EXPLORING THE PLUMBING SYSTEMS OF PROTEROZOIC FLOOD BASALT PROVINCES: SECULAR VARIABILITY OF MANTLE SOURCES IN DYKE SWARMS OF THE SOUTHERN AND SUPERIOR PROVINCES, CANADIAN SHIELD

Large igneous provinces (LIPs) represent anomalous within-plate magmatism that is mostly composed of mafic igneous rocks with subordinate intermediate to silicic rocks. They cover extensive (10⁵ km²) areas of continental and oceanic crust and represent mass transfer of mantle materials to the crust. Precambrian giant radiating dyke swarms are thought to represent the plumbing system of eroded ancient LIPs. Moreover, mafic dyke swarms can help to reconstruct ancient supercontinents, identify distinct mantle sources, and locate mineral deposits. The Superior Province of the Canadian Shield preserves one of the highest mafic dyke densities amongst all Archean cratons. Eight dyke/sill swarms from Sothern and Superior Provinces are selected for this study. They include Matachewan (2.5 Ga), Fort Frances (2.2 Ga), Marathon (2.12 Ga), Biscotasing (2.16 Ga), Nipissing (2.2 Ga), Sudbury (1.2 Ga), Abitibi (1.1 Ga), and Pukaskwa (1.1 Ga). The application of new geochemical fingerprinting (Th/Nb versus TiO₂/Yb) demonstrates that the Matachewan swarm and Nipissing sills are derived from a subduction-modified lithospheric mantle (SZLM). The Biscotasing and Marathon swarms are derived from a source transitional between MORB and OIB. The Fort Frances swarm is derived from the MORB domain. In comparison, the younger dyke swarms are related to an OIB source with the exception of the Pukaskwa, which shows a trend from transitional to SZLM source. The results indicate that the Superior Province underwent several magmatic events during the Proterozoic and that they were derived from both lithospheric and sub-lithosphere mantle sources.