今天是2018年12月18日

辽东鞍山齐大山韧性剪切带运动学解析及形成机制

DOI:10.3799/dqkx.2017.137

作者:刘昕悦,李婧,刘永江,李伟民,温泉波,梁琛岳,常瑞虹

联系地址:吉林大学地球科学学院,吉林长春 130061

摘要:关于太古宙早期地壳演化构造机制的争论已经持续了数十年,其焦点主要集中于水平构造还是垂向构造两大经典构造模式的探讨.对于早期地壳构造演化方面的研究,将会有助于我们更好地理解早前寒武纪的地球动力学机制.本文对华北克拉通东北部鞍山地区花岗-绿岩带内齐大山韧性剪切带的构造变形特征进行了详细的解析,揭示了该区新太古代垂向构造作用样式.研究结果表明,齐大山韧性剪切带内花岗质岩石长英质矿物塑性拉长特征明显,条带状构造发育,面理向NWW方向陡倾,不对称组构特征和矿物拉伸线理产状指示向NWW的陡倾正滑移剪切作用.变形岩石中的长英质矿物均发育中低温显微变形特征,石英C轴电子背散射衍射(EBSD)组构分析揭示石英以菱面<a>和底面<a>滑移系为主,岩石经历了中低温非共轴变形.根据矿物的变形行为以及石英的结晶优选方位推测变形温度约为400~500℃,岩石变形特征以位错蠕变为主.有限应变分析结果表明,靠近铁矿带方向,构造岩类型由L=S构造岩过渡为LS构造岩,岩石应变强度呈明显增强趋势.运动学涡度测量结果显示齐大山韧性剪切带内大多数岩石样品的Wk值大于0.75,岩石形成于以简单剪切作用为主的一般剪切作用.对比花岗-绿岩带西侧的白家坟韧性剪切带,显示二者均具有相向的陡倾正滑移运动学特征,表明新太古代时期鞍山地区地壳构造演化模式以垂向构造作用为主.

关键字:韧性剪切带;太古宙片麻岩;组构分析;拗沉作用;垂向构造作用;华北克拉通;构造.

Kinematics Analysis and Formation Mechanism of Qidashan Ductile Shear Zone, Eastern Anshan, Liaoning Province, NE China

Author:Liu Xinyue, Li Jing, Liu Yongjiang, Li Weimin, Wen Quanbo, Liang Chenyue, Chang Ruihong

Author Address:College of Earth Sciences, Jilin University, Changchun 130061, China

Abstract:The controversy over the Archean tectonic regimes has lasted several decades focused on the horizontal and vertical tectonics, the two classical tectonic models for Archean.Thus, more studies of the early crustal tectonic evolution are requisite for better understanding geodynamic regimes in the early Precambrian. In this study, detailed structural analysis of Qidashan down-slip ductile shear zones which developed in the eastern Anshan area was carried out and an example for revealing Neoarchean vertical tectonics is provided. The ribbon structures formed by intensely elongated felsic minerals are widespread in the deformed gneisses. The quartz C-axis fabric patterns obtained by electron backscatter diffraction technique imply low to middle temperature noncoaxial deformation with active rhomb <a> slip and basal <a> slip. Deformation behaviors of minerals and quartz crystallographic preferred orientations demonstrate that the rocks underwent mylonitization at a temperature of 400-500℃ under greenschist facies metamorphic conditions. Dislocation creep is the main rock deformation mechanism within the shear zones. Finite strain measurement results suggest that toward the iron ore belt, the tectonites change from L=S to LS-type and the strain intensity exhibits an enhanced trend across the shear zones. Kinematic vorticity values (>0.75) indicate that the deformed rocks in ductile shear zones were produced by steady-state simple-shear dominated general shear. Compared to the Baijiafen ductile shear zone to the west, the Qidashan and Baijiafen ductile shear zones both have mutually down-slip kinematic characteristics, indicating that the Neoarchean crust growth and tectonic evolution in Anshan area is dominated by vertical tectonics.

Keyword:ductile shear zone; Archean gneiss; fabric analysis; sag duction; vertical tectonic; North China craton; tectonics.

 

【点击数:395【下载数:426】【PDF预览】


作者简介:刘昕悦(1990-),男,博士研究生,构造地质学专业.ORCID: 0000-0002-0407-5152. E-mail: 1525023015@qq.com

参考文献