We have measured the titanium isotopic compositions of 23 silicon carbide grains from the Orgueil (CI) carbonaceous chondrites for which isotopic compositions of silicon, carbon, and nitrogen and aluminum-magnesium systematics had been measured previously. Using the 16 mostprecise measurements, we estimate the relative contributions of stellar nucleosynthesis during the asymptotic giant branch (AGB) phase and the initial compositions of the parent stars to the compositions of the grains. To do this, we compare our data to the results of several published stellar models that employ different values for some important parameters. Our analysis confirms that s-process synthesis during the AGB phase only slightly modified the titanium compositions in the envelopes of the stars where mainstream silicon carbide grains formed, as it did for silicon. Our analysis suggests that the parent stars of the >1 micrometer silicon carbide grains that we measured were generally somewhat more massive than the Sun (2-3 M(sun)) and had metallicities similar to or slightly higher than solar. Here we differ slightly from results of previous studies, which indicated masses at the lower end of the range 1.5-3 M(sun) and metallicities near solar. We also conclude that models using a standard 13C pocket, which produces a good match for the main component of s-process elements in the solar system, overestimate the contribution of the 13C pocket to s-process nucleosynthesis of titanium found in silicon carbide grains. Although previous studies have suggested that the solar system has a significantly different titanium isotopic composition than the parent stars of silicon carbide grains, we find no compelling evidence that the Sun falls off of the array defined by those stars. We also conclude that the Sun does lie on the low-metallicity end of the silicon and titanium arrays defined by mainstream silicon carbide grains.

A devitrified glass inclusion from the Guin (UNGR) iron consists of cryptocrystalline feldspars, pyroxenes, and silica and is rich in SiO2, Al2O3, and Na2O. It contains a rutile grain and is in contact with a large Cl apatite. The latter is very rich in rare earth elements (REEs) (~80 x CI), which display a flat abundance pattern, except for Eu and Yb, which are underabundant. The devitrified glass is very poor in REEs (<0.1 x CI), except for Eu and Yb, which have positive abundance anomalies. Devitrified glass and Cl apatite are out of chemical equilibrium and their complementary REE patterns indicate a genesis via condensation under reducing conditions. Inclusion 1 in the Kodaikanal (IIE) iron consists of glass only, whereas inclusion 2 consists of clinopyroxene, which is partly overgrown by low-Ca pyroxene, and apatite embedded in devitrified glass. All minerals are euhedral or have skeletal habits indicating crystallization from the liquid precursor of the glass. Pyroxenes and the apatite are rich in trace elements, indicating crystallization from a liquid that had 1050 CI abundances of REEs and refractory lithophile elements (RLEs). The co-existing glass is poor in REEs (~0.1-1 x CI) and, consequently, a liquid of such chemical composition cannot have crystallized the phenocrysts. Glasses have variable chemical compositions but are rich in SiO2, Al2O3, Na2O, and K2O as well as in HFSEs, Be, B, and Rb. The REE abundance patterns are mostly flat, except for the glass-only inclusion, which has heavy rare earth elements (HREEs) light rare earth elements (LREEs) and deficits in Eu and Yb—an ultrarefractory pattern. The genetic models suggested so far cannot explain what is observed and, consequently, we offer a new model for silicate inclusion formation in IIE and related irons. Nebular processes and a relationship with E meteorites (Guin) or Ca-Al-rich inclusions (CAIs) (Kodaikanal) are indicated. A sequence of condensation (CaS, TiN or refractory pyroxene-rich liquids) and vapor-solid elemental exchange can be identified that took place beginning under reducing and ending at oxidizing conditions (phosphate, rutile formation, alkali and Fe^2+ metasomatism, metasomatic loss of REEs from glasses).

We have used a variety of complementary microanalytical techniques to constrain the mineralogy, trace-element distributions, and oxygen-isotopic compositions in a 50 x 50 micrometer area of Acfer 094 matrix. The results reveal the exceptional mineralogical and compositional heterogeneity of this material at the sub-m level. We observe micrometer-scale and sub-micrometer grains with elemental associations suggesting feldspar, metal with widely varying Ni contents, and a Cr-Fe alloy (in addition to forsterite, pyroxene, sulfide, ferrihydrite, and amorphous groundmass previously described). A new class of micrometer-scale CAI (micro-CAI) is also observed, which show sub-m compositional zoning, and a range of oxygen isotopic compositions. Unlike the larger CAIs in Acfer 094, which are uniformly 16O-enriched, two of the three CAIs we analyzed are isotopically normal. We also observed a Li-rich hotspot that detailed analysis by ToF-SIMS suggests may be a LiCr-oxide grain. Within the resolution of the NanoSIMS, this grain has isotopically normal Li. Finally, in our 50 x 50 micrometer area, we positively identified a presolar grain that is the most 18O-rich silicate found so far in meteorites. The grain may originate from an asymptotic giant branch (AGB) star, or more likely, a supernova. In line with previous TEM studies (Greshake 1997), we find no evidence for clastic material (e.g., fragmental chondrules) in the matrix of Acfer 094: although the matrix is volatile-depleted, this depletion does not appear to result from dilution of a primordial starting material with (depleted) chondrule fragments. Assuming that matrix experienced the depletion event, our data on the detailed mineralogy of Acfer 094 are currently equivocal in constraining the nature of that event. We observe carrier phases for several elements consistent with conditions approaching equilibrium condensation; however, the presence of an amorphous groundmass is suggestive of more rapid cooling.

We performed a comprehensive study of the He, Ne, and Ar isotopic abundances and of the chemical composition of bulk material and components of the H chondrites Dhajala, Bath, Cullison, Grove Mountains 98004, Nadiabondi, Ogi, and Zag, of the L chondrites Grassland, Northwest Africa 055, Pavlograd, and Ladder Creek, of the E chondrite Indarch, and of the degrees C chondrites Hammadah al Hamra 288, Acfer 059, and Allende. We discuss a procedure and necessary assumptions for the partitioning of measured data into cosmogenic, radiogenic, implanted, and indigenous noble gas components. For stone meteorites, we derive a cosmogenic ratio 20Ne/22Ne of 0.80 +/- 0.03 and a trapped solar 4He/3He ratio of 3310 +/- 130 using our own and literature data. Chondrules and matrix from nine meteorites were analyzed. Data from Dhajala chondrules suggest that some of these may have experienced precompaction irradiation by cosmic rays. The other chondrules and matrix samples yield consistent cosmic-ray exposure (CRE) ages within experimental errors. Some CRE ages of some of the investigated meteorites fall into clusters typically observed for the respective meteorite groups. Only Baths CRE age falls on the 7 Ma double-peak of H chondrites, while Ogis fits the 22 Ma peak. The studied chondrules contain trapped 20Ne and 36Ar concentrations in the range of 10^(-6)-10^(-9) cm^3 STP/g. In most chondrules, trapped Ar is of type Q (ordinary chondritic Ar), which suggests that this component is indigenous to the chondrule precursor material. The history of the Cullison chondrite is special in several respects: large fractions of both CR-produced 3He and of radiogenic 4He were lost during or after parent body breakup, in the latter case possibly by solar heating at small perihelion distances. Furthermore, one of the matrix samples contains constituents with a regolith history on the parent body before compaction. It also contains trapped Ne with a 20Ne/22Ne ratio of 15.5 +/- 0.5, apparently fractionated solar Ne.

We describe a focused ion beam scanning electron microscope (FIB-SEM) technique that enables coordinated isotopic and mineralogic analysis of planetary materials. We show that site specific electron-transparent sections can be created and extracted in situ using a microtweezer and demonstrate that they are amenable to analysis by secondary ion mass spectrometry (SIMS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). These methods greatly advance the ability to address several fundamental questions in meteoritics, such as accretion and alteration histories of chondrules and the origin and history of preserved nebular and presolar materials.

We measured 36Cl-36S and 26Al-26Mg systematics and O isotopes of secondary phases in a moderately altered type B2 CAI (CAI#2) from the Allende CV3 chondrite. CAI#2 has two distinct alteration domains: the anorthite-grossular (An-Grs) domain that mostly consists of anorthite and grossular, and the Na-rich domain that mostly consists of sodalite, anorthite, and Fe-bearing phases. Large 36S excesses (up to ~400) corresponding to an initial 36Cl/35Cl ratio of (1.4 +/- 0.3) x 10^(-6) were observed in sodalite of the Na-rich domain, but no resolvable 26Mg excesses were observed in anorthite and sodalite of the Na-rich domain (the initial 26Al/27Al ratio 4.4 x 10^(-7)). If we assume that the 36Cl-36S and the 26Al-26Mg systematics were closed simultaneously, the 36Cl/35Cl ratio would have to be on the order of ~10^(-2) when CAIs were formed. In contrast to sodalite in Na-rich domain, significant 26Mg excesses (up to ~35 ppm) corresponding to an initial 26Al/27Al ratio of (1.2 +/- 0.2) x 10^(-5) were identified in anorthite of the An-Grs domain. The 26Al-26Mg systematics of secondary phases in CAI#2 suggest that CAIs experienced multiple alteration events. Some of the alteration processes occurred while 36Cl (half-life is 0.3 Myr) and 26Al (half-life is 0.72 Myr) were still alive, whereas others took place much later. Assuming that 26Al was homogeneously distributed in the solar nebula, our study implies that alteration of CAIs occurred as early as within 1.5 Myr of CAI formation and as late as 5.7 Myr after.

High-precision Mg isotopic compositions of Ca-Al-rich inclusions (CAIs) from both Ningqiang (ungrouped) and Allende (CV3) carbonaceous chondrites and amoeboid olivine aggregations (AOAs) from Allende were analyzed by multicollector inductively coupled plasma mass spectrometry (MC-ICP-MS). The CAIs from Allende plot on a line, with an inferred initial 26Al/ 27Al ratio of (4.77 +/- 0.39) 10^(-5) close to the canonical value. This indicates a relatively closed Al-Mg system in the CAIs and no significant Mg isotope exchange with ambient materials, although two of the CAIs are severely altered. The AOAs contain excess 26Mg and plot close to the CAI regression line, which is suggestive of their contemporary formation. The CAIs from Ningqiang define a different line with a lower inferred (26Al/27Al)0 ratio of (3.56 +/- 0.08) 10^(-5). None of the CAIs and AOAs studied in this work shows significant mass fractionation with enrichment of the heavier Mg isotopes, arguing against an evaporation origin.

Forty-three corundum grains (1-11 micrometers in size) and 5 corundum-hibonite grains with corundum overgrown by hibonite (4-7 micrometers in size), were found in the matrix of the mineralogically pristine, ungrouped carbonaceous chondrite Acfer 094 by using cathodoluminescence imaging. Some of the corundum and corundum-hibonite grains occur as aggregates of 2 to 6 grains having similar sizes. The oxygen isotopic compositions of some of the corundum-bearing grains suggest their solar nebula origin. 26Al-26Mg systematics of one corundum grain showed the canonical initial 26Al/27Al ratio, also suggesting a solar nebula origin. Quantitative evaluation of condensation and accretion processes made based on the homogeneous nucleation of corundum, diffusion-controlled hibonite formation, collisions of grains in the nebula, and critical velocity for sticking, indicates that, in contrast to the hibonite-bearing aggregates of corundum grains, the hibonite-free corundum aggregates could not have formed in the slowly cooling nebular region with solar composition. We suggest instead that such aggregates formed near the protosun, either in a region that stayed above the condensation temperature of hibonite for a long time or in a chemically fractionated, Ca-depleted region, and were subsequently physically removed from this hot region, e.g., by disk wind.

Textures, mineral assemblages, and Al-Mg isotope systematics indicate a protracted, episodic secondary mineralization history for Allende Ca-Al-rich inclusions (CAIs). Detailed observations from one type B1 CAI, one B2, one compact type A (CTA), and one fluffy type A (FTA) indicate that these diverse types of CAIs are characterized by two distinct textural and mineralogic types of secondary mineralization: (1) grossular-rich domains, concentrated along melilite grain boundaries in CAI interiors, and (2) feldspathoid-bearing domains, confined mostly to CAI margins just interior to the Wark-Lovering rim sequence. The Al-Mg isotopic compositions of most secondary minerals in the type B1 CAI, and some secondary minerals in the other CAIs, show no resolvable excesses of 26Mg, whereas the primary CAI phases mostly yield correlated excesses of 26Mg with increasing Al/Mg corresponding to canonical initial 26Al/27Al ~ 4.55 10^(-5). These secondary minerals formed at least 3 Ma after the primary CAI minerals. All but two analyses of secondary minerals from the fluffy type-A CAI define a correlated increase in 26Mg/24Mg with increasing Al/Mg, yielding (26Al/27Al)0 = (4.9 +/- 2.8) 10^(-6). The secondary minerals in this CAI formed 1.8-3.2 Ma after the primary CAI minerals. In both cases, the timing of secondary alteration is consistent with, but does not necessarily require, alteration in an asteroidal setting. One grossular from the type B2 CAI, and several grossular and secondary feldspar analyses from the compact type A CAI, have excesses of 26Mg consistent with initial 26Al/27Al ~ 4.5 10^(-5). Especially in the compact type A CAI, where 26Mg/24Mg in grossular correlates with increasing Al/Mg, these 26Mg excesses are almost certainly due to in situ decay of 26Al. They indicate a nebular setting for formation of the grossular. The preservation of these diverse isotopic patterns indicates that heating on the Allende parent body was not pervasive enough to reset isotopic systematics of fine-grained secondary minerals. Secondary mineralization clearly was not restricted to a short time interval, and at least some alteration occurred coincident with CAI formation and melting events (chondrule formation) in the nebula. This observation supports the possibility that alteration followed by melting affected the compositional evolution of CAIs.

Gamma rays from radioactive byproducts of cosmic nucleosynthesis are direct messengers from nuclear processes taking place in various cosmic sites, and can be measured with telescopes operated in space. Due to low detector sensitivity, up until now, only a handful of sources have been detected in that electromagnetic window. Cobalt lines from SN1987A and 44Ti lines from the Cassiopeia A (Cas A) supernova remnant offer unique constraints on the properties of the innermost regions of core collapse supernovae. Diffuse gamma-ray lines from the decay of radioactive 26Al and the annihilation of positrons are bright enough for mapping the Milky Way in the MeV regime, and are both measured by recent spaceborne spectrometers with unprecedented precision. This constrains the sources of Al production and the state of interstellar gas in the vicinity of these sites: the total mass of 26Al produced by stellar sources throughout the Galaxy is estimated to be ~3 M(sun) per Myr, and the interstellar medium near those sources appears to be characterized by velocities of ~100 km s^(-1). Positron annihilation must occur in a modestly ionized, warm phase of the interstellar medium, but at present the major positron production site(s) remain unknown. The spatial distribution of the annihilation gamma-ray emission constrains positron production sites and positron propagation in the Galaxy. 60Fe radioactivity has been clearly detected recently; the flux ratio relative to 26Al of about 15% is on the lower side of predictions from massive star and supernova nucleosynthesis models. Those views at nuclear and astrophysical processes in and around cosmic sources by space-based gamma-ray telescopes offer invaluable information on cosmic nucleosynthesis.