Antarctic Meteorite ALHA 81005, A piece from the ancient lunar crust (original) (raw)
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Possible lunar source areas of meteorite ALHA81005: Geochemical remote sensing information
Geophysical Research Letters, 1983
ß Antattic meteorite ALHA81005 is a regolith breccia apparently sent to earth by an impact event in the lunar highlands. Laboratory studies of this sample provide information that is used to understand the source region on the moon using remote sensing data. The meteorites' low Thorium content is inconsistent with Thorium values measured for the central lunar nearside from orbit with Apollo y-ray spectrometers. Similarly, the mineral assemblages inferred from near infrared spectra of small impact craters on the lunar nearside do not exhibit the significant component of olivine and Fe-bearing feldspar that is observed in the meteorite spectra. The existing remote sensing data suggest the most probable source region for ALHA81005 is the nearside limb or the lunar farside and that the composition of ALHA81005 represents a surface unit that has not previously been extensively sampled. The unusual Antartic meteorite ALHA81005, is presumed to have reached the earth through ejection by an impact event that occurred somewhere on the Moon. Reviewed here is evidence that can help locate the source area on the moon for this unique lunar sample. Since there are no global compositional data for the moon, information must be extrapolated from limited amounts of remote sensing data. Three properties of ALHA81005 provide information relevant to the search for its source area: bulk chemistry, a clast of very low-titanium basalt, and bulk mineralogy. This application of remote sensing data of the lunar surface requires the composition and general character of sample ALHA81005 to be representative of the area from which it originated. The fact that the sample is essentially a regolith breccia (e.g., Warren et al., 1983; Simon et al., 1983) is supportive evidence that this sample does indeed represent a surface unit. contain high abundances of K20 and Th). Furthermore, MgO values of all measurements for the meteorite are relatively high.
Geochemistry and petrography of the MacAlpine Hills lunar meteorites
Geochimica Et Cosmochimica Acta, 1991
Hills 88 104 and 88 105 are anorthositic lunar meteorites recovered from the same area in Antarctica which are demonstrated to be paired samples of the same fall. Petrographic studies of matrix and clasts show that MAC88104/5 is a polymict breccia dominated by impact melt clasts. It contains a small amount of highland impact glass and very few regolith glass spherules. It is better classified as a fragmental breccia than a regolith breccia. The bulk composition is ferroan (mg' = 63) and highly aluminous (Al203 = 28%). REE and other incompatible element concentrations are very low. Compositions of anorthositic, granulitic, and impact melt breccia clasts are very similar to, but distinct from, matrix composition. MAC88 104/5 is very similar in composition to the other anorthositic lunar meteorites, but each of the meteorites is distinct. The anorthositic lunar meteorites, especially MAC88104/5 and Y82 192/3/86032, are very similar to North Ray Crater feldspathic fragmental breccias in compositon and petrography. These fragmental lunar meteorites may have been ancient, deeply buried breccias from the megaregolith. Comparisons of chemical-petrographic features and exposure histories suggest that the twelve lunar meteorites were derived from two to nine, but probably four to seven, impacts onto the lunar surface. Discrepancies between the proportions of lunar meteorites and results of Apollo missions may be due to unrepresentative sampling. Lunar meteorites provide valuable new information on the nature of the lunar crust.
Geochimica et Cosmochimica Acta, 2007
Icefield (LAP) 02205 are consistent with derivation of the parent magma from a source region similar to that which produced the Apollo 12 low-Ti olivine basalts followed by mixing of the magma with small amounts (1 to 2 wt%) of trace element-enriched material similar to lunar KREEP-rich sample SaU 169. The crystallization age of LAP 02205 is most precisely dated by an internal Rb-Sr isochron of 2991 ±14 Ma, with an initial 87 Sr/ 88 Sr at the time of crystallization of 0.699836 ±0.000010. Leachable REE-rich phosphate phases of LAP 02205 do not plot on a Sm-Nd mineral isochron, indicating contamination or open system behavior of the phosphates. Excluding anomalous phases from the calculation of a Sm-Nd isochron yields a crystallization age of 2992 ±85 (initial ε 143 Nd = +2.9 ±0.8) that is within error of the Rb-Sr age, and in agreement with other independent age determinations for LAP 02205 from Ar-Ar and U-Pb methods. The calculated 147 Sm/ 144 Nd source ratios for LAP 02205, various Apollo 12 and 15 basalts, and samples with strong affinities to KREEP (SaU 169, NWA 773, 15386) are uncorrelated with their crystallization ages. This finding does not support the involvement of a common KREEP component as a heat source for lunar melting events that occurred after crystallization of the lunar magma ocean.
FIELD GROUP SUB GR 19. ABSTRACT tCanunue an moame It"ceaw,y and-den n/y by btock .umbra Recent results on the antarctic meteorite ALHA 77003 which contribute to understanding the alteration processes which produced matrix in unequilibrated chondrites are Presented. Also included are additional scanning electron microscope results confirming that the matrix in Allende formed by in situ alteration.
Geochimica Et Cosmochimica Acta, 2006
Antarctic lunar meteorites Meteorite Hills 01210 and Pecora Escarpment 02007 are breccias that come from different regolith lithologies on the Moon. MET 01210 is composed predominantly of fractionated low-Ti basaltic material and is classified as an immature, predominantly basaltic glassy matrix regolith breccia. PCA 02007 is a predominantly feldspathic regolith breccia consisting of metamorphosed feldspathic, noritic, troctolitic and noritic-anorthosite clasts, agglutinate and impact-glasses, as well as a number of basaltic clasts with mare and possible non-mare affinities. The basalt clasts in MET 01210 have undergone 'Fenner' trend enrichments in iron and may also have witnessed late-stage crystallization of zircon or a zirconium-rich mineral. Some of the features of MET 01210 are similar to other basaltic lunar breccia meteorites (e.g., Northwest Africa 773; Elephant Moraine 87521/96008; Yamato 793274/981031), but it is not paired with them. The presence of metamorphic anorthositic clasts as well as agglutinates indicates a small regolith component. Similarities with previously discovered evolved (e.g., LaPaz Icefield 02205; Northwest Africa 032) and ferroan (e.g., Asuka 881757; Yamato 793169) basaltic lunar meteorites suggest a similar mare source region for MET 01210. Despite lack of evidence for pairing, PCA 02007 shares many features with other feldspathic regolith breccias (e.g., Yamato 791197, Queen Alexandra Range 94281), including a high Mg/Fe whole-rock composition, glass spherules, agglutinate fragments and a diverse clast inventory spanning the range of ferroan anorthosite and high magnesium suite rocks. Some of the basalt fragments in this sample are fractionated and have an igneous origin. However, the majority of the basalt fragments are impact melt clasts. PCA 02007 supports previous studies of feldspathic lunar meteorites that have suggested an aluminous crust for the Moon, with compositions more similar to magnesium granulite breccias than ferroan anorthosites. A 'chondrule-like' fragment found in PCA 02007 and unlike any previously described lunar material is described and tentatively identified as the remnants of a chondritic lunar impactor. This clast is porphyritic with equant olivines that have forsterite-rich cores (Fo >98 ), extreme normal zonation to more fayalitic rims (Fo >44 ), and a mineral assemblage with rare earth element abundances distinct from described lunar material and more similar to chondrules found in ordinary or carbonaceous chondrites. Its discovery and description is significant for understanding the composition of lunar impactors. Previously, the main evidence for chondritic lunar impactors was from chondritic relative abundances and near chondritic ratios of highly siderophile elements in lunar impact melt breccias. However, the presence of this clast, along with two other chondritic clasts from Apollo soils 12037 and 15602, provides clues to the identity of ancient meteorite impactors on the Moon.
Lunar highland meteorites and the composition of the lunar crust
Geochimica Et Cosmochimica Acta, 1991
Major, minor, and trace element data obtained by neutron activation techniques and by spark source mass spectrometry (SSMS) on two lunar meteorites MAC88104 and MAC88105 are reported. Both MAC samples were also analysed for their contents and isotopic compositions of rare gases. Additional SSMS-data were obtained on four lunar highland meteorites previously found in Antarctica: ALHA81005, Y791197, Y82192, and Y86032.
Exposure histories of lunar meteorites: ALHA81005, MAC88104, MAC88105, and Y791197
Geochimica et Cosmochimica Acta, 1991
The cosmogenic radionuclides 41Ca, 36C1, 26A1 and "Be in the Allan Hills 8 1005, MacAlpine , Hills 88 104, MacAlpine Hills 88 105, and Yamato 79 1197 meteorites were measured by accelerator mass spectrometry (AMS). 53Mn in Allan Hills 8 1005 and Yamato 791197 was measured by neutron activation. These four lunar meteorites experienced similar histories. They were ejected from near the surface of the Moon ranging in depth down to 400 g/cm2 and had very short transition times (less than 0.1 Ma) from the Moon to the Earth. A comparison of the cosmogenic nuclide concentrations in MacAlpine Hills 88 104 and MacAlpine Hills 88 105 clearly indicates that they are a pair from the same fall. INTRODUCI'ION * This paper is part of a consortium study of the largest lunar meteorite MAC88104/5.
Paired lunar meteorites MAC88104 and MAC88105: A new “fan” of lunar petrology
Geochimica et Cosmochimica Acta, 1991
New lunar meteorite MAC88 104 / 5 represents an exciting new opportunity to study a potentially unsampled region of the Moon. We have analyzed six thin sections by electron microprobe and three bulk samples by Instrumental Neutron Activation (INA) in order to determine the chemical characteristics of this new lunar sample. Lunar meteorite MAC88 104/5 is dominated by lithologies of the ferroan anorthosite (FAN) suite and contains abundant granulitized highland clasts, devitrified glass beads of impact origin, and two small clasts which appear to be of basaltic origin. One of these "basaltic" clasts (clast E in MAC88 105,84) is probably mesostasis material, whereas the second larger clast (clast G) may be similar to the Very Low-Ti (VLT) or low-Ti/ high-alumina mare basalts. Impact melt clasts MAC88 105,69 and ,72 have major and trace element compositions similar to the bulk meteorite. There is little evidence of any LKFM (Low-K Fra Mauro or low-K KREEP) contribution to this meteorite, as MAC88104/5 and other brecciated lunar meteorites are Fe-rich and poor in the incompatible elements relative to Apollo 16 regolith and feldspathic breccias. While the exact site of origin for the lunar meteorites cannot be pinpointed, it is evident that they were derived from a relatively KREEP-free ferroan anorthosite terrain.
Siderophile, lithophile and mobile trace elements in the lunar meteorite Allan Hills 81005
Geophysical Research Letters, 1983
Contents of siderophilic As, Au, Co, Ga and Sb, volatile/mobile Ag, Bi, Cd, In, Se, Te, Tl and Zn and lithophilic Cs, Rb and U determined by radiochemical neutron activation analysis in ALHA81005 are similar to those of lunar highlands samples returned by Apollo missions, indicating this meteorite's lunar origin. Five elements (Co, Ga and lithophiles) reflect lunar crustal processes while the remaining 11 siderophile and mobile elements indicate 1.4±0.5% micrometeorite admixture or enrichment by thermal redistribution on the moon. Thus, in contrast to L chondrites where severe shock caused trace element loss, impact-launching of ALHA81005 to earth was free of substantial shock loading. In this light, a Martian origin for severely shocked SNC meteorites is plausible.