Abstract-Northwest Africa (NWA) 1068 is one of the few olivine-phyric shergottites (e.g., NWA 1068, Larkman Nunatak [LAR] 06319, and Roberts Massif [RBT] 04262) that is not depleted in light rare earth elements (LREE). Its REE pattern is similar to that of the basaltic shergottite Shergotty, suggesting a possible connection between the olivine-phyric and the basaltic shergottites. To test this possible link, we have investigated the high-pressure nearliquidus phase equilibria for the NWA 1068 meteorite bulk composition. Our results show that the NWA 1068 bulk composition does not represent an unmodified mantle-derived melt; the olivine and pyroxene in our near-liquidus experiments are more magnesian than in the rock itself, which suggests that NWA 1068 contains cumulate minerals (extra olivine). We have then used these experimental results combined with the pyroxene compositions in NWA 1068 to constrain the possible high-pressure crystallization history of the parental magma. These results suggest that NWA 1068 had a complex polybaric history. Finally, we have calculated a model parental magma composition for the NWA 1068 meteorite. The calculated parental magma is an evolved basaltic composition which is too ferroan to be a primitive melt directly derived from the mantle. We suggest that it ponded and crystallized at approximately the base of the crust. This provided an opportunity for the magma to become contaminated by an ''enriched'' crustal component prior to crystallization. The results and modeling from these experiments are applicable not only to the NWA 1068 meteorite, but also to LAR 06319 and possibly any other enriched olivine-phyric shergottite.

No abstract

Epitaxial VO/TiO thin film heterostructures were grown on (100) (m-cut) AlO substrates via pulsed laser deposition. We have demonstrated the ability to reduce the semiconductor-metal transition (SMT) temperature of VO to ∼44 °C while retaining a 4 order of magnitude SMT using the TiO buffer layer. A combination of electrical transport and X-ray diffraction reciprocal space mapping studies help examine the specific strain states of VO/TiO/AlO heterostructures as a function of TiO film growth temperatures. Atomic force microscopy and transmission electron microscopy analyses show that the columnar microstructure present in TiO buffer films is responsible for the partially strained VO film behavior and subsequently favorable transport characteristics with a lower SMT temperature. Such findings are of crucial importance for both the technological implementation of the VO system, where reduction of its SMT temperature is widely sought, as well as the broader complex oxide community, where greater understanding of the evolution of microstructure, strain, and functional properties is a high priority.

Space weathering on airless bodies includes a number of processes, such as micrometeorite impacts and solar wind bombardment, which leads to a variety of microscale to nanoscale alteration features, including vapor deposited layers on grain and rock surfaces and creation of nanophase opaque inclusions. The nanophase inclusions cause reddening and darkening of the visible to near-infrared spectra of space weathered material, features associated with increasing space exposure of many airless body regoliths. On the Moon, most nanophase inclusions are metallic iron (npFe 0 ), but recent work using aberration-corrected scanning transmission electron microscopy and electron energy loss spectroscopy has provided evidence of oxidized nanoparticles in space weathered lunar soil grains. We examined three different lunar soils in order to confirm the finding of oxidized nanophase inclusions and to provide detailed elemental and mineralogical information about the surrounding material. Our data show that substrate and rim composition are key factors in determining whether highly localized oxidation occurs; for example, nanophase inclusions in rims on low Fe substrates are more prone to oxidation. Detailed understanding of the phases and features present in these samples is necessary for the correct interpretation of remotely sensed data as well as extrapolation from processes on the lunar surface to those on other airless bodies.Plain Language Summary The Moon and asteroids are being constantly altered by interactions with the space environment, a process known as space weathering. These interactions, such as with solar wind ions and micrometeoroids, can be studied by examining samples from the Moon and analyzing the nanoscale features present in surface coatings or rims on small lunar dust grains. Using techniques such as energy dispersive X-ray spectroscopy and electron energy loss spectroscopy in the scanning transmission electron microscope, we are able to image and measure the composition and oxidation state of the nanoscale inclusions and layers in these rims. These data provide evidence of complex material interactions, such as formation of metallic iron inclusions at a variety of sizes contained within specific sublayers, and oxidation to magnetite of some of those inclusions. From this information, we can better interpret spacecraft and telescopic data of the Moon and asteroids that can be significantly influenced by space weathering and the presence of nanoscale inclusions. We can also compare these data to samples that have been experimentally space weathered in the laboratory using pulsed laser or ion irradiation in order to gain a better understanding of the conditions necessary to create observed features.

Without a protective atmosphere, space-exposed surfaces of airless Solar System bodies gradually experience an alteration in composition, structure and optical properties through a collective process called space weathering. The return of samples from near-Earth asteroid (162173) Ryugu by Hayabusa2 provides the first opportunity for laboratory study of space-weathering signatures on the most abundant type of inner solar system body: a C-type asteroid, composed of materials largely unchanged since the formation of the Solar System. Weathered Ryugu grains show areas of surface amorphization and partial melting of phyllosilicates, in which reduction from Fe3+ to Fe2+ and dehydration developed. Space weathering probably contributed to dehydration by dehydroxylation of Ryugu surface phyllosilicates that had already lost interlayer water molecules and to weakening of the 2.7 µm hydroxyl (–OH) band in reflectance spectra. For C-type asteroids in general, this indicates that a weak 2.7 µm band can signify space-weathering-induced surface dehydration, rather than bulk volatile loss.

[1] Absolute paleointensity estimates from submarine basaltic glass (SBG) typically are of high technical quality and accurately reflect the ambient field when known. SBG contains fine-grained, low-Ti magnetite, in contrast to the high-Ti magnetite in crystalline basalt, which has lead to uncertainty over the origin of the magnetite and its remanence in SBG. Because a thermal remanence is required for accurate paleointensity estimates, the timing and temperature of magnetite formation is crucial. To assess these factors, we generated a suite of synthetic glasses with variable oxygen fugacity, cooling rate, and FeO* content. Magnetic properties varied most strongly with crystallinity; less crystalline specimens are similar to natural SBG and have weaker magnetization, a greater superparamagnetic contribution, and higher unblocking temperatures than more crystalline specimens. Thellier-type paleointensity results recovered the correct field within 1s error with 2 (out of 10) exceptions that likely result from an undetected change in the laboratory field. Unblocking and ordering temperature data demonstrate that low-Ti magnetite is a primary phase, formed when the glass initially quenched. Although prolonged heating at high temperatures (during paleointensity experiments) may result in minor alteration at temperatures < 580°C, this does not appear to impact the accuracy of the paleointensity estimate. Young SBG is therefore a suitable material for paleointensity studies.

We use Raman scattering to study phase transition in the graphitic g-BC 8 phase and graphite at high pressure up to 84 GPa. The E 2g Raman active mode of graphite (G peak) can be detected up to 84 GPa. We demonstrate that there is (1) a phase transition in g-BC 8 and in graphite at 35 GPa and (2) that above 35 GPa, the g-BC 8 and graphite transform under high pressure to possibly fully sp 3 -bonded, disordered hp-BC 8 , and hp-C phases. Below the phase transition, a polynomial fit to the G peak position versus pressure data yielded a quadratic relation; above the phase transition, it demonstrates linear behavior. The phase transition at high pressure in BC 8 system and graphite is reversible. Quenched hp-BC 8 and hp-C phases have the Raman spectrum typical to that of the graphitic phases.

[1] As part of an experimental and observational study of the magnetic response of submarine basaltic glass (SBG), we have examined, using ion backscattering spectrometry (RBS), transmission and scanning electron microscopy, energy dispersive X-ray spectrometry, and surface X-ray diffraction, the textures wrought by the controlled, open and closed system oxidation of glasses prepared by the controlled environment remelting and quenching of natural SBG. Initial compositions with ∼9 wt % FeO* were melted at 1430°C with the oxygen fugacity buffered at fayalite-magnetite-quartz; melts were cooled at a rate of 200°C min −1 near the glass transition (T g = 680°C). In open system experiments, where chemical exchange is allowed to occur with the surrounding atmosphere, polished pieces of glass were reheated to temperatures both below and above T g for times 1-5000 h; undercooled melts were oxidized at 900°C and 1200°C for 18 and 20 h, respectively. RBS demonstrates unequivocally that the dynamics of open system oxidation involves the outward motion of network-modifying cations. Oxidation results in formation of a Fe-, Ca-, and Mg-enriched surface layer that consists in part of Ti-free nanometer-scale ferrites; a divalentcation-depleted layer is observed at depths >1 mm. Specimens annealed/oxidized above T g have magnetizations elevated by 1-2 orders of magnitude relative to the as-quenched material; this does not appear to be related to the surface oxidation. Quenched glass (closed system, i.e., no chemical exchange between sample and atmosphere) exhibits very fine scale chemical heterogeneities that coarsen with time under an electron beam; this metastable amorphous immiscibility is the potential source for the nucleation of ferrites with a wide range of Ti contents, ferrites not anticipated from an equilibrium analysis of the bulk basalt composition.