A multi-isotope approach to unravel melt sources, crustal evolution, and uranium enrichment in a Proterozoic active margin

Proterozoic magmatic provinces record lithospheric stabilization, supercontinent assembly, and emerging geodynamic and geochemical cycles that underpin plate tectonics and metallogenesis. The late Paleoproterozoic Makkovik Province, an accretionary orogen along Laurentia’s eastern margin in Canada, represents a window into these processes, yet links between crustal evolution and uranium mineralization remain unresolved. We integrate zircon U−Pb geochronology with zircon Hf−O and orthoclase Pb isotope analyses from 14 granitic, rhyolitic, and tuff samples (ca. 1900−1800 Ma) to evaluate crustal growth versus recycling during assembly of the supercontinent Nuna. The samples young from west to east and display a secular shift in zircon εHf from unradiogenic to juvenile values, accompanied by an increase in zircon δ18O from mantle-like (5.3‰ ± 0.6‰) to as high as 7.47‰ ± 0.64‰, indicating a shift from older, lower- to mid-crustal sources to younger sources with increasing supracrustal contributions. Orthoclase Pb isotopes imply two source endmembers: reworked Archean crust with low-μ (238U/204Pb), high-κ (232Th/238U) Pb evolution, and sediment-derived magmas with high-μ, low-κ Pb evolution. When linked to field observations and tectonic stages—backarc initiation, basin maturation, inversion, and post-accretionary plutonism—the isotopic architecture indicates episodic mantle addition superimposed on dominant recycling of Archean lithosphere and newly formed juvenile crust in the Paleoproterozoic. Modeling shows that elevated source-μ in ca. 1800 Ma magmas requires preexisting U enrichment, consistent with sedimentary accumulation and hydrothermal processes during basin evolution. The results suggest that volcano-sedimentary processes were key agents of metal preconditioning along ancient craton margins.