Nd,Sr, Pb,Ar, and 0 isotopic systematics of Sturgeon Lake kimberlite,Saskatchewan, Canada: constraints on emplacement age,alteration, and source composition

Rb-Sr isotopic dating of phlogopite megacryst samples separated from Sturgeon Lake kimberlite, Saskatchewan, yields a crystallization age of 98±1 Ma (2 , MSWD=1.2; ⁸⁷Sr/⁸⁶Sr(t)=0.7059). The ⁴⁰Ar/³⁹Ar analyses of a phlogopite megacryst sample indicate the presence of large amounts of excess ⁴⁰Ar and yield an excessively old age of 410 Ma. Assessment of the Ar data using isotope correlation plots indicates clustering of the data points about a mixing line between the radiogenic ⁴⁰Ar component at 98 Ma and a trapped component with uniform ³⁶Ar/⁴⁰Ar and Cl/⁴⁰Ar. Values of {ie212-1} as high as +20%. (VSMOW) for calcite from the groundmass and a whole-rock sample indicate pervasive lowtemperature alteration. The {ie212-2} of matrix carbonate is-11.3%. (PDB), slightly lighter than typical values from the literature. The {ie212-3} values of about +5%. (VSMOW) for brown phlogopite megacrysts may be primary, green phlogopites are interpreted to be an alteration product of the brown variety and are 2%. heavier. Initial Nd-Sr-Pb isotopic ratios for a whole-rock sample {ie212-4}; ⁸⁷Sr/⁸⁶Sr=0.7063, ²⁰⁶Pb/²⁰⁴Pb=18.67, ²⁰⁷Pb/²⁰⁴Pb=15.54, ²⁰⁸Pb/²⁰⁴Pb=38.97) suggest an affinity with group I kimberlites. Initial {ie212-5} values of +1.7 and +0.5 (⁸⁷Sr/ ⁸⁶Sr(t)=0.7053 and 0.7050) for eclogitic and lherzolitic garnet megacryst samples, and values of 0.0 for two phlogopite megacryst samples reflect an origin from an isotopically evolving melt due to assimilation of heterogeneous mantle. Lilac high-Cr lherzolitic garnet megacrysts give an unusually high {ie212-6} of +28.6 (⁸⁷Sr/⁸⁶Sr=0.7046) indicating a xenocrystic origin probably from the lithospheric mantle. The very radiogenic ⁸⁷Sr/⁸⁶Sr and ²⁰⁶Pb/²⁰⁴Pb ratios of the kimberlite are consistent with melting of EM II (enriched) mantle components.     

Transient dissolution patterns on stressed crystal surfaces

We present an experimental investigation on the dissolution of uniaxially stressed crystals of NaClO₃ in contact with brine. The crystals are immersed in a saturated fluid, stressed vertically by a piston and monitored constantly in situ with a CCD camera. The experiments are temperature-controlled and uniaxial shortening of the sample is measured with a high-resolution capacitance analyzer. Once the crystal is stressed it develops dissolution grooves on its free surface. The grooves are oriented with their long axis perpendicular to the direction of compressive stress and the initial distance between the parallel grooves is in accordance with the Asaro-Tiller-Grinfeld instability. We observe a novel, transient evolution of this roughness: The grooves on the crystal surface migrate upwards (against gravity), grow in size and the inter-groove distance increases linearly with time. During the coarsening of the pattern this switches from a one-dimensional geometry of parallel grooves to a two-dimensional geometry with horizontal and vertical grooves. At the end of the experiment one large groove travels across the crystal and the surface becomes smooth again. Uniaxial shortening of the crystal by pressure solution creep decays exponentially with time and shows no long term creep within the range of the resolution of the capacitance analyzer (accuracy of 100nm over a period of 14 days). This indicates that, while active, the fast transient processes on the free surface increase the solution concentration and thereby significantly slow down or stop pressure solution at the top of the crystal. This novel feedback mechanism can explain earlier results of cyclic pressure solution creep and demands development of a more complex theory of pressure-solution creep including processes that act on free surfaces.     

Magnetic properties and heavy metal content of sanitary leachate sludge in two landfill sites near Bandung,Indonesia

Magnetic properties and heavy metal content of landfill leachate sludge samples from two municipal solid waste disposal sites near Bandung, West Java, Indonesia, and their correlation with heavy metals are studied in the present work. Leachate was found to be sufficiently magnetic with mass-specific magnetic susceptibility that varies from 64.8 to 349.0 × 10⁻⁸ m³ kg⁻¹. It is, however, less magnetic than the soils around the landfill sites. The magnetic minerals are predominantly pseudo-single domain and multidomain magnetite. Leachate samples from the older but inactive disposal site, Jelekong, are found to be more magnetic than that from Sarimukti, the younger and active site. The enhancement of leachate due to the soil-derived ferrimagnetic particles is possibly the same for both Sarimukti and Jelekong. The fact that strong correlation between magnetic parameters and heavy metals is observed in Jelekong but is absent in Sarimukti suggests that the use of magnetic measurement as a proxy measurement for heavy metal content in leachate is plausible provided that the magnetic susceptibility exceeds certain threshold value. Moreover, the accumulation of magnetic minerals and heavy metals in leachate might depend on the activity and the age of landfill site.     

High-temperature,high-pressure granulites (retrogressed eclogites) in the central region of the Lewisian,NW Scotland: Crustal-scale subduction in the Neoarchaean

Eclogites and associated high-pressure (HP) rocks in collisional and accretionary orogenic belts preserve a record of subduction and exhumation, and provide a key constraint on the tectonic evolution of the continents. Most eclogites that formed at high pressures but low temperatures at > 10–11 kbar and 450–650 °C can be interpreted as a result of subduction of cold oceanic lithosphere. A new class of high-temperature (HT) eclogites that formed above 900 °C and at 14 to 30 kbar occurs in the deep continental crust, but their geodynamic significance and processes of formation are poorly understood. Here we show that Neoarchaean mafic–ultramafic complexes in the central granulite facies region of the Lewisian in NW Scotland contain HP/HT garnet-bearing granulites (retrogressed eclogites), gabbros, lherzolites, and websterites, and that the HP granulites have garnets that contain inclusions of omphacite. From thermodynamic modeling and compositional isopleths we calculate that peak eclogite-facies metamorphism took place at 24–22 kbar and 1060–1040 °C. The geochemical signature of one (G-21) of the samples shows a strong depletion of Eu indicating magma fractionation at a crustal level. The Sm–Nd isochron ages of HP phases record different cooling ages of ca. 2480 and 2330 Ma. We suggest that the layered mafic–ultramafic complexes, which may have formed in an oceanic environment, were subducted to eclogite depths, and exhumed as HP garnet-bearing orogenic peridotites. The layered complexes were engulfed by widespread orthogneisses of tonalite–trondhjemite–granodiorite (TTG) composition with granulite facies assemblages. We propose two possible tectonic models: (1) the fact that the relicts of eclogitic complexes are so widespread in the Scourian can be taken as evidence that a > 90 km × 40 km-size slab of continental crust containing mafic–ultramafic complexes was subducted to at least 70 km depth in the late Archaean. During exhumation the gneiss protoliths were retrogressed to granulite facies assemblages, but the mafic–ultramafic rocks resisted retrogression. (2) The layered complexes of mafic and ultramafic rocks were subducted to eclogite-facies depths and during exhumation under crustal conditions they were intruded by the orthogneiss protoliths (TTG) that were metamorphosed in the granulite facies. Apart from poorly defined UHP metamorphic rocks in Norway, the retrogressed eclogites in the central granulite/retrogressed eclogite facies Lewisian region, NW Scotland have the highest crustal pressures so far reported for Archaean rocks, and demonstrate that lithospheric subduction was transporting crustal rocks to HP depths in the Neoarchaean.     

uTshani BuyaKhuluma––The Grass Speaks: the political space and capacity of the South African Homeless People’s Federation

The point of departure for this article is the contemporary tendency towards localisation of politics in the context of neo-liberal globalisation. Mediated through institutional reforms, political discourses and localised struggles, this localisation of politics produce new and transformed local political spaces. The purpose of the article is to examine the capacity of popular movements to use and transform such political spaces within the South African housing sector. This analysis is done through a combination of conceptual examination of political space and actor capacity and a concrete case study of the political strategies and capacities of The South African Homeless People’s Federation. The article argues that the Federation has utilised political relations at different scales to mobilise resources such as land and subsidies for housing for its members. It has also influenced the formulation of housing policies through its discourses and practical experiences with people-driven housing processes. In consequence the Federation’s ability to function as a civil/political movement has granted them a certain capacity to participate in the complicated process of turning de jure rights to adequate shelter into de facto rights for the urban poor as citizens of a democratic South Africa.     

Competing Perceptions of the Rural Idyll: responses to threats from coal seam gas development in Gloucester,NSW, Australia

Threats to rural livelihoods and rural landscapes have increased over time as developed nations in particular look for cheaper and more locally based alternatives to traditional energy sources to drive national economies. In New South Wales, through the expansion of coal mines and coal seam gas (CSG), small towns such as Gloucester on the edge of the Upper Hunter are faced with competing visions which seek to redefine their future. Powerful and competing discourses over land use threaten not only the sustainability of the region but the integrity of its sense of place, centred on community, rurality, agricultural production and confrontation of risk from mining. The different discourses of local groups such as ‘tree-changers’, established residents and farmers conflict with those of external organisations such as the State government and mining/CSG companies which envisage Gloucester as a ‘balanced’ space of co-existence and position it as a new node in the carbon supply chain.