Comparative Geochemical Provenance Across Regional Granitoid Terranes

Thesis Abstract

This study investigates the geochemical provenance of granitoid terranes through a comparative analysis of regional-scale granitoid suites to address ambiguities in crustal formation processes and the temporal evolution of mantle-crust interaction. The central problem is the inconsistent attribution of source regions and tectonothermal histories across granitoid belts, which obscures models of crustal growth and reworking. The aim is to delineate provenance signals that reliably distinguish tectonic settings and crustal sources, and to assess how granitoid emplacement mechanisms influence geochemical signatures across regional terranes. Specific objectives are (1) to compile a comprehensive geochemical database for granitoid samples from four representative terranes with contrasting tectonic histories; (2) to identify discriminant trace-element and isotopic proxies (REE patterns, HFSE anomalies, Sm-Nd, Pb-Pb, and Lu-Hf isotopic systems) that differentiate crustal sources and mantle contributions; (3) to quantify regional provenance variation using multivariate statistical techniques and regression models; (4) to evaluate the role of crustal assimilation and fractional crystallization in shaping observed geochemical trends; and (5) to synthesize results within a comparative framework to refine models of continental crust formation and stabilization. The study employs a comparative research design, drawing on a population of granitoid bodies from four regional terranes with well-documented tectonic histories an Archean-Proterozoic cratonic granitoid belt, a Phanerozoic continental arc, a post-collision extensional granitoid province, and a mesoproterozoic accretionary orogen. A stratified sampling approach yields a dataset of 320 granitoid rock samples, with 80 samples per terrane, ensuring representation across lithologies, ages, and emplacement styles. Data collection integrates petrographic analysis, whole-rock major and trace element geochemistry (including REEs, HFSE, and LILE), and radiogenic isotopic ratios (Sr-Nd-Pb-Hf). Instrumentation includes X-ray fluorescence (XRF) for major elements, inductively coupled plasma mass spectrometry (ICP-MS) for trace elements, and thermal ionization mass spectrometry (TIMS)/multi-collector ICP-MS for isotopic measurements. Quality control employs certified reference materials, duplicate analyses, and matrix-matched standards to ensure analytical precision. Analytical methods comprise univariate and multivariate statistics, including principal component analysis (PCA) to reduce dimensionality and reveal provenance signals, discriminant function analysis (DFA) to classify granitoids by terrane, and hierarchical clustering to assess similarity networks among samples. Regression modeling and partial least squares (PLS) analysis test associations between geochemical proxies and inferred source characteristics. Isotopic data are interpreted in the context of established crustal evolutionary models, with particular attention to Lu-Hf systematics for mantle vs. crustal differentiation, Sm-Nd model ages (T_DM), and Pb isotopic compositions to constrain crustal reservoir contributions. A conceptual framework integrates the geochemical results with tectonic reconstructions, drawing on Neil theories of crustal growth and melt extraction in convergent-margin settings. Expected findings anticipate distinct provenance signatures among terranes cratonic granitoids showing depleted mantle-like Nd-Hf signatures with older T_DM model ages and non-arc REE patterns; Arc-related granitoids displaying positive Eu anomalies and enriched LILE with elevated radiogenic Pb isotopes; post-collision granitoids exhibiting mixed crustal signatures and elevated Th/U ratios; and accretionary terranes revealing variable crustal assimilation with heterogeneous isotopic compositions. The study will identify robust discriminants (e.g., Sm-Nd-Hf isotopic coherence, specific REE patterns, and HFSE fractions) that distinguish terrane sources and emplacement contexts, while clarifying the role of assimilation versus fractional crystallization in generating observed geochemical diversity. Contributions to knowledge include a validated cross-terrene Provenance Framework for granitoids, enhanced understanding of crustal growth pathways, and refined proxies for interpreting granitoid formation in complex tectonic environments. The study concludes with methodological guidelines for comparative geochemical provenance studies and recommendations for future high-resolution isotopic surveys, as well as proposals to integrate geochronology and thermochronology with geochemical provenance metrics to improve crustal evolution models.