American Geophysical Union Become an AGU Member
Subscribe to AGU Journals		 AGU Home AGU Publications

Read Full Article (file size: 186711 bytes)    Cited by

GEOPHYSICAL RESEARCH LETTERS, VOL. 32, L11305, doi:10.1029/2005GL022792, 2005

Nitrogen isotopes of the mantle: Insights from mineral separates

Tobias P. Fischer

Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, New Mexico, USA


Naoto Takahata

Ocean Research Institute, University of Tokyo, Tokyo, Japan


Yuji Sano

Ocean Research Institute, University of Tokyo, Tokyo, Japan


Hirochika Sumino

Laboratory for Earthquake Chemistry, University of Tokyo, Tokyo, Japan


David R. Hilton

Fluids and Volatiles Laboratory, Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California, USA


Abstract

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.

Index Terms: 1025 Geochemistry: Composition of the mantle; 1036 Geochemistry: Magma chamber processes (3618); 1031 Geochemistry: Subduction zone processes (3060, 3613, 8170, 8413); 1041 Geochemistry: Stable isotope geochemistry (0454, 4870); 1042 Geochemistry: Mineral and crystal chemistry (3620).

Read Full Article (file size: 186711 bytes)    Cited by

Citation: Fischer, T. P., N. Takahata, Y. Sano, H. Sumino, and D. R. Hilton (2005), Nitrogen isotopes of the mantle: Insights from mineral separates, Geophys. Res. Lett., 32, L11305, doi:10.1029/2005GL022792.