Metamorphism of pelites from the Higher Himalayan Crystalline Sequence (HHCS) in the Dhauliganga valley, Garhwal Himalaya has been studied. Two structurally lower lithounits of the HHCS, namely the Joshimath and Pandukeshwar Formations, contain kyanite-grade mineral assemblages with no evidence of partial melting and yield values in the ranges of 7.8–10.3 kbar and 646–735 °C. The Badrinath Formation, which is the upper lithounit, shows partial melting and increase in conditions from 5.5 to 7.0 kbar and 712–724 °C (sillimanite–K-feldspar grade) in its lower part to 10.5–11.9 kbar and 790–801 °C (kyanite–K-feldspar grade) in the upper part. Corona texture of plagioclase around relict kyanite in the uppermost part of the Badrinath Formation indicates decompression following peak metamorphism. Based on the sharp change in T/depth ratio (geothermal gradient), and diachroneity in peak metamorphism and exhumation from available geochronological data, a metamorphic discontinuity known as the Badrinath Shear Zone (BSZ) is suggested between the lower and upper Badrinath Formation. The upper HHCS, which comprises the upper Badrinath Formation, was tectonically extruded and juxtaposed over the lower HHCS along the BSZ. Decreasing trend of conditions of peak metamorphism and younging of exhumation ages southward from the upper to lower HHCS are compatible with critical taper model for the exhumation of the HHCS.

中文翻译：

---

喜马拉雅加瓦尔喜马拉雅道里甘加山谷高喜马拉雅结晶层序的构造演化：来自变质作用和部分熔融的 P-T 条件的见解

对来自喜马拉雅加瓦尔喜马拉雅 Dhauliganga 山谷的高喜马拉雅晶体层序 (HHCS) 的泥岩的变质作用进行了研究。 HHCS 的两个结构较低的岩石单元，即 Joshimath 组和 Pandukeshwar 组，含有蓝晶石级矿物组合，没有部分熔融的证据，屈服值在 7.8–10.3 kbar 和 646–735 °C 范围内。 Badrinath 组是上部岩石单元，显示出部分熔融，其下部的温度从 5.5 至 7.0 kbar 和 712–724 °C（硅线石-钾长石品位）上升至 10.5–11.9 kbar 和 790–801 °C C（蓝晶石-钾长石品位）位于上部。巴德里纳特地层最上部残余蓝晶石周围的斜长石的日冕结构表明峰值变质作用后的减压作用。根据 T/深度比（地温梯度）的急剧变化，以及峰值变质作用和折返的历时性，根据现有的地质年代学数据，建议在下巴德里纳特组和上巴德里纳特组之间存在一个称为巴德里纳特剪切带（BSZ）的变质不连续性。上部 HHCS 包括上部 Badrinath 地层，在构造上挤压并沿 BSZ 并列于下部 HHCS 之上。从上层到下层HHCS向南，峰值变质条件和折返年龄年轻化的趋势与HHCS折返临界锥度模型相一致。