Major-element trend for shergottite melts and their source materials

The major-element compositions of shergottite melts, plotted against their mg [Mg/(Mg+Fe)] atomic ratios, form a narrow trend, which is designated the shergottite melt trend". Although the mg ratios range from 0.7 to 0.2, the silica contents of the trend are nearly constant from 47 to 53wt%, indicating that the shergottite melts are basaltic, never andesitic nor komatiitic. The trend is enriched in FeO with the range from 15 to 22wt%, and poor in Al_2O_3 with the range from 4 to 14wt%. The melts for nakhlites are poorer in SiO_2 and Al_2O_3 and richer in FeO than the shergottite melt trend. Although the melts for chassignite are similar to the shergottite melt trend, the melts for chassignite and nakhlites are more enriched in K_2O contents than the shergottites melts, indicating that they have a different origin from the latter. The bulk major-element compositions of terrestrial basalts, lunar basalts, and eucrites are compared to the shergottite melt trend. The terrestrial basalts and komatiites are poorer in FeO and richer in Al_2O_3, CaO, and Na_2O than the shergottite melt trend. The lunar low-Ti mare basalts and eucrites have rather similar compositions to the shergottite trend. However, their alkali and P_2O_5 contents are low in comparison to the shergottite trend, reflecting their planetary compositions. A plausible source material for olivine-phyric shergottites was estimated, and it may be a plagioclase peridotite with an mg ratio of 0.81 depleted in alkalis, CaO and Al_2O_3 contents. The partial melting to produce the shergottite trend may have taken place at low pressures, whereas the nakhlites and chassignite may have been produced under moderate (1-30kb) pressure conditions. The chassignite may have fractionated under a low-pressure condition to produce a large amount of cumulus olivine, whereas the nakhlites have not

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

Magnetic properties of quadruple perovskites Ba4LnRu3O12 (Ln=La, Nd, Sm-Gd, Dy-Lu)

Quadruple perovskites Ba4LnRu3O12 (Ln=La, Nd, Sm-Gd, Dy-Lu) were prepared and their magnetic properties were investigated. They adopt the 12L-perovskite-type structure consisting of Ru3O12 trimers and LnO6 octahedra. All of these compounds show an antiferromagnetic transition at 2.5-30 K. For Ba4NdRu3O12, ferrimagnetic ordering has been observed at 11.5 K. The observed magnetic transition is due to the magnetic behavior of the Ru^[4.33+]3O12 trimer with S=1/2. Magnetic properties of Ba4LnRu3O12 were compared with those of triple perovskites Ba3LnRu2O9 and double perovskites Ba2LnRuO6

Magnetic and electrical properties of quadruple perovskites with 12 layer structures Ba4LnM3O12 (Ln=rare earths; M=Ru, Ir) : The role of metal-metal bonding in perovskite-related oxides

Structures and magnetic and electrical properties of quadruple perovskites containing rare earths Ba4LnM3O12 (Ln = rare earths; M=Ru, Ir) were investigated. They crystallize in the 12L-perovskite-type structure. Three MO6 octahedra are connected to each other by face-sharing and form a M3O12 trimer. The M3O12 trimers and LnO6 octahedra are alternately linked by corner-sharing, forming the perovskite-type structure with 12 layers. For Ln = Ce, Pr, and Tb, both the Ln and M ions are in the tetravalent state (Ba4Ln^[4+]M^[4+]_[3]O12), and for other Ln ions, Ln ions are in the trivalent state and the mean oxidation state of M ions is +4.33 (Ba4Ln^[3+]M^[4.33+]_[3]O12). All the Ba4Ln^[3+]Ru^[4.33+]_[3]O12 compounds show magnetic ordering at low temperatures, while any of the corresponding iridium-containing compounds Ba4Ln^[3+]Ir^[4.33+]_[3]O12 is paramagnetic down to 1.8K. Ba4Ce^[4+]Ir^[4+]_[3]O12 orders antiferromagnetically at 10.5 K, while the corresponding ruthenium-containing compound Ba4Ce^[4+]Ru^[4+]_[3]O12 is paramagnetic. These magnetic results were well understood by the magnetic behavior of M3O12. The effective magnetic moments and the entropy change for the magnetic ordering show that the trimers Ru^[4.33+]_[3]O12 and Ir^[4+]_[3]O12 have the S=1/2 ground state, and in other cases there is no magnetic contribution from the trimers Ru^[4+]_[3]O12 or Ir^[4.33+]_[3]O12. Measurements of the electrical resistivity of Ba4LnM3O12 and its analysis show that these compounds demonstrate two-dimensional Mott-variable range hopping behavior

Synthesis and magnetic properties of 12L-perovskites Ba4LnIr3O12 (Ln = lanthanides)

New quadruple perovskite oxides Ba4LnIr3O12 (Ln = lanthanides) were prepared and their magnetic properties were investigated. They crystallize in the monoclinic 12L-perovskite-type structure with space group C2/m. The Ir3O12 trimers and LnO6 octahedra are alternately linked by corner-sharing and form the perovskite-type structure with 12 layers. The Ln and Ir ions are both in the tetravalent state for Ln = Ce, Pr, and Tb compounds (Ba4Ln^[4+]Ir^[4+]3O12), and for other compounds (Ln = La, Nd, Sm-Gd, Dy-Lu), Ln ions are in the trivalent state and the mean oxidation state of Ir ions is +4.33(Ba4Ln^[3+]Ir^[4.33+]3O12). An antiferromagnetic transition has been observed for Ln = Ce, Pr, and Tb compounds at 10.5, 35, and 16 K, respectively, while the other compounds are paramagnetic down to 1.8 K