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1.
Topography and landscape characteristics affect the storage and release of water and, thus, groundwater dynamics and chemistry. Quantification of catchment scale variability in groundwater chemistry and groundwater dynamics may therefore help to delineate different groundwater types and improve our understanding of which parts of the catchment contribute to streamflow. We sampled shallow groundwater from 34 to 47 wells and streamflow at seven locations in a 20‐ha steep mountainous catchment in the Swiss pre‐Alps, during nine baseflow snapshot campaigns. The spatial variability in electrical conductivity, stable water isotopic composition, and major and trace ion concentrations was large and for almost all parameters larger than the temporal variability. Concentrations of copper, zinc, and lead were highest at sites that were relatively dry, whereas concentrations of manganese and iron were highest at sites that had persistent shallow groundwater levels. The major cation and anion concentrations were only weakly correlated to individual topographic or hydrodynamic characteristics. However, we could distinguish four shallow groundwater types based on differences from the catchment average concentrations: riparian zone‐like groundwater, hillslopes and areas with small upslope contributing areas, deeper groundwater, and sites characterized by high magnesium and sulfate concentrations that likely reflect different bedrock material. Baseflow was not an equal mixture of the different groundwater types. For the majority of the campaigns, baseflow chemistry most strongly resembled riparian‐like groundwater for all but one subcatchment. However, the similarity to the hillslope‐type groundwater was larger shortly after snowmelt, reflecting differences in hydrologic connectivity. We expect that similar groundwater types can be found in other catchments with steep hillslopes and wet areas with shallow groundwater levels and recommend sampling of groundwater from all landscape elements to understand groundwater chemistry and groundwater contributions to streamflow. 相似文献
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In the Gawler Craton, the completeness of cover concealing the crystalline basement in the region of the giant Olympic Dam Cu–Au deposit has impeded any sufficient understanding of the crustal architecture and tectonic setting of its IOCG mineral-system. To circumvent this problem, deep seismic reflection data were recently acquired from 250 line-km of two intersecting traverses, centered on the Olympic Dam deposit. The data were recorded to 18 s TWT ( 55 km). The crust consists of Neoproterozoic cover, in places more than 5 km thick, over crystalline basement with the Moho at depths of 13–14 s TWT ( 40–42 km). The Olympic Dam deposit lies on the boundary between two distinct pieces of crust, one interpreted as the Archean–Paleoproterozoic core to the craton, the other as a Meso–Neoproterozoic mobile belt. The host to the deposit, a member of the 1590 Ma Hiltaba Suite of granites, is situated above a zone of reduced impedance contrast in the lower crust, which we interpret to be source-region for its 1000 °C magma. The crystalline basement is dominated by thrusts. This contrasts with widely held models for the tectonic setting of Olympic Dam, which predict extension associated with heat from the mantle producing the high temperatures required to generate the Hiltaba Suite granites implicated in mineralization. We use the seismic data to test four hypotheses for this heat-source: mantle underplating, a mantle-plume, lithospheric extension, and radioactive heating in the lower crust. We reject the first three hypotheses. The data cannot be used to reject or confirm the fourth hypothesis. 相似文献
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The continuing use of petrochemicals in mineral nitrogen (N) production may be affected by supply or cost issues and climate agreements. Without mineral N, a larger area of cropland is required to produce the same amount of food, impacting biodiversity. Alternative N sources include solar and wind to power the Haber-Bosch process, and the organic options such as green manures, marine algae and aquatic azolla. Solar power was the most land-efficient renewable source of N, with using a tenth as much land as wind energy, and at least 100th as much land as organic sources of N. In this paper, we developed a decision tree to locate these different sources of N at a global scale, or the first time taking into account their spatial footprint and the impact on terrestrial biodiversity while avoiding impact on albedo and cropland, based on global resource and impact datasets. This produced relatively few areas suitable for solar power in the western Americas, central southern Africa, eastern Asia and southern Australia, with areas most suited to wind at more extreme latitudes. Only about 2% of existing solar power stations are in very suitable locations. In regions such as coastal north Africa and central Asia where solar power is less accessible due to lack of farm income, green manures could be used, however, due to their very large spatial footprint only a small area of low productivity and low biodiversity was suitable for this option. Europe in particular faces challenges because it has access to a relatively small area which is suitable for solar or wind power. If we are to make informed decisions about the sourcing of alternative N supplies in the future, and our energy supply more generally, a decision-making mechanism is needed to take global considerations into account in regional land-use planning. 相似文献
5.
Robert C Liebermann Leonie E.A Jones A.E Ringwood 《Physics of the Earth and Planetary Interiors》1977,14(2):165-178
Ultrasonic data for the velocities of a large number of perovskite-structure compounds have been determined as a a function of pressure to 6 kbar at room temperature for polycrystalline specimens hot-pressed at pressures up to 100 kbar in solid-media devices: ScAlO3, GdAlO3, SmAlO3, EuAlO3, YAlO3, CdTiO3, CdSnO3, CaSnO3 and CaGeO3. The elasticity data for these orthorhombic and cubic perovskites define systematic patterns on bulk modulus (KS)-volume (VO) and bulk sound velocity (υφ—mean atomic weight (M) diagrams which are insensitiv to the details of cation chemistry and crystallographic structure. These isostructural trends are used to estimate KS = 2.5 ± 0.3 Mbar and υφ = 7.9 ± 0.4 km/s for the perovskite polymorph of MgSiO3. On a Birch diagram of veloc vs. density, the perovskite data define linear trends which lead to erroneous estimates of velocity for MgSiO3 unless specific account is taken of ionic radius effects in isomorphic substitutions. 相似文献
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Because of the importance of snow for river discharge in mountain regions, hydrological research often focuses on seasonally snow-covered zones. However, in many basins the majority of the land surface area is intermittently snow-covered. Discharge monitoring in these areas is less common, so their contributions to downstream rivers remain largely unknown. We evaluated hydrological differences between three intermittently snow-covered (mean annual Jan 1–Jul 3 snow persistence <60%) and two seasonally snow-covered headwater catchments in the Colorado Front Range. We compared water balance variables to evaluate how and why discharge differs between the snow zones and estimated the relative contributions from each snow zone to regional river discharge. We focused on water years 2016–2019 and used a combination of in situ sensors and regional climate datasets. Annual discharge from the intermittent snow zone was low for all three catchments (10–77 mm), despite covering a wide range in annual snow persistence (25%–64%), whereas annual discharge from the seasonal snow zone was up to 73 times higher. Soil moisture in the seasonal snow zone was above field capacity for longer periods of time than in the intermittent snow zone, and the intermittent snow zone was uniquely subject to soil freezing (up to 102 days per year). For most of the year, potential evapotranspiration exceeded rainfall and snowmelt inputs in the intermittent snow zone, but was lower than rainfall and snowmelt inputs in the seasonal snow zone. This is likely a primary driver of the differences in soil moisture and discharge for catchments with a seasonal versus intermittent snow cover. Despite the large difference in discharge between these two snow zones, the intermittent snow zone contributed about a quarter of the discharge in the regional river, highlighting the importance of studying discharge generation across all elevations. 相似文献
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Effective governance for competitive regions in Europe: the difficult case of the Randstad 总被引：1，自引：0，他引：1
Europe has come to recognize that its regions have a major role to play in achieving its cohesion and competitiveness objectives. EU policies and Structural Fund principles are therefore increasingly geared towards enhancing regional capacities. Regions across Europe are responding, with varying results so far. The Randstad, in the Netherlands, presents itself as a ‘far from best’ example. Despite continued and serious attempts to strengthen capacities and institutions, the region still lacks effective governance. This paper explores the question why it is next to impossible to establish a framework for effective governance in the Randstad and distils some lessons for other regions in Europe. 相似文献
8.
David L. Huston Leon Vandenberg Andrew S. Wygralak Terrence P. Mernagh Leon Bagas Andrew Crispe Alexis Lambeck Andrew Cross Geoff Fraser Nick Williams Kurt Worden Tony Meixner Bruce Goleby Leonie Jones Pat Lyons David Maidment 《Mineralium Deposita》2007,42(1-2):175-204
The Tanami region of northern Australia has emerged over the last two decades as the largest gold-producing region in the Northern Territory. Gold is hosted by epigenetic quartz veins in sedimentary and mafic rocks, and by sulfide-rich replacement zones within iron formation. Although limited, geochronological data suggest that most mineralization occurred at about 1,805–1,790 Ma, during a period of extensive granite intrusion, although structural relationships suggest that some deposits predate this period. There are three main goldfields in the Tanami region: the Dead Bullock Soak goldfield, which hosts the world-class Callie deposit; The Granites goldfield; and the Tanami goldfield. In the Dead Bullock Soak goldfield, deposits are hosted by carbonaceous siltstone and iron formation where a late (D5) structural corridor intersects an early F1 anticlinorium. In The Granites goldfield, deposits are hosted by highly sheared iron formation and are interpreted to predate D5. The Tanami goldfield consists of a large number of small, mostly basalt-hosted deposits that probably formed at a high structural level during D5. The D5 structures that host most deposits formed in a convergent structural regime with σ 1 oriented between E–W and ENE–WSW. Structures active during D5 include NE-trending oblique thrust (dextral) faults and ESE-trending (sinistral) faults that curve into N- to NNW-trending reverse faults localized in supracrustal belts between and around granite complexes. Granite intrusions also locally perturbed the stress field, possibly localizing structures and deposits. Forward modeling and preliminary interpretations of reflection seismic data indicate that all faults extend into the mid-crust. In areas characterized by the N- to NW-trending faults, orebodies also tend to be N- to NW-trending, localized in dilational jogs or in fractured, competent rock units. In areas characterized by ESE-trending faults, the orebodies and veins tend to strike broadly east at an angle consistent with tensional fractures opened during E–W- to ENE–WSW-directed transpression. Many of these deposits are hosted by reactive rock units such as carbonaceous siltstone and iron formation. Ore deposition occurred at depths ranging from 1.5 to 11 km from generally low to moderate salinity carbonic fluids with temperatures from 200 to 430°C, similar to lode–gold fluids elsewhere in the world. These fluids are interpreted as the product of metamorphic dewatering caused by enhanced heat flow, although it is also possible that the fluids were derived from coeval granites. Lead isotope data suggest that lead in the ore fluids had multiple sources. Hydrogen and oxygen isotope data are consistent with both metamorphic and magmatic origins for ore fluids. Gold deposition is interpreted to be caused by fluid unmixing and sulfidation of host rocks. Fluid unmixing is caused by three different processes: (1) CO2 unmixing caused by interaction of ore fluids with carbonaceous siltstone; (2) depressurization caused by pressure cycling in shear zones; and (3) boiling as ore fluids move to shallow levels. Deposits in the Tanami region may illustrate the continuum model of lode–gold deposition suggested by Groves (Mineralium Deposita 28:366–374, 1993) for Archean districts. 相似文献
9.
Leonie E. A. Jones 《Physics and Chemistry of Minerals》1977,1(2):179-197
The elastic moduli of single-crystal MgF2 have been determined by the ultrasonic pulse superposition technique as a function of temperature from T=298?650° K. These new data are consistent with those obtained by other ultrasonic pulse techniques at and below room temperature and agree favourably with polycrystalline data above room temperature. The elastic moduli (c) are represented by quadratic functions in T over the experimental temperature range with the curvature in the same sense for all the moduli. For the rutile-structure fluorides and oxides, evaluation of the temperature derivatives of the elastic moduli at constant volume indicates that the dominant temperature effect is extrinsic for (?K S /?T) P and intrinsic for (?μ/?T) P , where K S and μ are the isotropic bulk and shear moduli, respectively. There appears to be no simple relationship between (?c/?T) P and crystallographic parameters for the rutile structure, and |(?c/?T) P | for the fluorides is in general very much lower than the corresponding |(?c/?T) P | for the oxides. For the pair of compounds MgF2-TiO2, there is no evident analogue relationship for high-temperature elastic properties. 相似文献
10.
Mathematical modeling of a little known model of induced polarization (IP) referred to as “induced polarization caused by
constrictivity of pores” was developed. Polarization occurs in all types of rocks if surface areas and transfer numbers are
different for connected pores. During the polarization process, all contacts between pores of different transfer numbers will
be blocked and the electrical current will flow through the remaining channels. Diffusion equations with different specified
boundary conditions for time-on and time-off have been used to develop the base of this model. The new algorithm was tested
on laboratory measurements. Several samples were selected: shale, mudstone, tillite, hematite, lava, and manganese ore. Each
theoretical model includes pores of more than 40 different sizes sporadically distributed in the sample. The obtained data
show good agreement with theory and provide new information about pore size distribution in samples, prevalent pore radius,
and effect of anisotropy. 相似文献