Comparative Geochemical Provenance of Sedimentary Rocks Across Tectonic Shields

Thesis Abstract

This study addresses the persistent gap in understanding geochemical provenance signals recorded in continental-margin and intracontinental sedimentary rocks by comparing lithologies across major tectonic shields to reveal shifts in source-area processes through time. The aim is to elucidate how provenance indicators—detrital zircon U-Pb ages, Hf isotopes, major and trace element compositions, REE patterns, and Nd isotopes—vary between shields and what these patterns reveal about crustal growth, weathering regimes, and sediment routing. Specific objectives are (1) to compile and harmonize a cross-shield dataset of 1,200 sedimentary rock samples representing Archaean to Phanerozoic successions from the North American, West African, Baltic, and Australian shields; (2) to characterize provenance using detrital zircon age distributions, Hf isotopic signatures, and Nd–Sr–Pb isotopic systems; (3) to quantify geochemical discrimination among shields through multivariate statistics and regression analyses linking sediment composition to source-type lithologies; (4) to assess temporal changes in provenance signals and their correlation with tectono-thermal events; and (5) to synthesize findings within established provenance frameworks, including the Tournaisian–Carboniferous orogeny and LIP-related crustal differentiation. Methodologically, the research adopts a comparative cross-sectional design anchored in a transectional sampling strategy across the four shields. The population comprises well-documented sedimentary rock units with available detrital zircon populations and isotopic datasets spanning pre-Cambrian to Paleozoic intervals. A stratified random sample of 1,200 specimens will be analyzed, prioritizing comparable lithofacies (sandstones,arkoses) and ensuring balanced representation across shields and time slices. Data collection integrates existing geochemical databases and targeted new measurements. Instrumentation includes laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) for trace elements, laser ablation multi-collector ICP-MS for U-Pb zircon dating, MC-ICP-MS for Hf isotope analyses, and TIMS for Nd isotopic compositions. Analytical precision targets include U–Pb concordance better than 1%, Hf isotope ?Hf(t) uncertainties ? ±2?, Nd isotopic ?Nd(t) within ±0.5, and REE patterns normalized to chondritic meteorites. Data analysis proceeds through a layered approach. Descriptive statistics summarize central tendencies and dispersion for each provenance proxy. Multivariate techniques—including principal component analysis (PCA), canonical variate analysis (CVA), and hierarchical clustering—identify cross-shield geochemical fingerprints. Regression models and analysis of variance (ANOVA) test the influence of shield identity, stratigraphic age, and sedimentary facies on provenance indicators. A Bayesian mixing-model framework tests hypothesized source contributions from crustal end-members, constrained by isotopic and trace-element signatures. The study evaluates theoretical constructs from tectonic continental growth theories and crustal recycling paradigms, with explicit use of theories of sedimentary geochemistry and detrital mineralogical provenance, alongside the Wilson–Daly model of crustal differentiation as reference points. Expected findings include distinct provenance fingerprints for each shield, with North American and Baltic shields showing Proterozoic crustal components, while West African and Australian shields display enhanced Archaean crustal signatures. Zircon U-Pb age spectra and ?Hf(t) values are anticipated to reflect differential crustal recycling and juvenile crust formation rates, accompanied by recognizable shifts in Nd isotopes indicative of mantle-crust interactions during major orogenic episodes. Variation in REE patterns and immobile trace-element ratios (e.g., Th/Nb, La/Nb) is expected to discriminate source terranes and weathering intensity, providing a robust cross-shield discrimination framework. The study contributes to knowledge by establishing a harmonized, cross-shield geochemical provenance framework for sedimentary rocks, enabling direct comparison of source-area processes and revealing regional differences in crustal growth histories and sediment-routing pathways. It will refine provenance interpretation in geological reconstructions, improve constraints on tectono-thermal histories, and offer a calibrated cross-shield dataset for future models of crustal evolution. The main conclusion anticipates that mantle-derived juvenile crust contributions and ancient crustal components vary systematically among shields, mirroring shield-specific tectonic histories. Recommendations include expanding isotopic coverage to incorporate additional radiogenic systems, integrating detrital mineralogy with geochronology for enhanced source discrimination, and applying the framework to cover transitional orogenic settings to test its generality.