喜马拉雅造山带中段定结地区拆离断层

定结地区位于喜马拉雅造山带中段,发育大量的低角度伸展拆离断层,这些拆离断层中部分构成了藏南拆离系的主体。它们基本上垂直于造山带走向伸展,各拆离断层特征显著,普遍发育糜棱岩,糜棱岩类型复杂,主要有硅质糜棱岩、长英质糜棱岩、花岗质糜棱岩。在研究区的北部,拆离断层呈环状产出,构成变质核杂岩三层结构中的中间层,规模一般较大;同时拆离断层使变质核杂岩体盖层中的部分地层拆离减薄;在研究区南部拆离断层呈线状延伸很远,总体上平行造山带延伸,构成了藏南拆离系重要组成部分。部分拆离断层同韧性剪切带平行产出,形成拆离剪切的脆韧性体系。

DETACHMENT FAULTS IN DINGJIE AREA, MIDDLE SEGMENT OF HIMALAYAN OROGENIC BELT

Dingjie lies in the middle section of Himalayan orogen. In Dingjie area, there formed a lot of low angle extensional detachment faults,Some of these detachment faults are the main body of the south Tibet detachment system. On the whole, all the detachment faults extend vertically to the orogenic belt's strike. Every detachment fault has its own special characters. Mylonites, which have complex styles, are formed widely in the detachment faults. As a whole,detachment faults can be classified into three developing sections. North of the studied area, detachment faults crop out in a ring shape and form the middle layer of metamorphic core complex, all these detachment faults have a large scale. South of the studied area, detachment faults occur in a linear shape and parallel to the orogenic belt. What's more, the detachment faults cropped out in southwest parallel to the ductile shear belt. They have a stable attitude and have two developing periods. One is the stage with hanging wall of ZεR Group strata and the other stage with hanging wall of the Jiachun Group. In east south,the detachment faults have a stable near southeastern strike and some of local sections of these detachment faults are distorted by the late faults and folds.