HP-UHP eclogites in the East Kunlun Orogen, China: P-T evidence for asymmetric suturing of the Proto-Tethys Ocean

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 highpressure (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 degrees C, retrograde conditions of 10 kbar at -650-700 degrees C, and then further retrograde conditions at 3-6 kbar and 500-580 degrees C. In the western EKO, LT-HP eclogite records peak conditions of -27 kbar at 570 degrees C and then retrograde conditions at 10 +/- 2 kbar/470-560 degrees 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. (c) 2021 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.

Automated summary

The Early Paleozoic eclogite belt in the East Kunlun Orogen provides valuable insights into the subduction history of the Proto-Tethys Ocean. By studying the P-T conditions and time-scales of the eclogites, we can better understand the process of subduction and collision in this tectonic system.