PROTRACTED PRECAMBRIAN AND MULTI-CYCLE PHANEROZOIC TECTONIC EVOLUTION OF THE QAIDAM BLOCK, NORTHERN TIBET

Despite a long-term history of research, the nature of Precambrian basement rocks and the overall tectonic evolution of the Qaidam block in northern Tibet remains debated. To clarify this issue and provide a new foundation for studying the Proterozoic–Phanerozoic tectonic evolution of the Qaidam block, we examined the geology of the entire block and its adjacent blocks by combining geological mapping, geochronology, and geochemistry analyses, and existing tectonostratigraphic, magmatism, sedimentation, and metamorphic records. This work provides a new, comprehensive view of the reconstruction of the paleogeographic configuration of central Asian Precambrian cratons and the Phanerozoic formation of northern Tibet and Eurasia. We propose the Qaidam block was part of a “Greater North China” block, which experienced early Paleoproterozoic post-collisional extension, continental collision along the Paleoproterozoic Northern Margin orogen to form the Columbia-Nuna supercontinent, and Mesoproterozoic extension related to supercontinent breakup. In addition, we propose that the Greater North China block was affixed to the western margin of Laurentia and Siberia as part of Rodinia in the Neoproterozoic and subsequently rifted and drifted as a series of microcontinents. The Qaidam block experienced two major Phanerozoic magmatic and collisional events in the early Paleozoic and late Paleozoic–Mesozoic. Early Paleozoic arc magmatism overlaps spatially and temporally with ultra-high-pressure metamorphism and an undefined ophiolite complex in the North Qaidam, which is related to the evolution of the Qilian Ocean. The Qaidam block contains a regional angular unconformity between Devonian and older strata, and all pre-Devonian metamorphic rocks are bounded by a north-dipping Cenozoic thrust. A Carboniferous magmatic lull was coeval with the development of a passive margin following extension and the intracontinental rift basin in the northern Qaidam. Permian-Triassic subduction-related arc magmatism with the early Triassic tectonic inversion of the rift basin, and the emplacement of granitoids during extension are associated with subduction and slab roll-back of the Paleo-Tethyan oceanic lithosphere, respectively. This suggests that the North Qaidam did not develop during a distinct orogenic cycle in the Phanerozoic as previously interpreted.