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Bulk Chemistry and Oxygen Isotopic Compositions of Lunar Meteorites Dhofar 025 and Dhofar 026
Abstract
The major- and trace-element composition of highlands meteorites Dh25 and Dh26 show that both are dominated by a FAN component. Incompatible element depletion and low Ti abundances suggest a farside origin. O-isotopes are typical for lunar meteorites.
... This 750 g highland regolith breccia ) is relatively immature as a regolith sample, based on its noble gas contents (Shukolyukov et al. 2001). Our bulk-rock results show generally good agreement with two previous analyses Korotev et al. 2003a), but we do not confirm the high Eu (1.3 μg/g) reported by Taylor et al. (2001), and trace elements, both incompatible and siderophile, are relatively low in our sample. Our Sr result is much lower, but still shows major desert evaporite contamination. ...
... Our bulk-rock data also agree fairly well with the analysis by Taylor et al. (2001) of the original Dhofar 026 stone. One difference is generally higher Na (average 2.24 mg/g) than found by Taylor et al. (1.80 mg/g). ...
... are perhaps the most rigorous test for lunar provenance. Lunar O-isotopic compositions have been determined for most of the samples in this study, e.g., for DaG 262 by Bischoff et al. (1998) for Dhofar 025 and 026 by Taylor et al. (2001). Also helpful for distinguishing lunar from other types of meteorites are ratios of elements that remain cohesive within the lunar crust after tending to be fractionated by solar system formational (e.g., condensation/volatilization) processes. ...
Abstract— We have analyzed nine highland lunar meteorites (lunaites) using mainly INAA. Several of these rocks are difficult to classify. Dhofar 081 is basically a fragmental breccia, but much of its groundmass features a glassy-fluidized texture that is indicative of localized shock melting. Also, much of the matrix glass is swirly-brown, suggesting a possible regolith derivation. We interpret Dar al Gani (DaG) 400 as an extremely immature regolith breccia consisting mainly of impact-melt breccia clasts; we interpret Dhofar 026 as an unusually complex anorthositic impact-melt breccia with scattered ovoid globules that formed as clasts of mafic, subophitic impact melt. The presence of mafic crystalline globules in a lunar material, even one so clearly impact-heated, suggests that it may have originated as a regolith. Our new data and a synthesis of literature data suggest a contrast in Al2O3-incompatible element systematics between impact melts from the central nearside highlands, where Apollo sampling occurred, and those from the general highland surface of the Moon. Impact melts from the general highland surface tend to have systematically lower incompatible element concentration at any given Al2O3 concentration than those from Apollo 16. In the case of Dhofar 026, both the bulk rock and a comparatively Al-poor composition (14 wt% Al2O3, 7 μg/g Sm) extrapolated for the globules, manifest incompatible element contents well below the Apollo 16 trend. Impact melts from Luna 20 (57°E) distribute more along the general highland trend than along the Apollo 16 trend. Siderophile elements also show a distinctive composition for Apollo 16 impact melts: Ni/Ir averaging ˜1.8x chondritic. In contrast, lunaite impact-melt breccias have consistently chondritic Ni/Ir. Impact melts from Luna 20 and other Apollo sites show average Ni/Ir almost as high as those from Apollo 16. The prevalence of this distinctive Ni/Ir ratio at such widely separated nearside sites suggests that debris from one extraordinarily large impact may dominate the megaregolith siderophile component of a nearside region 2300 km or more across.Highland polymict breccia lunaites and other KREEP-poor highland regolith samples manifest a strong anticorrelation between Al2O3 and mg. The magnesian component probably represents the chemical signature of the Mg-suite of pristine nonmare rocks in its most “pure” form, unaltered by the major KREEP-assimilation that is so common among Apollo Mg-suite samples. The average composition of the ferroan anorthositic component is now well constrained at Al2O3 ˜29–30 wt% (implying about 17–19 wt% modal mafic silicates), in good agreement with the composition predicted for flotation crust over a “ferroan” magma ocean (Warren 1990).
... It is paired with Dhofar 026 and Dhofar 457-468 based on their petrologic and mineralogic similarities (Warren et al. 2005). Oxygen isotopic compositions indicate Dhofar 026 has a lunar origin (Taylor et al. 2001). These lunar meteorites have a distinctly different petrographic texture from most other feldspathic lunar meteorites. ...
... These lunar meteorites have a distinctly different petrographic texture from most other feldspathic lunar meteorites. Up to date, only a few investigations were performed on Dhofar 026 and most of them are conference abstracts (Cohen et al. 2001 1 , Cohen et al. 2002Cohen et al. , 2004James et al. 2003 2 ; James et al. 2007;Taylor et al. 2001;Warren et al. 2001 3 , Warren et al. 2005;Fernandes et al. 2004;Demidova et al. 2007) 4 . These investigations show that Dhofar 026 was heavily shocked; however, its complex texture obscures the nature of the shock metamorphic events that affected it. ...
... These lunar meteorites have a distinctly different petrographic texture from most other feldspathic lunar meteorites. Up to date, only a few investigations were performed on Dhofar 026 and most of them are conference abstracts (Cohen et al. 2001 1 , Cohen et al. 2002Cohen et al. , 2004James et al. 2003 2 ; James et al. 2007;Taylor et al. 2001;Warren et al. 2001 3 , Warren et al. 2005;Fernandes et al. 2004;Demidova et al. 2007) 4 . These investigations show that Dhofar 026 was heavily shocked; however, its complex texture obscures the nature of the shock metamorphic events that affected it. ...
Abstract– Dhofar 458 is a lunar meteorite consisting mainly of olivine-plagioclase intergrowths, pyroxene-plagioclase intergrowths, and plagioclase fragments. Pyroxene-plagioclase globules are also common. In this study, we report the discovery of a polycrystalline zircon in this lunar meteorite. The polycrystalline zircon contains small vesicles and rounded baddeleyite grains at its margin. The polycrystalline and porous texture of the zircon indicates high-pressure shock-induced melting and degassing. Baddeleyite grains are derived from decomposition of zircon under high postshock temperature. The shock features in zircon indicates that the shock pressure in Dhofar 458 was greater than approximately 60 GPa and the postshock temperature greater than approximately 1700 °C. The polycrystalline and degassing texture and decomposition zircon also strongly indicates that Dhofar 458 is a clast-rich impact melt rock. During this shock event, most components were melted and grains of mafic minerals are interstitial to lath-like plagioclase grains. Large fragments of olivine and chromite also formed polycrystalline texture at margins and chemically reequilibrated with surrounding melts. We suggest that pyroxene-plagioclase globules could be remains of melted target clasts, whereas vesicles may form during shock-induced degassing of the rock. The U-Pb isotopic data plot on a well-defined discordant line, yielding the age of the zircon of 3434 ± 15 Ma (2σ). This age is interpreted as the time of the impact event that melted Dhofar 458 and caused decomposition and recrystallization of this zircon in Dhofar 458, which reset this zircon’s U-Pb age.
... We initially interpreted Dhofar 026 as an impact melt Taylor et al. 2001). Detailed study of the texture and mineralogy of this rock and comparison to Apollo sample 15418, however, indicate that both rocks are shocked breccias that were partially melted by post-shock heating. ...
... As illustrated in Fig. 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. ...
... The other meteorite groups are as follows: SNC, shergottite-nakhlite-chassignite meteorites, thought to be from Mars; HED, howardite-eucrite-diogenite meteorites; and CV and CM, two groups of carbonaceous chondrites. Data from Taylor et al. (2001), Clayton and Mayeda (1996), Fagan et al. (2002), and Zipfel et al. (1998). the adjacent plagioclase; thus, they must have nucleated on the adjacent plagioclase (the reverse cannot be the case because the adjacent plagioclase is devitrified maskelynite, and the orientation of crystallites in devitrified maskelynite is determined by the structure of the original crystal). ...
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.
... Not listed here is an unnamed lunar meteorite, a feldspathic regolith breccia (27.4% Al 2 O 3 ), described by Yanai (2000) but with no indication of its mass or place of origin. The data were compiled from this work, some unpublished data of this lab (Yamato 983885 and Northwest Africa 773) and other labs (Calcalong Creek, courtesy D. Hill), and the following sources: Arai and Warren (1999), Bischoff et al. (1987), Boynton and Hill (1983), Fagan et al. (2002, in press), Fukuoka (1990), Fukuoka et al. (1986a, 1986b), Greshake et al. (2001), Hill et al. (1991), Jolliff et al. (1991a), Kaiden and Kojima (2003), Kallemeyn and), Koeberl (1988), Koeberl et al. (1989), Korotev et al. (1983 Korotev et al. ( , 1996), Laul et al. (1983a),), Nishiizumi et al. (1996), Ostertag et al. (1986), Palme et al. (1983), Russell et al. (2002, 2003); Semenkova et al. (2000), Snyder et al. (1999), Spettel et al. (1995, Takahashi and Masuda (1987), Taylor et al. (2001a, 2001b), Thalmann et al. (1996), Verkouteren et al. (1983, Warren and Kallemeyn (1986),), Yanai (1991), and Zipfel et al. (1998. 4896 R. L. Korotev et al. ...
... Compositional data for three of them, Yamato 791197, Yamato 82192, and DaG (Dar al Gani) 262, have been presented by others (Fukuoka et al., 1986a; Lindstrom et al., , 1987 Lindstrom et al., , 1991a Ostertag et al., 1986; Kallemeyn, 1986, 1987; Bischoff et al., 1987 Bischoff et al., , 1998 Koeberl, 1988). Some data on bulk composition for the other three, DaG 400, Dhofar 025, and NWA (Northwest Africa) 482, have been presented in abstracts (Zipfel et al., 1998; Bukovanska et al., 1999; Taylor et al., 2001a;). We also review compositional aspects of lunar meteorites and note implications that they have for compositional remote sensing of the lunar surface and the composition of the lunar crust. ...
... On the basis of the low concentrations observed in Apollo rocks and lunar meteorites from Antarctica of otherwise similar composition (Fig. 2), we conclude that nearly all the W and most of the Au that we observe are contaminants from sawing (tungsten carbide?) and handling (jewelry). Our results for Dhofar 025 are largely consistent with those of Taylor et al. (2001a) and except that our results for Eu (0.82 ppm) do not confirm the unusually high concentration (1.3 ppm) reported by Taylor et al. (2001a).Table 2. Mass-weighted mean results of instrumental neutron activation analysis for 23 subsamples of 5 feldspathic lunar meteorites. Presumably as a result of contamination, all three of our subsamples have concentrations of Au that are large compared to feldspathic lunar meteorites from cold deserts with similar Ni and Ir concentrations (Fig. 2). ...
We present new compositional data for six feldspathic lunar meteorites, two from cold deserts (Yamato 791197 and 82192) and four from hot deserts (Dhofar 025, Northwest Africa 482, and Dar al Gani 262 and 400). The concentrations of FeO (or Al2O3) and Th (or any other incompatible element) together provide first-order compositional information about lunar polymict samples (breccias and regoliths) and regions of the lunar surface observed from orbit. Concentrations of both elements on the lunar surface have been determined from data acquired by orbiting spacecraft, although the derived concentrations have large uncertainties and some systematic errors compared to sample data. Within the uncertainties and errors in the concentrations derived from orbital data, the distribution of FeO and Th concentrations among lunar meteorites, which represent ∼18 source regions on the lunar surface, is consistent with that of 18 random samples from the surface. Approximately 11 of the lunar meteorites are low-FeO and low-Th breccias, consistent with large regions of the lunar surface, particularly the northern farside highlands. Almost all regoliths from Apollo sites, on the other hand, have larger concentrations of both elements because they contain Fe-rich volcanic lithologies from the nearside maria and Th-rich lithologies from the high-Th anomaly in the northwestern nearside. The feldspathic lunar meteorites thus offer our best estimate of the composition of the surface of the feldspathic highlands, and we provide such an estimate based on the eight most well-characterized feldspathic lunar meteorites. The variable but high (on average) Mg/Fe ratio of the feldspathic lunar meteorites compared to ferroan anorthosites confirms a hypothesis that much of the plagioclase at the surface of the feldspathic highlands is associated with high-Mg/Fe feldspathic rocks such as magnesian granulitic breccia, not ferroan anorthosite. Geochemically, the high-Mg/Fe breccias appear to be unrelated to the mafic magnesian-suite rocks of the Apollo collection. Models for the formation of the upper lunar crust as a simple flotation cumulate composed mainly of ferroan anorthosite do not account for the complexity of the crust as inferred from the feldspathic lunar meteorites.
... and d 18 O = +5.7&. Both of these samples plot on the Terrestrial Fractionation Line (TFL) and are consistent with other lunar meteorites, though Dhofar 1673 does plot relatively high compared to other meteorites (Fig. 8) Mayeda 1975, 1996;Zipfel et al. 1998;Taylor et al. 2001;Wiechert et al. 2001;Fagan et al. 2002;Kaiden and Kojima 2002;Anand et al. 2003;Cahill et al. 2004;Spicuzza et al. 2007;Joy et al. 2008;Haloda et al. 2009;Hallis et al. 2010;Herwartz et al. 2014;Young et al. 2016). ...
... As only the mesostasis was analyzed in the clastrich melt rock clasts, a comparison among the three Dhofar meteorites and other studies is based solely on measurements of the clast-free melt rock phases (pure Fig. 8. The oxygen isotopic composition of Dhofar 1673 and Dhofar 1983 compared to other lunar meteorites Mayeda 1975, 1996;Zipfel et al. 1998;Taylor et al. 2001;Wiechert et al. 2001;Fagan et al. 2002;Kaiden and Kojima 2002;Anand et al. 2003;Cahill et al. 2004;Spicuzza et al. 2007;Joy et al. 2008;Haloda et al. 2009;Hallis et al. 2010;Herwartz et al. 2014;Young et al. 2016). impact glass) and the spherules within the three Dhofar meteorites. ...
The Dhofar 1673, Dhofar 1983, and Dhofar 1984 meteorites are three lunar regolith breccias classified based on their petrography, mineralogy, oxygen isotopes, and bulk chemistry. All three meteorites are dominated by feldspathic lithic clasts; however, impact melt rock clasts and spherules are also found in each meteorite. The bulk chemistry of these samples is similar to other feldspathic highland meteorites with the Al2O3 content only slightly lower than average. Within the lithic clasts, the Mg # of mafic phases versus the anorthite content of feldspars is similar to other highland meteorites and is found to plot intermediate of the ferroan‐anorthositic suite and magnesian suite. The samples lack any KREEPy signature and have only minor indications of a mare basalt component, suggesting that the source region of all three meteorites would have been distal from the Procellarum KREEP Terrane and could have possibly been the Feldspathic Highland Terrane. All three meteorites were found within 500 m of each other in the Dhofar region of Oman. This, together with their similar petrography, stable isotope chemistry, and geochemistry indicates the possibility of a pairing.
... and δ 17 O = +2.81‰ (Taylor et al. 2001). This composition lies along the terrestrial-lunar fractionation line (TLFL) (Fig. 7) and is consistent with results for other lunar meteorites including DaG 262 and DaG 400. ...
Abstract— The petrogenesis of four lunar highlands meteorites, Dhofar 025 (Dho 025), Dhofar 081 (Dho 081), Dar al Gani 262 (DaG 262), and Dar al Gani 400 (DaG 400) were studied. For Dho 025, measured oxygen isotopic values and Fe-Mn ratios for mafic minerals provide corroboratory evidence that it originated on the Moon. Similarly, Fe-Mn ratios in the mafic minerals of Dho 081 indicate lunar origin.
Lithologies in Dho 025 and Dho 081 include lithic clasts, granulites, and mineral fragments. A large number of lithic clasts have plagioclase AN# and coexisting mafic mineral Mg# that plot within the “gap” separating ferroan anorthosite suite (FAN) and high-magnesium suite (HMS) rocks. This is consistent with whole rock Ti-Sm ratios for Dho 025, Dho 081, and DaG 262, which are also intermediate compared to FAN and HMS lithologies. Although ion microprobe analyses performed on Dho 025, Dho 081, DaG 262, and DaG 400 clasts and minerals show far stronger FAN affinities than whole rock data suggest, most clasts indicate admixture of ≤12% HMS component based on geochemical modeling. In addition, coexisting plagioclase-pyroxene REE concentration ratios in several clasts were compared to experimentally determined plagioclase-pyroxene REE distribution coefficient ratios. Two Dho 025 clasts have concordant plagioclase-pyroxene profiles, indicating that equilibrium between these minerals has been sustained despite shock metamorphism. One clast has an intermediate FAN-HMS composition.
These lunar meteorites appear to represent a type of highland terrain that differs substantially from the KREEP-signatured impact breccias that dominate the lunar database. From remote sensing data, it is inferred that the lunar far side appears to have appropriate geochemical signatures and lithologies to be the source regions for these rocks; although, the near side cannot be completely excluded as a possibility. If these rocks are, indeed, from the far side, their geochemical characteristics may have far-reaching implications for our current scientific understanding of the Moon.
... Our small subsample is compositionally distinct, however; see text. e (1,2) Bischoff et al. (1987 Bischoff et al. ( , 1998); (3) Boynton and Hill (1983); (4) Cohen et al. (2004); (5,6) Fukuoka et al. (1986a,b); (7) Greshake et al. (2001); (8) Haloda et al. (2005); (9) Jolliff et al. (1991); (10) Kallemeyn and Warren (1983); (11) Karouji et al. (2004); (13) Koeberl (1988); (14,15,16,17) Koeberl et al. (1989 Koeberl et al. ( , 1990 Koeberl et al. ( , 1991 Koeberl et al. ( , 1996); (18) Korotev and Irving (2005); (19,20,21) Korotev et al. (1983 Korotev et al. ( , 1996 Korotev et al. ( , 2003b); (22) Laul et al. (1983); (23, 24, 25, 27) Lindstrom et al. (1986 Lindstrom et al. ( , 1991a Lindstrom et al. ( ,b, 1995); (28) Nishiizumi et al. (1996); (29) Ostertag et al. (1986); (30,31) Palme et al. (1983 Palme et al. ( , 1991); (32) Spettel et al. (1995); (33) Takahashi and Masuda (1987); (34) Taylor et al. (2001); (35) Thalmann et al. (1996); (36,37,38) Kallemeyn (1986, 1991a,b); (39) Warren et al. (2005); (40) Zipfel et al. (1998); (41) this work; (42) unpublished data of this laboratory (Korotev, 2006a,b). f Symbol used in figures. ...
PCA (Pecora Escarpment) 02007 and Dhofar 489 are both meteorites from the feldspathic highlands of the Moon. PCA 02007 is a feldspathic breccia consisting of lithified regolith from the lunar surface. It has concentrations of both incompatible and siderophile elements that are at the high end of the ranges for feldspathic lunar meteorites. Dhofar 489 is a feldspathic breccia composed mainly of impact-melted material from an unknown depth beneath the regolith. Concentrations of incompatible and siderophile elements are the lowest among brecciated lunar meteorites. Among 19 known feldspathic lunar meteorites, all of which presumably originate from random locations in the highlands, concentrations of incompatible elements like Sm and Th tend to increase with those of siderophile elements like Ir. Feldspathic meteorites with high concentrations of both suites of elements are usually regolith breccias. Iridium derives mainly from micrometeorites that accumulate in the regolith with duration of surface exposure. Micrometeorites have low concentrations of incompatible elements, however, so the correlation must reflect a three-component system. We postulate that the correlation between Sm and Ir occurs because the surface of the Feldspathic Highlands Terrane has become increasingly contaminated with time in Sm-rich material from the Procellarum KREEP Terrane that has been redistributed across the lunar surface by impacts of moderate-sized, post-basin impacts. The most Sm-rich regolith breccias among feldspathic lunar meteorites are about 3× enriched compared to the most Sm-poor breccias, but this level of enrichment requires only a few percent Sm-rich material typical of the Procellarum KREEP Terrane. The meteorite data suggest that nowhere in the feldspathic highlands are the concentrations of K, rare earths, and Th measured by the Lunar Prospector mission at the surface representative of the underlying “bedrock;” all surfaces covered by old regolith (as opposed to fresh ejecta) are at least slightly contaminated. Dhofar 489 is one of 15 paired lunar-meteorite stones from Oman (total mass of meteorite: ⩾1037 g). On the basis of its unusually high Mg/Fe ratio, the meteorite is likely to have originated from northern feldspathic highlands.
... The analytical methods generally applied for the analysis of meteorites which can be used in the Earth are ICP-MS, EDS and XRF [9][10][11], while the easiest way of studying the elementary composition of meteorites in flight is based on the optical emission spectroscopy of the plasma generated when the space object crosses Earth's atmosphere [12][13][14]. The analysis and the consequent classification are based on the Local Thermodynamic Equilibrium (LTE) assumption and on a range of values associated to element ratios. ...
The classification of meteorites when geological analysis is unfeasible is generally made by the spectral line emission ratio of some characteristic elements. Indeed when a meteorite impacts Earth's atmosphere, hot plasma is generated, as a consequence of the braking effect of air, with the consequent ablation of the falling body. Usually, by the plasma emission spectrum, the meteorite composition is determined, assuming the Boltzmann equilibrium. The plasma generated during Laser Induced Breakdown Spectroscopy (LIBS) experiment shows similar characteristics and allows one to verify the mentioned method with higher accuracy. On the other hand the study of Laser Induced Breakdown Spectroscopy on meteorite can be useful for both improving meteorite classification methods and developing on-flight techniques for asteroid investigation.In this paper certified meteorites belonging to different typologies have been investigated by LIBS: Dofhar 461 (lunar meteorite), Chondrite L6 (stony meteorite), Dofhar 019 (Mars meteorite) and Sikhote Alin (irony meteorite).
... The data source for the lunar meteorites is from Clayton and Mayeda (1996). The data on the Apollo samples are from Wiechert et al. (2001), and the Dho 025 and Dho 026 values are from Taylor et al. (2001a). The plus sign on the plot indicates the analytical uncertainty in d 17 O and d 18 O measurements for the lunar meteorites. ...
Abstract— Dhofar 287 (Dho 287) is a new lunar meteorite, found in Oman on January 14, 2001. The main portion of this meteorite (Dho 287A) consists of a mare basalt, while a smaller portion of breccia (Dho 287B) is attached on the side. Dho 287A is only the fourth crystalline mare basalt meteorite found on Earth to date and is the subject of the present study. The basalt consists mainly of phenocrysts of olivine and pyroxene set in a finer-grained matrix, which is composed of elongated pyroxene and plagioclase crystals radiating from a common nucleii. The majority of olivine and pyroxene grains are zoned, from core to rim, in terms of Fe and Mg. Accessory minerals include ilmenite, chromite, ulvöspinel, troilite, and FeNi metal. Chromite is invariably mantled by ulvöspinel. This rock is unusually rich in late-stage mesostasis, composed largely of fayalite, Si-K-Ba-rich glass, fluorapatite, and whitlockite. In texture and mineralogy, Dho 287A is a low-Ti mare basalt, with similarities to Apollo 12 (A-12) and Apollo 15 (A-15) basalts. However, all plagioclase is now present as maskelynite, and its composition is atypical for known low-Ti mare basalts. The Fe to Mn ratios of olivine and pyroxene, the presence of FeNi metal, and the bulk-rock oxygen isotopic ratios, along with several other petrological features, are evidence for the lunar origin for this meteorite.
Whole-rock composition further confirms the similarity of Dho 287A with A-12 and A-15 samples but requires possible KREEP assimilation to account for its rare-earth-element (REE) contents. Cooling-rate estimates, based on Fo zonation in olivine, yield values of 0.2–0.8°C/hr for the lava, typical for the center of a 10–20 m thick flow. The recalculated major-element concentrations, after removing 10–15% modal olivine, are comparable to typical A-15 mare basalts. Crystallization modeling of the recalculated Dho 287A bulk-composition yields a reasonable fit between predicted and observed mineral abundances and compositions.
Dhofar 025 is a lunar highland breccia consisting mainly of anorthositic, with less common noritic, gabbronoritic, and troctolitic material. Rare fragments of low-Ti basalts are present as well, but no KREEP (component enriched in incompatible elements) was found in the meteorite. The cathodoluminescence study of this meteorite showed that its impact–melt matrix contains unusual cathodoluminescent (CL) objects of feldspathic composition, which frequently contain microlites of Fe-Mg spinel (pleonaste). They were presumably formed by impact mixing and melting of olivine and plagioclase with subsequent rapid quenching of the impact melts. Such mixing could happen either during assimilation of anorthosites by picritic/troctolitic magmas or during impact melting of troctolites. The enrichment of CL objects of Dhofar 025 in incompatible trace elements suggests that the mafic component of the impact mixture may be related to the high-magnesium suite rocks, which are frequently enriched in KREEP component. The depletion of CL objects in alkalis indicates their possible relation with residual glasses formed by evaporation. However, the presence of FeO in most objects points to the insignificant extent of evaporation. Thus, evaporation cannot explain the enrichment of the CL objects in Al2O3 and other refractory components, although this process definitely took place in their formation. Their similarity to the lunar pink spinel anorthosites, whose existence was predicted from orbital data, serves as an argument in support of the possible formation of the latters by impact mixing.
Ar-Ar ages of impact melt in lunar highlands breccia Dhofar 025 range from 500 Ma - 4.0 Ga from 3-5 different impact events. A ~500 Ma crystallization age for highlands melt breccia Dhofar 026 may be the same event as the young Dhofar 025 samples.
Detailed study of the texture of Dhofar 026, and comparison to textures of Apollo samples 15418 and 60017, indicate that Dhofar 026 is a shocked granulitic breccia in which post-shock temperature was well above the solidus and extensive partial melting took place.
Numerous new finds of lunar meteorites in Oman allow detailed constraints to be obtained on the intensity of the transfer of lunar matter to the Earth. Our estimates show that the annual flux of lunar meteorites in the mass interval from 10 to 1000 g to the entire Earth's surface should not be less than several tenths of a kilogram and is more likely equal to tens or even a few hundred kilograms, i.e., a few percent of the total meteorite flux. This corresponds to several hundred or few thousand falls of lunar meteorites on all of Earth per year. Even small impact events, which produce smaller than craters on the Moon smaller than 10 km in diameter, are capable of transferring lunar matter to the Earth. In this case, the Earth may capture between 10 to 100% of the mass of high-velocity crater ejecta leaving the Moon. Our estimates for the lunar flux imply rather optimistic prospects for the discovery of new lunar meteorites and, consequently, for the analyses of the lunar crust composition. However, the meteorite-driven flux of lunar matter did not play any significant role in the formation of the material composition of the Earth's crust, even during the stage of intense meteorite bombardment.
Abstract— Northwest Africa 482 (NWA 482) is a crystalline impact-melt breccia from the Moon with highlands affinities. The recrystallized matrix and the clast population are both highly anorthositic. Clasts are all related to the ferroan anorthosite suite, and include isolated plagioclase crystals and lithic anorthosites, troctolites, and spinel troctolites. Potassium-, rare-earth-element-, and phosphorus-bearing (KREEP) and mare lithologies are both absent, constraining the source area of this meteorite to a highland terrain with little to no KREEP component, most likely on the far side of the Moon. Glass is present in shock veins cutting through the sample and in several large melt pockets, indicating a second impact event.There are two separate events recorded in the 40Ar-39Ar system: one at ∼3750 Ma, which completely reset the K-Ar system, and one at ≲2400 Ma, which caused only partial degassing. These events could represent, respectively, crystallization of the impact-melt breccia and later formation of the glass, or the formation of the glass and a later thermal event.The terrestrial age of the meteorite is 8.6 ± 1.3 ka. This age corresponds well with the modest amount of weathering in the rock, in the form of secondary phyllosilicates and carbonates. Based on terrestrial age and location, lithology, and chemistry, NWA 482 is unique among known lunar meteorites.
Abstract— Mineralogy, major element compositions of minerals, and elemental and oxygen isotopic compositions of the whole rock attest to a lunar origin of the meteorite Northwest Africa (NWA) 032, an unbrecciated basalt found in October 1999. The rock consists predominantly of olivine, pyroxene and chromite phenocrysts, set in a crystalline groundmass of feldspar, pyroxene, ilmenite, troilite and trace metal. Whole-rock shock veins comprise a minor, but ubiquitous portion of the rock. Undulatory to mosaic extinction in olivine and pyroxene phenocrysts and micro-faults in groundmass and phenocrysts also are attributed to shock.Several geochemical signatures taken together indicate unambiguously that NWA 032 originated from the Moon. The most diagnostic criteria include whole-rock oxygen isotopic composition and ratios of Fe/Mn in the whole rock, olivine, and pyroxene. A lunar origin is documented further by the presence of Fe-metal, troilite, and ilmenite; zoning to extremely Fe-rich compositions in pyroxene; the ferrous oxidation state of all Fe in pyroxene; and the rare earth element (REE) pattern with a well-defined negative europium anomaly. This rock is similar in major element chemistry to basalts from Apollo 12 and 15, but is enriched in light REE and has an unusually high Th/Sm ratio. Some Apollo 14 basalts yield a closer match to NWA 032 in REE patterns, but have higher concentrations of Al2O3. Ar-Ar step release results are complex, but yield a whole-rock age of ˜2.8 Ga, suggesting that NWA 032 was extruded at 2.8 Ga or earlier. This rock may be the youngest sample of mare basalt collected to date. Noble gas concentrations combined with previously collected radionuclide data indicate that the meteorite exposure history is distinct from currently recognized lunar meteorites. In short, the geochemical and petrographic features of NWA 032 are not matched by Apollo or Luna samples, nor by previously identified lunar meteorites, indicating that it originates from a previously unsampled mare deposit.Detailed assessment of petrographic features, olivine zoning, and thermodynamic modelling indicate a relatively simple cooling and crystallization history for NWA 032. Chromite-spinel, olivine, and pyroxene crystallized as phenocrysts while the magma cooled no faster than 2 °C/h based on the polyhedral morphology of olivine. Comparison of olivine size with crystal growth rates and preserved Fe-Mg diffusion profiles in olivine phenocrysts suggest that olivine was immersed in the melt for no more than 40 days. Plumose textures in groundmass pyroxene, feldspar, and ilmenite, and Fe-rich rims on the phenocrysts formed during rapid crystallization (cooling rates ˜20 to 60 °C/h) after eruption.
The paper presents the first analyses of major and trace elements in 19 lunar meteorites newly found in Oman. These and literature
data were used to assay the composition of highland, mare, and transitional (highland-mare interface) regions of the lunar
surface. The databank used in the research comprises data on 44 meteorites weighing 11 kg in total, which likely represent
26 individual falls. Our data demonstrate that the lunar highland crust should be richer in Ca and Al but poorer in mafic
and incompatible elements than it was thought based on studying lunar samples and the first orbital data. The Ir concentration
in the highland crust and the analysis of lunar crater population suggest that most lunar impactites were formed by a single
major impact event, which predetermined the geochemical characteristics of these rocks. Lunar mare regions should be dominated
by low-Ti basalts, which are, however, enriched in LREEs compared to those sampled by lunar missions. The typical material
of mare-highland interface zones can contain KREEP and magnesian VLT basalts. The composition of the lunar highland crust
deduced from the chemistry of lunar meteorites does not contradict the model of the lunar magma ocean, but the average composition
of lunar mare meteorites is inconsistent with this concept and suggests assimilation of KREEP material by basaltic magmas.
The newly obtained evaluations of the composition of the highland crust confirm that the Moon can be enriched in refractory
elements and depleted in volatile and siderophile elements.
We report preliminary results for the cosmogenic radionuclides, Cl-36, Al-26, and Be-10 and noble gases in a basaltic shergottite Dhofar 019. We found long terrestrial age of Dhofar 019 even though this meteorite was found in hot desert, Oman. Additional information is contained in the original extended abstract.
Oxygen isotope abundances provide a powerful tool for recognizing genetic relationships among meteorites. Among the differentiated achondrites, three isotopic groups are recognized: (l ) SNC (Mars), (2) Earth and Moon, and (3) HED (howardites, eucrites, diogenites). The HED group also contains the mesosiderites, main-group pallasites, and silicates from IIIAB irons. The angrites may be marginally resolvable from the HED group. Within each of these groups, internal geologic processes give rise to isotopic variations along a slope- fractionation line, as is well known for terrestrial materials. Variations of Δ17O from one planet to another are inherited from the inhomogeneities in the solar nebula, as illustrated by the isotopic compositions of chondrites and their constituents. Among the undifferentiated achondrites, five isotopic groups are found: (1) aubrites, (2) winonaites and IAB-IIICD irons, (3) brachinites, (4) acapulcoites and lodranites, and (5) ureilites. The isotopic compositions of aubrites coincide with the Earth and Moon, and also with the enstatite chondrites. These bodies apparently were derived from a. common reservoir, the isotopic composition of which was established at the chondrule scale by nebular processes. Isotopic similarities between chondrites and achondrites are seen only for the following instances: (1) enstatite chondrites and aubrites, (2) H chondrites and HE irons, and (3) L or LL chondrites and IVA irons. The isotopic data also support the following genetic associations: (1) winonaites and IAB-IIICD irons, (2) acapulcoites and lodranites, and (3) ureilites and dark inclusions of C3 chondrites. An attempt to reconcile the whole-planet isotopic compositions of Earth, Mars, and the eucrite parent body with mixing models of their chemical compositions failed. It is not possible to satisfy both the chemical and isotopic compositions of the terrestrial planets using known primitive Solar System components.
Dh25 is an anorthositic regolith breccia. The mineral chemistry of most rock and melt clasts have compositions intermediate between FAN and HMS fields, indicative of a non-Apollo, FAN-rich locale, possibly the lunar farside.
An interpretative synthesis of current knowledge on the moon and the terrestrial planets is presented, emphasizing the impact of recent lunar research (using Apollo data and samples) on theories of planetary morphology and evolution. Chapters are included on the exploration of the solar system; geology and stratigraphy; meteorite impacts, craters, and multiring basins; planetary surfaces; planetary crusts; basaltic volcanism; planetary interiors; the chemical composition of the planets; the origin and evolution of the moon and planets; and the significance of lunar and planetary exploration. Photographs, drawings, graphs, tables of quantitative data, and a glossary are provided.