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Metamorphism and Oceanic Crust Exhumation—Constrained by the Jilang Eclogite and Meta-Quartzite from the Sumdo (U)HP Metamorphic Belt

  • Special Issue on Ophiolite, Orogenic Magmatism and Metamorphism Dedicated to IGCP 649: Diamonds and Recycled Mantle
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Abstract

The Sumdo eclogite-bearing (U)HP metamorphic belt extends over 100 km across the middle part of the Lhasa terrane in southern Tibet, which forms a Permian-Triassic oceanic subduction zone between the south and the north Lhasa sub-terranes, leading to the reinterpretation of the tectonic evolution of the Lhasa terrane in the Tibetan-Himalayan orogeny. Previous studies show that there are significant differences in temperature and pressure conditions of the eclogites in four areas, e.g., Sumdo, Xindaduo, Bailang and Jilang areas. Studying the peak metamorphic P-T conditions and path of eclogite in the Sumdo belt is of great significance to reveal the subduction and exhumation mechanism of Paleo-Tethys Ocean in the Lhasa terrane. In this contribution, eclogite in the Jilang area of the Sumdo belt is chosen as an example to study its metamorphic evolution. The mineral assemblage of the eclogite is garnet, omphacite, phengite, hornblende, epidote, quartz and minor biotite. Garnet has a “dirty” core with abundant inclusions such as epidote, amphibole, plagioclase and a “clear” rim with few inclusions of omphacite and phengite. From the core to the rim, pyrope content in garnet increases while grossular content decreases, showing typical growth zoning. The rim of garnet is wrapped by the pargasite+plagioclase corona, showing amphibolite facies overprint during retrogression. Three stages of metamorphism are inferred as (1) prograde stage, represented by the core of garnet and mineral inclusions therein; (2) peak stage, represented by the garnet rim, omphacite, lawsonite, phengite, and quartz; (3) retrograde stage characterized by decomposition of lawsonite to zoisite, followed by symplectite of omphacite and corona rimmed garnet. A P-T pseudosection contoured with isopleths of grossular and pyrope contents in garnet is used to constrain the near peak P-T condition at 2.85 GPa, 575 °C. In general, the Jilang eclogite shows a clockwise P-T path with a near isothermal decompression process during exhumation. Combined with the age peaks of 583, 911, and 1 134 Ma from the detrital zircons of the country metaquartzite, a continental margin material involving exhumation process at shallow depth after the subduction channel exhumation is inferred for the Jilang eclogite and may further indicate that the subduction direction of the Sumdo eclogite belt is from north to south.

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Acknowledgments

Prof. Chunjing Wei and two anonymous reviewers are thanked for their comprehensive, constructive suggestions to improve the content of the manuscript. We thank Dr. Lingmin Zhang from Tongji University for the help in electron microprobe analysis. This research was financially supported by the National Natural Science Foundation of China (Nos. 41572051, 41630207, 41872067 and 41703053), and Chinese Academy of Geological Sciences (No. YYWF201702). The final publication is available at Springer via https://doi.org/10.1007/s12583-019-0894-9.

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Correspondence to Cong Zhang.

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Li, Y., Zhang, C., Liu, X. et al. Metamorphism and Oceanic Crust Exhumation—Constrained by the Jilang Eclogite and Meta-Quartzite from the Sumdo (U)HP Metamorphic Belt. J. Earth Sci. 30, 510–524 (2019). https://doi.org/10.1007/s12583-019-0894-9

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  • DOI: https://doi.org/10.1007/s12583-019-0894-9

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