Detrital zircon geochronology and provenance of sediments within the Mesozoic basins: New insights into tectonic evolution of the Qinling Orogen

摘要

Mesozoic sedimentary units within the Nanzhao and Mashiping basins record the paleogeographic and tectonic evolution of the Qinling Orogen (QO). This study uses new detrital zircon U–Pb ages and Hf isotopic data to constrain the timing of deposition and provenance of the Taishanmiao, Taizishan, Nanzhao, and Mashiping formations of the North Qinling Orogen (NQO). The detrital zircons can be split by age peaks into five major groups, including Early Cretaceous, Late Triassic, Early Paleozoic, Neoproterozoic and Paleoproterozoic age peaks. On the basis of the youngest zircon ages and age-diagnostic fossils, we conclude that the Taishanmiao (youngest age of 234?Ma) and Taizishan (216?Ma) formations were deposited during the Late Triassic, whereas the Nanzhao Formation (110?Ma) was deposited during the Early Cretaceous rather than the Late Jurassic as previously thought. The Mashiping Formation (110?Ma) was also deposited during the Early Cretaceous. Combined with zircon Hf isotopic compositions, zircons from Late Triassic units were generally derived from the NQO, South Qinling Orogen (SQO), and North China Craton (NCC), with minor amounts derived from the Xing–Meng Orogenic Belt. The sediments within the Nanzhao Formation were mainly derived from the QO, with a minor contribution from the NCC. The Early Cretaceous conglomerates of the Mashiping Formation were generally derived from recycled earlier detritus. This implies that Late Triassic deposition was related to the final closure of the Mianlue Ocean, whereas Early Cretaceous deposition was correlated to the continued intercontinental subduction of the Yangtze Craton beneath the QO. The change in provenance within these Mesozoic sediments suggests the QO underwent two periods of significant uplift, which was a process generated sediments that were deposited in a series of basins of this area.