EGU23-3782, updated on 22 Feb 2023
https://doi.org/10.5194/egusphere-egu23-3782
EGU General Assembly 2023
© Author(s) 2023. This work is distributed under
the Creative Commons Attribution 4.0 License.

Metamorphic evolution of high-pressure garnet amphibolite from the Eastern Himalayan Syntaxis: Implications for the mechanism of crustal thickening and exhumation of southern Lhasa terrane during late Cretaceous

Yanling Zhang1,2, Changqing Yin1,2, Donald Wayne Davis3, Shun Li4, Jiahui Qian1,2, Jian Zhang1,2, Peng Gao1,2, Shangjing Wu1,2, Wangchao Li1,2, and Yanfei Xia1,2
Yanling Zhang et al.
  • 1Guangdong Provincial Key Laboratory of Geodynamics and Geohazards, School of Earth Sciences and Engineering, Sun Yat-sen University, Guangzhou, 510275, China
  • 2Southern Marine Science and Engineering Guangdong Laboratory (Zhuhai), Zhuhai, 519082, China
  • 3Department of Earth Sciences, University of Toronto, Toronto, Ontario M5S 3B1, Canada
  • 4School of Oceanography, Shanghai Jiao Tong University, Shanghai, 200030, China

This study presents a comprehensive metamorphic study of geochronology, petrography, mineral chemical, and P-T path for late Cretaceous high-pressure garnet amphibolite from the southern Lhasa terrane of the Eastern Himalayan Syntaxis. Mineral textures and reaction relationships suggest that these rocks have experienced three metamorphic stages (M1-M3). The M1 stage is characterized by peak mineral assemblages of Grt + Hb + Ab + Ru + Ms + Qz, followed by the post peak (M2) assemblages of Grt + Hb + Pl + Ep + Bi + Ru + Qz in the matrix. Late retrograde stage (M3) is defined by Hb + Pl coronae surrounding garnet porphyroblasts, indicating a decompression process. These mineral compositions in combination with whole-rock phase equilibria modelling of high-pressure garnet amphibolite give P-T conditions of three metamorphic stages at 14-19 kbar/660-720 ℃ (M1), 8-10 kbar/650-660 ℃ (M2), and <7 kbar/<600 ℃ (M3), respectively. In summary, a P-T path involving a near-isothermal decompression process and late cooling accompanied by decompression has been reconstructed for high-pressure garnet amphibolite. Moreover, SIMS zircon U-Pb dating results show that metamorphic zircons yield a concordant age of ~90 Ma, suggesting a peak metamorphic age. The results indicate that the southern Lhasa terrane underwent a sequence of tectonometamorphic processes that were initiated by crustal thickening (M1) of up to 60 km at 90 Ma, followed by rapid exhumation along a subduction channel to the depth of 32-26 km (M1-M2) and later slow uplift (M2-M3).

How to cite: Zhang, Y., Yin, C., Davis, D. W., Li, S., Qian, J., Zhang, J., Gao, P., Wu, S., Li, W., and Xia, Y.: Metamorphic evolution of high-pressure garnet amphibolite from the Eastern Himalayan Syntaxis: Implications for the mechanism of crustal thickening and exhumation of southern Lhasa terrane during late Cretaceous, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-3782, https://doi.org/10.5194/egusphere-egu23-3782, 2023.