| Summary: | Mafic volcanic sequences of tholeiitic basalt and associated komatiite are common to many Precambrian shields of the world. Recently discovered remnants of Archean greenstone belts in the northern Superior Province of Canada exhibit characteristics similar to larger belts of the southern Superior Province. Three of the best preserved belts are trapped in ca. 2.77--2.88 Ga tonalitic intrusives of the Faribault-Thury amphibolitic Complex (FTC), and provide direct evidence for the nature of the mantle prior to the major volcanic events of the late Archean (ca. 2.7 Ga). These belts consist of amphibolite facies rocks of volcanic and sedimentary origin, in one of which a wide variety of cumulates are preserved. The association of the lavas with meta-pelites, iron formations, marbles, and the lack of conglomerate and clearly crustally contaminated lavas suggest that the FTC lavas were erupted in an oceanic environment. The three belts are separated by over 100 km, but exhibit similar chemical characteristics and may represent the base of an extensive early mafic crust. (Abstract shortened by UMI.)
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