Indigenous nitrogen in the Moon: Constraints from coupled nitrogen–noble gas analyses of mare basalts

摘要: Nitrogen and noble gas (Ne–Ar) abundances isotope ratios, determined by step-wise CO2 laser-extraction, static-mass spectrometry analysis, are reported for bulk fragments mineral separates of ten lunar mare basalts (10020, 10057, 12008, 14053, 15555, 70255, 71557, 71576, 74255, 74275), one highland breccia (14321), ferroan anorthosite (15414). The basalt sub-samples 10057,183 71576,12 contain a large amount solar gases, whereas neon argon in all other samples purely cosmogenic, as shown their 21Ne/22Ne ratios ≈0.85 36Ar/38Ar ≈0.65. solar-gas-free two-component mixture cosmogenic 15N indigenous nitrogen (<0.5 ppm). Mare 74255 the olivine fraction 15555,876 record smallest proportion 15Ncosm; therefore, δ15Nδ15N values −0.2 to +26.7‰+26.7‰ (observed at low-temperature steps) thought well represent isotopic composition nitrogen. However, ≤−30‰≤−30‰ found several basalts, overlapping with signature Earth's primordial mantle or an enstatite chondrite-like impactor. While lowest allow trapped Moon's interior be inherited from proto-Earth and/or impactor, more 15N-enriched compositions require that carbonaceous chondrites provided magma ocean prior solidification crust. Since can efficiently incorporated into mafic minerals (olivine, pyroxene) under oxygen fugacities close below iron-wustite buffer (Li et al., 2013), source region is likely characterized high storage capacity. In contrast, 15414 shows no traces nitrogen, suggesting was not crust during differentiation.