Triassic provenance shifts and tectonic evolution of southeast Ordos Basin, Central China

Abstract

Tectonic evolution of the North China Craton underwent a complicated process during the early Mesozoic owing to almost simultaneous closures of the Mianlue Ocean to the south and the Palaeo-Asian Ocean to the north. The tectonic setting of the Triassic sedimentary basin in the southern North China Craton remains a subject of debate. The conventional view is that early Mesozoic basins resulted from plate collision and crustal shortening, whereas new petrological evidence of crustal extension has been identified in the southern North China Craton. In this study, we used petrology, sedimentology, subsidence and geochronology to trace basin provenance and reconstruct source-to-sink around the southeast Ordos Basin. The petrographic modal compositions showed that the provenance changed from recycled orogenic to a mixture of recycled orogenic and arc magmatic materials. Tectonic subsidence of the southeast Ordos Basin revealed two episodes of rapid subsidence, the second of which lasted ~10 Ma and caused the depocenter of the basin to move southward. Early Triassic detrital zircons with distinguishing ages of 1100–700 Ma were derived from the Central China Orogenic Belt and North China Craton; then, they were sourced from the Inner Mongolia Palaeo-uplift, based on zircon ages clustered at ~400–250 Ma. The petrographic modal composition, tectonic subsidence and zircon age distribution imply a provenance shift from short and rapid uplift (North Qinling Orogenic Belt) to remote continuous uplift (Inner Mongolia Palaeo-uplift); this is also supported by the palaeo-current direction. This shift defined a change in the Qinling Orogenic Belt from collision and uplift to extension, which caused the depositional centre of the Ordos Basin to move southward. This integrated tectono-sedimentary environment study provides new insight into the closure process of the Mianlue Ocean during the Triassic and its impact on the tectonic environment of the southern North China Craton.