The presence of shocked quartz is one of the key lines of evidence for the impact origin of rocks. Crystallographic orientations of planar deformation feature (PDF) sets in shocked quartz have been used to constrain the peak shock pressure that these grains have experienced. So far no systematic and comparative studies of the various orientation measurement methods and their biases are available. Therefore, three shocked-quartz-bearing thin sections from a meta-greywacke clast in breccia, a biotite-gneiss, and a sandstone, respectively, were independently analyzed by three operators (two experienced and one inexperienced) using a four-axis universal-stage (U-stage), in order to evaluate the quality, precision, repeatability, and representativeness of U-stage measurements. Based on the indexing of PDF sets using a new version of the commonly used stereographic projection template, the study of 1751 PDF set orientations in 666 quartz grains in three different shocked rocks shows that differences in abundance and orientation of various PDF sets, as measured by the three separate operators, are rather limited. The precision of U-stage measurements depends mainly on the number of PDF sets investigated, as the ability level of the operator (experienced versus inexperienced) is only responsible for minor deviations in the number of unindexed planes. The frequency percent of dominant PDF planes may vary by up to 20 percentage points (pp) or 81% for a given crystallographic orientation when only 25 sets are measured. When 100 PDF sets are measured, however, this deviation in dominant orientations is reduced to about 7 pp or 28%. We recommend the use of a new stereographic projection template, which plots the pole positions of five additional, commonly occurring PDF orientations, as it can allow indexing of up to 12 pp more PDF planes; these are planes that would previously be considered unindexed and potentially regarded as errors of measurement. Our results suggest that by following a strict measurement procedure, the reproducibility of Ustage measurements is good and the results of different studies can be readily compared. However, it is critical that published PDF orientation histograms clearly define what type of frequency measurement is used, whether or not unindexed PDF sets are included in the frequency calculations, the numbers of grains and sets analyzed, and the relative proportions of each PDF set population that are combined in the histograms. This information appears to be essential for effectively comparing datasets from different studies.

A quantitative analysis is presented for the irradiation contributions of the short-lived nuclides, specifically 26Al, by the X-wind scenario in the early solar system. The analysis is based on the comprehensive numerical simulations of the scenario that involves thermal processing of protoCAIs during the decades long X-wind cycle. It would be difficult to explain the canonical value of 26Al/27Al in Ca-Al-rich inclusions on the basis of its inferred irradiation yields. Hence, the bulk inventory of 26Al in the early solar system was not produced by the X-wind scenario. We suggest the predominant occurrence of gradual flares compared to impulsive flares in the early solar system as in the case of the modern solar flares. One tenth of the bulk 26Al was only produced by irradiation in case the entire solar inventory of 10Be was produced by local irradiation. The bulk 26Al inventory along with 60Fe was probably synthesized by a massive star. We present a qualitative model of the astrophysical settings for the formation of the solar system on the basis of a survey of the presently active star forming regions. We hypothesize that the formation of the solar system could have occurred almost contemporaneously with the formation of the massive star within a single stellar cluster. As the massive star eventually exploded as supernova Ib/c subsequent to Wolf-Rayet stages, the short-lived nuclides were probably injected into the solar proto-planetary disc. The dynamically evolving stellar cluster eventually dispersed within the initial ~10 million years prior to the major planetary formation episodes.

Two assumptions commonly employed in meteorite interpretation are that fusion crust compositions represent the bulk-rock chemistry of the interior meteorite and that the vesicles within the fusion crust result from the release of implanted solar wind volatiles. Electron microprobe analyses of thin sections from lunar meteorite Miller Range (MIL) 05035 and eucrite Bates Nunataks (BTN) 00300 were performed to determine if the chemical compositions of the fusion crust varied and/or represented the published bulk rock composition. It was determined that fusion crust compositions are significantly influenced by the incorporation of fragments from the substrate, and by the composition and grain size of those minerals. Because of compositional heterogeneities throughout the meteorite, one cannot assume that fusion crust composition represents the bulk rock composition. If the compositional variability within the fusion crust and mineralogical differences among thin sections goes unnoticed, then the perceived composition and petrogenetic models of formation will be incorrect. The formation of vesicles within these fusion crusts were also compared to current theories attributing vesicles to a solar wind origin. Previous work from the STONE-5 experiment, where terrestrial rocks were exposed on the exterior of a spacecraft heatshield, produced a vesicular fusion crust without prolonged exposure to solar wind suggesting that the high temperatures experienced by a meteorite during passage through the Earths atmosphere are sufficient to cause boiling of the melt. Therefore, the assumption that all vesicles found within a fusion crust are due to the release of implanted volatiles of solar wind may not be justified.

We report the results of an extensive study of the Fountain Hills chondritic meteorite. This meteorite is closely related to the CBa class. Mineral compositions and O-isotopic ratios are indistinguishable from other members of this group. However, many features of Fountain Hills are distinct from the other CB chondrites. Fountain Hills contains 23 volume percent metal, significantly lower than other members of this class. In addition, Fountain Hills contains porphyritic chondrules, which are extremely rare in other CBa chondrites. Fountain Hills does not appear to have experienced the extensive shock seen in other CB chondrites. The chondrule textures and lack of fine-grained matrix suggests that Fountain Hills formed in a dust-poor region of the early solar system by melting of solid precursors. Refractory siderophiles and lithophile elements are present in near-CI abundances (within a factor of two, related to the enhancement of metal). Moderately volatile and highly volatile elements are significantly depleted in Fountain Hills. The abundances of refractory siderophile trace elements in metal grains are consistent with condensation from a gas that is reduced relative to solar composition and at relatively high pressures (10^(-3) bars). Fountain Hills experienced significant thermal metamorphism on its parent asteroid. Combining results from the chemical gradients in an isolated spinel grain with olivine-spinel geothermometry suggests a peak temperature of metamorphism between 535 degrees C and 878 degrees degrees C, similar to type-4 ordinary chondrites.

Here we report the petrography, mineralogy, and bulk compositions of Ca,Al-rich inclusions(CAIs), amoeboid olivine aggregate (AOA), and Al-rich chondrules (ARCs) in Sayh al Uhaymir (SaU) 290 CH chondrite. Eighty-two CAIs (0.1% of the section surface area) were found. They are hibonite-rich (9%), grossite-rich (18%), melilite +/- spinel-rich (48%), fassaite +/- spinel-rich (15%), and fassaite-anorthite-rich (10%) refractory inclusions. Most CAIs are rounded in shape and small in size (average = 40 micrometers). They are more refractory than those of other groups of chondrites. CAIs in SaU 290 might have experienced higher peak heating temperatures, which could be due to the formation region closer to the center of protoplanetary disk or have formed earlier than those of other groups of chondrites. In SaU 290, refractory inclusions with a layered texture could have formed by gas-solid condensation from the solar nebula and those with an igneous texture could have crystallized from melt droplets or experienced subsequent melting of pre-existing condensates from the solar nebula. One refractory inclusion represents an evaporation product of pre-existing refractory solid on the basis of its layered texture and melting temperature of constituting minerals. Only one AOA is observed (75 micrometers across). It consists of olivine, Al-diopside, anorthite, and minor spinel with a layered texture. CAIs and AOA show no significant low-temperature aqueous alteration. ARCs in SaU 290 consist of diopside, forsterite, anorthite, Al-enstatite, spinel, and mesostasis or glass. They can be divided into diopsiderich, Al-enstatite-rich, glass-rich, and anorthite-rich chondrules. Bulk compositions of most ARCs are consistent with a mixture origin of CAIs and ferromagnesian chondrules. Anorthite and Al-enstatite do not coexist in a given ARC, implying a kinetic effect on their formation.