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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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摘要

The Annapurna Detachment (AD) is a low-angle (20°–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 marble–calc-silicates of the Greater Himalayan Sequence (GHS) below from unmetamorphosed Palaeozoic–Mesozoic sedimentary rocks of the Tethyan sedimentary zone above. It was active at ca. 22–18 Ma during south-vergent ductile extrusion (channel flow) and exhumation of the Himalayan mid-crust footwall. Restoration of the STD system suggests around 80–100 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 Nilgiri–Tukuche peaks were enhanced by backsliding during footwall extrusion, although this does not indicate "orogenic collapse," 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：安纳布尔纳峰分离带（AD）是低角度（20°–30° dip），北倾法向断层和钙镁铁矿中的韧性高应变剪切 带。 ，并且是沿着喜马拉雅山1800公里长的南藏族 分离队（STD）的一部分。 AD将蓝晶石和硅线石级片麻岩以及 未变质的 古生代-中生代的特提斯沉积岩 > 区域。它活跃于约。在南缘 延性挤压（通道流）和喜马拉雅山中地壳下盘掘出期间为22-18 Ma。 STD系统的恢复表明，相对于特提斯垂壁岩壁， 向南挤出约80–100 km的底盘片麻岩 。在正常断层之前，AD的悬挂 壁中形成褶皱，但轴向 平面弯曲成与剪切带对齐，表明 挤压被动 屋顶断层之下的变质底盘岩。 Nilgiri–Tukuche 峰的北向斜躺倒转在下盘挤压过程中通过向后滑动而得到增强， 尽管这并不表示“造山塌陷”，但降低了 地表高度升高或地壳厚度减小，因为 新材料不断从南方向下推进。 反折的轴向平面弯曲并逐渐旋转 从北部的垂直下方到 AD上方的水平以下。喜马拉雅山的低角度正断层在中新世早期活跃，并伴随着沿主中央冲断带（MCT）带的更深层 构造层推力。 / sup>在 内部分熔融和韧性流动的辅助下，低角度启动了被动法向断裂和韧性剪切带。它们不表示扩展 和压缩的交替周期，而是在完全压缩的环境中处于活动状态。 大喜马拉雅山和被动 低角度正断层的屋顶断层模型 充分解释了所有地质领域的构造和变质判据。

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  • 来源
    《Geosphere》 |2010年第4期|296-315|共20页
  • 作者

    Michael P. Searle;

  • 作者单位

    Department of Earth Sciences, Oxford University, Parks Road, Oxford OX1 3PR, UK;

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