Oxygen isotope systematics and Al-Mg chronology of chondrules: Implications to protoplanetary disk evolution

第6回極域科学シンポジウム[OA] 南極隕石11月17日（火）　国立国語研究所 2階 講

Chondrule age distribution and rate of heating events for chondrule formation

Chondrules are considered to be formed by flash heating events in the protoplanetary disk. In order to evaluate some basic factors in the heating mechanism, we examined the rate of heating events that explains the abundance and the observed age distribution of chondrules in unequilibrated ordinary chondrites. First, we compiled the literature data of ^(26)Al ages of chondrules from the least equilibrated ordinary chondrites (LL3.0-3.1), ranging from 1Myr to 3Myr with a peak at about 1.8Myr relative to the formation time of Ca, Al-rich inclusions (CAIs) in carbonaceous chondrites, the oldest solid materials formed in the solar system. Next, we made a simple phenomenological chondrule formation model assuming that each event heated only a small fraction of existing dust at one time and numerous heating events produced chondrules. Results indicate that (1) an average number of heating events experienced by a dust particle should be 1.2 or higher, (2) more than a half of the present chondrules were reheated, (3) chondrule formation started sometime between 0.4-1.5Myr and ended at 2.2-2.3Myr after the CAI formation, and (4) the rate of heating events has a peak at 0.1-0.8Myr earlier than the peak of the observed chondrule age distribution and should decrease monotonically with time after the peak

Construction of Tertiary Chiral Centers by Pd-catalyzed Asymmetric Allylic Alkylation of Prochiral Enolate Equivalents

The palladium-catalyzed decarboxylative allylic alkylation of enol carbonates derived from lactams and ketones is described. Employing these substrates with an electronically tuned Pd catalyst system trisubstituted chiral centers are produced. These stereocenters have been previously challenging to achieve using Pd complex/chiral P–N ligand systems

Primitive clasts in the Dar al Gani 319 polymict ureilite: Precursors of the ureilites

Primitive clasts in the polymict ureilite Dar al Gani (DaG) 319 include dark clasts, sulfide- or metal-rich clasts, and unusual chondritic fragments. The dark clasts consist mainly of phyllosilicates, sulfides and magnetite with or without fayalitic olivine. The sulfide-rich clasts consist of a silicate-rich matrix and heterogeneously distributed sulfide. The metal-rich clasts consist of a silicate-rich matrix with variable amounts of metal. The unusual chondritic fragments are chondrule and equilibrated chondrite fragments. Oxygen isotopic compositions of the silicate-rich matrices in the sulfide-rich or metal-rich clasts plot on the carbonaceous chondrite anhydrous mineral (CCAM) mixing line between Allende matrix and a dark clast in the Nilpena polymict ureilite. Their oxygen isotopic compositions are similar to those of the monomict ureilites. Considering its chondritic composition and oxygen isotopic composition, the silicate-rich matrix of the sulfide-rich clasts is the best candidate for the ureilite precursors. However, the matrix has an Mg/(Mg+Fe) ratio (mg ratio) of 0.56 and is too ferroan to produce the monomict ureilites with mg ratios of 0.74-0.95. Therefore, it may have experienced various degrees of reduction to produce precursors with the mg ratios, needed to form the monomict ureilites as residues during fractional melting. Oxygen isotopic compositions of the unusual chondritic fragments plot near the ordinary chondrites on a 3-isotope diagram, suggesting that they have no direct genetic relationship to the monomict ureilites. They were projectiles that collided with the ureilite parent body (UPB)

Evidence from Polymict Ureilite Meteorites for a Single "Rubble-Pile" Ureilite Parent Asteroid Gardened by Several Distinct Impactors

Ureilites are ultramafic achondrite meteorites that have experienced igneous processing whilst retaining heterogeneity in mg# and oxygen isotope ratios. Polymict ureilites represent material derived from the surface of the ureilite parent asteroid(s). Electron microprobe analysis of more than 500 olivine and pyroxene clasts in six polymict ureilites reveals that they cover a statistically identical range of compositions to that shown by all known monomict ureilites. This is considered to be convincing evidence for derivation from a single parent asteroid. Many of the polymict ureilites also contain clasts that have identical compositions to the anomalously high Mn/Mg olivines and pyroxenes from the Hughes 009 monomict ureilite (here termed the Hughes cluster ). Four of the six samples also contain distinctive ferroan lithic clasts that have been derived from oxidized impactors. The presence of several common distinctive lithologies within the polymict ureilites is additional evidence that the ureilites were derived from a single parent asteroid. Olivine in a large lithic clast of augite-bearing ureilitic has an mg# of 97, extending the compositional range of known ureilite material. Our study confirms that ureilitic olivine clasts with mg#s 85, which also show more variable Mn contents, including the melt-inclusion bearing "Hughes cluster" ureilites. We interpret this to indicate that the parent ureilite asteroid was disrupted by a major impact at a time when melt was still present in regions with a bulk mg# > 85, giving rise to the two types of ureilites: common ferroan ones that were already residual after melting and less common magnesian ones that were still partially molten when disruption occurred, some of which are the result of interaction of melts with residual mantle during disruption. A single daughter asteroid re-accreted from the disrupted remnants of the mantle of the proto-ureilite asteroid, giving rise to a "rubble-pile" body that had material of a wide variety of compositions and shock states present on its surface. The analysed polymict ureilite meteorites represent regolith that subsequently formed on this asteroidal surface, including impact-derived material from at least six different meteoritic sources

Search for 60Ni excesses in MET-78008 ureilite: An ion microprobe study

We have developed a technique for in-situ Ni isotopic analysis using the ion microprobe, in order to detect ^Ni excess from the decay of the short lived nuclide ^Fe (half life=1.5Ma) in ureilite samples. The silicate minerals from MET-78008 ureilite with an old U-Pb age of 4.563±0.006 Ga were analyzed. The ^Fe/^Ni ratios of olivine and orthopyroxene are between 2700 and 5400. In spite of the high Fe/Ni ratios, we could not observe any detectable ^Ni excess. From the mean value of olivine core data, we obtain an upper limit of the ^Fe/^Fe ratio at the time of ureilite formation of 1.8×10^. The time difference between CAI formation and ureilite formation was estimated to be more than 4 million years, which is consistent with the UPb data from the same meteorite. We concluded that the impact event for the disruption of the ureilite parent body happened more than 4 million years after CAI formation. However, a large uncertainty in the initial ^Fe/^Fe ratio is introduced by the possibility that the ^Ni excess observed in CAIs is of nucleosynthetic origin. Our conclusion may change if the initial ^Fe/^Fe ratio of the solar system using CAI data is too high

ブドウ球菌の表皮ケラチノサイトからの選択的抗菌ペプチドの誘導

Staphylococcus aureus (S. aureus) is one of the most clinically important inflammation-inducing pathogens, while Staphylococcus epidermidis (S. epidermidis) is nonpathogenic and hardly causes inflammation on skin. β-defensins, antimicrobial peptides, are secreted from keratinocytes constitutively or upon induction by various microorganisms. However, the difference between S. aureus and S. epidermidis is still unclear in terms of their influences on the production of β-defensins. In this study, we focused on the influences of S. aureus and S. epidermidis on the keratinocyte innate immune response. Pathogenic S. aureus mainly induced human β-defensin (hBD) 1 and hBD3, but not hBD2, and nonpathogenic S. epidermidis mainly induced hBD2 from human keratinocytes. Molecular weight fractions of >10 kDa prepared from S. aureus supernatants induced the production of hBD1 and hBD3. On the other hand, molecular weight fraction of >100 kDa prepared from S. epidermidis supernatants induced the production of hBD2.Furthermore, the secreted products of S. epidermidis used the toll-like receptor (TLR) 2 pathway in the induction of hBD2 production. The secreted products of S. aureus and S. epidermidis differentially induced subtypes of hBD through different receptors, which may be associated with the difference in virulence between these two bacteria.博士（医学）・甲第643号・平成28年3月15日Copyright © 2012 Elsevier Ltd. All rights reserved

Ion microprobe analysis of oxygen isotopes in garnets of complex chemistry

Accurate ion microprobe analysis of oxygen isotope ratios in garnet is possible if appropriate standards are employed to correct for instrumental bias, a component of which depends on the cation chemistry of the analyzed mineral. In this study, 26 garnet standards (including 14 new standards) that span the compositional range of pyrope, almandine, grossular, spessartine, and andradite were analyzed repeatedly by ion microprobe to develop a new method of correcting for instrumental bias in garnets. All analyses were normalized to a single master garnet standard (UWG-2) before bias from cation composition was considered. Bias due to cation composition in garnet was found to correlate with grossular content in pyralspite garnets and with andradite in ugrandite garnets. Bias is correlated with molar volume in garnets of all compositions in this study. Although this correlation is suitable as a correction scheme for bias, a more accurate correction scheme based on the grossular and andradite compositions of garnet is proposed. This method reproduces the bias of all but one standard to within a range of 0.4%%, an accuracy that is on the same order as the reproducibility (+/-0.3%%, 2S.D.) of the master garnet standard UWG-2, but that remains an independent source of error. The new correction scheme is used to successfully reproduce laser fluorination analyses along a traverse of a polymetamorphic, zoned skarn garnet from the Adirondack Mountains. While previous analyses were at the mm-scale, the new data resolve a gradient of δ^1^8O of 2.1%% over 16 m. If experimentally derived diffusion coefficients are correct, these new results show that granulite-facies metamorphism was significantly faster than previously assumed and the thermal peak was less than 5Myr

Petrology of a new basaltic shergottite: Dhofar 378

Dhofar 378 is a new basaltic shergottite, consisting mainly of pyroxenes, plagioclase glass, phosphates, titanomagnetite, and mesostasis. It is one of the most ferroan shergottites and resembles the Los Angeles shergottite. Pyroxenes show remarkable chemical zoning from 0.4 of Mg/(Mg+Fe) to less than 0.1, and their REE patterns are depleted in light REE whereas the REE pattern of the bulk Dhofar 378 is flat. All plagioclase grains in the original lithology completely melted by an intense impact shock, and the plagioclase melts crystallized fibrous plagioclase to form the rims surrounding the plagioclase melts. Then, the melts quenched as plagioclase glass to form the cores. The shock stage of Dhofar 378 is higher than that of the Los Angeles shergottite. The degree of impact shock for Dhofar 378 may be about 55-75GPa and is the highest among all known martian meteorites