滇西澜沧江构造带中段新生代多期构造变形特征及时代约束

Cenozoic polyphase structural deformation characterization in the middle segment of the Lancang tectonic zone, western Yunnan, and its geochronological constraints

澜沧江构造带是青藏高原东南缘保山-羌塘地块与兰坪-思茅地块之间的大型走滑剪切带。构造地质学、岩石学和40Ar-39Ar年代学研究结果表明构造带中段剪切带内部存在早期斜向挤出和晚期水平走滑的两期线理及早期指示右行韧性剪切变形、后期指示左行脆韧性剪切变形的构造指向。糜棱岩中石英晶格优选方位以中温（450~600℃）柱面轴底面滑移系为主,叠加中低温（300~550℃）底面轴滑移系;剪切带内云母片岩和花岗质糜棱岩中黑云母40Ar-39Ar坪年龄和等时线年龄都分布于15~17Ma,反映剪切带隆升过程中脆韧性左行剪切变形阶段的时代。结合前人成果进行分析认为新生代早期保山地块和兰坪-思茅地块向南南东挤出的同时沿澜沧江构造带中段发生大规模右行斜向走滑韧性剪切作用,后期保山地块南部沿北东向畹町和南汀河左行断裂带相对中北段向北东运动,致使隆升到中上构造层次的韧性剪切带发生左行脆韧性变形。

The Lancang tectonic zone is a large strike-slip shearing zone in the southeastern Tibet,which is the boundary between the Lanping-Simao block in the east and the Baoshan-Qiangtang block in the west. There are early oblique stretching lineations with fabrics showing dextral ductile deformation and late horizontal stretching lineations with fabrics showing sinistral brittle-ductile deformation in the middle segment of the Lancang tectonic zone. C-axis LPO patterns of quartz indicate the principal slip systems is prism a slip in medium temperature（ 450 ~ 600℃） relating with dextral ductile deformation,and superimposed by basal a slip in low temperature（ 300 ~ 550℃） relating with sinistral brittle-ductile deformation. The biotite40Ar-39 Ar dating is ranging from15 Ma to 17 Ma,which represent the change age from dextral ductile to sinistral brittle-ductile deformation according to the closure temperature of the biotite,that is the same as the temperature of the sinistral brittle-ductile deformation. The early dextral oblique strike-slip shearing was related with the extrusion of the Lanping-Simiao block during the Early Miocene,and the sinistral horizontal brittle-ductile deformation was formed by the shearing of the southern part of the Baoshan block toward NEE along the NE Nandinghe and Wanding sinistral slip faults during exhumation of the ductile shear zone.