Geochemical characterization and geochronology of Earth's primitive crust

点击翻译按钮获取中文摘要

Our knowledge of the Earth's early evolution is very limited due to the scarcity of preserved rock samples from this era of Earth history. Most information on the primitive Earth comes from the study of detrital zircons dated at ~4.4 billion years old found in much younger sediments in Western Australia. The oldest surviving rock samples available at the surface of the Earth are between 4.0 and 3.7 billion years old, leaving the first 500 million years of our planet's history unrepresented in the rock record. Therefore the nature of the Earth's early crust and the processes responsible for its formation remain largely speculation. Recent work using 142-Neodymium, an isotopic tool particularly sensitive to rock formation prior to 4 billion years old, suggests that rocks from the Nuvvuagittuq terrane in Northern Quebec are as old as 4.4 billion years. These rocks would therefore represent the oldest rock on Earth. This terrane is however only a very small portion of crust and the study of other old crustal terranes is critical in order to understand how and when the first continents formed. This proposal seeks funding to support research focused on ancient terrains. Their study will help to constrain the evolution of the early Earth and the geological processes responsible for the formation of the primitive crust. This research will focus on three ancient Canadian terranes: 1) The Saglek Gneiss Complex (Labrador) which is a terrane comprising rocks as old as 3.8 billion years. This area is still relatively uncharacterized and its precise evolution through time is largely unknown. 2) The Central Slave Basement Complex (Northwest Territories) comprises rocks dated at ~4 billion years called the Acasta gneisses. The Acasta gneiss formed from granitic rocks derived by the melting of older basaltic rocks. Further investigation of basaltic rocks in this area could allow the identification of an older precursor to the Acasta gneisses. 3) The Nuvvuagittuq Greenstone Belt (Ungava peninsula, Quebec) is interpreted to represent the oldest preserved crust on Earth. Research in this area will help to better constrain the geological processes responsible for early crust formation and could also lead to the identification of more preserved fragments of early crust in this region.