Atacamite formation by deep saline waters in copper deposits from the Atacama Desert,Chile: evidence from fluid inclusions,groundwater geochemistry,TEM, and <Superscript>36</Superscript>Cl data   总被引：2，自引：2，他引：0  

Martin Reich  Carlos Palacios  Miguel A. Parada  Udo Fehn  Eion M. Cameron  Matthew I. Leybourne  Alejandro Zúñiga 《Mineralium Deposita》2008,43(6):663-675

The presence of large amounts of atacamite in oxide zones from ore deposits in the Atacama Desert of northern Chile requires saline solutions for its formation and hyperarid climate conditions for its preservation. We investigated the nature and origin of atacamite-forming solutions by means of coupling groundwater geochemical analyses with fluid inclusion data, high-resolution mineralogical observations, and chlorine-36 (³⁶Cl) data in atacamite from the Mantos Blancos and Spence Cu deposits. In both deposits, the salinities of fluid inclusions in atacamite are comparable to those measured in saline groundwaters sampled from drill holes. The average salinity of fluid inclusions in atacamite for the Mantos Blancos and Spence deposits (~7–9 and 2–3 wt.% NaCl_eq, respectively) are strongly correlated to the salinities at which gypsum supersaturates from groundwaters in both deposits (total dissolved solids ~5–9 and 1–3 wt.% NaCl_eq, respectively). This correlation is confirmed by transmission electron microscopy observations of atacamite-bearing samples, revealing an intimate association between atacamite and gypsum that can be traced down to the nanometer scale. ³⁶Cl data in atacamite provide new lines of evidence concerning the origin and age of the saline waters that formed atacamite in various stratabound and porphyry Cu deposits from the Atacama Desert. All atacamite samples show very low ³⁶Cl-to-Cl ratios (11 × 10⁻¹⁵ to 28 × 10⁻¹⁵ at at⁻¹), comparable to previously reported ³⁶Cl-to-Cl ratios of deep formation waters and old groundwaters. In addition, ³⁶Cl-to-Cl ratios in atacamite correlate with U and Th concentration in the host rocks but are independent from distance to the ocean. This trend supports an interpretation of the low ³⁶Cl-to-Cl ratios in atacamite as representing subsurface production of fissiogenic ³⁶Cl in secular equilibrium with the solutions involved in atacamite formation. Therefore, ³⁶Cl in atacamite strongly suggest that the chlorine in saline waters related to atacamite formation is old (>1.5 Ma) but that atacamite formation occurred more recently (<1.5 Ma) than suggested in previous interpretations. Our data provide new constraints on the origin of atacamite in Cu deposits from the Atacama Desert and support the recent notion that the formation of atacamite in hyperarid climates such as the Atacama Desert is an ongoing process that has occurred intermittently since the onset of hyperaridity.  相似文献   

A description of the tides and effect of Qeshm canal on that in the Persian Gulf using two-dimensional numerical model     

Hossein Mashayekh Poul  Jan Backhaus  Udo Huebner 《Arabian Journal of Geosciences》2016,9(2):148

The main semidiurnal (M2 and S2) and diurnal (K1 and O1) tidal constituents are simulated in the Persian Gulf (PG). The topography is discretized on a spherical grid with a resolution of 30 s in both latitude and longitude. It includes coastal areas prone to flooding. The model permits flooding of drying banks up to 5 m above mean sea level. At the open boundary, it is forced by 13 harmonic constituents extracted from a global tidal model. The model results are in good agreement with tide gauge observations. Co-tidal charts and flow extremes are presented for each tidal constituent. The co-tidal charts show two amphidromic points for semidiurnal and one for diurnal tidal constituents. Maximum amplitudes of sea level are obtained for the north-western part of the PG, where coastal flooding prevails in wide areas. Strong tidal currents occur in different parts of the PG for different types of constituents. Maximum velocities are found in shallow regions. Particularly, high amplitudes of elevations and high speed currents are founded in the canal between Qeshm Island and the mainland. Rectification of tides around Qeshm Island affects the propagation of tides in the PG as far as the coast of Saudi Arabia and the northern part of the PG.  相似文献   

Rangeland degradation assessment in Kyrgyzstan: vegetation and soils as indicators of grazing pressure in Naryn Oblast     

Franziska Hoppe  Taalaigul Zhusui Kyzy  Adilet Usupbaev  Udo Schickhoff 《山地科学学报》2016,13(9):1567-1583

Rangelands occupy more than 80% of the agricultural land in Kyrgyzstan. At least 30% of Kyrgyz pasture areas are considered to be subject to vegetation and soil degradation. Since animal husbandry is the economic basis to sustain people’s livelihoods, rangeland degradation presents a threat for the majority of the population. We present for the first time an ecological assessment of different pasture types in a remote area of the Naryn Oblast, using vegetation and soils as indicators of rangeland conditions. We analysed the current degree of utilization (grazing pressure), the amount of biomass, soil samples, and vegetation data, using cluster analysis as well as ordination techniques. Winter pastures (kyshtoo) are characterized by higher pH values (average of 7.27) and lower organic matter contents (average of 12.83%) compared to summer pastures (dzailoo) with average pH values of 6.03 and average organic matter contents of 21.05%. Additionally, summer pastures show higher above-ground biomass, and higher species richness and diversity. Our results support the hypothesis that winter pastures, which are located near settlements, suffer from over-utilisation, while the more distant summer pastures are subjected to much lower grazing pressure.  相似文献   

VIRGO: Experiment for helioseismology and solar irradiance monitoring   总被引：1，自引：0，他引：1  

Claus Fröhlich  José Romero  Hansjörg Roth  Christoph Wehrli  Bo N. Andersen  Thierry Appourchaux  Vicente Domingo  Udo Telljohann  Gabrielle Berthomieu  Philippe Delache  Janine Provost  Thierry Toutain  Dominique A. Crommelynck  André Chevalier  Alain Fichot  Werner Däppen  Douglas Gough  Todd Hoeksema  Antonio Jiménez  Maria F. Gómez  José M. Herreros  Teodoro Roca Cortés  Andrew R. Jones  Judit M. Pap  Richard C. Willson 《Solar physics》1995,162(1-2):101-128

The scientific objective of the VIRGO experiment (Variability of solar IRradiance and Gravity Oscillations) is to determine the characteristics of pressure and internal gravity oscillations by observing irradiance and radiance variations, to measure the solar total and spectral irradiance and to quantify their variability over periods of days to the duration of the mission. With these data helioseismological methods can be used to probe the solar interior. Certain characteristics of convection and its interaction with magnetic fields, related to, for example, activity, will be studied from the results of the irradiance monitoring and from the comparison of amplitudes and phases of the oscillations as manifest in brightness from VIRGO, in velocity from GOLF, and in both velocity and continuum intensity from SOI/MDI. The VIRGO experiment contains two different active-cavity radiometers for monitoring the solar constant, two three-channel sunphotometers (SPM) for the measurement of the spectral irradiance at 402, 500 and 862 nm, and a low-resolution imager (LOI) with 12 pixels, for the measurement of the radiance distribution over the solar disk at 500 um. In this paper the scientific objectives of VIRGO are presented, the instruments and the data acquisition and control system are described in detail, and their measured performance is given.died 13 October 1994  相似文献   

Advances in oxide and sulfide mineral surface chemistry     

Udo Becker 《Geochimica et cosmochimica acta》2003,67(5):797

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Flow of winter-transformed Pacific water into the Western Arctic   总被引：1，自引：0，他引：1  

Robert S. Pickart  Thomas J. Weingartner  Lawrence J. Pratt  Sarah Zimmermann  Daniel J. Torres 《Deep Sea Research Part II: Topical Studies in Oceanography》2005,52(24-26):3175

The dynamics of the flow of dense water through Barrow Canyon is investigated using data from a hydrographic survey in summer 2002. The focus is on the winter-transformed Bering water—the highest volumetric mode of winter water in the Chukchi Sea—which drains northward through the canyon in spring and summer. The transport of this water mass during the time of the survey was 0.2–0.3 Sv. As the layer flowed from the head of the canyon to the mouth, it sank, decelerated, and stretched. Strong cyclonic relative vorticity was generated on the seaward side of the jet, which compensated for the stretching. This adjustment was incomplete, however, in that it did not extend across the entire current, possibly because of internal mixing due to shear instabilities. The resulting vorticity structure of the flow at the canyon mouth was conducive for baroclinic instability and eddy formation. Multiple eddies of winter-transformed Bering water were observed along the Chukchi–Beaufort shelfbreak. Those to the west of Barrow Canyon were in the process of being spawned by the eastward-flowing shelfbreak current emanating from Herald Canyon, while the single eddy observed to the east originated from the Barrow Canyon outflow. It is argued that such an eddy formation is a major source of the ubiquitous cold-core anti-cyclones observed historically throughout the Canada Basin. Implications for the ventilation of the upper halocline of the Western Arctic are discussed.  相似文献   

Influence of improved performance monitoring on the consistency of a bottom trawl survey   总被引：1，自引：0，他引：1  

Zimmermann  Mark; Wilkins  Mark E; Weinberg  Kenneth L; Lauth  Robert R; Shaw  Franklin R 《ICES Journal of Marine Science》2003,60(4):818-826

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Mapping of desert locust habitats in Africa using Landsat Thematic Mapper data   总被引：1，自引：0，他引：1  

Udo Dreiser 《GeoJournal》1994,32(1):55-60

The results of the research at the Sudan Red Sea coast, which is part of the GTZ project Integrated Biological Control of Grasshoppers and Locusts will be presented. For detecting desert locust biotopes multitemporal Landsat Thematic Mapper data and ground truth information are analyzed. The Normalized Difference Vegetation Index (NDVI) shows the areas covered with vegetation. These areas are masked and then classified with the maximum likelihood classifier. Rectification and ground truthing are carried out by means of a GPS (Global Positioning System). The results of the multitemporal classification are merged with an enhanced satellite scene. The final map shows the potential desert locust biotopes. The current desert locust breeding area can be demarcated by combining the classification results with up-to-date data from monitoring satellites, such as Meteosat and NOAA. Further research is carried out in Mali and Mauritania.  相似文献   

Decreasing nutrient concentrations in soils and trees with increasing elevation across a treeline ecotone in Rolwaling Himal,Nepal   总被引：1，自引：0，他引：1  

Simon Drollinger  Michael Müller  Timo Kobl  Niels Schwab  Jürgen Böhner  Udo Schickhoff  Thomas Scholten 《山地科学学报》2017,14(5):843-858

At a global scale, tree growth in alpine treeline ecotones is limited by low temperatures. At a local scale, however, tree growth at its upper limit depends on multiple interactions of influencing factors and mechanisms. The aim of our research was to understand local scale effects of soil properties and nutrient cycling on tree growth limitation, and their interactions with other abiotic and biotic factors in a near-natural Himalayan treeline ecotone. Soil samples of different soil horizons, litter, decomposition layers, and foliage samples of standing biomass were collected in four altitudinal zones along three slopes, and were analysed for exchangeable cations and nutrient concentrations, respectively. Additionally, soil and air temperature, soil moisture, precipitation, and tree physiognomy patterns were evaluated. Both soil nutrients and foliar macronutrient concentrations of nitrogen (N), magnesium (Mg), potassium (K), and foliar phosphorus (P) decrease significantly with elevation. Foliar manganese (Mn) concentrations, by contrast, are extraordinarily high at high elevation sites. Potential constraining factors on tree growth were identified using multivariate statistical approaches. We propose that tree growth, treeline position and vegetation composition are affected by nutrient limitation, which in turn, is governed by low soil temperatures and influenced by soil moisture conditions.  相似文献   

Rock salt — the mechanical properties of the host rock material for a radioactive waste repository     

Udo Hunsche  Andreas Hampel 《Engineering Geology》1999,52(3-4):271-291

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