From granitoid to kyanite-bearing micaschist during fluid-assisted shearing (Ile d’Yeu, France)     

Caroline Sassier  Philippe Boulvais  Denis Gapais  Ramon Capdevila  Hervé Diot 《International Journal of Earth Sciences》2006,95(1):2-18

We describe amphibolite-facies shear zones affecting an orthogneiss from the Armorican Hercynian belt (Ile d’Yeu, western France). The deformation pattern is consistent with top-to-the-South thrusting followed by E–W extension, as documented elsewhere in the region. Shearing was accompanied by channelled fluid flow that transformed the orthogneiss into a peraluminous micaschist. Structural and mineralogical data indicate rather early strain localization. Then, temperature increase associated with crustal thickening favoured more distributed deformations marked by shear zone stretching and the development of a HT regional foliation. Chemical analyses made across five shear zones show mass transfers that mainly implied losses in Ca and Na, and gains in H₂O, Mg, and K. Most results indicate constant volume transformation, but some suggest records of either gains or losses of volume (between +20% and −30%). This might reflect variable records of fluid-rock interactions according to the timing of initiation and subsequent evolution of individual shear zones, early thrusting stages being marked by up-temperature flow, and late thrusting stages by down-temperature flow. δ¹⁸O analyses suggest that fluids experienced significant isotopic exchange with orthogneisses.  相似文献   

Human Impact Since Medieval Times and Recent Ecological Restorationin a Mediterranean Lake: The Laguna Zoñar, Southern Spain     

Blas L. Valero-Garcés  Penélope González-Sampériz  Ana Navas  Javier Machín  Pilar Mata  Antonio Delgado-Huertas  Roberto Bao  Ana Moreno  José S. Carrión  Antje Schwalb  Antonio González-Barrios 《Journal of Paleolimnology》2006,35(3):441-465

The multidisciplinary study of sediment cores from Laguna Zoñar (37°29′00′′ N, 4°41′22′′ W, 300 m a.s.l., Andalucía, Spain) provides a detailed record of environmental, climatic and anthropogenic changes in a Mediterranean watershed since Medieval times, and an opportunity to evaluate the lake restoration policies during the last decades. The paleohydrological reconstructions show fluctuating lake levels since the end of the Medieval Warm Period (ca. AD 1300) till the late 19th century and a more acute dry period during the late 19th century – early 20th century, after the end of the Little Ice Age. Human activities have played a significant role in Laguna Zoñar hydrological changes since the late 19th century, when the outlet was drained, and particularly in the mid-20th century (till 1982) when the spring waters feeding the lake were diverted for human use. Two main periods of increased human activities in the watershed are recorded in the sediments. The first started with the Christian conquest and colonization of the Guadalquivir River Valley (13th century) particularly after the fall of the Granada Kingdom (15th century). The second one corresponds to the late 19th century when more land was dedicated to olive cultivation. Intensification of soil erosion occurred in the mid-20th century, after the introduction of farm machinery. The lake was declared a protected area in the early 1980s, when some agricultural practices were restricted, and conservation measures implemented. As a consequence, the lake level increased, and some littoral zones were submerged. Pollen indicators reflect this limnological change during the last few decades. Geochemical indicators show a relative decrease in soil erosion, but not changes in the amount of chemical fertilizers reaching the lake. This study provides an opportunity to evaluate the relative significance of human vs. climatic factors in lake hydrology and watershed changes during historical times. Paleolimnological reconstructions should be taken into account by natural resources agencies to better define lake management policies, and to assess the results of restoration policies.  相似文献   

Distribution of diatoms, chironomids and cladocera in surface sediments of thirty mountain lakes in south-eastern Switzerland   总被引：6，自引：0，他引：6  

Christian Bigler  Oliver Heiri  Renata Krskova  André F. Lotter  Michael Sturm 《Aquatic Sciences - Research Across Boundaries》2006,68(2):154-171

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Arsenic in the groundwater of Ouro Preto (Brazil): its temporal behavior as influenced by the hydric regime and hydrogeology     

José Augusto Costa Gonçalves  Jorge Carvalho de Lena  José Fernando Paiva  Hermínio Arias Nalini Jr  Janice Cardoso Pereira 《Environmental Geology》2007,53(4):785-793

In the city of Ouro Preto (MG), water catchment for public supply originates from superficial drainage, springs, old abandoned mines and some driven wells. In the rocks of the region, As is originally found in gold-enriched sulphide-bearing mineral deposits. The weathering process introduces As into the hydrological system by dissolution of this element into the leachate. Measurement of the As content in the groundwater of some catchments was carried out during 1 year and these measurements demonstrated high As content—up to 224 μg L⁻¹ of As(V)—during the rainy season (the maximum concentration limit according to World Health Organization is 10 μg L⁻¹). Lower values were observed during the dry season and in some sampling stations, As was not even detected. The As concentration variability during 1 year shows a strict and direct relationship to seasonal and hydrological conditions. For city authorities, responsible for public water supply, it is necessary to perform a complete inventory of the water sources used and constantly monitor the As content in the water.  相似文献   

Dynamics and contribution of karst groundwater to surface flow during Mediterranean flood     

Hervé Jourde  Axel Roesch  Vincent Guinot  Vincent Bailly-Comte 《Environmental Geology》2007,51(5):725-730

This paper describes the role of groundwater contribution to surface flow at the Causse d’Aumelas, a karst system near Montpellier (France), which is traversed by an intermittent river, the Coulazou. A first hydrologic model integrating a digital terrain model shows the inability of a standard rainfall-runoff model to replicate recorded flood hydrographs. While the flood peaks are routed through the karstic system along the Coulazou without a phase lag, the peak magnitude is somewhat modified. These results indicate an initial karst system recharge followed by a significant contribution to surface flow. A hydrodynamic analysis of ground-water flow confirms these results: the karst system first absorbs part of the rainfall, which induces a general water table rise within the aquifer, and then contributes to surface flow in the Coulazou.  相似文献   

Precursory Subsurface 222Rn and 220Rn Degassing Signatures of the 2004 Seismic Crisis at Tenerife, Canary Islands     

Nemesio M. Pérez  Pedro A. Hernández  Eleazar Padrón  Gladys Melián  Rayco Marrero  Germán Padilla  José Barrancos  Dácil Nolasco 《Pure and Applied Geophysics》2007,164(12):2431-2448

Precursory geochemical signatures of radon degassing in the subsurface of the Tenerife Island were observed several months prior to the recent 2004 seismic-volcanic crisis. These premonitory signatures were detected by means of a continuous monitoring of ²²²Rn and ²²⁰Rn activity from a bubbling CO₂-rich gas spot located at 2.850 m depth inside a horizontal gallery for groundwater exploitation at Tenerife. Multivariate Regression Analysis (MRA) on time series of the radon activity was applied to eliminate the radon activity fluctuation due to external variables such as barometric pressure, temperature and relative humidity as well as power supply. Material Failure Forecast Method (FFM) was successfully applied to forecast the anomalous seismicity registered in Tenerife Island in 2004. The changes in the ²²²Rn/²²⁰Rn ratio observed after the period of anomalous seismicity might suggest a higher gas flow rate and/or changes in the vertical permeability induced by seismic activity.  相似文献   

The ionization of the shell of Novae: A time-dependent model     

J. A. de Freitas Pacheco  Laerte Sodré Jr. 《Astrophysics and Space Science》1979,61(1):91-100

The authors describe a simple model of an ionization-front propagating in a homogeneous expanding Nova shell. They have estimated the ejected shell mass, the shell ionization time and the Ly-c output from the remnant for several Novae, and present some correlations between these quantities and other Nova parameters.  相似文献   

Semi-automated filtering of data outliers to improve spatial analysis of piezometric data     

Yohann Tremblay  Jean-Michel Lemieux  Richard Fortier  John Molson  René Therrien  Pierre Therrien  Guillaume Comeau  Marie-Catherine Talbot Poulin 《Hydrogeology Journal》2015,23(5):851-868

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Hydro-economic analysis of groundwater pumping for irrigated agriculture in California’s Central Valley,USA     

Josué Medellín-Azuara  Duncan MacEwan  Richard E. Howitt  George Koruakos  Emin C. Dogrul  Charles F. Brush  Tariq N. Kadir  Thomas Harter  Forrest Melton  Jay R. Lund 《Hydrogeology Journal》2015,23(6):1205-1216

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New investigations in southwestern Guinea: consequences for the Rokelide belt (West Africa)     

Michel Villeneuve  Hervé Bellon  Michel Corsini  Joël Le Metour  Sébastien Chatelee 《International Journal of Earth Sciences》2015,104(5):1267-1275

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