Experimental Study of Noble Gas Behavior in the Mantle

Brown University, Providence RI

Investigators

Abstract

The motions of the Earth's interior control and organize much of what goes on at the surface. From earthquakes and volcanoes, to oil and mineral deposits, even the evolution of life itself; the world humans live in is largely the product of the deep processes within our planet's interior. Because one cannot directly sample the deep Earth, one has to use indirect physical and chemical measurements to understand what is happening below our feet. The proposed study seeks to further our understanding of the inner motions and composition of the Earth's interior using the concentrations of noble gases (He, Ne, Ar, Kr, Xe) and their isotopes in lavas as probes of the high pressure processes that have such a large effect on our lives. Due to their lack of charge, it has generally been assumed that noble gases are inert and are not retained in mantle minerals. A number of paradigms about the Earth use this as a key assumption: from the understanding structure of mantle convection to quantifying the volatile content of the planet. However, recent high-pressure experimental studies suggest that in fact noble gases have surprisingly high solubilities in the mantle, potentially requiring a wide range of theories to be revamped. In fact, there are few experimental measurements of noble gas behavior at mantle conditions. Utilizing new analytical and experimental advances, this study will measure the partitioning and diffusivities of noble gases in a range of mantle minerals, many for the first time, including orthopyroxene, garnet, wadsleyite, ringwoodite and majorite. A range of high-pressure devices (piston-cylinder, multi-anvil, internally-heated gas pressure) will be employed to produce pressures over 20 GPa and temperatures up to 2000 oC, simulating conditions in the upper and lower mantle. Samples will be measured by new generation laser-ablation mass spectrometry. The unprecedented data set will be used to reevaluate current ideas about the structure and composition of the Earth.