Ductile deformation within Upper Himalaya Crystalline Sequence and geological implications,in Nyalam area,Southern Tibet  

作　　者：LIU XiaoBing LIU XiaoHan LELOUP P.H. MAHEO G. PAQUETTE J.L. ZHANG XinGang ZHOU XueJun 

机构地区：[1]Key Laboratory,of Continental Collision and Plateau Uplift,Institute of Tibetan Plateau Research,Chinese Academy of Sciences,Beijing 100085,China [2]Laboratoire des sciences de la terre de Lyon,Terre,Planktes,Environement,CNRS UMR 5276,Universitd Lyonl-ENS Lyon,Villeurbanne,69622,France [3]Graduate University of Chinese Academy of Scienees,Beijing 100049,China [4]Laboratoire Magmas et Volcans,CNRS UMR 6524,Universite Blaise Pascal,Clermont-Ferrand,63038,France

出　　处：《Chinese Science Bulletin》2012年第26期3469-3481,共13页

基　　金：supported by Synthetic Investigation on the Environment in Polar Region (CHINARE2012-02-02);the SYSTER Program of the French INSU-CNRS

摘　　要：The South Tibet Detachment System(STDS) is a flat normal fault that separates the Upper Himalaya Crystalline Sequence(UHCS) below from the Tethyan Sedimentary Sequence(TSS) above.Timing of deformations related to the STDS is critical to understand the mechanism and evolution of the Himalaya collision zone.The Nyalam detachment(ND)(～86°E) locates in the middle portion of STDS(81°-89°E).Dating of deformed leucocratic dykes that are most probably syntectonic at different depth beneath the ND,allow us to constrain the timing of deformation.(1) Dyke T11N37 located ～3500 m structurally below the ND emplaced at 27.4± 0.2 Ma;(2) Dyke T11N32 located ～1400 m structurally below the ND emplaced at 22.0±0.3 Ma;(3) T11N25 located within the top to the north STD shear zone,～150 m structurally below the ND,emplaced at 17.1±0.2 Ma.Combining ND footwall cooling history and T11N25 deformation temperature,we indicate a probable onset of top to the north deformation at ～16 Ma at this location.These results show an upward younging of the probable timing of onset of the deformation at different structural distance below the ND.We then propose a new model for deformation migration below the ND with deformation starting by pure shear deformation at depth prior to ～27.5 Ma that migrates upward at a rate of ～ 0.3 mm/a until ～18 Ma when deformation switches to top to the north shearing in the South Tibet Detachment shear zone(STDsz).As deformation on the ND stops at 14-13 Ma this would imply that significant top to the North motion would be limited to less than 5 Ma and would jeopardize the importance of lower channel flow.The South Tibet Detachment System （STDS） is a flat normal fault that separates the Upper Himalaya Crystalline Sequence （UHCS） below from the Tethyan Sedimentary Sequence （TSS） above. Timing of deformations related to the STDS is critical to understand the mechanism and evolution of the Himalaya collision zone. The Nyalam detachment （ND） （-86E） locates in the middle portion of STDS （8 l ^-89~E）. Dating of deformed leucocratic dykes that are most probably syntectonic at different depth beneath the ND, allow us to constrain the timing of deformation. （1） Dyke T11N37 located -3500 m structurally below the ND emplaced at 27.4-＋ 0.2 Ma; （2） Dyke T1 lN32 located -1400 m structurally below the ND emplaced at 22.0-＋0.3 Ma; （3） TI 1N25 located within the top to the north STD shear zone, -150 m structurally below the ND, emplaced at 17.1-＋0.2 Ma. Combining ND footwall cooling history and T11 N25 deformation temperature, we indicate a probable onset of top to the north deformation at -16 Ma at this loca- tion. These results show an upward younging of the probable timing of onset of the deformation at different structural distance below the ND. We then propose a new model for deformation migration below the ND with deformation starting by pure shear deformation at depth prior to -27.5 Ma that migrates upward at a rate of - 0.3 mm/a until -18 Ma when deformation switches to top to the north shearing in the South Tibet Detachment shear zone （STDsz）. As deformation on the ND stops at 14-13 Ma this would imply that significant top to the North motion would be limited to less than 5 Ma and would jeopardize the importance of lower channel flow.

关 键 词：喜马拉雅碰撞带 塑性变形 聂拉木地区 西藏南部 地质意义 序列 结晶 藏南拆离系 

分 类 号：P542[天文地球—构造地质学]