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BACKGROUND Head and neck cancer (HNC) is common worldwide. Given poor outcomes for patients with HNC, research into targeted therapies is needed. Ataxia telangiectasia mutated (ATM) is a DNA damage kinase which is activated by double-strand DNA breaks. We tested the effects of a novel ATM inhibitor on HNC cell lines and xenografts. MATERIALS AND METHODS p53-Binding protein 1 and phosphorylated ATM were localized in cultured cells by immunofluorescence microscopy. Protein expression was determined by western blot. Tumor xenografts were established by injecting HNC lines into immunocompromised mice. Tumor sections were characterized by immunohistochemistry. Apoptotic cells were determined by terminal transferase-mediated dUTP nick-end labeling assay. RESULTS ATM inhibition increased double-strand DNA breaks at replication foci in HNC cell lines. ATM inhibition affected cell-cycle regulatory protein expression, blocked cell-cycle progression at the G2/M phase and resulted in apoptosis. CONCLUSION ATM inhibition may be therapeutically useful in treating HNC.

Introduction: Frailty and decreased physical performance are associated with poor outcomes after kidney transplant. Less is known about their relationship with pretransplant outcomes. The aim of this study was to characterize associations between frailty and physical performance with death on the kidney transplant waiting list. Design: Since December 2014, high-risk kidney transplant candidates at our center (age > 59, diabetic and/or history of >3 years dialysis) have undergone frailty and physical performance testing using Fried Criteria and the Short Physical Performance Battery. Results: Between December 2014 and November 2016, 272 high-risk candidates underwent testing and were approved for transplant. Both frailty and physical performance score were significantly associated with death on the waiting list (hazard ratio [HR]: 6.7, confidence interval [CI]: 1.5-30.1; P = .01; HR: 0.8 per 1-point increase, CI: 0.7-1.0; P = .02, respectively). The relationship between frailty, physical performance score, and death on the waiting list appeared to be independent of age, diabetes, or duration of dialysis. Discussion: Frailty and decreased physical performance appear to be independently associated with increased mortality on the kidney transplant waiting list. Further studies are needed to determine whether improving frailty and physical performance prior to transplant can decrease waiting list mortality.

This study determines the ages of 191 discrete lunar regolith samples from the Apollo, Luna, and meteorite collections. Model closure ages (for lithified breccias) and appearance ages (for unconsolidated soils) are calculated using the trapped 40Ar and 36Ar abundances of each sample, determined from published Ar data. Model closure ages of regolith breccias span ~3.9 to 0.01 Ga and appearance ages of soils range from ~3.6 to 0.03 Ga; 169 of these ages are published here for the first time, while 22 are recalculated ages. The regolith breccias with the oldest closure ages originate from the ancient highlands and oldest mare surfaces sampled by the Apollo missions. Soils generally have similar ages to each other, regardless of location and collection depth, with most model ages

The lunar regolith is exposed to irradiation from the solar wind and to bombardment by asteroids, comets and inter-planetary dust. Fragments of projectiles in the lunar regolith can potentially provide a direct measure of the sources of exogenous material being delivered to the Moon. Constraining the temporal flux of their delivery helps to address key questions about the bombardment history of the inner Solar System. Here, we use a revised antiquity calibration (after Eugster et al., 2001 ) that utilises the ratio of trapped 40Ar/36Ar (‘parentless’ 40Ar derived from radioactive decay of 40K, against solar wind derived 36Ar) to semi-quantitatively calculate the timing of the assembly of the Apollo 16 regolith breccias. We use the trapped 40Ar/36Ar ratios reported by McKay et al. (1986) . Our model indicates that the Apollo 16 ancient regolith breccia population was formed between ∼3.8 and 3.4 Ga, consistent with regoliths developed and assembled after the Imbrium basin-forming event at ∼3.85 Ga, and during a time of declining basin-forming impacts. The material contained within the ancient samples potentially provides evidence of impactors delivered to the Moon in the Late-Imbrian epoch. We also find that a young regolith population was assembled, probably by local impacts in the Apollo 16 area, in the Eratosthenian period between ∼2.5 and 2.2 Ga, providing insights to the sources of post-basin bombardment. The ‘soil-like’ regolith breccia population, and the majority of local Apollo 16 soils, were likely closed in the last 2 Ga and, therefore, potentially provide an archive of projectile types in the Eratosthenian and Copernican periods.

– We report measurements of cosmogenic nuclides in up to 11 bulk samples from various depths in Norton County. The activities of 36Cl, 41Ca, 26Al, and 10Be were measured by accelerator mass spectrometry; the concentrations of the stable isotopes of He, Ne, Ar, and Sm were measured by electron and thermal ionization mass spectrometry, respectively. Production rates for the nuclides were modeled using the LAHET and the Monte Carlo N-Particle codes. Assuming a one-stage irradiation of a meteoroid with a pre-atmospheric radius of approximately 50 cm, the model satisfactorily reproduces the depth profiles of 10Be, 26Al, and 53Mn (

This case study describes inter-disciplinary treatment of chronic food refusal and tube dependency in a 2-year-old female with a pediatric feeding disorder. Evidence-based behavioral components—including escape extinction (EE), differential reinforcement of alterative mealtime behavior (DRA), and stimulus fading—were introduced sequentially as the focus of treatment shifted to address refusal topographies along the chain of behaviors associated with consumption. The assessment process, treatment planning and sequencing, and generalization of treatment gains to caregivers are presented in detail. In doing so, the study illustrates the core features involved in applying a flexible, evidenced-based approach to treat severe feeding difficulties.

Portales Valley, Sombrerete, and Northwest Africa (NWA) 176 are three unrelated meteorites, which consist of silicate mixed with substantial amounts of metal and which likely formed at elevated temperatures as a consequence of early impacts on their parent bodies. Measured 39 Ar– 40 Ar ages of these meteorites are 4477 ± 11 Ma and 4458 ± 16 Ma (two samples of Portales Valley), 4541 ± 12 Ma, and 4524 ± 13 Ma, respectively (Ma = million years; all one-sigma errors). The Ar–Ar data for Portales Valley show no evidence of later open system behavior suggested by some other chronometers. Measured 129 I– 129 Xe ages of these three meteorites are 4559.9 ± 0.5 Ma, 4561.9 ± 1.0 Ma, and ∼4544 Ma, respectively (relative to Shallowater = 4562.3 ± 0.4 Ma). From stepwise temperature release data, we determined the diffusion characteristics for Ar and Xe in our samples and calculated approximate closure temperatures for the K–Ar and I–Xe chronometers. Adopting results and interpretations about these meteorites from some previous workers, we evaluated all these data against various thermal cooling models. We conclude that Portales Valley formed 4560 Ma ago, cooled quickly to below the I–Xe closure temperature, then cooled deep within the parent body at a rate of ∼4 °C/Ma through K–Ar closure. We conclude that Sombrerete formed 4562 Ma ago and cooled relatively quickly. NWA 176 likely formed and cooled quickly ∼4544 Ma ago, or later than formation times of most meteorite parent bodies. For all three meteorites, the Ar–Ar ages are in better agreement with I–Xe ages and preferred thermal models if we increase these Ar–Ar ages by ∼20 Ma. Such age corrections would be consistent with probable errors in 40 K decay parameters in current use, as suggested by others. The role of impact heating and possible disruption and partial reassembly of meteorite parent bodies to form some meteorites likely was an important process in the early solar system.

Multiple lines of evidence show that the Rb–Sr, Sm–Nd, and Ar–Ar isotopic systems individually give robust crystallization ages for basaltic (or diabasic) shergottite Northwest Africa (NWA) 1460. In contrast to other shergottites, NWA 1460 exhibits minimal evidence of excess 40Ar, thus allowing an unambiguous determination of its Ar–Ar age. The concordant Rb–Sr, Sm–Nd, and Ar–Ar results for NWA 1460 define its crystallization age to be 346 ± 17 Ma (2σ). In combination with petrographic and trace element data for this specimen and paired meteorite NWA 480, these results strongly refute the suggestion by others that the shergottites are ∼4.1 Ga old. Current crystallization and cosmic-ray exposure (CRE) age data permit identification of a maximum of nine ejection events for Martian meteorites (numbering more than 50 unpaired specimens as of 2008) and plausibly as few as five such events. Although recent high resolution imaging of the Martian surface has identified limited areas of sparsely cratered terrains, the meteorite data suggest that either these areas are representative of larger areas from which the meteorites might come, or that the cratering chronology needs recalibration. Time-averaged 87Rb/86Sr = 0.16 for the mantle source of the parent magma of NWA 1460/480 over the ∼4.56 Ga age of the planet is consistent with previously estimated values for bulk silicate Mars in the range 0.13–0.16, and similar to values of ∼0.18 for the “lherzolitic” shergottites. Initial eNd for NWA 1460/480 at 350 ± 16 Ma ago was +10.6 ± 0.5, which implies a time-averaged 147Sm/144Nd of 0.217 in the Martian mantle prior to mafic melt extraction, similar to values of 0.211–0.216 for the “lherzolitic” shergottites. These time-averaged values do not imply a simple two-stage mantle/melt evolution, but must result from multiple episodes of melt extractions from the source regions. Much higher “late-stage” eNd values for the depleted shergottites imply similar processes carried to a greater degree. Thus, NWA 1460/480, the “lherzolitic” shergottites and perhaps EET 79001 give the best (albeit imperfect) estimate of the Sr- and Nd-isotopic characteristics of bulk silicate Mars.

We report new 39Ar-40Ar measurements on 15 plagioclase, pyroxene, and/or whole rock samples of 8 Martian shergottites. All age spectra suggest ages older than the meteorite formation ages, as defined by Sm-Nd and Rb-Sr isochrons. Employing isochron plots, only Los Angeles plagioclase and possibly Northwest Africa (NWA) 3171 plagioclase give ages in agreement with their formation ages. Isochrons for all shergottite samples reveal the presence of trapped Martian 40Ar(40Arxs), which exists in variable amounts in different lattice locations. Some 40Arxs is uniformly distributed throughout the lattice, resulting in a positive isochron intercept, and other 40Arxs occurs in association with K-bearing minerals and increases the isochron slope. These samples demonstrate situations where linear Ar isochrons give false ages that are too old. After subtracting 40Ar* that would accumulate by 40K decay since meteorite formation and small amounts of terrestrial 40Ar, all young age samples give similar 40Arxs concentrations of ~1-2 x 10^(-6) cm^3/g, but a variation in K content by a factor of ~80. Previously reported NASA Johnson Space Center data for Zagami, Shergotty, Yamato (Y-) 000097, Y-793605, and Queen Alexandra Range (QUE) 94201 shergottites show similar concentrations of 40Arxs to the new meteorite data reported here. Similar 40Arxs in different minerals and meteorites cannot be explained as arising from Martian atmosphere carried in strongly shocked phases such as melt veins. We invoke the explanation given by Bogard and Park (2008) for Zagami, that this 40Arxs in shergottites was acquired from the magma. Similarity in 40Arxs among shergottites may reveal common magma sources and/or similar magma generation and emplacement processes.

We report an 39 Ar– 40 Ar age determination of a whole rock sample of the olivine-rich, martian meteorite Northwest Africa (NWA) 2737. Those extractions releasing 0–48% of the 39 Ar define an 39 Ar– 40 Ar isochron age of 160–190 Ma, when evaluated in various ways. Higher temperature extractions show increasing ages that eventually exceed the reported Sm–Nd age of 1.42 Ga. At least part of this excess 40 Ar may have been shock implanted from the martian atmosphere. We considered two possible interpretations of the Ar–Ar isochron age, utilizing the measured Ar diffusion characteristics of NWA 2737 and a thermal model, which relates Ar diffusion to the size of a cooling object after shock heating. One interpretation, that 40 Ar was only partially degassed by an impact event ~ 11 Ma ago (the CRE age), appears possible only if NWA 2737 was shock-heated to temperatures > 600 °C and was ejected from Mars as an object a few 10 s of cm in diameter. The second interpretation, which we prefer, is that NWA experienced an earlier, more intense shock event, which left it residing in a warm ejecta layer, and a less intense event ~ 11 Ma ago, which ejected it into space. Our evaluation would require NWA 2737 to have been heated by this first event to a temperature of ~ 300–500 °C and buried in ejecta to a depth of ~ 1–20 m. These conclusions are compared to model constraints on meteorite ejection from Mars reported in the literature. The second, Mars-ejection impact ~ 11 Ma ago probably heated NWA 2737 to no more than ~ 400 °C. NWA 2737 demonstrates that some martian meteorites probably experienced shock heating in events that did not eject them into space.

The Zagami shergottite experienced a complex, petrogenetic formation history (McCoy et al. 1992, 1999). Like several shergottites, Zagami contains excess 40Ar relative to its formation age. To understand the origin of this excess 40Ar, we made 39Ar-40Ar analyses on plagioclase and pyroxene minerals from two phases representing different stages in the magma evolution. Surprisingly, all these separates show similar concentrations of excess 40Ar, ~1 x 10^(-6) cm^(3)/g. We present arguments against this excess 40Ar having been introduced from the Martian atmosphere as impact glass. We also present evidence against excess 40Ar being a partially degassed residue from a basalt that actually formed ~4 Gyr ago. We utilize our experimental data on Ar diffusion in Zagami and evidence that it was shock-heated to only ~70 °C, and we assume this heating occurred during an ejection from Mars ~3 Myr ago. With these constraints, thermal considerations necessitates either that its ejected mass was impossibly large, or that its shock-heating temperature was an order of magnitude higher than that measured. We suggest that this excess 40Ar was inherited from the Zagami magma, and that it was introduced into the magma either by degassing of a larger volume of material or by early assimilation of old, K-rich crustal material. Similar concentrations of excess 40Ar in the analyzed separates imply that this magma maintained a relatively constant 40Ar concentration throughout its crystallization. This likely occurred through volatile degassing as the magma rose toward the surface and lithostatic pressure was released. These concepts have implications for excess 40Ar in other shergottites.

The L chondrite Patuxent Range (PAT) 41 91501 is an 8.5-kg unshocked, homogeneous, igneous-textured impact melt that cooled slowly compared to other meteoritic impact melts in a crater floor melt sheet or sub-crater dike. We conducted mineralogical and tomographic studies of previously unstudied mm- to cm-sized metal-sulfide-vesicle assemblages and chronologic studies of the silicate host. Metal-sulfide clasts constitute about 1 vol.%, comprise zoned taenite, troilite and pentlandite, and exhibit a consistent orientation between metal and sulfide and of metal-sulfide contacts. Vesicles make up approximately 2 vol.% and exhibit a similar orientation of long axes. Ar-39-Ar-40 measurements date the time of impact at 4.461 +/- 0.008 Gyr B.P. Cosmogenic noble gases and Be-10 and Al-2l activities suggest a pre-atmospheric radius of 40-60 cm and a cosmic ray exposure age of 25-29 Myr, similar to ages of a cluster of L chondrites. PAT 91501 dates the oldest known impact on the L chondrite parent body. The dominant vesicle-forming gas was S2 (approximately 15-20 ppm), which formed in equilibrium with impact-melted sulfides. The meteorite formed in an impact melt dike beneath a crater, as did other impact melted L chondrites, such as Chico. Cooling and solidification occurred over approximately 2 hours. During this time, approximately 90% of metal and sulfide segregated from the local melt. Remaining metal and sulfide grains oriented themselves in the local gravitational field, a feature nearly unique among meteorites. Many of these metal sulfide grains adhered to vesicles to form aggregates that may have been close to neutrally buoyant. These aggregates would have been carried upward with the residual melt, inhibiting further buoyancy-driven segregation. Although similar processes operated individually in other chondritic impact melts, their interaction produced the unique assemblage observed in PAT 91501.

Yamato (Y)-86032 is a relatively large, feldspathic lunar highlands meteorite composed of a variety of highland lithologies. Low bulk contents of Th and Fe indicated that it came from a region of the moon far distant from the Procellarum KREEP Terrain (PKT) and the Apollo landing sites, perhaps from the farside. A large (5.2 x 3.6 cm) slab was cut from Y-86032 . We report results from coordinated textural, mineralogical-petrological, chemical, and isotopic studies of lithologies identified in the slab, emphasizing the results of Ar-39/Ar-40, Rb-Sr, and Sm-Nd chronological studies as well as Sm-isotopic studies. These studies characterize the history of Y-86032 and its precursors in the farside mega-regolith, leading to inferences about the formation and evolution of the lunar crust. Textural studies establish that the Y-86032 breccia is composed of a variety of highland components including feldspathic breccias, and other components, such as possible VLT mare basalts. Impact melt veins smoothly abut the other lithologies. Thus, Y-86032 experienced at least two impact events. These impacts occurred on a predominantly feldspathic protolith, which formed 4.43+/-0.03 Ga ago as determined from a Sm-Nd isochron for mineral clasts separated from the two dominant lithologies. Initial Nd-143/Nd-144 in the protolith at that time was -0.64+/-0.13 epsilon-units below Nd-143/Nd-144 in reservoirs having chondritic Sm/Nd ratios, consistent with prior fractionation of mafic cumulates from the LMO. Although the mineral chemistry of these clasts differs in detail from that of minerals in Apollo 16 Ferroan Anorthosites (FANs), the Rb-Sr studies establish that the initial Sr-87/Sr-86 in them was the same as in the FANs.

Among over thirty lunar meteorites recovered from the hot deserts and Antarctica, Dhofar 489 is the most depleted in thorium (0.05 ppm), FeO, and rare earth elements (REE). Dhofar 489 is a crystalline matrix anorthositic breccia and includes clasts of magnesian anorthosites and a spinel troctolite. The Mg / (Mg + Fe) mol% (Mg numbers = 75–85) of olivine and pyroxene grains in this meteorite are higher than those of the Apollo ferroan anorthosites. Such materials were not recovered by the Apollo and Luna missions. However, remote sensing data suggest that the estimated concentrations of Th and FeO are consistent with the presence of such samples on the farside of the Moon. The differentiation trend deduced from the mineralogy of the anorthositic clasts define a magnesian extension of the ferroan anorthosite (FAN) trend constructed from the Apollo samples. The presence of magnesian anorthositic clasts in Dhofar 489 still offers a possibility that the farside trend with magnesian compositions is more primitive than the FAN trend, and may require a revision of this classical differentiation trend. The Ar–Ar age of Dhofar 489 is 4.23 ± 0.034 Gyr, which is older than most Ar ages reported for highland rocks returned by Apollo. The old Ar–Ar age of impact formation of this breccia and the presence of a fragment of spinel troctolite of deep crustal origin suggest that a basin forming event on the farside excavated the deep crust and magnesian anorthosites before formation of Imbrium.

Isotopic analysis of the Martian meteorite Chassigny yields a Rb–Sr age of 1406 ± 14 Ma with an initial 87 Sr/ 86 Sr ratio of 0.702251 ± 0.000034, a Sm–Nd age of 1386 ± 28 Ma with an initial e 143Nd -value of + 16.9 ± 0.3 and an 39 Ar– 40 Ar age of 1360 + 40 − 20 Ma. The concordance of these ages and the Rb–Sr and Sm–Nd initial isotopic signatures suggest that Chassigny crystallized from low Rb/Sr, light rare earth element depleted source materials ∼ 1390 Ma ago. The ages and e 143Nd -values of Chassigny and the nakhlites Governador Valadares and Lafayette overlap, suggesting that they could have come from very similar mantle sources. Nakhla, Northwest Africa 998 and Yamato 000593 appear to be from similar but distinct sources. Chassigny and all nakhlites so far studied have undergone similar evolution histories. That is, chassignites/nakhlites were derived from a region where volcanism lasted at least 50 Ma and crystallized from different lava flows or subsurface sills. They probably were launched from Mars by a single impact event. The trapped Martian atmospheric 40 Ar/ 36 Ar ratios in Chassigny, nakhlites and shergottite impact glass are similar and possibly indicate minimal change in this ratio over the past ≥ 600 Ma.

GRA 95209 may provide our best opportunity to date to understand the earliest stages of core formation in asteroidal bodies. This lodranite preserves a physically, chemically, and mineralogically complex set of metal–sulfide veins. High-resolution X-ray computed tomography revealed three distinct lithologies. The dominant mixed metal–silicate–sulfide matrix is cut by metal-rich, graphite-bearing veins exceeding 1 cm in width and grades into a volumetrically minor metal-poor region. Silicate compositions and modal abundances are typical for lodranites, while the mineralogy of the metal–sulfide component is complex and differs among the three lithologies. Kamacite and troilite occur with chromite, tetrataenite, schreibersite, graphite, and a range of phosphates. An 39 Ar– 40 Ar age of 4.521 ± 0.006 Ga measures the time of closure of the K–Ar system. Carbon rosettes within the metal-rich vein are nitrogen-poor, well crystallized, include kamacite sub-grains of composition comparable to the host metal, and are essentially isotopically homogeneous (d 13 C 33&). In contrast, carbon rosettes within metal of the metal-poor lithology are N-poor, poorly crystallized, include kamacite grains that are Ni-poor compared to their host metal, and are isotopically heterogeneous (d 13 C ranging from 50 to +80&) even within a single metal grain. The silicate portion of GRA 95209 is similar to the lodranite EET 84302, sharing a common texture, silicate mineral compositions, and Ar–Ar age. GRA 95209 and EET 84302 are intermediate between acapulcoites and lodranites. Both experienced Fe,Ni-FeS melting with extensive melt migration, but record only the onset of silicate partial melting with limited migration of silicate melt. The complex metal–sulfide veins in GRA 95209 resulted from low-degree partial melting and melt migration and intruded the matrix lithology. Reactions between solid minerals and melt, including oxidation–reduction reactions, produced the array of phosphates, schreibersite, and tetrataenite. Extensive reduction in the metal-rich vein resulted from its origin in a hotter portion of the asteroid. This difference in thermal history is supported by the graphite structures and isotopic compositions. The graphite rosettes in the metal-rich vein are consistent with high-temperature igneous processing. In contrast, the carbon in the metal-poor lithology appears to preserve a record of formation in the nebula prior to parent-body formation. Carbon incorporated from the solar nebula into a differentiating asteroid is preferentially incorporated in metal–sulfide melts that form a core, but does not achieve isotopic homogeneity until extensive thermal processing occurs.

Although a direct link between the HED meteorites and the asteroid 4 Vesta is generally acknowledged, several issues continue to be actively examined that tie Vesta to early processes in the solar system. Vesta is no longer the only basaltic asteroid in the Main belt. In addition to the Vestoids of the Vesta family, the small asteroid Magnya is basaltic but appears to be unrelated to Vesta. Similarly, diversity now identified in the collection of basaltic meteorites requires more than one basaltic parent body, consistent with the abundance of differentiated parent bodies implied by iron meteorites. The timing of the formation of the Vestoids (and presumably the large crater at the south pole of Vesta) is unresolved. Peaks in Ar-Ar dates of eucrites suggest this impact event could be related to a possible late heavy bombardment at least 3.5 Gyr ago. On the other hand, the optically fresh appearance of both Vesta and the Vestoids requires either a relatively recent resurfacing event or that their surfaces do not weather in the same manner thought to occur on other asteroids such as the ordinary chondrite parent body. Diversity across the surface of Vesta has been observed with HST and there are hints of compositional variations (possibly involving minor olivine) in near-infrared spectra.

The unequilibrated eucrite Yamato 82202 (Y82202) contains a network of glass veins, which are relatively thick (up to 1 mm in width) and are not devitrified. The host of the meteorite represents volcanic rock that crystallized >4.3 Gyr ago, probably as a lava flow on the surface of 4 Vesta. The impact event that formed the glass veins occurred at approx. 3.9 Gyr under conditions of low effective fo2 and very rapid cooling. A S-rich vapor probably was generated by impact vaporization of sulfides. The impact melt was not superheated and it retains some disordered structural characteristics of the original pyroxene and feldspar of the eucritic target lithology. The unequilibrated pyroxenes of this eucrite and the pristine character of the glass indicate that the meteorite experienced no significant metamorphism after initial crystallization. Hence, it was not buried to a significant depth or covered by a lava flow or hot layer of impact ejecta. The meteorite resided at a shallow level (though not at the surface) on 4 Vesta or on one of the vestoids until it was ejected and traveled to Earth, probably with other HED materials that have Ar-36 exposure ages of approx. 13 Myr.

Studies of several samples of the large Caddo County IAB iron meteorite reveal andesitic material, enriched in Si, Na, Al and Ca, which is essentially unique among meteorites. This material is believed to have formed from a chondritic source by partial melting and to have further segregated by grain coarsening. Such an origin implies extended metamorphism of the IAB parent body. New Ar-39- Ar-40 ages for silicate from three different Caddo samples are consistent with a common age of 4.50-4.51 Gyr ago. Less well defined Ar-Ar degassing ages for inclusions from two other IABs, EET8333 and Udei Station, are approx.4.32 Gyr, whereas the age for Campo del Cielo varies considerably over approx.3.23-4.56 Gyr. New I-129-Xe-129 ages for Caddo County and EET8333 are 4557.9+/-0.1 Myr and 4557-4560 Myr, respectively, relative to an age of 4562.3 Myr for Shallowater. Considering all reported Ar-Ar degassing ages for IABs and related winonaites, the range is approx.4.32-4.53 Gyr, but several IABs give similar Ar ages of 4.50-4.52 Gyr. We interpret these older Ar ages to represent cooling after the time of last significant metamorphism on the parent body, and the younger ages to represent later 40Ar diffusion loss. The older Ar-Ar ages for IABs are similar to Sm-Nd and Rb-Sr isochron ages reported in the literature for Caddo County. Considering the possibility that IAB parent body formation was followed by impact disruption, reassembly, and metamorphism (e.g., Benedix et al. 2000), the Ar-Ar ages and IAB cooling rates deduced from Ni concentration profiles in IAB metal (Herpfer et al., 1994) are consistent if the time of the post-assembly metamorphism was as late as approx.4.53 Gyr ago. However, I-Xe ages reported for some IABs define much older ages of approx.4558-4566 Myr, which cannot easily be reconciled with the much younger Ar-Ar and Sm-Nd ages. An explanation for the difference in radiometric ages of IABs may reside in combinations of the following: a) I-Xe ages have very high closure temperatures and were not reset during metamorphism approx.4.53 Gyr ago; b) a bias exists in the 40K decay constants which makes these Ar-Ar ages approx.30 Myr too young; c) the reported Sm-Nd and Rb-Sr ages for Caddo are in error by amounts equal to or exceeding their reported 2-sigma uncertainties; and d) about 30 Myr after the initial heating that produced differentiation of Caddo silicate and mixing of silicate and metal, a mild metamorphism of the IAB parent body reset the Ar-Ar ages.

We determined Ar-39-Ar-40 ages of eight LL chondrites, and one igneous inclusion from an LL chondrite, with the object of understanding the thermal history of the LL-chondrite parent body. The meteorites in this study have a range of petrographic types from LL3.3 to LL6, and shock stages from S1 to S4. These meteorites reveal a range of K-Ar ages from 23.66 to 24.50 Ga, and peak ages from 23.74 to 24.55 Ga. Significantly, three of the eight chondrites (LL4, 5, 6) have K-Ar ages of -4.27 Ga. One of these (MIL99301) preserves an Ar-39-Ar-40 age of 4.23 +/- 0.03 Ga from low-temperature extractions, and an older age of 4.52 +/- 0.08 Ga from the highest temperature extractions. In addition, an igneous-textured impact melt DOM85505,22 has a peak Ar-39-Ar-40 age of >= 4.27 Ga. We interpret these results as evidence for impact events that occurred at about 4.27 Ga on the LL parent body that produced local impact melts, reset the Ar-39-Ar-40 ages of some meteorites, and exhumed (or interred) others, resulting in a range of cooling ages. The somewhat younger peak age of 3.74 Ga from GR095658 (LL3.3) suggests an additional impact event close to timing of impact-reset ages of some other ordinary chondrites between 3.6-3.8 Ga. The results from MIL99301 suggest that some apparently unshocked (Sl) chondrites may have substantially reset Ar-39-Ar-40 ages. A previous petrographic investigation of MIL99301 suggested that reheating to temperatures less than or equal to type 4 petrographic conditions (600C) caused fractures in olivine to anneal, resulting in a low apparent shock stage of S1 (unshocked). The Ar-39-Ar-40 age spectrum of MIL99301 is consistent with this interpretation. Older ages from high-T extractions may date an earlier impact event at 4.52 +/- 0.08 Ga, whereas younger ages from lower-T extractions date a later impact event at 4.23 Ar-39-Ar-40 0.03 Ga that may have caused annealing of feldspar and olivine

The Hera mission is a proposed Discovery class mission to collect three samples from each of three near-Earth asteroids. Returned samples would have information on geological context and possibly stratigraphy, would provide fresh regolith, and conceivably samples that would not naturally reach the Earth. During the development of a simple touch-and-go sample collector, questions arose concerning the nature of the samples to be collected, their maximum science return, and the simplest engineering designs. This article reports the results of a small workshop convened to discuss this topic. It is argued that the maximum science return for the Hera samples would be obtained if asteroids of different major spectral classes were visited, samples were disturbed as little as possible during collection, and samples from the very surface were obtained. Surface samples would have the utmost value in interpreting links between asteroids and meteorites, would yield maximum information in solar exposure, would avoid planetary protection concerns, and would produce material not reaching Earth as meteorites. At the same time, they would be simpler to sample than subsurface samples. � 2004 COSPAR. Published by Elsevier Ltd. All rights reserved.

We have done petrologic studies of brachinites Allan Hills (ALH) 84025, Elephant Moraine (EET) 99402, and EET 99407; bulk geochemical studies of EET 99402 and EET 99407; Ar- Ar studies of Brachina and EET 99402; and a Xe isotopic study of Brachina. Textural, mineral compositional, and bulk compositional evidence show that EET 99402 and EET 99407 are paired. ALH 84025, EET 99402, and EET 99407 have igneous textures. Petrofabric analyses of ALH 84025 and EET 99407 demonstrate the presence of lineations and probable foliations of olivine grains that support formation as igneous cumulates. Mineral minor element chemistry and bulk rock incompatible lithophile element contents of the brachinites are distinct from those of acapulcoite- lodranite clan meteorites, a suite of high-grade metamorphic rocks and anatectic residues. The differences demonstrate a higher blocking temperature of equilibration for the brachinites and that cumulus plagioclase is present in EET 99402, EET 99407, and probably ALH 84025, thus indicating an igneous origin. Brachinites are differentiated, ultramafic achondrites, and are not part of a suite of primitive achondrites. We infer that their parent asteroid is a differentiated body. Brachina has an excess of 129Xe correlated with reactor-produced 128Xe, demonstrating that short-lived 129I was present at the time of formation. This, plus literature data, attests to early formation of the brachinites, within a few Ma of the formation of chondrites. Ar-Ar age data show that Brachina and EET 99407 were degassed about 4.13 Ga ago, possibly by a common impact event. EET 99402 and EET 99407 show petrographic evidence for shock, including possible conversion of plagioclase to maskelynite followed by devitrification. Brachina is unshocked, making a direct association between the Ar-Ar age and textures ambiguous.

Eucrite meteorites are igneous rocks that derived from a large asteroid, probably 4 Vesta. Past studies have shown that after most eucrites formed, they underwent metamorphism in temperatures up to ≥800°C. Much later, many were brecciated and heated by large impacts into the parent body surface. The less common basaltic, unbrecciated eucrites also formed near the surface but, presumably, escaped later brecciation, while the cumulate eucrites formed at depths where metamorphism may havepersisted for a considerable period. To further understand the complex HED parent body thermal history, we determined new 39Ar- 40Ar ages for 9 eucrites classified as basaltic but unbrecciated, 6 eucrites classified as cumulate, and several basaltic-brecciated eucrites. Precise Ar-Ar ages of 2 cumulate eucrites (Moama and EET 87520) and 4 unbrecciated eucrites give a tight cluster at 4.48 ± 0.02 Gyr (not including any uncertainties in the flux monitor age). Ar-Ar ages of 6 additional unbrecciated eucrites are consistent with this age within theirrelatively larger age uncertainties. By contrast, available literature data on Pb-Pb isochron ages of 4 cumulate eucrites and 1 unbrecciated eucrite vary over 4.4-4.515 Gyr, and 147Sm-143Nd isochron ages of 4 cumulate and 3 unbrecciated eucrites vary over 4.41-4.55 Gyr. Similar Ar-Ar ages for cumulate and unbrecciated eucrites imply that cumulate eucrites do not have a younger formation age than basaltic eucrites, as was previously proposed. We suggest that these cumulate and unbrecciated eucrites resided at a depth where parent body temperatures were sufficiently high to cause the K-Ar and some other chronometers to remain as open diffusion systems. From the strong clustering of Ar-Ar ages at ~4.48 Gyr, we propose that these meteorites were excavated from depth in a single large impact event ~4.48 Gyr ago, which quickly cooled the samples and started the K-Ar chronometer. A large (~460 km) crater postulated to exist on Vesta may be the source of these eucrites and of many smaller asteroids thought to be spectrally or physically associated with Vesta. Some Pb-Pb and Sm-Nd ages of cumulate and unbrecciated eucrites are consistent with the Ar-Ar age of 4.48 Gyr, and the few older Pb-Pb and Sm-Nd ages may reflect an isotopic closure before the large cratering event. One cumulate eucrite gives an Ar-Ar age of 4.25 Gyr; 3 additional cumulate eucrites give Ar-Ar ages of 3.4-3.7 Gyr; and 2 unbrecciated eucrites give Ar-Ar ages of ~3.55 Gyr. We attribute these younger ages to a later impact heating. Furthermore, the Ar-Ar impact-reset ages of several brecciated eucrites and eucritic clasts in howardites fall within the range of 3.5-4.1 Gyr. Among these, Piplia Kalan, the first eucrite to show evidence for extinct 26Al, was strongly impact heated ~3.5 Gyr ago. When these data are combined with eucrite Ar-Ar ages in the literature, they confirm that several large impact heating events occurred on Vesta between ~4.1-3.4 Gyr ago. The onset of major impact heating may have occurred at similar times for both Vesta and the moon, but impact heating appears to have persisted for a somewhat later time on Vesta.

The petrology, major and trace element geochemistry, and Nd-Ar-Sr isotopic compositions of a ferroan noritic anorthosite clast from lunar breccia 67215 have been studied in order to improve our understanding of the composition, age, structure, and impact history of the lunar crust. The clast (designated 67215c) has an unusually well preserved igneous texture. Mineral compositions are consistent with classification of 67215c as a member of the ferroan anorthositic suite of lunar highlands rocks, but the texture and mineralogy show that it cooled more rapidly and at shallower depths than did more typical ferroan anorthosites (FANs). Incompatible trace element concentrations are enriched in 67215c relative to typical FANs, but diagnostic signatures such as Ti/Sm, Sc/Sm, plagiophile element ratios, and the lack of Zr/Hf and Nb/Ta fractionation show that this cannot be due to the addition of KREEP. Alternatively, 67215c may contain a greater fraction of trapped liquid than is commonly present in lunar FANs. 147Sm-143Nd isotopic compositions of mineral separates from 67215c define an isochron age of 4.40 ± 0.11 Gyr with a near-chondritic initial 143Nd of +0.85 0.53. The 40Ar-39Ar composition of plagioclase from this clast records a post-crystallization thermal event at 3.93 ± 0.08 Gyr, with the greatest contribution to the uncertainty in this age deriving from a poorly constrained correction for lunar atmosphere 40Ar. Rb-Sr isotopic compositions are disturbed, probably by the same event recorded by the Ar isotopic compositions. Trace element compositions of FANs are consistent with crystallization from a moderately evolved magma ocean and do not support a highly depleted source composition such as that implied by the positive initial 143Nd of the ferroan noritic anorthosite 62236. Alternatively, the Nd isotopic systematics of lunar FANs may have been subject to variable degrees of modification by impact metamorphism, with the plagioclase fraction being more strongly affected than the mafic phases. 147Sm-143Nd isotopic compositions of mafic fractions from the 4 ferroan noritic anorthosites for which isotopic data exist (60025, 62236, 67016c, 67215c) define an age of 4.46 0.04 Gyr, which may provide a robust estimate for the crystallization age of lunar ferroan anorthosites.

Impact-produced glasses in some martian meteorites have trapped significant amounts of the recent martian atmosphere. From literature data, we estimate that ∼9% of the trapped 80 Kr in these meteorites was produced from neutron capture on 79 Br. Estimates of neutron fluences made from 80 Kr and 149 Sm for bulk samples of meteorite EET79001 indicate that 80 Kr excesses in the impact glass were not produced in situ . Theoretical calculations independently predict production of a large neutron-capture component of 80 Kr and 36 Ar in the martian regolith, and part of this component presumably escaped into the martian atmosphere. These calculations were made by using the Los Alamos High-Energy Transport Code to calculate the fluxes of galactic cosmic ray (GCR)-produced thermal neutrons as a function of depth in the uppermost 500 g cm −2 of the martian surface, and by adopting average Cl, Br, and I concentrations of the upper martian surface of ∼0.3%, ∼20 ppm, and ∼0.5 ppm, respectively. Combining these data with the appropriate neutron-capture cross sections, we calculate Mars global production rates of 80 Kr n =2.4×10 16 atoms sec −1 , 36 Ar n =5.5×10 18 atoms sec −1 , and 128 Xe n =3×10 13 atoms sec −1 . Calculated global production rates of spallogenic 80 Kr sp , and 36 Ar sp , are smaller by factors of ∼770 and ∼29, respectively. It would require ∼330 Myr to produce an amount of 80 Kr n equivalent to the amount inferred to be present today in the martian atmosphere (∼2.5×10 32 atoms). Production of these neutron-capture components probably has occurred over the past ∼4 Gyr, as only an atmospheric pressure substantially higher than today's would appreciably decrease the neutron flux in the regolith. Thus, most of the neutron-capture noble gases produced over time probably remain in the martian regolith and would make sensitive indicators of the time period a sample has resided near the martian surface. Assuming mixing of the martian surface to an average depth of 100 m, the predicted average regolith concentrations of 80 Kr n , 36 Ar n , and 128 Xe n are ∼4×10 −9 cm −3 g −1 , ∼1×10 −6 cm 3 g −1 , and ∼5×10 −12 cm 3 g −1 , respectively. If similar fractions of these neutron-capture isotopes have escaped into the atmosphere, they would comprise ∼3% and ∼0.2% of the present atmospheric inventories of 36 Ar and 128 Xe, respectively. The fractional excess of 80 Kr n in ancient martian meteorite ALH84001 appears similar to that in shock-glass phases of young shergottite meteorites. If ALH84001 acquired its atmospheric gases ∼4 Gyr ago, this implies that, prior to that time, halogens were greatly concentrated at the martian surface by crustal formational and weathering processes, impacts efficiently degassed the regolith, and Mars did not have a significant atmosphere to shield the surface.

In the framework of the ITER broader approach, the International Fusion Materials Irradiation Facility (IFMIF) deuteron accelerator (2 × 125 mA at 40 MeV) is an irradiation tool dedicated to high neutron flux production for future nuclear plant material studies. During the validation phase, the Linear IFMIF Prototype Accelerator (LIPAc) machine will be tested on the Rokkasho site in Japan. This demonstrator aims to produce 125 mA/9 MeV deuteron beam. Involved in the LIPAc project for several years, specialists from CEA/Saclay designed the injector based on a SILHI type ECR source operating at 2.45 GHz and a 2 solenoid low energy beam line to produce such high intensity beam. The whole injector, equipped with its dedicated diagnostics, has been then installed and tested on the Saclay site. Before shipment from Europe to Japan, acceptance tests have been performed in November 2012 with 100 keV deuteron beam and intensity as high as 140 mA in continuous and pulsed mode. In this paper, the emittance measurements done for different duty cycles and different beam intensities will be presented as well as beam species fraction analysis. Then the reinstallation in Japan and commissioning plan on site will be reported.

We performed petrologic, radiometric (Ar-Ar, Sm-Nd, and Mn-Cr ages), and ion microprobe studies of the basaltic eucrite, EET90020. This is one of the few rare basaltic eucrites whose 39Ar-40Ar age has not been reset during impact bombardment on the HED parent body ≤4 Ga ago and, thus, should provide a unique opportunity to study the nature of the early thermal events on its parent body (presumably asteroid 4Vesta). Hand specimen inspection shows that the rock consists of a fine-grained and a coarse-grained lithology. Microscopy indicates that the fine-grained lithology has a granulitic texture, with a coarser-grained area and a large opaque assemblage embedded in the granulitic matrix. The coarse-grained lithology has an igneous, subophitic texture. The rock has pyroxenes similar to those in type 5 eucrites (type 5 pyroxene) and experienced prolonged thermal metamorphism after rapid crystallization from a near-surface melt. However, minor mineral assemblages are unusual and suggest a complex thermal history. Tridymite occurs as large laths, irregular crystals ( 1–5 GPa after the reheating event. EET90020 seems to have experienced the following thermal history; (1) crystallization during rapid cooling near the surface; (2) some brecciation by impact; (3) thermal metamorphism that produced type 5 pyroxene; and (4) short reheating that caused partial melting and rapid cooling. 39Ar-40Ar measurements show a relatively flat pattern and an age of 4.49±0.01 Ga, which is consistent with rapid cooling from high temperature (event 4). Resetting of the Sm-Nd ages at 4.51 ± 0.04 Ga appears to be closely related to the remelting of Ca-phosphates. Rb-Sr data suggest Rb-loss from tridymite during partial melting. The resetting of the Mn-Cr age may have been related to the formation of Cr-ulvospinels (event 4). We suggest that all these ages were reset by partial melting (event 4). We further suggest that the partial melting event (event 4) that reset the ages ∼4.50 Ga ago was caused by an impact into EET90020 which was part of the hot crust of 4Vesta and resulted in an increase in the temperature from the ambient temperature of ∼ 870°C to above the subsolidus temperature of eucrites of ∼1060°C.

Information about the composition of volatiles in the Martian atmosphere and interior derives from Viking spacecraft and ground-based measurements, and especially from measurements of volatiles trapped in Martian meteorites, which contain several distinct components. One volatile component, found in impact glass in some shergottites, gives the most precise measurement to date of the composition of Martian atmospheric Ar, Kr, and Xe, and also contains significant amounts of atmospheric nitrogen showing elevated 15N/14N. Compared to Viking analyses, the 36Ar/132Xe and 84Kr/132Xe elemental ratios are larger in shergottites, the 129Xe/132Xe ratio is similar, and the 40Ar/36Ar and 36Ar/38Ar ratios are smaller. The isotopic composition of atmospheric Kr is very similar to solar Kr, whereas the isotopes of atmospheric Xe have been strongly mass fractionated in favor of heavier isotopes. The nakhlites and ALH84001 contain an atmospheric component elementally fractionated relative to the recent atmospheric component observed in shergottites. Several Martian meteorites also contain one or more Martian interior components that do not show the mass fractionation observed in atmospheric noble gases and nitrogen. The D/H ratio in the atmosphere is strongly mass fractionated, but meteorites contain a distinct Martian interior hydrogen component. The isotopic composition of Martian atmospheric carbon and oxygen have not been precisely measured, but these elements in meteorites appear to show much less variation in isotopic composition, presumably in part because of buffering of the atmospheric component by larger condensed reservoirs. However, differences in the oxygen isotopic composition between meteorite silicate minerals (on the one hand) and water and carbonates indicate a lack of recycling of these volatiles through the interior. Many models have been presented to explain the observed isotopic fractionation in Martian atmospheric N, H, and noble gases in terms of partial loss of the planetary atmosphere, either very early in Martian history, or over extended geological time. The number of variables in these models is large, and we cannot be certain of their detailed applicability. Evolutionary data based on the radiogenic isotopes (i.e., 40Ar/36Ar, 129Xe/132Xe, and 136Xe/132Xe ratios) are potentially important, but meteorite data do not yet permit their use in detailed chronologies. The sources of Mars’ original volatiles are not well defined. Some Martian components require a solar-like isotopic composition, whereas volatiles other than the noble gases (C, N, and H2O) may have been largely contributed by a carbonaceous (or cometary) veneer late in planet formation. Also, carbonaceous material may have been the source of moderate amounts of water early in Martian history.

— The Monahans H-chondrite is a regolith breccia containing light and dark phases and the first reported presence of small grains of halite. We made detailed noble gas analyses of each of these phases. The 39Ar-40Ar age of Monahans light is 4.533 ± 0.006 Ma. Monahans dark and halite samples show greater amounts of diffusive loss of 40Ar and the maximum ages are 4.50 and 4.33 Ga, respectively. Monahans dark phase contains significant concentrations of He, Ne and Ar implanted by the solar wind when this material was extant in a parent body regolith. Monahans light contains no solar gases. From the cosmogenic 3He, 21Ne, and 38Ar in Monahans light we calculate a probable cosmic-ray, space exposure age of 6.0 ± 0.5 Ma. Monahans dark contains twice as much cosmogenic 21Ne and 38Ar as does the light and indicates early near-surface exposure of 13–18 Ma in a H-chondrite regolith. The existence of fragile halite grains in H-chondrites suggests that this regolith irradiation occurred very early. Large concentrations of 36Ar in the halite were produced during regolith exposure by neutron capture on 35Cl, followed by decay to 36Ar. The thermal neutron fluence seen by the halite was (2–4) × 1014 n/cm2. The thermal neutron flux during regolith exposure was ∼0.4-0.7 n/cm2/s. The Monahans neutron fluence is more than an order of magnitude less than that acquired during space exposure of several large meteorites and of lunar soils, but the neutron flux is lower by a factor of ≤5. Comparison of the 36Arn/21Necos ratio in Monahans halite and silicate with the theoretically calculated ratio as a function of shielding depth in an H-chondrite regolith suggests that irradiation of Monahans dark occurred under low shielding in a regolith that may have been relatively shallow. Late addition of halite to the regolith can be ruled out. However, irradiation of halite and silicate for different times at different depths in an extensive regolith cannot be excluded.

— We measured cosmogenic radionuclides (10Be, 26Al, and 36Cl) and noble gases (He, Ne, and Ar) in 10 specimens of the Mocs L6 chondrite to determine the exposure history and preatmospheric relationship among fragments from known locations in the strewn field. Cosmogenic noble gas contents alone are consistent with a simple irradiation exposure of 15.2 Ma. However, Mocs has very low 22Ne/21Ne ratios indicative of deep burial in a large meteoroid, but radionuclide levels at saturation values typical for much smaller meteoroids: this paradox suggests a possible complex exposure. For the latter case, we propose a two-stage exposure history in which Mocs initially was deeply buried in a large object for 110 Ma, followed by exposure in a 65 cm object for 10.5 Ma. Relative shielding was inferred from the measured 22Ne/21Ne ratios assuming constant 22Ne/21Ne production for all samples during the first stage. These shielding levels, which are supported by estimates based on 36Cl production by neutron capture, indicate a possible relationship between depth of samples in the Mocs meteoroid and fall location in the strewn field.

The thirteen SNC meteorites are all igneous rocks, either basalts or basaltic cumulates. They are inferred to be from Mars, based on direct comparison with martian materials and on consistency with inferences about Mars. Most telling is that the SNC meteorites contain traces of gas which is very similar in elemental and isotopic compositions to the modem Martian atmosphere as measured by Viking. The martian atmosphere appears to be unique in the solar system, so its presence in the SNCs is accepted as virtually unequivocal proof that they formed on Mars. Independent of this link, the SNC meteorites must be from a planet with a significant atmosphere because they contain several abundant gas components, some of which carry large isotopic fractionations characteristic of atmospheric processing. The chemical compositions of the SNC meteorites are also consistent with data from in situ analyses of martian soils and rocks, and are quite different from compositions of other meteorites, rocks from the Earth, and rocks from the Moon. The range of formation ages for the SNC meteorites, 4.5 Ga to 0. 18 Ga, is consistent with the varied ages of the Martian surface (based on its cratering record) and inconsistent with surface ages on any other solar system body. The extreme chemical fractionations in the SNC meteorites suggest complex internal processes on a large planet, which is inconsistent with an asteroidal origin. Some SNCs were altered by aqueous solutions at greater than 0.7 Ga, consistent with the recent presence of liquid groundwater in Mars inferred independently from the geology of its surface. There seems little likelihood that the SNCs are not from Mars. If they were from another planetary body, it would have to be substantially identical to Mars as it now is understood.

IIE iron meteorites contain silicate inclusions whose characteristics suggest a parent body similar to that of H-chondrites. However, these silicates show a wide range of alteration, ranging from Netschadvo and Techado, whose inclusions are little altered. to highly differentiated silicates like-those in Kodaikanal, Weekeroo Station and Colomera, which have lost metal and sulfur and are enriched in feldspar. We find these inclusions to show varying degrees of shock alteration. Because only a limited amount of data on - isotopic ages of HE silicates were available, we made Ar-39 - Ar-40 age determinations of Watson, Techado, miles Colomera, and Sombrerete. Watson has an Ar-Ar age of 3.653 +/- 0.012 Gyr, similar to previously reported ages for Kodaikanal and Netschadvo. We suggest that the various determined radiometric ages of these three meteorites were probably reset by a common impact event. The space exposure ages for these three meteorites are also similar to each other and are considerably younger than exposure ages of other IIEs. Ar-39 - Ar-40 ages inferred for the other four meteorites analyzed are considerably older than Watson and are: Techado =4.49 +/- 0.01 Gyr, Miles =4.412 +/- 0.016 Gyr, Colomera =4.469 +/- 0.012 Gyr, and Sombrerete =4.535 +/- 0.005 Gyr. These ages are in fair agreement with previously reported Rb-Sr isochron ages for Colomera and Weekeroo Station. Although several mechanisms to form HE meteorites previously were suggested, it is not obvious that a single mechanism could produce a suite of meteorites with very different degrees of silicate differentiation and with isotopic ages that differ by >0.8 Gyr. We suggest that those IIEs with older isotopic ages are a product of partial melting and differentiation within the parent body, followed by mixing of silicate and metal while both were relatively hot. Netschadvo and Watson may have formed by this same process or by impact mixing about 4.5 Gyr ago, but their isotopic ages were subsequently reset by shock heating. Kodaikanal apparently is required to have formed more recently, in which case impact melting and differentiation seems the only viable process. We see no compelling reasons to believe that IIE silicate and metal derived from different parent bodies or that the parent body of IIEs was the same as that of H-chondrites.

We found coarse-grained gabbroic material rich in plagioclase and diopside in the Caddo County IAB iron meteorite. The polished thin sections studied were made from areas rich in Al and Ca detected by a micro-focus X-ray fluorescence (XRF) mapping technique. The gabbro is not a clast within a breccia, but rather this area is located mainly at silicate-metal boundaries only a few cm away from an area with fine-grained, ultramafic silicate similar to winonaites. Medium-grained orthopyroxene and olivine are found in transitional areas showing no disturbance of their crystalline textures. A vein-like region, starting at the area rich in fine-grained mafic silicate, extends towards the gabbroic area with a gradual increase in abundance of plagioclase and diopside. This texture and our accumulated knowledge of the formation mechanism of IAB/winonaltes meteorites, suggest that the gabbroic materials were formed by inhomogeneous segregation of partial melts of chondritic source materials. Compositional data on two mineralogically distinct samples of the gabbro-rich portion of the inclusion were obtained by INAA. Compared to an average of LAB silicate inclusions or winonaites, the Caddo County gabbro is enriched in the incompatible lithophile elements Na, Ca, Sc, REE and Hf, which is consistent with a melt origin for the gabbro. The cosmogenic space exposure age of Caddo County (511 Ma) is significantly younger than exposure ages of some other IAB meteorites, An 39Ar-40Ar age determination of the gabbroic material indicates a series of upward steps in age from 4.516 Ga to 4.523 Ga, with a few high temperature ages up to 4.54 Ga. The older age could approximate the primary recrystallization age of silicates. The stepped Ar age spectrum may indicate differences in Ar closure temperatures during slow cooling of -2-20'C/Myr in the parent body. Alternatively, the younger Ar-Ar ages may date a shock event which occurred while Caddo County was hot and which also created textures such as a linear metal vein with rounded zigzag walls in a diopside crystal and slightly miss-oriented rounded plagioclase domain.

— We used the nuclear reaction 37Cl (n,γ) 38Ar, achieved during neutron irradiation for dating meteorites by the 39Ar-40Ar technique, to calculate the elemental Cl concentration of 132 samples of 94 different meteorites (mostly finds) representing several different classes. determined k and ca concentrations are also reported. Total [Cl] varies considerably, both among meteorites of the same class and among different meteorite classes. The range in [Cl] is approximately 15–177 ppm for ordinary chondrites; approximately 24–650 ppm for enstatite chondrites; approximately 4–177 ppm for eucrites; approximately 7–128 ppm for mesosiderites; approximately 35–268 ppm for acapulcoites and lodranites; and approximately 12–507 ppm for winonaites and iron silicates. As expected, most differentiated meteorites have lower [Cl] compared to chondrites and iron silicates. Analyses of 11 interior samples (∼0.1 g each) of a large L6 chondrite varied over 68–129 ppm, which is a measure of the homogeneity of Cl distribution. By evaluating Ar release during stepwise sample degassing, we separated the Cl into low-temperature and high-temperature components, the former of which may consist of terrestrial contamination. Most samples show low-temperature Cl concentrations of

— Argon-isotopic abundances were measured in neutron-irradiated samples of Martian meteorites Chassigny, Allan Hills (ALH) 84001, ALH 77005, Elephant Moraine (EET) 79001, Yamato (Y) 793605, Shergotty, Zagami, and Queen Alexandra Range (QUE) 94201, and in unirradiated samples of ALH 77005. Chassigny gives a 39Ar-40Ar age of 1.32 ± 0.07 Ga, which is similar to radiometric ages of the nakhlites. Argon-39-Argon-40 data for ALH 84001 indicate ages between 3.9 and 4.3 Ga. A more precise definition of this age requires detailed characterization of the multiple trapped Ar components in ALH 84001 and of 39Ar recoil distribution. All six shergottite samples show apparent 39Ar-40Ar ages substantially older than the ∼165–200 Ma range in ages given by other isotope dating techniques. Shergottites appear to contain ubiquitous Ar components acquired from the Martian atmosphere, the Martian mantle, and commonly terrestrial atmospheric contamination. Zagami feldspar also suggests inherited radiogenic 40Ar. These data analyses indicate that the recent Martian atmospheric component trapped in shergottites has a 40Ar/36Ar ratio possibly as low as ∼1750 and no greater than ∼1900. These ratios are less than the value of 3000 ± 500 reported by Viking. The 40Ar/36Ar ratio for the Martian mantle component is probably

Isotopic abundances of the noble gases were measured in the following Martian meteorites: two shock glass inclusions from EET79001, shock vein glass from Shergotty and Y793605, and whole rock samples of ALH84001 and QUE94201. These glass samples, when combined with literature data on a separate single glass inclusion from EET79001 and a glass vein from Zagami, permit examination of the isotopic composition of Ne, Ar, Kr, and Xe trapped from the Martian atmosphere in greater detail. The isotopic composition of Martian Ne, if actually present in these glasses, remains poorly defined. The Ar-40/Ar-36 ratio of Martian atmospheric Ar may be much less than the ratio measured by Viking and possibly as low as approx. 1900. The atmospheric Ar-36/Ar-38 ratio is less than or equal to 4.0. Martian atmospheric Kr appears to be enriched in lighter isotopes by approx. 0.4%/amu compared to both solar wind Kr and to the Martian composition previously reported. The Martian atmospheric Ar-36/Xe-132 and Kr-84/Xe-132 Xe elemental ratios are higher than those reported by Viking by factors of approx. 3.3 and approx. 2.5, respectively. Cosmogenic gases indicate space exposure ages of 13.9 +/- 1 Myr for ALH84001 and 2.7 +/- 0.6 Myr for QUE94201. Small amounts of Ne-21 produced by energetic solar protons may be present in QUE94201, but are not present in ALH84001 or Y793605. The space exposure age for Y793605 is 4.9 +/- 0.6 Myr and appears to be distinctly older than the ages for basaltic shergottites.

We have conducted detailed petrologic, chemical, and isotopic studies of winonaites to ascertain the genesis of this group of meteorites. Winonaites have reduced mineral compositions and mineralogy, and oxygen isotopic compositions distinct from primitive achondrite groups other than silicate inclusions in IAB and IIICD irons. However, winonaites differ from IAB and IIICD irons in that they lack the metallic matrices of the latter and consist mostly of silicates. On the basis of these criteria, Winona, Mount Morris (Wisconsin), Tierra Blanca, Pontlyfni, Y-74025, Y-75300, Y-8005, and QUE 94535 are winonaites and Y-75305 and Y-75261 may be winonaites. Winonaites are fine- to medium-grained, mostly equigranular rocks. Pontlyfni and Mount Morris (Wisconsin) contain what appear to be relict chondrules. Several winonaites contain mm-sized areas that differ substantially in grain size and/or silicate mineralogy from the surrounding matrix. Fe,Ni-FeS veins are common in many winonaites. Mineral compositions are intermediate between E and H chondrites, and reduced sulfides are observed in low-FeO winonaites. Bulk major element compositions are roughly chondritic, although REE elements are fractionated. The 39Ar-40Ar ages of three winonaites range from ≥4.40 Ga (Mount Morris, Wisconsin) to 4.54 Ga (Pontlyfni). Cosmic-ray exposure ages are ∼20–80 Ma. Trapped noble gases in these winonaites resemble those in enstatite chondrites. We suggest that the winonaites formed from a chondritic precursor material unlike that of known chondrites in mineral and oxygen isotopic compositions, and this material may have been heterogeneous in composition. Extensive heating caused metamorphism and partial melting of both Fe,Ni-FeS and silicate material. Impact brecciation during cooling mixed lithologies with different thermal histories, and subsequent metamorphism produced recrystallization, grain growth, and reduction of mafic silicates. The 39Ar-40Ar ages indicate that cooling may have been more rapid than observed in IAB irons, although later resetting may have occurred.

We determined the concentrations of trapped Ar, Kr, and Xe in impact-melt glasses from Shergotty, Y793605, and two inclusions of EET79001 not previously analyzed. When combined with literature noble gas data on a single glass inclusion in EET79001 and a glass vein in Zagami, these data give more accurate estimates of the composition of Martian atmospheric gases trapped in these glasses. For the geological recent composition of the Martian atmospheric we infer 129Xe/132Xe = 2.60 ± 0.05, 36Ar/132Xe = 900 ± 100, and 84Kr/132Xe = 20.5 ± 2.5. These elemental ratios differ from those measured by Viking by factors of 2.5 and 1.8, respectively. The 36Ar/132Xe and 84Kr/132Xe ratios in ALH84001 are considerably less than those in impact glasses and suggest preferential adsorption (in carbonate?) of Xe over Ar and Xe over Kr by factors of ∼11 and ∼2.6, respectively. We suggest that noble gases dissolved in water may have largely determined the trapped noble gas abundance pattern in ALH84001.

Determinations of 39Ar-40Ar ages for plagioclase separates of three clasts from the Vaca Muerta and Mount Padbury mesosiderites give similar results. Ages increase monotonically by ∼0.2–0.3 Ga when plotted against increasing 39Ar release from the samples and give average values of ∼3.95 Ga. When combined with revised ages for mesosiderite analyses previously reported, nineteen analyses of thirteen mesosiderites give an average Ar-Ar age of 3.94 ± 0.10 Ga. The average age at 90% 39Ar release is 4.13 ±0.14 Ga, and the ages at 10% 39Ar release range over 3.32–3.97 Ga. It seems unlikely that the 39Ar-40Ar ages were produced by direct impact heating, but they probably are independent evidence for slow cooling deep within the mesosiderite parent body. We conclude that the sloped age plateaus and the significant range in Ar-Ar closure temperatures calculated for these mesosiderites (∼75–340°C) are due to significant differences in Ar diffusion properties among samples. From the Ar diffusion data, we estimate an approximate mesosiderite cooling rate of ∼0.2°C/Ma, which is similar to the preferred cooling rate of 0.1–0.5°C/Ma derived by others from Ni diffusion and metal textures. The 39Ar/40Ar ages seem incompatible with very slow cooling rates of

Previous studies have shown that the Kapoeta howardite, as well as several other meteorites, contains excess concentrations of cosmogenic Ne in the darkened, solar-irradiated phase compared to the light, non- irradiated phase. The two explanations offered for the nuclear production of these Ne excesses in the parent body regolith are either from galactic cosmic-ray proton (GCR) irradiation or from a greatly enhanced flux of energetic solar "cosmic-ray" protons (SCR), as compared to the recent solar flux. Combining new isotopic data we obtained on acid-etched, separated feldspar from Kapoeta light and dark phases with literature data, we show that the cosmogenic 21Ne/22Ne ratio of light phase feldspar (0.80) is consistent with only GCR ir- radiation in space for -3 Ma. However, the 21Ne/22Ne ratio (0.68) derived for irradiation of dark phase feld- spar in the Kapoeta regolith indicates that cosmogenic Ne was produced in roughly equal proportions from galactic and solar protons. Considering a simple model of an immature Kapoeta parent body regolith, the du- ration of this early galactic exposure was only -3-6 Ma, which would be an upper limit to the solar exposure time of individual grains. Concentrations of cosmogenic 21Ne in pyroxene separates and of cosmogenic 126Xe in both feldspar and pyroxene are consistent with this interpretation. The near-surface irradiation time of in- dividual grains in the Kapoeta regolith probably varied considerably due to regolith mixing to an average GCR irradiation depth of -10 cm. Because of the very different depth scales for production of solar -Fe tracks, SCR Ne, and GCR Ne, the actual regolith exposure times for average grains probably differed cor- respondingly. However, both the SCR *1Ne and solar track ages appear to be longer because of enhanced production by early solar activity. The SCWGCR production ratio of 21Ne inferred from the Kapoeta data is iarger by a at least a factor of 10 and possibly as much as a factor of -50 compared to recent solar particle fluxes. Thus, this study indicates that our early Sun was much more active and emitted a substantially higher flux of energetic (>lo MeVInucleon) protons.

Monomict eucrites Y792510 and Y791186 of pyroxene metamorphic type 6 contain areas of recrystallized mesostasis and granoblastic pyroxene. Textural comparisons suggest that the mesostasis areas in these eucrites originally resembled analogous areas in the pristine basaltic eucrite clast Y75011,84. 39Ar 40Ar ages were determined for microbreccias Y791186,87 and Y792510,62 and crystalline clast Y792510,65. The 39Ar 40Ar ages for Y791186,87 and Y792510,62 are identical within error limits at 3.46 ± 0.18 Ga and 3.40 ± 0.16 Ga (2σ), respectively. Both these samples were involved in an impact event in which Ar was quantitatively degassed 3.43 ± 0.10 Ga ago. Y792510,65 has an apparently older 39Ar 40Ar age of 3.60 ± 0.04 Ga (2σ) suggesting that it was degassed in a separate event, or to a lesser degree. Rb Sr and Sm Nd ages were determined for both Y792510 clasts. The Rb Sr age of 3.26 ± 0.24 Ga (2σ), for Y792510,65 was totally reset by the impact event(s), whereas the Rb Sr age of 4.26 ± 0.62 Ga (2σ) for Y792510,62 either was partially reset by the same event(s), or by earlier recrystallization of mesostasis. The 147Sm 143Nd age calculated for Y792510,65 including all data is 4.67 ± 0.22 Ga (2σ), but is likely to have been affected by weathering in the Antarctic. It becomes 4.57 ± 0.09 Ga if only data for the major minerals plagioclase and pyroxene are included in the isochron. The 147Sm 143Nd age of Y792510,62 is 4.34 ± 0.06 Ga (2σ) for the same mineral phases but may be biased by the presence of weathered Ca-phosphates in the pyroxene separate. The 146Sm 142Nd age of Y792510,65 is 4.42−0.06+0.04 Ga corresponding to initial 146Sm/144Sm= 0.0030 ± 0.0010 relative to (146Sm/144Sm)lew = 0.0076 ± 0.0009 for the LEW86010 angrite at 4.558 Ga ago. The Y792510,65 ages from the two Sm Nd chronometers are concordant at ∼4.48 Ga, which may be the crystallization age of this eucritic basalt (late crystallization). Alternatively, these Sm Nd ages may have been affected by the event in which Ca-phosphate and augite in mesostasis were recrystallized and augite and chromite in granoblastic areas were derived from cloudy pyroxenes (late recrystallization). The subsolidus recrystallization may be a consequence of a thermal spike in the midst of an otherwise monotonically cooling environment resulting from impact cratering of the hot crust of the newly formed eucrite parent body. Pyroxene homogenization probably occurred prior to formation of granoblastic pyroxene and close to the time of initial crystallization. Mn Cr data provide only a hint of live 53Mn (t1/2 = 3.7Ma) and imply either chromium isotopic equilibration after decay of 53Mn or late crystallization. Impact brecciation and lithification probably accompanied thermal annealing ∼3.4–3.6 Ga ago as given by the 39Ar-40Ar ages; the Rb Sr age of Y792510,65 is consistent with this interpretation. The 39Ar-40Ar and Rb Sr systematics of minute K-rich inclusions in plagioclase and pyroxene formed by previous impact and thermal annealing events probably were reset then. These young impact-metamorphic ages demonstrate that impact resetting of radiometric ages on the HED parent body (asteroid 4 Vesta?) occurred over an interval of at least 0.7 Ga.

We have conducted petrologic, chemical, and isotopic studies of lodranites in an attempt to constrain their genesis. Lodran, Gibson, Y-791491, Y-791493, Y-74357, Y-8002, Y-75274, MAC 88177, LEW 88280, EET 84302, FRO 90011, and QUE 93148 are classified as lodranites. Lodranites and acapulcoites are indistinguishable on the basis of oxygen isotopic compositions but are distinct in average grain sizes of their mafic silicates, with lodranites being significantly coarser-grained. Lodranites exhibit a diverse range of petrologic and mineralogic features: they range widely in mafic silicate compositions (Fa3–13), plagioclase (0–11.4 vol%), Fe,Ni metal (0.5–20 vol%), and troilite (0.2–5.3 vol%) contents; and shock levels (S1–S4) . They appear to have experienced high peak temperatures and rapid cooling in the temperature range recorded by metallographic cooling rates (i.e., 700-350°C). The only dated lodranite, Gibson, cooled to Ar closure temperatures at 4.49 ± 0.01 Ga. Lodranites formed from chemically and isotopically heterogeneous precursors in which the mineral and oxygen isotopic compositions were correlated. Heating of their parent body to temperatures between ∼ 1050–1200°C resulted in formation of Fe,NiFeS and basaltic partial melts. Depletions of troilite and/ or plagioclase in most lodranites testify to the removal of some of these partial melts, although melt migration was complex. Lodranites appear to have experienced a complex cooling history of slow cooling at high temperatures, followed by rapid cooling at intermediate temperatures, possibly related to breakup of the parent body. Lodranites were liberated from their parent body during 1–3 impact events, with most having cosmic ray exposure ages of 5.5–7 Ma. The acapulcoites are samples from the same parent body but were heated to lower temperatures and, thus, experienced lower degrees of partial melting.

We have conducted petrologic, chemical, and isotopic studies of acapulcoites (Acapulco, Monument Draw, Yamato 74063, ALH A77081, ALH A81261, ALH A81315, ALH 78230, ALH A81187 and ALH 84190) in an attempt to constrain their genesis. Acapulcoites have distinctly different oxygen isotopic compositions than silicate inclusions in IAB and IIICD irons, winonaites and ureilites and, thus, formed on a different parent body. Oxygen isotopic compositions, which are slightly heterogeneous within the group, overlap with lodranites, indicating a likely origin on a common parent body. These groups can be distinguished on the basis of mafic silicate grain size. All acapulcoites have mafic silicate compositions intermediate between E and H chondrites, roughly chondritic mineralogies, achondritic, equigranular textures, micrometer to centimeter sized veins of Fe,NiFeS which cross-cut silicate phases, rapid metallographic cooling rates at ∼600−400°C (103–105°C/Myr) and trapped noble gas abundances comparable to type 3–4 ordinary chondrites. They exhibit variable mafic silicate zoning, abundance of Fe,NiFeS veins, REE abundances and patterns and, possibly, cosmic ray exposure ages (∼5–7 Ma). Momument Draw and Yamato 74063 retain rare relict chondrules. Phosphates are associated with Fe,NiFeS veins or form separate veins in Monument Draw and Acapulco. Heating and cooling of acapulcoites occurred very early in the history of the Solar System, as evidenced by the 39Ar40Ar ages of ∼4.51 Ga. These ages appear distinctly younger than the likely formation time for Acapulco of 4.557 Ga, but are older than analogous 39Ar40Ar ages for most chondrites. Acapulcoites formed from a precursor chondrite which differs from known chondrites in mineral and oxygen isotopic compositions. Heating to ∼950–1000°C resulted in melting at the Fe,NiFeS cotectic, but silicates did not melt. Silicate textures resulted from extensive solid-state recrystallization. Heating was by noncollisional sources (e.g., 26Al, electromagnetic induction). Despite uncertainties owing to a lack of data, acapulcoites may have experienced a three-stage thermal history of slow cooling at high temperature, rapid cooling at intermediate temperatures, and slow cooling at low temperatures, possibly resulting from breakup and gravitational reassembly of the parent body. The complex thermal history is also reflected in disequilibrium REE abundances. One or at most two impact events (∼7 Ma and possibly ∼5 Ma ago) are consistent with the cosmic ray exposure ages of all four acapulcoites for which cosmogenic noble gas data exist.

We have performed petrologic and geochemical studies of five primitive achondrites: ALHA81187 and ALHA81261 (Acapulco-like), EET 84302 (transitional, but Acapulco-like), and LEW 88280 and MAC 88177 (Lodran-like). We have also performed 39Ar-40Ar chronology on ALHA81187, ALHA81261, and EET 84302. LEW 88280 and MAC 88177 contain more ferroan olivines, orthopyroxenes, clinopyroxenes, and chromites than do the Acapulco-like achondrites. Plagioclase is present in only ALHA81187, ALHA81261, and EET 84302. Its composition does not track that of the mafic silicates; EET 84302, with the most calcic plagioclase, contains olivine and pyroxene with an mg# intermediate between ALHA81187 and ALHA81261. Similarly, spinels in EET 84302 have the same mg# as those in ALHA81187, while pyroxenes in the former are more ferroan than in the latter. Acapulco-like achondrites have Sm/Sc ratios between 0.8–1.5 times H chondrites, and Na/Sc ratios are between 0.81.0 times H chondrites, indicating that silicate partial melts have not been lost from these rocks. Siderophile and chalcophile elements are fractionated and show a trend of increasing Ir/Ni ratios with decreasing Se/Co ratios. This variation is consistent with fractionation by partial melting in the Fe-Ni-S system. EET 84302 is very depleted in Se and troilite is a accessory phase, indicating essentially total loss of the low temperature Fe-Ni-S melt. In contrast, the Lodran-like achondrites are depleted in the highly incompatible lithophile elements relative to more compatible elements: Sm/Sc ratios are 0.2−0.7 times and Na/Sc ratios are 0.04–0.18 times H chondrites. These data are consistent with a model for formation of the Lodran-like achondrites as partial melting residues. However, the low Ir/Ni and high Se/Co ratios in two Lodran-like achondrites suggest the metal + troilite in these rocks is dominated by the low melting fraction in the Fe-Ni-S system. This metal + troilite was added to the silicates after partial melting depleted them in a basaltic fraction. The Ar-Ar release spectra yield good plateau ages of 4.507 ± 0.024 Ga (ALHA81187), 4.511 ± 0.007 Ga (ALHA81261), and 4.519 ± 0.017 Ga (EET 84302), in good agreement with previously determined Ar-Ar ages for other Acapulco-like achondrites. Together, the Ar-Ar ages demonstrate that metamorphism on the Acapulco-Lodran parent body occurred 4.51 ± 0.02 Ga ago, roughly 50 Ma after its formation. The geochemical and petrologic evidence on the Acapulco- and Lodran-like achondrites suggest that heating on the parent body was localized and heterogeneous in space and time. The parent body was probably not subjected to parent body-wide magmatism, in contrast to the case for 4 Vesta and the HED meteorites.

ACC NIM; International audience; SILHI (High Intensity Light Ion Source) is an ECR ion source producing high intensity proton ordeuteron beams at 95 keV. It is now installed in the IPHI site building, on the CEA/Saclay center. IPHI is a frontend demonstrator of high power accelerator. The source regularly delivers more than 130 mA protons in CWmode and already produced more than 170 mA deuterons in pulsed mode at nominal energy. The last beamcharacterisations, including emittance measurements, space charge compensation analysis and diagnosticimprovements, will be reported. Taking into account the SILHI experience, new developments are in progress tobuild and test a 5 mA deuteron source working in CW mode. This new source will also operate at 2.45 GHz andpermanent magnets will provide the magnetic configuration. This source, of which the design will be discussed,will have to fit in with the SPIRAL 2 accelerator developed at GANIL to produce Radioactive Ion Beams. TheH- test stand status is briefly presented here and detailed in companion papers.This work is partly supported by the European Commission under contract n°: HPRI-CT-2001-50021.

— Measured Ne isotopes in samples of shergottite ALHA77005 show variations in 21Ne/22Ne ratios and 21Ne abundances that are consistent with the presence of two cosmogenic components: a component produced by nuclear interactions of galactic cosmic rays (GCR) and a component produced at shallow shielding depths (∼0–3 cm) by energetic solar flare protons (SCR). We suggest that the 21Ne/22Ne ratio generally can be used to distinguish between SCR and GCR components in many meteorite types. Analysis of cosmogenic Ne produced in chondrite mineral separates, eucrites, and anorthositic lunar rocks, all having diverse major element compositions, indicate that the GCR 21Ne/22Ne ratio increases modestly with relative Mg content. Data for hundreds of chondrite analyses suggest that SCR Ne is present in no more than a very small fraction of chondrites. Examination of literature data for other shergottites, however, indicate that all of these meteorites contain SCR Ne but that it is apparently absent in other SNC meteorites. The ubiquitous presence of SCR Ne in shergottites, in contrast to most other types of meteorites, suggests that the martian origin of shergottites gave them different orbital parameters compared to other meteorites. This in turn may have contributed to slower entry velocities and lesser surface ablation in the atmosphere or even to higher SCR production rates.

We determined a 39 Ar 40 Ar age of 4.495 ± 0.015 Ga for the unbrecciated ibitira eucrite. This age ranks among the oldest 39 Ar 40 Ar ages for eucrites and suggests that Ibitira escaped the widespread impact resetting of KAr ages ∼4.1−3.5 Ga ago indicated by other HED meteorites. Ibitira exhibits a relatively high degree of chemical equilibration of its pyroxene caused by prolonged annealing. This equilibration must have occurred subsequent to the reported 207 Pb- 206 Pb formation age for Ibitira of 4.556–4.560 Ga, but prior to its determined ArAr age. If pyroxene equilibration occurred during burial at significant depths or in a large impact deposit, then the ArAr age may date this event.