Komatiites are ultramafic magmas which only formed during the Archean because of hotter mantle conditions. Because they are an extinct form of magmatism, their volcanology and environmental interactions are poorly constrained. Komatiites of the 2.7 Ga Shebandowan greenstone belt, near Thunder Bay, Ontario, Canada, are particularly well-exposed and provide a unique opportunity to describe komatiite-sediment interactions and the formation of peperites – a product of lava and unconsolidated, water-saturated sediment interactions. The contact between komatiites and argillites and brecciated textures were described in detail to compare with modern magma-sediment mingling products. In the contact zone between the komatiites and argillites, samples have an argillite matrix with angular shaped aphanitic komatiite pieces. When fractured, the komatiite would accommodate sediment, creating wispy flow like structures and globular pyrite. This creates a “mixed” look to the argillite with fractures cutting across its surface. Peperites give insight into how komatiites and other high-temperature lavas may interact with wet sedimentation during emplacement. Additionally, heated basin waters can produce hydrothermal activity and crustal assimilation within komatiites that may result in mobilization of metals and formation of sulfide mineral deposits.
