Chemistry of the Calcalong Creek lunar meteorite and its relationship to lunar terranes
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CitationHill, D. H., & Boynton, W. V. (2003). Chemistry of the Calcalong Creek lunar meteorite and its relationship to lunar terranes. Meteoritics & Planetary Science, 38(4), 595-626.
PublisherThe Meteoritical Society
JournalMeteoritics & Planetary Science
AbstractThe Calcalong Creek lunar meteorite is a polymict breccia that contains clasts of both highlands and mare affinity. Reported here is a compilation of major, minor, and trace element data for bulk, clast, and matrix samples determined by instrumental neutron activation analysis (INAA). Petrographic information and results of electron microprobe analyses are included. The relationship of Calcalong Creek to lunar terranes, especially the Procellarum KREEP Terrane and Feldspathic Highlands Terrane, is established by the abundance of thorium, incompatible elements and their KREEP-like CI chondrite normalized pattern, FeO, and TiO2. The highlands component is associated with Apollo 15 KREEP basalt but represents a variant of the KREEP-derived material widely found on the moon. Sources of Calcalong Creek's mare basalt components may be related to low-titanium (LT) and very low-titanium (VLT) basalts seen in other lunar meteorites but do not sample the same source. The content of some components of Calcalong Creek are found to display similarities to the composition of the South Pole-Aitken Terrane. What appear to be VLT relationships could represent new high aluminum, low titanium basalt types.
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"New" lunar meteorites: Implications for composition of the global lunar surface, lunar crust, and the bulk MoonWarren, Paul H. (The Meteoritical Society, 2005-01-01)New data for lunar meteorites and a synthesis of literature data have significant implications for the interpretation of global Th data and for the Moons bulk composition. As presently calibrated (Prettyman et al. 2002), the Lunar Prospector gamma-ray data imply that the average global surface Th = 1.58 micrograms/g. However, that calibration yields implausibly high concentrations for the three most Th-poor documented sampling sites, it extrapolates to a nonzero Lunar Prospector Th, ~0.7 micrograms/g, at zero sample Th, and it results in a misfit toward too-high Th when compared with the global regolith Th spectrum as constrained using mainly lunaite regolith breccias. Another problem is manifested by Th versus K systematics. Ground truth data plot consistently to the high-Th/K side of the Prospector data trend, offset by a factor of 1.2. A new calibration is proposed that represents a compromise between the Th levels indicated by ground truth constraints and the Prettyman et al. (2002) calibration. Conservatively assuming that the Th versus K issue is mostly a K problem, the average global surface Th is estimated to be ~1.35 micrograms/g. The Moons remarkable global asymmetry in KREEP abundance is even more pronounced than previously supposed. The surface Th concentration ratio between the hemisphere antipodal to the Procellarum basin and the hemisphere centered on Procellarum is reduced to 0.24 in the new calibration. This extreme disparity is most simply interpreted as a consequence of Procellarums origin at a time when the Moon still contained at least a thin residual layer of a global magma ocean. Allowing for diminution of Th with depth, the extrapolated bulk crustal Th is ~0.73 micrograms/g. Further extrapolation to bulk Moon Th yields ~0.07 micrograms/g, which is nearly identical to the consensus estimate for Earths primitive mantle. Assuming chondritic proportionality among refractory lithophile elements implies Al2O3 of approximately 3.8 wt%. The Moons bulk mantle mg ratio is only weakly constrained by seismic and mare-basaltic data. KREEPand mare-free lunaite regolith samples, other thoroughly polymict lunar meteorites, and a few KREEP-free Apollo highland samples manifest a remarkable anticorrelation on a plot of Al2O3 versus mg. This trend implies that an important component of the Moon is highly magnesian. The bulk Moon is inferred to have an Earth-like oxide mg ratio of ~87-88 mol%. The close resemblance between the bulk Moon and Earths primitive mantle extends to moderately volatile elements, most clearly Mn. Unless major proportions of Cr and V are sequestered into deep mantle spinel, remarkably Earth-like depletions (versus chondrites) are also inferred for bulk Moon Cr and V.
Geochemistry and 40Ar-39Ar geochronology of impact-melt clasts in feldspathic lunar meteorites: Implications for lunar bombardment historyCohen, B. A.; Swindle, T. D.; Kring, D. A. (The Meteoritical Society, 2005-01-01)We studied 42 impact-melt clasts from lunar feldspathic regolith breccias MacAlpine Hills (MAC) 88105, Queen Alexandra Range (QUE) 93069, Dar al Gani (DaG) 262, and DaG 400 for texture, chemical composition, and/or chronology. Although the textures are similar to the impactmelt clasts identified in mafic Apollo and Luna samples, the meteorite clasts are chemically distinct from them, having lower Fe, Ti, K, and P, thus representing previously unsampled impacts. The 40Ar- 39Ar ages on 31 of the impact melts, the first ages on impact-melt samples from outside the region of the Apollo and Luna sampling sites, range from ~4 to ~2.5 Ga. We interpret these samples to have been created in at least six, and possibly nine or more, different impact events. One inferred impact event may be consistent with the Apollo impact-melt rock age cluster at 3.9 Ga, but the meteorite impact-melt clasts with this age are different in chemistry from the Apollo samples, suggesting that the mechanism responsible for the 3.9 Ga peak in lunar impact-melt clast ages is a lunar-wide phenomenon. No meteorite impact melts have ages more than 1 older than 4.0 Ga. This observation is consistent with, but does not require, a lunar cataclysm.
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