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.

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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).