Defining the noble gas composition of highly depleted mantle domains

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The noble gases play an important role in understanding mantle structure and in quantifying mass and volatile fluxes in and out of the mantle. The isotopic composition of non-radiogenic noble gases in the Earth's mantle can constrain the sources of volatile sources on our planet and the mechanisms through which volatiles are incorporated into the solid Earth. Furthermore, the isotopic composition of the noble gases in Earth's mantle can provide important clues to the origin and evolution of the atmosphere. For example, the modern atmosphere was traditionally thought to be secondary, i.e, derived from mantle degassing after the dissipation of a primary atmosphere that the Earth might have acquired during the accretion process. Theories on the origin of the early atmosphere through degassing of the mantle are now being challenged by new noble gas data and neon isotopes. This research will use new developments in noble gas mass spectrometry that allow much higher resolution and precision measurements than previously available to examine a suite of heavy noble gases and their isotopic ratios to determine the composition of the most depleted mantle domains and understand how they relate to normal and enriched Mid Ocean Ridge Basalt sources. Issues such as: (1) the noble gas elemental abundance ratios in depleted, normal and enriched mantle domains, (2) whether isotopic anomalies in argon and xenon in different mantle domains are related to ancient mantle differentiation events or to the on going process of plate subduction and recirculation that introduces atmospheric noble gases into the mantle; (3) the proportion of Pu- to U-derived, fission generated Xe in depleted, normal, and enriched mantle domains; (4) whether there time-constants associated with mantle degassing can be determined; and (5) whether the non-radiogenic isotopic compositions of Xe and Kr are solar, chondritic, or air-like, will be addressed. Answers to these questions will allow determination of the flux of volatiles and material from plumes in the mantle into the mid-ocean ridge basalt (MORB) source and the degree of mixing between MORB and plume sources. It will also provide key insights on Earth structure and mantle flow. In addition, the research seeks to constrain sources of Earth volatiles and the recycling of noble gases between the crust and atmosphere and the mantle, and the formation of Earth's atmosphere. Broader impacts of the work include new analytical method development that will increase the infrastructure for science, use of a an NSF-funded mass spectrometry facility, and student support, including support of a student whose gender is under-represented in the sciences. Additional impacts include incorporation of research results into graduate and undergraduate courses.