We have studied magnetic fractions of five acapulcoites, three lodranites, and two winonaites to investigate chemical compositions of their precursor materials and metallic partial melting processes occurring on their parent bodies. One winonaite metal is similar in composition to low Au, low Ni IAB iron subgroup, indicating genetic relationship between them. Magnetic fractions of chondrule-bearing acapulcoite and winonaite have intermediate chemical compositions of metals between H chondrites and EL chondrites. This fact indicates that the precursor materials of acapulcoite-lodranites and winonaites were similar to H and/or EL chondrites in chemical compositions. Magnetic fractions in acapulcoite-lodranites have a large variety of chemical compositions. Most of them show enrichments of W, Re, Ir, Pt, Mo, and Rh, and one of them shows clear depletion in Re and Ir relative to those of chondrule-bearing acapulcoite. Chemical compositional variations among acapulcoite-lodranite metals cannot be explained by a single Fe-Ni-S partial melting event, but a two-step partial melting model can explain it.

© 2017 Cambridge University Press. The Tsenkher structure in the Gobi-Altai, Mongolia is a c. 3.7 km diameter crater with a well-preserved ejecta blanket. It has been hypothesized to be either of impact or volcanic origin in our previous work. Observations during our 2007 expedition and related sample analyses give further support for an impact origin. The evidence includes the presence of a structurally uplifted near-circular rim surrounded by an ejecta blanket, and abundant breccias, some of which are melt- A nd millimetre-scale spherule-bearing. Planar deformation features (PDFs) were found in one quartz grain in a breccia sample. Fe-rich grains are found in a vesicular melt sample that is also characterized by elevated platinum group element (PGE) abundances with respect to the sedimentary bedrock of the area (approximately an order of magnitude). Noble gas analysis of one breccia sample yielded an elevated 3 He/ 4 He value of (5.0±0.2) × 10 -6 . Although not conclusive alone, these geochemical results are consistent with a contribution of meteoritic components. A volcanic origin, in particular a maar formation, would require explanations for the unusual conditions associated with Tsenkher, including its large size occurring in isolation, the structurally uplifted rim and the lack of a bedded base surge deposit. A pronounced rampart structure observed at the eastern ejecta is also unusual for any volcanic origin. 40 Ar- 39 Ar dating of a vesicular melt sample gives an age of the Tsenkher structure of 4.9±0.9 Ma. The rampart structure could provide insights into the formation of similar ejecta morphologies associated with numerous impact craters on Mars.

<p></p>

A simple and effective instrumental neutron activation analysis for iron meteorites is presented in this study. In order to design the analytical procedure, self-absorption of gamma-rays on samples, interfering nuclides and their respective reactions were examined. Seventeen elements (Fe, Co, Ni, Cu, Ga, Ge, As, Mo, Ru, Rh, Sb, W, Re, Os, Ir, Pt and Au) could be nondestructively determined in Canyon Diablo and Cape York iron meteorites. Our data of these two iron meteorites are consistent with the corresponding literature values. This study confirms that our analytical procedure with INAA is simple and effective in classification of iron meteorites.

We have studied the feldspathic lunar meteorite Dhofar 1428 chemically and petrologically to better understand the evolution of the lunar surface. Dhofar 1428 is a feldspathic regolith breccia derived from the lunar highland. Bulk chemical and mineral compositions of Dhofar 1428 are similar to those of other feldspathic lunar meteorites. We found a few clasts of evolved lithologies, such as K-rich plagioclases and quartz monzogabbro. Dhofar 1428 contains approximately 1 wt% of chondritic materials like CM chondrite on the basis of abundances of platinum group elements (Ru, Rh, Pd, Os, Ir, and Pt).

誘導結合プラズマ質量分析計 (ICP-MS) や実験室の維持管理に必要な消耗品類や実験器具の購入に必要な費用の捻出を行えたため、装置の定常運用が可能となり、希土類元素測定や親鉄・親銅元素測定のための実験を行う環境を整えることが出来た。それにより実試料の分析を行い、本年度は環境試料測定、地球岩石の希土類元素測定、親鉄・親銅元素組成測定などを行った。

昨年度に移管した誘導結合プラズマ質量分析計 (ICP-MS) や実験室の維持管理に必要な消耗品類や実験器具の購入に必要な費用の捻出を行えたため、装置の定常運用が可能となり、希土類元素測定や親鉄・親銅元素測定のための実験を行う環境を整えることが出来た。それにより実試料の分析を開始し、本年度はCBおよびCHコンドライト隕石についての確度の良い親鉄・親銅元素の全岩組成を得ることが出来た。その他、地球の岩石試料の希土類元素分析への着手も開始しており、分析例の少ない標準試料の高確度・高精度の希土類元素組成情報を得られるよう、継続して実験を行っている。