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首页> 外文期刊>Geosphere >Low-angle normal faults in the compressional Himalayan orogen; Evidence from the Annapurna–Dhaulagiri Himalaya, Nepal
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Low-angle normal faults in the compressional Himalayan orogen; Evidence from the Annapurna–Dhaulagiri Himalaya, Nepal

机译：喜马拉雅造山带低角度正断层;来自尼泊尔安纳布尔纳峰-道拉吉里喜马拉雅山的证据

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The Annapurna Detachment (AD) is a low-angle (a??20?°a€“30?° dip), north-dipping normal fault and ductile high-strain shear zone in calc-mylonites, and forms part of the South Tibetan Detachment (STD) that runs along 1800 km length of the Himalaya. The AD separates kyanite and sillimanite grade gneisses and tremolite + clinopyroxene ?± hornblende-bearing marblea€“calc-silicates of the Greater Himalayan Sequence (GHS) below from unmetamorphosed Palaeozoica€“Mesozoic sedimentary rocks of the Tethyan sedimentary zone above. It was active at ca. 22a€“18 Ma during south-vergent ductile extrusion (channel flow) and exhumation of the Himalayan mid-crust footwall. Restoration of the STD system suggests around 80a€“100 km of southward extrusion of the footwall gneisses relative to the Tethyan hanging-wall rocks. Folds in the hanging wall of the AD were formed prior to normal faulting, but axial planes are curved into alignment with the shear zone suggesting extrusion of the metamorphic footwall rocks beneath a passive roof fault. North-vergent recumbent backfolds in the Nilgiria€“Tukuche peaks were enhanced by backsliding during footwall extrusion, although this does not indicate a€?orogenic collapse,a€? lowering of surface elevation, or decreasing crustal thickness because new material was continually being underthrust from the south. Axial planes of backfolds are curved and progressively rotate from subvertical in the north to subhorizontal immediately above the AD. Low-angle normal faults in the Himalaya were active during the Early Miocene, concomitantly with thrusting at deeper structural levels along the Main Central Thrust (MCT) zone. The passive normal faults and ductile shear zone were initiated at low angles aided by partial melting and ductile flow within the GHS. They do not indicate alternating periods of extension and compression but were active in a wholly compressional environment. The Channel Flow model for the Greater Himalaya and the passive roof fault model for the low-angle normal faults adequately explain all geological field structural and metamorphic criteria.
机译：Annapurna支队（AD）是低角度（倾角20°？a？30°？），在钙镁长石中呈北倾正断层和延性高应变剪切带，是南部的一部分。西藏支队（STD）沿喜马拉雅山全长1800公里。 AD将下面的蓝晶石和硅线石级片麻岩和透闪石+斜辉石？含角闪石的大喜马拉雅层序（GHS）硅酸盐与上面特提斯沉积带的未变质古生界“中生代沉积岩”分开。它活跃于约。朝南的韧性延展挤压（河道水流）和喜马拉雅中地壳下盘的掘出过程中的时间为22a-18 Ma。 STD系统的恢复表明，相对于特提斯垂壁岩体，底盘片麻岩向南挤压约80至100公里。 AD悬挂壁中的褶皱是在正常断层之前形成的，但是轴向平面弯曲成与剪切带对齐，这表明变质的下盘壁岩石在被动屋顶断层之下被挤出。 Nilgiria的北缘斜背褶皱：“ Tukuche峰在下盘挤压过程中通过向后滑动而增强，尽管这并不表示造山作用塌陷”。降低表面海拔高度，或降低地壳厚度，因为新材料不断从南方向下推进。折返的轴向平面是弯曲的，并逐渐从北部的垂直以下旋转到AD上方的水平以下。在中新世早期，喜马拉雅山的低角度正断层活动，同时伴随着沿主中央冲断带（MCT）带更深的构造水平的逆冲作用。 GHS内部分熔融和延性流辅助低角度启动了被动法向断层和延性剪切带。它们不表示拉伸和压缩的交替周期，而是在完全压缩的环境中起作用。大喜马拉雅山的通道流模型和低角度正断层的被动顶板断层模型充分解释了所有地质领域的构造和变质标准。

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