Geochemistry of pyroxene-phyric komatiites in the Southern Superior Province; Implications for Archean geodynamics

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Despite decades of research the nature of Archean plate tectonic processes remains the subject of considerable debate. The current discussion focuses on whether these processes were vertical or horizontal. This study of Archean pyroxene spinifex komatiites will help to resolve these questions by providing an improved model for Archean crustal evolution and the formation of the southern Superior margin during continental growth at ~2.7 Ga. By combining geochemical and isotopic studies of komatiites and associated siliceous high-magnesian basalts in well-mapped and geochronologically well-constrained greenstone belts along the length of the margin from Lake of the Woods to the Abitibi, it will be possible to evaluate the nature of Archean tectonic processes and compare them with those of the Phanerozoic. ***This study will examine the occurrences of subduction–style lithologies (e.g. boninites and adakites) and a spectrum of komatiitic rocks types ranging from classic Al-depleted and Al-undepleted types recognized in the Abitibi and Wawa areas to more unusual types found in the Shebandowan and Lake of the Woods areas, as well as in the Abitibi greenstone belt. These unusual, generally pyroxene spinifex-bearing rock types are compositionally and texturally similar to occurrences in the Yilgarn which has traditionally been considered very distinct from the southern Superior. However, the common association of various komatiitic rocks and boninites indicates that, to some extent, they share a similar geodynamic history that may represent a key feature of the Neoarchean crustal growth processes. By assessing the geochemistry of pyroxene-phyric komatiites and associated rocks in the southern Superior Province we will be able to test these models in the world's largest Archean craton.***Whole rock geochemistry, radiogenic isotopes and mineral chemistry will be used to investigate the nature and origin of the pyroxene-phyric komatiites on the southern margin of the Superior Province. The combination of methodologies and the integrated study of komatiites and associated rock types across the Superior Province to probe the nature of Archean subduction zones is truly innovative. Results from this research will help to enhance the international reputation of Canadian science. Improved understanding of the tectonic processes that distinguish the rare, highly mineralized greenstone belts of the Superior Province from the numerous less prospective examples will promote mineral exploration in Canada. In the longer term, the results will contribute to the debate about the nature of Archean plate tectonics and greenstone belt formation and will provide a platform for a comprehensive, long-term study of the relationship between igneous petrogenesis and ore deposit genesis.