Provenance of Late Mesozoic Strata and Tectonic Implications for the Southwestern Ordos Basin, North China: Evidence from Detrital Zircon U-Pb Geochronology and Hf Isotopes

In order to determine the provenance and variation characteristics of sandstone-type uranium deposits located in the southwest Ordos Basin, U-Pb geochronology and Hf isotope analyses were conducted on detrital zircons from the Late Mesozoic strata of the SD01 well in the Zhenyuan area. The detrital zircon U-Pb ages of four samples exhibited four main peaks at 250-330, 420-500, 1 720-2 000, and 2 340-2 580 Ma, with a small number of zircons dated at 770-1 100 Ma. The detrital zircon age spectrum and further restriction provided by the in-situ Hf isotopic data suggest that the provenance of each stratum was mainly derived from the crystalline basement rock series (Khondalites, intermediate-acidic intrusive rocks, and metamorphic rocks) of the Alxa Block to the northwest and the Yinshan Block to the north, with minor amounts of Caledonian magmatic rocks and Jingning Period rocks from the western part of the northern Qilian orogenic belt to the west and the northern Qinling orogenic belt to the south. The provenance of the sandbody has not changed significantly and is of the Middle Jurassic-Early Cretaceous. The clear variations in the zircon ages of the samples from the Zhiluo and Anding formations were likely influenced by climate change during the Middle-Late Jurassic. The Triassic zircon age (<250 Ma) first appeared in Early Cretaceous strata, suggesting that tectonic activity was relatively strong in the northern Qinling orogenic belt during the Late Jurassic and produced extensive outcrops of Indo-Chinese granite, which were a source of basin sediments.

Automated summary

We conducted U-Pb geochronology and Hf isotope analyses on detrital zircons from the Late Mesozoic strata in the Zhenyuan area to determine the source and variation characteristics of sandstone-type uranium deposits in the southwest Ordos Basin. The results suggest that the provenance of the sandbody mainly originated from the Alxa Block to the northwest and the Yinshan Block to the north, with minor contributions from the Caledonian magmatic rocks and Jingning Period rocks to the west and south. The variations in zircon ages in different formations were likely influenced by climate change during the Middle-Late Jurassic.