Evidence for an early nitrogen isotopic evolution in the solar nebula from volatile analyses of a CAI from the CV3 chondrite NWA 8616

Nitrogen and noble gas (Ne-Ar) abundances and isotope ratios, determined by CO2 laser extraction static mass spectrometry analysis, as well as Al-Mg and O isotope data from secondary ion mass spectrometry (SIMS) analyses, are reported for a type B calcium-aluminum-rich inclusion (CAI) from the CV3 chondrite NWA 8616. The high (Al-26/Al-27)(i) ratio of (5.06 +/- 0.50) x 10(-5) dates the last melting event of the CAI at 39(-99)(+109) ka after time zero, limiting the period during which high-temperature exchanges between the CAI and the nebular gas could have occurred to a very short time interval. Partial isotopic exchange with a O-16-poor reservoir resulted in Delta O-17 > -5 parts per thousand for melilite and anorthite, whereas spinel and Al-Ti-pyroxene retain the inferred original O-16-rich signature of the solar nebula (Delta O-17 <= -20 parts per thousand). The low Ne-20/Ne-22 (<= 0.83) and Ar-36/Ar-38 (<= 0.75) ratios of the CAI rule out the presence of any trapped planetary or solar noble gases. Cosmogenic Ne-21 and Ar-38 abundances are consistent with a cosmic ray exposure (CRE) age of similar to 14 to 20 Ma, assuming CR fluxes similar to modern ones, without any evidence for pre-irradiation of the CAI before incorporation into the meteorite parent body. Strikingly, the CAI contains 1.4-3.4 ppm N with a delta N-15 value of +8 parts per thousand to + 30 parts per thousand. Even after correcting the measured delta N-15 values for cosmogenic N-15 produced in situ, the CAI is highly enriched in N-15 compared to the protosolar nebula (delta(15) N-PSN = -383 +/- 8 parts per thousand; Marty et al., 2011), implying that the CAI-forming region was contaminated by N-15-rich material within the first 0.15 Ma of Solar System history, or, alternatively, that the CAI was ejected into the outer Solar System where it interacted with a N-15-rich reservoir. (C) 2015 Elsevier Ltd. All rights reserved.