Heather A. Viles
School of Geography and the Environment, University of Oxford, Oxford OX1 3QY, UK
We currently do not have a copyright agreement with this publisher and cannot display the abstract here.
Reference
Viles HA (2014) Solar system: Cracking up on asteroids. Nature 508:190.
[doi:10.1038/nature13222]
Marco Delbo1 et al.*
*Find the extensive, full author and affiliation list on the publishers website.
aLaboratoire Lagrange, UNS-CNRS, Observatoire de la Côte d’Azur, Boulevard de l’Observatoire-CS 34229, 06304 Nice Cedex 4, France
We currently do not have a copyright agreement with this publisher and cannot display the abstract here.
Reference
Delbo M (2014) Thermal fatigue as the origin of regolith on small asteroids. Nature 508:233.
[doi:10.1038/nature13153]
Justin Filiberto1, Juliane Gross2, Jarek Trela1,† and Eric C. Ferré1
1Department of Geology, Southern Illinois University, 1259 Lincoln Drive, MC 4324, Carbondale, Illinois 62901, U.S.A.
2Department of Earth and Planetary Sciences, The American Museum of Natural History, Central Park West at 79th Street, New York, New York 10024, U.S.A.
†Virginia Tech, Department of Geosciences, 4044 Derring Hall (0420), Blacksburg, Virginia 24061, U.S.A.
Meteorite Northwest Africa (NWA) 6963 was classified as a basaltic shergottite based on mineralogy, but here we show that it is a gabbroic rock with a quartz-alkali feldspar intergrowth that represents a late-stage granitic melt. NWA 6963 contains clinopyroxene and maskelynite grains up to 5 mm in length, with minor ferroan olivine, spinel, ilmenite, merrillite, apatite, Fe-sulfides, and high-Si glass. NWA 6963 also contains areas of quartz and alkali-feldspar intergrowths up to ~1 mm in size. Based on mineral abundances and textural analysis, we suggest that NWA 6963 is an intrusive rock similar to a terrestrial gabbro. Infiltration of the martian crust by young gabbroic bodies would suggest that estimates of crustal composition, density, and thickness based on the surface chemistry alone would be problematic and the martian crust may be even more heterogenous than is seen from orbit alone. Investigations of crater walls, where intrusive crustal rocks would be exposed, are needed to discover the launch sites of the shergottites and the full heterogeneity of the martian crust.
Reference
Filiberto J, Gross J, Trela J and Ferré EC (2014) Gabbroic Shergottite Northwest Africa 6963: An intrusive sample of Mars‡. American Mineralogist 99:601.
[doi:10.2138/am.2014.4638]
Copyright: The Mineralogical Society of America
Chi Ma*, John R. Beckett and George R. Rossman
Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125, U.S.A.
During a nanomineralogy investigation of the Allende meteorite with analytical scanning electron microscopy, two new minerals were discovered; both occur as micro- to nano-crystals in an ultrarefractory inclusion, ACM-1. They are allendeite, Sc4Zr3O12, a new Sc- and Zr-rich oxide; and hexamolybdenum (Mo,Ru,Fe,Ir,Os), a Mo-dominant alloy. Allendeite is trigonal, R3̄, a = 9.396, c = 8.720, V = 666.7 Å3, and Z = 3, with a calculated density of 4.84 g/cm3 via the previously described structure and our observed chemistry. Hexamolybdenum is hexagonal, P63/mmc, a = 2.7506, c = 4.4318 Å, V = 29.04 Å3, and Z = 2, with a calculated density of 11.90 g/cm3 via the known structure and our observed chemistry. Allendeite is named after the Allende meteorite. The name hexamolybdenum refers to the symmetry (primitive hexagonal) and composition (Mo-rich). The two minerals reflect conditions during early stages of the formation of the Solar System. Allendeite may have been an important ultrarefractory carrier phase linking Zr-,Sc-oxides to the more common Sc-,Zr-enriched pyroxenes in Ca-Al-rich inclusions. Hexamolybdenum is part of a continuum of high-temperature alloys in meteorites supplying a link between Os- and/or Ru-rich and Fe-rich meteoritic alloys. It may be a derivative of the former and a precursor of the latter.
Reference
Ma C, Beckett JR and Rossman GR (2014) Allendeite (Sc4Zr3O12) and hexamolybdenum (Mo,Ru,Fe), two new minerals from an ultrarefractory inclusion from the Allende meteorite. American Mineralogist 99:654.
[doi:10.2138/am.2014.4667]
Copyright: The Mineralogical Society of America
Andrei A. Shiryaev1,2 and and Fabrice Gaillard3
1Institute of Physical Chemistry and Electrochemistry RAS, Leninsky pr. 31, 119071 Moscow, Russia
2Institute of Geology of Ore Deposits, Petrography, Mineralogy and Geochemistry RAS, Staromonetny per. 35, 119017 Moscow, Russia
3CNRS/INSU, Institut des Sciences de la Terre d’Orléans – UMR 6113, Université d’Orléans, Campus Géosciences, 1A rue de la Férollerie, 41071 Orléans cedex 2, France
Grains of natural SiC, moissanite, are encountered in various geological settings. According to thermodynamic calculations and high-pressure experiments, SiC formation requires very reducing conditions, approx. 6–10 orders of magnitude in fO2 more reducing than the present-day mantle redox state. SiC occurrences have motivated several studies but the required extremely reducing conditions remain a major inconsistency that has not been solved. It is shown here that such reducing conditions can be achieved during the ultimate steps of ascent of carbon-saturated melts, when pressure is lower than 100 bars. At these conditions, the redox buffering by carbon can impose fO2 similar to IW-6. Conditions favorable to SiC growth can therefore be reached around carbonaceous grains during the shallow emplacement of silicate melts or kimberlites and do not necessarily imply extremely localized oxygen-depleted regions in the mantle. Such reduced conditions can also explain the presence of elemental Si and ironcarbide inclusions in association with moissanite grains.
Reference
Shiryaev AA and and Gaillard F (2014) Local redox buffering by carbon at low pressures and the formation of moissanite – natural SiC. European Journal of Mineralogy 26:53.
[doi:10.1127/0935-1221/2013/0025-2339]
Copyright: E. Schweizerbart’sche Verlagsbuchhandlung
Cosmochemistry Papers 