Neoproterozoic three-stage evolution in the northern margin of the lower Yangtze Block: Evidence from low-grade metamorphic sedimentary sequence in the Zhangbaling uplift

Abstract

Neoproterozoic magmatic and sedimentary records in Yangtze Block are widely used to investigate the assembly and breakup processes of the supercontinent Rodinia. However, the tectonic setting of the Yangtze Block and its paleoposition within Rodinia still remain highly controversial. To address these issues, we conducted an integrated provenance study—combining field observations, whole-rock geochemistry, heavy mineral analysis, and detrital zircon U–Pb–Hf isotopes—on the well-preserved Cryogenian to Ediacaran sedimentary sequence in the Zhangbaling uplift along the northern margin of the lower Yangtze Block. Results indicate that the Zhougang and Sujiawan formations as Cryogenian units (ca. 700–635 Ma) and the Beijiangjun and Doushantuo formations as Ediacaran units (ca. 600–565 Ma). The Cryogenian deposits were derived from the underlying late Tonian volcanics and were deposited in a back-arc setting. Conversely, the Ediacaran sediments were formed in a cratonic rift setting, with the interior of the lower Yangtze Block as the primary source and the early Ediacaran arc as the secondary one. Notably, the trace element characteristics of the Neoproterozoic detrital zircons reveal two stages of arc-related magmatism along the northern margin of the lower Yangtze Block, with peak ages around 827–820 Ma and 781–757 Ma. This evidence, combined with the comparison with the northwestern Yangtze, indicates three evolutionary stages: two-stage island arcs during the Tonian, a residual back-arc basin during the Cryogenian, and a passive continental margin during the Ediacaran. The Neoproterozoic tectonics and evolutionary processes of the northern Yangtze Block suggest its peripheral position within Rodinia and offer new constraints for Neoproterozoic supercontinental reconstructions.