Geochemical and detrital zircon age constraints on Meso- to Neoproterozoic sedimentary basins in the southern Yangtze Block: Implications on Proterozoic geodynamics of South China and Rodinia configuration

Abstract

The late Mesoproterozoic to early Neoproterozoic sedimentary sequences in the southwestern Yangtze Block, represented by the Julin, Huili, and Kunyang groups, provide vital evidence for deciphering the tectonic evolution of the Yangtze Block that have implications on the reconstruction of the Rodinia supercontinent. Zircon geochronological data reveal that the Julin and Huili groups were deposited at 1167–982 Ma and 1176–958 Ma, respectively. The Haizishao Formation, the conventionally thought the upper most of the Julin Group, was deposited after 982 Ma. The stratigraphicphic position of the Haizishao Formation basal conglomerate and diversity in its detritus source, and tectonic setting, suggest that the Haizishao Formation may not be a part of the Julin Group but represents an independent sedimentary event. Geochemical tectonic discrimination characteristics based on major elements, Th-Sc-Zr/10, Ti/Zr-La/Sc, La/Th-Hf and Sc/Th-La/Sc plots, in combination with detrital zircon age distribution pattern and bimodal magmatism, point toward a transition from continental rift to passive continental margin setting followed by an active continental margin setting for Julin and Huili groups. However, the Huili Group is significantly different from both the Julin and Kunyang groups in terms of lithological composition, depositional environment, detrital zircon age distribution, and tectonic setting, implying that the Julin and Huili basins may have been located in different microcontinents during the late Mesoproterozoic - early Neoproterozoic times.Detrital zircon U-Pb ages and Lu-Hf isotopic characteristics of Julin and Huili groups indicate detritus sourced from the continental interior and exotic terranes, such as the Yudongzi, Douling, and Kongling complexes and magmatic rocks at the southwestern margin of Yangtze Block, the Gawler Craton in Australia, the Transantarctic Mountains in East Antarctica, and the Ongole domain in the Eastern Dharwar Craton of India. Combining provenance analyses and comparison of detrital zircon data, the Yangtze Block was paleogeographically placed in the external position to the Rodinia supercontinent, close to north-central India, Australia, and East Antarctica during the late Mesoproterozoic to early Neoproterozoic.