Determination of Fe<Superscript>3+</Superscript>/ΣFe ratios in chrome spinels using a combined Mössbauer and single-crystal X-ray approach: application to chromitites from the mantle section of the Oman ophiolite

We present the results of a comparative study in which we have measured Fe³⁺/ΣFe ratios in chromites from mantle chromitites in the Oman ophiolite using Mössbauer spectroscopy and single-crystal X-ray diffraction. We have compared these results with ratios calculated from mineral stoichiometry and find that mineral stoichiometry calculations do not accurately reflect the measured Fe³⁺/ΣFe ratios. We have identified three groups of samples. The majority preserve Fe³⁺/ΣFe ratios which are thought to be magmatic, whereas a few samples are highly oxidized and have high Fe³⁺/ΣFe ratios. There is also a group of partially oxidized samples. The oxidized chromites show anomalously low cell edge (a ₀) values and their oxygen positional parameters among the lowest ever found for chromites. Site occupancy calculations show that some chromites are non-stoichiometric and contain vacancies in their structure randomly distributed between both the T and M sites. The field relationships suggest that the oxidation of the magmatic chromitites took place in association with a ductile shear zone in mantle harzburgites. Primary magmatic Fe³⁺/ΣFe ratios measured for the Oman mantle chromitites are between 0.193–0.285 (X-ray data) and 0.164–0.270 (Mössbauer data) and preserve a range of Fe³⁺/ΣFe ratios which we propose is real and reflects differences in the composition of the magmas parental to the chromitites. The range of values extends from those MORB melts (0.16 ± 0.1) to those for arc basalts (0.22–0.28).     

Organic sedimentary deposits in Titan’s dry lakebeds: Probable evaporite

We report the discovery of organic sedimentary deposits at the bottom of dry lakebeds near Titan’s north pole in observations from the Cassini Visual and Infrared Mapping Spectrometer (VIMS). We show evidence that the deposits are evaporitic, making Titan just the third known planetary body with evaporitic processes after Earth and Mars, and is the first that uses a solvent other than water.     

Initial Calibration of the Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory (SDO)

The Atmospheric Imaging Assembly (AIA) instrument onboard the Solar Dynamics Observatory (SDO) is an array of four normal-incidence reflecting telescopes that image the Sun in ten EUV and UV wavelength channels. We present the initial photometric calibration of AIA, based on preflight measurements of the response of the telescope components. The estimated accuracy is of order 25%, which is consistent with the results of comparisons with full-disk irradiance measurements and spectral models. We also describe the characterization of the instrument performance, including image resolution, alignment, camera-system gain, flat-fielding, and data compression.     

Prediction of hydrothermal copper,gold, silver and lead-zinc in northwestern Yunnan using weight of evidence model

This paper discusses the application of the model in predicting for hydrothermal Cu, Ag, Au and Pb?Zn occurrences in northwestern Yunnan. Geochemical, lineament and lithology data were the selected recognition criteria. The mentioned criteria varied against 75 known hydrothermal occurrences; the geochemical data had a weight of (W+=1.2097,W?=?0.7481) being the maximum among the three and the rest lineament and lithology have (W+=0.7424,W?=?0.4496), (W+=0.3787,W?=?0.6243) respectively. The application was successful since the predicted results covers about 70% of the known deposits and predicted unknown areas.     

The Spatial Dialectics of Modernity and Retail Affect at Abasto Shopping,Buenos Aires,Argentina

Abstract

The paper is about the political life of a building: the Abasto. Located in what was called the “most porteño” neighborhood in the first part of the 20th century (“porteño” is someone from central Buenos Aires) when it functioned as the city's main food market, the Abasto became a massive shopping mall in 1998 amid rapid neoliberal restructuring. This paper charts the political life of this building in two steps. First, by drawing on theories of socio-spatial dialectics, this paper charts the history of the Abasto as an urban object in a wider political landscape of porteño modernity. Second, by incorporating recent theories of affect and presenting findings from field work carried out at the mall in 2010 and 2011, this paper develops a framework for understanding the politics of consumption in a “post-neoliberal” urban landscape.     

Solute and geothermal flux monitoring using electrical conductivity in the Madison,Firehole, and Gibbon Rivers,Yellowstone National Park

The thermal output from the Yellowstone magma chamber can be estimated from the Cl flux in the major rivers in Yellowstone National Park; and by utilizing continuous discharge and electrical conductivity measurements the Cl flux can be calculated. The relationship between electrical conductivity and concentrations of Cl and other geothermal solutes (Na, SO₄, F, HCO₃, SiO₂, K, Li, B, and As) was quantified at monitoring sites along the Madison, Gibbon, and Firehole Rivers, which receive discharge from some of the largest and most active geothermal areas in Yellowstone. Except for some trace elements, most solutes behave conservatively and the ratios between geothermal solute concentrations are constant in the Madison, Gibbon, and Firehole Rivers. Hence, dissolved concentrations of Cl, Na, SO₄, F, HCO₃, SiO₂, K, Li, Ca, B and As correlate well with conductivity (R² > 0.9 for most solutes) and most exhibit linear trends. The 2011 flux for Cl, SO₄, F and HCO₃ determined using automated conductivity sensors and discharge data from nearby USGS gaging stations is in good agreement with those of previous years (1983–1994 and 1997–2008) at each of the monitoring sites. Continuous conductivity monitoring provides a cost- and labor-effective alternative to existing protocols whereby flux is estimated through manual collection of numerous water samples and subsequent chemical analysis. Electrical conductivity data also yield insights into a variety of topics of research interest at Yellowstone and elsewhere: (1) Geyser eruptions are easily identified and the solute flux quantified with conductivity data. (2) Short-term heavy rain events can produce conductivity anomalies due to dissolution of efflorescent salts that are temporarily trapped in and around geyser basins during low-flow periods. During a major rain event in October 2010, 180,000 kg of additional solute was measured in the Madison River. (3) The output of thermal water from the Gibbon River appears to have increased by about 0.2%/a in recent years, while the output of thermal water for the Firehole River shows a decrease of about 10% from 1983 to 2011. Confirmation of these trends will require continuing Cl flux monitoring over the coming decades.     

Degassing of Cl, F, Li, and Be during extrusion and crystallization of the rhyolite dome at Volcán Chaitén, Chile during 2008 and 2009

We investigated the distribution of Cl, F, Li, and Be in pumices, obsidians, and crystallized dome rocks at Chaitén volcano in 2008?C2009 in order to explore the behavior of these elements during explosive and effusive volcanic activity. Electron and ion microprobe analyses of matrix and inclusion glasses from pumice, obsidian, and microlite-rich dome rock indicate that Cl and other elements were lost primarily during crystallization of the rhyolitic dome after it had approached the surface. Glass in pumice and microlite-free obsidian has 888?±?121?ppm Cl, whereas residual glass in evolved microlite-rich dome rock generally retains less Cl (as low as <100?ppm). Estimated Cl losses were likely >0.7?Mt Cl, with a potential maximum of 1.8?Mt for the entire 0.8-km³ dome. Elemental variations reflect an integrated bulk distribution ratio for Cl?>?1.7 (1.7 times more Cl was degassed or incorporated into crystals than remained in the melt). Because Cl is lost dominantly as the very last H₂O is degassed, and Cl is minimally (if at all) partitioned into microlites, the integrated vapor/melt distribution ratio for Cl exceeds 200 (200 times more Cl in the evolved vapor than in the melt). Cl is likely lost as HCl, which is readily partitioned into magmatic vapor at low pressure. Cl loss is accelerated by the change in the composition of the residual melt due to microlite growth. Cl loss also may be affected by open-system gas fluxing. Integrated vapor-melt distribution ratios for Li, F, and Be all exceed 1,000. On degassing, an unknown fraction of these volatiles could be immediately dissolved in rainwater.     

Numerical modelling of coastal inundation from Cascadia Subduction Zone tsunamis and implications for coastal communities on western Vancouver Island,Canada

Natural Hazards - In the present study, numerical simulations were conducted to estimate the spatio-temporal characteristics of tsunami inundation for municipalities on Vancouver Island, Canada, as...     

Integrated climate model-oxygen isotope evidence for a North American monsoon during the Late Cretaceous

During the Late Cretaceous, western North America was characterized by a close geographic association between the Sevier highlands and the Western Interior Seaway. In this paper, an atmospheric general circulation model (AGCM) is used to simulate the impact of this geographic association on surface pressure, wind direction, and precipitation, and it is predicted that seasonal changes in these variables resulted in a strong monsoon along the eastern flank of the Sevier Highlands. Confirmation that these model simulations are accurate is provided by isotopic data from foreland basin sediments. In particular oxygen isotope records from different environments (large rivers, small streams and ponds) and proxies (unionid bivalve shells and paleosol carbonates) indicate that foreland basin streams were recharged by local precipitation with high oxygen isotope ratios while large trunk rivers were recharged by high-elevation precipitation. This hydrologic pattern is observed from Alberta to Utah and is consistent with east to west monsoonal air mass movements and associated seasonal rainfall. Recognition of a highland-driven monsoon has implication in regard to studies of fossil taphonomy, of water vapor transport, and of links between climate and mountain uplift and exhumation in this region.     

The Role of Groundwater for Lake‐Water Quality and Quantification of N Seepage

The heterogeneous nature of both groundwater discharge to a lake (inflow) and nitrate concentrations in groundwater can lead to significant errors in calculations of nutrient loading. Therefore, an integrated approach, combining groundwater flow and transport modelling with observed nitrate and ammonium groundwater concentrations, was used to estimate nitrate loading from a catchment via groundwater to an oligotrophic flow‐through lake (Lake Hampen, Denmark). The transport model was calibrated against three vertical nitrate profiles from multi‐level wells and 17 shallow wells bordering a crop field near the lake. Nitrate concentrations in groundwater discharging to the lake from the crop field were on average 70 times higher than in groundwater from forested areas. The crop field was responsible for 96% of the total nitrate loading (16.2 t NO₃/year) to the lake even though the field only covered 4.5% of the catchment area. Consequently, a small change in land use in the catchment will have a large effect on the lake nutrient balance and possible lake restoration. The study is the first known attempt to estimate the decrease of nitrate loading via groundwater to a seepage lake when an identified catchment source (a crop field) is removed.