The metamorphic architecture of the Onaman-Tashota greenstone belt, eastern Wabigoon subprovince, Ontario

Abstract

A detailed metamorphic study of the Onaman-Tashota greenstone belt (OTGB) indicates peak metamorphic mineral assemblages in mafic metavolcanic and metapelitic supracrustal rocks developed during transitional greenschist-amphibolite facies or amphibolite facies metamorphism at mid-crustal levels. This metamorphism resulted in metamorphic devolatilization over large areas of the OTGB, and is an important requirement in metamorphic gold mobilization models. Episodic M1A contact metamorphism (ca. 2705-2685 Ma) produced localized amphibolite facies contact aureoles with variable temporal relationships to rock fabric depending on pluton age. M1B regional metamorphism was relatively concurrent with M1A, and occurred during D1 north-south compression (ca. <2699 – >2685 Ma) producing porphyroblasts with syn-deformational geometries and minerals that define the strong S1 fabric across the OTGB. Finally, M2 regional metamorphism occurred during D2 deformation (ca. 2671-2667 Ma), and can be identified in the Albert-Gledhill assemblage and the Humboldt Bay deformation zone where the dominant S2 fabric is defined by M2 mineralogy.