A robust discrimination scheme for ocean island basalts based on Ce/Rb, Tb/La, and Ba/Nb ratios

A ternary Ce/Rb – (Tb/La)*100 – (Ba/Nb)/5 plot proposed here for classifying ocean island basalts (OIB) is considered as a reliable and robust approach not only for identifying the geochemical affinities of their mantle source regions, but also for appraisal of their source region lithologies. Sr-Nd-Pb-Hf-He isotopic ratios are traditionally regarded as the most reliable means for the classification of OIBs. However, these are not as easily nor quickly obtained as trace elements analyses. Therefore, the ternary plot proposed here is regarded as a suitable equivalent for the classification of OIB end-members using trace elements alone. The ternary Ce/Rb – (Tb/La)*100 – (Ba/Nb)/5 plot was tested by a screened OIB global data set for which the geodynamic settings were recognized based on their isotopic data. It provided precise, sharp boundaries for HIMU, EMI, EMII, and DMM affinities of OIB that correspond with their isotopic counterparts, indicating that these trace element ratios are controlled by their source regions and settings. The ternary plots also identify the geochemical affinity of the source mantle regions for intraplate continental basalts. Mantle geochemical affinity and lithology of source region suggested by the present ternary model are also comparable with the mantle source characteristics and lithology based on the studies of olivine phenocrysts hosted by unmodified OIB.