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

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.     

Petrography and geochemistry of lunar meteorites Dhofar 1673, 1983, and 1984

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.     

Dhofar 081: A new lunar highland meteorite

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 (An_96.5–99.5), pyroxene (FS_21.9–46.2Wo_3.0–41.4), and olivine (Fa_29.3–47.8); 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.     

Thermal and irradiation history of lunar meteorite Dhofar 280

Dhofar 280 recorded a complex history on the Moon revealed by high‐resolution ⁴⁰Ar‐³⁹Ar dating. Thermal resetting occurred less than 1 Ga ago, and the rock was exposed to several impact events before and afterwards. The cosmic ray exposure (CRE) age spectrum indicates a 400 ± 40 Ma CRE on the lunar surface. A unique feature of this lunar sample is a partial loss of cosmogenic ³⁸Ar, resulting in a (low‐temperature) CRE age plateau of about 1 Ma. This was likely caused by the same recent impact event that reset the (low‐temperature) ⁴⁰Ar‐³⁹Ar age spectrum and preceded the short transit phase to Earth of ≤1 Ma. Dhofar 280 may be derived from KREEP‐rich lunar frontside terrains, possibly associated with the Copernicus crater or with a recent impact event on the deposits of the South Pole–Aitken basin. Although Dhofar 280 is paired with Dhofar 081, their irradiation and thermal histories on the Moon were different. An important trapped Ar component in Dhofar 280 is “orphan” Ar with a low ⁴⁰Ar/³⁶Ar ratio. It is apparently a mixture of two components, one endmember with ⁴⁰Ar/³⁶Ar = 17.5 ± 0.2 and a second less well‐constrained endmember with ⁴⁰Ar/³⁶Ar ≤10. The presence of two endmembers of trapped Ar, their compositions, and the breccia ages seem to be incompatible with a previously suggested correlation between age or antiquity and the (⁴⁰Ar/³⁶Ar)_trapped ratio (Eugster et al. 2001; Joy et al. 2011a). Alternatively, “orphan” Ar of this impact melt breccia may have an impact origin.     

KREEPy lunar meteorite Dhofar 287A: A new lunar mare basalt

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.     

Petrography and geochemistry of the LaPaz Icefield basaltic lunar meteorite and source crater pairing with Northwest Africa 032

Abstract— We report on the bulk composition and petrography of four new basaltic meteorites found in Antarctica—LAP (LaPaz Icefield) 02205, LAP 02224, LAP 02226, and LAP 02436—and compare the LAP meteorites to other lunar mare basalts. The LAP meteorites are coarse‐grained (up to 1.5 mm), subophitic low‐Ti basalts composed predominantly of pyroxene and plagioclase, with minor amounts of olivine, ilmenite, and a groundmass dominated by fayalite and cristobalite. All of our observations and results support the hypothesis that the LAP stones are mutually paired with each other. In detail, the geochemistry of LAP is unlike those of any previously studied lunar basalt except lunar meteorite NWA (Northwest Africa) 032. The similarities between LAP and NWA 032 are so strong that the two meteorites are almost certainly source crater paired and could be two different samples of a single basalt flow. Petrogenetic modeling suggests that the parent melt of LAP (and NWA 032) is generally similar to Apollo 15 low‐Ti, yellow picritic glass beads, and that the source region for LAP comes from a similar region of the lunar mantle as previously analyzed lunar basalts.     

Mineralogy and geochemistry of lunar meteorite Queen Alexandra Range 93069

Abstract— Queen Alexandra Range (QUE) 93069 is a glass-rich regolith breccia derived from the lunar highlands. The high abundance of glassy fragments, the presence of agglutinates, the small size of all mineral and glass fragments, the presence of mostly melt rocks, and the low abundance of pristine lunar crustal rocks, all indicate that QUE 93069 is derived from a mature regolith. This conclusion is also supported by its high siderophile element content. The most common mafic mineral is pyroxene, with compositions that indicate derivation from ferroan ANT suite rocks. Rare gabbro differentiation products may be indicated by the presence of silica, fayalitic olivine, and one pyroxferroite grain. Lithic fragments are mostly meta-melt rocks of ANT composition. The glass compositions are dominated by troctolitic anorthosite compositions, followed by gabbroic anorthosite and noritic anorthosite. Most glasses are ol-normative in composition. Some rare basic glasses of noritic composition were observed. Glass fragments and matrix glasses are alkali-poor, except for some rare alkali-rich shards. The bulk chemical composition of QUE 93069, as well as the rare-earth-element (REE) abundance pattern, is very similar to that of other highlands meteorites, such as MAC 88105 and Y-86032 and to average lunar highlands crust. One small porous clast was found to be very rich in volatile elements, as well as in most lithophile and siderophile elements. As this sample also contains abundant sulfides, the enrichments could be related to element mobilization and redistribution by volatile sulfur species.     

Impact melting of lunar meteorite Dhofar 458: Evidence from polycrystalline texture and decomposition of zircon

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.     

Minor element zoning and trace element geochemistry of pallasites

Abstract— I report here on an ion probe study of minor element spatial distributions and trace element concentrations in six pallasites. Pallasite olivines exhibit ubiquitous minor element zoning that is independent of grain size, morphology, and adjacent phases. Ca, Cr, Ti, V, and Ni concentrations decrease from center to rim by factors of up to 10, while Mn is generally unzoned or increases slightly at the very edge of some olivine grains. The maximum concentrations of these elements at the center of olivine vary from grain to grain within the same meteorite and among the pallasites studied. These zoning profiles are consistent with thermal diffusion during rapid cooling. The inferred cooling rates at high temperature regimes are orders of magnitude faster than the low‐temperature metallographic cooling rates (?0.5 to 2°C/Ma). This suggests that pallasites, like mesosiderites, have experienced rather complicated thermal histories, i.e., cooling rapidly at high temperatures and slowly at low temperatures. Pallasite olivines are essentially free of REEs. However, the phosphates display a wide range of REE abundances (0.001 to 100 x CI) with distinct patterns. REEs are generally homogeneous within a given grain but vary significantly from grain to grain by a factor of up to 100. Albin and Imilac whitlockite are highly enriched in HREEs (?50 x CI) but are relatively depleted in LREEs (?0.1 to 1 x CI). Eagle Station whitlockite has a very unusual REE pattern: flat LREEs at a 0.1 x CI level, a large positive Eu anomaly, and a sharp increase from Gd (0.1 x CI) to Lu (70 x CI). Eagle Station stanfieldite has a similar REE pattern to that of whitlockite but with much lower REEs by a factor of 10 to 100. Springwater farringtonite has relatively low REE concentrations (0.001 to 1 x CI) with a highly fractionated HREE‐enriched pattern (CI‐normalized Lu/La ?100). Postulating any igneous processes that could have fractionated REEs in these phosphates is difficult. Possibly, phosphates were incorporated into pallasites during mixing of olivine and IIIAB‐like molten Fe. These phosphates preserve characteristics of a previous history. Pallasites have not necessarily formed at the mantle‐core boundary of their parent bodies. The pallasite thermal histories suggest that pallasites may have formed at a shallow depth and were subsequently buried deep under a regolith blanket.     

Petrography,mineralogy, and geochemistry of deep gravelly sands in the Eyreville B core,Chesapeake Bay impact structure

The ICDP–USGS Eyreville drill cores in the Chesapeake Bay impact structure reached a total depth of 1766 m and comprise (from the bottom upwards) basement‐derived schists and granites/pegmatites, impact breccias, mostly poorly lithified gravelly sand and crystalline blocks, a granitic slab, sedimentary breccias, and postimpact sediments. The gravelly sand and crystalline block section forms an approximately 26 m thick interval that includes an amphibolite block and boulders of cataclastic gneiss and suevite. Three gravelly sands (basal, middle, and upper) are distinguished within this interval. The gravelly sands are poorly sorted, clast supported, and generally massive, but crude size‐sorting and subtle, discontinuous layers occur locally. Quartz and K‐feldspar are the main sand‐size minerals and smectite and kaolinite are the principal clay minerals. Other mineral grains occur only in accessory amounts and lithic clasts are sparse (only a few vol%). The gravelly sands are silica rich (～80 wt% SiO₂). Trends with depth include a slight decrease in SiO₂ and slight increase in Fe₂O₃. The basal gravelly sand (below the cataclasite boulder) has a lower SiO₂ content, less K‐feldspar, and more mica than the higher sands, and it contains more lithic clasts and melt particles that are probably reworked from the underlying suevite. The middle gravelly sand (below the amphibolite block) is finer‐grained, contains more abundant clay minerals, and displays more variable chemical compositions than upper gravelly sand (above the block). Our mineralogical and geochemical results suggest that the gravelly sands are avalanche deposits derived probably from the nonmarine Potomac Formation in the lower part of the target sediment layer, in contrast to polymict diamictons higher in the core that have been interpreted as ocean‐resurge debris flows, which is in agreement with previous interpretations. The mineralogy and geochemistry of the gravelly sands are typical for a passive continental margin source. There is no discernible mixing with marine sediments (no glauconite or Paleogene marine microfossils noted) during the impact remobilization and redeposition. The unshocked amphibolite block and cataclasite boulder might have originated from the outer parts of the transient crater.     

SIMS U-Pb dating of micro-zircons in the lunar meteorites Dhofar 1528 and Dhofar 1627

About half of the lunar meteorites in our collections are feldspathic breccias. Acquiring geochronologic information from these breccias is challenging due to their low radioactive-element contents and their often polymict nature. We used high-spatial-resolution (5 μm) NanoSIMS (nanoscale secondary ion mass spectrometry) U-Pb dating technique to date micro-zircons in the lunar feldspathic meteorites Dhofar 1528 and Dhofar 1627. Three NanoSIMS dating spots of two zircon grains from Dhofar 1528 show a discordia with an upper intercept at 4354 ± 76 Ma and a lower intercept at 332 ± 1407 Ma (2σ, MSWD = 0.01, p = 0.91). Three spots of two zircon grains in Dhofar 1627 define a discordia with an upper intercept at 3948 ± 30 Ma and a lower intercept at 691 ± 831 Ma (2σ, MSWD = 0.40, p = 0.53). Both samples likely experienced shock metamorphism caused by impacts. Based on the clastic nature, lack of recrystallization and the consistent U-Pb and Pb-Pb dates of the zircons in Dhofar 1528, the U-Pb date of 4354 Ma is interpreted as the crystallization age of its Mg-suite igneous precursor. Some of the Dhofar 1627 zircons show poikilitic texture, a crystallization from the matrix impact melt, so the U-Pb date of 3948 Ma corresponds to an impact event, likely the Imbrium basin-forming event. These data are the first radiometric ages for these two meteorites and demonstrate that in situ (high spatial resolution) U-Pb dating has potential for extracting geochronological information about igneous activities and impact events from lunar feldspathic and polymict breccias.     

Petrology and trace element geochemistry of Tissint,the newest shergottite fall

The fall and recovery of the Tissint meteorite in 2011 created a rare opportunity to examine a Martian sample with a known, short residence time on Earth. Tissint is an olivine‐phyric shergottite that accumulated olivine antecrysts within a single magmatic system. Coarse olivine grains with nearly homogeneous cores of Mg# >80 suggest slow re‐equilibration. Many macroscopic features of this sample resemble those of LAR 06319, including the olivine crystal size distribution and the presence of evolved oxide and olivine compositions. Unlike LAR 06319, however, no magmatic hydrous phases were found in the analyzed samples of Tissint. Minor and trace element compositions indicate that the meteorite is the product of closed‐system crystallization from a parent melt derived from a depleted source, with no obvious addition of a LREE‐rich (crustal?) component prior to or during crystallization. The whole‐rock REE pattern is similar to that of intermediate olivine‐phyric shergottite EETA 79001 lithology A, and could also be approximated by a more olivine‐rich version of depleted basaltic shergottite QUE 94201. Magmatic oxygen fugacities are at the low end of the shergottite range, with log fO₂ of QFM‐3.5 to ‐4.0 estimated based on early‐crystallized minerals and QFM‐2.4 estimated based on the Eu in pyroxene oxybarometer. These values are similarly comparable to other depleted shergottites, including SaU 005 and QUE 94201. Tissint occupies a previously unsampled niche in shergottite chemistry: containing olivines with Mg# >80, resembling the enriched olivine‐phyric shergottite LAR 06319 in its crystallization path, and comparable to intermediate olivine‐phyric shergottite EETA 79001A, depleted olivine‐phyric shergottite DaG 476, and depleted basaltic shergottite QUE 94201 in its trace element abundances and oxygen fugacity. The apparent absence of evidence for terrestrial alteration in Tissint (particularly in trace element abundances in the whole‐rock and individual minerals) confirms that exposure to the arid desert environment results in only minimal weathering of samples, provided the exposure times are brief.     

Petrogenesis of lunar highlands meteorites: Dhofar 025, Dhofar 081, Dar al Gani 262, and Dar al Gani 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.     

Lunar meteorite,Dhofar 1428: Feldspathic breccia containing KREEP and meteoritic components

We have studied the feldspathic lunar meteorite Dhofar 1428 chemically and petrologically to better understand the evolution of the lunar surface. Dhofar 1428 is a feldspathic regolith breccia derived from the lunar highland. Bulk chemical and mineral compositions of Dhofar 1428 are similar to those of other feldspathic lunar meteorites. We found a few clasts of evolved lithologies, such as K‐rich plagioclases and quartz monzogabbro. Dhofar 1428 contains approximately 1 wt% of chondritic materials like CM chondrite on the basis of abundances of platinum group elements (Ru, Rh, Pd, Os, Ir, and Pt).     

Chondrule trace element geochemistry at the mineral scale

Abstract– We report trace element analyses from mineral phases in chondrules from carbonaceous chondrites (Vigarano, Renazzo, and Acfer 187), carried out by laser ablation inductively coupled plasma‐mass spectrometry. Results are similar in all three meteorites. Mesostasis has rare earth element (REE) concentrations of 10–20 × CI. Low‐Ca pyroxene has light REE (LREE) concentrations near 0.1 × CI and heavy REE (HREE) near 1 × CI, respectively. Olivine has HREE concentrations at 0.1–1 × CI and LREE around 10^?2 × CI. The coarsest olivine crystals tend to have the most fractionated REE patterns, indicative of equilibrium partitioning. Low‐Ca pyroxene in the most pyroxene‐rich chondrules tends to have the lowest REE concentrations. Type I chondrules seem to have undergone a significant degree of batch crystallization (as opposed to fractional crystallization), which requires cooling rates slower than 1–100 K h^?1. This would fill the gap between igneous calcium‐aluminum‐rich inclusions (CAIs) and type II chondrules. The anticorrelation between REE abundances and pyroxene mode may be understood as due to dilution by addition of silica to the chondrule melt, as in the gas‐melt interaction scenario of Libourel et al. (2006). The rapid cooling rate (of the order of 1000 K h^?1) which seems recorded by low‐Ca pyroxene, contrasted with the more diverse record of olivine, may point to a nonlinear cooling history or suggest that formation of pyroxene‐rich chondrule margins was an event distinct from the crystallization of the interior.     

EH3 matrix mineralogy with major and trace element composition compared to chondrules

We investigated the matrix mineralogy in primitive EH3 chondrites Sahara 97072, ALH 84170, and LAR 06252 with transmission electron microscopy; measured the trace and major element compositions of Sahara 97072 matrix and ferromagnesian chondrules with laser‐ablation, inductively coupled, plasma mass spectrometry (LA‐ICPMS); and analyzed the bulk composition of Sahara 97072 with LA‐ICPMS, solution ICPMS, and inductively coupled plasma atomic emission spectroscopy. The fine‐grained matrix of EH3 chondrites is unlike that in other chondrite groups, consisting primarily of enstatite, cristobalite, troilite, and kamacite with a notable absence of olivine. Matrix and pyroxene‐rich chondrule compositions differ from one another and are distinct from the bulk meteorite. Refractory lithophile elements are enriched by a factor of 1.5–3 in chondrules relative to matrix, whereas the matrix is enriched in moderately volatile elements. The compositional relation between the chondrules and matrix is reminiscent of the difference between EH3 pyroxene‐rich chondrules and EH3 Si‐rich, highly sulfidized chondrules. Similar refractory element ratios between the matrix and the pyroxene‐rich chondrules suggest the fine‐grained material primarily consists of the shattered, sulfidized remains of the formerly pyroxene‐rich chondrules with the minor addition of metal clasts. The matrix, chondrule, and metal‐sulfide nodule compositions are probably complementary, suggesting all the components of the EH3 chondrites came from the same nebular reservoir.     

Chemistry of the Calcalong Creek lunar meteorite and its relationship to lunar terranes

Abstract— The 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.     

Major and trace element geochemistry of S‐type cosmic spherules

Micrometeorites that pass through the Earth's atmosphere undergo changes in their chemical compositions, thereby making it difficult to understand if they are sourced from the matrix, chondrules, or calcium–aluminum‐rich inclusions (CAIs). These components have the potential to provide evidence toward the understanding of the early solar nebular evolution. The variations in the major element and trace element compositions of 155 different type (scoriaceous, relict bearing, porphyritic, barred, cryptocrystalline, and glass) of S‐type cosmic spherules are investigated with the intent to decipher the parent sources using electron microprobe and laser ablation inductively coupled plasma‐mass spectrometry. The S‐type cosmic spherules appear to show a systematic depletion in volatile element contents, but have preserved their refractory trace elements. The trends in their chemical compositions suggest that the S‐type spherules comprise of components from similar parent bodies, that is, carbonaceous chondrites. Large fosteritic relict grains observed in this investigation appear to be related to the fragments of chondrules from carbonaceous chondrites. Furthermore, four spherules (two of these spherules enclose spinels and one comprised entirely of a Ca‐Al‐rich plagioclase) show enhanced trace element enrichment patterns that are drastically different from all the other 151 cosmic spherules. The information on the chemical composition and rare earth elements (REEs) on cosmic spherules suggest that the partially to fully melted ones can preserve evidences related to their parent bodies. The Ce, Eu, and Tm anomalies found in the cosmic spherules have similar behavior as that of chondrites. Distinct correlations observed between different REEs and types of cosmic spherules reflect the inherited properties of the precursors.     

Petrography and composition of Martian regolith breccia meteorite Northwest Africa 7475

The Northwest Africa (NWA) 7475 meteorite is one of the several stones of paired regolith breccias from Mars based on petrography, oxygen isotope, mineral compositions, and bulk rock compositions. Its inventory of lithic clasts is dominated by vitrophyre impact melts that were emplaced while they were still molten. Other clast types include crystallized impact melt rocks, evolved plutonic rocks, possible basalts, contact metamorphosed rocks, and siltstones. Impact spherules and vitrophyre shards record airborne transport, and accreted dust rims were sintered on most clasts, presumably during residence in an ejecta plume. The clast assemblage records at least three impact events, one that formed an impact melt sheet on Mars ≤4.4 Ga ago, a second that assembled NWA 7475 from impactites associated with the impact melt sheet at 1.7–1.4 Ga, and a third that launched NWA 7475 from Mars ~5 Ma ago. Mildly shocked pyroxene and plagioclase constrain shock metamorphic conditions during launch to >5 and <15 GPa. The mild postshock‐heating that resulted from these shock pressures would have been insufficient to sterilize this water‐bearing lithology during launch. Magnetite, maghemite, and pyrite are likely products of secondary alteration on Mars. Textural relationships suggest that calcium‐carbonate and goethite are probably of terrestrial origin, yet trace element chemistry indicates relatively low terrestrial alteration. Comparison of Mars Odyssey gamma‐ray spectrometer data with the Fe and Th abundances of NWA 7475 points to a provenance in the ancient southern highlands of Mars. Gratteri crater, with an age of ~5 Ma and an apparent diameter of 6.9 km, marks one possible launch site of NWA 7475.     

Petrology and geochemistry of feldspathic impact‐melt breccia Abar al' Uj 012, the first lunar meteorite from Saudi Arabia

Abar al' Uj (AaU) 012 is a clast‐rich, vesicular impact‐melt (IM) breccia, composed of lithic and mineral clasts set in a very fine‐grained and well‐crystallized matrix. It is a typical feldspathic lunar meteorite, most likely originating from the lunar farside. Bulk composition (31.0 wt% Al₂O₃, 3.85 wt% FeO) is close to the mean of feldspathic lunar meteorites and Apollo FAN‐suite rocks. The low concentration of incompatible trace elements (0.39 ppm Th, 0.13 ppm U) reflects the absence of a significant KREEP component. Plagioclase is highly anorthitic with a mean of An_96.9Ab_3.0Or_0.1. Bulk rock Mg# is 63 and molar FeO/MnO is 76. The terrestrial age of the meteorite is 33.4 ± 5.2 kyr. AaU 012 contains a ~1.4 × 1.5 mm² exotic clast different from the lithic clast population which is dominated by clasts of anorthosite breccias. Bulk composition and presence of relatively large vesicles indicate that the clast was most probably formed by an impact into a precursor having nonmare igneous origin most likely related to the rare alkali‐suite rocks. The IM clast is mainly composed of clinopyroxenes, contains a significant amount of cristobalite (9.0 vol%), and has a microcrystalline mesostasis. Although the clast shows similarities in texture and modal mineral abundances with some Apollo pigeonite basalts, it has lower FeO and higher SiO₂ than any mare basalt. It also has higher FeO and lower Al₂O₃ than rocks from the FAN‐ or Mg‐suite. Its lower Mg# (59) compared to Mg‐suite rocks also excludes a relationship with these types of lunar material.