An accreted micro-continent in the north of the Dabie Orogen, East China: Evidence from detrital zircon dating

Abstract

Continent–continent collision between the North China Block (NCB) and South China Block (SCB) took place along the Qinling–Tongbai–Hong'an–Dabie orogens during the Triassic. A micro-continent with Paleozoic arc magmatism has been recognized in the northern Qinling–Tongbai orogens; however, it remains unclear whether the micro-continent extended to the Dabie Orogen to form a ribbon-shaped micro-continent, due to later burial by the Hefei Basin in the north. To solve this problem, we conducted LA–ICP–MS UPb dating of zircons from Silurian to Cretaceous sandstones and volcanic rocks from the southern margin of the basin. The age spectra of detrital zircons suggest that the Dabie Orogen and later basin cover were the sources of the analyzed sandstones. The detrital and inherited zircons indicate Neoproterozoic, early and late Paleozoic magmatism in the Beihuaiyang unit in the north of the Dabie Orogen. The zircon and previous geophysical data show that a micro-continent bounded by the Feizhong Suture in the north and the Xiaotian–Mozitang Suture in the south existed between the NCB and the Triassic Dabie Orogen, and its northern half is buried by the Jurassic–Paleogene Hefei Basin. The Beihuaiyang micro-continent experienced early Paleozoic arc magmatism caused by southward subduction of the Erlangping oceanic crust and late Paleozoic magmatism related to northward subduction of the Paleotethyan oceanic crust. The micro-continent was accreted to the southern edge of the NCB at the end of the Early Devonian (ca. 400Ma) via arc–continent collision. Similarly to the Qinling–Tongbai orogens, the Dabie Orogen contains a Paleozoic accretionary system in the north and a Triassic collisional system in the south; thus, it is suggested that a ribbon-shaped micro-continent, >900km long and 50–100km wide, was present along the entire Qinling–Tongbai–Hong'an–Dabie orogens prior to the middle Paleozoic. This micro-continent might have originated as a result of middle Neoproterozoic rifting along the margin of the SCB.