The Yamato 980459 olivine-phyric shergottite consortium

Among 4100 meteorite samples found around the Yamato Mountain area during the field season of 1998-1999, Yamato (Y) 980459, weight of 82g, is identified as a new shergottite. In ordered to improve our knowledge of the shergottite parent body, possibly Mars, a coordinated consortium study of the Y980459 shergottite was organized. Petrological, mineralogical, chemical and isotopic studies revealed that Y980459 is related to the olivine-phyric shergottites and the most primitive Martian basalt so far reported. Y980459 has solidified much faster than other shergottites, as indicated by its lack of plagioclase or maskelynite. Y980459 shows a light REE depleted pattern similar to other depleted shergottites" Dhofar 019, Dal al Gani (DaG) 476, Sayh al Uhamir (SaU) 005 and Queen Alexandra Range 94201. The Sm-Nd isotopic data suggest that Y980459 crystallized at 470Ma and derived from a highly depleted source region. Cosmic-ray exposure age of Y980459 is calculated to be 1Ma based on 10Be concentration, which is similar to those of olivine-phyric shergottites DaG 476 and SaU 005. I here present an outline of the consortium and implications for Martian geological history on the basis of ongoing studies. The first petrographical description of Y980459 by Ansgar Greshake, Jorg Fritz and Dieter Stoffler was not submitted to Antarctic Meteorite Research, but to Geochimica et Cosmochimica Acta on August 15, 2003, and was published in the May 15, 2004 issue. The other papers concerning Y980459 appeared in the Antarctic Meteorite Research, 17 issue are of equal scientific importance and priority

Stable Sr isotopes of the Middle Permian carbonate: its implication of ocean Sr budget change

The Tenth Symposium on Polar Science/Ordinary sessions: [OG] Polar Geosciences, Wed. 4 Dec. / 3F Seminar room, National Institute of Polar Researc

U-Th-Pb isotopic systematics of lunar meteorite Asuka-31

U-Th-Pb isotopic systematics indicate that Asuka-31 is of lunar origin and was formed 3940±8Ma. The Pb isotopic composition is extremely nonradiogenic compared with those of typical Apollo mare basalts. The Pb-Pb, U-Pb, and Th-Pb ages are concordant at 3.94Ga. The U-Pb data from maskelynitized plagioclase does not plot on the internal isochrons defined by other mineral separates, indicating that it was disturbed by a later shock event(s). The U-Th-Pb systematics of Asuka-31,combined with previous results, suggest a scenario for the early Pb isotope evolution of the Moon. According to the currently popular hypothesis for lunar origin, following a collision between the Earth and another large planetesimal, the Moon was formed mainly from the Earth\u27s mantle and partially from the other impactor. The primary ^U/^Pb (μ) value of the Moon had been increased four to five times that of the Earth\u27s mantle value (∿8) by volatilization of Pb during the impact. Further depletion of Pb within the Moon\u27s mantle is believed to have occurred during lunar core formation. The chalcophile behavior of Pb and large partition coefficient of Pb in silicate minerals compared to those of U and Th helped to decrease μ values of early cumulates that formed from the magma ocean and settled in the deep lunar mantle. The μ values of later cumulates gradually increased as a result of extensive fractionation. We suggest that Asuka-31 originated from partial melting of early cumulates enriched with sulfides

Barium isotopic compositions of ordinary chondrites

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

Evaluation of the shock-resetting conditions of U-Pb isotopic systematics for baddeleyite in the Martian shergottites

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

Compositions of REE, K, Rb, Sr, Ba, Mg, Ca, Fe, and Sr isotopes in Antarctic"unique" meteorites

The abundances of Mg, Ca, Fe, K, Rb, Sr, Ba, and REE in five Antarctic "unique" meteorites, acapulcoite-lodranite type, Yamato (Y)-74063,Y-74357,Y-8002,and Allan Hills (ALH)-78230,and winonaite type, Y-75300 were determined by isotope dilution mass spectrometry. The Sr isotopic compositions of Y-74063,Y-75300,Y-8002,and ALH-78230 were also measured to investigate the whole-rock Rb-Sr isotopic systematics. In terms of the REE abundance pattern, these meteorites are grouped as follows; (1) Y-74063 and ALH-78230 with chondritic REE patterns, (2) Y-74357 with light REE depletion plus alkali and alkaline earth element depletion, and (3) Y-75300 and Y-8002 with middle REE depletion (V-shaped REE pattern) plus a positive Eu anomaly). The mineralogy of these meteorites is closely related to the above REE classification. The ^Rb-^Sr age determined from \u27whole-rock samples\u27 for Y-74063,Y-75300,Y-8002,and ALH-78230 is consistent with their formation of 4.5Ga, albeit with a large uncertainty due to the blank correction. Using the mineral/liquid partition coefficients of trace elements, the petrogenetic model calculations were performed. The results give indication on the origin of these "unique" meteorites. Y-74063 and ALH-78230 could be formed through a small degree of partial melting (less than a few%) from a chondritic starting material. Y-74357 could be formed by a larger degree (12%) of partial melting. On the other hand, the V-shaped REE pattern of the third group (Y-75300 and Y-8002) could not be explained by a simple partial melting process. The V-shaped REE pattern may be explained only by assuming the solid state equilibration within a reservoir with chondritic composition. It is suggested that Y-75300 and Y-8002 might be derived from parental materials depleted in phosphate and clinopyroxene

Minor element chemistry of low-Ca pyroxene in Allan Hills-77252, an L3-6 regolith breccia

Allan Hills (ALH-) 77252 is a regolith breccia consisting of various types of clasts differing in metamorphic grades (L3-6). Titanium/aluminum ratios of low-Ca pyroxene in ALH-77252 are bimodally distributed. In equilibrated clasts, Ti/Al ratios of low-Ca pyroxene are ∿0.5 which are quite different from those in unequilibrated clasts of ∿0.07. Among equilibrated and unequilibrated clasts, the Ti/Cr ratio of low-Ca pyroxene also shows large differences. Because titanium and aluminum are not diffusive elements in the pyroxene crystal structure, diffusional redistribution of titanium and aluminum in low-Ca pyroxene requires significantly higher metamorphic temperature than Fe-Mg homogenization, possibly above ∿800℃. Alternatively, if the source materials of L-group chondrites were initially different, the fingerprints of mineral properties resistant to thermal metamorphism remain unchanged. If this was the case, the distinctly higher Ti/Al ratios of low-Ca pyroxene in equilibrated clasts originated from the primary signatures of low-Ca pyroxene prior to thermal metamorphism

The Yamato nakhlite consortium

Among 3550 meteorite samples found near the Yamato Mountains area during the field season of 2000-2001, three meteorites, Yamato (Y) 000593, Y000749, and Y000802 of total weight of about 15 kg, are identified as new paired nakhlites. In ordered to improve our knowledge of the nakhlite parent body, possibly Mars, a coordinated consortium study of the Yamato nakhlites was organized. We here present an outline of the Yamato nakhlite consortium and implications for Martian geological history on the basis of ongoing studies

U-Th-Pb isotopic systematics of lherzolitic shergottite Yamato-793605

We have undertaken U-Th-Pb isotopic studies on lherzolitic shergottite, Yamato-793605. Four mineral separates (olivine, plagioclase, and two phases of pyroxene) and a whole-rock sample were leached with dilute acid in order to remove secondary Pb contamination. However, preferential leaching of U and Th over Pb occurred. The Pb isotopic data points of five residue fractions scattered, and a calculated Pb-Pb age does not clearly indicate either crystallization from a melt or a later disturbance to the U-Pb system, in contrast with other shergottites. The chord through U-Pb data points for pyroxene (PXl) leaches and residue intersects concordia at 4439±9 Ma and 212±62 Ma, suggesting a young disturbance event resulting in Pb loss. The later disturbance event partially reset the U-Pb system. The estimated ^U/^Pb (≡μ) value from the whole-rock residue for the source of Y-793605 is about 5,suggesting that Y-793605 was derived from a volatile-rich source environment and confirms a low-μ source for shergottites compared to volcanic rocks of the Earth