Stratigraphic and U-PbSHRIMP detrital zircon evidence for a Neoproterozoic continental arc, central China: Rodinia implications

The Bikou terrane of central China is located within the southwest Qinling Mountains along the northwest margin of the Yangtze Plate. The terrane consists of a volcanic assemblage, the Bikou Group, and a correlative volcaniclastic turbidite sequence, the Hengdan Group. U-Pb SHRIMP detrital zircon dating of 181 grains collected from the Hengdan Group indicates ages from ca. 850 to 700 Ma, with a peak near 770 Ma. Given the predominance of volcanic, single-cycle zircons within the Hengdan Group and the thick succession of coarsening-upward volcaniclastic marine sediments, the sequence is best interpreted as a fore-arc basin. This interpretation is supported by previous U-Pb SHRIMP and conventional U-Pb zircon dating performed within the Bikou Group that indicates subduction-related magmatism persisted from at least ca. 850 to as recently as 700 Ma. Together, these data indicate that the Bikou terrane is a fragment of a Neoproterozoic continental arc system and that the Yangtze Plate was bordered by a convergent oceanic margin. The South China Block must therefore occupy an outboard position with respect to Rodinia reconstruction models.