Metamorphism and geological significance of pelitic high-pressure granulites in the Tongka microcontinent block, eastern Xizang
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    Abstract:

    The Tongka microcontinent block, situated in the eastern segment of the Bangong-Nujiang suture zone in the central Tibetan Plateau, preserves key evidence of the Early Jurassic tectonic evolution of the Tethyan Ocean through its metamorphic and magmatic records. Pelitic high-pressure granulites occur as interlayers within dominant felsic gneisses and are accompanied by leucosomes of varying scales. These granulites are primarily composed of garnet, kyanite, biotite, K-feldspar, quartz, with minor accounts of plagioclase, muscovite, sillimanite, and rutile. Integrated analyses—petrography, mineral chemistry, geochronology, and phase equilibrium modeling—reveal a clockwise metamorphic p-T-t path that can be divided into three distinct stages: ① Near-isobaric heating prograde metamorphic stage: this stage is characterized by prograde conditions of 0.70~0.88 GPa and 655~680℃, constrained by the compositions of garnet cores and associated biotite inclusions; ② Peak metamorphic stage: the peak mineral assemblage—garnet + kyanite + biotite + K-feldspar + quartz + rutile + melt ±plagioclase—formed under conditions of 0.98~1.06 GPa and 770~790℃, as indicated by phase stability fields and the compositions of garnet mantles and matrix biotite. Zircon U-Pb dating yields a metamorphic age of 175 Ma, representing the timing of high-pressure granulite-facies metamorphism; ③ Cooling and decompression retrograde stage: The retrograde assemblage of biotite + plagioclase + sillimanite + muscovite reflects post-peak conditions of 0.32~0.68 GPa and 600~725℃. This clockwise p-T-t path reflects crustal thickening associated with the collision between the Tongka microcontinent block and the Qiangtang terrane. The near-isobaric heating stage likely records prolonged thermal input from upwelling asthenosphere into the thickened lower crust of the microcontinent.

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田作林,张泽明,陈言飞,董昕,2026,藏东同卡微陆块泥质高压麻粒岩的变质作用及地质意义[J].岩石矿物学杂志,45(1):1~18. TIAN Zuo-lin, ZHANG Ze-ming, CHEN Yan-fei, DONG Xin,2026,Metamorphism and geological significance of pelitic high-pressure granulites in the Tongka microcontinent block, eastern Xizang[J]. Acta Petrologica et Mineralogica,45(1):1~18.

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History
  • Received:January 13,2024
  • Revised:September 03,2025
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  • Online: January 19,2026
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