During the past 40 years trace element indiscrimination diagrams have been widely used as a reliable method to determine the tectonic settings of mafic-ultramafic rocks. Li et al. argue that these diagrams, while widely utilized and cited, have often been based on small data sets, containing limited numbers of trace elements and using outdated analytical techniques. Although they are still widely cited, such plots are not representative of the new global data sets.
Using data from constantly updated online resources such as PetDB, Li et al. show that in both binary and ternary diagrams of trace element compositions there is significant overlap of all types of basalts. The authors conclude that, although trace element data from basalts provide useful information on source compositions and melt generation processes, all indiscrimination diagrams tested using the new data show significant overlap and fail to discriminate between any types of basalt other than mid-ocean ridge basalt (MORB) and ocean island basalt (OIB).
Fig. 4. Th-Hf-Ta ternary diagrams comparing the old (grey) and new (this study, colour and in black) discrimination fields for basalts.
Li, C., Arndt, N.T., Tang, Q., Ripley, E.M. (2015) Trace element indiscrimination diagrams. Lithos 232: 76-83. DOI:10.1016/j.lithos.2015.06.022.