U-Pb geochronology of Upper Triassic - Lower Jurassic detrital sequences from SE margin of the South China Block: implications for Palaeo-Pacific subduction and tectonic evolution

We performed U-Pb dating of detrital zircons and conducted petrological and whole-rock geochemical analyses to assess the provenance of the Upper Triassic - Lower Jurassic clastic rocks in the southeastern margin of the South China Block. Detrital zircon U-Pb ages are mainly classified into age groups of 2000-1700, 900-700, 490-390 and 280-210 Ma, consistent with derivation from the Jiangnan orogenic belt, Nanling Belt, as well as Wuyi and Yunkai domains. Lower Jurassic samples yield a special main age population of 200-190 Ma, and these detrital zircon grains have low Th/U and Nb/Hf ratios and high Th/Nb and Hf/Th ratios, showing they are derived from a continental magmatic arc. However, the cross-correlation and likeness coefficients of kernel density estimates of Upper Triassic and Lower Jurassic sandstones are 0.8608 and 0.8403, indicating that their populations are highly similar. Since the tectonic setting is the key factor in controlling the relationship between source and sink, the stable supply of identical provenance suggests that the tectonic setting did not significantly change during Late Triassic - Early Jurassic time. Sandstone petrography, regional facies distribution and the detrital zircon age patterns all reflect a consistent tectonic setting for the South China Block during Late Triassic - Early Jurassic time. The Palaeo-Pacific subduction therefore did not control the tectonic evolution of the South China Block until after the Early Jurassic Epoch.

Automated summary

In this study, detrital zircons from Upper Triassic - Lower Jurassic clastic rocks in the southeastern margin of the South China Block were analyzed using U-Pb dating and petrological analyses to determine their provenance. The results show that these rocks mainly originated from the Jiangnan orogenic belt, Nanling Belt, and Wuyi and Yunkai domains. It was also found that the Lower Jurassic samples have a unique population with characteristics of a continental magmatic arc. Furthermore, the similarity between the Upper Triassic and Lower Jurassic sandstone populations suggests that the tectonic setting did not change significantly during this time period.