西藏仲巴地体北缘构造变形分析及地质意义

Structural deformation analysis of the northern margin of Zhongba terrane,Tibet and its geological significance

西藏仲巴地体是雅鲁藏布江缝合带西段南北蛇绿岩带之间的重要地质单元。在野外地质调查基础上,采用构造分析方法确定仲巴地体北缘构造变形特征,并对其俯冲构造演化进行探讨。研究结果表明:仲巴地体北缘主体变形层次为中-浅构造层次,主导变形作用是压扁作用,代表性构造是相似褶皱、顶厚褶皱与高角度逆断层,反映出仲巴地体在向北拼合过程中以强烈的向北俯冲作用为特征,形成了与之相关的逆冲型构造组合;通过与雅鲁藏布江缝合带北亚带及仲巴地体南缘的构造变形对比分析,从构造变形的角度证明了仲巴地体的构造属性与喜马拉雅地块更具亲缘性。初步建立了北亚带特提斯洋盆在俯冲消减阶段的构造演化模型。

The Zhongba terrane in Tibet is an important geological unit between the north-south ophiolite belt in the western section of the Yarlung Zangbo Suture Zone(YZSZ).In this study,based on the geological field investigation,structural feature of the northern margin of Zhongba terrane is determined with structural analysis method.The tectonic evolution of this terrane is discussed as well.The study result shows that the typical structures are similar folds,top thick folds and high-angle reverse faults,corresponding to the shallow-middle deformation level and compressing and flattening deformation.It is suggested that southward thrust structural combination in the northern margin of the Zhongba terrane is formed during intense northward subduction.Generally,through the comparative analysis of the tectonic deformation with the YZSZ North Subzone and the southern margin of the Zhongba terrane,it is proved from the perspective of tectonic deformation that the tectonic attribution of the Zhongba terrane is more related to the Himalayan terrane.The tectonic evolution model of the Tethys Ocean basin in the North Subzone during subduction and downthrusting process is preliminarily established.