Discrimination of OIB Volcanic Rocks of Bikou Group and Their Tectonic Implication

Geochemical analysis of the volcanic rocks of the Bikou group from the southern Tongqianban-Tuohe region reveals that they are of the alkaline basalts and subalkaline tholeiitic basalts,which have an affinity to the typical ocean island basalts (OIB) in the contents of Nb,Ta,Ce and the Ba/Ce,Ti/Y and Zr/Y ratios. In addition,the N-MORB-normalized spider diagram and the Chondrite-normalized REE pattern show that the two kinds of rocks were generated from the same parental magmatic source. The tectonic discrimination diagrams of the 2Nb-Zr/4-Y,TiO₂-MnO-P₂O₅,Ti/Y-Ba/Zr and Ti/Y-Ba/Nb have fairly signified that the rocks occurred in an intra-oceanic tectonic setting,which would be a critical evidence to confirm an oceanic basin developed in the study region in the Neoproterozioc time.