Detrital zircon U-Pb age and Hf isotopic composition and whole-rock geochemical characteristics of the Statherian Huangqikou Formation, western margin of the North China Craton: Implications for provenance and tectonic evolution

Proterozoic sedimentary covers in the Helan-Qianli Mountain area, western margin of the North China Craton (NCC), include the Huangqikou, Wangquankou and Zhengmuguan formations from bottom to top. The Huangqikou Formation, mainly distributed in the Middle Helan Mountain (MHM), North Helan Mountain (NHM) and Qianli Mountain (QM), is composed of conglomerate, quartz sandstone and silty-argillaceous shale that are locally metamorphosed into quartzite and slate. Detrital zircon U-Pb dating and stratigraphic correlation bracket that the Huangqikou Formation deposited during 1.75-1.60 Ga. Petrologic and geochemical features suggest that the provenance was sourced from felsic rocks and pre-existed sedimentary rocks. U-Pb ages of detrital zircons from the Huangqikou Formation in the MHM area yield age ranges at 2.5-2.35 Ga, 2.2-2.0 Ga and 1.95-1.8 Ga, while those in the NHM-QM areas yield age ranges at 2.5-2.4 Ga, 2.0-1.95 Ga and 1.85-1.78 Ga. The remarkable geochronological and isotopic similarity suggests that the early Paleoproterozoic granitic gneiss in the Ordos Block and Zhaochigou complex in the Khondalite Belt are the dominant source rocks for the Huangqikou Formation in the MHM. However, the provenances of the Huangqikou Formation in the NHM-QM are dominated by the granitoids in Guyang area of the Yinshan Block, the S-type granites and para-gneisses in the Khondalite Belt and the TTG gneisses, Bayanwulashan complex and Boluositanmiao complex in the Alxa Block, as well as a small amount basement rocks in Alxa Block. The characteristics of geochemistry, provenance and regional geological data indicate that the Huangqikou Formation deposited in a rift basin. Besides, detritus sourced from the Alxa Block in the clastic sedimentary rocks of the Huangqikou Formation imply that the Alxa Block was already a part of the NCC before ca.1.75 Ga. The U-Pb age and Lu-Hf isotopic characteristics of detrital zircons from the Statherian show that rapid generation of juvenile crust in the western Block was at 2.9-2.7 Ga, yet the ca.2.5 Ga magmatic activity strongly reworked pre-existed crust with negligible juvenile crust generation. The magmatic activities quite possibly developed in the Western Block during the global magmatic shutdown (2.45-2.2 Ga).