Origins of the mantle and crust: Isotopic studies from an adolescent earth

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The Precambrian Shields around the world contain the oldest rocks on the planet and as such, they lie at the heart of our understanding of the formation and evolution of our planet's mantle and continental crust. The growth and stabilization of the continents and formation of the ocean basins also represent a fundamental difference between the Earth and other rocky planets of the solar system. The details of the initial formation and subsequent modification of the continental crust and mantle constitute the principal focus of my research. My research program proposes to continue the study a newly discovered tract of ancient crust (3.8 billion ears: Ga) that rates among the oldest on the planet. This old crust is located in the Canadian Shield of northern Quebec (Inukjuak region) and in studying this crust we can place constraints on some of the fundamental questions of our planet's geological evolution; such as: How and why did continents begin forming? Did the Earth's mantle evolve in a similar fashion as those of the Moon and Mars (a planetary evolution) or follow different path (a terrestrial evolution). Rocks from oceanic islands and ocean ridges indicate that the present day mantle consists of depleted and enriched reservoirs. How were these different reservoirs generated? The answer to this latter question is being addressed in an isotopic study of the Monteregian Hills in SW Quebec. Studying the isotopic composition of the Canadian Shield has also allowed us to constrain changes in the source of sediments to the North Atlantic Ocean through past glacial cycles. The same technique can be applied to the Arctic Ocean to study the effects of changes in oceanic circulation as a result o melting the Arctic ice pack. This work will be carried out through a combination of geological field studies and geochemical and isotopic analyses (Lu-Hf, Sm-Nd, Rb-Sr) of the rocks collected in the field. The field studies will constrain the degree of deformation, metamorphism and stratigraphy of the rocks in the Inukjuak region. The analytical studies will constrain the sources of the rocks. Funding for these projects will provide support, training and research costs for 4 graduate students over 5 years.