Geology of an Archean Greenstone Belt at Point Lake, Northwest Territories, Canada

• Main Author: Considine, Patrick Rowan
• Format: Text
• Language: unknown
• Published: ODU Digital Commons 1995
• Subjects: Archean greenstone belt; Point Lake (Canada); Supracrustal sequence; Geology; Canada; Northwest Territories
• Online Access: https://digitalcommons.odu.edu/oeas_etds/22; https://digitalcommons.odu.edu/cgi/viewcontent.cgi?article=1017&context=oeas_etds

Several well-preserved circa 2.6 Ga Archean granite-greenstone belts are exposed in the Slave Province of Northwest Territories, Canada. At Point Lake, a "supracrustal sequence" comprised mainly of mafic volcanic and metasedimentary rocks lies over and east of a granitoid gneissic terrane. Field and laboratory studies have helped to clarify the petrography and structural relationships of this fold-and-thrust belt. Traditional models have suggested that granite-greenstone belts in the Slave Province are relict continental rifts in which volcanic and sedimentary rocks filled troughs in older sialic crust. However, this study supports a collisional model for the Slave Province, in which oceanic crust and an accretionary wedge were scraped off an eastward subducting plate. The supracrustal sequence consists of a west-verging fold-and-thrust belt which contains metamorphosed graywacke turbidites, ultramafic and gabbroic rocks, pillow basalts, limestone, shale and tuff. A mylonite zone separates the gneissic terrane from the supracrustal sequence. The mylonite is interpreted to be a basal decollement along which the supracrustal sequence was emplaced over gneissic terrane. The sequence of lithologies and structures at Point Lake resembles Phanerozoic collision zones where rocks of oceanic affinity have been emplaced upon continental crust.