The Early Paleozoic eclogite belt extends discontinuously for ~500 km within the East Kunlun Orogen (EKO) and records the subduction history of the Proto-Tethys Ocean. This eclogite belt, therefore, is an excellent site for studying the first-order transition in convergent-margin tectonic systems, and the tectonic events associated with subduction and collision can be determined by reconstructing the high-pressure (HP)–ultrahigh-pressure (UHP) P–T–time path. In this contribution, we present P–T results from phase equilibrium modeling and Zr-in-rutile/titanite thermometry for eclogites located on the east and west sides of the EKO. In the eastern EKO, MT–UHP eclogite records peak conditions of ~30 kbar/650–720 °C, retrograde conditions of 10 kbar at ~650–700 °C, and then further retrograde conditions at 3–6 kbar and 500–580 °C. In the western EKO, LT–HP eclogite records peak conditions of ~27 kbar at 570 °C and then retrograde conditions at 10 ± 2 kbar/470–560 °C. These two types of eclogite record oceanic subduction (west) and continental collision (east), respectively. The EKO, therefore, contains two types of eclogites that indicate two end-member subduction complexes within the orogenic belt, further indicating that there are differences in the subduction-depth and collision-time from east to west. This finding is consistent with asymmetric suturing of the subducted Proto-Tethys Ocean within the EKO. Together, the P–T conditions and time-scales of the HP–UHP metamorphism can be applied to understand the process from subduction to collision between the Qaidam Block and the South Kunlun Block, as a consequence of asymmetric closure of the Proto-Tethys Ocean.
Bibliographical noteFunding Information:
We thank Li Xiaoli for the help with the electronic microbe analyses, and Anette von der Handt at the University of Minnesota for developing the protocols for the Zr-in-rutile/titanite analysis. We also thank Duan Zhanzhan, Liu Ting for help of correction with the phase modeling. This research was financially supported by the National Natural Science Foundation of China (grants 91955202), the Key Program of China Geological Survey, China (grant DD20190370) and the Second Tibetan Plateau Scientific Expedition and Research (STEP) program (2019QZKK0703). Bi Hengzhe wishes to acknowledge the Chinese Scholarship Council for financial support during his visit to the University of Minnesota (grant number 201906010039).
© 2021 International Association for Gondwana Research
- Asymmetric suturing
- East Kunlun Orogen
- HP–UHP metamorphism
- Orogenic evolution
- Proto-Tethys Ocean