Depositional environments of the 3.0 Ga. Finlayson and Lumby Lake greenstone belts, Superior Province, Ontario, Canada

Abstract

The Finlayson and Lumby Lake Greenstone BeHs are located approximately 200km west of Thunder Bay, Ontario, nom of Atikokan, Ontario. Within both the Finlayson Lake and Lumby Lake Grsenstom belts two distinct sequences af sedimentary rocks are present. €a& of the belts contains an upper and a lower sedimentary rocù sequence which differ in age and chernical composition- The lower sequence of the Finlayson Lake Greenstone Belt is represented by the Little Falls Lake metasedimentary rocks and the laterally equivalent lower Finlayson Lake rnetasedimentary rocks. These rocks consist of coarse-grained sandstones, conglomerates, and lesser interbedded mafic detritusiich metasedimentary rocks and are Iaterally continwus with felsic volcanic rocks to the south. Deposition of these sedimentary rocks was by highdensity turbidity ainent processes. Their chemical composition is distinct from that of the upper Finlayson Lake metasedimentary rocks and suggests a single felsic volcanic source with composition similar to that of the Steep Rock Upper Felsic unit and the Old Tonalite unit.