Sedimentary and provenance constraints on Carboniferous multiple-stage paleogeographic and tectonic transitions in the East Kunlun-Qaidam

The Carboniferous tectonic settings of the East Kunlun-Qaidam region, which is located at the present-day northern part of the Tibetan Plateau, are of a great significance for understanding the tectonic evolution of the Paleo-Tethyan Ocean. There is a debate concerning Carboniferous source-to-sink relation and topographic background of the East Kunlun-Qaidam, associated with contrasting views on tectonic processes of the Paleo-Tethyan South Kunlun Ocean during Carboniferous. Some previous studies proposed that the East Kunlun-Qaidam was located in a passive continental margin that tilted southward to the South Kunlun Ocean, the construction of which was related to the continuous oceanic crust spreading. In contrast, other research results indicate that, in response to the subduction of the South Kunlun Ocean lithosphere, the East Kunlun-Qaidam was positioned in the north-dipping back-arc region inboard the East Kunlun Andean-type magmatic arc. To resolve this debate, we investigated the well-exposed Carboniferous sedimentary successions in the Qimantagh, Dulan, and the northern Qaidam in the East Kunlun-Qaidam region. A set of new provenance data were obtained and complied, including paleocurrents, sandstone petrologic composition, and detrital zircon U-Pb chronology. These results have shown that the main peaks of detrital zircon ages are concentrated at ca. 350–250 Ma. The existence of Carboniferous-age detrital zircons, in combination with northward-directed paleocurrents, constrains magmatic activity of the East Kunlun magmatic arc during this period and further implies the subduction of the South Kunlun Ocean lithosphere. Combined with sedimentary evidence such as paleocurrents, the East Kunlun-Qaidam area, as a whole, was a northward-tilting back-arc extension basin during the Carboniferous. The sources mainly came from the south, and the Paleo-Tethys South Kunlun Ocean was in the subduction stage at that period. The obvious spatial differences in the provenance of the Carboniferous reflect complicated source-sink systems that existed in this paleogeographic pattern. Furthermore, percentage of zircons with Precambrian ages significantly varies through time, indicating changing in provenances along with a rapid uplift and exhumation of the basement. The dominance of detrital zircons with ages of ca. 2500–1700 Ma suggests additional sediment dispersal from the basement of East Kunlun and Qaidam, as well as the remnants of the Northern Qaidam Orogenic Belt during the early stage.