Yamato-793605: A new lherzolitic shergottite from the Japanese Antarctic meteorite collection

Y-793605 is a new martian meteorite from Antarctica that can be classified as a lherzolitic shergottite. Y-793605 mainly shows a poikilitic texture (large pyroxene oikocryst with enclosed olivine and chromite), but partly contains non-poikilitic areas (mainly maskelynite, olivine, and pigeonite). Olivine in the non-poikilitic area is more Fe-rich and shows a narrower compositional distribution than that in the poikilitic area. Low-Ca pyroxenes in the non-poikilitic area are also more Fe-rich (En_Fs_Wo_7∿En_Fs_Wo_) than those in the poikilitic area (En_Fs_Wo_3∿En_Fs_Wo_). Augites in the poikilitic area are usually present rimming the oikocrysts (En_Fs_Wo_ to En_Fs_Wo_). The crystallization sequence of minerals in Y-793605 is considered to have begun by initial crystallization of cumulus phases (olivine and chromite) from the parent magma. Then, low-Ca pyroxenes and later augite poikilitically enclosed cumulus phases, and became a large oikocryst. Due to accumulation of phases, small interstitial melts formed between the oikocryst boundaries, and plagioclase crystallized from the Ca-Fe-rich melt along with pigeonite. After minor augite crystallization in the non-poikilitic area, all phases experienced re-equilibration (e. g., homogenization of olivine). Y-793605 shows a close relationship to previously known lherzolitic shergottites ALH77005 and LEW88516. Especially, olivine composition of Y-793605 is nearly identical to that of LEW88516. Pyroxene and maskelynite compositions are almost the same among these three meteorites. Although it is hardly possible to consider that Y-793605 is paired with ALH77005 or LEW88516 in the sense that Y-793605 was in the same fall with them, it can be concluded that Y-793605 originated from the same igneous body or rock in Mars as ALH77005 and LEW88516

Lherzolitic Martian meteorites Allan Hills 77005, Lewis Cliff 88516 and Yamato-793605: Major and minor element zoning in pyroxene and plagioclase glass

Three lherzolitic Martian meteorites (ALH77005,LEW88516 and Y-793605) show very similar petrography and mineralogy. They consist of the poikilitic and non-poikilitic (interstitial) areas that are heterogeneous on a cm-scale. A detailed electron microprobe analysis of pyroxene and plagioclase glass from these meteorites gives characteristic distributions of major and minor elements. It is striking that pyroxene and plagioclase glass in all three meteorites have nearly identical zoning patterns of these elements, while olivine shows different chemistry. This is because olivine chemistry was largely controlled by a late-stage re-equilibration which did not significantly modify the major and minor element distributions in pyroxene and plagioclase glass. However, a close look at minor element zoning in plagioclase glass exhibits slightly different zoning patterns among these three meteorites, corresponding to different degrees of re-equilibration (degrees of re-equilibration : ALH77005>LEW88516>Y-793605). Nevertheless, it is evident that they experienced a very similar igneous crystallization history and they are likely to have originated from the same igneous unit on Mars

Mineralogy and olivine cooling rate of the Dhofar 019 shergottite

Dhofar 019 is a new basaltic shergottite found in Oman. It is mainly composed of pyroxenes, plagioclase glass, and olivine. Olivine grains show variable size distributions from large (∿1mm) non-euhedral zoned grains with magnesian cores (Fa_) to small euhedral homogeneous grains with variable compositions (Fa_). This may suggest that some of the Dhofar 019 olivines are xenocrysts and others are phenocrysts. The Dhofar 019 olivines are compositionally distinct from those in other shergottites. Pyroxenes are extensively zoned, and pigeonite cores are usually surrounded with augite rims, suggesting undercooling of magma to a similar degree as that of EETA 79001 (lithology A) and Zagami. There appears to be a compositional change in major and minor elements from the magnesian pyroxenes to ferroan pyroxenes for both pigeonite and augite. The magnesian parts have similar compositions to EETA 79001 (lithology A) pyroxenes, and the ferroan parts are similar to Zagami pyroxenes. Plagioclase zoning in Dhofar 019 more closely resembles that of Zagami. Spinel compositions in Dhofar 019 overlap those of EETA79001,and the Dhofar 019 chromite may be a xenocryst like EETA79001. The cooling rate of Dhofar 019 calculated from Fe-Mg zoning profiles of olivine is 0.05-0.1℃/hour. This corresponds to a burial depth of ∿5m from the martian surface, possibly in a lava flow. Thus, the groundmass crystallization of Dhofar 019 occurred near the martian surface, although it is likely that Dhofar 019 has experienced a complex history

Diffuse reflectance spectra for heated samples of an H5 chondrite: Importance of oxygen fugacity at heating

We obtained (biconical) diffuse reflectance spectra of the Nuevo Mercurio (H5) ordinary chondrite in the 200-2500 nm wavelength region. The samples were heated in the temperature range of 800-1200℃ at constant oxygen fugacities at one log unit below the iron-wustite (IW) buffer (IW-1) and two log units above the IW buffer (IW+2). The spectra of the samples heated to temperatures lower than 1050℃ at IW+2 show low spectral contrast and shorter wavelength positions of UV drop-off compared with the unheated <100 μm sample. On the basis of our heating experiments, this work suggests that oxygen fugacity affects the spectra of the heated samples especially at IW+2,implying that oxygen-fugacity control is important for heating experiment and that oxygen fugacity may play a role in the surface processes on asteroids

Increasing the Receptor Tyrosine Kinase EphB2 Prevents Amyloid-β-induced Depletion of Cell Surface Glutamate Receptors by a Mechanism That Requires the PDZ-binding Motif of EphB2 and Neuronal Activity.

Diverse lines of evidence suggest that amyloid-β (Aβ) peptides causally contribute to the pathogenesis of Alzheimer disease (AD), the most frequent neurodegenerative disorder. However, the mechanisms by which Aβ impairs neuronal functions remain to be fully elucidated. Previous studies showed that soluble Aβ oligomers interfere with synaptic functions by depleting NMDA-type glutamate receptors (NMDARs) from the neuronal surface and that overexpression of the receptor tyrosine kinase EphB2 can counteract this process. Through pharmacological treatments and biochemical analyses of primary neuronal cultures expressing wild-type or mutant forms of EphB2, we demonstrate that this protective effect of EphB2 depends on its PDZ-binding motif and the presence of neuronal activity but not on its kinase activity. We further present evidence that the protective effect of EphB2 may be mediated by the AMPA-type glutamate receptor subunit GluA2, which can become associated with the PDZ-binding motif of EphB2 through PDZ domain-containing proteins and can promote the retention of NMDARs in the membrane. In addition, we show that the Aβ-induced depletion of surface NMDARs does not depend on several factors that have been implicated in the pathogenesis of Aβ-induced neuronal dysfunction, including aberrant neuronal activity, tau, prion protein (PrP(C)), and EphB2 itself. Thus, although EphB2 does not appear to be directly involved in the Aβ-induced depletion of NMDARs, increasing its expression may counteract this pathogenic process through a neuronal activity- and PDZ-dependent regulation of AMPA-type glutamate receptors

Cooling rates of olivine xenocrysts in the EET79001 shergottite

The chemical zoning profiles of olivine xenocrysts in lithology A of the Elephant Moraine (EET) 79001 basaltic shergottite have been measured in order to investigate its cooling history. Olivines are zoned from Fa_ in the cores to Fa_ in the rims. The major and minor element compositions of olivine xenocryst cores in EET79001 correspond to those of homogeneous olivines in the lherzolitic shergottites, reconfirming the previous studies. We assume that the initial profile of olivine was uniform and it was modified by atomic diffusion due to contact with the Fe-rich surrounding melt when olivine was incorporated as a xenocryst. Comparing the observed Fe zoning profiles with the calculated ones, we have estimated the minimum cooling rates of the xenocrystic olivines by numerically solving the diffusion equation. The inferred minimum cooling rates (0.07-0.5℃) are faster than that for Zagami estimated from the width of pyroxene lamella, consistent with a hypothesis that EET79001 experienced significant undercooling unlike Shergotty and Zagami. We also performed the calculations by applying two different Fe-Mg interdiffusion coefficients to evaluate them. There is no significant difference in the curvature of the calculated profiles between the two diffusion coefficients, whereas one gives roughly fivefold higher cooling rates than the other