Do major oxide tectonic discrimination diagrams work? Evaluating new log‐ratio and discriminant‐analysis‐based diagrams with Indian Ocean mafic volcanics and Asian ophiolites

Many geochemical diagrams exist that classify old volcanic terranes of ambiguous provenance into various modern plate tectonic settings, with variable success. Recently proposed diagrams, based on log‐ratios and linear discriminant analysis with large datasets of major oxides, were tested here with data for ocean island, arc and mid‐ocean ridge lavas from the Indian Ocean. Success rates are 45–100%, with misclassifications potentially caused by alteration, although alteration demonstrably need not cause misclassification. The diagrams were further applied to some Asian ophiolites, representing Tethyan and Indian ocean crusts, to see if the diagrams confirm their tectonic setting inferred from trace and isotopic data. Lower success rates (30–60%, but 75–100% for specific suites) are not surprising in view of the ubiquitous and complex alteration in ophiolites. Log‐ratio transformation and linear discriminant analysis appear to be powerful methods when discrimination diagrams are based on major oxide data alone.