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Volcanic framework and geochemical evolution of the Archean Hope Bay Greenstone Belt, Nunavut, Canada Shannon, Andrew J.

Abstract

Part of the Slave Structural Province, the Hope Bay Greenstone Belt is a 82 km long north-striking sequence of supracrustal rocks dominated by mafic volcanic rocks with lesser felsic volcanic and sedimentary rocks. Mapping of two transects in the southern section and two transects in the northern section have contributed to a robust stratigraphic framework the belt. Three recently discovered Archean lode gold deposits in the Hope Bay Greenstone belt have associations with major structures and specific lithologies (Fe-Ti enriched basalts). The Flake Lake and the Clover Transects are in the southern part of the belt and the Wolverine and Doris-Discovery Transects are in the northern part of the belt. This work subdivides the volcanic rocks into distinct suites based upon field, petrologic, geochemical, and geochronologic criteria. Some of the suites are stratigraphically continuous and can be correlated tens of kilometres along strike thereby linking the two parts of the Hope Bay Greenstone Belt. U-Pb geochronology supports work by Hebel (1999) concluded that virtually all the supracrustal rocks in the Hope Bay Greenstone Belt were deposited over at least 53 m.y. (2716-2663 Ma), with the majority of the volcanism occurring after 2700 Ma. A number of basalt groups are identified and include the normal basalt, the LREE-enriched basalt, the Ti-enriched basalt and the Ti-enriched Al-depleted basalt groups. They have chemical signatures that vary in trace elements particularly HFSE and REE’s, and can be easily be distinguished by geochemical screening. The felsic volcanic suites are also divided into three main groups, tholeiitic rhyolite, calc-alkaline dacite and calc-alkaline rhyolite groups. Nd and Hf isotope signatures are consistent with trace element signatures in identifying mafic and felsic volcanic groups, with the tholeiitic rhyolite showing highly variable signature. The Hope Bay Greenstone Belt has been show to have a number of felsic and volcanic cycles. An early construction phase of the belt is made up of primarily mafic volcanics which is followed by felsic volcanism equalled mafic volcanism which lacks basalts enriched in Ti. The geodynamic environment that created the Hope Bay Greenstone Belt can be explained by plume influenced subduction zone.

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