The Meteoritical Bulletin,No. 80, 1996 July

Abstract— The Meteoritical Bulletin No. 80 lists data for 178 meteorites. Noteworthy are 3 HED meteorites (ALH 88102, Hammadah al Hamra (HaH) 059, and Monticello); 3 ureilites (HaH 064, HaH 126, and Dar al Gani (DaG) 084); 4 irons (Baygorria (IAB), Ste. Croix (IIIAB), Sargiin Gobi (IAB), and Tarahumara (IIE)); an unusual metal-rich meteorite (Vermillion); 8 carbonaceous chondrites (HaH 043 (C03), HaH 073 (C4), DaG 055 (C3) and 5 C03 chondrites (probably paired) from DaG); an R chondrite (DaG 013); and 6 unequilibrated ordinary chondrites (ALH 88105 (L3), Camel Donga 016 (L3), HaH 093 (LL3.9), HaH 096 (LL(L)3), Richfield (LL3.7), and Sarir Quattusah (LL(L)3)). Three recent falls of ordinary chondrites (Coleman (LL5), St. Robert (H5), and Tsukuba (H5-6)) are described.     

A comparison of FeO-rich,porphyritic olivine chondrules in unequilibrated chondrites and experimental analogues

Abstract Experimentally produced analogues of porphyritic olivine (PO) chondrules in ordinary chondrites provide an important insight into chondrule formation processes. We have studied experimental samples with PO textures grown at three different cooling rates (2, 5 and 100 *C/h), and samples that have been annealed at high temperatures (1000–1200 °C) subsequent to cooling. These are compared with natural chondrules of similar composition and texture from the ordinary chondrites Semarkona (LL3.0) and ALH 81251 (LL3.3). Zoning properties of olivine grains indicate that the Semarkona chondrules cooled at comparable rates to the experiments. Zoning in olivine from chondrules in ALH 81251 is not consistent with cooling alone but indicates that the chondrules underwent an annealing process. Chromium loss from olivine is very rapid during annealing and calculated diffusion coefficients for Cr in olivine are very similar to those of Fe-Mg interdiffusion coefficients under the same conditions. Annealed experimental samples contain an aluminous, low-Ca pyroxene which forms by reaction of olivine and liquid. No similar reaction texture is observed in ALH 81251 chondrules, and this may be evidence that annealing of the natural samples took place at considerably lower temperatures than the experimental analogues. The study supports the model of chondrule formation in a cool nebula and metamorphism of partly equilibrated chondrites during reheating episodes on the chondrite parent bodies.     

Cosmic‐ray exposure age and heliocentric distance of the parent bodies of enstatite chondrites ALH 85119 and MAC 88136

Abstract— We measured concentrations and isotopic ratios of noble gases in enstatite (E) chondrites Allan Hills (ALH) 85119 and MacAlpine Hills (MAC) 88136. These two meteorites contain solar and cosmogenic noble gases. Based on the solar and cosmogenic noble gas compositions, we calculated heliocentric distances, parent body exposure ages, and space exposure ages of the two meteorites. The parent body exposure ages are longer than 6.7 Ma for ALH 85119 and longer than 8.7 Ma for MAC 88136. The space exposure ages are shorter than 2.2 Ma for ALH 85119 and shorter than 3.9 Ma for MAC 88136. The estimated heliocentric distances are more than 1.1 AU for ALH 85119 and 1.3 AU for MAC 88136. Derived heliocentric distances indicate the locations of parent bodies in the past when constituents of the meteorites were exposed to the Sun. From the mineralogy and chemistry of E chondrites, it is believed that E chondrites formed in regions within 1.4 AU from the Sun. The heliocentric distances of the two E chondrite parent bodies are not different from the formation regions of E chondrites. This may imply that heliocentric distances of E chondrites have been relatively constant from their formation stage to the stage of exposure to the solar wind.     

Amino acid analyses of Antarctic CM2 meteorites using liquid chromatography‐time of flight‐mass spectrometry

Abstract— Amino acid analyses of the Antarctic CM2 chondrites Allan Hills (ALH) 83100 and Lewis Cliff (LEW) 90500 using liquid chromatography‐time of flight‐mass spectrometry (LC‐ToF‐MS) coupled with UV fluorescence detection revealed that these carbonaceous meteorites contain a suite of indigenous amino acids not present in Antarctic ice. Several amino acids were detected in ALH 83100, including glycine, alanine, β‐alanine, γ‐amino‐n‐butyric acid (γ‐ABA), and α‐aminoisobutyric acid (AIB) with concentrations ranging from 250 to 340 parts per billion (ppb). In contrast to ALH 83100, the CM2 meteorites LEW 90500 and Murchison had a much higher total abundance of these amino acids (440–3200 ppb). In addition, ALH 83100 was found to have lower abundances of the α‐dialkyl amino acids AIB and isovaline than LEW 90500 and Murchison. There are three possible explanations for the depleted amino acid content in ALH 83100: 1) amino acid leaching from ALH 83100 during exposure to Antarctic ice meltwater, 2) a higher degree of aqueous alteration on the ALH 83100 parent body, or 3) ALH 83100 originated on a chemically distinct parent body from the other two CM2 meteorites. The high relative abundance of ?‐amino‐n‐caproic acid (EACA) in the ALH 83100 meteorite as well as the Antarctic ice indicates that Nylon‐6 contamination from the Antarctic sample storage bags may have occurred during collection.     

Amino acids in Antarctic CM1 meteorites and their relationship to other carbonaceous chondrites

Abstract— CM2 carbonaceous chondrites are the most primitive material present in the solar system, and some of their subtypes, the CM and CI chondrites, contain up to 2 wt% of organic carbon. The CM2 carbonaceous chondrites contain a wide variety of complex amino acids, while the CI1 meteorites Orgueil and Ivuna display a much simpler composition, with only glycine and β‐alanine present in significant abundances. CM1 carbonaceous chondrites show a higher degree of aqueous alteration than CM2 types and therefore provide an important link between the CM2 and CI1 carbonaceous chondrites. Relative amino acid concentrations have been shown to be indicative for parent body processes with respect to the formation of this class of compounds. In order to understand the relationship of the amino acid composition between these three types of meteorites, we have analyzed for the first time three Antarctic CM1 chondrites, Meteorite Hills (MET) 01070, Allan Hills (ALH) 88045, and LaPaz Icefield (LAP) 02277, using gas chromatography‐mass spectrometry (GC‐MS) and high performance liquid chromatography‐fluorescence detection (HPLC‐FD). The concentrations of the eight most abundant amino acids in these meteorites were compared to those of the CM2s Murchison, Murray, Mighei, Lewis Cliff (LEW) 90500, ALH 83100, as well as the CI1s Orgueil and Ivuna. The total amino acid concentration in CM1 carbonaceous chondrites was found to be much lower than the average of the CM2s. Relative amino acid abundances were compared in order to identify synthetic relationships between the amino acid compositions in these meteorite classes. Our data support the hypothesis that amino acids in CM‐ and CI‐type meteorites were synthesized under different physical and chemical conditions and may best be explained with differences in the abundances of precursor compounds in the source regions of their parent bodies in combination with the decomposition of amino acids during extended aqueous alteration.     

Extraterrestrial amino acids identified in metal‐rich CH and CB carbonaceous chondrites from Antarctica

Carbonaceous chondrites contain numerous indigenous organic compounds and could have been an important source of prebiotic compounds required for the origin of life on Earth or elsewhere. Extraterrestrial amino acids have been reported in five of the eight groups of carbonaceous chondrites and are most abundant in CI, CM, and CR chondrites but are also present in the more thermally altered CV and CO chondrites. We report the abundance, distribution, and enantiomeric and isotopic compositions of simple primary amino acids in six metal‐rich CH and CB carbonaceous chondrites that have not previously been investigated for amino acids: Allan Hills (ALH) 85085 (CH3), Pecora Escarpment (PCA) 91467 (CH3), Patuxent Range (PAT) 91546 (CH3), MacAlpine Hills (MAC) 02675 (CBb), Miller Range (MIL) 05082 (CB), and Miller Range (MIL) 07411 (CB). Amino acid abundances and carbon isotopic values were obtained by using both liquid chromatography time‐of‐flight mass spectrometry and fluorescence, and gas chromatography isotope ratio mass spectrometry. The δ¹³C/¹²C ratios of multiple amino acids fall outside of the terrestrial range and support their extraterrestrial origin. Extracts of CH chondrites were found to be particularly rich in amino acids (13–16 parts per million, ppm) while CB chondrite extracts had much lower abundances (0.2–2 ppm). The amino acid distributions of the CH and CB chondrites were distinct from the distributions observed in type 2 and 3 CM and CR chondrites and contained elevated levels of β‐, γ‐, and δ‐amino acids compared to the corresponding α‐amino acids, providing evidence that multiple amino acid formation mechanisms were important in CH and CB chondrites.     

Distribution of aliphatic amines in CO,CV, and CK carbonaceous chondrites and relation to mineralogy and processing history

The analysis of water‐soluble organic compounds in meteorites provides valuable insights into the prebiotic synthesis of organic matter and the processes that occurred during the formation of the solar system. We investigated the concentration of aliphatic monoamines present in hot acid water extracts of the unaltered Antarctic carbonaceous chondrites, Dominion Range (DOM) 08006 (CO3) and Miller Range (MIL) 05013 (CO3), and the thermally altered meteorites, Allende (CV3), LAP 02206 (CV3), GRA 06101 (CV3), Allan Hills (ALH) 85002 (CK4), and EET 92002 (CK5). We have also reviewed and assessed the petrologic characteristics of the meteorites studied here to evaluate the effects of asteroidal processing on the abundance and molecular distributions of monoamines. The CO3, CV3, CK4, and CK5 meteorites studied here contain total concentrations of amines ranging from 1.2 to 4.0 nmol g^?1 of meteorite; these amounts are 1–3 orders of magnitude below those observed in carbonaceous chondrites from the CI, CM, and CR groups. The low‐amine abundances for CV and CK chondrites may be related to their extensive degree of thermal metamorphism and/or to their low original amine content. Although the CO3 meteorites, DOM 08006 and MIL 05013, do not show signs of thermal and aqueous alteration, their monoamine contents are comparable to those observed in moderately/extensively thermally altered CV3, CK4, and CK5 carbonaceous chondrites. The low content of monoamines in pristine CO carbonaceous chondrites suggests that the initial amounts, and not asteroidal processes, play a dominant role in the content of monoamines in carbonaceous chondrites. The primary monoamines, methylamine, ethylamine, and n‐propylamine constitute the most abundant amines in the CO3, CV3, CK4, and CK5 meteorites studied here. Contrary to the predominance of n‐ω‐amino acid isomers in CO3 and thermally altered meteorites, there appears to be no preference for the larger n‐amines.     

Nitrogen isotopic composition of CK chondrites

Abstract— Nitrogen abundances and isotopic compositions of four CK chondrites (ALH85002, EET92002, Yamato6903 and Karoonda) were measured by a stepped-combustion method. Neon and Ar were also measured for the same samples. Two types of isotopically light N were observed. One of them is labile N released at low temperatures (～300 °C). This N is observed only in ALH85002. The other N is extracted at high temperatures (900?1200 °C) from all CK chondrites; although, the isotopic compositions are somewhat variable. There is a fair correlation between the excess ¹⁵N values and the abundance of trapped ³⁶Ar for the high-temperature component, suggesting presolar origin of these species. The light N (δ¹⁵N = ?106.8‰) observed in Karoonda is one of the lightest N components ever reported for bulk chondrites.     

Thermally metamorphosed carbonaceous chondrites from data for thermally mobile trace elements

Abstract— We report radiochemical neutron activation analysis (RNAA) data for U, Co, Au, Sb, Ga, Rb, Cs, Se, Ag, Te, Zn, In, Bi, Tl, and Cd (ordered by increasing ease of vaporization and loss from the Murchison CM2 chondrite during open-system heating) in nine Antarctic C2 and C3 chondrites. These meteorites exhibit properties (obtained by reflectance spectroscopy, O isotopic mass spectrometry and/or mineralogy-petrology) suggesting thermal metamorphism in their parent bodies. Five of these meteorites (Asuka (A) 881655, Yamato (Y) 793495, Y-790992, Pecora Escarpment (PCA) 91008, and Y-86789—paired with Y-86720) exhibit significant depletion of the most thermally mobile 1–5 trace elements, which is consistent with open-system loss during extended parent-body heating (under conditions duplicated by week-long heating of the Murchison C2 chondrite, heated at 500–700 °C in a low-pressure (initially 10^?5atm) H₂ atmosphere). From earlier data, three other C3 chondrites—Allan Hills (ALH) 81003, ALH 85003, and Lewis Cliffs (LEW) 85332—show significant Cd depletion. Nine additional C2 and C3 chondrites show no evidence of mobile trace element depletion—including Y-793321, which by all other criteria was mildly metamorphosed thermally. Either metamorphism of these nine meteorites occurred under closed conditions and/or alteration took place under such mild conditions that even Cd could not be lost. The RNAA data suggest that 10 of the 46 Antarctic carbonaceous chondrites (including 4 of 37 from Victoria Land and 6 of 9 from Queen Maud Land) exhibit open-system loss of at least some thermally mobile trace elements by heating in their parent bodies, whereas none of the 25 non-Antarctic falls experienced this. These results are consistent with the idea that the Antarctic sampling of near-Earth material differs from that being sampled today.     

Alteration and metamorphism of CO3 chondrites: Evidence from oxygen and carbon isotopes

Abstract— Carbonaceous chondrites of the Ornans‐type (CO3) form a well‐documented metamorphic series. To investigate the conditions under which metamorphism took place, whole rock oxygen and carbon isotope analysis has been carried out on 10 CO3 chondrites (ALH A77307 [3.0], Colony [3.0], Kainsaz* [3.1], Felix* [3.2], Ornans* [3.3], ALH 82101 [3.3], Lancé* [3.4], ALH A77003 [3.5], Warrenton* [3.6], and Isna [3.7] [*denotes a fall]). Whole rock oxygen isotope analysis was carried out by laser‐assisted fluorination, whole rock carbon isotope analysis by continuous flow mass spectrometry. The results of this study indicate that the oxygen and carbon isotopes in CO3 finds have been significantly disturbed by terrestrial weathering processes. Conclusions based on the isotopic composition of such weathered finds may be significantly flawed. In particular, the Antarctic meteorite ALH A77307 (3.0), suggested as being close in composition to CO‐CM chondrite precursor material, has experienced significant terrestrial contamination. Oxygen isotope data for CO3 falls indicates that there is a subtle increase in Δ¹⁷O values with increasing metamorphic grade for sub‐types 3.1 to 3.4. This increase does not persist to higher sub‐types, i.e., Warrenton (3.6). These relationships are explicable in terms of the progressive formation of phyllosilicates, coupled with loss of primary phases such as melilite, and suggest that an aqueous fluid phase was present during metamorphism. Carbon abundance and δ¹³C values of CO3 falls decrease with increasing metamorphic grade. These trends reflect progressive changes in the nature of the organic macromolecular component during metamorphic heating and lend additional support to the evidence that CO3 chondrites are part of a metamorphic series. The most likely setting for metamorphism was on the CO3 parent body. The “Ornans paradox,” whereby Ornans (3.3) should belong to a higher sub‐type based on chemical compared to petrographic evidence, may result from local‐scale redox differences on the CO3 parent body. A wide variety of classification schemes have been proposed for CO3 chondrites. In view of its simplicity and applicability, the scheme of Scott and Jones (1990) is regarded as the most useful in assigning sub‐types to new CO3 samples.     

Heavily‐hydrated lithic clasts in CH chondrites and the related,metal‐rich chondrites Queen Alexandra Range 94411 and Hammadah al Hamra 237

Abstract— Fine‐grained, heavily‐hydrated lithic clasts in the metal‐rich (CB) chondrites Queen Alexandra Range (QUE) 94411 and Hammadah al Hamra 237 and CH chondrites, such as Patuxent Range (PAT) 91546 and Allan Hills (ALH) 85085, are mineralogically similar suggesting genetic relationship between these meteorites. These clasts contain no anhydrous silicates and consist of framboidal and platelet magnetite, prismatic sulfides (pentlandite and pyrrhotite), and Fe‐Mn‐Mg‐bearing Ca‐carbonates set in a phyllosilicate‐rich matrix. Two types of phyllosilicates were identified: serpentine, with basal spacing of ?0.73 nm, and saponite, with basal spacings of about 1.1–1.2 nm. Chondrules and FeNi‐metal grains in CB and CH chondrites are believed to have formed at high temperature (>1300 K) by condensation in a solar nebula region that experienced complete vaporization. The absence of aqueous alteration of chondrules and metal grains in CB and CH chondrites indicates that the clasts experienced hydration in an asteroidal setting prior to incorporation into the CH and CB parent bodies. The hydrated clasts were either incorporated during regolith gardening or accreted together with chondrules and FeNi‐metal grains after these high‐temperature components had been transported from their hot formation region to a much colder region of the solar nebula.     

The Meteoritical Bulletin,No. 107

Meteoritical Bulletin 107 contains 2714 meteorites including 16 falls (Aba Panu, Ablaketka, Andila, Gueltat Zemmour, Hamburg, Karimati, Mahbas Arraid, Mangui, Mazichuan, Mukundpura, Ozerki, Parauapebas, Renchen, San Pedro de Urabá, Sokoto, Tintigny), with 2226 ordinary chondrites, 168 HED achondrites, 132 carbonaceous chondrites (including 41 CM, 34 CV, 26 CO, 21 CK, 4 CR, 5 ungrouped), 43 ureilites, 30 iron meteorites (including 2 ungrouped), 29 lunar meteorites, 22 Martian meteorites, 16 primitive achondrites (including 3 brachinites), 12 Rumuruti chondrites, 9 enstatite chondrites, 7 ungrouped achondrites, 6 pallasites, 5 mesosiderites, 3 enstatite achondrites, 3 ungrouped chondrites, and 2 angrites. 1569 meteorites are from Antarctica, 835 from Africa, 206 from South America, 62 from Asia, 21 from North America, 11 from unknown locations, 8 from Europe (including one from Russia), and 1 from Oceania.     

Raman spectroscopy of shocked enstatite-rich meteorites

We present Raman patterns of enstatite in different classes of enstatite-rich chondrites and achondrites of various shock levels as previously reported from petrographic observations and X-ray diffraction analyses. Thin sections or mineral separates of four enstatite chondrites (LaPaz Icefield [LAP] 02225, MacAlpine Hills [MAC] 02837, Pecora Escarpment [PCA] 91020, and Itqiy), three aubrites (Larkman Nunatak [LAR] 04316, Khor Temiki, and Allan Hills [ALH] 84008), and a ureilite (Sayh al Uhaymir [SaU] 559) were examined by laser Raman spectroscopy. We find that the frequencies of fundamental Raman peaks of enstatites from the chondrites and aubrites deviate by ≤2 cm⁻¹ from the values for unshocked enstatite. This small difference implies a negligible effect of shock metamorphism on peak positions. Significant differences (<6 cm⁻¹) for peak positions are found for the pyroxenes of SaU 559 and may be attributed to minor substitution of Fe and Ca for Mg. Linear regressions of peak widths of enstatite chondrites against their established shock stages show a strong positive correlation for each mode (r² > 0.94). From this linear relationship, the 343 and 1014 cm⁻¹ peaks of the aubrites coincide with S4 determined from petrography. For Itqiy, we find S4–5, while the shock levels of SaU 559 exceed the petrologic scheme (S1–6), suggesting that the ureilite might have sustained multiple shock events or have been deformed in a high-pressure environment. Alternatively, for Itqiy (peak 343 cm⁻¹) and SaU 559 (all peaks) enstatites, minor substitutions of Fe and Ca for Mg may have further broadened their peak widths.     

Compound‐specific carbon,nitrogen, and hydrogen isotopic ratios for amino acids in CM and CR chondrites and their use in evaluating potential formation pathways

Abstract– Stable hydrogen, carbon, and nitrogen isotopic ratios (δD, δ¹³C, and δ¹⁵N) of organic compounds can reveal information about their origin and formation pathways. Several formation mechanisms and environments have been postulated for the amino acids detected in carbonaceous chondrites. As each proposed mechanism utilizes different precursor molecules, the isotopic signatures of the resulting amino acids may indicate the most likely of these pathways. We have applied gas chromatography with mass spectrometry and combustion isotope ratio mass spectrometry to measure the compound‐specific C, N, and H stable isotopic ratios of amino acids from seven CM and CR carbonaceous chondrites: CM1/2 Allan Hills (ALH) 83100, CM2 Murchison, CM2 Lewis Cliff (LEW) 90500, CM2 Lonewolf Nunataks (LON) 94101, CR2 Graves Nunataks (GRA) 95229, CR2 Elephant Moraine (EET) 92042, and CR3 Queen Alexandra Range (QUE) 99177. We compare the isotopic compositions of amino acids in these meteorites with predictions of expected isotopic enrichments from potential formation pathways. We observe trends of decreasing δ¹³C and increasing δD with increasing carbon number in the α‐H, α‐NH₂ amino acids that correspond to predictions made for formation via Strecker‐cyanohydrin synthesis. We also observe light δ¹³C signatures for β‐alanine, which may indicate either formation via Michael addition or via a pathway that forms primarily small, straight‐chain, amine‐terminal amino acids (n‐ω‐amino acids). Higher deuterium enrichments are observed in α‐methyl amino acids, indicating formation of these amino acids or their precursors in cold interstellar or nebular environments. Finally, individual amino acids are more enriched in deuterium in CR chondrites than in CM chondrites, reflecting different parent‐body chemistry.     

Oxide‐bearing and FeO‐rich clasts in aubrites

Abstract— We report the occurrence of an oxide‐bearing clast and an FeO‐rich clast from aubrites. The FeO‐rich clast in Pesyanoe is dominated by olivine and pyroxene phenocrysts with mineral compositions slightly less FeO‐rich than is typical for H chondrites. In Allan Hills (ALH) 84008, the oxide‐bearing clast consists of a single forsterite grain rimmed by an array of sulfides, oxides, and phosphides. We consider a number of possible origins. We can exclude formation by melting of oxide‐bearing chondrules and CAIs formed in enstatite chondrites. The Pesyanoe clast may have formed in a more oxidized region of the aubrite parent body or, more likely, is a foreign clast from a more oxidized parent body. The ALH 84008 clast likely formed by reaction between sulfides and silicates as a result of cooling, oxidation, or de‐sulfidization. This clast appears to be the first oxide‐bearing clast from an aubritic breccia that formed on the aubrite parent body. Identification of additional oxide‐bearing clasts in aubrites could shed light on whether this was a widespread phenomenon and the origin of these enigmatic objects.     

Iron‐rich aureoles in the CM carbonaceous chondrites Murray,Murchison, and Allan Hills 81002: Evidence for in situ aqueous alteration

Abstract— Iron‐rich aureoles in CM carbonaceous chondrites are previously unidentified domains of aqueously altered matrix material, whose FeO content may exceed that of the surrounding matrix by up to more than 15 wt%. We describe the petrography and mineralogy of these objects in the CM chondrites Murray, Murchison, and Allan Hills (ALH) 81002. The size of Fe‐rich aureoles ranges from a few hundred microns to several millimeters in diameter and appears to be a function of the degree of alteration of the host chondrite. The origin of Fe‐rich aureoles is related to the alteration of large metal grains that has resulted in the formation of characteristic PCP‐rich reaction products that are frequently observed at the centers of the aureoles. This suggests that Fe‐rich aureoles in CM chondrites are the result of the mobilization of Fe from altering metal grains into the matrix. The fact that Fe‐rich aureoles enclose numerous chondritic components such as chondrules, calcium‐aluminum‐rich inclusions (CAIs), and mineral fragments, as well as their radial symmetric appearance, are strong evidence that they formed in situ and that significant directional fluid flow was not involved in the alteration process. This and additional constraints, such as the distribution of S and other elements, as well as the inferred alteration conditions, are consistent with in situ parent‐body alteration. The observations are, however, entirely incompatible with preaccretionary alteration models in which the individual CM chondrite components have experienced diverse alteration histories. The presence of numerous intact aureoles in the brecciated CM chondrites Murray and Murchison further suggests that the alteration occurred largely after brecciation affected these meteorites. Therefore, the progressive aqueous alteration of CM chondrites may not be necessarily coupled to brecciation as has been previously proposed.     

The Meteoritical Bulletin,No. 101

Meteoritical Bulletin 101 contains 2639 meteorites accepted by the Nomenclature Committee in 2012, including 1 fall (Battle Mountain), with 2308 ordinary chondrites, 156 carbonaceous chondrites, 63 HED achondrites, 17 relict meteorites, 16 Rumuruti chondrites, 15 enstatite chondrites, 15 ureilites, 10 iron meteorites, 9 lunar meteorites, 9 primitive achondrites, 8 ungrouped achondrites, 7 mesosiderites, 4 Martian meteorites, and 2 Pallasites, and with 1812 from Antarctica, 437 from Asia, 301 from Africa, 43 from South America, 21 from Europe (including Russia), 21 from North America, 3 from Oceania, and 1 from unknown. Information about approved meteorites can be obtained from the Meteoritical Bulletin Database (MBD) available on line at http://www.lpi.usra.edu/meteor/ .     

Chemical characterization of a unique chondrite: Allan Hills 85085

Abstract— Allan Hills 85085 is a new and very important addition to the growing list of unique carbonaceous chondrites because of its unique chemical and mineralogical properties. Previously published data on ALH85085 have established its bulk composition, gross levels of volatile depletion, siderophile enrichment, and the unique character of this unique meteorite. This chemical study provides more precise data on the major, minor, and trace element characteristics of ALH85085. ALH85085 has compositional, petrological, and isotopic affinities to Al Rais and Renazzo, and to Bencubbin-Weatherford. The similarities to Al Rais and Renazzo, in particular, suggest similar formation locations and thermal processing, possibly in the vicinity of CI chondrites. Petrologic, compositional and isotopic studies indicate that the components that control the abundance of the various refractory and volatile elements were not allowed to equilibrate with the nebula as conditions changed. This lack of equilibration could explain some of the compositional and petrologic variations within and between these meteorites and the inconsistencies in the classification of these meteorites using known taxonomic parameters. It is also apparent that the compositional trends implied by the application of taxonomic parameters probably did not vary simply with heliocentric distance. In addition, variations in the agglomeration of diverse nebular phases along with local and regional temperature events may strongly influence the bulk composition of meteorites.     

Fine-grained chondrule rims in Mighei-like carbonaceous chondrites: Evidence for a nebular origin and modification by impacts and recurrent solar radiation heating

The Mighei-like carbonaceous (CM) chondrites, the most abundant carbonaceous chondrite group by number, further our understanding of processes that occurred in their formation region in the protoplanetary disk and in their parent body/bodies and provide analogs for understanding samples returned from carbonaceous asteroids. Chondrules in the CMs are commonly encircled by fine-grained rims (FGRs) whose origins are debated. We present the abundances, sizes, and petrographic observations of FGRs in six CMs that experienced varying intensities of parent body processing, including aqueous and thermal alteration. The samples studied here, in approximate order of increasing thermal alteration experienced, are Allan Hills 83100, Murchison, Meteorite Hills 01072, Elephant Moraine 96029, Yamato-793321, and Pecora Escarpment 91008. Based on observations of these CM chondrites, we recommend a new average apparent (2-D) chondrule diameter of 170 μm, which is smaller than previous estimates and overlaps with that of the Ornans-like carbonaceous (CO) chondrites. Thus, we suggest that chondrule diameters are not diagnostic for distinguishing between CM and CO chondrites. We also argue that chondrule foliation noted in ALH 83100, MET 01072, and Murchison resulted from multiple low-intensity impacts; that FGRs in CMs formed in the protoplanetary disk and were subsequently altered by both aqueous and thermal secondary alteration processes in their parent asteroid; and that the heat experienced by some CM chondrites may have originated from solar radiation of their source body/bodies during close solar passage as evidenced by the presence of evolved desiccation cracks in FGRs that formed by recurrent wetting and desiccation cycles.     

Noble gases and mineralogy of meteorites from China and the Grove Mountains,Antarctica: A 0.05 Ma cosmic ray exposure age of GRV 98004

Abstract— We determined the mineralogical and chemical characteristics and the He, Ne, and Ar isotopic abundances of 2 meteorites that fell in China and of 2 meteorites that were recovered by the 15th Chinese Antarctic Research Expedition. Guangmingshan (H5), Zhuanghe (H5), and Grove Mountain (GRV) 98002 (L5) yield cosmic ray exposure (CRE) ages of 68.7 ± 10.0 Ma, 3.8 ± 0.6 Ma, and 17.0 ± 2.5 Ma, respectively. These ages are within the range typically observed for the respective meteorite types. GRV 98004 (H5) had an extremely short parent body‐Earth transfer time of 0.052 ± 0.008 Ma. Its petrography and mineral chemistry are indistinguishable from other typical H5 chondrites. Only 3 other meteorites exist with similarly low CRE ages: Farmington (L5), Galim (LL6), and ALH 82100 (CM2). We show that several asteroids in Earth‐crossing orbits, or in the main asteroid belt with orbits close to an ejection resonance, are spectrally matching candidates and may represent immediate precursor bodies of meteorites with CRE ages ≤0.1 Ma.