The collisional history between Greater India and the Eurasian plate has been well constrained by the study of exhumed Barrovian metamorphic sequence (BMS) rocks in the Himalayan Range. However, in the southeastern Tibetan Plateau, the collisional records have been obscured by intense, regional-scale strike-slip overprinting and recrystallization. Here, in BMS rocks from the Ailao Shan–Red River shear zone (ARSZ), we report the first discovery of a >250 km long, high-pressure (high-P) granulite belt (>1.0 GPa), identified by the presence of relict kyanite and associated decompression reaction textures. Petrological phase equilibrium modeling showed that exposed micaschists in the region represent exhumed middle crust (20–25 km, 600–670°C), while the high-P granulite rocks are remnants of thickened lower crust (45–55 km, 800–850°C). This indicates that the northeast edge of the ARSZ experienced an additional ∼25 km of uplift and exhumation compared to the southwest side, facilitated by brittle thrusting/imbrication along the Ailao Shan fault (micaschists) and ductile extrusion along the Red River fault (granulite). Geochronological study shows that the upper portion of the BMS preserves older metamorphic ages (52–34 Ma) than the lower portion (32–29 Ma), which was attributed to spatial variation in cooling rates. Using calculated P–T–t–d paths, we also examined variation in density and seismic wave speeds for BMS in the ARSZ. Our data correlate with fieldwork conducted elsewhere within the Himalayan Range indicating that the kyanite to sillimanite transition zone may serve as a “cap” for the horizontal migration of melt within the lower crust.

中文翻译：

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哀牢山-红河剪切带巴罗夫变质层序岩的热物理性质及其对地壳河道流的影响

对喜马拉雅山脉中挖掘出的巴罗夫变质层序（BMS）岩石的研究很好地证实了大印度与欧亚板块之间的碰撞历史。然而，在青藏高原东南部，碰撞记录被强烈的区域性走滑叠印和重结晶所掩盖。在此，在哀牢山-红河剪切带 (ARSZ) 的 BMS 岩石中，我们首次发现了一条 >250 公里长的高压（高压）麻粒岩带 (>1.0 GPa)，其存在可确定为残余蓝晶石和相关的减压反应纹理。岩石学相平衡模型表明，该地区出露的云母片岩代表了中地壳的掘出物（20~25 km，600~670°C），而高磷麻粒岩则是加厚的下地壳的残余物（45~55 km，800~850°C ）。 ℃）。这表明，与西南侧相比，ARSZ 的东北边缘经历了额外约 25 公里的隆起和折返，这是由沿哀牢山断层（云母岩）的脆性逆冲/叠瓦和沿红河断层（麻粒岩）的韧性挤压推动的。地质年代学研究表明，BMS 的上部保留了比下部（32-29 Ma）更古老的变质年龄（52-34 Ma），这归因于冷却速率的空间变化。使用计算的P–T–t –d 路径，我们还检查了 ARSZ 中 BMS 的密度和地震波速度的变化。我们的数据与喜马拉雅山脉其他地方进行的实地考察相关，表明蓝晶石到硅线石的过渡带可能充当下地壳内熔体水平迁移的“上限”。