Revealing Unmapped Tectonic Settings through Geochemical Fingerprinting of Th-Nb-Yb

Abstract

The widely used tectonic discrimination diagram, “Th/Yb-Nb/Yb,” has long served as a global standard. However, it is limited in scope, as it primarily distinguishes igneous rock samples within well-established tectonic settings, such as nonsubduction environments (e.g. midoceanic ridge and oceanic island basalts) and subduction-related volcanic arcs (e.g. continental and island arcs). This study presents a novel approach to geochemical modeling for Th-Nb-Yb systematics, aimed at enhancing our understanding of various magmatic and tectonic settings. We developed a new geochemical discrimination diagram based on Nb/Yb versus Th/Nb ratios, which successfully identifies and differentiates a wider range of tectonic environments than previous models. Our findings demonstrate that this diagram can distinguish between intracontinental rifting, mixed oceanic-continental rifts producing low-alkaline-enriched tholeiitic magmatism, within-plate continental extensional settings (early lithospheric rifts), and alkaline arcs. Additionally, the model identifies magmatic interactions associated with active continental margin that occur due to oceanic slab break-off. Furthermore, our research refines the use of Th/Yb, Nb/Yb, and La/Yb ratios for improved and more accurate magmatic alkalinity discrimination, enabling clearer differentiation among tholeiitic, calc-alkaline, enriched tholeiitic, and alkaline rock types. These advancements provide a more comprehensive framework for interpreting magmatic processes and their tectonic implications, offering valuable insights to the fields of geochemistry and tectonics.