Temporal evolution of the Neoarchean Central Hearne supracrustal belt: rapid generation of juvenile crust in a suprasubduction zone setting

New U–Pb zircon ages are reported for 17 volcanic, plutonic and sedimentary rocks from the Neoarchean Central Hearne supracrustal belt in the Western Churchill Province of the Canadian Shield. The Central Hearne supracrustal belt, historically referred to as the Rankin-Ennadai greenstone belt, is a major granite-greenstone terrain with a strike length of over 700 km. This study, focused on the central and eastern segments of the belt in the Kaminak Lake area, represents the first detailed chronological study of this extensive greenstone belt. The geochronological data indicate rapid formation of crust between 2711 and 2667 Ma. Rocks of the oldest assemblage (I) formed between 2711 and 2691 Ma and consist of mixed tholeiitic and calc-alkaline mafic and felsic, submarine to subaerial volcanic rocks. Minor plutonic rocks (Group 1) are associated with this interval. A younger assemblage (II) of volcanic rock with significant calc-alkaline plutonic rocks (Group 2) developed between 2686 and 2679 Ma. A period of deformation (D1) locally separates the two assemblages. Major regional, penetrative deformation and metamorphism developed during the latter stages of the plutonic event at ca. 2680 Ma. An extensive belt of metasedimentary rocks and associated iron formation was deposited after 2681 Ma, based on ages of detrital zircon. The youngest events include intrusion of 2666.4±1.1 Ma post-deformational granite (Group 3), 2659 Ma carbonatite [Can. J. Earth Sci. 29 (1992) 896], and deposition of post-2660 Ma conglomerates and arenites of possible “Timiskiming”-type. There is no indication of contributions from Mesoarchean crust either in inherited grains in igneous rocks, or as detrital grains in sedimentary rocks. Although the evolutionary sequence has parallels to greenstone belts such as the Abitibi belt, in terms of the rock types and relative timing of events, there are some differences. We envision development of the belt in an extensional, oceanic suprasubduction environment.