Tracking the formation and evolution of the Ordos Block basement, North China Craton: U-Pb age and Lu-Hf isotope record of detrital zircons from the early Mesoproterozoic sandstones

The Ordos Block (OB) is generally considered to be an important micro-block concerning the early geological evolution of the North China Craton (NCC). Previous geophysical and limited geological researches for the OB basement have provided a preliminary understanding of the lithological assemblages and geological structure of the basement, but little was discussed about its formation time and early Precambrian evolution. In this contribution, to better understand the formation and evolution of the OB basement, the new LA-ICP-MS U-Pb ages, Lu-Hf isotope, and trace element composition have been carried for the detrital zircons from the sandstones of the Changcheng System overlying the OB basement. The youngest concordant U-Pb age constrains the Changcheng System to be deposited after-1.7 Ga, consistent with the Changcheng System in the other regions of the NCC. The 3.6-3.3 Ga detrital zircons preserved in the sandstones from the Changcheng System, associated with the 3.4 Ga inherited zircon in basement rocks, indicate the potential presence of Paleoarchean crustal materials in the OB. The 2.8-2.6 Ga zircons with positive epsilon Hf(t) values (+0.6 to +6.4) have the two-stage model ages (TDM C = 3.23-2.75 Ga) close to their formation ages, combined with the crustal thickening during this period, suggesting a major crustal growth in the early Neoarchean. In addition, the main age clusters of the 2.5-2.4 Ga, 2.2-2.0 Ga, and 1.95-1.8 Ga yield epsilon Hf(t) values of-6.9 to +7.7 with TDMC of 3.39-2.47 Ga,-13.4 to +7.5 with TDMC of 3.49-2.19 Ga, and-14.0 to +2.2 with TDMC of 3.41-2.40 Ga, respectively, indicative of three main stages of crustal reworking associated with two stage of minor juvenile crustal growth around 2.5-2.4 Ga and 2.2-2.0 Ga. They were corresponding to partial melting of the continental crust in the late Neoarchean, magmatism resulting from the plate subduction in the mid-Paleoproterozoic, and the collision and amalgamation between eastern and western blocks in the late Paleoproterozoic, respectively. All demonstrate that the OB was an ancient block formed mainly in the early Neoarchean and then subjected to three strong tectonothermal events of 2.5-2.4 Ga, 2.2-2.0 Ga, and 1.95-1.8 Ga, which occurred in the peripheral orogenic belts.