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首页> 外文期刊>Journal of Asian earth sciences >The Chako antiform: A folded segment of the Greater Himalayan sequence, Nar valley, Central Nepal Himalaya
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The Chako antiform: A folded segment of the Greater Himalayan sequence, Nar valley, Central Nepal Himalaya

机译：查科反形：尼泊尔中部喜马拉雅山纳尔谷大喜马拉雅层序的折叠部分

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摘要

Recent and previously published mapping in the Nar valley, north of the Annapurna massif in central Nepal, recognised an enigmatic metamorphic culmination of the Greater Himalayan sequence, surrounded by rocks correlated with the Tethyan sedimentary sequence. The map area is re-interpreted as two structural levels within the Greater Himalayan sequence. The Lower Level is correlated to the well-studied Greater Himalayan sequence of the Annapurna region, based on characteristic rock types, high-strain zones with south-verging shear-sense indicators, and high-grade metamorphism. The rocks of the Upper Level, previously mapped as the sub-greenschist or zeolite facies Tethyan sedimentary sequence, are garnet-bearing schists. Petrography and garnet-biotite thermometry suggest the Upper Level equilibrated at amphibolite facies (500-650 ℃). These results support the recent contention that the Upper Level rocks are a component of the Greater Himalayan sequence, and thus indicate that components of the Himalayan metamorphic core vary considerably along strike. Structural, metamorphic and age constraints are integrated into a cohesive regional tectonometamorphic model. The Lower and Upper Levels both experienced D, deformation and peak metamorphism before ～ 20 Ma. The Lower and Upper Levels were juxtaposed along the synmetamorphic Chame detachment after 20 Ma during retrograde metamorphism. After ～ 19 Ma, the Phu detachment placed the unmetamorphosed Tethyan sedimentary sequence above the Lower and Upper Levels. The entire package was then subsequently folded, after 19 Ma, by a non-cylindrical antiform-synform pair with a ～ 25 km wavelength creating an apparent dome. The proposed tectonometamorphic model reconciles previously contradictory interpretations of the transition between metamorphic core and overlying sediments in the Nar valley.
机译：在尼泊尔中部安纳布尔纳峰地块以北的纳尔河谷，最近和以前发表的地图显示出大喜马拉雅层序的神秘变质顶点，周围是与特提斯沉积层序相关的岩石。地图区域被重新解释为大喜马拉雅序列中的两个结构层。较低的水平与安纳布尔纳峰地区经过充分研究的大喜马拉雅层序相关，这取决于特征性的岩石类型，具有南向切变指示的高应变区和高品位变质作用。上层的岩石，以前被映射为特绿岩沉积的次绿片岩或沸石相，是带石榴石的片岩。岩石学和石榴石-黑云母的测温表明在闪石岩相（500-650℃）时，其上层平衡。这些结果支持了最近的论点，即上层岩石是大喜马拉雅层序的一个组成部分，因此表明喜马拉雅变质岩心的组成沿走向变化很大。结构，变质和年龄约束被整合到一个内聚的区域构造变型模型中。在〜20 Ma之前，下层和上层都经历了D，变形和峰值变质作用。在逆行变质作用20 Ma后，沿同形变质Chame脱离将上下两层并列。 〜19 Ma之后，Phu支队将未变质的特提斯沉积序列置于上下两层以上。然后在19 Ma之后，将整个包装用波长约25 km的非圆柱形反型-同型对折叠，形成一个明显的圆顶。拟议的构造变态模型调和了纳尔河谷中变质岩心与上覆沉积物之间过渡的先前矛盾解释。

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