The Upper Mustang region of west-central Nepal contains exposures of metamorphosed Tethyan Sedimentary Sequence rocks that have been interpreted to reflect either contact metamorphism related to the nearby Mugu pluton or regional metamorphism associated with the North Himalayan domes. New monazite geochronology results show that the Mugu leucogranite crystallized at c. 21.3 Ma, while the dominant monazite age peaks from the surrounding garnet ± staurolite ± sillimanite schists range between c. 21.7 and 19.4 Ma, generally decreasing in age away from the pluton. Metamorphic temperature estimates based on Ti-in-biotite and garnet–biotite thermometry are highest in the specimens closest to the pluton (648 ± 24°C and 615 ± 25°C, respectively) and lowest in those furthest away (578 ± 24°C and 563 ± 25°C, respectively), while pressure estimates are all within uncertainty of one another, averaging 5.0 ± 0.5 kbar. These results are interpreted to be consistent with contact metamorphism of the rocks in proximity to the Mugu pluton, which was emplaced at c. 18 ± 2 km depth after local movement across the South Tibetan detachment system had ceased. While this new dataset helps to characterize the metamorphic rocks of the Tethyan Sedimentary Sequence and provides new constraints on the thickness of the upper crust, it also emphasizes the importance of careful integration of metamorphic conditions and inferred processes that may affect interpretation of currently proposed Himalayan models.

中文翻译：

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尼泊尔中西部上木斯塘地区特提斯沉积层序的接触变质作用

尼泊尔中西部的上木斯塘地区暴露了变质的特提斯沉积层序岩石，这些岩石被解释为反映与附近的穆古岩体相关的接触变质作用或与北喜马拉雅圆顶相关的区域变质作用。新的独居石年代学结果表明，木固淡色花岗岩在C。21.3 Ma，而周围石榴石±十字石±硅线石片岩的主要独居石年龄峰介于C。21.7 和 19.4 Ma，远离岩体的年龄普遍递减。基于黑云母中钛和石榴石-黑云母测温法的变质温度估计在最靠近岩体的样本中最高（分别为 648 ± 24°C 和 615 ± 25°C），在最远的样本中最低（578 ± 24° C 和 563 ± 25°C），而压力估计值都在彼此不确定的范围内，平均为 5.0 ± 0.5 kbar。这些结果被解释为与穆古岩体附近岩石的接触变质作用一致，该岩体位于C。穿越藏南支队系统的局部运动停止后，深度为 18 ± 2 公里。虽然这个新数据集有助于表征特提斯沉积层序的变质岩，并为上地壳的厚度提供了新的限制条件，但它也强调了仔细整合可能影响当前提出的喜马拉雅模型解释的变质条件和推断过程的重要性.