Petrogenetic and geodynamic investigation of Archean anorthosite-bearing layered intrusion and greenstone belt associations: implications for the early evolution of the Earth

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The geological models proposed to explain the origin of Archean anorthosite-bearing layered complex and greenstone associations in the Superior Province of Canada require re-evaluation within the context of new high-precision geochemical data. Over the next five years, I plan to study the field, petrographic and geochemical characteristics of Archean anorthosite-bearing layered complex and greenstone associations in the Superior Province, to constrain their petrogenesis, geodynamic setting and geological significance. The anorthosite-bearing layered complex and greenstone associations to be studied include the Neoarchean Bad Vermilion Lake (Ontario) and Doré Lake (Quebec) complexes. I will systematically sample each lithological unit in these associations and analyze them for major and trace elements and isotopes (Sm-Nd, Th-U-Pb, Lu-Hf, O), to improve our understanding the petrogenetic origin of these rocks. The geochemical characteristics of each rock type in the layered complexes and spatially associated volcanic rocks are expected to reflect petrological processes responsible for the compositional and isotopic variations in these rocks and their sources. Trace elements and Nd, Pb, Hf and O isotopes are sensitive to petrogenetic processes and thus can be used to distinguish different processes. These petrological processes can then be linked to the regional scale Neoarchean geodynamic processes in the Superior Province, and the geochemistry of these rocks can be used to understand their significance for Archean Earth evolution. Zircon grains from anorthosites, gabbros and felsic volcanic rocks will be dated using U-Pb isotopes, and these grains will also be analyzed for Hf isotopes. Three hypotheses will be tested: (1) anorthosite-bearing layered intrusions and greenstone belts are genetically related and represent relict Archean oceanic crust formed at either divergent or convergent plate margins; (2) they are genetically related and represent fragments of an oceanic plateau derived from a mantle plume; and (3) anorthosite-bearing layered intrusions are unique to the Archean and originated through non-uniformitarian geologic processes. The results of this project will have the following significance: (1) enhance our knowledge on the petrogenetic origin of Archean layered anorthosites and associated mafic to ultramafic intrusive rocks; and (2) the Canadian resource industry will benefit from this research program given that anorthosites and associated ultramafic rocks have high potential for chromite, vanadium, copper, nickel, and PGE (Platinum Group Elements) mineral deposits.