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Nitrogen isotopes of the mantle: Insights from mineral separates
Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, New Mexico, USA
Ocean Research Institute, University of Tokyo, Tokyo, Japan
Ocean Research Institute, University of Tokyo, Tokyo, Japan
Laboratory for Earthquake Chemistry, University of Tokyo, Tokyo, Japan
Fluids and Volatiles Laboratory, Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California, USA
We present the first nitrogen (N) isotope measurements determined by in-vacuo crushing of mineral separates from arc lavas, OIBs (Ocean Island Basalts), and mantle xenoliths. Measured OIB δ15N values range from ∼−8‰ for the northern rift zone in Iceland to +3.1‰ for a dunite nodule from Hawaii. Most arc-related olivines show distinctly positive values - up to +6.2‰ (Cerro Negro, Nicaragua). The measured N isotope values in olivine separates are similar to gas samples collected at the same localities, suggesting that both media (olivines and gases) sample volatiles primarily derived from the magma. This observation also implies that N isotope fractionation does not occur during magma degassing, a notion supported by 4He/40Ar* data. Our results indicate a heterogeneous mantle source region, in terms of N isotopic composition, that may have resulted from surface recycling of N at some localities.
Received 22 February 2005; accepted 5 May 2005; published 10 June 2005.
Citation: (2005), Nitrogen isotopes of the mantle: Insights from mineral separates, Geophys. Res. Lett., 32, L11305, doi:10.1029/2005GL022792.
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