Simultaneous analysis of abundance and isotopic composition of nitrogen, carbon, and noble gases in lunar basalts: Insights into interior and surface processes on the Moon

Abstract

a b s t r a c tSimultaneous static-mode mass spectrometric measurements of nitrogen, carbon, helium, neon, and argon extracted from the same aliquot of sample by high-resolution stepped combustion have been made for a suite of six lunar basalts.Collecting abundance and isotopic data for several elements simultaneously from the same sample aliquot enables more detailed identification of different volatile components present in the basalts by comparing release patterns for volatiles across a range of temperature steps. This approach has yielded new data, from which new insights can be gained regarding the indigenous volatile inventory of the Moon.By taking into account N and C data for mid-temperature steps, unaffected by terrestrial contamination or cosmogenic additions, it is possible to determine the indigenous N and C signatures of the lunar basalts. With an average d 15 N value of around +0.35‰, the indigenous N component seen in these samples is similar within error to other (albeit limited in number) isotopic measurements of indigenous lunar N. Average C/N ratios for indigenous volatiles in these six basalt samples are much lower than those of the terrestrial depleted mantle, or bulk silicate Earth, possibly suggesting much less C in the lunar interior, relative to N, than on Earth.Cosmogenic isotopes in these samples are well-correlated with published sample exposure ages, and record the rate of in situ production of spallogenic volatiles within material on the lunar surface.

Magmatic volatiles (H, C, N, F, S, Cl) in the lunar mantle, crust, and regolith: Abundances, distributions, processes, and reservoirs

“…Magmatic troilite is typically found as discrete grains or in late-stage mesostasis pockets, sometimes intergrown with Fe-metal (e.g., Skinner 1970). Vapor or fluid deposited troilite is often found to fill cracks or as intergrowths (Boyce et al 2010;Butler and Meyer 1976;Duncan et al 1973;Fegley and Swindle 1993;Gibson and Moore 1974;Goldberg et al 1976;Haskin and Warren 1991;Hauri et al 2011;Jovanovic et al 1976;Reed 1973, 1975;Liu et al 2012a;Mathew and Marti 2001;McCubbin et al 2011McCubbin et al , 2010bMortimer et al 2015;Muller 1974;Jovanovic 1973a, 1973b;Reed et al 1977;Saal et al 2008;Tartèse et al , 2014aTaylor et al 2004;Wang et al 2012;Wänke et al 1976). a When only an upper value is given, the lower bound value reported is below analytical detection, otherwise a range is reported.…”

“…S abundances of mare basalts range from approximately 300 to 3200 ppm Haskin and Warren 1991; Table 2). Mare basalts typically contain less than 1 ppm of indigenous N (Becker et al 1976;Des Marais 1978Mathew and Marti 2001;Mortimer et al 2015;Muller 1974), which has hampered measurement efforts to date, but N abundances have been measured as high as 20 ppm N (Haskin and Warren 1991). Similar to N and H, there is much debate over the indigenous inventory of C in lunar basalts vs. the fraction that can be attributed to secondary processes.…”

“…Similar to N and H, there is much debate over the indigenous inventory of C in lunar basalts vs. the fraction that can be attributed to secondary processes. Of the mare basalts that have been measured, their carbon contents range from 3-70 ppm C (Haskin and Warren 1991;Mortimer et al 2015; Table 2), with reports of 3.3-7.0 ppm indigenous C in mare basalts (Mortimer et al 2015).…”

“…Between 1991-2008, there was a hiatus in analyzing volatile abundances in lunar samples, although isotope compositions of hydrogen, oxygen, nitrogen, and noble gases of lunar soil grains have been studied to understand the composition of the Sun (Benkert et al 1993;Hashizume and Chaussidon 2005;Hashizume et al 2000;Heber et al 2003;Ireland et al 2006;Nier and Schlutter 1994;Wieler et al 1999). Although recent interests peaked again after discoveries of OH/H 2 O on the surface of the Moon (Clark 2009;Pieters et al 2009;Sunshine et al 2009), only a few studies re-analyzed lunar soils for their volatile contents (Furi et al 2012;Liu et al 2012aLiu et al , 2013Mortimer et al 2015;Sharp et al 2010b). Thus, pre-1991 data still forms the basis of our understanding of volatiles in lunar soils.…”

“…N in mare basalts and pyroclastic glasses. Lunar rocks contain much less N than soils, typically less than 1 ppm of indigenous N (Becker et al 1976;Des Marais 1978Mathew and Marti 2001;Mortimer et al 2015;Muller 1974), which has hampered measurement efforts to date. At such low abundances, indigenous lunar isotopic signatures are masked by those of cosmogenic components (Mathew and Marti 2001).…”