ISOTOPIC COMPOSITION OF NITROGEN IN PHASE-Q

An acid residue from the Dhajala meteorite which carries the noble gas component of the pure Q-phase, has been analyzed for nitrogen and nob le 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 delta(15)N = -1 5 parts per thousand in all temperature fractions except for a small f raction (0.26%) of N in 1200 degrees C with delta(15)N = -55 parts per thousand has been observed. The sharp fall in the delta(15)N for the 1200 degrees C fraction, in all likelihood, is due to the signature of microdiamonds in Dhajala. We calculate an abundance of similar to 30 ppb for microdiamonds in Dhajala. The uniform delta(15)N of -15 parts per thousand in all other temperature fractions is interpreted as the isotopic composition of nitrogen in phase-Q. The peak release of nitro gen occurs at 1400 degrees C, while for the noble gases, the peak rele ase occurs at 1200 degrees C, indicating that nitrogen is more tightly bound in phase-Q as compared to the noble gases.