Dar al Gani 872 (DaG 872) is a new meteorite from Libya that we classified by means of Instrumental Neutron Activation Analysis (INAA), electron microprobe, and optical microscopy. According to our results, DaG 872 is a Mg-rich main group eucrite, i.e., a monomict noncumulate basaltic eucrite displaying a predominant coarse-grained relict subophitic and a fine-grained granulitic texture. The meteorite also shows pockets of late-stage mesostasis and is penetrated by several calcite veins due to terrestrial weathering. Finally, it exhibits shock phenomena of stage 1-2 including heavily fractured mineral components, undulose extinction of plagioclase, kinked lamellae, and mosaicism in pyroxenes corresponding to peak pressures of ~20 GPa. In view of petrographic criteria as well as compositional and exsolution characteristics of its pyroxenes, the sample represents a metamorphic type 5 eucrite. Assuming the metamorphic type to be a function of burial depth on the parent body and taking into account the relatively high shock stage, the excavation of DaG 872 was likely induced by a major impact event. Prior to this point, DaG 872 apparently underwent a 4-stage geological evolution that is reflected by intricate textural and mineralogical features.

Noble gases in two ureilites, Kenna and Allan Hills (ALH) 78019, were measured with two extraction methods: mechanical crushing in a vacuum and heating. Large amounts of noble gases were released by crushing, up to 26.5% of 132Xe from ALH 78019 relative to the bulk concentration. Isotopic ratios of the crush-released Ne of ALH 78019 resemble those of the trapped Ne components determined for some ureilites or terrestrial atmosphere, while the crush-released He and Ne from Kenna are mostly cosmogenic. The crush-released Xe of ALH 78019 and Kenna is similar in isotopic composition to Q gas, which indicates that the crush-released noble gases are indigenous and not caused by contamination from terrestrial atmosphere. In contrast to the similarities in isotopic composition with the bulk samples, light elements in the crush-released noble gases are depleted relative to Xe and distinct from those of each bulk sample. This depletion is prominent especially in the 20Ne/132Xe ratio of ALH 78019 and the 36Ar/132Xe ratio of Kenna. The values of measured 3He/ 21Ne for the gases released by crushing are significantly higher than those for heating-released gases. This suggests that host phases of the crush-released gases might be carbonaceous because cosmogenic Ne is produced mainly from elements with a mass number larger than Ne. Based on our optical microscopic observation, tabular-foliated graphite is the major carbon mineral in ALH 78019, while Kenna contains abundant polycrystalline graphite aggregates and diamonds along with minor foliated graphite. There are many inclusions at the edge and within the interior of olivine grains that are reduced by carbonaceous material. Gaps can be seen at the boundary between carbonaceous material and silicates. Considering these petrologic and noble gas features, we infer that possible host phases of crush-released noble gases are graphite, inclusions in reduction rims, and gaps between carbonaceous materials and silicates. The elemental ratios of noble gases released by crushing can be explained by fractionation, assuming that the starting noble gas composition is the same as that of amorphous carbon in ALH 78019. The crush-released noble gases are the minor part of trapped noble gases in ureilites but could be an important clue to the thermal history of the ureilite parent body. Further investigation is needed to identify the host phases of the crush-released noble gases.

We have measured the elemental abundances and isotopic compositions of noble gases in Muong Nong-type tektites from the Australasian strewn field by crushing and by total fusion of the samples. We found that the abundances of the heavy noble gases are significantly enriched in Muong Nong-type tektites compared to those in normal splash-form tektites from the same strewn field. Neon enrichments were also observed in the Muong Nong-type tektites, but the Ne/Ar ratios were lower than those in splash-form tektites because of the higher Ar contents in the former. The absolute concentrations of the heavy noble gases in Muong Nong-type tektites are similar to those in impact glasses. The isotopic ratios of the noble gases in Muong Nong-type tektites are mostly identical to those in air, except for the presence of radiogenic 40Ar. The obtained K-Ar ages for Muong Nong-type tektites were about 0.7 Myr, similar to ages of other Australasian tektites. The crushing experiments suggest that the noble gases in the Muong Nong-type tektites reside mostly in vesicles, although Xe was largely affected by adsorbed atmosphere after crushing. We used the partial pressure of the heavy noble gases in vesicles to estimate the barometric pressure in the vesicles of the Muong Nong-type tektites. Likely, Muong Nong-type tektites solidified at the altitude (between the surface and a maximum height of 8-30 km) lower than that for splash-form tektites.

Clasts of alkaline (the second find in meteorites) and subalkaline rocks were found in the Kaidun meteorite. One of them (#d4A) is a large crystal of albite with inclusions of fluorapatite, arfvedsonite, aenigmatite, and wilkinsonite. The two latter minerals were previously unknown in meteorites. Another clast (#d[3-5]D) has a melt crystallization texture of mainly feldspar (oligoclase) composition and contains relict grains of both high-Ca and low-Ca pyroxene and fluorapatite. The mineralogical characteristics of these clasts suggest a genetic relationship and an origin from the same parent body. The textural and mineralogical characteristics of the clasts indicate origin by extensive igneous differentiation. Such processes most likely took place in a rather large differentiated body. The material of clast #d(3-5)D is similar in some mineralogical respects to basaltic shergottites.

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 greater than or equal to 800 degrees 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.