Petrography and composition of Martian regolith breccia meteorite Northwest Africa 7475

The Northwest Africa (NWA) 7475 meteorite is one of the several stones of paired regolith breccias from Mars based on petrography, oxygen isotope, mineral compositions, and bulk rock compositions. Its inventory of lithic clasts is dominated by vitrophyre impact melts that were emplaced while they were still molten. Other clast types include crystallized impact melt rocks, evolved plutonic rocks, possible basalts, contact metamorphosed rocks, and siltstones. Impact spherules and vitrophyre shards record airborne transport, and accreted dust rims were sintered on most clasts, presumably during residence in an ejecta plume. The clast assemblage records at least three impact events, one that formed an impact melt sheet on Mars ≤4.4 Ga ago, a second that assembled NWA 7475 from impactites associated with the impact melt sheet at 1.7–1.4 Ga, and a third that launched NWA 7475 from Mars ~5 Ma ago. Mildly shocked pyroxene and plagioclase constrain shock metamorphic conditions during launch to >5 and <15 GPa. The mild postshock‐heating that resulted from these shock pressures would have been insufficient to sterilize this water‐bearing lithology during launch. Magnetite, maghemite, and pyrite are likely products of secondary alteration on Mars. Textural relationships suggest that calcium‐carbonate and goethite are probably of terrestrial origin, yet trace element chemistry indicates relatively low terrestrial alteration. Comparison of Mars Odyssey gamma‐ray spectrometer data with the Fe and Th abundances of NWA 7475 points to a provenance in the ancient southern highlands of Mars. Gratteri crater, with an age of ~5 Ma and an apparent diameter of 6.9 km, marks one possible launch site of NWA 7475.     

Geochemical and isotopic evidence for upward flow of saline fluid to the Mississippi River Valley alluvial aquifer,southeastern Arkansas,USA

Hydrogeology Journal - Groundwater from the Quaternary Mississippi River Valley Alluvial (MRVA) aquifer in southeastern Arkansas (SE AR), USA, has higher salinity compared to other MRVA...     

Supernova remnants, planetary nebulae and the distance to NGC 4214

We present narrow band, continuum subtracted Hα, [S ii], Hβ, [O iii] and [O ii] data taken with the Wide Field Camera 3 on the Hubble Space Telescope in the nearby dwarf starburst galaxy NGC 4214. From these images, we identify seventeen new planetary nebula candidates, and seven supernova remnant candidates. We use the observed emission line luminosity function of the planetary nebulae to establish a new velocity-independent distance to NGC 4214. We conclude that the PNLF technique gives a reddening independent distance to NGC 4214 of 3.19±0.36 Mpc, and that our current best-estimate of the distance to this galaxy ids 2.98±0.13 Mpc.     

Radar observations and a physical model of Asteroid 4660 Nereus, a prime space mission target

Near-Earth Asteroid 4660 Nereus has been identified as a potential spacecraft target since its 1982 discovery because of the low delta-V required for a spacecraft rendezvous. However, surprisingly little is known about its physical characteristics. Here we report Arecibo (S-band, 2380-MHz, 13-cm) and Goldstone (X-band, 8560-MHz, 3.5-cm) radar observations of Nereus during its 2002 close approach. Analysis of an extensive dataset of delay-Doppler images and continuous wave (CW) spectra yields a model that resembles an ellipsoid with principal axis dimensions X=510±20 m, Y=330±20 m and . The pole direction is approximately located at ecliptic pole longitude and latitude of λ=+25°, β=+80° with the uncertainty radius of 10°. Our modeling yields a refined rotation period of 15.16±0.04 h. Nereus has a circular polarization (SC/OC) ratio of 0.74±0.08, which implies substantial near-surface centimeter-to-decimeter scale roughness. Dynamical analysis of our model suggests that YORP alteration of the rotation period may become evident within a few years. Nereus has two stable synchronous orbits where natural material may remain in orbit, while most asteroids observed to date do not have such stable synchronous orbits. We also find that spacecraft orbits about Nereus are feasible.     

Compositional and lithological diversity among brecciated lunar meteorites of intermediate iron concentration

Abstract— We present new compositional data for 30 lunar stones representing about 19 meteorites. Most have iron concentrations intermediate to those of the numerous feldspathic lunar meteorites (3–7% FeO) and the basaltic lunar meteorites (17–23% FeO). All but one are polymict breccias. Some, as implied by their intermediate composition, are mainly mixtures of brecciated anorthosite and mare basalt, with low concentrations of incompatible elements such as Sm (1–3 μg/g). These breccias likely originate from points on the Moon where mare basalt has mixed with material of the FHT (Feldspathic Highlands Terrane). Others, however, are not anorthosite‐basalt mixtures. Three (17–75 μ/g Sm) consist mainly of nonmare mafic material from the nearside PKT (Procellarum KREEP Terrane) and a few are ternary mixtures of material from the FHT, PKT, and maria. Some contain mafic, nonmare lithologies like anorthositic norites, norites, gabbronorites, and troctolite. These breccias are largely unlike breccias of the Apollo collection in that they are poor in Sm as well as highly feldspathic anorthosite such as that common at the Apollo 16 site. Several have high Th/Sm compared to Apollo breccias. Dhofar 961, which is olivine gabbronoritic and moderately rich in Sm, has lower Eu/Sm than Apollo samples of similar Sm concentration. This difference indicates that the carrier of rare earth elements is not KREEP, as known from the Apollo missions. On the basis of our present knowledge from remote sensing, among lunar meteorites Dhofar 961 is the one most likely to have originated from South Pole‐Aitken basin on the lunar far side.     

Intercomparison of Boron Isotope and Concentration Measurements. Part II: Evaluation of Results

The Istituto di Geoscienze e Georisorse (IGG), on behalf and with the support of the International Atomic Energy Agency (IAEA), prepared eight geological materials (three natural waters and five rocks and minerals), intended for a blind interlaboratory comparison of measurements of boron isotopic composition and concentration. The materials were distributed to twenty seven laboratories - virtually all those performing geochemical boron isotope analyses in the world -which agreed to participate in the intercomparison exercise. Only fifteen laboratories, however, ultimately submitted the isotopic and/or concentration results they obtained on the intercomparison materials. The results demonstrate that interlaboratory reproducibility is not well reflected by the precision values reported by the individual laboratories and this observation holds true for both boron concentration and isotopic composition. The reasons for the discrepancies include fractionations due to the chemical matrix of materials, relative shift of the zero position on the δ¹¹B scale and a lack of well characterized materials for calibrating absolute boron content measurements. The intercomparison materials are now available at the IAEA (solid materials) and IGG (waters) for future distribution.     

Test of a model for trace element partition during closed-system solidification of a silicate liquid

Distributions of trace elements during solidification of a basalt are adequately described by the model of Helmkeet al. (1972) for crystallization as a closed system. A hypidiomorphic granular basalt was coarsely crushed to particles < 2 mm in size, was sieved, and materials from nine size fractions were analyzed by neutron activation for REE, Co, Cr, Fe, Hf, Na, Sc, and Ta. Mineral separates from one of the size fractions were also analyzed.Trace-element concentrations of analyzed samples containing statistically significant numbers of mineral grains were matched very well by a mixing model whose end-member components were the analyzed major minerals and mesostasis. Highly accurate modal analyses of the analyzed materials were obtained from the mixing model. Differences in proportions of mesostasis (range 0.57–2%) were shown to be responsible for large differences in trace element concentrations among 0.25–1 g chips from a single hand-specimen of the basalt. Ilmenite in the basalt is badly contaminated with mesostasis.The closed-system model for crystallization yields values for temperature- and composition-averaged distribution coefficients for incompatible elements that are accurate to ? 15 to + 30%, and relative to each other are accurate to a few percent. The model demonstrates why some current practices for estimating values of distribution coefficients or of parent liquid compositions lead to errors of factors of several times.     

土地利用方式对流域氮输入输出关系的影响——以加州San Joaquin流域为例

土地利用方式影响流域氮输入的空间分布和氮素的迁移输出过程,与非点源污染的防治密切相关.本文利用加州San Joaquin流域数据,考虑不同土地利用方式的影响,在GIS平台上分析了流域氮输入与输出的关系及其空间分布.本文提出了一个新的指标(F=CN/(L/Q))来衡量河流氮输出的变化趋势,该指标综合考虑了田间产流和河道输移两个过程的影响因子,能够描述土地利用类型对流域氮素迁移转化的影响.在实例研究中,通过该指标能够指示出研究区氮素流失的高风险区,为流域土地利用规划和非点源污染防治提供了重要的科学依据.