Lunar meteorite Queen Alexandra Range 93069 and the iron concentration of the lunar highlands surface

Section: Lunar Provenancesupporting

confidence: 66%

Petrography, mineralogy, and geochemistry of lunar meteorite Sayh al Uhaymir 300

Hsu

Zhang

Bartoschewitz³

et al. 2008

“…Several authors (e.g., Korotev et al 1996;Gnos et al 2002;Day et al 2006) have used the average of a few fusioncrust analyses to approximate the bulk composition of the meteorite. Indeed, this may produce an acceptable compositional value depending on the accuracy that is needed.…”

Section: Discussionmentioning

confidence: 99%

“…Although it is difficult to determine exactly where meteorites come from, many are believed to be from the asteroid belt in the solar system based on their chemical and physical similarities. Previously, it was assumed that the bulk composition of a meteorite could be approximated from an analysis of its fusion crust and that the average of a few fusion crust analyses represents the bulk composition of the meteorite (e.g., Korotev et al 1996;Genge and Grady 1999;Gnos et al 2002;Day et al 2006). Although some cases show this can provide an acceptable approximation of the bulk rock composition (Genge and Grady 1999;Gnos 2002), other samples, even those combining several analyses, may not adequately represent the significant compositional variation within some fusion crusts, let alone the composition of the entire rock.…”

Section: Fusion Crusts and Bulk Compositionsmentioning

confidence: 99%

Meteorite fusion crust variability

Thaisen

Taylor

2009

It was determined that fusion crust compositions are significantly influenced by the incorporation of fragments from the substrate, and by the composition and grain size of those minerals. Because of compositional heterogeneities throughout the meteorite, one cannot assume that fusion crust composition represents the bulk rock composition. If the compositional variability within the fusion crust and mineralogical differences among thin sections goes unnoticed, then the perceived composition and petrogenetic models of formation will be incorrect.The formation of vesicles within these fusion crusts were also compared to current theories attributing vesicles to a solar wind origin. Previous work from the STONE-5 experiment, where terrestrial rocks were exposed on the exterior of a spacecraft heatshield, produced a vesicular fusion crust without prolonged exposure to solar wind suggesting that the high temperatures experienced by a meteorite during passage through the Earth's atmosphere are sufficient to cause boiling of the melt. Therefore, the assumption that all vesicles found within a fusion crust are due to the release of implanted volatiles of solar wind may not be justified.

“…5a, at the margin of many pyroxene-plagioclase intergrowths, small plagioclase laths that project into the intergrowth have subparallel orientations; these orientations are the same as those of crystallites in the adjacent devitrified maskelynite. The orientations of these plagioclase laths indicate that their crystal structures were determined by the crystal structures of Korotev et al (1996), Palme et al (1991), Taylor et al (2001), and Zipfel et al (1998). The compositional envelopes of Apollo 14 and 16 regoliths (Korotev, personal communication) are shown for reference.…”

Section: Evidence For In Situ Post-shock Crystallization Of Pyroxenepmentioning

confidence: 93%

Lunar highland meteorite Dhofar 026 and Apollo sample 15418: Two strongly shocked, partially melted, granulitic breccias

Cohen

James

Taylor

et al. 2004

Abstract-Studies of lunar meteorite Dhofar 026, and comparison to Apollo sample 15418, indicate that Dhofar 026 is a strongly shocked granulitic breccia (or a fragmental breccia consisting almost entirely of granulitic breccia clasts) that experienced considerable post-shock heating, probably as a result of diffusion of heat into the rock from an external, hotter source. The shock converted plagioclase to maskelynite, indicating that the shock pressure was between 30 and 45 GPa. The post-shock heating raised the rock's temperature to about 1200 °C; as a result, the maskelynite devitrified, and extensive partial melting took place. The melting was concentrated in pyroxene-rich areas; all pyroxene melted. As the rock cooled, the partial melts crystallized with fine-grained, subophitic-poikilitic textures. Sample 15418 is a strongly shocked granulitic breccia that had a similar history, but evidence for this history is better preserved than in Dhofar 026. The fact that Dhofar 026 was previously interpreted as an impact melt breccia underscores the importance of detailed petrographic study in interpretation of lunar rocks that have complex textures. The name "impact melt" has, in past studies, been applied only to rocks in which the melt fraction formed by shock-induced total fusion. Recently, however, this name has also been applied to rocks containing melt formed by heating of the rocks by conductive heat transfer, assuming that impact is the ultimate source of the heat. We urge that the name "impact melt" be restricted to rocks in which the bulk of the melt formed by shock-induced fusion to avoid confusion engendered by applying the same name to rocks melted by different processes.