Dear Editor,
I have reviewed the manuscript by Chen et al., entitled “Provenance shift during Early-Middle Triassic and its response to the paleogeographic and tectonic evolution of the southwestern South China Block” with pleasure. This manuscript presents new and extensive analyses including detrital zircon dating, Hf isotope for Lower-Middle Triassic turbidite system in the Youjiang Basin and biotite 40Ar/39Ar thermochronology of the adjacent Lingshan granite. They argues a provenance shift during Eatly-Middle Triassic as the turbidite system was filled primarily from the east to the west during the Early Triassic, mainly controlled by the Paleo-Pacific plate subduction while the Middle Triassic turbidite system involved juvenile and volcanic components from the eastern SCB and northeastern Indochina Block in addition to the Early Triassic provenance, as a result of dual impact from the Paleo-Pacific plate subduction and Indochina Block collision. Detrital zircon dating is widely used for paleo-tectonic reconstruction, which provides independent evidence besides other works and should be encouraged. The manuscript is well organized and I generally agree with the data interpretation. Therefore, I recommend its publication by GJ after a minor reversion.
My major concern includes the interpretation of Silurian-Devonian sedimentary rocks in Lingshan granitic rocks belt provided detritus to the turbidite. As Silurian-Devonian sedimentary rocks in Lingshan granitic rocks have very limited exposure, I doubt its ability to provide so much 1000Ma zircons. Furthermore, 1000Ma zircon mostly are not well rounded, this is also in contrast to its recycling. The second concern about the interpretation that an arc related to Pacific subduction provided detritus to the turbidite. As shown in last figure, the arc is located eastern margin of SCB while Youjiang basin is at west margin, how these detritus can be transported across the block? Is there any modern equivalent of such a scenario? The same concern also existed on Indochina as provenance. Recent publications have suggest double subduction of Paleo-Tythes ocean and there is an arc system at the western margin of SCB, these papers can’t be ignored and their implications on the new data presented here should be discussed.