The Ennadai Greenstone Belt, northern Saskatchewan

The Archaean Ennadai Greenstone Belt in northeastern Saskatchewan (EGBS), is a little studied and poorly understood component of the Hearne Domain, Western Churchill Province. Petrographic, geochemical and isotope studies of representative EGBS lithologies are utilised to help identify and constrain the origin and tectonic environment of this supracrustal sequence, as well as its position within the Hearne. EGBS comprise a sequence of metamorphosed basaltic to rhyolitic and mafic-felsic volcaniclastic rocks; these include pillowed and massive flows and their hypabyssal equivalents. These have attained regional greenschist- and, locally, lower amphibolite-facies metamorphic conditions. EGBS rocks are mostly subalkaline/tholeiitic in character; a calcalkaline suite is also present. Their trace element chemistries suggest a complex origin that may involve a variety of mantle sources, including depleted mantle and a subduction component, while Sm-Nd whole-rock isotope analyses indicate that the rocks are mostly juvenile, with only minor contamination with older crust (either continental or oceanic). A favoured model is that the sequence was generated in a developing arc or arc/back-arc basin environment. The findings of this study are similar to those published data relating to rocks from the Central Hearne supracrustal belt in the Northwest Territories and Nunavut. As such, these two greenstone belts are thought to have a correlative origin that is related to the environment and tectonic processes that operated during the Neoarchaean in this part of the Western Churchill Province. Both segments are now thought to be part of the Central Hearne Subdomain.