Funds are requested to support collaborative research on the evolution of the early Archean gneiss complex in the Saglek- Hebron area, northern Labrador. The study area forms part of the North Atlantic Craton, a major Archean block that preserves fragmentary evidence of pre-3800 Ma crust formation. Objectives of the study are to: North Atlantic Craton by documenting examples of pre-3800 Ma crust; regions from a terrane that contains extremely ancient crust; and to crustal evolutionary models. Research will carried out on: (1) tonalitic and trondhjemitic Uivak and pre-Uivak gneisses; and (2) a variety of ultramafic lithologies, some of which occur as tectonically emplaced rafts within pre-3600 Ma Uivak gneisses. Petrogenetic information for Uivak and pre-Uivak tonalitic gneisses will be obtained from major and trace element geochemistry. Age data will be derived through analysis of Sm-Nd, Rb-Sr, and Pb-Pb isotopic systems and by application of the Kober (1986) single zircon TIMS technique. This will provide additional petrogenetic data, and will enable mantle separation ages, source compositions and metamorphic histories of the suites to be determined. Information on the composition, age and crustal residence history of early Archean ultramafic units will be achieved by a geochemical and Sm-Nd, Pb-Pb and Rb-Sr isotopic study of whole rocks and separated mineral phases. Isotope geochemistry will be carried out at UCSC. Major and trace element (including REE) geochemistry will be carried out by Weaver at the University of Oklahoma. The study will provide direct constraints on the chronology and chemical evolution of early Archean crust in the North Atlantic Craton. These constraints will be important for models of the early fractionation of the Earth.
