Chemical Geology 447 (2016) 27–39 Contents lists available at ScienceDirect Chemical Geology journal homepage: www.elsevier.com/locate/chemgeo Analyzing nitrogen in natural and synthetic silicate glasses by secondary ion mass spectrometry Margo E. Regier a, * , Richard L. Hervig a , Madison L. Myers b , Kurt Roggensack a , Colin J.N. Wilson c a School of Earth and Space Exploration, Arizona State University, Tempe, AZ, United States b Department of Geological Sciences, University of Oregon, Eugene, OR 97403-1272, United States c School of Geography, Environment and Earth Sciences, Victoria University, PO Box 600, Wellington 6140, New Zealand ARTICLE INFO Article history: Received 20 June 2016 Received in revised form 1 October 2016 Accepted 8 October 2016 Available online 11 October 2016 Keywords: Secondary ion mass spectrometry Nitrogen cycling Melt inclusions Explosive volcanism ABSTRACT Volatile releases through volcanic eruptions are one of the major processes contributing to the global nitrogen cycle. Past studies have often estimated the magnitude of this flux using volcanic emission mea- surements, which are limited to currently active systems and sensitive to atmospheric contamination. Another possible approach is the measurement of nitrogen in melt inclusions, which are parcels of magmatic melt trapped prior to eruption. This methodology requires appropriate analytical parameters for nitrogen analysis in silicate glasses by secondary ion mass spectrometry (SIMS), which have not yet been established. To this end, calibrations for nitrogen were obtained using ion implanted basaltic and rhyolitic glasses. We demonstrate that water content significantly affects the ion yields of 14 N + and 14 N 16 O − , as well as the back- ground intensity of 14 N + and 12 C + . Application of implant-derived calibrations to natural samples provide the first reported concentrations of nitrogen in melt inclusions. These measurements were made on sam- ples from the Bishop Tuff in California, the Huckleberry Ridge Tuff of the Yellowstone Volcanic Center, and material from the Okaia and Oruanui eruptions in the Taupo Volcanic Center. In studied material, we often find maximum nitrogen contents of less than 45 ppm and that nitrogen concentration varies positively with CO 2 concentration, which reflects a partial degassing trend. Using the maximum measured nitrogen con- tents for each eruption, we find that the Bishop released >3.4 × 10 13 , the Huckleberry Ridge released >1.4 × 10 14 , the Okaia released >1.0 × 10 11 , and the Oruanui released >4.5 × 10 13 g of nitrogen. Simple calcu- lations suggest that with concentrations such as these, rhyolitic eruptions may ephemerally increase the nitrogen flux to the atmosphere, but are insignificant compared to the 4 × 10 21 g of nitrogen stored in the atmosphere. © 2016 Elsevier B.V. All rights reserved. 1. Introduction 1.1. Nitrogen cycling and solubility The foundations of a global nitrogen cycle model are well- constrained reservoir estimates and a thorough understanding of the fluxes between these reservoirs. Estimates of nitrogen con- tained within the crust and mantle have large uncertainties, but together may be larger than that of the atmospheric reservoir (Fig. 1; Johnson and Goldblatt, 2015). The greater part of crustal nitrogen was likely sourced from a draw down of the atmospheric reservoir through biological fixation. However, smaller inputs included light- ning (Raymond et al., 2004) and volcanic-related thermal fixation * Corresponding author. E-mail address: margoregier@gmail.com (M. Regier). (Mather et al., 2004), which began prior to the evolution of life. Two distinct models have been proposed for the origin of mantle nitro- gen. The first model requires large scale storage during magma ocean crystallization (Li et al., 2013; Mikhail and Sverjensky, 2014), while the other posits that large amounts of nitrogen were sequestered in the mantle after the introduction of nitrogen-rich crust to the mantle via subduction (Goldblatt et al., 2009). Volcanic degassing is one of the important processes that off- sets the subduction-related input of nitrogen into the mantle. It also may limit the amount of nitrogen that is sequestered into the crust via fixation. However, the stability of this flux over geologic time, and the controls on its variability are relatively unknown. Prior attempts to quantify the volcanic degassing flux have often used N 2 /noble gas systematics from volcanic and geothermal gases, water, and vapor condensate samples (Sano et al., 2001; Hilton et al., 2002; Elkins et al., 2006). However, these methods are limited to cur- rently active systems, sensitive to surface contamination, and may http://dx.doi.org/10.1016/j.chemgeo.2016.10.019 0009-2541/© 2016 Elsevier B.V. All rights reserved.