Isotopic composition of nitrogen in 'phase-Q'

Abstract

An acid residue from the Dhajala meteorite which carries the noble gas component of the pure Q-phase, has been analyzed for nitrogen and noble gases by step-wise heating pyrolysis. From Ne data we derive (20/22)Q = 10.48 ± 0.15. A nitrogen content of 48 ppm with δ¹⁵N = -15% in all temperature fractions except for a small fraction (0.26%) of N in 1200°C with δ¹⁵N = -55% has been observed. The sharp fall in the δ¹⁵N for the 1200°C fraction, in all likelihood, is due to the signature of microdiamonds in Dhajala. We calculate an abundance of ~30 ppb for microdiamonds in Dhajala. The uniform δ¹⁵N of -15% in all other temperature fractions is interpreted as the isotopic composition of nitrogen in phase-Q. The peak release of nitrogen occurs at 1400°C, while for the noble gases, the peak release occurs at 1200°C, indicating that nitrogen is more tightly bound in phase-Q as compared to the noble gases.