SHRIMP Age and Geochemistry of the Bikou Volcanic Terrane: Implications for Neoproterozoic Tectonics on the Northern Margin of the Yangtze Craton

The Bikou volcanic terrane is predominated by subalkaline tholeiitic lavas. Rock samples display lower initialratios of Sr and Nd, 0.701248-0.704413 and 0.511080-0.512341 respectively. 207pb and 208pb are significantly enriched inthe lavas. Most samples have positive εNd, which indicates that the magma was derived from EM-type mantle source,while a few samples with negative εNd indicate that there was contamination in the magma evolution. Magmadifferentiation is demonstrated by variations of LREE and LILE from depletion to enrichment. Additionally, normalizedREE patterns and trace elements showed that lavas from the Bikou volcanic terrane have similar characteristics to those ofbasalts in arc settings caused by subduction and collision. Analyses showed that the Bikou volcanic terrane is a volcanicarc. New evidence proved that the Hengdan Group, north of the Bikou arc, is a turbidite terrane filling a forearc basin.Consequently, the Bikou volcanic terrane and the Hengdan turbidite terrane construct an arc-basin system. New SHRIMPages showed that this arc-basin system developed on the northern margin of the Yangtze craton in the Neoproterozoic(846-776 Ma), and this arc-basin system is in agreement with the tectonic processes of Rodinia in the Neoproterzoic.