COMPOSITIONAL VARIATION IN LUNAR AGGLUTINITIC GLASS

Current consensus predicts that compositions of micrometeorite impact melts that quench to form agglutinitic glass, on average should be the same as that of the finest fraction of the soil in which the melt had formed. We agree in principle. However, a puzzle is presented by the fact that compositions of agglutinitic glass have a very large range. Part of the reason is that random micrometeorite impacts may melt all or parts of larger grains in lunar soils, which may not necessarily homogenize with the rest of the melt. Additionally, recycling of older agglutinates may also produce glassy domains of different composition. Here we propose yet another process to explain the observation. Nanophase pure iron globules are abundant in agglutinitic glass; however, neither their distribution nor their concentration is systematic. If pure iron globules separate from a silicate melt, possibly through reduction by solar wind hydrogen, then the melt would be depleted in iron. Variability of the extent of iron-reduction, dependent on the availability of solar wind hydrogen and therefore on maturity, would impart variability in the composition of the quenched glass.