Paleoproterozoic Detrital Zircons in Mesozoic Sediments From the Yangtze Craton: Where did They Come From?

Detrital zircons from the Late Triassic to Early Jurassic continental sandstones in the Yangtze craton have been dated by SHRIMP and LA-ICP-MS methods. The samples show similar age patterns clustering in the 1.7-2.0 Ga range, with three minor age probability peaks at ca. 2.4-2.6 Ga, 700-850 Ma and 210-250 Ma. The occurrence of 1.7-2.0 Ga detrital zircons in South China were commonly interpreted as associated with the North China craton. However, the present Paleoproterozoic zircons may have no relation with the North China craton because (1) the unimodal age distribution of the Late Paleoproterozoic (1.8-1.9 Ga) zircons and the paucity of Neoarchean-Early Paleoproterozoic zircons from samples are not consistent with the formation of the major blocks of the North China craton prior to 2.5 Ga; (2) the Triassic Qinling-Dabie Orogen is possibly a high-relief uplift compared to the southern margin of North China craton and likely served as a barrier to southward transportation of detritus; and (3) detrital zircon age patterns of the Late Proterozoic to Early Paleozoic clastic rocks from the North China craton are different form those of the present Triassic rocks. Likewise, the Yangtze craton is not a major source as it comprises numerous Neoproterozoic granitoids, incompatible with the Predominance of Paleoproterozoic zircons in most of the Mesozoic sediments. Alternatively, the Cathaysia block is a more favorable provenance of the 1.7-2.0-Ga zircons as various Paleoproterozoic crystalline rocks have been recognized there. This result is consistent with paleogeographic studies and Paleocurrent data. Abundant Paleoproterozoic detrital zircons were also found in the Middle-Late Triassic Songpan-Ganzi Complex, west of the Yangtze craton, which might also have been sourced by the Cathaysia block. The extensive occurrence of 1.8-1.9 Ga zircons is indicative of the existence of a vast Cathaysia Oldland that has formed largely in the Late Paleoproterozoic and a westward draining pan-Yangtze river system in the Early Mesozoic which have fed the contemporaneous basins in and outside South China.