsoid axis and Flyning-like diagram show that the whole region is subjected to a unified South-North compressive stress, which is shown as flattened strain. At the same time, the microscopic structural characteristics of deformed rocks and quartz EBSD rock formation reflect the columnar area of Kaladawan area under the condition of moderate temperature 400 掳C). What is it? In the southern part of the study area, there is a local superposition of 10 ~ (10)? under the high temperature condition of 500 ~ (600 鈩，

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