Pathways and Processes of Ocean-Crust-Mantle Nitrogen Cycling

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The nitrogen (N) isotope system shows great potential for tracing the transfer of organic components from the surface/near-surface realm into the deeper Earth. Study of the processes by which organic N is incorporated into and redistributed within the crust and mantle is key to understanding modern mantle-ocean volatiles recycling and longer-term Earth degassing and atmosphere evolution. However, the lack of information regarding fractionation of N isotopes among fluids and minerals limits any quantitative modeling of fluid-rock interactions and their impact on larger-scale N cycling. In this project, the P.I. and his graduate students will experimentally investigate mica-fluid N isotope fractionation over a range of temperatures appropriate for devolatilization and partial melting, and examine important pathways for the ocean-to-lithosphere transfer of organic N, including partial melting of sedimentary rocks and the deep subduction of basaltic rocks previously hydrothermally altered on the seafloor.This study will utilize a carrier-gas-based analytical system recently developed at Lehigh University for analyses of extremely small amounts of N extracted from silicate minerals and rocks. The methods being developed in the P.I.'s laboratory could facilitate wider application of N isotopes in earth science disciplines (particularly those examining the biosphere-geosphere interface) and in cosmochemistry.