We present structural analysis and zircon and monazite geochronology of the Greater Himalayan Sequence (GHS) in the Kali Gandaki valley, central Nepal. Although the foliation is moderately NE-dipping, the upper GHS shows a top-to-WNW shear sense, whereas the lower GHS developed top-to-SW ductile shear zones. Quartz fabrics from mylonitic gneisses indicate deformation temperature from >650°C to ~450°C. Monazite from the GHS recorded anatexis at “near peak” conditions from ~43 to 28 Ma and exhumation near the sillimanite-kyanite transition at 25–21 Ma. Ages of zircon rims constrain the onset of exhumation. From the upper GHS to the Main Central Thrust zone, pervasive deformation and anticlockwise rotation of the lineation from the orogen-parallel to orogen-perpendicular direction suggest exhumation of the GHS by general shear from ~31 to 21 Ma. A two-stage exhumation model is proposed to explain the diffuse strain distribution and anatexis during early crustal thickening.

中文翻译：

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尼泊尔中部大喜马拉雅层序中始新世-渐新世的断层和发掘

我们展示了尼泊尔中部 Kali Gandaki 山谷的大喜马拉雅层序 (GHS) 的结构分析以及锆石和独居石年代学。尽管叶理是适度的 NE 倾斜，但上部 GHS 显示出从顶部到 WNW 的剪切感，而下部 GHS 则形成了从顶部到 SW 的韧性剪切带。糜棱片麻岩的石英织物表明变形温度从 >650°C 到 ~450°C。来自 GHS 的独居石在约 43 至 28 Ma 的“接近峰值”条件下记录了精沸石，并在 25-21 Ma 时在硅线石-蓝晶石转变附近折返。锆石边缘的年龄限制了挖掘的开始。从上 GHS 到主中央冲断带，从平行于造山带到垂直于造山带方向的线状结构的普遍变形和逆时针旋转表明 GHS 在大约 31 到 21 Ma 的一般剪切作用下剥露。