苏鲁造山带西北缘韧性剪切变形特征、年代学制约及区域构造意义

发布时间：2018-05-27 18:08

  本文选题：韧性剪切带 + 变形特征　； 参考：《中国地质大学(北京)》2017年硕士论文

【摘要】：苏鲁造山带作为印支期华北与扬子板块碰撞的产物,形成以来经历了多期构造事件,其演化过程一直以来都是研究热点。位于其西北缘的皇华-铁镢山地区构造变形较为强烈并发育韧性剪切带,由于韧性剪切带与造山过程有着非常密切的联系,所以对韧性剪切带变形特征及年代学的研究有利于加深对苏鲁造山带构造演化的认识。本文通过详细地野外调查和显微构造特征研究,对剪切带几何学和运动学进行了分析。结果显示,研究区韧性剪切带呈北东东向展布,几何学形态表现为背形,并经历了两期韧性变形作用:(1)早期韧性变形是在区域挤压应力下,由SEE向NWW近水平的滑脱作用造成;(2)晚期韧性变形是在区域伸展应力下,由NNW-SSE的伸展滑覆作用造成。结合显微镜下矿物变形特点并依据定向样品中石英c轴组构EBSD图像,对两期韧性变形温度进行限定。结果显示:(1)早期韧性变形发生在低角闪岩相-高绿片岩相环境中,变质-变形温度在500℃~600℃之间,局部达到高角闪岩相,温度在600℃以上;(2)晚期韧性变形发生在低绿片岩相环境中,变质-变形温度在350℃~450℃之间。根据研究区岩浆作用及变形矿物的年龄,对两期韧性变形的时代进行限定。结果显示:(1)研究区出露较多伟晶岩脉或淡色脉体,变形特征显示其形成于早期剪切作用的晚期阶段,且LA-ICP-MS锆石U-Pb谐和年龄为150.1±1.1 Ma,表明早期韧性变形启动时间不晚于150 Ma。(2)晚期形成的白云母40Ar-39Ar坪年龄为137.09±0.32 Ma,与反等时线年龄一致,且侵入剪切带内无变形的岩体(闪长玢岩)的LA-ICP-MS锆石U-Pb谐和年龄分别为123.5±0.8 Ma和127.1±1.6 Ma,表明晚期韧性变形启动时间不晚于137 Ma,并结束于127 Ma之前。综合研究区内已有的研究成果,本次研究认为苏鲁造山带西北缘早期韧性变形应发生于陆内造山的晚期阶段,而晚期韧性变形发生于造山后的伸展阶段,两期构造活动反映了苏鲁造山带构造体制转换过程,该转换过程受制于晚中生代中国东部岩石圈的伸展减薄及太平洋板块的俯冲。
[Abstract]:The Sulu orogenic belt, as the product of the collision between North China and Yangtze plate in Indosinian period, has undergone many tectonic events since its formation, and its evolution process has always been a hot research topic. The tectonic deformation and ductile shear zone in the Huanghua-Tieshan area, located on the northwest margin of the region, are relatively strong. The ductile shear zone is closely related to the orogenic process, and the ductile shear zone is closely related to the orogenic process. Therefore, the study of deformation characteristics and geochronology of ductile shear zone is beneficial to further understanding the tectonic evolution of the Sulu orogenic belt. In this paper, the geometry and kinematics of shear zone are analyzed by detailed field investigation and microstructural study. The results show that the ductile shear zone in the study area is east-west distribution, geometry shape is back shape, and it has undergone two stages of ductile deformation: 1) the early ductile deformation is under regional compressive stress. The late ductile deformation caused by the near horizontal slippage of SEE to NWW is caused by the extension and slip of NNW-SSE under regional extensional stress. Combined with the characteristics of mineral deformation under microscope and according to the c-axis EBSD images of quartz in oriented samples, the two-stage ductile deformation temperature was limited. The results show that the early ductile deformation occurred in the environment of low amphibolite facies and high greenschist facies, and the metamorphic deformation temperature was between 500 鈩，

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