The Spi Lake Formation of the central Hearne domain, western Churchill Province, Canada: an axial intracratonic continental tholeiite trough above the cogenetic Kaminak dyke swarm
The Spi Group is a package of plagioclase porphyritic, amygdaloidal basalt flows and sandstone (Spi Lake Formation) conformably overlain by coarse conglomerate and sandstone (Old Boot Formation). These unconformably overlie the Kaminak Lake segment of the Central Hearne supracrustal belt, western Churchill Province. The Spi Group developed in a small, isolated basin (8 km2) and is older than the Paleoproterozoic Hurwitz Group. Our data demonstrate that the basalts of the Spi Lake Formation are genetically related to the ca. 2450 Ma Kaminak dyke swarm, a speculation previously promoted by some workers based on field characteristics alone. They are continental tholeiites with large ion lithophile and light rare-earth element enriched multielement profiles with prominent high field-strength element troughs. The 143Nd/144Nd compositions overlap the contemporaneous chondritic bulk-earth data. All of these are features we infer to have resulted from mixing of melts from dominantly depleted mid-ocean ridge basal...