Detrital zircon U–Pb ages of metasedimentary rocks from the Neoproterozoic Zhoutan Group in the northern Cathaysia Block (South China): Provenance and tectonic implications

The Neoproterozoic Zhoutan Group, located at the conjunction area between the Yangtze and the Cathaysia Blocks, preserves an important record of the Neoproterozoic sedimentary system of the South China Block. However, its accurate depositional age, provenance, and tectonic affinity remain poorly studied. Here, we report new LA-ICP-MS detrital zircon U–Pb age data of four meta-sedimentary samples from the Zhoutan Group in the Nancheng area for complemental decipherment of its sedimentary and tectonic histories. Concordant detrital zircon ages reveal proportions of 54% latest Mesoproterozoic to early Neoproterozoic (ca. 1050–820 Ma), 24% early Paleoproterozoic (ca. 2500–2150 Ma), and 22% late Paleoproterozoic to early Mesoproterozoic (ca. 2000–1500 Ma) populations. Youngest detrital zircon age clusters exhibit a consistent weighted mean age of ca. 827 Ma, suggesting the maximum Tonian depositional age of the Zhoutan Group. Provenance interpretations reveal that the detritus of investigated samples were mainly sourced from the proximal Jiangnan Orogen with some additionally derived from the Cathaysia Block, the interior Yangtze Block, and/or extraneous terranes. In addition, the appearance of some later early Palaeozoic-aged (ca. 437 Ma) metamorphic rims and grains suggest that the Zhoutan Group has locally experienced an intense metamorphism during the early Palaeozoic (Silurian) time, which has been consistently recorded by the Neoproterozoic meta-strata in the Cathaysia Block. These new data, together with those from previous studies, indicate that the Zhoutan Group belongs to the early Neoproterozoic sedimentary successions between the Yangtze and the Cathaysia Blocks. Subsequently, it might be thrusted onto the present side of the Cathaysia Block during later tectonic processes and was affected by locally metamorphism during the Silurian time. Thus, such observations suggest that the potential border between the Yangtze and the Cathaysia Blocks should be to the north of the current position of the Zhoutan Group.