Detrital-zircon geochronology of the Jurassic coal-bearing strata in the western Ordos Basin, North China: Evidences for multi-cycle sedimentation

摘要

The western Ordos Basin (WOB), situated in a tectonic transition zone in the North China Craton, acts as an excellent example for studying the Mesozoic intraplate sedimentation and deformation in Asia. In this study, U-Pb ages for 1203 detrital zircons of 14 sandstone samples collected from 11 sections are presented to unravel the sediment source locations and paleogeographic environments of the Early–Middle Jurassic coal-bearing Yan'an Formation in the WOB. Data show that there are five prominent age groups in the detrital zircons of the Yan'an Formation, peaking at ca. 282?Ma, 426?Ma, 924?Ma, 1847?Ma, and 2468?Ma. Samples from the northern, middle, and southern parts of the WOB contain these five age categories in various proportions. In the northern region, the Yan'an Formation exclusively contains Early Permian detrital zircons with a single age group peaking at 282?Ma, matching well with the crystallizing ages of the widespread Early Permian granites in the Yinshan Belt to the north and the Alxa Block to the northwest. While in the southern region, the Yan'an Formation mainly contains three groups of detrital zircons, with age peaks at 213?Ma, 426?Ma, and 924?Ma. These zircon ages resemble those of the igneous rocks in the Qilian-Qinling Orogenic Belt to the south-southwest. Samples in the middle region, characterized by a mixture age spectrum with peaks at 282?Ma, 426?Ma, 924?Ma, 1847?Ma and 2468?Ma, are previously thought to have mixed derivations from surrounding ranges. However, by referring to the detrital-zircon age compositions of the pre-Jurassic sedimentary successions and combining with paleontological and petrographic analysis, we firstly propose that the sediments of the Yan'an Formation in the middle region were partly recycled from the Triassic and Paleozoic sedimentary strata in the WOB. The occurrence of recycled sedimentation suggests that the Late Triassic–Early Jurassic intraplate compressional deformation was very intense in the WOB, especially for regions in front of the Qilian Orogenic Belt. Graphical abstract Display Omitted Highlights ? First synthetical presentation of detrital-zircon U-Pb ages of Yan'an Fm. in western Ordos Basin. ? Western Ordos Basin is divided into three sub-regions by provenance distinction. ? Sediments of the Yan'an Fm. were partly recycled from pre-Jurassic strata. ? Late Triassic intraplate deformation was very intense in middle western Ordos Basin. ? Qilian Orogenic Belt acted as main force indentation in intraplate deformation.