Precambrian tectonic evolution of the Qaidam block, northern Tibet: Implications for the assembly and breakup of Proterozoic supercontinents

Abstract

The nature of Precambrian metamorphic basement rocks and overall tectonic evolution of the Qaidam block in northern Tibet remains debated despite being important to understanding the assembly of Asia. Paleogeographic reconstructions of Precambrian supercontinents rarely consider Phanerozoic tectonic modification of its constituent Precambrian blocks. This issue is particularly relevant for the Qaidam block and its neighboring crustal fragments, which experienced significant Phanerozoic overprinting from multiple tectonic episodes. To address this problem, we systematically reviewed key geological observations and regional datasets related to Proterozoic magmatism, metamorphism, and sedimentation of major Precambrian blocks in China. This synthesis provided new constraints on the Proterozoic tectonic evolution of the Qaidam block, including paleogeographic supercontinent configurations and nature of multiple continental-drift-collision events. New results of field mapping, geochronological, and geochemical analyses allow us to divide the Precambrian rocks of the Qaidam block into four divisions: (1) Paleoproterozoic gneiss and schist; (2) Meso- and (3) Neoproterozoic metasedimentary rocks; and (4) Proterozoic intrusions. We propose that the Qaidam block was part of a “Greater North China” block, which experienced early Paleoproterozoic post-collisional extension and continental collision along the Paleoproterozoic Northern Margin orogen to form the Columbia-Nuna supercontinent. The Greater North China block subsequently experienced 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, rifted in the late Neoproterozoic, and drifted in the early Paleozoic as a series of microcontinents.