Practical applications and limitations of basalt discrimination diagrams

Determining the tectonic setting of unknown volcanic rocks continues to be one of the key challenges in geoscience. While discrimination diagrams have been successfully employed due to their ease of use, recently, validation with big data has raised questions about their performance. In this study, the discrimination boundaries of Th/Yb versus (vs.) Nb/Yb and TiO2/Yb vs. Nb/Yb diagrams, which are the most used types of discrimination diagrams, were redefined based on a large amount of compiled data and support vector machine, a machine learning method. The effectiveness of discrimination diagrams was verified, and the limitations and conditions when using them were clarified. The results show that when using the Th/Yb vs. Nb/Yb diagram, only basalts with Th/Yb ratios higher than the discrimination boundary can be identified as volcanic arcs in origin. In contrast, a significant overlap occurs across boundaries in other cases when using these diagrams, particularly for enriched samples with Nb/Yb ratios higher than five. Therefore, when using these diagrams to determine the tectonic setting of unknown samples, their limitations must be considered when interpreting their results.