Electron probe microanalysis. Electron probe microanalysis data acquisition was performed at Rice University on a JEOL JXA 8530F Hyperprobe using five wavelength-dispersive spectrometers (WDSs). Silicate melt analysis was performed on C-coated samples. Natural glass standards provided by the Smithsonian Institute and mineral standards from SPI Supplies were used for measuring the characteristic Kα x-ray lines of the measured elements as follows: Na (Glass 5 Reference A NMNH-117218-4), Si (Glass 6 Reference B NMNH-117218-1), Ca (Glass 3 Basalt_NMNH-113716-1), K (Glass 8 Reference D NMNH-117218-3), S (Glass 6 Reference B NMNH-117218-1), Fe (Glass_3_Basalt_NMNH-113716-1), Cr (chromite), Mn (rhodonite), Ni (pentlandite), Al (Glass 10 IR-W NMNH 117084), and Mg (Glass 3 Basalt NMNH-113716-1).

Analytical sessions with various accelerating voltages (10, 15, 20, and 25 kV), beam currents (10, 20, 50, and 100 nA), and counting times (10 s/5 s, 80 s/60 s, and 100 s/80 s per peak on each of the lower [bk−] and upper [bk+] backgrounds, respectively) were performed to determine the optimum peak/background ratio when analyzing N Kα with the N standard [boron nitride (BN)] for silicate melt. An accelerating voltage of 15 kV, a beam current of 50 nA, and counting times of 80 s/60 s were found to be the optimum conditions to analyze N in silicate melts. To incorporate a more robust matrix correction, in contrast to N analyzed separately by a previous study (12), N was measured during the same analytical routine as all the other major and minor elements with a spot size of 20 μm. The use of a defocused electron beam also allowed the integration of quenched FeS microinclusions in the silicate melt, which are interpreted to be a portion of the dissolved S in the melt under experimental conditions (44). Some of the silicate melts were also analyzed for major elements using an accelerating voltage of 15 kV and a beam current of 10 nA, and it was verified that concentrations of nonvolatile and volatile elements, such as Na and K, were similar to the measurements taken when using a higher beam current of 50 nA. After several peak searches for N in the glass samples, narrow background offsets were set manually ([bk−], 2.2 mm; [bk+], 2.5 mm) to (i) avoid errors in measuring the high lower background (bk) of N, (ii) lower the effect of the background curvature of N, and (iii) avoid or minimize the interferences of the background measurements with x-ray lines or fluorescence peaks of other elements (45). The average detection limit of N in the glass analysis lies between ~100 to 200 ppm, with an average instrumental SD (1σ) of ~12%. The N Kα line was measured using an LDE2 diffracting crystal. An LDE2 diffracting crystal was preferred over an LDE1 because of its significantly higher counts per second for a similar accelerating voltage and beam current. In addition, several WDS scans in the L-value region of the N peak on BN and Ti metal standards show that both LDE1 and LDE2 crystals give similar critical interferences between N Kα and Ti secondary peaks, especially when the two elements are similar in concentration or Ti > N. A low curvature of the background between the narrow offsets ([bk−], 2.2 mm; [bk+], 2.5 mm) under the N peak meant that a straight background method approximated well the correct background values and net N intensity. The alloy phase was analyzed in separate sessions using freshly aluminum-coated samples and standards in the same coating session. Natural- and laboratory-synthesized standards used for the alloy phase analyses were Si (Si metal), C [laboratory-synthesized stoichiometric Fe3C (46, 47)], Fe (Fe metal), and S (natural troilite). Fe3N was the standard material used for N calibration in the alloy. The Fe3N standard was synthesized in a PC apparatus using a similar BaCO3/MgO assembly to the one mentioned earlier. Fe3N powder was loaded in a crushable MgO assembly and held at 1.5 GPa and 750°C for 120 hours. To determine whether the targeted stoichiometry of Fe3N was achieved, x-ray diffraction (XRD) spectra of the run product were obtained using a Rigaku D/MAX West Micro XRD system at Rice University. The obtained XRD pattern was in good agreement with the previously published spectra of Fe3N (48). Larger background offsets were manually selected for N analysis in alloys ([bk−], 5 mm; [bk+], 10 mm) as the concentration of N in metals is much higher and the peak is relatively wide.

To minimize hydrocarbon contamination (relevant for C analyses) on the alloy surface during analysis, an accelerating voltage of 12 kV and an emission current of 80 nA was used to produce a stable and high peak/background ratio for C Kα, following the findings of a previous study (46). A spot size of 20 μm was used, and the counting times were 10 s for peak and 5 s on each of the lower and upper backgrounds, respectively, except for N where 80 s for peak and 60 s for background were used. A ZAF matrix correction method was used for the quantification of both glasses and alloys.

Secondary ion mass spectrometry. The total amount of C and H dissolved in the experimental glasses was determined using a Cameca IMS 1280 ion microprobe at the Woods Hole Oceanographic Institution. Repolished samples were placed in an indium mount, cleaned, and then dried in a vacuum oven at 100°C. The mounts were coated with gold and placed under vacuum before analysis. A spot size of 10 μm in diameter was focused on by a beam of 133Cs+ ions with a 1- to 1.5-nA current and 12-kV energy and rastered over a 30 μm by 30 μm area. Negatively charged ions were accelerated at 10 kV into a double-focusing mass spectrometer. The central 15 μm by 15 μm portion of the beam-rastered area was analyzed by placing a mechanical aperture in the focal plane of the secondary ion optics. Spots were presputtered for 240 s and then measured over at least 10 cycles of ion intensities. 12C, 1H16O, and 30Si were recorded, and intensity ratios of 12C/30Si and 1H16O/30Si were converted to C and H2O contents during each cycle using the calibration curves developed in the same analytical session as was done in previous studies (3, 4, 24).

Raman spectroscopy. The nature of dissolved C-O-N-H in glassy samples was determined using a Renishaw inVia Raman microscope at Rice University following the methodologies detailed in previous studies (3, 4, 24). A 514-nm laser was used to measure the spectra in the frequency range of 200 to 5000 cm−1 using a 50× objective lens and an output power of 23 mW. Each spectrum was accumulated five times at an exposure time of 30 s to increase the signal/noise ratio.

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