Evolution of earth's crust: experimental and field based studies

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Earth's continental and oceanic crust, the combination of which is unique in the solar system, has played a central role in the evolution of the planet's lithosphere, atmosphere, and biosphere. The mechanisms by which this crust formed and stabilized early in Earth history remains one of the outstanding questions in the geological sciences. In this application, I propose three lines of research that address the topic of crustal evolution. Project 1 involves laboratory experiments aimed at understanding the genesis of granitic composition igneous rocks that make up a large fraction of Archean (>2.5 billion year old) continental crust. There is wide agreement that granitic magmas are produced through partial melting of the more silica-poor rocks found in oceanic crust. Experimental work done to date has focused on the partial melting of basaltic rocks, similar to those present in modern-day oceanic crust. However, because of higher temperatures in the early Earth, it is likely that Archean oceanic crust was significantly more magnesium-rich. Thus, experiments investigating the partial melting of Mg-rich basalts rather than standard basalts would be more relevant to the issue of Archean crustal evolution. I propose to conduct such experiments and document the chemical compositions of minerals and melts produced therein. In project 2, I propose to investigate the >4.0 billion year old Acasta gneisses of the Canadian Shield. The project aims to determine the major-element, trace-element and oxygen isotope composition of these rocks and use these data to understand the processes responsible for the formation of this most ancient of preserved continental crust. Project 3 relates to the origin of diamonds that are strongly depleted in 13C, the heavy stable isotope of carbon. A variety of models have been proposed to account for such diamonds, including a model suggesting that the carbon in these diamonds is of crustal origin (i.e., organic carbon), which was taken from the surface to great depth by tectonic processes. To evaluate these models, I propose to conduct experiments that will determine quantitatively the carbon isotope partitioning between diamond and the most common diamond growth medium, carbonate melt.