Abstract

Tholeiitic metabasalts and metaandesites from sub-greenschist metavolcanics in the Abitibi volcanic belt northeast of Noranda–Rouyn display delicate and ornamental crystals indicative of rapid or supercooling. These textures compare directly with those observed in modern sea-floor basalts. The textural and chemical data suggest that these Archean rocks may represent a complete (?) section of an island arc, from the deeper stratigraphic levels (mostly monotonous tholeiites) to the more typical island-arc superstructure with intermingled calcalkaline and tholeiitic series. The deeper section can only be a relic of ancient oceanic lithosphere if the Archean sea floor had a wider range in chemistry than the modern-day equivalent.

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