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1.
Abstract— Lunar meteorite QUE 93069 found in Antarctica is a mature, anorthitic regolith breccia with highland affinities that was ejected from the Moon <0.3 Ma ago. The frequency distribution of mineral and lithic clasts gives information about the nature of the regolith and subregolith basement near the ejection site as well as about the abundances of rock types shocked to different degrees prior to the breccia formation. Thin section QUE 93069,37 consists of 67.5 vol% fine-grained (<～130 μm) constituents and 32.5 vol% mineral and lithic clasts and an impact melt vein. The most abundant types of these clasts are intragranularly recrystallized anorthosites and plagioclases (together 26.3 vol%) and feldspathic fine-grained to microporphyritic crystalline melt breccias (21.9 vol%). Mafic crystalline melt breccias are extremely rare (1.3 vol%). Granulitic lithologies are 10.4 vol%, recrystallized feldspathic melt breccias are 15.0 vol%, and glasses are 3.5 vol%. The impact melt vein cutting across the entire thin section was probably formed subsequent to the lithification process of the bulk rock at pressures below 20 GPa, because the bulk rock never experienced a higher peak shock pressure. Lunar meteorite QUE 93069 has a higher abundance of clear glass, occurring within melt spherules, glassy fragments, and an impact melt vein than lunar meteorites ALHA81005, Y-791197, Y-82192/3, Y-86032, or MAC 88104/5. The high abundance of melt spherules indicates that this lunar meteorite contains the highest content of typical regolith components. Mafic crystalline melt breccias are much rarer in QUE 93069 than in all other lunar highland regolith breccias. The extremely low abundance of mafic components may constrain possible areas of the Moon, from which the breccia was derived. The source area of QUE 93069 must be a highland terrain lacking significant mafic impact melts or mare components.  相似文献   

2.
Northwest Africa (NWA) 10986 is a new mingled lunar meteorite found in 2015 in Western Sahara. This impact melt breccia contains abundant impact melt glass and clasts as large as 0.75 mm. Clasts are predominantly plagioclase and pyroxene‐rich and represent both highland and basalt lithologies. Highland lithologies include troctolites, gabbronorites, anorthositic norites, and troctolitic anorthosites. Basalt lithologies include crystalline clasts with large zoned pyroxenes representing very low titanium to low titanium basalts. In situ geochemical analysis of minerals within clasts indicates that they represent ferroan anorthosite, Mg‐suite, and gabbronorite lithologies as defined by the Apollo sample collection. Clasts representing magnesian anorthosite, or “gap” lithologies, are prevalent in this meteorite. Whole rock and in situ impact glass measurements indicate low incompatible trace element concentrations. Basalt clasts also have low incompatible trace element concentrations and lack evolved KREEP mineralogy although pyroxferroite grains are present. The juxtaposition of evolved, basaltic clasts without KREEP signatures and highland lithologies suggests that these basaltic clasts may represent cryptomare. The lithologies found in NWA 10986 offer a unique and possibly a complete cross section view of the Moon sourced outside of the Procellarum KREEP Terrane.  相似文献   

3.
Northwest Africa (NWA) 7611/10480 are lunar regolith breccia meteorites, composed of mineral fragments and various clasts including mare basalts, volcanic glasses, gabbroic lithologies, and a diverse variety of highland materials (ferroan anorthosite, Mg-suite, magnesian anorthosite, and alkali suite rocks) as well as different subvarieties of impact melt breccia. The Apollo two-component mixing model calculation reveals that the NWA 7611 source region contains 58 wt% mare materials and 42 wt% highland components, but the estimated mare components in NWA 10480 have a higher abundance (66 wt%). The predominantly very low-Ti (VLT) composition in both fine-grained basaltic and coarse-grained gabbroic lithologies indicates a provenance associated with a thick lava flow or a single magmatic system. The co-occurrence of zoning patterns and fine-scale exsolution lamellae in pyroxene debris supports a cryptomare deposit as the best candidate source. Phosphate Pb–Pb ages in matrix fragments, impact melt breccia, and basaltic clast indicate that the breccia NWA 7611 records geological events spanning approximately 4305–3769 Ma, which is consistent with the ages of ancient lunar VLT volcanism and the products of basin-forming impacts on the lunar nearside. The youngest reset age at ~3.2 Ga is potentially related to the strong shock lithification process of breccia NWA 7611. Moreover, the similar petrology, texture, geochemistry, cosmic-ray exposure data, and crystallization ages support that basaltic component in Yamato (Y)-793274, and Queen Alexandra Range (QUE) 94281, NWA 4884, and NWA 7611 clan came from the same basalt flow.  相似文献   

4.
Abstract— 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 1s? older than 4.0 Ga. This observation is consistent with, but does not require, a lunar cataclysm.  相似文献   

5.
Lunar meteorite Northwest Africa (NWA) 5744 is a granulitic breccia with an anorthositic troctolite composition that may represent a distinct crustal lithology not previously described. This meteorite is the namesake and first‐discovered stone of its pairing group. Bulk rock major element abundances show the greatest affinity to Mg‐suite rocks, yet trace element abundances are more consistent with those of ferroan anorthosites. The relatively low abundances of incompatible trace elements (including K, P, Th, U, and rare earth elements) in NWA 5744 could indicate derivation from a highlands crustal lithology or mixture of lithologies that are distinct from the Procellarum KREEP terrane on the lunar nearside. Impact‐related thermal and shock metamorphism of NWA 5744 was intense enough to recrystallize mafic minerals in the matrix, but not intense enough to chemically equilibrate the constituent minerals. Thus, we infer that NWA 5744 was likely metamorphosed near the lunar surface, either as a lithic component within an impact melt sheet or from impact‐induced shock.  相似文献   

6.
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).  相似文献   

7.
Meteorites ejected from the surface of the Moon as a result of impact events are an important source of lunar material in addition to Apollo and Luna samples. Here, we report bulk element composition, mineral chemistry, age, and petrography of Miller Range (MIL) 090036 and 090070 lunar meteorites. MIL 090036 and 090070 are both anorthositic regolith breccias consisting of mineral fragments and lithic clasts in a glassy matrix. They are not paired and represent sampling of two distinct regions of the lunar crust that have protoliths similar to ferroan anorthosites. 40Ar‐39Ar chronology performed on two subsplits of MIL 090070,33 (a pale clast impact melt and a dark glassy melt component) shows that the sample underwent two main degassing events, one at ~3.88 Ga and another at ~3.65 Ga. The cosmic ray exposure data obtained from MIL 090070 are consistent with a short (~8–9 Ma) exposure close to the lunar surface. Bulk‐rock FeO, TiO2, and Th concentrations in both samples were compared with 2‐degree Lunar Prospector Gamma Ray Spectrometer (LP‐GRS) data sets to determine areas of the lunar surface where the regolith matches the abundances observed on the sample. We find that MIL 090036 bulk rock is compositionally most similar to regolith surrounding the Procellarum KREEP Terrane, whereas MIL 090070 best matches regolith in the feldspathic highlands terrane on the lunar farside. Our results suggest that some areas of the lunar farside crust are composed of ferroan anorthosite, and that the samples shed light on the evolution and impact bombardment history of the ancient lunar highlands.  相似文献   

8.
Abstract— We report here the petrography, mineralogy, and geochemistry of lunar meteorite Sayh al Uhaymir 300 (SaU 300). SaU 300 is dominated by a fine‐grained crystalline matrix surrounding mineral fragments (plagioclase, pyroxene, olivine, and ilmenite) and lithic clasts (mainly feldspathic to noritic). Mare basalt and KREEPy rocks are absent. Glass melt veins and impact melts are present, indicating that the rock has been subjected to a second impact event. FeNi metal and troilite grains were observed in the matrix. Major element concentrations of SaU 300 (Al2O3 21.6 wt% and FeO 8.16 wt%) are very similar to those of two basalt‐bearing feldspathic regolith breccias: Calcalong Creek and Yamato (Y‐) 983885. However, the rare earth element (REE) abundances and pattern of SaU 300 resemble the patterns of feldspathic highlands meteorites (e.g., Queen Alexandra Range (QUE) 93069 and Dar al Gani (DaG) 400), and the average lunar highlands crust. It has a relatively LREE‐enriched (7 to 10 x CI) pattern with a positive Eu anomaly (?11 x CI). Values of Fe/Mn ratios of olivine, pyroxene, and the bulk sample are essentially consistent with a lunar origin. SaU 300 also contains high siderophile abundances with a chondritic Ni/Ir ratio. SaU 300 has experienced moderate terrestrial weathering as its bulk Sr concentration is elevated compared to other lunar meteorites and Apollo and Luna samples. Mineral chemistry and trace element abundances of SaU 300 fall within the ranges of lunar feldspathic meteorites and FAN rocks. SaU 300 is a feldspathic impact‐melt breccia predominantly composed of feldspathic highlands rocks with a small amount of mafic component. With a bulk Mg# of 0.67, it is the most mafic of the feldspathic meteorites and represents a lunar surface composition distinct from any other known lunar meteorites. On the basis of its low Th concentration (0.46 ppm) and its lack of KREEPy and mare basaltic components, the source region of SaU 300 could have been within a highland terrain, a great distance from the Imbrium impact basin, probably on the far side of the Moon.  相似文献   

9.
Abstract— –Sayh al Uhaymir (SaU) 169 is a composite lunar meteorite from Oman that consists of polymict regolith breccia (8.44 ppm Th), adhering to impact‐melt breccia (IMB; 32.7 ppm Th). In this contribution we consider the regolith breccia portion of SaU 169, and demonstrate that it is composed of two generations representing two formation stages, labeled II and III. The regolith breccia also contains the following clasts: Ti‐poor to Ti‐rich basalts, gabbros to granulites, and incorporated regolith breccias. The average SaU 169 regolith breccia bulk composition lies within the range of Apollo 12 and 14 soil and regolith breccias, with the closest correspondence being with that of Apollo 14, but Sc contents indicate a higher portion of mare basalts. This is supported by relations between Sm‐Al2O3, FeO‐Cr2O3‐TiO2, Sm/Eu and Th‐K2O. The composition can best be modeled as a mixture of high‐K KREEP, mare basalt and norite/troctolite, consistent with the rareness of anorthositic rocks. The largest KREEP breccia clast in the regolith is identical in its chemical composition and total REE content to the incompatible trace‐element (ITE)‐ rich high‐K KREEP rocks of the Apollo 14 landing site, pointing to a similar source. In contrast to Apollo 14 soil, SaU 169 IMB and SaU 169 KREEP breccia clast, the SaU 169 regolith is not depleted in K/Th, indicating a low contribution of high‐Th IMB such as the SaU 169 main lithology in the regolith. The data presented here indicate the SaU 169 regolith breccia is from the lunar front side, and has a strong Procellarum KREEP Terrane signature.  相似文献   

10.
Dar al Gani (DaG) 400, Meteorite Hills (MET) 01210, Pecora Escarpment (PCA) 02007, and MacAlpine Hills (MAC) 88104/88105 are lunar regolith breccia meteorites that provide sampling of the lunar surface from regions of the Moon that were not visited by the US Apollo or Soviet Luna sample return missions. They contain a heterogeneous clast population from a range of typical lunar lithologies. DaG 400, PCA 02007, and MAC 88104/88105 are primarily feldspathic in nature, and MET 01210 is composed of mare basalt material mixed with a lesser amount of feldspathic material. Here we present a compositional study of the impact melt and impact melt breccia clast population (i.e., clasts that were generated in impact cratering melting processes) within these meteorites using in situ electron microprobe and LA‐ICP‐MS techniques. Results show that all of the meteorites are dominated by impact lithologies that are relatively ferroan (Mg#<70), have high Sc/Sm ratios (typically >10), and have low incompatible trace element (ITE) concentrations (i.e., typically <3.2 ppm Sm, <1.5 ppm Th). Feldspathic impact melt in DaG 400, PCA 02007, and MAC 88104/05 are similar in composition to that estimated composition for upper feldspathic lunar crust ( Korotev et al. 2003 ). However, these melt types are more mafic (i.e., less Eu, less Sr, more Sc) than feldspathic impact melts returned by the Apollo 16 mission (e.g., the group 3 and 4 varieties). Mafic impact melt clasts are common in MET 01210 and less common in PCA 02007 and MAC 88104/05. We show that unlike the Apollo mafic impact melt groups ( Jolliff 1998 ), these meteorite impact melts were not formed from melting large amounts of KREEP‐rich (typically >10 ppm Sm), High Magnesium Suite (typically >70 Mg#) or High Alkali Suite (high ITEs, Sc/Sm ratios <2) target rocks. Instead the meteorite mafic melts are more ferroan, KREEP‐poor and Sc‐rich, and represent mixing between feldspathic lithologies and low‐Ti or very low‐Ti (VLT) basalts. As PCA 02007 and MAC 88104/05 were likely sourced from the Outer‐Feldspathic Highlands Terrane our findings suggest that these predominantly feldspathic regions commonly contain a VLT to low‐Ti basalt contribution.  相似文献   

11.
The meteorite Mount DeWitt (DEW) 12007 is a polymict regolith breccia mainly consisting of glassy impact‐melt breccia particles, gabbroic clasts, feldspathic clasts, impact and volcanic glass beads, basaltic clasts, and mingled breccia clasts embedded in a matrix dominated by fine‐grained crystals; vesicular glassy veins and rare agglutinates are also present. Main minerals are plagioclase (typically An>85) and clinopyroxene (pigeonites and augites, sometimes interspersed). The presence of tranquillityite, coupled with the petrophysical data, the O‐isotope data (Δ17O = ?0.075), and the FeOtot/MnO ratios in olivine (91), pyroxene (65), and bulk rock (77) indicate a lunar origin for DEW 12007. Impactites consist of Al‐rich impact‐melt splashes and plagioclase‐rich meta‐melt clasts. The volcanic products belong to the very low titanium (VLT) or low titanium (LT) suites; an unusual subophitic fragment could be cryptomare‐related. Gabbroic clasts could represent part of a shallow intrusion within a volcanic complex with prevailing VLT affinity. DEW 12007 has a mingled bulk composition with relatively high incompatible element abundances and shows a high crustal diversity comprising clasts from the Moon's major terranes and rare lithologies. First‐order petrographic and chemical features suggest that DEW 12007 could be launch‐paired with other meteorites including Y 793274/981031, QUE 94281, EET 87521/96008, and NWA 4884.  相似文献   

12.
Abstract— The lunar meteorite Dhofar 081, found as a single fragment of 174 g in the Dhofar region of Oman, is a shocked feldspathic fragmental highland breccia dominated by anorthosite‐rich lithic and mineral clasts embedded into a fine‐grained mostly shock melted clastic matrix. Major mineral phases in the bulk rock are Ca‐rich plagioclase (An96.5–99.5), pyroxene (FS21.9–46.2Wo3.0–41.4), and olivine (Fa29.3–47.8); accessory phases include Fe‐Ni metal, ilmenite, and Ti‐Cr‐rich spinel. Dhofar 081 contains subordinate crystalline fragments of large anorthosites, intersertal impact‐melt rocks, microporphyritic impact‐melt breccias, dark fine‐grained impact‐melt breccias, large cataclastic feldspars, and irregularly shaped brown glass clasts. Mafic components are rare and no genuine regolith components were found in the sections studied. Minerals in Dhofar 081 show homogeneously distributed shock features: intergranular recrystallization, strong fracturing and mosaicism in feldspar as well as a high density of mostly irregular fractures in pyroxene and olivine. Localized impact melting caused by one or several impacts led to a strong lithification. Based on these effects an equilibration shock pressure of about 15–20 GPa is estimated for the strongest shock event in Dhofar 081. Devitrification of the “glassy” material in the rock indicates thermal annealing after shock melting suggesting that the 15–20 GPa shock event predated the ejection event. According to the concentrations of implanted solar noble gases Dhofar 081 represents a polymict clastic breccia deposit with possibly a minor regolith component. A similar noble gas record of Dhofar 081 and MacAlpine Hills 88104/05 suggests the possibility of a source crater pairing of both meteorites. As indicated by noble gas measurements pairing of Dhofar 081 with the other lunar meteorites found in Oman, Dhofar 025 and Dhofar 026, is unlikely.  相似文献   

13.
The Northwest Africa (NWA) 773 clan of lunar meteorite stones are coarse‐grained breccias that provide an opportunity to examine a lunar igneous system that includes inferred intrusive and extrusive lithologies, possibly related through a common liquid line of descent from a single source region. Such extensive sampling of a single very low‐Ti (VLT) magmatic system on the Moon is unprecedented among the lunar samples. This study focuses on the olivine gabbro (OG), anorthositic gabbro (AG), and ferroan gabbro (FG) lithologies variably contained in NWA 773, NWA 2727, NWA 3160, NWA 3170, NWA 7007, and NWA 10656. Mineral compositions in the three gabbros indicate the crystallization sequence OG → AG → FG. Petrologic modeling of these three lithologies, and an olivine phyric basalt that also occurs in the NWA 773 clan, however, suggests that the relationship among the lithologies is more complex. The OG and basalt can be modeled as originating from a VLT KREEP‐bearing parental melt similar to the Apollo 14 Green Glass b1 composition through mainly equilibrium crystallization. The AG and FG, however, do not fit this simple model and require either a more complex crystallization sequence involving fractional crystallization, magma chamber recharge, or perhaps heterogeneity in the source region.  相似文献   

14.
Abstract– Lunar meteorite Northeast Africa (NEA) 001 is a feldspathic regolith breccia. This study presents the results of electron microprobe and LA‐ICP‐MS analyses of a section of NEA 001. We identify a range of lunar lithologies including feldspathic impact melt, ferroan noritic anorthosite and magnesian feldspathic clasts, and several very‐low titanium (VLT) basalt clasts. The largest of these basalt clasts has a rare earth element (REE) pattern with light‐REE (LREE) depletion and a positive Euanomaly. This clast also exhibits low incompatible trace element (ITE) concentrations (e.g., <0.1 ppm Th, <0.5 ppm Sm), indicating that it has originated from a parent melt that did not assimilate KREEP material. Positive Eu‐anomalies and such low‐ITE concentrations are uncharacteristic of most basalts returned by the Apollo and Luna missions, and basaltic lunar meteorite samples. We suggest that these features are consistent with the VLT clasts crystallizing from a parent melt which was derived from early mantle cumulates that formed prior to the separation of plagioclase in the lunar magma ocean, as has previously been proposed for some other lunar VLT basalts. Feldspathic impact melts within the sample are found to be more mafic than estimations for the composition of the upper feldspathic lunar crust, suggesting that they may have melted and incorporated material from the lower lunar crust (possibly in large basin‐forming events). The generally feldspathic nature of the impact melt clasts, lack of a KREEP component, and the compositions of the basaltic clasts, leads us to suggest that the meteorite has been sourced from the Outer‐Feldspathic Highlands Terrane (FHT‐O), probably on the lunar farside and within about 1000 km of sources of both Low‐Ti and VLT basalts, the latter possibly existing as cryptomaria deposits.  相似文献   

15.
Lunar breccias preserve the records of geologic processes on the Moon. In this study, we report the occurrence, petrography, mineralogy, and geologic significance of the observed secondary olivine veinlets in lunar feldspathic breccia meteorite Northwest Africa (NWA) 11273. Bulk‐rock composition measurements show that this meteorite is geochemically similar to other lunar highland meteorites. In NWA 11273, five clasts are observed to host veinlets that are dominated by interconnecting olivine mineral grains. The host clasts are mainly composed of mafic minerals (i.e., pyroxene and olivine) and probably sourced from a basaltic lithology. The studied olivine veinlets (~5 to 30 μm in width) are distributed within the mafic mineral host, but do not extend into the adjacent plagioclase. Chemically, these olivine veinlets are Fe‐richer (Fo41.4–51.9), compared with other olivine grains (Fo54.3–83.1) in lithic clasts and matrix of NWA 11273. By analogy with the secondary olivine veinlets observed in meteorites from asteroid Vesta (howardite–eucrite–diogenite group samples) and lunar mare samples, our study suggests that the newly observed olivine veinlets in NWA 11273 are likely formed by secondary deposition from a lunar fluid, rather than by crystallization from a high‐temperature silicate melt. Such fluid could be sulfur‐ and phosphorous‐poor and likely had an endogenic origin on the Moon. The new occurrence of secondary olivine veinlets in breccia NWA 11273 reveals that the fluid mobility and deposition could be a previously underappreciated geological process on the Moon.  相似文献   

16.
Abstract— Lunar meteorite Dar al Gani 262 (DG 262)—found in the Libyan part of the Sahara—is a mature, anorthositic regolith breccia with highland affinities. The origin from the Moon is undoubtedly indicated by its bulk chemical composition; radionuclide concentrations; noble gas, N, and O isotopic compositions; and petrographic features. Dar al Gani 262 is a typical anorthositic highland breccia similar in mineralogy and chemical composition to Queen Alexandra Range (QUE) 93069. About 52 vol% of the studied thin sections of Dar al Gani 262 consist of fine-grained(100 μm) constituents, and 48 vol% is mineral and lithic clasts and impact-melt veins. The most abundant clast types are feldspathic fine-grained to microporphyritic crystalline melt breccias (50.2 vol%; includes recrystallized melt breccias), whereas mafic crystalline melt breccias are extremely rare (1.4 vol%). Granulitic lithologies are 12.8 vol%, intragranularly recrystallized anorthosites and cataclastic anorthosites are 8.8 and 8.2 vol%, respectively, and (devitrified) glasses are 2.7 vol%. Impact-melt veins (5.5 vol% of the whole thin sections) cutting across the entire thin section were probably formed subsequent to the lithification process of the bulk rock at pressures below 20 GPa, because the bulk rock never experienced a higher peak shock pressure. Mafic crystalline melt breccias are very rare in Dar al Gani 262 and are similar in abundance to those in QUE 93069. The extremely low abundance of mafic components and the bulk composition may constrain possible areas of the Moon from which the breccia was derived. The source area of Dar al Gani 262 must be a highland terrain lacking significant mafic impact melts or mare components. On the basis of radionuclide activities, an irradiation position of DG 262 on the Moon at a depth of 55–85 g/cm3and a maximum transit time to Earth <0.15 Ma is suggested. Dar al Gani 262 contains high concentrations of solar-wind-implanted noble gases. The isotopic abundance ratio 40Ar/36Ar < 3 is characteristic of lunar soils. The terrestrial weathering of DG 262 is reflected by the occurrence of fractures filled with calcite and by high concentrations of Ca, Ba, Cs, Br, and As. There is also a large amount of terrestrial C and some N in the sample, which was released at low temperatures during stepped heating. High concentrations of Ni, Co, and Ir indicate a significant meteoritic component in the lunar surface regolith from which DG 262 was derived.  相似文献   

17.
Miller Range (MIL) 13317 is a heterogeneous basalt‐bearing lunar regolith breccia that provides insights into the early magmatic history of the Moon. MIL 13317 is formed from a mixture of material with clasts having an affinity to Apollo ferroan anorthosites and basaltic volcanic rocks. Noble gas data indicate that MIL 13317 was consolidated into a breccia between 2610 ± 780 Ma and 1570 ± 470 Ma where it experienced a complex near‐surface irradiation history for ~835 ± 84 Myr, at an average depth of ~30 cm. The fusion crust has an intermediate composition (Al2O3 15.9 wt%; FeO 12.3 wt%) with an added incompatible trace element (Th 5.4 ppm) chemical component. Taking the fusion crust to be indicative of the bulk sample composition, this implies that MIL 13317 originated from a regolith that is associated with a mare‐highland boundary that is KREEP‐rich (i.e., K, rare earth elements, and P). A comparison of bulk chemical data from MIL 13317 with remote sensing data from the Lunar Prospector orbiter suggests that MIL 13317 likely originated from the northwest region of Oceanus Procellarum, east of Mare Nubium, or at the eastern edge of Mare Frigoris. All these potential source areas are on the near side of the Moon, indicating a close association with the Procellarum KREEP Terrane. Basalt clasts in MIL 13317 are from a very low‐Ti to low‐Ti (between 0.14 and 0.32 wt%) source region. The similar mineral fractionation trends of the different basalt clasts in the sample suggest they are comagmatic in origin. Zircon‐bearing phases and Ca‐phosphate grains in basalt clasts and matrix grains yield 207Pb/206Pb ages between 4344 ± 4 and 4333 ± 5 Ma. These ancient 207Pb/206Pb ages indicate that the meteorite has sampled a range of Pre‐Nectarian volcanic rocks that are poorly represented in the Apollo, Luna, and lunar meteorite collections. As such, MIL 13317 adds to the growing evidence that basaltic volcanic activity on the Moon started as early as ~4340 Ma, before the main period of lunar mare basalt volcanism at ~3850 Ma.  相似文献   

18.
Abstract— Dhofar 287 (Dho 287), a recently found lunar meteorite, consists in large part (95%) of low‐Ti mare basalt (Dho 287A) and a minor, attached portion (?5%) of regolith breccia (Dho 287B). The present study is directed mainly at the breccia portion of this meteorite. This breccia consists of a variety of lithic clasts and mineral fragments set in a fine‐grained matrix and minor impact melt. The majority of clasts and minerals appear to have been mainly derived from the low‐Ti basalt suite, similar to that of Dho 287A. Very low‐Ti (VLT) basalts are a minor lithology of the breccia. These are significantly lower in Mg# and slightly higher in Ti compared to Luna 24 and Apollo 17 VLT basalts. Picritic glasses constitute another minor component of the breccia and are compositionally similar to Apollo 15 green glasses. Dho 287B also contains abundant fragments of Mg‐rich pyroxene and anorthite‐rich plagioclase grains that are absent in the lithic clasts. Such fragments appear to have been derived from a coarse‐grained, Mg#‐rich, Na‐poor lithology. A KREEP component is apparent in chemistry, but no highlands lithologies were identified. The Dho 287 basaltic lithologies cannot be explained by near‐surface fractionation of a single parental magma. Instead, magma compositions are represented by a picritic glass; a low‐Ti, Na‐poor glass; and a low‐Ti, Na‐enriched source (similar to the Dho 287A parental melt). Compositional differences among parent melts could reflect inhomogeneity of the lunar mantle. Alternatively, the low‐Ti, Na‐poor, and Dho 287A parent melts could be of hybrid compositions, resulting from assimilation of KREEP by picritic magma. Thus, the Dho 287B breccia contains lithologies from multiple magmatic eruptions, which differed in composition, formational conditions, and cooling histories. Based on this study, the Dho 287 is inferred to have been ejected from a region located distal to highlands terrains, possibly from the western limb of the lunar nearside, dominated by mare basalts and KREEP‐rich lithologies.  相似文献   

19.
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.  相似文献   

20.
Lunar meteorites provide important new samples of the Moon remote from regions visited by the Apollo and Luna sample return missions. Petrologic and geochemical analysis of these meteorites, combined with orbital remote sensing measurements, have enabled additional discoveries about the composition and age of the lunar surface on a global scale. However, the interpretation of these samples is limited by the fact that we do not know the source region of any individual lunar meteorite. Here, we investigate the link between meteorite and source region on the Moon using the Lunar Prospector gamma ray spectrometer remote sensing data set for the elements Fe, Ti, and Th. The approach has been validated using Apollo and Luna bulk regolith samples, and we have applied it to 48 meteorites excluding paired stones. Our approach is able broadly to differentiate the best compositional matches as potential regions of origin for the various classes of lunar meteorites. Basaltic and intermediate Fe regolith breccia meteorites are found to have the best constrained potential launch sites, with some impact breccias and pristine mare basalts also having reasonably well‐defined potential source regions. Launch areas for highland feldspathic meteorites are much less well constrained and the addition of another element, such as Mg, will probably be required to identify potential source regions for these.  相似文献   

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