Ductile deformation within Upper Himalaya Crystalline Sequence and geological implications, in Nyalam area, Southern Tibet
Ductile deformation within Upper Himalaya Crystalline Sequence and geological implications, in Nyalam area, Southern Tibet
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DOI：
10.1007/s11434-012-5228-6
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发表时间：
2012-05
影响因子：
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通讯作者：
Xiaobing Liu;Xiaohan Liu;P. Leloup;G. Mahéo;J. Paquette;Xingang Zhang;XueJun Zhou
中科院分区：
文献类型：
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作者：
Xiaobing Liu;Xiaohan Liu;P. Leloup;G. Mahéo;J. Paquette;Xingang Zhang;XueJun Zhou
与STDS相关的变形时间对于理解喜马拉雅碰撞带的演化机制至关重要。Nyalam分离（ND）（~ 86°E）位于STDS中部（81°-89°E）。对变形的白垩质岩脉进行测年，使我们能够确定变形的时间，这些岩脉很可能是在ND之下不同深度的同构造岩脉。(1) T11N37堤防位于ND下方~ 3500 m处，位置为27.4±0.2 Ma；(2) T11N32堤位于ND下方约1400 m处，位置为22.0±0.3 Ma；(3) T11N25位于STD剪切带顶部偏北，结构上位于ND下方约150 m，位置为17.1±0.2 Ma。结合ND下盘冷却历史和T11N25变形温度，我们认为该位置可能在~ 16 Ma发生顶部向北变形。这些结果表明，在ND以下不同的构造距离上，变形的可能开始时间向上年轻化。然后，我们提出了ND以下变形迁移的新模型，其中变形始于深度为~ 27.5 Ma之前的纯剪切变形，以~ 0的速率向上迁移。由于ND上的变形停止在14-13 Ma，这意味着显著的顶部向北运动将被限制在小于5 Ma，并将危及下游通道流动的重要性。
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.