Proterozoic tectonic affinity and evolution of the East Kunlun-Qaidam Block, NW China: Insight from Precambrian metasedimentary rocks and early Neoproterozoic granitoids

The East Kunlun-Qaidam Block, situated in the northeastern margin of the Qinghai-Tibet Plateau, preserves numerous geological records associated with the evolution of the Rodinia supercontinent. However, the Precambrian tectonic evolutionary history and continental affinity of the East Kunlun-Qaidam Block have long been controversial. In the present study, the results of zircon U-Pb dating reveal that the precursor rocks of the granitic gneisses from the East Kunlun-Qaidam Block were formed between 935 and 928 Ma. The geochemical and Nd-Hf isotope data of these granitic gneisses, coupled with the fact that they contain Paleo-Mesoproterozoic inherited zircons and Al-rich minerals, reveal that their protoliths are S-type granites formed through the partial melting of the Paleo-Mesoproterozoic sedimentary rocks. Combined with available regional geological data, we suggest that the protoliths of the studied granitic gneisses most likely formed in syn-collisional settings during the amalgamation of Rodinia. The 1.0-0.9 Ga granitic magmatism in the East Kunlun-Qaidam and Qilian areas recorded tectonic conversion from oceanic subduction, continental collision, and post-collision. The detrital zircon ages of the studied Mesoproterozoic metasedimentary rocks in the North Qaidam ultrahigh-pressure metamorphic belt show a major age population at 1.97-1.72 Ga, and the Yangtze Block might be the dominant sedimentary provenance, contributing a large volume of the exotic detritus. The Mesoproterozoic metasedimentary rocks from the Shaliuhe Group might have been deposited in a passive continental margin environment during the late Mesoproterozoic. The youngest detrital zircon ages (713-618 Ma) from the Neoproterozoic metasedimentary rocks in the East Kunlun-Qaidam Block suggest that they were most probably formed in the middle-late Neoproterozoic era. Zircons from the Neoproterozoic strata both have a major age cluster of 1.0-0.9 Ga, which were mainly derived from the East Kunlun-Qaidam Block. The Neoproterozoic strata were deposited in a continental rift setting during the breakup of Rodinia. Our study further supports that the East Kunlun-Qaidam Block has a tectonic affinity with the western Yangtze Block from late Mesoproterozoic to Neoproterozoic.