Model of geomagnetic paleosecular variations for the Northern Hemisphere     

Ana M. Sinito  Juan F. Vilas 《Studia Geophysica et Geodaetica》1991,35(4):334-343

Summary A model of radial drifting and oscillating dipoles to represent geomagnetic palaeosecular variations, which showed to be appropriate for the Southern Hemisphere, is evaluated for the Northern Hemisphere. After a new fitting of some involved parameters, its theoretical results are compared with the palaeomagnetic data of Lake de Bouchet (France) and the Black Sea. A time lag between the declination and inclination profiles is observed in both cases. A good cross-correlation coefficient is obtained for the declination and inclination data.Presented at 2nd conference on New Trends in Geomagnetism, Castle of Bechyn, Czechoslovakia, September 24–29, 1990.  相似文献   

Quiescent prominence threads models     

Juan Manuel Fontenla  Marta Rovira 《Solar physics》1985,96(1):53-92

We have calculated prominence thread models for different values of the center temperature and pressure. We have simultaneously solved the radiative transfer, statistical equilibrium and ionization equilibrium equations assuming a three-level atom plus continuum. We have also computed the energy balance equation including the hydrogen radiative losses from our calculations, plus other radiative losses and heat conduction. Some models have been calculated assuming possible variations in thermal conductivity and heating terms. We computed the lines and continua emitted by a number of threads, in order to compare with the observations and evaluate how the different values of the parameters affect the profiles and absolute intensities of L, L, H, and Ly continuum.Member of the Carrera del Investigador, CONICET, Argentina.c.c.67 Suc. 28 Buenos Aires 1428, Argentina.  相似文献   

Detailed <Superscript>40</Superscript>Ar/<Superscript>39</Superscript>Ar dating of geologic events associated with the Mantos Blancos copper deposit,northern Chile     

Verónica Oliveros  Gilbert Féraud  Luis Aguirre  Luis Ramírez  Michel Fornari  Carlos Palacios  Miguel Parada 《Mineralium Deposita》2008,43(3):281-293

The ⁴⁰Ar/³⁹Ar geochronological method was applied to date magmatic and hydrothermal alteration events in the Mantos Blancos mining district in the Coastal Cordillera of northern Chile, allowing the distinction of two separate mineralization events. The Late Jurassic Mantos Blancos orebody, hosted in Jurassic volcanic rocks, is a magmatic-hydrothermal breccia-style Cu deposit. Two superimposed mineralization events have been recently proposed. The first event is accompanied by a phyllic hydrothermal alteration affecting a rhyolitic dome. The second mineralization event is related to the intrusion of bimodal stocks and sills inside the deposit. Because of the superposition of several magmatic and hydrothermal events, the obtained ⁴⁰Ar/³⁹Ar age data are complex; however, with a careful interpretation of the age spectra, it is possible to detect complex histories of successive emplacement, alteration, mineralization, and thermal resetting. The extrusion of Jurassic basic to intermediate volcanic rocks of the La Negra Formation is dated at 156.3 ± 1.4 Ma (2σ) using plagioclase from an andesitic lava flow. The first mineralization event and associated phyllic alteration affecting the rhyolitic dome occurred around 155–156 Ma. A younger bimodal intrusive event, supposed to be equivalent to the bimodal stock and sill system inside the deposit, is probably responsible for the second mineralization event dated at ca. 142 Ma. Other low-temperature alteration events have been dated on sericitized plagioclase at ca. 145–146, 125, and 101 Ma. This is the first time that two distinct mineralization events have been documented from radiometric data for a copper deposit in the metallogenic belt of the Coastal Cordillera of northern Chile. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.  相似文献   

Soil contamination from urban and industrial activity: example of the mining district of Linares (southern Spain)   总被引：1，自引：0，他引：1  

J. Martínez  J. F. Llamas  E. de Miguel  J. Rey  M. C. Hidalgo 《Environmental Geology》2008,54(4):669-677

The Linares region (southern Spain) has been subjected to two important sources of pollution: the intensive mining works and the urban-industrial activity. To obtain a geochemical characterisation of the soil, 31 trace elements were analysed and 669 soil samples were collected. By means of clustering analysis, we identified groups of elements and grid squares in which relations could be established concerning soil lithology, urban and industrial activities and the degree of pollution impact; in addition, we were able to characterise the geochemical background of the study area. The multivariate study led us to identify four factors. Particularly important was factor 2, which represented the elements associated with mineral paragenesis (Cu, Pb, As, Co, Mn, Zn, Sn, Ba). This factor also contains elements related with an urban-industrial activity, such as Pb, Cu, Zn, As and Ba. Furthermore, we identified factor 4, associating Ni, V and Cr, and which is related to the use of fuels.  相似文献   

Mobilization analysis of the dolmen of Dombate (Northwest Spain)     

Vicente Navarro  Luis E. Romera  ngel Yustres  Miguel Candel 《Engineering Geology》2008,100(1-2):59-68

This paper presents an analysis of the mobilization of the dolmen of Dombate, a megalithic monument situated in the Northwest of Spain. The study is founded on simple static principles, with the application of basic concepts of soil mechanics (soil reactions were computed by the reaction modulus method) and rock mechanics (a simple secant approach was adopted to model the contact between orthostats). In addition, a simplified geometric model for dolmens was adopted. On the basis of these concepts, a numerical solver able to provide quick estimations of the system's mobilization was developed. Using this tool, a number of sensitivity analyses were conducted to estimate the mobilization that could be caused by a conservation project currently under consideration. It was found that mobilization might be excessive, and therefore, a safer procedure is proposed. In short, this paper puts forth a new rational approach for archaeological practices which may help to estimate the possible consequences of excavations and rehabilitations on megalithic structures.  相似文献   

Geochemical and mineralogical evidence of tectonic and sedimentary factors controlling the origin of ferromanganese crusts associated to stratigraphic discontinuities (Betic Cordilleras, SE of Spain)     

Juan Jiménez-Millán  Luis M. Nieto 《Chemie der Erde / Geochemistry》2008,68(3):323-336

Ferromanganese crusts were found in carbonates of tectonostratigraphic units located in the northern and southern areas of the eastern External Subbetic of the Betic Cordilleras (SE Spain). The crusts are associated with four stratigraphic discontinuities of the Jurassic pelagic swells sequences: D1 (Late Carixian-Early Domerian), D2 (Middle Toarcian-Early Bajocian), D3 (Middle Bathonian-Middle Oxfordian), D4 (Early Tithonian-Late Albian). Two main textural types of crusts are distinguished. Type I crusts are thin and characterized by the presence of goethite, quartz, albite and phyllosilicates. Moreover, they show Si, Al, Mg, Na, Ti and K contents close to the European Shale Composite contents and Fe/Mn ratios (>350) higher than type II crusts. Type II crusts occur as thicker banded laminae and/or macrooncoids. They consist mainly of goethite and Mn-oxyhydroxides, which are enriched in REE, Co, Ni and Cu and show a strong Ce positive anomaly. After stratigraphical, mineralogical and geochemical data, the crust formation would be produced by the exposition of bottom sediments during long periods to a thin layer of oxidizing sea and porewater enriched in metallic elements. The textural and compositional variations between crusts can be explained by taking into account the bathymetric conditions. In shallower swells, the precipitation of a thick layer of banded type II crusts and in deeper areas, thin type I crusts were formed. Organic influence was only important in crusts from D3 of the northern area where textural evidence indicates the existence of seasonal periodically alternation between organism accretion and fine sedimentation. These were preceded and followed by phases in which the inorganic precipitation of oxides prevailed together with the fine sedimentation.  相似文献   

Models of natural and human dynamics in forest landscapes: Cross-site and cross-cultural synthesis   总被引：1，自引：0，他引：1  

Miguel F. Acevedo  J. Baird Callicott  Donald Lyons  Judith Rosales  Magdiel Ablan  Giorgio Tonella  Emilio Vilanova 《Geoforum》2008,39(2):846-866

We synthesize the study of coupled natural and human systems across sites and cultures through a process of simplification and abstraction based on multiple dimensions of human-nature connectedness: satisfaction of basic needs, psycho-cultural connectedness and regulation of use of natural resources. We thus provide both a place-based and general understanding of value-driven anthropogenic environmental change and response. Two questions guide this research: what are the crucial stakeholder values that drive land use decisions and thus land cover change? And how can knowledge of these values be used to make decisions and policies that sustain both the human and natural systems in a place? To explore these questions we build simulation models of four study sites, two in the State of Texas, United States, and two in Venezuela. All include protected areas, though they differ in the specifics of vegetation and land use. In the Texas sites, relatively affluent individuals are legally converting forests to residential, commercial, and industrial uses, while in Venezuela landless settlers are extra-legally converting forests for purposes of subsistence agriculture. Contemporary modeling techniques now facilitate simulations of stakeholder and ecosystem dynamics revealing emergent patterns. Such coupled human and natural systems are currently recognized as a form of biocomplexity. Our modeling framework is flexible enough to allow adaptation to each of the study sites, capturing the essential features of the respective natural and anthropogenic land use changes and stakeholder reactions. The interactions between human stakeholders are simulated using multi-agent models that act on forest landscape models, and receive feedback of the effects of these actions on ecological habitats and hydrological response. The multi-agent models employ a formal logic-based method for the Venezuelan sites and a decision analysis approach using multi-attribute utility functions for the Texas sites, differing more in style and emphasis than in substance. Our natural-systems models are generic and can be tailored according to site-specific conditions. Similar models of tree growth and patch transitions are used for all the study sites and the differing responses to environmental variables are specified for each local species and terrain conditions.  相似文献   

Sulfur isotopic study of sulfate in the aquifer of Costa de Hermosillo (Sonora,Mexico) in relation to upward intrusion of saline groundwater,irrigation pumping and land cultivation     

Anna Szynkiewicz  Miguel Rangel Medina  Magdalena Modelska  Rogelio Monreal  Lisa M. Pratt 《Applied Geochemistry》2008

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Coupled hydrogeological and reactive transport modelling of the Simpevarp area (Sweden)     

Jorge Molinero  Juan R. Raposo  Juan M. Galíndez  David Arcos  Jordi Guimerá 《Applied Geochemistry》2008

The Simpevarp area is one of the alternative sites being considered for the deep geological disposal of high level radioactive waste in Sweden. In this paper, a coupled regional groundwater flow and reactive solute transport model of the Simpevarp area is presented that integrates current hydrogeological and hydrochemical data of the area. The model simulates the current hydrochemical pattern of the groundwater system in the area. To that aim, a conceptual hydrochemical model was developed in order to represent the dominant chemical processes. Groundwater flow conditions were reproduced by taking into account fluid-density-dependent groundwater flow and regional hydrogeologic boundary conditions. Reactive solute transport calculations were performed on the basis of the velocity field so obtained. The model was calibrated and sensitivity analyses were carried out in order to investigate the effects of heterogeneities of hydraulic conductivity in the subsurface medium. Results provided by the reactive transport model are in good agreement with much of the measured hydrochemical data. This paper emphasizes the appropriateness of the use of reactive solute transport models when water-rock interaction reactions are involved, and demonstrates what powerful tools they are for the interpretation of hydrogeological and hydrochemical data from site geological repository characterization programs, by providing a qualitative framework for data analysis and testing of conceptual assumptions in a process-oriented approach.  相似文献   

Wenchuan Earthquake： Way of thinking is changed   总被引：9，自引：0，他引：9  

Yong Chen Li Li Juan Li Gang Li 《《幕》》2008,31(4):374-377

On 12 May, 2008, at 14：28：04 local time, an Ms 8.0 earthquake struck the Wenchuan County, Sichuan Province, in southwest China （Figure 1）. This quake left about 70,000 people dead, 18,000 missing and over 370,000 injured. In the 75 days after the main shock, 20,000 aftershocks were recorded, which included 241 with Ms≥4.0, 205 with 4.0≤M≤4.9, 30 with 5.0≤Ms≤5.9, and 6 with Ms≥6.0. The largest aftershock took place 13 days after the main shock, in Qingchuan County, 110 km northeast of the epicenter of the quake （Chen, 2008）. The losses from the quaketriggered geological disasters accounted for over a third of the total quake losses, which is extremely rare in the history of earthquake disasters. Secondary disasters, such as landslides, rockslides, landfalls, debris flows, etc., were widely distributed. Large numbers of buildings collapsed, including ones with steel reinforcing in the area of the epicenter. Infrastructure was badly damaged. In many areas, communications, and power and water supplies were cut off. The earthquake left over 35 large quake-dammed lakes, which threatened further disasters in the catchment areas.  相似文献