The giant Shakhdara migmatitic gneiss dome, Pamir, India‐Asia collision zone: 1. Geometry and kinematics
The giant Shakhdara migmatitic gneiss dome, Pamir, India‐Asia collision zone: 1. Geometry and kinematics
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DOI：
10.1002/tect.20057
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发表时间：
2013-07
期刊：
影响因子：
4.2
通讯作者：
K. Stübner;L. Ratschbacher;D. Rutte;K. Stanek;V. Minaev;M. Wiesinger;R. Gloaguen
中科院分区：
文献类型：
--
作者：
K. Stübner;L. Ratschbacher;D. Rutte;K. Stanek;V. Minaev;M. Wiesinger;R. Gloaguen
新生代片麻岩穹丘占帕米尔地表暴露面积的三分之一，为了解印度-亚洲碰撞的地壳深部过程提供了一个窗口。其中最大的是帕米尔西南部、塔吉克斯坦和阿富汗的双重聚散复合沙赫达拉-阿利丘尔圆顶;它们被低应变地垒隔开。南帕米尔剪切带顶部至南偏东方向的非共轴普适流在约250 × 80 km的Shakhdara穹丘中从30-40 km深度挖出地壳;顶部至北北东方向的Alichur剪切带在约125 × 25 km的Alichur穹丘中暴露出上地壳岩石。冈特剪切带的边界在北部的Shakhdara圆顶和记录交替的正常剪切和右旋平移，它有助于小批量折返。下盘折返沿着两个低角度、正向构造导致了长达90 km的同造山期~ N-S伸展。帕米尔西南部的伸展作用与穹隆北部褶皱冲断带的缩短作用相反，特别是在塔吉克凹陷，那里的奥陶质滑脱作用促进了上地壳的缩短。帕米尔高原边缘的重力塌陷推动了帕米尔西南部核杂岩的形成，并缩短了与高原相邻的软弱前陆。总的来说，这种几何形状定义了一个“垂直挤压”的场景，包括正面和基底的下冲和增厚，以及悬挂重力驱动的正常剪切。与喜马拉雅垂直挤压情景相反，帕米尔的侵蚀较小，保留了大部分挤压的深部地壳，包括整个圆顶最高海拔的南帕米尔剪切带顶部。
Cenozoic gneiss domes comprise one third of the surface exposure of the Pamir and provide a window into the deep crustal processes of the India‐Asia collision. The largest of these are the doubly vergent, composite Shakhdara‐Alichur domes of the southwestern Pamir, Tajikistan, and Afghanistan; they are separated by a low‐strain horst. Top‐to‐SSE, noncoaxial pervasive flow over the up to 4 km thick South Pamir shear zone exhumed crust from 30–40 km depth in the ~250 × 80 km Shakhdara dome; the top‐to‐NNE Alichur shear zone exposed upper crustal rocks in the ~125 × 25 km Alichur dome. The Gunt shear zone bounds the Shakhdara dome in the north and records alternations of normal shear and dextral transpression; it contributed little to bulk exhumation. Footwall exhumation along two low‐angle, normal‐sense detachments resulted in up to 90 km syn‐orogenic ~N‐S extension. Extension in the southwestern Pamir opposes shortening in a fold‐thrust belt north of the domes and in particular in the Tajik depression, where an evaporitic décollement facilitated upper crustal shortening. Gravitational collapse of the Pamir‐plateau margin drove core‐complex formation in the southwestern Pamir and shortening of the weak foreland adjacent to the plateau. Overall, this geometry defines a “vertical extrusion” scenario, comprising frontal and basal underthrusting and thickening, and hanging gravitationally driven normal shear. In contrast to the Himalayan vertical extrusion scenario, erosion in the Pamir was minor, preserving most of the extruded deep crust, including the top of the South Pamir shear zone at peak elevations throughout the dome.