Provenance and paleogeography of the Early Paleozoic basin in the northern Yangtze Block: Constraints from detrital zircon U-Pb-Hf data

Abstract

The Proto-Tethys was a significant post-Rodinia breakup ocean that eventually vanished during the Paleozoic. The closure timing and amalgamation history of numerous microblocks within this ocean remain uncertain, while the Early Paleozoic strata on the northern margin of the Yangtze Block archive valuable information about the evolution of the Shangdan Ocean, the branch of the Proto-Tethys. By comparing the detrital zircon U-Pb-Hf isotopic data from Cambrian, Ordovician, and Silurian sedimentary rocks in the northern Yangtze Block with adjacent blocks, it was found that detrital zircons in Cambrian strata exhibit a prominent age peak at ∼ 900–700 Ma, which indicates that the primary source of clastic material in the basin was the uplifted inner and margin regions of the Yangtze Block. In the Silurian, abundant detrital material from the North Qinling Block was transported to the basin due to the continuous subduction and eventual closure of the Shangdan Ocean. This process led to two distinct age peaks at ∼500–400 Ma and ∼900–700 Ma, indicating a bidirectional provenance contribution from both the North Qinling Block and the Yangtze Block. This shift demonstrates that the initial collision between these two blocks occurred no later than the Silurian. The northern Yangtze Basin transitioned from a passive continental margin basin in the Cambrian to a peripheral foreland basin in the Silurian. Major blocks in East Asia, including South Tarim, North Qilian, North Qinling, and North Yangtze, underwent peripheral subduction and magmatic activity to varying degrees during the late Early Paleozoic, signifying the convergence and rapid contraction of microplates within northern Gondwana and the Proto-Tethys Ocean. These findings provide new insights on the tectonic evolution of the Proto-Tethys Ocean.