Program > Browse abstracts by speaker > Tardres Zacharie

The origin of Nitrogen on Earth is not clearly identified. A key observation is the 15N/14N difference between Earth's building blocks, the modern atmosphere and mantle. Here, we explore the possibility that magma ocean degassing may account for the isotopic difference between air and the mantle. For this, we will experimentally make use of variable nitrogen solubility relative to oxygen fugacity. Nitrogen solubility is generally low in silicate melts, such that most nitrogen is anticipated to be partitioned into a gas phase during degassing. However, under highly reducing conditions, below IW-2 (IW standing for the Iron-Wustite redox buffer), nitrogen solubility dramatically increases. We will determine whether nitrogen isotopic ratios are fractionated in gas-melt equilibrium experiments. We synthesized and quenched silicate melts in equilibrium with N-rich vapour under medium to high pressure (from 1100 to 3150 bar) and temperature (1250 to 1300 °C) conditions in Internal Heated Pressure Vessel (IHPV) to replicate those of magma ocean degassing. Basaltic powder will be used as a starting material, mixed with nitrides such as Fe3,5 N. Oxygen fugacity is controlled experimentally (from IW+1 to IW-5) by varying the partial pressure of H2. The use of Si3N4 starting material also contributes to a reducing environment. Bulk composition will be established with a scanning electron microscope and nitrogen isotopes in the gas and glass will then be measured in a Thermo Finnigan Deltaplus XP isotopic ratio mass spectrometer. These data will offer a better understanding of the influence of fO2 on nitrogen partitioning and isotopic fractionation and thus more precisely identify the sources of Earth's nitrogen and primordial redox conditions.