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https://doi.org/10.5194/se-2020-95
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/se-2020-95
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  29 Jun 2020

29 Jun 2020

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A revised version of this preprint is currently under review for the journal SE.

First report of ultra-high pressure metamorphism in the Paleozoic Dunhuang orogenic belt (NW China): Constrains from P-T paths of garnet clinopyroxenite and SIMS U-Pb dating of titanite

Zhen M. G. Li1, Hao Y. C. Wang1, Qian W. L. Zhang1, Meng-Yan Shi1, Jun-Sheng Lu2, Jia-Hui Liu1, and Chun-Ming Wu1 Zhen M. G. Li et al.
  • 1College of Earth and Planetary Sciences, University of Chinese Academy of Sciences, P.O. Box 4588, Beijing 100049, China
  • 2State Key Laboratory of Continental Dynamics, Department of Geology, Northwest University, Xi'an 710069, China

Abstract. Ultra-high pressure (UHP) metamorphism is recorded by garnet clinopyroxenite enclaves enclosed in an undeformed, unmetamorphosed granitic pluton, northeastern Paleozoic Dunhuang orogenic belt, northwest China. Three to four stages of metamorphic mineral assemblages have been found in the garnet clinopyroxenite, and clockwise metamorphic pressure-temperature (P-T) paths were retrieved, indicative of metamorphism of a possible subduction environment. Peak metamorphic P-T conditions (790~920 °C/28~41 kbar) of garnet clinopyroxenite suggest that they experienced high pressure to UHP metamorphism, and the UHP metamorphism occurred in the coesite- or diamond-stability field. The UHP metamorphic event is further confirmed by the occurrence of high-Al titanite enclosed in the garnet, along with at least three groups of aligned rutile lamellae exsolved from within the garnet. SIMS U-Pb dating of metamorphic titanite indicates that the post peak, subsequent tectonic exhumation of the UHP rocks occurred in the Devonian (~ 389~370 Ma). These data suggest that part of the Paleozoic Dunhuang orogenic belt experienced UHP metamorphism, and diverse metamorphic facies series prevailed in this orogen in the Paleozoic. It can be further inferred that most of the UHP rocks of this orogen are now buried in the depth.

Zhen M. G. Li et al.

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Zhen M. G. Li et al.

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Short summary
This manuscript provides the first evidence of ultra-high metamorphism in the Paleozoic Dunhuang orogenic belt (NW China). Though no coesite or diamond was found in the samples or in this orogen, the geothermobarometric computation results and petrographic textures all suggest that the garnet clinopyroxenite experienced ultra-high pressure metamorphism, and SIMS U-Pb dating of titanite indicates that the post peak, subsequent tectonic exhumation of the UHP rocks occurred in the Devonian.
This manuscript provides the first evidence of ultra-high metamorphism in the Paleozoic Dunhuang...
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