U-Pb ages and Hf isotopes of detrital zircons from the Cretaceous succession in the southwestern Ordos Basin, Northern China: Implications for provenance and tectonic evolution

摘要

The Ordos Basin is located in the western part of the North China Craton, and was developed based on Paleozoic shallow marine sediments and Mesozoic continental deposits. In the southwestern Ordos Basin (SWOB), Paleozoic to Mesozoic sedimentary successions are well preserved and display variable deformation. However, the Cretaceous source-to-source evolution of the SWOB is poorly known but is significant to understand the tectonic evolution of the Ordos Basin. In this study, U-Pb ages and Hf isotopic analyses on detrital zircons from sandstones of the Cretaceous succession in the SWOB were performed, with an aim to trace the Cretaceous sediment provenances and the tectonic-paleogeographic configuration of the Ordos Basin. The new analyses clearly reveal four major age peaks for detrital zircons from Cretaceous sedimentary rocks in the SWOB: 274, 438, 1852, and 2474 Ma, and two minor peaks at 880-950 Ma and 3000 Ma. These zircons have epsilon((t))(Hf) values with a normal distribution from -15.8 to 11.4 and T-DM2 ages with multiple peaks mostly at 2985-2720 Ma. Combined with the paleogeographic reconstruction and tectonic evolution of the Ordos Basin, the isotopic analyses prove that the detrital zircons in the Cretaceous succession were mostly sourced from the Alxa Block, Qilian Orogenic Belt, and Yinshan Orogenic Belt, and secondarily from the Qinling Orogenic Belt. Influenced by the formation of the Late Jurassic-Early Cretaceous paleo-uplifts, the Cretaceous sedimentary rocks in the SWOB were sourced from these paleo-uplifts and recycled from the underlying pre-Cretaceous rocks situated in the western Ordos Basin. The migration of the Mesozoic sedimentary depocenter and provenance in the Ordos Basin was controlled by the regional compression of multiple directions.