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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.

The enriched basaltic (martian) shergottite Ksar Ghilane (KG) 002, discovered in 2010, is exceptionally rich in coexisting but discrete apatite and merrillite crystals. It has been selected to better constrain the formation conditions and post-crystallization processes, and thus the evolution of martian rocks based on Ca-phosphates. A petrological, chemical, chronological and microstructural approach using a series of high-spatial resolution techniques including Raman spectroscopy, electron microscopy (SEM, EPMA, CL-imaging) and secondary ion mass spectrometry (SIMS) analysis has been applied to a representative number of Ca-phosphate grains. Analytical results for apatite and merrillite reveal: (i) zoning in F, Cl, Br and I concentrations, (ii) elevated Cl concentrations in the range of ∼11,900–35,300 µg/g and halogen ratios, i.e., Cl/Br and Cl/I, as well as stable chlorine isotope composition, reported as δ37Cl values rel. to Standard Mean Ocean Chloride (SMOC, defined as 0‰) with a value of +0.67 ± 0.14‰ (1σ), distinguishing KG 002 phosphates from that of other enriched and depleted shergottites. The halogen and heavier δ37Cl record indicate a slightly higher degree of ∼3.5% assimilation of Cl-rich and isotopically heavier crustal reservoir on Mars when compared to other enriched shergottites. (iii) Structural investigations together with the chemical and petrological context of the grains confirm the occurrence of hydroxyl-poor merrillite, indicate weak if any alteration effects induced by metamictization, only minor structural modifications due to shock metamorphism, and absence of replacement reactions. Therefore, igneous crystallization of Ca-phosphates from a fractionated, hydrous and ferrous mantle source, rich in volatiles including the halogens and Na and lithophile rare earth-elements, and absence of interaction with crustal fluids/brines of the sample is deduced. (iv) The Pb isotopic composition of six apatite and three merrillite grains is highly unradiogenic and the 238U-206Pb record yields a phosphate crystallization time at 395 ± 240 Ma (2σ), which is similar to those of other enriched shergottites.

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.

In order to clarify the origin of the eclogitic clasts found in the NWA801 (CR2) chondrite (Kimura et al., 2013), especially, that of the high pressure and temperature (P–T) condition (∼3 GPa and ∼1000 °C), we conducted ion microprobe analyses of oxygen isotopes and rare earth element (REE) abundances in the clasts. Oxygen isotopic compositions of the graphite-bearing lithology (GBL) and graphite-free lithology (GFL) show a slope ∼0.6 correlation slightly below the CR-CH-CB chondrites field in the O three-isotope-diagram, with a large variation for the former and almost homogeneous composition for the latter. The average REE abundances of the two lithologies show almost unfractionated patterns. Based on these newly obtained data, as well as mineralogical observations, bulk chemistry, and considerations about diffusion timescales for various elements, we discuss in detail the formation history of the clasts. Consistency of the geothermobarometers used by Kimura et al. (2013), suggesting equilibration of various elements among different mineral pairs, provides a strong constraint for the duration of the high P–T condition. We suggest that the high P–T condition lasted 102–103 years. This clearly precludes a shock high pressure (HP) model, and hence, strongly supports a static HP model. A static HP model requires a Moon-sized planetary body of ∼1500 km in radius. Furthermore, it implies two successive violent collisions, first at the formation of the large planetary body, when the clasts were placed its deep interior, and second, at the disruption of the large planetary body, when the clasts were expelled out of the parent body and later on transported to the accretion region of the CR chondrites. We also discuss possible origin of O isotopic variations in GBL, and presence/absence of graphite in GBL/GFL, respectively, in relation to smelting possibly occurred during the igneous process(es) which formed the two lithologies. Finally we present a possible formation scenario of the eclogitic clasts.

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.

53 Mn– 53 Cr ages have been measured for dolomites in three CI chondrites and an ungrouped C2 chondrite Tagish Lake. For an accurate age determination, we utilized, in contrast to previous works, a matrix-matched carbonate standard to appropriately correct the observed Mn/Cr ratios. The Mn–Cr data of the dolomites most likely represent isochrons with chronological significances and the obtained ages are concentrated in 4563.8–4562.5 million years ago (4.4–5.7 million years after the birth of the solar system). The ages of the CI and Tagish Lake dolomites are very similar to those of carbonates in CM chondrites, although CI and CM chondrites are likely to have different alteration histories. The similar carbonate ages in various carbonaceous chondrites suggest that the aqueous activities in hydrous asteroids initiated almost concurrently. If this is the case, the most plausible heat source for the aqueous alteration is the decay energy of short-lived radionuclides, especially 26 Al. We carried out a model calculation for the thermal history of the CI chondrite parent body assuming that 26 Al is the dominant heat source. By two different approaches to estimate the accretion time of the CI chondrite parent body, we conclude that it accreted 3.0–3.9 million years after the birth of the solar system. This is also likely to be the case for the CM chondrite and Tagish Lake parent bodies, because the result of the calculation is not sensitive to the ice abundance. Therefore, we stress that near the condensation front of water ice, meteorite parent bodies with abundant ice accreted almost simultaneously at 3–4 million years after CAI formation. Combining our Mn–Cr ages of the dolomites with those of breunnerites reported previously (the youngest one is 4554.6 million years ago), we found that the aqueous alteration in the CI chondrite parent body lasted for at least 9 million years. Therefore, the parent body should be large enough (>50 km in radius) so that the internal heat had been kept for 9 million years.

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.

Cr anomaly is Cr-rich, this result implies a low abundance and a huge isotopic anomaly of the carrier, and/or its ex-tremely fine grain size. In the former case, the maximum abundance of the presolar Cr-rich grains is roughly estimated tobe ~1 ppm. In that case the minimum isotopic anomaly would be ~90‰.

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.

Bulk chemical compositions and oxygen isotopic compositions were analyzed for 48 stony cosmic spherules (melted micrometeorites) collected from the Antarctic ice sheet using electron- and ion-microprobes. No clear correlation was found between their isotopic compositions and textures. The oxygen isotopic compositions showed an extremely wide range from −28‰ to +93‰ in δ18O and from −21‰ to +13‰ in Δ17O. In δ18O-δ17O space, most samples (38 out of 48) plot close to the terrestrial fractionation line, but 7 samples plot along the carbonaceous chondrite anhydrous mineral (CCAM) line. Three samples plot well above the terrestrial fractionation line. One of these has a Δ17O of +13‰, the largest value ever found in solar system materials. One possible precursor for this spherule could be 16O-poor planetary material that is still unknown as a meteorite. The majority of the remaining spherules are thought to be related to carbonaceous chondrites.

Deep-sea corals hold a great potential as a key to important aspects of paleoceanography for at least two reasons, 1) they offer temporal high resolution records of deep-sea environment, because they have growth banding structures, 2) and they are well suited for studying vital effects, because the deep-sea environment does not change over short time scales. However, the relationship between the chemical composition of deep-sea coral skeletons and environmental factors is not well understood. In this study, the chemical composition of deep-sea corals was measured in bulk individuals and along skeletal micro-structures. Among the bulk individuals, δ 18 O value and Sr / Ca ratio show a negative but weak correlation with ambient temperature. On the other hand, the Mg / Ca ratio has a positive, weak correlation with the temperature. Large variations were found among samples collected from similar temperature. The variation is up to 3.8‰ for δ 18 O, 0.9 mmol/mol for Sr / Ca ratios, and 0.78 mmol/mol for Mg / Ca ratios among samples with ambient average temperature within 1 °C. This variation may be due to a large vital effect. The centers of calcification (COCs), which were formed at high calcification rate, have lower Sr / Ca, U / Ca and higher Mg / Ca ratios than surrounding fasciculi. This chemical distribution supports the model that elemental incorporation depends on calcification rate. This suggests that calcification rate is a very important factor for the chemical composition in deep-sea corals and is one of the most significant mechanisms of the vital effect. Because of this large vital effect, further investigations are essential to use the deep-sea coral as a temperature proxy.

Studies of oxygen isotopes and rare earth elements in CAIs, the oldest rocks in the solar system, are briefly reviewed and inferences for their formation processes are discussed. Various models have been proposed for the origin of 16O-rich oxygen isotopic compositions in CAIs: (1) existence of an 16O-rich presolar component, (2) some kind of chemical reactions producing mass-independent isotopic anomalies, such as photo-dissociation of ozone to produce atomic oxygen, (3) self-shielding effect in the photo-dissociation of CO in the nebula. An 16O-rich presolar component origin is highly unlikely. Chemical reactions producing mass-independent isotopic effect have been suggested but not established by experiments nor theory and also no process has been proposed to fix such isotopic anomaly in CAIs. At present, self-shielding effect in photo-dissociation of CO in the nebula seems to be the most promising model to explain the observed oxygen isotopic variations in the solar system. Direct measurement of oxygen isotopic composition in the solar wind implanted in lunar soils or in metal foils recovered by GENESIS Mission would provide important constraints on the origin of oxygen isotopic variations in the solar system. Abundance patterns of rare earth elements (REEs) in CAIs are highly variable: unfractionated patterns (Groups I, III or V), Group II pattern (depleted in ultra-refractory, heavy REEs) and ultra-refractory pattern (complementary to Group II). The latter two patterns suggest that very effective gas/dust separation occurred at high temperatures (e.g., ∼1700 K) in the early solar system.

We have investigated the chemical and isotopic behavior of beryllium (Be) during acid leaching for removing meteoric 10Be in volcanic samples. Determination of the Be isotopic ratio in the leachate was carried out using accelerator mass spectrometry (AMS) and inductivity coupled plasma mass spectrometer (ICP-MS). Elemental distribution of Be and other incompatible elements including boron (B) were also examined by ion microprobe (SIMS) for a deeper understanding of their chemical behavior in volcanic samples. SIMS analysis show that Be is concentrated in the groundmass together with B. However, the behavior of their elements during acid leaching is quite different. The Be concentration decreases through progressive leaching, while the concentration of B remains constant. Furthermore, the variation in the Be isotopic ratio after acid leaching is different between the two samples, neither of which has altered minerals under microscopic observation. It is demonstrated that meteoric 10Be resides in a rather narrow region of the rock and can be removed by acid leaching with minimum loss of the main host phase of Be.

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.

Solubility experiments for nitrogen and noble gases (Ar and Ne) in silicate melts were conducted using two experimental configurations: one was conducted at 1 atmospheric pressure, T =1300°C and oxygen fugacity (fO2) of IW + 0.9 (i.e., 0.9 log units higher than the iron-wustite buffer) and the other at high pressures (Ptotal ∼ 2 × 108 Pa), 1500°C and fO2 ∼ IW + 6. For the former experiment, isotopically labeled-nitrogen (15N15N-enriched) was used to distinguish dissolved nitrogen from contaminating atmospheric or organic nitrogen and to examine dissolution mechanisms of nitrogen in silicate melts. The results obtained for the two series of experiments are consistent with each other, suggesting that Henry's law is satisfied for fN2 of up to ∼250 atm (2.5 × 107 Pa). The results are also consistent with our earlier results (Miyazaki et al., 1995) obtained at highly oxidizing conditions (fO2 ∼ IW + 10). All these results support physical dissolution of nitrogen as N2 molecules in silicate melts for fO2 from ∼IW + 10 down to ∼IW. The observed solubility (Henry's constant) of nitrogen (3–5 × 10−9 mol/g/atm) is comparable to that of Ar (2–4 × 10−9 mol/g/atm), and much lower than that of Ne (11–14 × 10−9 mol/g/atm) at 1300°C. A preliminary experiment was also performed for partitioning of nitrogen and noble gases between clinopyroxene (cpx) and basaltic melt using a piston cylinder-type apparatus at 1.5 GPa and at 1270 to 1350°C. The obtained cpx/melt partition coefficient of nitrogen is 0.06, slightly lower than those of noble gases (∼0.1 for Ne to Xe), suggesting that nitrogen is as incompatible as or even slightly more incompatible than noble gases. The present results imply that a large nitrogen/Ar fractionation would not be produced by magmatic processes. Therefore, the two orders of magnitude difference between the N2/36Ar ratios in the Earth's atmosphere (∼104) and that in the mantle (∼106) must be explained by some other processes, such as incomplete segregation of metal blobs into the core and their later oxidation.

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.

In this paper we report petrological and chemical data of the unusual chondritic meteorites Yamato (Y)-792947, Y-93408 and Y-82038. The three meteorites are very similar in texture and chemical composition, suggesting that they are pieces of a single fall. The whole-rock oxygen isotopes and the chemical compositions are indicative ofH chondrites. In addition, the mineralogy, and the abundances of chondrule types, opaque minerals and matrices suggest that these meteorites are H3 chondrites. They were hardly affected by thermal and shock metamorphism. The degree of weathering is very low. We conclude that these are the most primitive H chondrites, H3.2-3.4 (SI), known to date. On the other hand, these chondrites contain extraordinarily high amounts of refractory inclusions, intermediate between those of ordinary and carbonaceous chondrites. The distribution of the inclusions may have been highly heterogeneous in the primitive solar nebula. The mineralogy, chemistry and oxygen isotopic compositions of inclusions studied here are similar to those in CO and E chondrites.

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.

Recently, precise noble gas analyses of many types of mantle-derived materials have proved that isotopic composition of Ne in the Earth's interior (mantle) is quite different from that of the Earth's atmosphere (20Ne/22Ne=9.8), but much similar to the solar-type composition (20Ne/22Ne-13). This observation challenges the prevailing idea that the Earth's atmosphere was simply derived from the Earth's interior, because both the atmosphere and its source (=mantle) must have identical isotopic compositions. One possibility that can account for this observation is an extensive loss of the primordial atmosphere at an early stage of the Earth's history. This model assumes a solar-type Ne both for the primordial atmosphere and the mantle, but later on, Ne in the primordial atmosphere became fractionated due to hydrodynamic escape of the atmosphere, which resulted in the “heavy” Ne isotopic composition of the present atmosphere. This paper reviews the discovery of the solar-type Ne in the Earth's interior and discuss its importance in earth and planetary sciences.

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.

Isotopic and elemental compositions of noble gases in glass samples from mid-oceanic ridges (Mid-Atlantic Ridge, East Pacific Rise, and Galapagos Ridge) and from Loihi seamount (Hawaii) were analyzed with a sector-type mass spectrometer system. Our results for MORB (Mid-Oceanic Ridge Basalt) samples are consistent with the well-known MORB-type noble gas signatures: rather uniform 3 He/ 4 He ratios (R/R a ~ 8), variable 40 Ar/ 36 Ar ratios from nearly the atmospheric ratio to 15,200, and the presence of excesses in 129 Xe and 132−136 Xe. We also observed linearly correlated anomalies in 20 Ne/ 22 Ne ratios (up to ~ 13) and 21 Ne/ 22 Ne ratios (up to ~0.06), which are consistent with the MORB correlation found by Sarda et al. (1988). High 20 Ne/ 22 Ne ratios (up to 11.74) and relatively high 40 Ar/ 36 Ar ratios (up to 2780) are also found in some Loihi samples. Neon isotopic compositions for these samples are quite consistent with the Loihi-Kilauea correlation line recently found by Honda et al. (1991) but inconsistent with the MORB correlation line. Loihi data plotted in a 3 He/ 4 He vs. 20 Ne/ 22 Ne diagram also suggest that the high 20 Ne/ 22 Ne ratios found in Loihi samples are not the results of contamination of MORB-type neon but are indigenous to the source of Loihi. This suggests that the solar-type high 20 Ne/ 22 Ne ratios are not only the signature of the source mantle of MORB (upper mantle) but also that of the source of Loihi (possibly lower mantle), and hence, possibly the signature of the whole mantle. The fact that isotopic composition in the mantle ( 20 Ne/ 22 Ne ~ solar) and in the present atmosphere ( 20 Ne/ 22 Ne = 9.8) are different seems to contradict a simple degassing model of the atmosphere, which implies isotopically identical compositions for the mantle and the atmosphere. A possible scenario would be that neon in the present atmosphere had been fractionated from the original solar-type ratio ( 20 Ne/ 22 Ne ~ 13.6) down to the present ratio (9.8) by extensive loss of the (proto-) atmosphere at an early stage of the Earth's history. If the Earth's accretion was “heterogeneous,” mixing of a solar-type Ne (derived from most of the mantle) and a planetary-type Ne (derived from late-veneer, volatile-rich material) would be an alternative explanation for the present atmospheric Ne. In either case, the model should be consistent with other noble gas data, especially xenon isotopic data.

It was recently proposed that subduction of interplanetary dust particles (IDPs) contained in deep sea sediments could have introduced substantial solar helium and neon to the Earth's mantle. However, it is not certain if IDPs would retain solar noble gases during subduction. A diffusion experiment that examined He and Ne in IDPs in a magnetic separate from Pacific Ocean sediments showed that He and Ne would be lost from IDPs within 3 years at 500 degrees C, and possibly within 10(5) years at 200 degrees C, which suggests that they would be lost from subducting slabs at shallow depths.

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 measured solubilities of nitrogen and argon in basalt melt at 1300 °C under highly oxidizing conditions (P(O2)=0.16‐0.37 atm) using 15N15N‐labeled air (Ptotal=1 atm). The obtained solubilities (Henry’s constants) are K(N2)=(1.3‐2.9)×10−9 mol/g/atm and K(Ar)=(2.6‐4.5)×10−9 mol/g/atm, respectively, showing that the solubility of nitrogen is slightly lower than that of Ar under highly oxidizing conditions. The 15N15N‐labeled gas used in the solubility experiment was not isotopically in equilibrium but highly enriched in 15N15N, that is, the ratios of 14N14N: 14N15N: 15N15N in the gas were not 1: 2r: r2, where r=15Ntotal/14Ntotal. The recovered gas from the synthetic basalt glass also showed similar isotopic disequilibrium. This suggests that isotopic exchange among N2 molecules did not occur during dissolution of the gas in the melt. In other words, nitrogen dissolved in the basalt melt as molecules in the present (highly oxidizing) experimental conditions.

Air standard neon (3.7×10-9 cm3 STP or 1.7×10-13 mol of Ne) was repeatedly analyzed with a sector type mass spectrometer VG5400 under various partial pressures of helium with the 4He/20Ne ratio from 0.24 to 27500 (or total pressure in the mass spectrometer, P(MS) from 1×10-7 Pa to 4.3×10-4 Pa by ion gauge reading). The measured 20Ne/22Ne ratios were kept almost constant when 4He/20Ne 400 or P(MS) 7×10-6 Pa (by ion gauge reading), but increased by up to a factor of ~3% at higher partial pressure of helium. The present result demonstrates the importance of He-Ne separation for a precise measurement of neon isotopic ratios in samples with high He/Ne ratios, such as MORB (Mid Oceanic Ridge Basalt) glasses.

The distribution coefficients (Ki) of noble gases were determined for synthesized olivine-basalt melt pairs. Seven samples (BH-series) were synthesized at 1370 ~ 1300°C under a one atmospheric pressure (~ 105 Pa) noble gas mixture, and four samples (HPP- and HPG-series) at 1360-1050°C at high pressures (0.2–1.5 GPa). The two different experiments gave consistent results with each other. Some BH-series olivine samples were apparently contaminated with gas-rich inclusions or the glass phase, and the effects of such interferences on the calculated distribution coefficients were evaluated. The possible ranges of the distribution coefficients of noble gases thus obtained are: KHe ≲ 0.07, KNe = 0.006−0.08, KAr = 0.05−0.15, KKr ≲ 0.15, and KXe ≲ 0.3. These show remarkable features compared to solid element distribution coefficients: the distribution coefficients of noble gases are rather insensitive to, or even positively correlated with the atomic size of noble gases. The striking contrast between the partition of noble gases and that of solid elements may be attributed to the electrical neutrality of noble gases and the increasing electronic polarizability from He to Xe.

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.

We have measured δ13C values and CO2/3He ratios of vesicle-gas, and chemical compositions of North Fiji Basin basalt glasses, to estimate the contribution of subducted carbon in back-arc basin basalt quantitatively. It has made clear that the CO2/3He ratio increases and the δ13C value decreases with K2O content. Since the variety of K2O content of North Fiji Basin basalt is the result of two-component mixing, the variety of the CO2/3He ratio and δ13C value of the North Fiji Basin basalt should be mainly a result of mixing between the mantle component (low-CO2/3He, high-δ13C and low-K2O) and the subducted component (high-CO2/3He, low-δ13C and high-K2O). From a simple mass-balance calculation, it is derived that the subducted end-member source has 70% carbonate and 30% organic matter in origin. Assuming that complete decomposition of the subducted organic matter has occurred, most (∼90%) carbonates, which subducted without accretion to wedge, is free from decomposition in North Fiji back-arc, since the subducting carbonate and organic matter throughout the North Fiji subduction zone are estimated in a proportion of 20:1. This may be one clue that carbonate can be transported into the mantle through the subduction zones.