Stratigraphy, sedimentology and physical volcanology of the Henik Group, central Ennadai-Rankin greenstone belt, Northwest Territories, Canada: late Archean paleogeography of the Hearne Province and tectonic implications

Abstract

Extensive areas of the Hearne and Rae provinces are underlain by Archean metavolcanic and metasedimentary rocks. In the Rae Province, supracrustal sequences with prominent continental to shallow-water quartz arenites have been interpreted by others as rift and passive margin deposits. In the Hearne Province to the southeast, the Ennadai-Rankin greenstone belt is exposed in an area ca. 700 × 200 km, forming the second largest greenstone belt in Canada. It comprises mainly greenschist-facies-grade mafic and felsic volcanic, siliciclastic, chemogenic and volcaniclastic rocks. Stratigraphic, sedimentologic and physical volcanologic data based on 1:50,000-scale mapping in the central part of the belt indicate deposition in a subaqueous mafic volcanic plateau-slope-basin system that was well removed from a continental influence. Water depth was below storm wave base as indicated by preservation of delicate lamination in pelitic and iron-formation units, absence of features suggestive of subaerial exposure, oscillatory flow or tidal currents, and lack of interfingering rocks that could represent laterally adjacent shelf, coastal or continental environments. Reconnaissance-level regional geologic and geochronologic data indicate an overall pattern of supracrustal deposition in the Hearne Province consisting of a large mafic volcanic plain (± isolated felsic volcanic centres) with lenses and belts of deep-water sedimentary rocks. At least two speculative, yet testable, tectonic models are consistent with the inferred paleogeography. For both, the Rae Province is considered to be the western continental hinterland to the ensimatic Hearne Province. The Rae and Hearne provinces may record late Archean continental extension, sea floor spreading, oceanic volcanic arc growth, diachronous back-arc spreading and collapse, and arc-continent collision, with thrusting of oceanic rocks on to attenuated Rae crust. Alternatively, the Hearne Province may represent northwestward accretion of multiple volcanic arc-trench pairs.