Zircon geochronology of the deformed matrix in the NE Jiangxi ophiolitic mélange belt: Time constraints on the Neoproterozoic evolution of the Paleo–South China Ocean and assembly of the Yangtze and Cathaysia blocks

Abstract

The NE Jiangxi ophiolitic mélange belt is the key area for understanding the evolution of the Paleo-South China Ocean and the assembly of the Yangtze and Cathaysia blocks. The age of the deformed matrix is closer to the tectonic emplacement time of the ophiolitic mélange than that of the blocks. However, the rock types, ages and structural deformation of the matrix in the NE Jiangxi ophiolitic mélange belt lack comprehensive understanding. Based on the zircon U–Pb geochronology, Hf isotope and trace element analyses of the deformed matrix in the NE Jiangxi ophiolitic mélange belt, we report the ages of meta-rhyolite and tuffaceous phyllite to be 800–760 Ma, and the maximum depositional age of the clastic matrix is ~760 Ma. The youngest deformed matrix ages of 800–760 Ma constrain the tectonic emplacement age of the NE Jiangxi ophiolitic mélange belt to the late Qingbaikou period after 800–760 Ma and before the deposition of the Xiuning Formation (765–732 Ma). Zircon ages, trace element and Hf isotope compositions indicate that the 800–760 Ma matrix was formed in a back-arc basin environment with obvious addition of 1000–800 Ma arc materials and recycled Paleoproterozoic crustal materials. The detrital material source areas were the 800–760 Ma arc and earlier accretionary wedge as juvenile crust. The multi-stage arc magmatism, metamorphism and deformation in the NE Jiangxi ophiolitic mélange belt suggest that multi-stage subduction of the Paleo-South China Ocean and Neoproterozoic accretionary orogeny occurred during 1–0.76 Ga at the southeast margin of the Yangtze Block. Combined with the regional geological data, the Neoproterozoic back-arc basin or the foreland basin around the Yangtze Block closed after ~760 Ma. The collision and amalgamation of the Yangtze and Cathaysia blocks resulted in the final closure of the Paleo-South China Ocean, which have occurred in the early Paleozoic.