Deformation,metamorphism, and mobilization of Ni–Cu–PGE sulfide ores at Garson Mine,Sudbury

The Garson Ni–Cu–platinum group element deposit is a deformed, overturned, low Ni tenor contact-type deposit along the contact between the Sudbury Igneous Complex (SIC) and stratigraphically underlying rocks of the Huronian Supergroup in the South Range of the 1.85-Ga Sudbury structure. The ore bodies are coincident with steeply south-dipping, north-over-south D₁ shear zones, which imbricated the SIC, its ore zones, and underlying Huronian rocks during mid-amphibolite facies metamorphism. The shear zones were reactivated as south-over-north, reverse shear zones during D₂ at mid-greenschist facies metamorphism. Syn-D₂ metamorphic titanite yields an age of 1,849?±?6 Ma, suggesting that D₁ and D₂ occurred immediately after crystallization of the SIC during the Penokean Orogeny. The ore bodies plunge steeply to the south parallel to colinear L₁ and L₂ mineral lineations, indicating that the geometry of the ore bodies are strongly controlled by D₁ and D₂. Sulfide mineralization consists of breccia ores, with minor disseminated sulfides hosted in norite, and syn-D₂ quartz–calcite–sulfide veins. Mobilization by ductile plastic flow was the dominant mechanism of sulfide/metal mobilization during D₁ and D₂, with additional minor hydrothermal mobilization of Cu, Fe, and Ni by hydrothermal fluids during D₂. Metamorphic pentlandite overgrows a S₁ ferrotschermakite foliation in D₁ deformed ore zones. Pentlandite was exsolved from recrystallized polygonal pyrrhotite grains after cessation of D₁, which resulted in randomly distributed large pentlandite grains and randomly oriented pentlandite loops along the grain boundaries of polygonal pyrrhotite within the breccia ore. It also overgrows a S₂ chlorite foliation in D₂ shear zones. Pyrrhotite recrystallized and was flattened during D₂ deformation of breccia ore along narrow shear zones. Exsolution of pentlandite loops along the grain boundaries of these flattened grains produced a pyrrhotite–pentlandite layering that is not observed in D₁ deformed ore zones. The overprinting of the two foliations by pentlandite and exsolution of pentlandite along the grain boundaries of flattened pyrrhotite grains suggest that the Garson ores reverted to a metamorphic monosulfide solid solution at temperatures ranging between 550 and 600 °C during D₁ and continued to deform as a monosulfide solid solution during D₂.     

Mapping the narrative positions of new political groups under the UNFCCC

Since the mid-1990s, the aim of keeping climate change within 2?°C has become firmly entrenched in policy discourses. In the past few years, the likelihood of achieving it has been increasingly called into question. The debate around what to do with a target that seems less and less achievable is, however, only just beginning. As the UN commences a two-year review of the 2?°C target, this article moves beyond the somewhat binary debates about whether or not it should or will be met, in order to analyse more fully some of the alternative options that have been identified but not fully explored in the existing literature. For the first time, uncertainties, risks, and opportunities associated with four such options are identified and synthesized from the literature. The analysis finds that the significant risks and uncertainties associated with some options may encourage decision makers to recommit to the 2?°C target as the least unattractive course of action.     

Variable circular polarization associated with relativistic ejections from GRS 1915 + 105

We describe H α , SCUBA and MERLIN imaging of the interacting galaxy pair NGC 4490 and 4485. We detect an H α filament emerging from the disc of NGC 4490 to a projected distance of 3 kpc which has counterparts in both the radio continuum and H  i . The H  i counterpart extends to a projected distance of ∼30 kpc from NGC 4490 and we argue that this is evidence that the giant H  i envelope in this system has its origins in star formation. We use SCUBA and radio continuum data to attempt to place constraints on the distribution of dust with respect to the star forming regions. This analysis is limited by the lack of an independent estimate of the dust temperature, something that both 'SIRTF' and 'SOFIA' will be able to provide, however we find some evidence that most obscuring dust is not located within H  ii regions themselves.     

Spectral, polarization and time-lag properties of GRS 1915+105 radio oscillations

We report high-sensitivity dual-frequency observations of radio oscillations from GRS 1915+105 following the decay of a major flare event in 2000 July. The oscillations are clearly observed at both frequencies, and the time-resolved spectral index traces the events between optically thin and thick states. While previously anticipated from sparse observations and simple theory, this is the first time a quasi-periodic signal has been seen in the radio spectrum, and is a clear demonstration that flat radio spectra can arise from the combination of emission from optically thick and thin regions. In addition, we measure the linear polarization of the oscillations, at both frequencies, at a level of about  1–2  per cent, with a flat spectrum. Cross-correlating the two light curves we find a mean delay, in the sense that the emission at 8640 MHz leads that at 4800 MHz, of around 600 s. Comparison with frequency-dependent time-delays reported in the literature reveals that this delay is variable between epochs. We briefly discuss possible origins for a varying time-delay, and suggest possible consequences.     

The Influence of Large-Scale Circulation on the Summer Hydrological Cycle in the Haihe River Basin of China

In this study, we focus on changes in three important components of the hydrological-cycle in the Haihe River basin (HRB) during 1957-2005: precipitation (Prep), actual evaportranspiration (ETa), and pan evaporation (PE)-a measure of potential evaporation. The changes in these components have been evaluated in relation to changes in the East Asian summer monsoon. Summer Prep for the whole basin has decreased significantly during 1957-2005. Recent weakening of the convergence of the integrated water vapor flux, in combination with a change from cyclonic-like large-scale circulation conditions to anti-cyclonic-like conditions, led to the decrease in the summer Prep in the HRB. ETa is positively correlated with Prep on the interannual timescale. On longer timescales, however, ETa is less dependent on Prep or the large-scale circulation. We found negative trends in ETa when the ERA40 reanalysis data were used, but positive trends in ETa when the NCEP/NCAR reanalysis data were used. PE declined during the period 1957-2001. The declining of PE could be explained by a combination of declining solar radiation and declining surface wind. However, the declining solar radiation may itself be related to the weakening winds, due to weaker dispersion of pollution. If so, the downward trend of PE may be mainly caused by weakening winds.     

Methods to Estimate Surface Fluxes of Momentum and Heat from Routine Weather Observations for Dispersion Applications under Stable Stratification

We examine the efficacy of two methods commonly used to estimate the vertical turbulent fluxes of momentum and sensible heat from routinely observed mean quantities in the surface layer under stable stratification. The single-level method uses mean wind speed and temperature measurements at a single height, whereas the two-level method uses mean wind speed measurements at a single height and mean temperature measurements at two heights. These methods are used in popular meteorological processors such as the U.S. Environmental Protection Agency approved AERMET and CALMET to generate inputs for dispersion simulations. We use data from a flux station of the U.K. Met Office at Cardington for comparison. It is found that the single-level method does not describe the flux variation in the weakly stable regime at all, because of its assumption that the temperature scale, i.e. the ratio of the kinematic sensible heat flux to the friction velocity, is constant, which is plausible only under strongly stable conditions. On the other hand, the two-level method provides a physically realistic variation of the fluxes with stability, but the required temperature measurements at two levels are usually not available on a routine basis. If measurements of the standard deviation of temperature are also available, in addition to the mean temperature at a single level, then they can be usefully employed in a third (single-level) method, with the consequence that the computed fluxes are very similar to those obtained from the two-level method. An improvement to the original single-level method is considered, and flux calculations under low wind conditions are also discussed.     

Square Kilometre Array: The radio telescope of the XXI century

The Square Kilometre Array (SKA) will be the world’s largest and most sensitive radio telescope. It will address fundamental unanswered questions about our Universe including how the first stars and galaxies formed after the Big Bang, how dark energy is accelerating the expansion of theUniverse, the role of magnetism in the cosmos, the nature of gravity, and the search for life beyond Earth. This project envisages the construction of 133 15-m antennas in South Africa and 131072 log-periodic antennas in Australia, together with the associated infrastructure in the two desert sites. In addition, the SKA is an exemplar Big Data project, with data rates of over 10 Tbps being transported from the telescope to HPC/HTC facilities.     

Modelling Near-Surface Low Winds over Land under Stable Conditions: Sensitivity Tests,Flux-Gradient Relationships,and Stability Parameters

Low or weak wind-speed conditions, roughly defined as the periods when the mean wind speed at 10 m above the ground is 2 ms⁻¹ or less, are of considerable practical interest. However, they are not readily amenable to treatment within prognostic meteorological models and, consequently, difficult to predict, especially when the ambient stability is strong. In this paper, we apply an E − ε prognostic meteorological model to simulate near-surface meteorology and, focusing on low wind speeds, compare the predictions with measurements from two independent datasets. A sensitivity analysis is performed to investigate the possible reasons for the relatively inferior model performance for low winds when the atmosphere is stably stratified. A comprehensive data analysis is carried out to study low wind stable conditions, concentrating on the validity of various forms of flux–gradient relationships for momentum and heat within the framework of the Monin-Obukhov similarity theory, which models employ for calculating surface fluxes. The observed behaviour of various stability parameters, such as the Richardson number, is investigated. The results point to inadequacies of the current flux–gradient relationships, especially regarding momentum, under strongly stable conditions as being a dominant reason for the poor low wind predictions. The modelling issues identified are not just restricted to the present model, but are general in nature. The use of an alternative stability function for momentum under strongly stable conditions is explored. It results in improved model performance for low winds; however, further research is needed to better understand strongly stable flows in the lower atmosphere and to develop methods that can translate that understanding to operational meteorological modelling.     

Greening in the circumpolar high-latitude may amplify warming in the growing season

We present a study that suggests greening in the circumpolar high-latitude regions amplifies surface warming in the growing season (May–September) under enhanced greenhouse conditions. The investigation used a series of climate simulations with the Community Atmospheric Model version 3—which incorporates a coupled, dynamic global vegetation model—with and without vegetation feedback, under both present and doubled CO₂ concentrations. Results indicate that climate warming and associated changes promote circumpolar greening with northward expansion and enhanced greenness of both the Arctic tundra and boreal forest regions. This leads to additional surface warming in the high-latitudes in the growing season, primarily through more absorption of incoming solar radiation. The resulting surface and tropospheric warming in the high-latitude and Arctic regions weakens prevailing tropospheric westerlies over 45–70N, leading to the formation of anticyclonic pressure anomalies in the Arctic regions. These pressure anomalies resemble the anomalous circulation pattern during the negative phase of winter Arctic Oscillation. It is suggested that these circulation anomalies reinforce the high-latitude and Arctic warming in the growing season.