Petrogenesis of basaltic shergottite Northwest Africa 8657: Implications for fO2 correlations and element redistribution during shock melting in shergottites

Northwest Africa (NWA) 8657 is an incompatible trace element-enriched, low-Al basaltic shergottite, similar in texture and chemistry to Shergotty, Zagami, and NWA 5298. It is composed of zoned pyroxene, maskelynite, merrillite, and Ti-oxide minerals with minor apatite, silica, and pyrrhotite. Pyroxene grains are characterized by patchy zoning, with pigeonite or augite cores zoned to Fe-rich pigeonite mantles. The cores have rounded morphologies and irregular margins. Combined with the low Ti/Al of the cores, the morphology and chemistry of the pyroxene grains are consistent with initial crystallization at depth (30–70 km) followed by partial resorption en route to the surface. Enriched rare earth element (REE) equilibrium melt compositions and calculated oxygen fugacities (fO₂) conditions for pigeonite cores indicate that the original parent melts were enriched shergottite magmas that staged in chambers at depth within the Martian crust. NWA 8657 does not represent a liquid but rather entrained a proportion of pyroxene crystals from magma chambers where fractional crystallization was occurring at depth. Variation between fO₂ and bulk-rock (La/Yb)_N of the enriched and intermediate shergottites suggests that oxidation conditions and degree of incompatible element enrichment in the source may not be correlated, as thought previously. Shock melt pockets are characterized by an absence of phosphates and oxide minerals. It is likely that these phases were melted during shock. REEs were redistributed during this process into maskelynite and to a lesser extent the shock melt; however, the overall normalized REE profile of the shock melt is like that of the bulk-rock, but at lower absolute concentrations. Overall, shock melting has had a significant effect on the mineralogy of NWA 8657, especially the distribution of phosphates, which may be significant for geochronological applications of this meteorite and other Martian meteorites with extensive shock melt.     

Reactions in Amphibolite, Greenschist and Blueschist

Mineral assemblages in which chlorite [CHL], epidote [EPI],clinoamphibole [AMP], plagioclase [PLG] and quartz [QTZ] aremajor phases are characteristic of many low-grade mafic schists.The possible heterogeneous reactions in such an assemblage maybe separated into two types, exchange reactions and net-transferreactions. Only the latter alter significantly the modal proportionsof the minerals. A set of linearly independent reactions defines a reaction spaceof as many dimensions as there are independent reactions. Thespace defined by the net-transfer reactions alone is a sub-spacethat can be portrayed in three dimensions for the above assemblage.A procedure is presented herein that gives a set of independentreactions that may be taken as basis reactions for definingsuch a reaction space. All other reactions that can be writtenfor this assemblage, as well as observed whole-rock reactions,can be portrayed as vectors in these reaction spaces. Thesevectors connect the region (mineral facies) accessible to theabove assemblage. The whole-rock reactions of Laird (1980) relatinggreenschist, blueschist and various low-grade amphibolites fromVermont, provide informative examples, as do the whole-rockexperiments of Liou et al. (1974). Although reaction spaces apply to both equilibrium and disequilibriumassemblages the reactions selected as basis vectors correspondone-for-one to the chemical conditions for equilibrium thatmust obtain in any fully equilibrated assemblage. The set selectedis one that provides maximum sensitivity for geothermometric,geobarometric and geohygrometric purposes.     

菲律宾Zambales蛇绿岩套的再研究：对其特提斯来源的启示

A number of geological studies have already been conducted on the Zambales Ophiolite Complex (ZOC), a north-south trending complete ophiolite sequence exposed in the western portion of Central Luzon, Philippines. Previous works recognized the ZOC as being made up of two blocks, the Acoje and the Coto, acting as an arc-back arc pair sometime during the Eocene.     

The Spectroscopic Orbit of the Planetary Companion Transiting HD 209458

Three new silicon-bearing radicals of astrophysical interest, SiCCH and the two nearly isoenergetic isomers SiCN and SiNC, were detected in a laboratory discharge in their X2Pi ground states by Fourier transform microwave and millimeter-wave absorption spectroscopy. Hyperfine structure was observed in the low rotational transitions of the (2)Pi(1/2) ladder, and well-resolved Lambda-doubling was observed in both fine-structure ladders. With the spectroscopic constants derived from the laboratory measurements, the spectra of all three can be calculated to an uncertainty of less than 0.1 km s(-1) in equivalent radial velocity over the entire range of interest to radio astronomers. SiCN, with a dipole moment of 2.9 D, is probably the most promising of the three for astronomical discovery.     

Available Clay and Feldspar Reference Samples As Standards for Archaeological Pottery Studies

The available clay and feldspar reference samples, rather than the frequently used rock reference samples, are suggested as standards for archaeological pottery studies because their trace-element contents are more like those of the artefacts. Such samples may provide a basis for correlating archaeological studies throughout the world. The assumption that bottles of such reference samples should have homogeneous trace-element contents because of the nature of the materials has been confirmed by the analysis of variance of trace -element data by instrumental neutron activation analysis.     

Stadial subdivisions of early Pleistocene glaciations in central United States - a developing chronology

Recently recognized field evidence clearly indicates that both the Nebraskan and Kansan Glaciations are divisible into stades on the basis of a stratigraphic record of ice-margin fluctuations. Two Nebraskan stades and three Kansan stades have been identified; it is suggested that others will be found. Recognition of multiple stades requires a thorough review of all Early Pleistocene stratigraphic and paleontologic age assignments applied in the American Midwest.     

安徽巢湖凤凰山剖面石炭系微相和层序地层特征

应用露头层序地层学基本原理和方法 ,对巢湖凤凰山石炭系剖面进行重新研究。巢湖凤凰山石炭系总厚度为79.0 2 m ,在这个剖面中可以识别出 6种主要岩相、18种微相和 11个三级沉积层序 ,其中六个三级沉积层序属于 I型沉积层序 ,三个属于 II型沉积层序 ,缺失第 9和第 10沉积层序。三级沉积层序在不同的古地理单元和不同的沉积环境中可以进行对比。根据各微相特征和成因 ,揭示了沉积间断面上存在的多期古岩溶现象。阐述了三级层序及其对应的三级海平面升降旋回的特征     

Deep-water fan-channel conglomerates of Late Cretaceous age, southern Chile

The exceptionally well exposed Lago Sofia conglomerate and sandstone lenses in the Upper Cretaceous Cerro Toro Formation of southern Chile are interpreted as the channel and channel margin facies of a deep-sea fan. The north-to-south oriented channels formed on an elongate fan in a narrow retroarc basin between a rising cordillera to the west and the South American craton to the east. The great length of some of the channels (> 120 km) seems to reflect the long duration (> 30 m.y.) and stable nature of the basin. Enclosing the lenses is the fine-grained Cerro Toro Formation which represents overbank turbidite flows and hemipelagic sedimentation on levee and levee flank areas. Foraminiferal assemblages suggest deposition in 1000-2000 m of water. Most of the conglomerate has features developed by tractive currents (parallel- and cross-stratified conglomerate). Most is moderately well sorted, imbricated, and has parallel to inclined stratification; large-scale dunes up to 4 m high are exposed. Typical sediment, gravity flow structures and bedding styles (e.g. pebbly mudstones, graded conglomerate, giant flutes) are not as common in the channel deposits as are tractive features. Tractive features in the gravels apparently were developed by rolling, sliding, and saltation as the bed-load component of highly turbulent, moderate- to low-density turbidity currents flowing in a confined channel. Graded-to-massive conglomerates appear to have been deposited rapidly from fully turbulent flows; diamictites were deposited from debris flows in which fluid viscosity, yield strength, and buoyancy of the fluid were dominant. The three major conglomerate classes recognized do not occur in a systematic manner; vertical and lateral heterogeneity is the rule.     

Occurrence of polar seabirds at sea in relation to prey concentrations and oceanographic factors

The distribution and abundance of breeding and foraging seabirds is usually a reflection of the availability of prey in the marine ecosystems on which the birds depend. At the scale of hundreds of km, differences in marine communities may be reflected in variation in the species composition of resident seabirds. At small scales, environmental features such as fronts or ice can influence where birds will aggregate to forage. Features at which prey become concentrated near the surface are of particular importance to bird species dependent upon small planktonic organisms. Concentrations of foraging seabirds frequently indicate the presence of such features, or of areas of unusually high prey biomass. The absence of birds does not mean that concentrations of potential prey are absent. "Assembly rules," by which one might predict aspects of the marine environment that birds should use in selecting foraging areas are proposed.