Assembling the Proto-Yangtze Block in the late Paleoproterozoic: Constraints from a refined Magmatic-Metamorphic framework of the Cuoke Complex, SW China

The Archean-Paleoproterozoic records of the southwestern and northern Yangtze are key components in establishing the early history of the Yangtze Block as a whole. To date, knowledge of the late Paleoproterozoic evolutionary history of the Yangtze Block has been largely derived from its northern margin. This study documents the presence of ca. 1.93 Ga metamorphic zircons and 1.89–1.86 Ga metamorphic-hydrothermal reset zircons from igneous rocks in the Cuoke Complex of southwestern Yangtze, as well as ca. 1.93 Ga and 1.86 Ga xenotime growths in a meta-volcaniclastic rock (tuff). In addition, the origin of 2.0–1.85 Ga zircons from magmatic rocks in both the Cuoke and Phan Si Pan complexes of the southwestern Yangtze Block are reassessed. Based on new and published CL images, U contents and REE patterns, we argue that the 2.0–1.85 Ga ages are reset from primary 2.3 Ga magmatic zircons during a widespread metamorphic-hydrothermal overprinting event. Integrated U-Pb data reveal two metamorphic peaks at 2.0–1.95 Ga and ca. 1.85 Ga in both northern and southwestern Yangtze, indicating the two domains came together at 2.0–1.95 Ga to form the proto-Yangtze Block. The geological records of northern and southwestern Yangtze match well with those of northern Laurentia and Siberia, respectively, suggesting an internal location for the proto-Yangtze Block within Nuna. This contrasts with its inferred external location within the Rodinia supercontinent, suggesting the transition between the two Proterozoic supercontinents involved significant reconfiguration of at least some of the constituent core continental blocks.