Zircon U-Pb ages and Hf isotope analysis of Neoproterozoic Yaolinghe Group sedimentary rocks in the Chengkou area, South Qinling: Provenance and paleogeographic implications

Abstract

The Yaolinghe Group sedimentary rocks exposed along the Dabashan fault zone are rich in pyroclastics and are thousands of meters thick. They provide key information for studying the tectonic location relationship between the Yangtze and Qinling blocks and the tectonic-sedimentary environment of the late Neoproterozoic continental margin. This study reports U–Pb and Lu-Hf isotope data of 438 and 408 detrital zircons from five samples of Yaolinghe Group sedimentary rock, collected in the Chengkou area, China. Combining the youngest detrital zircon U–Pb age for gravelly sandstone with data from previous studies, we constrained the maximum depositional time of the Yaolinghe Group sedimentary rocks in this area to ca. 650–635 Ma (i.e., Neoproterozoic Cryogenian). In the Chengkou area, the predominantly Neoproterozoic (1000–635 Ma) detrital zircons, with wide εHf(t) values ranging from −31.03 to 13.07 and an average of 2.00, were primarily derived from the adjacent regions of exhumed igneous rock in the South Qinling and Northern Yangtze blocks. Several minor age peaks at more than 1000 Ma indicate that this formation contains a small amount of recycled zircon. Further study indicates that the Yaolinghe Group sedimentary rocks were formed by near-source accumulation in a rift setting, located at the north margin of the Yangtze Block, during the breakup of Rodinia. As in previous studies, the retreat of the subducted slab may have led to continental rifting and extension of the Northern Yangtze Block, and the Yaolinghe Group sedimentary rocks in the Chengkou area recording the history of the last stage of Rodinia breakup.