Comparative Geochemical Signatures of Basaltic Volcanoes Across Tectonic Settings

Thesis Abstract

Basaltic volcanism exhibits pronounced geochemical diversity that reflects mantle source heterogeneity, tectonic setting, and magmatic differentiation processes, yet a coherent cross-setting synthesis remains incomplete. This study addresses the problem of inconsistent cross-comparisons of basaltic geochemistry across divergent tectonic environments by developing an integrated framework to quantify how major and trace element signatures, isotopic compositions, and volatile contents vary with tectonic context, magma genesis, and crustal interaction. The aim is to identify robust geochemical discriminants that distinguish basaltic magmatism in divergent, convergent, oceanic island arc, and intraplate settings, and to test whether canonical mantle-derived signatures are preserved or modified by crustal processes. Specific objectives are (i) to compile a harmonized global geochemical database of basaltic rocks (n ? 2,000 analyses) with corresponding tectonic classifications; (ii) to evaluate major, trace element, and Sr–Nd–Pb–Hf isotopic systems using multivariate statistics and hierarchical clustering to discern tectonic setting fingerprints; (iii) to quantify the influence of crustal assimilation and fractional crystallization through mass balance modeling and trace element thermometry; (iv) to test the applicability of theoretical frameworks such as the source-related variation model and the crustal contamination continuum across settings; and (v) to propose a standardized cross-setting interpretive protocol for basaltic geochemistry. A mixed-methods approach integrates geochemical data with geodynamic context. The population comprises basaltic rocks from well-documented suites across four primary tectonic settings mid-ocean ridges (MOR), subduction-zone arcs, oceanic island arcs, and intraplate regions. The sample comprises 2,000 whole-rock major and trace element analyses and 600 isotope data points (Sr, Nd, Pb, Hf) drawn from published databases and targeted field campaigns. Data collection instruments include X-ray fluorescence (XRF) for major elements, inductively coupled plasma mass spectrometry (ICP-MS) for trace elements, and multi-collector ICP-MS for isotopes, complemented by LA-ICP-MS for in-situ trace element mapping on selected mineral phases. Quality control employs standard reference materials, duplicate analyses, and inter-laboratory cross-checks to ensure reproducibility. Data analysis proceeds through (i) normalization and elemental ratio computation to highlight incompatibilities with fractional crystallization; (ii) multivariate techniques (principal component analysis, canonical correlation analysis) to identify tectonic setting–geochemical linkages; (iii) hierarchical clustering and discriminant analysis to test the predictability of tectonic setting from geochemical fingerprints; (iv) isotope-tracer modeling to interpret source characteristics and crustal contamination; and (v) mass balance and melting column simulations to constrain degrees of partial melting and assimilation. The analytical framework incorporates the source-related variation model and the crustal contamination continuum, with uncertainty quantified via bootstrapping and Monte Carlo simulations. Expected findings include (i) a defined geochemical signature matrix that differentiates MOR, subduction-related arcs, oceanic islands, and intraplate basalts, particularly in radiogenic isotope ratios (Sr-Nd-Pb-Hf) and trace element ratios (Ce/Yb, Sm/Yb, Nb/U, Th/Yb); (ii) a quantifiable contribution of crustal assimilation in arc and intraplate settings relative to MOR basalts, evidenced by systematic deviations in isotopic arrays and enriched incompatible trace element patterns; (iii) evidence that crustal contamination modulates but does not erase mantle-derived signatures in all settings, with varying degrees of fractional crystallization contributing to secondary differentiation trends; and (iv) a reproducible cross-setting interpretive protocol that enhances comparability across studies. The study contributes to knowledge by providing a unified, cross-tectonic framework for basalt geochemistry, clarifying the extent to which tectonic setting controls mantle source signatures versus crustal processes, and offering standardized analytical pathways for future comparative research. The main conclusion anticipates that while mantle source characteristics imprint robust baseline signatures, secondary processes such as crustal assimilation introduce setting-dependent modifications that must be explicitly modeled to avoid misattribution of tectonic context. Recommendations include the adoption of a standardized geochemical discriminant toolkit for basaltic rocks, expanded isotopic datasets for underrepresented regions, and integrated petrogenetic modeling that couples melting with crustal interaction to improve interpretations of basaltic magmatism in diverse tectonic environments.