1Department of Earch Sciences, University of Minnesota, Minneapolis, Minnesota, 55455
2Centre de Recherches Pétrographiques et Géochimiques, CNRS-UL, 54501 Vandœuvre-lès Nancy,France
3Schoolof Earth & Space Exploration, Arizona State University, Tempe, AZ 8528701404
4 Division
of Geological and Planetary Sciences, California Institute of Technology,
A
quantative understanding of nitrogen incorporation in Earth materials
is important for constraining volatile evolution in planetary bodies.
We used a combination of chemical (SIMS< EPMA, and laser-extraction
mass spectrometry) and spectroscopic (FTIR) data to study nitrogen
contents and speciation mechanisms in silicate glasses, metal alloys,
and a N-bearing silicate mineral (hyalophane). One suite of Fe-free
basaltic glasses was studied by all four methods. Concentrations of N
in these glasses determined by EMPA are systematically higher than
those measured by laser extraction, but agree within mutual 2 sigma
uncertainties, demonstrating the general veracity of the EPMA method.
SIMS calibrations based on measurement of 14N+ and 14N16O-
as a function of N content determined by EPMA (or laser extraction) are
best fit with exponential curves rather than the linear regressions
that are most commonly applied to SIMS data. On the other hand, a
calibration based on 12C14N- for C-poor, Fe-free glasses is exceptionally well fit to a linerar regression (r2 = 1), in contrast to expectations from previous work on glasses with lower N contents. Matrix effects associated with Fe or H2O
content are ot justified by the SIMS data, but volatile data (both N
and H) for hyalophane, which contains 20 wt% BaO, reveal matrix effects
possibly induced by its high average molar mass. A combination of FTIR
and chemical data, together with a thorough review of the literature,
was used to determine incorpation mechanisms for N in the Fe-free
glasses. We infer that under reducing conditions at high pressure and
temperature N is dissolved in basaltic melts chierly as NH2- and NH2- with N2 and/or nitride (X-N3-) complexes becoming increasingly important at lof fO2,
increasing N content, and decreasing H content. Our results have
implicationsf for future studies seeking to accurately measure N by
SIMS and for studies of N partitioning at high pressure relevant to
planetary accretion and differentiation.