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.