西秦岭天水地区新阳—元龙韧性剪切带构造变形特征及其地质意义

doi:10.12029/gc20150104

首页 > 过刊浏览>2015年第42卷第1期 >51-70. DOI:10.12029/gc20150104

西秦岭天水地区新阳—元龙韧性剪切带构造变形特征及其地质意义
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                        10.12029/gc20150104
                    
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基金项目:国家自然科学基金项目(41172186、40972136、41472191)、教育部高等学校博士学科点专项科研基金项目（20110205110004）、中央高校基本科研业务费专项资金项目（CHD2011TD020，2013G1271091，2013G1271092）联合资助。

Structural deformation of Xinyang-Yuanlong ductile shear zone in Tianshui area，Western Qinling Mountains，and its geological significance

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提要：西秦岭北缘新阳—元龙韧性剪切带作为西秦岭造山带与北祁连造山带之间的区域韧性构造边界，带内构造样式复杂多样，多期构造叠加，不同部位韧性变形强度不同，兼具左行、右行剪切特征，但以右行为主，宏观构造显示由NNE向SSW斜向逆冲特征，且多被后期构造改造。EBSD组构分析结果显示，石英C轴优选方位指示非共轴变形，显示明显的中温柱面-中低温菱面-低温底面组构的右行剪切及不太明显的低温底面组构（偶见中低温组构）左行剪切特征；方解石C轴组构显示e1双晶滑移与r1平移滑动，兼具左行、右行剪切特征。组构特征反映该剪切带可能经历了中温—中低温—低温、以右行韧性走滑为主并曾出现过左行逆冲的复杂变形过程，综合分析推断该韧性剪切带经历了低绿片岩相—高绿片岩相—低角闪岩相韧性变形环境。区域对比分析认为，新阳—元龙韧性剪切带响应古生代构造演化的构造变形记录主要为2期：一是志留纪天水—武山洋闭合导致大规模NNE-SSW向的陆-弧或陆-陆碰撞逆冲造成的左行逆冲剪切变形；二是晚泥盆世—早石炭世秦祁结合部位强烈的大规模右行走滑拼贴运动形成的右行剪切变形和反“S”构造样式。

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Abstract：The Xinyang-Yuanlong ductile shear zone on the north margin of Western Qinling Mountains is the main ductile tectonic boundary which separates the Western Qinling orogenic belt from the Northern Qilian orogenic belt．The deformation style in the ductile shear zone is complex and diverse, with multiphase structural superposition，and deformation varies in intensity in different parts．From the macro- and micro-structure，it is revealed that the deformation has both sinistral and dextral shear，but the major part of the deformation is right-handed．Macro-structure shows characteristics of oblique thrust from NNE to SSW; nevertheless, the structure is mainly reformed and superposed．According to EBSD fabric analysis, LPOs of quartz indicate non-coaxial deformation and reveal that the quartz grains displaying dextral shear are apparently characterized by medium-temperature prismatic fabric ，low-medium temperature rhombohedral fabric，and low-temperature basal fabric．The quartz grains displaying sinistral shear are indistinctly characterized by low-temperature basal fabric（occasionally medium-temperature prismatic fabric）；LPOs of calcite show that the grains are dominated by e1 twinning glide and r1 translation glide，and reveal both sinistral and dextral shear characteristics．All these data indicate that the shear zone probably experienced a complex deformation process from medium-temperature through low-medium temperature to low temperature，with the deformation environment from low greenschist facies through high greenschist facies to low amphibolite facies．The transformation of shear sense suggests that dextral strike-slip ductile shear is dominant，while sinistral thrusting shear is subordinate in the shear zone．According to regional comparative analysis，Xinyang-Yuanlong ductile shear zone has marked two main structural deformational records responding to the tectonic evolution in the Paleozoic: The early record is sinistral thrusting shear deformation that was the adjustment to the thrusting in a direction of NNE to SSW，caused by the continent-arc or continent-continent collision related to the closure of the Tianshui-Wushan Ocean in the Silurian；The later record is dextral shear deformation and the inversional S-type tectonic style caused by the intense dextral strike-slip at the conjunction of Qinling and Qilian orogen in the Late Devonian to Early Carboniferous period．

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魏博裴先治刘成军裴磊李瑞保李佐臣陈有炘胥晓春刘图杰王元元任厚州陈伟男. 西秦岭天水地区新阳—元龙韧性剪切带构造变形特征及其地质意义[J]. 中国地质, 2015, 42(1): 51-70.
WEI Bo, PEI Xian-zhi, LIU Cheng-jun, PEI Lei, LI Rui-bao, LI Zuo-chen, CHEN You-xin, XU Xiao-chun, LIU Tu-jie, WANG Yuan-yuan, REN Hou-zhou, CHEN Wei-nan. Structural deformation of Xinyang-Yuanlong ductile shear zone in Tianshui area，Western Qinling Mountains，and its geological significance[J]. Geology in China, 2015, 42(1): 51-70(in Chinese with English abstract).

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在线发布日期: 2015-02-02
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