Multicyclic Phanerozoic orogeny recorded in the Qaidam continent, northern Tibet: Implications for the tectonic evolution of the Tethyan orogenic system

The growth and evolution of the Eurasian continent involved the progressive closure of major ocean basins during the Phanerozoic, including the Tethyan and Paleo-Asian oceanic realms. Unraveling this complicated history requires interpreting multiple overprinted episodes of subduction-related magmatism and collisional orogeny, the products of which were later affected by the Cenozoic construction of the Himalayan-Tibetan orogen due to the India-Asia collision. In particular, the tectonic evolution of northern Tibet surrounding the Cenozoic Qaidam Basin is poorly resolved due to several phases of Phanerozoic orogeny that have been reactivated during the Cenozoic deformation. In this study, we investigated the geology of the northern Qaidam continent, which experienced Paleozoic−Mesozoic tectonic activity associated with the development of the Eastern Kunlun orogen to the south and the Qilian orogen to the north. We combined new and published field observations, geochronologic and thermochronologic ages, and geochemical data to construct regional tectonostratigraphic sections and bracket phases of Paleozoic−Mesozoic magmatism associated with oceanic subduction and continental collision. Results suggest that the Qaidam continent experienced two major phases of subduction magmatism and collision. First, a Cambrian−Ordovician magmatic arc developed in the northern Qaidam continent due to south-dipping subduction. This phase was followed by the closure of the Qilian Ocean and the collision of the North China craton and Qaidam continent, resulting in Silurian−Devonian orogeny and the development of a regional unconformity across northern Tibet. A subsequent Permian−Triassic magmatic arc developed across the northern Qaidam continent due to north-dipping subduction. This phase was followed by the closure of the Neo-Kunlun Ocean and the collision of the Songpan Ganzi terrane in the south and Qaidam continent. These interpretations are incorporated into a new and comprehensive model for the Phanerozoic formation of northern Tibet and the Eurasia continent.