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Buoyancy-driven exhumation of lawsonite-bearing eclogites and blueschists in the Lanling area, central Qiangtang Terrane, Tibetan Plateau
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  • Shilin Wang,
  • Jinxue Du,
  • Zhao Zhongbao,
  • Yi Cao,
  • Xiao Liang,
  • Gen-Hou Wang,
  • Xiaosai Wang
Shilin Wang
China University of Geosciences (Beijing), School of Earth Science and Resources
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Jinxue Du
China University of Geosciences (Beijing)

Corresponding Author:[email protected]

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Zhao Zhongbao
Chinese Academy of Geologi­cal Sciences
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Yi Cao
China University of Geosciences (Wuhan)
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Xiao Liang
China University of Geosciences (Beijing)
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Gen-Hou Wang
China University of Geosciences
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Xiaosai Wang
Institute of Exploration Techniques, Chinese Academy of Geosciences
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The exhumation mechanism of the low-temperature/high-pressure (LT/HP) rocks, is critical for understanding the formation of the central Qiangtang metamorphic belt (CQMB), Tibetan Plateau, but it is still hotly debated. Here, we report field, petrological, phase-equilibria and petro-physical modelling data on the newly discovered lawsonite-bearing eclogites, epidote eclogite and lawsonite-bearing blueschists from the Lanling area in the CQMB. The mineral characteristics and phase equilibria modeling reveal that the LT/HP rocks record peak P-T conditions from peak pressure (Pmax) of 22.5–23.5 kbar at 460–480 °C to peak temperature (Tmax) of 530–550 °C at 20–22.5 kbar. Combined with previous documented geochronological data, a clockwise P-T-t path for these LT/HP rocks is obtained, which is characterized by pronounced heating decompression (~223–221 Ma), subsequent isothermal decompression (~221–219 Ma), and final cooling decompression (~219–212 Ma). Modeled densities and net buoyancies (defined as the density difference between Preliminary Reference Earth Model and LT/HP rocks) show that all LT/HP samples are buoyant at Pmax, but gradually become denser during heating decompression and evolve to neutrally or negatively buoyant around Tmax. Later mixing with lower-density garnet-phengite schists at Tmax, help the density of the exhuming LT/HP unit reduce to lower than that of the surrounding mantle again during continued isothermal decompression. We concluded that exhumation of eclogites and blueschists is short-lived (~10 Ma) and multi-stage buoyancy-driven characterized by early self-exhumation via diapiric rise and post-Tmax carried-exhumation along subduction channel.