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– We used instrumental neutron activation analysis and petrography to determine bulk and phase compositions and textural characteristics of 15 carbonaceous chondrites of uncertain classification: Acfer 094 (type 3.0, ungrouped CM-related); Belgica-7904 (mildly metamorphosed, anomalous, CM-like chondrite, possibly a member of a new grouplet that includes Wisconsin Range (WIS) 91600, Dhofar 225, and Yamato-86720); Dar al Gani (DaG) 055 and its paired specimen DaG 056 (anomalous, reduced CV3-like); DaG 978 (type 3 ungrouped); Dominion Range 03238 (anomalous, magnetite-rich CO3.1); Elephant Moraine 90043 (anomalous, magnetite-bearing CO3); Graves Nunataks 98025 (type 2 or type 3 ungrouped); Grosvenor Mountains (GRO) 95566 (anomalous CM2 with a low degree of aqueous alteration); Hammadah al Hamra (HaH) 073 (type 4 ungrouped, possibly related to the Coolidge-Loongana [C-L] 001 grouplet); Lewis Cliff (LEW) 85311 (anomalous CM2 with a low degree of aqueous alteration); Northwest Africa 1152 (anomalous CV3); Pecora Escarpment (PCA) 91008 (anomalous, metamorphosed CM); Queen Alexandra Range 99038 (type 2 ungrouped); Sahara 00182 (type 3 ungrouped, possibly related to HaH 073 and/or to C-L 001); and WIS 91600 (mildly metamorphosed, anomalous, CM-like chondrite, possibly a member of a new grouplet that includes Belgica-7904, Dhofar 225, and Y-86720). Many of these meteorites show fractionated abundance patterns, especially among the volatile elements. Impact volatilization and dehydration as well as elemental transport caused by terrestrial weathering are probably responsible for most of these compositional anomalies. The metamorphosed CM chondrites comprise two distinct clusters on the basis of their Δ17O values: approximately −4‰ for PCA 91008, GRO 95566, DaG 978, and LEW 85311, and approximately 0‰ for Belgica-7904 and WIS 91600. These six meteorites must have been derived from different asteroidal regions.

We have used neutron activation and electron-probe fused-bead techniques to analyze the bulk major and trace-element compositions of 104 named HED meteorites (about 100–102 distinct meteorites, depending upon pairings), including 32 polymict eucrites, 30 howardites and six diogenites. Most were not previously analyzed for siderophile trace elements; many not even for major elements. Our typical sample was 350 mg, and in some cases two separate chips were analyzed as a test of meteorite heterogeneity. Meteorites with extraordinary compositions include Bluewing 001, an unequilibrated eucrite that is rich in Ti, Sm and other incompatible elements; Y-791192, a cumulate-dominated polymict eucrite; and LEW 87002, an oddly Sm-rich howardite dominated by a ferroan variety of diogenite. The eucrite:diogenite mixing ratio is the single most important factor determining the compositions of polymict HEDs, but wide ranges in eucrite incompatible element contents, in diogenite Cr and V contents, and in Sc contents of both eucrites and diogenites, make for diversity among the polymict HEDs. As our new siderophile data help to show, the common practice of describing the entire class of howardites as regolith breccias is erroneous. Most howardites are fragmental breccias showing no sign of origin from true (in the lunar sense, i.e., soil-like) near-surface regolith. Howardites are highly diverse in Ni content, often remarkably Ni-poor, compared to lunar regolith breccias. However, the few (8) howardites with between 300 and 1200 lg/g Ni consistently show some combination of other traits suggestive of regolith origin. Most importantly, all four cases (or five if we include Malvern, which appears to have been altered by annealing) of howardites known to have enrichments in solar-wind noble gases belong to the >300 lg/g Ni group. In many cases, an abundance of glasses, particularly in spheroidal or turbid-brown form, provides additional evidence for regolith origin. We propose that the important subset of howardites that are regolith breccias be formally distinguished by the designation regolithic howardite. Apart from high siderophile levels, the regolithic howardites are compositionally distinctive in having Al2O3 consistently near 8–9 wt%; corresponding to a eucrite:diogenite mixing ratio of precisely 2:1. Assuming the HEDs are reasonably representative of the ancient (i.e., pre-vestoid-launch) surface of Vesta, this clustering of regolith composition is difficult to explain unless most of the ancient diogenite component was brought to the surface in a single early episode (i.e., probably a single great impact), after which smaller-scale cratering (with no further major excavations of diogenite until the vestoid-forming event), efficiently homogenized the surface. Such a single-excavation model may also help to explain why diogenites, in marked contrast with eucrites, are seldom polymict; and why Al2O3-poor (diogenite-dominated) howardites consistently lack major siderophile enrichments. The low siderophile contents of polymict eucrites are most enigmatic. Possibly in the HEDasteroidal context (low collision velocities, etc.), only materials blended by multiple impacts consistently acquire major enrichments in siderophile elements. 2009 Elsevier Ltd. All rights reserved.

CK chondrites constitute the most oxidized anhydrous carbonaceous chondrite group; most of the Fe occurs in magnetite and in FeO-rich mafic silicates. The two observed CK falls (Karoonda and Kobe), along with thirteen relatively unweathered CK finds, have unfractionated siderophile-element abundance patterns. In contrast, a sizable fraction of CK finds (9 of 24 investigated) shows fractionated siderophile abundance patterns including low abundances of Ni, Co, Se and Au; the most extreme depletions are in Ni (0.24 of normal CK) and Au (0.14 of normal CK). This depletion pattern has not been found in other chondrite groups. Out of the 74 CK chondrites listed in the Meteoritical Bulletin Database (2006; excluded considerably paired specimens; see http://tin.er.usgs.gov/meteor/ metbull.php) we analyzed 24 and subclassified the CK chondrites in terms of their chemical composition and sulfide mineralogy: sL (siderophiles low; six samples) for large depletions in Ni, Co, Se and Au (>50% of sulfides lost); sM (siderophiles medium; two CKs) for moderately low Ni and Co abundances (sulfides are highly altered or partly lost); sH (siderophiles high; one specimen) for enrichments in Ni, Co, Se and Au; 'normal' for unfractionated samples (13 samples). The sole sH sample may have obtained additional sulfide from impact redistribution in the parent asteroid. We infer that these elements became incorporated into sulfides after asteroidal aqueous processes oxidized nebular metal; thermal metamorphism probably also played a role in their mineral siting. The siderophile losses in the SL and sM samples are mainly the result of oxidation of pentlandite, pyrite and violarite by terrestrial alteration followed by leaching of the resulting phases. Some Antarctic CK chondrites have lost most of their sulfides but retained Ni, Co, Se and Au, presumably as insoluble weathering products.

New bulk-compositional data, including trace siderophile elements such as Ir, Os, Au, and Ni, are presented for 25 ureilites. Without exception, ureilites have siderophile abundances too high to plausibly have formed as cumulates. Ureilites undoubtedly underwent a variety of “smelting,” by which C was oxidized to CO gas while olivine FeO was reduced to Fe-metal. However, pressure-buffered equilibrium smelting is not a plausible model for engendering the wide range (75–96 mol%) of mafic-silicate core mg among ureilites. The smelting reaction produces too much CO gas. Even supposing a disequilibrium process with the smelt-gas leaking out of the mantle, none of the ureilites, least of all the ureilite with the most “reduced” (highest) olivine-core mg (ALH84136), has the high Fe-metal abundance predicted by the smelted-cores model. In principle, the Fe-metal generated by smelting could have been subsequently lost, but siderophile data show that ureilites never underwent efficient depletion of Fe-metal. Ureilites display strong correlations among siderophile ratios such as Au/Ir, Ni/Ir, Co/Ir, As/Ir, Se/Ir, and Sb/Ir. Ureilite siderophile depletion patterns loosely resemble siderophile fractionations, presumably nebular in origin, among carbonaceous chondrites. However, Zn, for an element of moderate volatility, is anomalously high in ureilites. A tight correlation between Au and Ni extrapolates to the low-Ni/Au side of the compositional range of carbonaceous chondrites. From this mismatch, mild but nonetheless significant depletions of refractory siderophile elements such as Ir and Os, and moderate depletions of strongly siderophile, weakly chalcophile elements such as Ni and Au, we infer that the ureilite siderophile fractionations are largely the result of a non-nebular process, i.e., removal of S-rich metallic melt, possibly with minor entrainment of Fe-metal. Several lines of trace-element evidence indicate that melt porosity during ureilite anatexis was at least moderate. The ureilite pattern of very mild depletions of extremely siderophile elements, but much deeper depletions of moderately siderophile, chalcophile elements, suggests that asteroidal core formation probably occurs in two discrete stages. In general, separation of a considerable proportion (several wt%) of S-rich metallic melt probably occurs long before, and at a far lower temperature than, separation of the remaining S-poor Fe-metal. Apart from the Fe-metal itself, only extremely siderophile elements wait until the second stage to sequester mainly into the core.

Chondritic clast PV1 from the Plainview H-chondrite regolith breccia is a subrounded, 5-mm- diameter unequilibrated chondritic fragment that contains 13 wt% C occurring mainly within irregularly shaped 30 - 400-m-size opaque patches. The clast formed from H3 chondrite material as indicated by the mean apparent chondrule diameter (310 m vs. 300 m in H3 chondrites), the mean Mg-normalized refractory lithophile abundance ratio (1.00 0.09H), the previously determined O-isotopic composition ( 17 O 0.66‰ vs. 0.68 0.04‰ in H3 chondrites and 0.73 0.09‰ in H4-6 chondrites), the heteroge- neous olivine compositions in grain cores (with a minimum range of Fa1-19), and the presence of glass in some chondrules. Although the clast lacks the fine-grained, ferroan silicate matrix material present in type 3 ordinary chondrites, PV1 contains objects that appear to be recrystallized clumps of matrix material. Similarly, the apparent dearth of radial pyroxene and cryptocrystalline chondrules in PV1 is accounted for by the presence of some recrystallized fragments of these chondrule textural types. All of the chondrules in PV1 are interfused indicating that temperatures must have briefly reached 1100°C (the approximate solidus temper- ature of H-chondrite silicate). The most likely source of this heating was by an impact. Some metal was lost during impact heating as indicated by the moderately low abundance of metallic Fe-Ni in PV1 (14 wt%) compared to that in mean H chondrites (18 wt%). The carbon enrichment of the clast may have resulted from a second impact event, one involving a cometary projectile, possibly a Jupiter-family comet. As the clast cooled, it experienced hydrothermal alteration at low water/rock ratios as evidenced by the thick rims of ferroan olivine around low-FeO olivine cores. The C-rich chondritic clast was later incorporated into the H-chondrite parent-body regolith and extensively fractured and faulted. Copyright © 2005 Elsevier Ltd

Gujba is a coarse-grained meteorite fall composed of 41 vol% large kamacite globules, 20 vol% large light-colored silicate globules with cryptocrystalline, barred pyroxene and barred olivine textures, 39 vol% dark-colored, silicate-rich matrix, and rare refractory inclusions. Gujba resembles Bencubbin and Weatherford in texture, oxygen-isotopic composition and in having high bulk delta N-15 values (approximately +685%0). The He-3 cosmic-ray exposure age of Gujba (26 +/- 7 Ma) is essentially identical to that of Bencubbin, suggesting that they were both reduced to meter-size fragments in the same parent-body collision. The Gujba metal globules exhibit metal-troilite quench textures and vary in their abundances of troilite and volatile siderophile elements. We suggest that the metal globules formed as liquid droplets either via condensation in an impact-generated vapor plume or by evaporation of preexisting metal particles in a plume. The lower the abundance of volatile elements in the metal globules, the higher the globule quench temperature. We infer that the large silicate globules also formed from completely molten droplets; their low volatile-element abundances indicate that they also formed at high temperatures, probably by processes analogous to those that formed the metal globules. The coarse-grained Bencubbin-Weatherford-Gujba meteorites may represent a depositional component from the vapor cloud enriched in coarse and dense particles. A second class of Bencubbin-like meteorites (represented by Hammadah a1 Hamra 237 and QUE 94411) may be a finer fraction derived from the same vapor cloud

Northwest Africa 468 (NWA 468) is a new ungrouped, silicate-rich member of the IAB complex of nonmagmatic iron meteorites. The silicates contain relatively coarse (∼300 μm) grains of low-Ca clinopyroxene with polysynthetic twinning and inclined extinction. Low-Ca clinopyroxene is indicative of quenching from high temperatures (either from protoenstatite in a few seconds or high-temperature clinoenstatite in a few hours). It seems likely that NWA 468 formed by impact melting followed by rapid cooling to ≤660°C. After the loss of a metal-sulfide melt from the silicates, sulfide was reintroduced, either from impact-mobilized FeS or as an S 2 vapor that combined with metallic Fe to produce FeS. The O isotopic composition (Δ 17 O = −1.39‰) indicates that the precursor material of NWA 468 was a metal-rich (e.g., CR) carbonaceous chondrite. Lodranites are similar in bulk chemical and O isotopic composition to the silicates in NWA 468; the MAC 88177 lodranite (which also contains low-Ca clinopyroxene) is close in bulk chemical composition. Both NWA 468 and MAC 88177 have relatively low abundances of rare earth and plagiophile elements. Siderophiles in the metal-rich areas of NWA 468 are similar to those in the MAC 88177 whole rock; both samples contain low Ir and relatively high Fe, Cu, and Se. Most unweathered lodranites contain ∼20 to 38 wt.% metallic Fe-Ni. These rocks may have formed in an analogous manner to NWA 468 (i.e., by impact melting of metal-rich carbonaceous chondrite precursors) but with less separation of metal-rich melts from silicates.

We present new data or iron meteorites that are members of group IAB or are closely related to this large group, and we have also reevaluated some of our earlier data for these irons. In the past it was not possible to distinguish IAB and IIICD irons on the basis of their positions on element-Ni diagrams. We now find that plotting, the new and revised data yields six sets of compact fields on element-Au diagrams, each set corresponding to a compositional group. The largest set includes the majority (approximately equal to 70) of irons previously designated IA: We christened this set the IAB main group. The remaining five sets we designate subgroups within the IAB complex. Three of these subgroups have Au contents similar to the main group, and form parallel trends in most element-Ni diagrams. The groups originally designated IIIC and IIID are two of these subgroups: they are now well resolved from each other and from the main group. The other low-Au subgroup has Ni contents just above the main group. Two other IAB subgroups have appreciably higher Au contents than the main group and show weaker compositional links to it. We have named these five subgroups on the basis of their Au and Ni contents. The three subgroups having Au contents similar to the main group are the low-Au (L) subgroups the two others the high-Au (H) subgroups. The Ni contents are designated high (H), medium (M), or low (L). Thus the old group IIID is now the sLH subgroup. the old group IIIC is the sLM subgroup. In addition, eight irons assigned to two grouplets plot between sLL and sLM on most element-Au diagrams. A large number (27) of related irons plot outside these compact fields but nonetheless appear to be sufficiently related to also be included in the IAB complex.

— The carbonaceous chondrite MacAlpine Hills (MAC) 88107 has bulk composition and mineralogy that are intermediate between those of CO and CM chondrites. This meteorite experienced minor alteration and a low degree of thermal metamorphism (petrologic type 3.1) and escaped post-accretional brecciation. The alteration resulted in the formation of fayalite (Fa90–100). Al-free hedenbergite (∼Fs50Wo50), phyllosilicates (saponite-serpentine intergrowths), magnetite, and Ni-bearing sulfides (pyrrhotite and pentlandite). Fayalite and hedenbergite typically occur as veins, which start at the opaque nodules in the chondrule peripheries, crosscut fine-grained rims and either terminate at the boundaries with the neighboring fine-grained rims or continue as layers between these rims. These observations suggest that fayalite and hedenbergite crystallized after accretion and compaction of the fine-grained rims. Fayalite also overgrows isolated forsteritic (Fa1–5) and fayalitic (Fa20–40) olivine grains without any evidence for Fe-Mg interdiffusion; it also replaces massive magnetite-sulfide grains. The initial 53Mn/55Mn ratio of (1.58 ± 0.26) × 10−6 in the MAC 88107 fayalite corresponds to an age difference between the formation of fayalite and refractory inclusions in Allende of either ∼9 or 18 Ma, depending upon the value of the solar system initial abundance of 53Mn used in age calculations. Formation of secondary fayalite and hedenbergite requires mobilization and transport of Ca, Si, and Fe either through a high-temperature gaseous phase (Hua and Buseck, 1995) or low-temperature aqueous solution (Krot et al., 1998a, b). The high-temperature nebular model for the origin of fayalite (Hua and Buseck, 1995) fails to explain (a) formation of fayalite-hedenbergite assemblages after accretion of fine-grained rims that lack any evidence for high-temperature processing; (b) extreme fractionation of refractory lithophile elements of similar volatility, Ca and Al, in hedenbergite; and (c) absence of Fe-Mg interdiffusion along fayalite-forsterite boundaries. We conclude that fayalite and hedenbergite in MAC 88107 formed during late-stage, low-temperature (approximately 150–200 °C) aqueous alteration. The data for MAC 88107 extend the evidence for an early onset of aqueous activity on chondrite parent bodies and reinforce the conclusion that liquid water played an important role in the chemical and mineralogical evolution of the first chondritic planetesimals.

We studied 14 chondrules separated from LEW85332, an ungrouped type-3 carbonaceous chondrite related to CR chondrites; 23 elements were determined by neutron activation and the chondrules were characterized petrographically. Oxygen isotopic compositions were determined by R. N. Clayton and T. K. Mayeda for seven chondrules. Chondrule abundance ratios tend to form one of two distinct patterns. In low FeO chondrules, refractory lithophile patterns are flat (i.e., unfractionated); siderophile abundances are high and show a small decrease with increasing volatility. Although high FeO chondrules also have flat refractory lithophile abundance patterns, siderophile abundances are highly fractionated; refractory Ir is very low and Fe is very high relative to other siderophiles. We suggest that the low FeO chondrules in LEW85332 formed early in nebular history when metal was intimately mixed with silicates in the chondrule precursors, and that the viscosity of the liquid-solid mix was too high to permit expulsion of the metal by centrifugal action; their porphyritic structures are consistent with incomplete melting, which would result in relatively high viscosities. When the high FeO chondrules formed somewhat later, much of the Fe was oxidized and the melting of precursors was more extensive, FeO and other oxidized siderophiles were retained in the silicate liquid, and metal was lost, possibly expelled from low viscosity chondrule melts. The O isotopic compositions of the chondrules form a linear array of slope 0.93 +/- 0.05 on a three-isotope diagram, parallel to the carbonaceous chondrite anhydrous minerals (CCAM) line and a CR chondrule array, but offset from the latter by -1% in (delta)O-18. Some or all of this offset may reflect incorporation of O from Antarctic water during weathering. Chondrule (Delta)O-17 values correlate positively with FeO, possibly indicating that the (Delta)O-17 of the nebular gas composition increased with time. The chemical and O isotopic data suggest a temporal sequence extending from early, low FeO to late high FeO chondrules.

We present new bulk compositional data for 6 martian meteorites, including highly siderophile elements Ni, Re, Os, Ir and Au. These and literature data are utilized for comparison versus the siderophile systematics of igneous rocks from Earth, the Moon, and the HED asteroid. The siderophile composition of ALH84001 is clearly anomalous. Whether this reflects a more reducing environment on primordial Mars when this ancient rock first crystallized, or secondary alteration, is unclear. QUE94201 shows remarkable similarity with EET79001-B for siderophile as well as lithophile elements; both are extraordinarily depleted in the “noblest” siderophiles (Os and Ir), to roughly 0.00001 × CI chondrites. As in terrestrial igneous rocks, among martian rocks Ni, Os and Ir show strong correlations vs. MgO. In the case of MgO vs. Ni, the martian trend is displaced toward lower Ni by a large factor (5), but the Os and Ir trends are not significantly displaced from their terrestrial counterparts. For Mars, Re shows a rough correlation with MgO, indicating compatible behavior, in contrast to its mildly incompatible behavior on Earth. Among martian MgO-rich rocks, Au shows a weak anticorrelation vs. MgO, resembling the terrestrial distribution except for a displacement toward 2–3 times lower Au. The same elements (Ni, Re, Os, Ir and Au) show similar correlations with Cr substituted for MgO. Data for lunar and HED rocks generally show less clear-cut trends (relatively few MgO-rich samples are available). These trends are exploited to infer the compositions of the primitive Earth, Mars, Moon and HED mantles, by assuming that the trend intercepts the bulk MgO or Cr content of the primitive mantle at the approximate primitive mantle concentration of the siderophile element. Results for Earth show good agreement with earlier estimates. For Mars, the implied primitive mantle composition is remarkably similar to the Earth’s, except for 5 times lower Ni. The best constrained of the extremely siderophile elements, Os and Ir, are present in the martian mantle at 0.005 times CI, in comparison to 0.007 times CI in Earth’s mantle. This similarity constitutes a key constraint on the style of core-mantle differentiation in both Mars and Earth. Successful models should predict similarly high concentrations of noble siderophile elements in both the martian and terrestrial mantles (“high” compared to the lunar and HED mantles, and to models of simple partitioning at typical low-pressure magmatic temperatures), but only predict high Ni for the Earth’s mantle. Models that engender the noble siderophile excess in Earth’s mantle through a uniquely terrestrial process, such as a Moon-forming giant impact, have difficulty explaining the similarity of outcome (except for Ni) on Mars. The high Ni content of the terrestrial mantle is probably an effect traceable to Earth’s size. For the more highly siderophile elements like Os and Ir, the simplest model consistent with available constraints is the veneer hypothesis. Core-mantle differentiation was notably inefficient on the largest terrestrial planets, because during the final ∼ 1% of accretion these bodies acquired sufficient H2O to oxidize most of the later-accreting Fe-metal, thus eliminating the carrier phase for segregation of siderophile elements into the core.

The Kakangari, LEW 87232, and Lea Co. 002 chondrites have a similar set of petrologic and oxygen isotopic characteristics that distinguishes them from other chondrite groups. They are here established to constitute a single chondrite grouplet—the K (after Kakangari) chondrites. The K chondrites have (1) high matrix abundances (33–77 vol%) as do carbonaceous chondrites, (2) metal abundances (6–10 vol%) that are similar to the H group ordinary chondrites, (3) average mafic silicate compositions (average Kakangari olivine = Fa2.2; enstatite Fs4.4) that indicate an oxidation state intermediate between H and E chondrites, (4) matrix that differs from that in other chondrite groups in being enstatite-rich with compositions more Mg-rich (average = Fs3) than those in the chondrules, (5) refractory lithophile element abundances (

Bulk compositional and petrographic data clearly define the new R (Rumuruti) group of chondrites consisting of Rumuruti (the only fall), ALH85151, Acfer 217, Carlisle Lakes, Dar al Gani 013, PCA91002, PCA91241, Y-75302, Y-793575, and Y-82002. Compositional, petrographic, rare-gas, and 0-isotopic data strongly suggest that PCA91002 and PCA91241 are paired. The Yamato specimens are probably not paired. The matrices of the known R chondrites have experienced similar, minor degrees of metamorphism; petrographic types are 3.8-3.9 with the exception of ALH85151, 3.6. All except Carlisle Lakes contain equilibrated (R5-R6) clasts. Petrographically, the R chondrites are characterized by a low chondrule/matrix modal abundance ratio, high states of oxidation (reflected by abundant NiO-bearing olivine with Fa37-40), relatively small chondrules (mean apparent diameters of ∼400 μ) abundant (up to ∼11 wt%) sulfides (mainly pyrrhotite and pentlandite), and negligible amounts of metallic Fe-Ni. Refractory lithophile abundances are ∼0.95 X Cl, intermediate between those in ordinary chondrites (OC) and CI chondrites. Abundances of the volatile elements Se and Zn are greatly enhanced relative to OC. The R chondrites are clearly distinguished from other chondrite groups on the basis of Al/Mn and Zn/Mn abundance ratios. The oxygen isotopic data plot roughly along a slope-12 line, with whole-rock Δ17O values higher than for any other chondrite group. Rumuruti, Acfer 217, ALH85151, PCA91002, and PCA91241 have light/ dark structures and solar-wind-implanted rare gases indicating that they are regolith breccias. The Yamato specimens also have light/dark structures and are inferred to be regolith breccias. Carlisle Lakes lacks solar rare gases and is unbrecciated. Based on similarities in refractory lithophile abundances 00.95 X CI), oxygen isotope compositions (Δ17O ≥ 0), and refractory inclusion abundances (

A 6 mm-diameter dark spherule, 15434,28, from the regolith on the Apennine Front at the Apollo 15 landing site has a homogeneous glass interior with a 200 microns-thick rind of devitrified or crystallized melt. The rind contains abundant small fragments of Apollo 15 olivine-normative mare basalt and rare volcanic Apollo 15 green glass. The glass interior of the spherule has the chemical composition, including a high FeO content and high CaO/Al2O3, of a mare basalt. Whereas the major element and Sc, Ni, and Co abundances are similar to those of low-Ti mare basalts, the incompatible elements and Sr abundances are similar to those of high-Ti mare basaits. The relative abundance patterns of the incompatible trace elements are distinct from any other lunar mare basalts or KREEP; among these distinctions are a much steeper slope of the heavy rare earth elements. The 15434,28 glass has abundances of the volatile element Zn consistent with both impact glasses and crystalline mare basalts, but much lower than in glasses of mare volcanic origin. The glass contains siderophile elements such as Ir in abundances only slightly higher than accepted lunar indigenous levels, and some, such as Au, are just below such upper limits. The age of the glass, determined by the Ar-40/Ar-39 laser incremental heating technique, is 1647 +/- 11 Ma (2 sigma); it is expressed as an age spectrum of seventeen steps over 96% of the Ar-38 released, unusual for an impact glass. Trapped argon is negligible. The undamaged nature of the sphere demonstrates that it must have spent most of its life buried in regolith; Ar-38 cosmic ray exposure data suggest that it was buried at less than 2m but more than a few centimeters if a single depth is appropriate. That the spherule solidified to a glass is surprising; for such a mare composition, cooling at about 50 C/s is required to avoid crystallization, and barely attainable in such a large spherule. The low volatile abundances, slightly high siderophile abundances, and the young age are perhaps all most consistent with an impact origin, but nonetheless not absolutely definitive.

— We report neutron activation analyses, including radiochemical determination of trace siderophile elements (Au, Ge, Ir, Ni, Os and Re), for three SNC/martian meteorites, and Os and Re results for numerous eucrites. Ratios such as Ga/Al in the SNC orthopyroxenite ALH84001 confirm its martian affinity—its many distinctive characteristics, most notably its near-primordial age, notwithstanding. To the list of ALH84001's idiosyncrasies can now be added extraordinarily low concentrations of Au, Ni and, especially, Re (17 pg/g), for a martian meteorite. We consider several possible origins for the anomalously low Re content in ALH84001, including metasomatism or alteration. The pyroxene-cumulate nature of this rock probably does not account for its low Re content. Other SNC meteorites are also cumulates. An examination of Re-Nd variations among terrestrial basalts and komatiites suggests that Re is compatible with mantle minerals in general and only incompatible with olivine (however, olivine dominates the mantle residuum, especially during komatiite genesis). Our preferred model is that the ALH84001 parent melt formed in a mantle source region that was far more Re-depleted, and/or at a substantially lower oxygen fugacity, than the sources of the young SNC meteorites. Such a contrast is consistent with models that replenish siderophile elements in planetary mantles by gradual admixture of late-accreting matter and similarly derive most planetary water (which serves as an oxidant) very late in accretion. According to this model, ALH84001 formed before the siderophile-rich matter and water had been mixed well into the martian interior. Possibly the martian mantle never became generally as Re-rich and/or oxidized as the source region(s) of the younger SNCs.

— We have determined the abundances of Ir and other elements by neutron activation analysis on annual dust samples from an ice core from Site B in the Crete region in central Greenland covering the years 1905–1914. Iridium was detected in all samples, but we found no excess Ir above the background in the years following the Tunguska event. The lack of an Ir anomaly in the years after the Tunguska impact combined with the knowledge of the energy released during the impact and our present knowledge about stratospheric transport implies either a very low Ir content of the impactor or an exceptionally high geocentric velocity for the impactor.

Four of the magmatic IVA iron meteorites contain tridymite or clinobronzite-orthobronzitetridymite which are quite unlike silicate assemblages in other iron meteorites. The textures, the bulk chemistry, and the zoning preserved in the pyroxenes strongly suggest that they are igneous cumulates. The pyroxenes have extremely low Fe/Mn-ratios (less than 20) and low contents of REEs and other incompatible elements. These cumulates crystallized from magmas of unusual composition, with some similarity to terrestrial boninites, at the protobronzite-tfdymite cotectic in the olivine-plagioclase-silica system. A liquidus temperature in the range 1400-1350°C was inferred for the Steinbach meteorite from the estimated distribution coefficient for Cr in pyroxene (DCrsolid/liquid ∼ 0.66). The low levels of incompatible elements show that less than 1% of the residual liquid was trapped in the cumulates. During cooling at subsolidus temperatures, most of the protobronzite transformed to orthobronzite and the rest inverted to a fine inter-growth of clino- and orthobronzite. In addition, the igneous zoning of Ca, Fe, Mg, and Mn was modified by diffusion, whereas Ti, Al, and Cr were not or only slightly affected. The silica-saturated magmas could not have evolved in an olivine-rich mantle. We assume that the magmas became incorporated in the metal core, possibly due to solidification shrinkage of the metal. We propose that the IVA parent magmas were formed by high degrees of partial melting (>40%) of a chondritic precursor along the olivine-pyroxene peritectic reaction curve in the olivine-plagioclase-silica system at low pressures. The precursor may have been depleted in incompatible elements by a preceding melting episode. The partial melts were then separated from the olivine residue and subsequently reduced to account for the low Fe Mn - ratios and the unusually high Si content.

— Petrographic and bulk compositional data suggest the existence of a new grouplet of carbonaceous chondrites consisting of Coolidge and Loongana 001. Coolidge is a carbonaceous chondrite find from Kansas, USA, previously considered a metamorphosed CV chondrite. Loongana 001 is a recent find from Western Australia. It has a high matrix/chondrule modal abundance ratio, 1–2 vol% refractory inclusions and high refractory lithophile abundance ratios (∼1.35x CI), indicating that it is a carbonaceous chondrite. Coolidge and Loongana 001 have many compositional and petrographic similarities. They have refractory element abundances in the range of CV chondrites, significantly higher than those in the CR chondrites. They have similar volatile element abundance patterns showing low volatile element abundances relative to both CR and CV chondrites. Coolidge and Loongana 001 have similar chondrule dimensions and shapes, oxidation states and opaque mineral assemblages. They are also similar in petrologic type (3.8–4) and shock stage (S2). Although both Coolidge and Loongana 001 may be related to the CV clan, they are not CV chondrites, nor are they formed by metamorphism of a CV precursor. They are distinctly different in composition from CV chondrites and their chondrules are smaller and have a much lower abundance of coarse-grained chondrule rims. Coolidge and Loongana 001 constitute a distinct carbonaceous chondrite grouplet.

A study of enstatite grains separated from EL6 chondrites shows ferrosilite contents to be approx. 0.02-0.04 mol%, about an order of magnitude lower than reported in the literature. The higher values reported earlier can probably be attributed to the excitation of Fe atoms in Fe-Ni and FeS, in part from micrometer-sized blebs of FeS and Fe-Ni commonly present in enstatite grains but mainly from large neighboring opaque grains excited by bremsstrahlung or by doubly backscattered electrons. Our EL6 ferrosilite contents are similar to those observed in coarse enstatite grains in some aubrites. The equilibrium between ferrosilite and Si-bearing kamacite is highly temperature dependent. At constant Si concentration in kamacite, the equilibrium ferrosilite mole fraction drops by a factor of roughly 2.5 for each 100 K decrease in the equilibrium temperature. As a result, the compositions of these two most common EL6 phases can be used to estimate metamorphic equilibration temperatures. The inferred temperatures are near 1200 K.

New analytical data combined with recent studies by other researchers allow the definition of a Renazzo (CR) group of carbonaceous chondrites. We analyzed nine CR chondrites (Acfer 187, Acfer 209, El Djouf 001, Elephant Moraine 87747, Elephant Moraine 87770, Elephant Moraine 87847, MacAlpine Hills 87320, PCA91082, and Yamato 793495) constituting at least five independent fall events by instrumental neutron activation analysis for twenty-seven elements. Along with previously analyzed Renazzo, six or more closely related fall events are represented. Key CR properties include refractory lithophile abundances ~1.0 × CI levels, Zn/Mn ratios ~0.3 × CI levels, metal contents of 100–160 mg/g, (unusually high for a carbonaceous chondrite group), relatively large chondrules (mean size ~ 700 μm), and the presence of magnetite framboids. Al Rais is a close relative but too different in chemical and isotopic composition to be considered a normal member of the CR group; we suggest that it be treated as an anomalous member (CR-an), but that its properties not be included in CR ranges and means. MAC87320, PCA91082, EET87770, and Acfer 187 were studied petrographically along with Renazzo and Al Rais. Renazzo has a lineation possibly caused by fluid-lubricated, impact-induced shearing. The CR chondrites experienced some reduction during weak thermal metamorphism; the heating must have taken place prior to hydrothermal alteration. We suggest that formation of magnetite (and framboidal magnetite in particular) in CI and CR chondrites is due to hydrothermal alteration of metal-rich (or opaque-rich) precursors, and that the low abundance of magnetite in CM chondrites relative to CI indicates that the CM precursors were metal poor. Some carbonates in CI and CR chondrites may have formed by H2O reaction with cohenite or poorly crystallized graphite.

— Pecora Escarpment (PCA)91002 is a light/dark-structured chondrite breccia related to Carlisle Lakes and Rumuruti; the meteorite contains ∼10–20 vol% equilibrated (type −5 and −6) clasts within a clastic groundmass, much of which was metamorphosed to type-3.8 levels. The olivine compositional distribution forms a tight cluster that peaks at Fa38–40; by contrast, low-Ca pyroxene compositions are highly variable. Opaque phases identified in PCA91002 and its paired specimen, PCA91241, include pyrrhotite, pentlandite, pyrite, chromite, ilmenite, metallic Cu and magnetite. The majority of the rock is of shock stage S3-S4; there are numerous sulfide-rich shock veins and 50-μm plagioclase melt pockets. Instrumental neutron activation analysis shows that, unlike Carlisle Lakes and ALH85151, PCA91002 exhibits no Ca enrichment or Au depletion; because PCA91002 is relatively unweathered, it seems probable that the Ca and Au fractionations in Carlisle Lakes and ALH85151 were caused by terrestrial alteration. The Rumuruti-like (formerly Carlisle-Lakes-like) chondrites now include eight separate meteorites. Their geochemical and petrographic similarities suggest that they constitute a distinct chondrite group characterized by unfractionated refractory lithophile abundances (0.95 ± 0.05x CI), high bulk Δ17O, a low chondrule/groundmass modal abundance ratio, mean chondrule diameters in the 400 ± 100 μm range, abundant NiO-bearing ferroan olivine, sodic plagioclase, titanian chromite, abundant pyrrhotite and pentlandite and negligible metallic Fe-Ni. We propose that this group be called R chondrites after Rumuruti, the only fall. The abundant NiO-bearing ferroan olivine grains, the occurrence of Cu-bearing sulfide, and the paucity of metallic Fe-Ni indicate that R chondrites are highly oxidized. It is unlikely that appreciable oxidation took place on the parent body because of the essential lack of plausible oxidizing agents (e.g., magnetite or hydrated silicates). Therefore, oxidation of R chondrite material must have occurred in the nebula. A few type-I porphyritic olivine chondrules containing olivine grains with cores of Fa3–4 composition occur in PCA91002; these chondrules probably formed initially as metallic-Fe-Ni-bearing objects at high nebular temperatures. As temperatures decreased and more metallic Fe was oxidized, these chondrules accreted small amounts of oxidized material and were remelted. The ferroan compositions of the >5-μm olivine grains in the R chondrites reflect equilibration with fine-grained FeO-rich matrix material during parent body metatnorphism.

Three type 3 chondrite finds, Willaroy, Suwahib (Buwah) and Moorabie, and one type 4 find, Cerro los Calvos, are ordinary chondrites (OC) in all respects except redox state: (a) they have OC abundances of refractory lithophiles (Cerro los Calvos data are ambiguous), Zn and other taxonomic elements, (b) they have OC matrix/chondrule abundance ratios, and their chondrule sizes are consistent with bulk-siderophile indicators of group membership—H for Willaroy and Cerro los Calvos, L for Suwahib (Buwah) and Moorabie, and (c) their oxygen isotope compositions are far closer to those of OC than to those of any other chondrite group. In each of the four chondrites the range of olivine compositions is relatively narrow; fayalite modes and means are distinctly below those of other members of their respective groups having similar or greater degrees of equilibration. The most plausible explanation of these properties is that these four OC experienced reduction during metamorphism. This is consistent with reverse zoning in olivine from one type II chondrule in Willaroy. The reducing agents may have been foreign clasts incorporated during an earlier accretional history; alternatively, these chondrites could themselves have been foreign materials incorporated into a reduced regolith. Examples of reducing clasts are the C-rich aggregates in Sharps; examples of reducing host regoliths are the host materials in Bencubbin and Cumberland Falls. Confirmation of this interpretation will require identification of the reduced foreign material or their relicts in the four reduced OC; initial searches have been unsuccessful.

A major component of the moon's crust is fundamentally unrelated to the plagioclase flotation crust that is believed to have accumulated over the primordial magma ocean, as evidenced by the geochemical bimodality of pristine lunar rocks. This bimodality and the apparent ratio of ferroan-anorthositic suite rocks to non-ferroan-anorthositic suite rocks in the lunar crust are used to determine the proportion of the moon that was melted during the development of the primordial magma ocean. Models of the origin of the earth-moon system are constrained by this proportion. Another constraint, suggesting that the bulk-moon pyroxene/(pyroxene + olivine) ratio is higher than generally estimated, is also derived.

A new model of the production of the uniformly low plagioclase and Al contents of ureilites is proposed. It is argued that those contents are consequences of widespread explosive volcanism during the evolution of the parent asteroid(s). It is noted that the great abundance of graphite on the ureilite asteroid(s) made them ideal sites for explosive volcanism driven by oxidation of graphite in partial melts ascending within the asteroid(s).

The MAC88104/105 meteorite, a lunar highlands regolith breccia, is described. The rock and a number of its component clasts are characterized. One of the clasts is considered to be a rare pristine nonmare rock containing extraordinarily Fe-rich (Fo40) olivine; the other has silicate compositions that extend the range of the Mg-suite in the direction of the high-mg* end of the ferroan-anorthositic suite. For the major element composition of the crust, the highlands meteorites confirm that the two low-Th central nearside sites, Luna 20 and Apollo 16, are approximately representative. The high Al2O3 composition indicated for the upper crusts supports the magmasphere hypothesis. For the trace-element composition of the crust, the highlands meteorites indicate that the central nearside Apollo and Luna sites are in several respects grossly unrepresentative.

Petrographie and bulk compositional data reveal the existence of a new group of carbonaceous chondrites consisting of the observed fall, Karoonda, one large find from Maralinga, Australia, and 6–11 small finds from five sites in Antarctica. Ningqiang, also a fall, is genetically related to the group. Compositional, textural, and O-isotope data show that the new group is closely related to CV and CO chondrites. In keeping with the practice of naming carbonaceous chondrite groups after a prominent member, we designate it the Karoonda or CK group. All normal CK members are metamorphosed; petrographie grades range from 4 to 6. Some contain shock veins and all exhibit various degrees of blackening due to the dispersion of fine particles of sulfides and magnetite in silicates. Only one other group (EL) has no unequilibrated members. The unequilibrated Ningqiang chondrite is more similar to CK than to CV or CO chondrites, but differs significantly (e.g., low refractory lithophiles, high Mn and Na) in detailed composition. Elemental abundance patterns in CK chondrites are similar to those in CO chondrites, and even more similar to those in CV chondrites. Refractory lithophile abundances are about 1.21× greater than in CI chondrites, a level intermediate between those in CO and CV chondrites; CK refractory siderophile abundances are also intermediate between CV and CO levels. The CK volatile abundance pattern is quite similar to the CV pattern, with CK abundances of most volatiles 10–20% lower than CV values. It appears that nebular conditions and processes were closely similar at the CK and CV formation locations. Although precise probability calculations are difficult because of uncertainties regarding pairing and because so few samples are known, the exceptional abundance of CK chondrites in Antarctica requires an explanation. We suggest that compared to other groups, such as CO or CV, the fragmentation of the CK parent object(s) produced a substantially larger proportion of small meteoroids.

Allan Hills 85085 is a tiny (12-g) meteorite whose closest relatives are the Renazzo and Al Rais chondrites and the subchondritic host material in the Bencubbin meteorite. Its bulk composition is generally chondritic but siderophile abundances are tens of per cent higher and abundances of moderately volatile elements factors of 2–4 × lower than in known authentic chondrites. In addition to this unusual composition ALH85085 has an extremely small particle size, metal that shows no evidence of metamorphic equilibration and a very high abundance of pyroxenitic lithic particles. Chondrules are rare and small; most are pyroxenitic and chemically similar to the lithic particles. Previous workers have inferred that most or all of these strange features of ALH85085 resulted from nebular processes, but we suggest that melting, vaporization, outgassing, condensation and size-sorting in a cloud of impact ejecta offer a more viable alternative. Until additional similar materials have been discovered and characterized, it seems safest to infer nebular properties and processes on the basis of the record in chondrites regarding which there is little doubt that nebular processes were dominant.

— Lewis Cliff 85332 (LEW85332) is a highly unequilibrated (type 3.0–3.1) unique carbonaceous chondrite. It resembles CI and “CR” chondrites in its abundance ratios of refractory lithophiles and refractory siderophiles, but differs significantly from these groups in important ways: relative to CI chondrites, LEW85332 has low abundances of Mn, Se, Zn and most volatile siderophiles; relative to “CR” chondrites, LEW85332 has high abundance ratios of Mn and most volatile siderophiles. Although several petrologic characteristics of LEW85332 resemble those of CO chondrites, LEW85332 differs from this group in having lower abundance ratios of refractory lithophiles and higher abundance ratios of common and volatile siderophiles. Chondrules (mean diameter of 170 μm) are smaller than those in CV and CM chondrites and bigger than those in most CO chondrites. Two melilite-rich (Ak 22) fluffy type-A refractory inclusions were observed. Weathering of LEW85332 has resulted in the formation of 6.2 vol.% limonite; 3.9 vol.% metallic Fe-Ni remains. The inferred original metallic Fe-Ni abundance (13–15 wt.%) is very high for a carbonaceous chondrite and is most similar to those of Kainsaz and Colony (both CO3). LEW85332 is a breccia: the one thin section we examined contains (a) ≥ 10 primitive carbonaceous chondrite clasts (with both C1 and C2 affinities) that contain magnetite framboids and platelets, (b) two clasts containing numerous 10-μm-size clusters of troilite grains, and (c) one clast containing small needles of schreibersite embedded in fine-grained silicate matrix. The unique nature of LEW85332 underscores the wide diversity of materials produced in the solar nebula.

Data for 10 siderophile elements in all of the known lunar meteorites except for Y793274 are reported. Bulk compositional data for Ni, Ge, Cd, Re, Os, Ir, and Au were obtained from radiochemical neutron activation analysis (Warren et al., 1986). Data for Fe, Co, and Zn, and additional data for Ni, Ir, and Au were obtained by instrumental neutron activation analysis (Kallemeyn et al., 1988). Except for the case of Au in Y791197, there was good agreement between the results obtained by the two methods. The differences observed between the lunar-meteoritic regolith samples and central nearside highlands regolith samples are discussed.

Seven carbonaceous chondrites (Allan Hills A77307, Adelaide, Al Rais, Coolidge, Grosnaja, Karoonda and Renazzo) with uncertain classifications were analyzed by instrumental and radiochemical neutron activation analysis for 29 elements: Na, Mg, Al, K, Ca, Sc, V, Cr, Mn, Fe, Co, Ni, Zn, Ga, Ge, As, Se, Br, Ru, Cd, Sb, La, Sm, Eu, Yb, Lu, Os, Ir and Au. Five of these chondrites (A77307, Adelaide, Al Rais, Karoonda and Renazzo) are unique ‘grouplets’, not closely related to other groups or to each other. Only Coolidge (CV4) and Grosnaja (CV3-an) are members of previously established groups. A77307 and Adelaide have refractory lithophile abundances similar to those in the CM-CO clan; A77307 probably is a member of that clan, but Adelaide, which shows CV-like petrographic characteristics, cannot as yet be assigned to a clan. Al Rais and Renazzo have similar refractory lithophile abundances (essentially at CI levels) and probably belong to the same clan, i.e., formed in the same region of the nebula. There are insufficient data to determine whether they formed at the same general region as the CI chondrites, but separates having O-isotope compositions near the terrestrial fractionation line indicate that this is plausible. Karoonda has refractory lithophile abundances ~ 1.21 × CI and appears to belong to a new clan distinct from CM-CO (1.11 × CI) and CV (1.34×).

Carlisle Lakes and Allan Hills 85151 (ALH85151) are members of a new grouplet of chondrites characterized by FeO-rich silicates (olivine Fa = 38–41 mol%), unusual oxygen isotopic composition, and abundant (∼35 vol%) recrystallized matrix material. Yamato 75302 is not as well-characterized, but is probably also a member of this grouplet. Siderophile elements in Carlisle Lakes and ALH85151 are fractionated relative to CI chondrites: refractory and common siderophiles are at ∼ 1 × CI, Ga and As are lower (0.6-0.9 × CI), and Au is very low (0.17 × CI and 0.36 × CI in Carlisle Lakes and ALH85151, respectively). The low Au abundance may indicate that Au resided mainly in fine-grained metal particles that were suspended in the nebular gas during the time these chondrites agglomerated. The oxidation state of chondrites may be controlled by the presence of oxidizing agents (e.g., magnetite) in agglomerated matrix material. The high matrix abundance that characterizes this new grouplet may thus be responsible for the high oxidation state of these meteorites.

Concentrations of 26 elements were determined by replicate neutron-activation analysis in 66 ordinary chondrites (22 H, 20 L, 17 LL, 2 intermediate between H and L and 5 intermediate between L and LL). Olivine and kamacite compositions were determined in adjacent samples; about 20% of the chondrites contain kamacite or olivine grains with aberrant compositions > 3s from the mean. The sample set was biased in favor of the reduced, siderophile-rich and oxidized, siderophile-poor members of the groups and in favor of chondrites reported to have unusual compositional features. Several chondrites were reclassified: e.g., the photographed fall, Innisfree, is L, not LL; Albareto is LL, not L; and Xingyang and Zhovtnevyi are H6, not H5. On a plot of kamacite Co concentration versus Fa content of olivine, there is a hiatus between H and L, but no hiatus between L and LL. Five chondrites (Bjurbole, Cynthiana, Knyahinya, Qidong, Xi Ujimgin) fall between the main L and LL clusters. Cosmic-ray and U, Th-He outgassing age data do not demonstrate relationships to either group. Our siderophile data support the previous group assignments of unequilibrated chondrites in all cases but two: Bremervorde and Tieschitz have siderophile levels intermediate between H and L. Our mean group compositions are in good agreement with those previously reported. We confirm that the Co/Ni ratio decreases about 5% through the H-L-LL sequence and that Na and Mn abundances are about 7% lower in H than in L and LL. Selenium and Zn show similar abundances in the three groups; the very low (~0.1 × CI) Zn abundance is attributed to condensation as fine, ZnS aerosols that inefficiently settled to the midplane. Abundances of V and Cr decrease by only ~2% between H and LL; thus, only a small fraction was in nebular siderophile components. With the exception of highly volatile Br, no significant differences in abundance are observed among the petrographic types of each group. This conflicts with earlier conclusions that intertype differences (including a systematic increase in siderophile abundance with increasing type) are present. The small differences we observed are attributable to anomalously low or high contents of one or two phases (generally metal and/or troilite) in a few replicates. The absence of a relationship between composition and petrographic type is consistent with models calling for the progressive thermal metamorphism of primitive unequilibrated materials to produce the observed spectrum of petrographic grades, and places narrow limits on the relative accretion efficiencies of nebular components in those models calling for the sequential accretion of nebular materials.

Geochemically, ALHA 81005 has all the attributes expected of a regolith sample from the lunar highlands. Most important is its Fe/Mn ratio (77), within an uncertainty the same as the mean lunar ratio. There are significant differences, however, in comparison to previously sampled lunar regoliths. The closest precedents are the Apollo-16 and Luna-20 regoliths, particularly the latter, but ALHA 81005 has lower contents of Na, Ti, and incompatible elements. Feldspathic granulitic breccias such as 72559, which texturally resemble the most abundant type of clast in ALHA 81005, are also similar compositionally. From its low KREEP and Na contents ALHA 81005 is inferred to have originated well away from the K, Th, and U-rich region near the center of the nearside, at least as far away as the eastern limb.

We report concentrations of 30 elements in 34 replicate samples of 17 enstatite chondrites, including 8 EH3 chondrites. Unweathered EH3 and EH4,5 chondrites appear to be compositionally indistinguishable, and, therefore, observed differences in phase compositions reflect metamorphism of EH4,5 chondrites. The system EH3 kamacite and perryite is essentially equivalent to EH4,5 kamacite, suggesting that perryite 1. (1) condensed on metal at high nebular temperatures, 2. (2) dissolved into the kamacite during the metamorphism of the EH4,5 chondrites. Our data revealed some unexpected fractionations between closely related elements in EL chondrites: the La Sm ratio is resolvably lower and the Co Ni ratio resolvably higher than in EH chondrites. The EL chondrites have a fractionated “refractory lithophile” abundance pattern relative to CI, unlike other chondrite groups. Ni-normalized refractory siderophile abundances are higher and volatile siderophile abundances lower in EL relative to EH. The Au Ni ratio is ~1.4× the CI ratio in both EL and EH. Antarctic EH chondrites show similar patterns of element loss during weathering, independent of petrologic type. Factor analysis suggests that appreciable La condensed together with sulfides that nucleated on the metal; Na and Br are also associated with this component. The remaining rare earths are in an oldhamite-rich component. Vanadium and Cr are strongly correlated. The highly reduced state of the enstatite chondrites as well as their unique EL fractionation patterns seem most consistent with formation in the innermost part of the solar nebula.

Six pristine rocks, two mare basalts, and four nonpristine highlands rocks were separated from breccia 14304 for consortium study. The pristine highlands rocks include representatives of the Mg troctolite-anorthosite and alkali suites of the Apollo 14 site. Two troctolite clasts have olivine and plagioclase compositions similar to one group of Apollo 14 troctolites and one also contains spinel. Incompatible element abundances in one are similar to those of 14305 troctolites, although the heavy rare earth elements pattern is distinct among Apollo 14 troctolites. Alkali lithologies include an alkali anorthosite and an alkali norite, the latter having a pristine igneous texture and resembling alkali gabbronites from Apollo 14 and 67975 in mineralogy and mineral compositions. It is suggested that Apollo 14 alkali lithologies and PO4-bearing Mg anorthosites formed from Mg-rich magmas that assimilated various amounts of material rich in P and REE. Another pristine clast from 14304 is an Mg-gabbronorite. The two mare basalt clasts are very high potassium basalts, whose parent magmas could have formed from a typical low-Ti, high-Al basaltic magmas by assimilation of K-rich material. Nonpristine 14304 clasts include melt-textured anorthosites and an augite-rich poikilitic melt rock.

— Ningqiang is an anomalous CV chondrite (oxidized subgroup) containing a high abundance of aggregational inclusions (13.7 vol.%) and low abundances of refractory inclusions (1.0+1.0–0.5 vol.%) and bulk refractory lithophiles (∼0.82 × CV). Ningqiang may have agglomerated after most refractory inclusions at the nebular midplane had already been incorporated into other objects. Coarse-grained rims surround only ∼5% of Ningqiang chondrules, compared to ∼50% in normal CV chondrites. Aggregational inclusions appear to have formed by incipient melting of fine-grained aggregates at relatively low temperatures in the solar nebula, possibly by the mechanism responsible for chondrule formation. Granoblastic porphyritic chondrules, which contain olivines forming 120° triple junctures and no mesostasis, probably formed in the solar nebula by incomplete melting of precursor materials that were olivine normative and had relatively low concentrations of Si, Ca, Al, Fe and Na.

Bulk-compositional data for the EET83309 polymict ureilite were obtained using INAA and radiochemistry procedures and electron probe analysis. It was found that the EET83309 has a bulk composition indistinguishable from ordinary ('monomict') ureilites for all elements except light-middle REEs (which are present in much higher concentrations), suggesting that polymict ureilites are mixtures of ordinary ureilites which were mixed on a very small number of parent bodies. Despite the light-REE enrichments, polymict ureilites are nearly devoid of basaltic (Al-rich) material. It is suggested that the missing basalt may have been blown off the parent body by a partially disruptive collision with a large C-rich projectile. This impact model of ureilite origin reconciles many paradoxical aspects of ureilite composition.

We present new data from a neutron activation analysis of four enstatite chondrites including the taxonomically important St. Sauveur, and discuss the classification of enstatite chondrites. The enstatite chondrites can be divided into two compositionally distinct sets; in one set abundances of nonrefractory siderophiles and moderately volatile chalcophiles and alkalis are 1.5–2.0× higher than in the other. A well-resolved compositional hiatus separates these two sets. The differences in composition are as great as those between the groups of ordinary chondrites, and therefore it appears best to treat these sets as separate groups. By analogy with the symbols used for ordinary chondrites we propose to designate the high-Fe, high siderophile group EH and the low-Fe, low-siderophile group EL. Known members of the EH group belong to petrologic types 4 and 5, whereas all EL members are petrologic type 6. Within the EH group no correlation is observed between petrologic type and abundance of nonrefractory siderophiles or moderately volatiles or alkalis. Two physical properties show only modest overlap between the EH and EL groups. Cosmic-ray ages for EH chondrites are 0.5–7 Ma, while those for EL chondrites are 4–18 Ma. Relative to Bjurbole, I-Xe formation intervals are −1.3 ± 0.6 Ma for EH chondrites and 2.9 ± 0.5 Ma for EL chondrites. The weight of the chemical and physical evidence indicates that the EH and EL groups formed separate bodies at similar distances from the Sun. The available evidence for Shallowater and Happy Canyon, two strongly recrystallized silicate-rich meteorites containing > 40 mg/g Fe-Ni, indicates that the former is an enstatite-clan chondrite altered by loss of sulfide- and plagioclase-rich melts, whereas the latter is intermediate in composition between EL chondrites and the chondritic silicates in the Pine River IAB-anomalous meteorite.

Results of elemental analyses, performed either by instrumental neutron activation analysis (NAA) or radiochemical NAA, of 19 lunar rock samples obtained by the Apollo 15, 17, and 12 missions are presented. Two of the samples are most extraordinary: 'large' (1 g) felsite from Apollo 12 and a pristine ferroan anorthosite from Apollo 15. The felsite is mainly a graphic intergrowth of K-feldspar and a silica phase, with about 6 pct plagioclase and 1 pct each of ferroaugite, ilmenite, and fayalitic olivine. The Fe-metal content of ferroan anorthosite is 1.2 wt pct in the thin section studied (but, based on mass balance for Co and Ni, must have been lower in the chip used for bulk-rock analysis); the measured bulk-rock concentrations of siderophile elements Re, Os, and Ir are far higher than previously observed among pristine lunar anorthosites. These results underscore the uncertainty associated with any attempt to estimate the overall siderophile element contents of the moon's crust.

A compilation of data on 78 elements in the nine groups of chondrites shows each to be isochemical with the exception of a few volatiles. With the exception of the most volatile elements, the groups have solar abundances to within a factor of two. The solar abundances and the chemical and physical properties of phases in the leastaltered chondrites indicate formation by grain agglomeration in the preplanetary nebula. Planets formed by the gradual growth of bodies in the solar nebula. Because there is no evidence for the formation of non-chondritic bodies in the nebula, the simplest model calls for the bulk compositions of the terrestrial planets to be chondritic. Mercury is enriched in metal, perhaps either because of high loss of silicates due to enhanced radial drag in the innermost part of the nebula, or because of enhanced accretion of metallic cores from disrupted asteroids. Chondritic compositions should be considered as boundary conditions for planetary models.

The anorthosite fragment, 76504,18, the first of the Apollo 17's pristine anorthosites, was found to have: (1) a higher ratio of high-Ca pyroxine to low-Ca pyroxene, (2) higher Na in its plagioclase, (3) higher contents of incompatible elements, and (4) a higher Eu/Al ratio in comparison to ferroan anorthosites. With a parent melt having a negative Eu anomaly, 76504,18 closely resembles a typical mare basalt. This anorthosite was among the latest to be formed by plagioclase flotation above a primordial magmasphere; typical mare basalt regions accumulated at about the same time or even earlier. Another fragment 14181c, a very high potassium basalt, was studied and found to be similar to typical Apollo 14 mare basalt though it has a K/La ratio of 1050. It is suggested that this lithology formed after a normal Apollo 14 mare basaltic melt partially assimilated granite. New data for siderphile elements in Apollo 12 mare basalts indicate that only the lowest of earlier data are trustworthy as being free of laboratory contamination.

The concentrations of 25 major, minor and trace elements have been determined in four clasts, a metal-rich inclusion and two dark metal-poor inclusions from the Abee enstatite chondrite. The clasts are heterogeneous, displaying 2-fold enrichments or depletions in some elements. The data suggest that there are two generations of metal, one with low, the other with high concentrations of refractory siderophiles. The other elemental patterns can be understood in terms of variations in the abundance of major minerals. We infer that Sc and Mn are located largely in the niningerite ((Fe,Mg)S), V in the troilite (FeS) and rare earth elements in the oldhamite (CaS). Heterogeneities among the clasts are probably primary, resulting from the accretion-agglomeration process, although shock processes in a regolithic setting remain a possibility provided that they were followed by a period of metamorphism sufficient to erase petrologic evidence. In the dark inclusions the concentrations of the rare earths, Eu excepted, are 4 × higher than mean EH levels; this infers enhanced amounts of CaS. The dark inclusions are low in siderophiles, Sc, Mn, K, Na and Al, implying low amounts of metal, niningerite and feldspar. The origin of the dark inclusions is unclear; they do not appear to be the result of a simple, single-stage process.

Six specimens of unusual chondritic materials were analyzed by neutron activation for 30 elements in order to assess their degree of chondritic compositional pristinity and to search for evidence of genetic links to other chondrites. Five have highly recrystallized textures; the other, the Cumberland Falls chondrite, has suffered minor metamorphic recrystallization. Acapulco and Allan Hills A77081, are closely related and have subpristine compositions; they are more distantly related to Enon which has an altered composition. Udei Station appears to be a IAB meteorite even though its FeO (FeO + MgO) ratio is slightly above the IAB field. The highly weathered meteorite Tierra Bianca is closely related to IAB but has a δ18O value 5 standard deviations higher than the IAB mean and is designated ungrouped. Udei Station and Tierra Bianca have altered compositions; rare earth element patterns indicate loss of a phosphate phase. The elemental composition of the Cumberland Falls chondrite is virtually identical to that of LL chondrites and its O-isotope composition is closely similar to those of some unequilibrated ordinary chondrites including LL Semarkona. The FeO (FeO + MgO) ratios in its olivine are generally much lower than those in pyroxene, a relationship we show to be indicative of in situ reduction resulting from exchange with the aubritic host. The names winonaites and forsterite chondrites have no taxonomic utility.

The Bencubbin meteorite is a polymict breccia consisting of a host fraction of ~60% metal and ~40% ferromagnesian silicates and a selection of carbonaceous, ordinary and ‘enstatite’ chondritic clasts. Concentrations of 27 elements were determined by neutron activation in replicate samples of the host silicates and the ordinary and carbonaceous chondritic clasts; 12 elements were determined in the host metal. Compositional data for the ordinary chondrite clast indicate a classification of LL4 ± 1. Refractory element data for the carbonaceous chondrite clast indicate that it belongs to the CI-CM-CO clan; its volatile element abundances are intermediate between those of CM and CO chondrites. Abundances of nonvolatile elements in the silicate host are similar to those in the carbonaceous chondrite clast and in CM chondrites; the rare earths are unfractionated. We conclude that it is not achondritic as previously designated, but chondritic and that it is probably related to the CI-CM-CO clan; its volatile abundances are lower than those in CO chondrites. Oxygen isotope data are consistent with these classifications. Host metal in Bencubbin and in the closely related Weatherford meteorite has low abundances of moderately volatile siderophiles; among iron meteorite groups its nearest relative is group IIIF. We suggest that Bencubbin and Weatherford formed as a result of an impact event on a carbonaceous chondrite regolith. The impact generated an ‘instant magma’ that trapped and surrounded regolithic clasts to form the polymict breccia. The parent of this ‘magma’ was probably the regolith itself, perhaps mainly consisting of the so-called ‘enstatite’ chondrite materials. Accretion of such a variety of materials to a small parent body was probably only possible in the asteroid belt.

This paper presents the results of trace-element analyses and detailed petrography obtained for the Elephant Moraine 87521 meteorite (EET87521) found recently in Antarctica. Its high values found for the Fe/Mn ratio and the bulk-Co content indicate that the EET87521 is not, as was originally classified, a eucrite. Moreover, its low Ga/Al and Na/Ca ratios exclude the possibility that it is an SNC meteorite. These and other characteristics (e.g., a very low Ti content) of the EET87521 suggest its affinity with very-low-Ti high-alumina varieties of lunar mare basalt.

Chondritic meteorites consist of collections of grains formed in the solar nebula. Chondritic materials can often be resolved into components that formed in differing nebular conditions. Carbonaceous chondrites are often accorded special significance in planetary models, especially because abundances of most elements in the CI group are indistinguishable from those in the Sun. Abundances of refractory lithophiles are among the most useful parameters for the classification of chrondrites, because they systematically decrease through the sequence carbonaceous→ordinary→enstatite1,2. They are also the most general parameter linking groups of very similar chondrites into clans which consist of groups having certain common properties that may indicate formation within a narrow range of distances from the Sun3. We report here newly discovered differences in refractory abundances among the different groups of carbonaceous chondrites.

Seventeen nonmare samples, most of them pristine, are characterized, and implications of the new data are discussed. Five pristine samples are from Apollo 14, near the center of the KREEP-rich zone in the moon's western hemisphere. Three of them are alkali anorthosites rich in Ca-phosphate (whitlockite), which apparently crystallized from magmas with REE contents roughly 6 x those of high-K KREEP. The alkali anorthosites probably formed from Mg-rich magmas that assimilated large amounts of urKREEP, but some might have formed by metasomatism of ferroan anorthosite by urKREEP. The gabbronorite/norite classification scheme is not well suited to western hemisphere lithologies, probably due mainly to the overriding effects of longitude-petrochemistry correlations. A diopside-bearing Mg-rich lithology indicates that a low degree of melting was not a prerequisite for producing gabbroic (high-Ca pyroxene-rich) Mg-rich magmas, and suggests that some source regions of Mg-rich magmas were relatively Ca-rich. Several pristine KREEP fragments from Apollo 15 station 2 are texturally and compositionally much like other pristine KREEP, and thus reinforce the evidence that KREEP is highly uniform. The pristine anorthosites, on the other hand, demonstrate further that lunar anorthosites are diverse.

A compositional and petrographic characterization of 11 nonmare samples shows five to be pristine, and four probably pristine. Five of the 11 are unique anorthosites that considerably extend the diversity of lunar anorthosites. Alkali anorthosites are rich in incompatible elements. The nature of the correlations between longitude and such parameters as Eu and Sm concentrations, and Sc/Sm, Ti/Sm, and Ca/Na ratios, has been elucidated for the case of the pristine samples because five are fro a western site (Apollo 14). The ratios determined for the ferroan anorthosite 14312c are close to normal, but significantly displaced in the direction of the nonferroan, western pristine rocks. This suggests that the composition-longitude relationships are as old as the late stages of the crystallization of the putative magma ocean.