Metamorphic evolution and tectonic implications of the granulitized eclogites from the central East Kunlun orogen, northwest China

Granulitized eclogites from an orogen provide critical insights into how subducted slab dynamics interact with mantle-derived thermal anomalies to drive transient (ultra)high-temperature metamorphism in continental collision zones. Here we present an integrated petrological and geochronological investigation into newly identified granulitized eclogites from the central East Kunlun orogen, northern Tibet. Thermobarometry and microstructural relations reveal four metamorphic stages: (1) eclogite-facies conditions at ∼19 kbar and 540 °C, (2) high-pressure granulite-facies overprint at ∼15 kbar and 750−800 °C, (3) medium-pressure granulite-facies overprint at ∼8 kbar and 900 °C (maximum temperature, Tmax), and (4) final amphibolite-facies retrogression at <6 kbar and 740 °C. Zircon U-Pb dating reveals two episodes of metamorphism: The age of ca. 430 Ma dates eclogite-facies metamorphism, while the age of ca. 410 Ma represents the post-Tmax cooling with melt crystallization. Whole-rock geochemistry and U-Pb dating on inherited zircon cores (920−880 Ma) indicate that protoliths of the eclogites are Neoproterozoic continental basaltic rocks formed during assembly or breakup of Rodinia, which were subsequently subducted during early Paleozoic continental collision. High-temperature to ultrahigh-temperature granulite-facies overprinting of the eclogites occurred at mid-crustal residence during Devonian exhumation. Integrated metamorphic and magmatic data reveal pronounced along-strike variations in subduction geometry and postcollisional thermal evolution of the East Kunlun orogen. Steep subduction in the eastern and western segments caused rapid exhumation, while low-angle subduction in the central segment led to delayed heating, lithospheric delamination, and (ultra)high-temperature overprinting. These findings constrain the transition from Proto-Tethyan accretion to collisional orogenesis, revealing spatial-temporal coupling between (ultra)high-temperature metamorphism and postcollisional magmatism and emphasizing that spatially heterogeneous deep processes exert a primary control on metamorphic and magmatic architectures in continental collision zones.