Nearly 200 analyses of meltwaters, ice and snow from three alpine glacial sites in carbonate terrain are summarized and discussed in terms of sources of solutes and kinetic controls on the progress of weathering reactions. Most data derive from the Swiss Glacier de Tsanfleuron which is based on Cretaceous and Tertiary pure and impure limestones. Two other sites (Marmolada, Italian Dolomites and the Saskatchewan Glacier, Alberta) are based on a mixed calcitic-dolomitic substrate. Most solutes originate from carbonate dissolution; moreover, where pyrite is present its oxidation supplies significant sulphate and forces more dissolution of carbonate. The ratios Sr2+/Ca2+ and Mg2+/Ca2+ are much higher in Tsanfleuron melt-waters than local bedrock, a phenomenon that can be reproduced in the laboratory at small percentages of dissolution. These anomalous ratios are attributed to incongruent dissolution of traces of the metastable carbonates Mg-calcite and aragonite. These phases also provide Na+ to solution. K+ is argued to originate mainly by ion-exchange on clays with solute Ca2+. Quartz and very minor feldspar dissolution are also inferred. Locally enhanced input from atmospheric sources is recognized by high Cl? and associated Na+. The progress of weathering reactions has been evaluated by the trends in the data, computer modelling and some simple laboratory experiments. The most dilute samples show a trend towards removal of CO2 to low partial pressures (c. 10?5.5 atmospheres), reflecting initially rapid carbonate dissolution and relatively slow dissolution of gaseous CO2. Later addition of atmospheric CO2 or acid from pyrite oxidation allows further carbonate dissolution, but solutions show a wide range of saturations, and CO2 pressures as high as 10?2.2 where pyrite oxidation is important. In a carbonate terrain, measurement of electroconductivity (corrected to 25°C) and alkalinity in the field allows the following preliminary deductions (where meq stands for milliequivalents): where S is the minimum meq(Ca2+ + Mg2+) produced by simple dissolution of carbonate unconnected with pyrite oxidation. As with any proxy method, these deductions do not remove the need for chemical analysis of waters in a given study area. 相似文献
The solubility of nantokite (CuCl(s)) and the structure of the predominant copper species in supercritical water (290-400 bar at 420 °C; 350-450 °C at 290 bar; 500 °C at 350 bar; density = 0.14-0.65 g/cm3) were investigated concurrently using synchrotron X-ray absorption spectroscopy (XAS) techniques. These conditions were chosen as they represent single phase solutions near the critical isochore, where the fluid density is intermediate of typical values for vapour and brine and is highly sensitive to even small changes in pressure. X-ray absorption near edge spectroscopy (XANES) and extended X-ray absorption spectroscopy (EXAFS) analyses show that aqueous copper occurs in a slightly distorted linear coordination in the solutions studied, with an average of 1.35(±0.3) Cl and 0.65(±0.3) O neighbours. The solubility of CuCl(s) decreases exponentially with decreasing water density (i.e., decreasing pressure at constant temperature), in a manner similar to the solubility behaviour of salts such as NaCl in water vapour. Based on this similarity, an apparent equilibrium constant for the dissolution reaction of 0.5 ± 0.4 was calculated from a regression of the data at 420 °C, and it was determined that each Cu atom is solvated by approximately three water molecules. This indicates that under these conditions, copper solubility is controlled mainly by the structure of the second-shell hydration, which is essentially invisible to the XAS techniques used in this study.These results demonstrate that for a supercritical fluid near the critical isochore, decreasing pressure may initiate precipitation of copper even before boiling or phase separation. Such a process could be responsible for near-surface ore deposition in seafloor hydrothermal systems, where supercritical fluids experience rapid pressure changes during the transition between lithostatic and hydrostatic domains. 相似文献
Reanalyses, based on numerical weather prediction methods assimilating past observations, provide continuous precipitation datasets and represent interesting options for assessing the climatology of regions with sparse station networks (e.g., northern Canada). However, reanalysis series cannot be used directly because of possible biases and mismatch between their spatial and temporal resolutions with that needed for local applications. To address these issues, a Stochastic Model Output Statistics (SMOS) approach was selected to post-process precipitation series simulated by the Climate Forecast System Reanalysis (CFSR) across Canada. This approach uses CFSR precipitation as a covariate and is based on two regression models: the first one is a logistic regression that deals with precipitation occurrence, and the second is a vector generalized linear model for precipitation intensity. At-site post-processed daily precipitation series are randomly generated using the SMOS approach, and selected climate indicators from the Expert Team on Climate Change Detection and Indices, which is jointly sponsored by the Commission for Climatology of the World Meteorological Organization's (WMO) World Climate Data and Monitoring Programme, the Climate Variability and Predictability Programme of the World Climate Research Programme, and the Joint WMO-IOC Technical Commission for Oceanography and Marine Meteorology (CCI/CLIVAR/JCOMM) are estimated and compared with corresponding observed and CFSR values. The two models in the SMOS approach, in addition to adequately correcting systematic biases, produced better predictions than the climatology of the wet and dry and intensity sequences. Additionally, the SMOS generally yields consistent climate indices when compared with those from CFSR without post-processing, though there is still room for improvement for specific indices (e.g., annual maximum of cumulative wet days). 相似文献
In the Pyrenees, in association with the rotation of the Iberian plate around Europe during the Mid-Cretaceous, a Na–Ca metasomatism is recognized as a complementary record of the hydrothermal activity that led to Na-metasomatism (albitization) and talc–chlorite mineralization. It affected metasedimentary rocks as well as Hercynian granites. In situ laser ablation ICP-MS U–Pb analyses of titanite grains formed in albitites during metasomatism date the Na–Ca metasomatism between 110 and 92 Ma. The temperature of the Na–Ca metasomatism is estimated to be approximately 550 °C. Both the time constraints and temperature estimates suggest that the Na–Ca metasomatism is related to the low-P high-T North Pyrenean metamorphism. 相似文献
Energy piles make use of constant and moderate ground temperature for efficient thermal control of buildings. However, this use introduces new engineering challenges because the changes of temperature in the foundation pile and ground induce additional deformations and forces in the foundation element and coupled thermo-hydro-mechanical phenomena in the soil. Several published full-scale tests investigated this aspect of energy piles and showed thermally induced deformation and forces in the foundation element. In parallel, significant progress has been made in the understanding of thermal properties of soils and on the effect of cyclic thermal load on ground and foundation behavior. However, the effect of temperature on the creep rate of energy piles has received practically no attention in the past. This paper reports the experimental results of an in situ tension thermo-mechanical test on an energy pile performed in a very stiff high plasticity clay. During the in situ test, the pile was subjected to thermal loading by circulating hot water in fitted pipes, simulating a thermal load in a cooling-dominated climate, at different levels of mechanical loading. The axial strain and temperature in the pile, and the load–displacement of the pile were monitored during the tension test at different locations along the center of the pile and at the pile head, respectively. The data showed that as the temperature increases, the observed creep rate of the energy pile in this high plasticity clay also increases, which will lead to additional time-dependent displacement of the foundation over the life time of the structure. It was also found that the use of geothermal piles causes practically insignificant thermally induced deformation and loads in the pile itself. 相似文献
Dating the magmatism in the Montagne Noire gneiss dome in the southern French Massif Central is a key point for understanding the Late Palaeozoic evolution of this part of the Variscan belt, which is characterised by compressive tectonics during the Carboniferous and extensional tectonics during Stephanian-Permian times. The Montalet granite crops out in the north-western part of the dome and was first considered as an early syntectonic intrusion related to compressive deformation. More recently, it has been dated at 327 Ma and considered as contemporaneous with the diapiric ascent of the Montagne Noire gneiss dome before the Stephanian-Permian extension. We show that in fact, this pluton was emplaced 294 ± 1 Ma ago and is therefore contemporaneous with the Stephanian-Permian extension. This age is consistent with the interpretation of the Montagne Noire Massif as an extensional gneiss dome. 相似文献
Pollen and dinoflagellate cysts from marine sediments in core A180-48 (15°19′N, 18°06′W; 2450 m water depth; 530 cm length) are used to reconstruct palaeoenvironmental conditions of nearshore tropical west Africa during the last deglaciation. High concentrations and influxes of pollen and dinoflagellate cysts between 11 000 and 10 000 yr BP are interpreted as reflecting an increase in continental trade-wind circulation and related coastal upwelling at 15°N latitude. The sea-surface temperature difference between glacial and interglacial times was not as strong as previously suggested. Together with local (fresh) ground-water input, this smaller temperature difference may explain the persistence of the Rhizophora mangrove and Guinean gallery forests near the shore until their massive extension during the early Holocene humid maximum around 9500 yr BP. Pollen data from the core are compared with data from Rosilda N110-Z, from the continental shelf at the same latitude. 相似文献
