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)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 1200oC with δ15N = -55%% has been observed. The sharp fall in the δ15N for the 1200oC 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 1400oC, while for the noble gases, the peak release occurs at 1200oC, indicating that nitrogen is more tightly bound in phase-Q as compared to the noble gases.