Detrital zircon U-Pb geochronology of Ediacaran siliciclastic carbonate rocks in eastern South China: Insights into the Precambrian assembly of the Yangtze and Cathaysia blocks

The Cathaysia block, a composite terrane comprising West and East Cathaysia along the East Asian continental margin, forms a critical constituent of the South China block. Despite its tectonic significance, the timing of the Cathaysia–Yangtze amalgamation remains contentious, with proposed ages spanning from the Precambrian to the Mesozoic. We present integrated sedimentological and geochronological constraints derived from Ediacaran carbonate sequences in the Yuhang section of the southeastern Yangtze craton. Systematic analyses that combine sedimentary petrology with detrital zircon U-Pb-Hf isotopes reveal the following: 1) clastic components (30–45 % by volume) dominated by quartz exhibit a mixed siliciclastic carbonate rocks; 2) detrital zircon populations yield predominant Paleoproterozoic ages (2.0–1.75 Ga), showing remarkable similarities to the Precambrian basement of East Cathaysia, particularly through a characteristic age peak of 1.83–1.81 Ga; 3) Hf isotopic compositions demonstrate crustal residence ages that are indistinguishable from those of East Cathaysia sources. These convergent lines of evidence establish East Cathaysia as the primary sediment source for the southeastern Yangtze Ediacaran deposits. Consequently, we propose that the final amalgamation of the composite Cathaysia block with the Yangtze craton occurred during Precambrian crustal stabilization, fundamentally revising previous models that advocated for Phanerozoic accretion.