Petrogenetic insights on the largest volcanic pulse in the Archean Abitibi greenstone belt, Canada: the Stoughton-Roquemaure assemblage

The Stoughton-Roquemaure (S-R) assemblage represents the largest and most rapidly emplaced (~3 m.y.) volcanic sequence within the Abitibi greenstone belt, yet, much of its petrogenetic history remains unexplored. To address this, we compile 1,319 whole-rock geochemical analyses, comprising 1.0% komatiites, 2.6% komatiitic basalts, 37.1% tholeiitic basalts, 0.5% tholeiitic intermediate volcanics, 8.1% medium-Th basalts, 19.1% high-Th basalts, 0.4% low-Zr basalts, 4.2% transitional intermediate volcanic rocks, 17.1% calc-alkaline intermediate volcanic rocks, and 9.9% felsic volcanic rocks. Primary magma estimates for komatiites and tholeiitic basalts reveal two clusters of mantle potential temperatures (TP) of 1637 ± 65 °C and 1575 ± 105 °C, suggesting a mantle plume influence. Fractional crystallization (FC) models, under varying pressures and H₂O contents, explain the evolution of the tholeiitic suite. However, more than half of the S-R samples exhibit transitional to calc-alkaline affinities, modeled as the result of assimilation–fractional crystallization (AFC) or magma mixing between tholeiitic basalt and a TTG-like crustal end-member. The generation of these volcanic rock signatures implies the development of complex crustal magmatic systems. Spatial analysis reveals that these signatures are prevalent in the north whereas ultramafic and tholeiitic rocks dominate central and southern zones, defining a north-south geochemical zonation. This likely reflects rapid ascent through a thinner crust in the south versus enhanced crustal interaction in the north. Our results underscore the interplay between the mantle-derived magmas and crustal architecture in controlling volcanic evolution. These results offer new insights into the geochemical diversity and voluminous magmatism of the S-R assemblage and contribute to our understanding of Archean lithospheric development.