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We have performed in situ analyses of Li-Be-B and Al-Mg isotope systematics, and abundances of rare earth elements (REEs) in two Ca-Al-rich inclusions (CAIs) from the Ornans-like carbonaceous chondrite Yamato-81020 (CO3.05). The present CO CAIs are depleted in ultra-refractory heavy REEs (group II REE pattern), suggesting condensation of these CAIs or their precursors from the solar nebula. Initial 26Al/27Al ratios, (26Al/27Al)0, of these CO CAIs are found to be (4.8 ± 0.5) × 10–5 and (4.9 ± 0.3) × 10–5 (95% confidence), indicating their contemporaneous formation with a majority of CAIs from Vigarano-like carbonaceous (CV) chondrites. Melilite grains in the present CO CAIs show clear excesses in 10B, ranging from ∼370 to ∼4300‰ relative to the chondritic B isotopic composition, which are correlated well with 9Be/11B ratios. The correlation indicates in situ decay of 10Be in the present CO CAIs and yields initial 10Be/9Be ratios, (10Be/9Be)0, for the individual CAIs of (2.9 ± 0.6) × 10–3 and (2.2 ± 1.0) × 10–3 (95% confidence), which are significantly greater than the average (10Be/9Be)0 = ∼0.7 × 10–3 recorded in CAIs from CV chondrites. The apparent variation in (10Be/9Be)0 between the CO and CV CAIs, despite having indistinguishable (26Al/27Al)0 of ∼5 × 10–5, provides evidence for heterogeneous distribution of 10Be in the CAI forming-regions at the very beginning of the Solar System. The elevated (10Be/9Be)0 and group II REE patterns in the CO CAIs may reflect that compared with the CV CAIs having unfractionated REEs the present CO CAIs have formed closer to the Sun where 10Be was produced more efficiently through solar cosmic ray irradiation caused by solar flares. Alternatively, if the present CO CAIs and CV CAIs formed in the same region, and 26Al was distributed homogeneously at the CAI-forming region, our results indicate that solar cosmic ray fluxes at the forming region have fluctuated by a factor of six within a short duration (∼0.2 million years) inferred from the Al-Mg chronology.

Oxygen isotope ratios and corresponding 26Al–26Mg isotope systematics of refractory inclusions from the least metamorphosed carbonaceous chondrites, Acfer 094 (C-ungrouped 3.00) and Yamato 81020 (CO3.05), were measured with an ion microprobe. Most of the samples are fine-grained refractory inclusions which are considered as condensates from high temperature solar nebular gas. The refractory inclusions consistently exhibit 16O-enriched signatures among their interior phases (spinel, melilite, and high-Ca pyroxene), as well as phases within their rim structures (spinel, high-Ca pyroxene, and adjacent anorthite). This observation indicates that aggregated refractory condensates and the formation of rim structures occurred in the same 16O-rich environment. Evidence for mass-dependent isotopic fractionation in oxygen and magnesium, which would indicate a later flash heating process, was not observed in rims. All oxygen isotope data from fine-grained CAIs are distributed between the Carbonaceous Chondrite Anhydrous Mineral (CCAM) line and the Primitive Chondrule Mineral (PCM) regression line based on oxygen isotope data from the Acfer 094 chondrules. The inferred initial 26Al/27Al ratios, (26Al/27Al)0, of spinel-melilite-rich CAIs are (4.08 ± 0.75) × 10−5 to (5.05 ± 0.18) × 10−5 (errors are 2σ), which are slightly lower than the canonical value of 5.25 × 10−5. As there is no petrologic evidence for re-melting after condensation, the lower (26Al/27Al)0 values of these CAIs indicate either they formed up to ∼0.3 Ma after canonical CAIs or they formed before 26Al was homogeneously distributed in the solar nebula. A pyroxene-anorthite-rich CAI, G92, has an 16O-rich signature like other CAIs but also has an order-of-magnitude less 26Mg-excess in anorthite, corresponding to a (26Al/27Al)0 of (5.21 ± 0.54) × 10−6. As there is no evidence for a later Mg isotopic disturbance, G92 anorthite is interpreted to have formed by interaction with 16O-rich nebular gas at 2–3 Ma after CAI formation. With the observation that 16O-rich refractory inclusions, relatively 16O-poor chondrules, and extremely 16O-poor cosmic symplectites within Acfer 094 all plot on the PCM line, it suggests that 16O-rich nebular gas and extremely 16O-poor primordial volatiles represent mass-independent fractionated endmembers in the early solar system and that the PCM line represents a mixing line of these two endmembers.

We report mineral assemblages from three clasts in the Northwest Africa 801 CR chondrite. The clasts, 1–3 mm in size, are ellipsoidal to irregular shaped, and show similar granular texture. The constituent minerals in the clasts are omphacite-rich clinopyroxene and pyrope-rich garnet, in addition to olivine and orthopyroxene. The omphacite contains jadeite (34 mol%) and diopside-hedenbergite (37%), and a significant amount of an enstatite-ferrosilite component (19%), which distinguishes it from terrestrial omphacite. The omphacite has a disordered C 2/ c structure. Graphite, phlogopite, chlorapatite, Fe-Ni metal, troilite, and pentlandite are present as minor minerals in the clasts. The minerals commonly found in chondrites, such as plagioclase and spinel group minerals, are not found in these clasts. Aluminum and sodium in the clasts are completely partitioned into omphacite and garnet. The mineral assemblages and compositions of the clasts are similar to those in terrestrial eclogite, except for the occurrence of olivine and some mineral chemistry, and this is the first discovery of an extraterrestrial eclogitic mineral assemblage. The clasts formed under high-pressure conditions, 2.8–4.2 GPa and 940–1080 °C, as estimated from a set of conventional geothermobarometers, indicative of formation in a large parent body. Another possibility is impact-induced origin, although the formation conditions would have been different from those for known shock veins. Meteorites usually consist of minerals that formed under low-pressure conditions, except for ultrahigh-pressure minerals found in shock veins. However, this study suggests that the pressure conditions for meteorite formation vary much wider than previously understood.

Ion microprobe analyses of rare earth elements (REEs), Ba, and Hf were performed for various types of refractory inclusions including amoeboid olivine aggregates (AOAs) from the Ningqiang ungrouped carbonaceous chondrite to search for possible relationships between REE abundance patterns and bulk chemical compositions of the inclusions. Four types of CI-normalized REE patterns were recognized: (1) nearly flat (unfractionated) pattern with or without Eu (and Yb) anomalies (Groups I, III, or V), (2) depletions of ultrarefractory heavy REEs (HREEs) relative to light REEs (LREEs), and depletions of Eu and Yb ( Group II , but without depletion of Yb in some cases), (3) depletions of ultrarefractory HREEs with positive anomalies in Ce, (Eu), and Yb ( Modified Group II ), and (4) nearly flat pattern with positive anomalies in Ce, (Eu), and Yb ( Modified Group I ). No systematic correlation was found between bulk chemical compositions and REE patterns of the inclusions. This suggests that the observed REE fractionations occurred prior to condensation of major elements (e.g., Mg and Si) which defined bulk chemical compositions of the inclusions. It is remarkable that 7 out of 19 inclusions show positive anomalies in Ce, Yb, and in some cases, Eu as well (Modified Group I and Modified Group II), suggesting that such anomalies are rather common among inclusions in the Ningqiang and possibly in other primitive meteorites. Two possible mechanisms are considered for the formation of Modified Group II and Modified Group I patterns. In Model 1 , Modified Group II is formed by a process similar to that produced Group II but removal of ultrarefractory dust occurred at slightly lower temperatures, where not only ultrarefractory HREEs but some fraction of LREEs had been condensed and removed from the system. Modified Group I may be explained by addition of an unfractionated component to the Modified Group II component, or alternatively, by partial removal of ultrarefractory dust from the system. In Model 2 , Modified Group II is formed by later addition of Ce, (Eu), and Yb onto fine-grained dust or inclusions having HREE-depleted, Group II-like REE patterns. Similarly, Modified Group I is explained by later addition of Ce, (Eu), and Yb onto those with almost unfractionated REE patterns. The observed REE data show that both the degree of HREE-depletion (e.g., Er-depletion) and that of fractionation among HREEs (e.g., depletion in the Er/Gd ratio) for Modified Group II are very similar to those for Group II. Model 1 predicts almost complete removal of ultrarefractory HREEs from the system, resulting in much higher HREE-depletion for Modified Group II, which is not consistent with the present observations. Addition of an unfractionated component may explain moderate depletion of HREEs in Modified Group II, but it will diminish fractionation among HREEs, which is not consistent with the present observations. In contrast, Model 2 predicts no correlations between Ce–(Eu)–Yb-enrichment and HREE-depletion or between Ce–(Eu)–Yb-enrichment and fractionation among HREEs, consistent with the present observations. Hence, Model 2 seems more likely. If this is the case, at least two distinct regions with different REE characteristics are required for the formation of Modified Group II inclusions: one is a high temperature region where Group II-like (HREE-depleted) inclusions or their precursors are formed by condensation from a fractionated gas after removal of ultrarefractory dust, and another is a low temperature region enriched in Ce, Eu, and Yb in the gas phase. Abundant occurrence of positive Ce–(Eu)–Yb anomalies suggests that migration of solid materials from one region to another occurs rather frequently in the solar nebula. The most likely place satisfying such conditions for the formation of these inclusions may be the innermost part of the protoplanetary disk.

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‰) 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.

We found a unique hibonite (CaAl 12 O 19 ) inclusion Kz1–2 from the Kainsaz (CO3) chondrite, which exhibits evidence for a strong link between “normal” CAIs and FUN inclusions. Kz1–2 shows strongly fractionated isotopic compositions of O, Ca, and Ti preferring heavy isotopes and a characteristic REE abundance pattern similar to those of FUN (or HAL-type hibonite) inclusions, suggesting an intensive distillation process in the formation of this inclusion. Unlike FUN inclusions, however, Kz1–2 shows large excesses in 26 Mg and possibly in 41 K most likely from the decays of now-extinct nuclides 26 Al and 41 Ca with the inferred initial ratios of ( 26 Al/ 27 Al) 0 ∼ 5.3 × 10 − 5 and ( 41 Ca/ 40 Ca) 0 ∼ 1.1 × 10 − 8 , respectively, and no detectable mass-independent isotopic anomalies in Ca and Ti, both of which are characteristic of “normal” CAIs. These observations suggest that the distillation process which produced isotopic fractionation in Kz1–2 occurred as early as the formation of “normal” CAIs. It is also inferred that the formation process of FUN inclusions is closely related to that of “normal” CAIs.

We carried out a systematic study of spinel group minerals in LL3.00–3.9 and LL4–6 chondrites. With increasing petrologic type, the size and abundance of spinel increase. The compositions of spinel group minerals in type 3 chondrites depend on the occurrence; Mg–Al-rich spinel occurs mainly in chondrules. Some chromite occurs in chondrules and matrix, and nearly pure chromite is exclusively encountered in the matrix. The occurrence of nearly pure chromite and the wide compositional variations distinguish spinel group minerals in types 3.00–3.3 from those in the other types. Spinel group minerals in types 3.5–3.9 show a narrower range of compositions, and those in types 4–6 are homogeneous. The changes in composition and abundance of spinel in type 3 chondrites are most likely due to thermal metamorphism. Therefore, the chemistry of spinel group minerals could be used as a sensitive indicator of metamorphic conditions, not only for type 3–6, but also 3.00–3.9. They can be applied to identify the most primitive (least metamorphosed) chondrites. The bulk compositions of spinel-bearing chondrules and the textural setting of the spinel indicate that most spinel group minerals crystallized directly from chondrule melts. However, some spinel grains, especially those enclosed in olivine phenocrysts, can not be explained by in situ crystallization in the chondrule. We interpret these spinel grains to be relic phases that survived chondrule melting. This is supported by the oxygen isotopic composition of a spinel grain, which has significantly lighter oxygen than the coexisting olivine. The oxygen isotopic composition of this spinel is similar to those of Al-rich chondrules. Our discovery of relic spinel in chondrules is an indication of the complexities in the early solar nebular processes that ranged from formation of refractory inclusion, through Al-rich chondrule, to ferromagnesian chondrules, and attests to the recycling of earlier formed materials into the precursors of later formed materials. The characteristic features of spinel group minerals are not only sensitive to thermal metamorphism, but also shed light on chondrule formation processes.

Si and Mg isotopic compositions of melilite in three coarse-grained CAIs were measured by SIMS. Isotopic compositions of these elements were fractionated (1.0 to 2.9 ‰/amu for Si and 4.6 to 9.6 ‰/amu for Mg) relative to terrestrial values. These fractionations are similar to those reported for bulk CAIs (Clayton et al., 1988) and suggest that coarsegrained CAIs were formed by evaporative loss of some Si and Mg from high-temperature condensates as proposed by Grossman et al. (2000). No significant zoning of isotopic fractionations was observed in these CAIs. This suggests that the evaporative loss of these elements from CAIs were slow compared with diffusive homogenization and also suggests that evaporative loss ceased early before crystallization of Mg-rich melilite.

Sixty-eight refractory inclusions and fragments were found in two polished thin sections of the Sahara 97159 EH3 chondrite, indicative of the highest abundance of refractory inclusions (22/cm2, or 0.06 vol.%) in enstatite chondrites studied to date. All of the inclusions are intensely altered, mainly producing feldspathoids and albite, CaO depletion and minor Ti-rich compounds, such as Ti-sulfides. The alteration assemblages and FeO-poor spinel suggest that the reactions took place under reducing and SiO2-rich conditions. This is consistent with the redox state of the host enstatite chondrite. The presence of Ti sulfides and low FeO alteration phases distinguishes alteration of E chondrite refractory inclusions from that of carbonaceous and ordinary chondrites. Most of the inclusions are referred to as Type A–like (35) and spinel-rich (26), respectively. Assuming melilite has been altered, these inclusions could be analogues of individual concentrically zoned objects of fluffy melilite-spinel-rich (Type A) and spinel-pyroxene-rich inclusions from carbonaceous chondrites such as the Ningqiang (CV anomalous) and Y 81020 (CO3) chondrites. Two inclusions consist mainly of Ca-pyroxene, fine-grained alteration products (feldspathoids and albite) and spinel. They are probably altered fragments of Ca-pyroxene-plagioclase-rich (Type C) inclusions, assuming all plagioclase has been altered to produce the fine-grained groundmass. Five other inclusions are hibonite and/or corundum bearing, similar to those reported in carbonaceous chondrites. Abundance ratios of various types of the inclusions from Sahara 97159 are similar to those from Ningqiang and Y 81020. Most of the observations, including mineral assemblages, mineral chemistry, texture, bulk compositions, O isotopic compositions and REE patterns, of the Sahara inclusions suggest a common reservoir of refractory inclusions in enstatite, ordinary and carbonaceous chondrites. The apparent differences, such as absence of melilite and anorthite, rare Wark-Lovering rim and small size, can be explained by intense alteration due to large change of postformation environment of these inclusions, size sorting and collision during transfer. Hence, these differences are not inconsistent with the common reservoir model. Refractory inclusions in non-carbonaceous chondrites may put additional constraints on origins of refractory inclusions, and provide hints for a spatial relationship of their host meteorites.

We report the mineralogy and oxygen isotopic compositions of FeO-rich silicates in the Sahara 97159 EH3 chondrite. This component is referred to as FeO-rich because it contains substantially more FeO than the characteristic FeO-poor silicates in the highly reduced enstatite meteorites. These FeO-rich silicates are mostly low-Ca pyroxene (Fs535) and their compositions suggest an origin under more oxidizing conditions, like those for the ordinary chondrites. However, the mafic silicates in ordinary and carbonaceous chondrites are dominantly olivine, and the FeO-rich silicates in the E chondrites are less commonly olivine. The oxygen isotopic compositions of the FeO- rich silicates are indistinguishable from those of FeO-poor silicates in Sahara 97159. These observations suggest that both the FeO-rich silicates and the FeO-poor silicates in EH chondrites formed from the same oxygen reservoir where redox conditions varied widely.

Isotopic compositions of the noble gases (He, Ne, Ar, Kr, Xe) were obtained by stepwise heating of separated mineral phases from carbonatites from Brazil (Jacupiranga, Tapira) and Canada (Borden, Oka, and Prairie Lake) as well as one syenite (Poohbah Lake, Canada). Mineral phases used were apatite, forsterite, diopside, calcite, monticellite, and perovskite. Large amount of in situ produced 238U-fissiogenic 131–136Xe, along with lesser amounts of 238U-fissio-genic 83–86Kr and in situ 4He were found in most samples. An apatite sample from the Prairie Lake carbonatite showed a 136Xe130Xe ratio of about 1400. Some samples, mostly apatites, showed excess 129Xe relative to air in the high temperature (1800°C) gas fractions. The highest 129Xe130Xe ratios, between 7.0 and 8.6, are similar to those found in other mantle-derived materials such as MORBs and diamonds. The excess `Xe is considered to be primordial and attributed to now extinct nuclide 129I once present in the early history of the Earth. Neon isotopic compositions were also anomalous showing very low 20Ne22Ne ratios (down to 0.01) and high 21Ne22Ne ratios (up to 1.25). They are attributed to Wetherill reactions, such as 18O(α,n)21Ne, 19F(α,n)22Na(β+)22Ne, and so on. The measured 40Ar/36Ar ratios are extremely variable and range from values that are close to atmospheric to values as high as 42400. Stepwise heating studies of an apatite from the Jacupiranga carbonatite indicate that the high temperature fractions retain the original noble gas signature of the carbonatite source. The 40Ar/36Ar ratios for the high temperature gas fractions are about 6400 or smaller. A plot of 40Ar/36Ar vs. 129Xe/130Xe shows that the source of carbonatites is different and less degassed than that of MORBs. The presence of excess 129Xe in carbonatites suggests that carbon in carbonatites is unlikely to be recycled C related to subduction processes.

Two carbonado diamonds were studied for helium diffusion by employing incremental stepwise-heating for temperature ranges from 350 to 1800°C. Arrhenius plots of experimental data demonstrate that there exist two degassing mechanisms of helium from diamond; the lower temperature degassing (T 1600°C) is essentially governed by graphitization of diamond. Diffusivity calculated from the observed release rates of the lower temperature range assuming spherical grains and initially homogeneous helium distributions defines Arrhenius relations with an activation energy of 103.5 ± 4.8 kJ/mol and a pre-exponential factor, D0 = 10−13.2±0.2 cm2/s in carbonado diamond. Using these values, we can estimate the diffusion coefficient of He to be 3 × 10−17 cm2/s at 1300°C.

Large excesses of129Xe,131Xe and132Xe relative to the atmospheric Xe were first reported by Jeffery in an Archaean anorthosite (2.9 Ga) from the Fisken˦sset Complex in West Greenland. Later, Zadnik and Jeffery observed excess21Ne and22Ne in the same anorthosite. Since the isotopic anomalies recorded in the rock may be a reflection of specific Archaean geological conditions, we decided to re-examine the problem. We studied an anorthosite from the same complex. Hornblende and anorthite were separated from the anorthosite and isotopic analyses were carried out on the mineral separates. Xe is essentially atmospheric, except for minor excesses of Xe produced by238U spontaneous fission in gases released from hornblende at higher temperatures in stepped heating experiments. The result did not confirm earlier observations. However, we also observed considerable excesses of both21Ne and22Ne, in accordance with the results of Zadnik and Jeffery, and consistent with nucleogenic Ne in many fluids in the crust. The former excess is most reasonably attributable to18O(α,n)21Ne, and the latter to19F(α,n) →22Ne. We conclude that these excesses are trapped components and that this anorthosite trapped these excess noble gases from a hydrous fluid derived from a crustal region enriched in U, Th and F during the 2.9 Ga metamorphism.

In situ ion microprobe analyses of oxygen isotopes in Yamato-86009 and Murchison chondrites show that they contain abundant olivine-rich inclusions that have large oxygen-16 ( 16 O) excesses, similar to those in spinel grains in calcium-aluminium–rich inclusions in Allende and other carbonaceous chondrites. The existence of 16 O-enriched olivine-rich inclusions suggests that oxygen isotopic anomalies were more extensive in the early solar system than was previously thought and that their origin may be attributed to a nebular chemical process rather than to an unidentified 16 O-rich carrier of presolar origin.

Shock‐recovery experiments were performed on 4He‐40Ar‐irradiated olivine samples. The estimated peak pressures were ∼30, ∼40, and ∼50 GPa. Noble gases were extracted from the recovered samples (OL‐30, ‐40, and ‐50) and an unshocked sample (UOL2) by stepwise heating and analyzed with a sector‐type mass spectrometer. Three peaks were observed in the 40Ar release pattern for UOL2 at 700‐800 °C, 1100‐1300 °C, and 1500‐1600 °C, suggesting three different trapping sites of Ar in olivine. In spite of significant loss of 40Ar from OL‐30 and OL‐40 (62‐86%), they also showed three release peaks, very similar to those for UOL2. If thermally‐induced diffusion was responsible for 40Ar loss, preferential loss from the lower temperature peaks must have occurred, which was not the case. Furthermore, degassed fractions of 40Ar and 4He were very similar to each other: 62% and 67% for OL‐30, and 86% and 89% for OL‐40, respectively. These observations are consistent with the idea of ‘‘all or nothing’’‐type degassing, where some portion was severely destroyed with the shock and released the gas completely while the other portion had little damage and retained most of the gas.

Three samples of a magnetic fraction of Pacific Ocean sediment were heated to 500 °C, 800 °C, and 950 °C, respectively, for two hours in a vacuum furnace in the same condition as that for the diffusion experiment. The run products as well as an unheated sample were examined with an x‐ray diffraction method. The results show that (1) major magnetic mineral was magnetite for all the samples, (2) no peaks of hematite, wustite, nor metallic iron were observed, (3) however, magnetite in the unheated sample had been partly oxidized to form maghemite, which has essentially the same crystal structure as that of magnetite. These observations suggest that the effect of phase changes, if present, would be negligibly small in the diffusion experiment. The present results further support the reliability of the diffusion data obtained in the previous study and support the conclusion that solar He and Ne would be lost from subducting slabs at shallow depths.

We studied the partition of Ar and Kr between synthetized crystals (clinopyroxene, olivine) and a basalt-melt. Clinopyroxene-glass pairs were synthetized in a platinum capsule containing air with a piston-cylinder-type high-pressure apparatus at 1.5 GPa at1250∼1175°C; olivine-glass pairs were synthesized at1350∼1300°C in an electric furnace with Ar flow. Distribution coefficients (noble gas content in crystal/noble gas content in melt) measured for these crystal-melt pairs are0.2∼0.5 for clinopyroxene-glass for Ar and Kr and0.08∼0.18 for olivine-glass for Ar.