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Al-Mg isotope systematics of twelve FeO-poor (type I) chondrules from CR chondrites Queen Alexandra Range 99177 and Meteorite Hills 00426 were investigated by secondary ion mass spectrometry (SIMS). Five chondrules with Mg#’s of 99.0 to 99.2 and Δ(17)O of −4.2‰ to −5.3‰ have resolvable excess (26)Mg. Their inferred ((26)Al/(27)Al)(0) values range from (3.5 ± 1.3) × 10(‒6) to (6.0 ± 3.9) × 10(‒6). This corresponds to formation times of 2.2 (–0.5/+1.1) Myr to 2.8 (‒0.3/+0.5) Myr after CAIs, using a canonical ((26)Al/(27)Al)(0) of 5.23 × 10(˗5), and assuming homogeneously distributed (26)Al that yielded a uniform initial (26)Al/(27)Al in the Solar System. Seven chondrules lack resolvable excess (26)Mg. They have lower Mg#’s (94.2 to 98.7) and generally higher Δ(17)O (−0.9‰ to −4.9‰) than chondrules with resolvable excess (26)Mg. Their inferred ((26)Al/(27)Al)(0) upper limits range from 1.3 × 10(‒6) to 3.2 × 10(‒6), corresponding to formation >2.9 to >3.7 Myr after CAIs. Al-Mg isochrons depend critically on chondrule plagioclase, and several characteristics indicate the chondrule plagioclase is unaltered: (1) SIMS (27)Al/(24)Mg depth profile patterns match those from anorthite standards, and SEM/EDS of chondrule SIMS pits show no foreign inclusions; (2) transmission electron microscopy (TEM) reveals no nanometer-scale micro-inclusions and no alteration due to thermal metamorphism; (3) oxygen isotopes of chondrule plagioclase match those of coexisting olivine and pyroxene, indicating a low extent of thermal metamorphism; and (4) electron microprobe data show chondrule plagioclase is anorthite-rich, with excess structural silica and high MgO, consistent with such plagioclase from other petrologic type 3.00–3.05 chondrites. We conclude that the resolvable ((26)Al/(27)Al)(0) variabilities among chondrules studied are robust, corresponding to a formation interval of at least 1.1 Myr. Using relationships between chondrule ((26)Al/(27)Al)(0), Mg#, and Δ(17)O, we interpret spatial and temporal features of dust, gas, and H(2)O ice in the FeO-poor chondrule-forming environment. Mg# ≥ 99, Δ(17)O ~−5‰ chondrules with resolvable excess (26)Mg initially formed in an environment that was relatively anhydrous, with a dust-to-gas ratio of ~100×. After these chondrules formed, we interpret a later influx of (16)O-poor H(2)O ice into the environment, and that dust-to-gas ratios expanded (100× to 300×). This led to the later formation of more oxidized Mg# 94–99 chondrules with higher Δ(17)O (−5‰ to –1‰), with low ((26)Al/(27)Al)(0), and hence no resolvable excess (26)Mg. We refine the mean CR chondrite chondrule formation age via mass balance, by considering that Mg# ≥ 99 chondrules generally have resolved positive ((26)Al/(27)Al)(0) and that Mg# < 99 chondrules generally have no resolvable excess (26)Mg, implying lower ((26)Al/(27)Al)(0). We obtain a mean chondrule formation age of 3.8 ± 0.3 Myr after CAIs, which is consistent with Pb-Pb and Hf-W model ages of CR chondrite chondrule aggregates. Overall, this suggests most CR chondrite chondrules formed immediately before parent body accretion.

We compare the observed composition ranges of olivine, pyroxene, and Fe-Ni sulfides in Wild 2 grains with those from chondritic interplanetary dust particles (IDPs) and chondrite classes to explore whether these data suggest affinities to known hydrous materials in particular. Wild 2 olivine has an extremely wide composition range, from Fa096, with a pronounced frequency peak at Fa1. The composition range displayed by the low-calcium pyroxene is also very extensive, from Fs48 to Fs0, with a significant frequency peak centered at Fs5. These ranges are as broad or broader than those reported for any other extraterrestrial material. Wild 2 Fe-Ni sulfides mainly have compositions close to that of FeS, with less than 2 atom% Ni; to date, only two pentlandite grains have been found among the Wild grains, suggesting that this mineral is not abundant. The complete lack of compositions between FeS and pentlandite (with intermediate solid solution compositions) suggests (but does not require) that FeS and pentlandite condensed as crystalline species, i.e., did not form as amorphous phases, which later became annealed. While we have not yet observed any direct evidence of water-bearing minerals, the presence of Ni-bearing sulfides, and magnesium-dominated olivine and low-Ca pyroxene does not rule out their presence at low abundance. We do conclude that new investigations of major- and minorelement compositions of chondrite matrix and IDPs are required.

We carried out a petrologic and instrumental neutron activation analysis (INAA) whole chondrite compositional study of Grosvenor Mountains (GRO) 95577. GRO 95577 has many petrological similarities to the CR chondrites. Although the INAA data show patterns indicative of terrestrial weathering, some of the elemental abundances are consistent with a relationship to CR chondrites. The oxygen isotopic composition of GRO 95577 plots close to the Renazzo CR chondrite on the three-isotope diagram. However, GRO 95577 is remarkable in that the chondrules are completely hydrated, consisting almost entirely of phyllosilicates, magnetite, and sulfides. Although GRO 95577 is completely hydrated, the initial chondrule textures are perfectly preserved. The chondrules are in sharp contact with the matrix, their fine-grained rims are clearly visible, and the boundaries of the dark inclusions can be easily discerned. Many chondrules in GRO 95577 have textures suggestive of type I chondrules, but the phenocrysts have undergone perfect pseudomorphic replacement by yellow to brownish serpentine-rich phyllosilicate, with sharp original crystal outlines preserved. The chondrule mesostasis is a green aluminous chlorite-rich material, most likely a hydration product of the feldspathic mesostasis commonly found in anhydrous type I chondrules. Some chondrules contain magnetite spheres, most likely formed by oxidation of metal. We propose that GRO 95577 be classified as a CR1 chondrite, making it the first known CR1 chondrite and expanding the range of alteration conditions on the CR parent body.

Laser ablation inductively coupled plasma mass spectrometry was used to measure abundances of P, Cr, Fe, Co, Ni, Cu, Ga, Ge, As, Mo, Ru, Rh, Pd, Sn, Sb, W, Re, Os, Ir, Pt, and Au in metal grains in the Bencubbin-like chondrites Bencubbin, Weatherford, and Gujba to determine the origin of large metal aggregates in bencubbinites. A strong volatility-controlled signature is observed among the metal grains. The refractory siderophiles Ru, Rh, Re, Os, Ir, and Pt are unfractionated from one another, and are present in approximately chondritic relative abundances. The less refractory elements Fe, Co, Ni, Pd, and Au are fractionated from the refractory siderophiles, with a chondritic Ni/Co ratio and a higher than chondritic Pd/Fe ratio. The moderately volatile siderophile elements Ga, Ge, As, Sn, and Sb are depleted in the metal, relative to chondritic abundances, by up to 3 orders of magnitude. The trace siderophile element data are inconsistent with the following proposed origins of Bencubbin-Weatherford-Gujba metal: (1) condensation from the canonical solar nebula, (2) oxidation of an initially chondritic metal composition, and (3) equilibration with a S-rich partial melt. A condensation model for metal-enriched (10 7 CI) gas is developed. Formation by condensation or evaporation in such a high-density, metal-enriched gas is consistent with the trace element measurements. The proposed model for generating such a gas is protoplanetary impact involving a metal-rich body. Copyright © 2002 Elsevier Science Ltd

In this chapter, we review current classification of meteorites, which is based on several primary classification parameters the whole-rock chemical compositions, oxygen isotopic compositions, carbon and nitrogen abundances and isotopic compositions, stable-isotope anomalies, mineralogy and petrography. Secondary classification parameters – petrologic type and shock metamorphism stages – provide clues to the thermal and shock history of meteorites, and degree of terrestrial weathering. We summarize the major mineralogical and geochemical characteristics of chondrite groups (H, L, LL, EH, EL, R, K, CI, CM, CR, CO, CK, CV, CH, and CB), and nonchondritic meteorites, both asteroidal (winonaites, acapulcoites-lodranites, brachinites, ureilites, angrites, howardites–eucrites–diogenites, mesosiderites, pallasites, and irons) and planetary (lunar and Martian – shergottites, nakhlites, chassignites, and orthopyroxenites). Finally, we discuss possible genetic relationships among meteorite groups.

— -Nitrogen-isotopic compositions of the bencubbinites—Bencubbin, Hammadah al Hamra (HH) 237, and Queen Alexandra Range (QUE) 94411—and in a petrographically similar chondrite Grosvenor Mountains (GRO) 95551 were measured by stepped-combustion static mass spectrometry. Hammadah al Hamra 237 and QUE 94411 contain isotopically heavy N, but not as heavy as that in Bencubbin or Weatherford. Grosvenor Mountains 95551 contains isotopically near-normal N and light N and, hence, it is not related to the bencubbinites, which is also indicated by its O-isotopic composition. The N carriers in these meteorites were investigated using secondary ion mass spectrometry. In the bencubbinites, N is mostly located around sulfide in metal clasts and in impact-melt areas. The N carriers in the former are taenite, carbide, or both; whereas those in the latter are molten metal, tiny graphitic carbon in metal, oxi-nitride glass, or both. In the various N carriers, N is isotopically equilibrated, and therefore the carriers are not pristine presolar grains. Isotopically near-normal N in GRO 95551 is located in graphite. The carrier of isotopically light N in GRO 95551 has not been found.

The Kakangari, LEW 87232, and Lea Co. 002 chondrites have a similar set of petrologic and oxygen isotopic characteristics that distinguishes them from other chondrite groups. They are here established to constitute a single chondrite grouplet—the K (after Kakangari) chondrites. The K chondrites have (1) high matrix abundances (33–77 vol%) as do carbonaceous chondrites, (2) metal abundances (6–10 vol%) that are similar to the H group ordinary chondrites, (3) average mafic silicate compositions (average Kakangari olivine = Fa2.2; enstatite Fs4.4) that indicate an oxidation state intermediate between H and E chondrites, (4) matrix that differs from that in other chondrite groups in being enstatite-rich with compositions more Mg-rich (average = Fs3) than those in the chondrules, (5) refractory lithophile element abundances (

著者人数: 75名, 資料番号: SA1003700000

The incidence of carotid artery disease and cerebrovascular symptoms were determined in 102 consecutive patients with peripheral arterial disease. Symptoms were correlated with risk factors of age, hypertension, smoking and diabetes and with the extent of disease at the carotid bifurcation. The incidence of stroke with permanent neurological deficit was twice as high in diabetics as in non-diabetics with equivalent atherosclerotic vascular disease (p less than .05). In women, the incidence of stroke was three times higher in diabetics (p less than .02). The number of transient ischemic attacks was significantly higher in non-diabetics (p less than .02). The total number of ischemic episodes in diabetics and non-diabetics was equivalent. This indicates that diabetics are more prone to irreversible destruction of ischemic brain tissue regardless of the nature of the circulatory disturbance.