Mineralisation and plate tectonics     

J. Pereira  C. J. Dixon 《Mineralium Deposita》1971,6(4):404-405

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Pb / Pb-ages of zircons from syn-collisional I-type porphyritic granites of the central Ribeira belt, SE Brazil     

Julio Cezar Mendes  Ciro Alexandre vila  Ronaldo Mello Pereira  Mnica P.L. Heilbron  Candido A.V. Moura 《Gondwana Research》2006,9(3):326-336

In the central segment of the Ribeira belt, southeast Brazil, several foliated porphyritic granitic bodies intrude high-grade migmatitic gneisses of the Andrelândia and Juiz de Fora domains and Embú Complex. Results of geological, geochemical and geochronological investigations of the Maromba, Pedra Selada, Serra do Lagarto and Funil porphyritic I-type granites provide profound similarities, except for the distinct geochemical behavior of the Funil Granite, perhaps related to a different crustal source. These granitoids show similar structural, textural and mineralogical features. Pb-evaporation of single zircons provided ages of 586 ± 6, 579.6 ± 6.3, 586.3 ± 4.8 and 584 ± 5 Ma for the granites, respectively, coincident with the syn-collision I episode of the central Ribeira belt. The intrusion of I-type porphyritic granitoids coeval with the main collisional event has not often been reported in the geological literature. The most common syn-collisional granitic magmatism has normally an S-type signature or even a slightly peraluminous I-type character. However, the occurrence of coeval I- and S-type syn-tectonic granites along the central Ribeira belt, as observed in the investigated area and discussed in this paper is noteworthy.  相似文献   

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   

Sedimentation–consolidation of a double porosity material     

Henry Wong  Chin J. Leo  J.M. Pereira  Ph. Dubujet 《Computers and Geotechnics》2007,34(6):532-538

This paper studies the sedimentation–consolidation of a double porosity material, such as lumpy clay. Large displacements and finite strains are accounted for in a multidimensional setting. Fundamental equations are derived using a phenomenological approach and non-equilibrium thermodynamics, as set out by Coussy [Coussy, Poromechanics, Wiley, Chichester, 2004]. These equations particularise to three non-linear partial differential equations in one dimensional context. Numerical implementation in a finite element code is currently being undertaken.  相似文献   

A locally conservative Eulerian–Lagrangian numerical method and its application to nonlinear transport in porous media     

Jim Douglas Jr.  Felipe Pereira  Li-Ming Yeh 《Computational Geosciences》2000,4(1):1-40

Eulerian-Lagrangian and Modified Method of Characteristics (MMOC) procedures provide computationally efficient techniques for approximating the solutions of transport-dominated diffusive systems. The original MMOC fails to preserve certain integral identities satisfied by the solution of the differential system; the recently introduced variant, called the MMOCAA, preserves the global form of the identity associated with conservation of mass in petroleum reservoir simulations, but it does not preserve a localized form of this identity. Here, we introduce an Eulerian-Lagrangian method related to these MMOC procedures that guarantees conservation of mass locally for the problem of two-phase, immiscible, incompressible flow in porous media. The computational efficiencies of the older procedures are maintained. Both the original MMOC and the MMOCAA procedures for this problem are derived from a nondivergence form of the saturation equation; the new method is based on the divergence form of the equation. A reasonably extensive set of computational experiments are presented to validate the new method and to show that it produces a more detailed picture of the local behavior in waterflooding a fractally heterogeneous medium. A brief discussion of the application of the new method to miscible flow in porous media is included. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Evaluation of susceptibility for terrain collapse and subsidence in karst areas,municipality of Iraquara,Chapada Diamantina (BA), Brazil     

Lucas de Queiroz Salles  Paulo Galvão  Luiz Rogério Bastos Leal  Ricardo Galeno Fraga de Araujo Pereira  Carlos Gleidson Campos da Purificação  Fernando Verassani Laureano 《Environmental Earth Sciences》2018,77(16):593

The morphological evolution of the karstic systems is associated with a set of physical and chemical processes, triggered by the dissolution of the rocks, related to percolation of groundwater and surface water, which consequently open underground voids and carve out peculiar forms of relief. Due to environmental and geotechnical aspects, this system is naturally more fragile and vulnerable than other natural systems and, therefore, has increasingly received the attention of the scientific community over the past decades. The objective of the study was to delimit zones with varying degrees of susceptibility for collapses and subsidence of sinkholes in the municipality of Iraquara, Chapada Diamantina (BA), Brazil, and to understand their geological and morphological determinant factors. Geological data, karst phenomenon map, and visual analysis in the field were used to categorize zones with different types of susceptibilities to the nucleation of new sinkholes based on a Hazard Index. This index was defined from the sum of geological hazard factors, lineament density, and sinkhole density. The areas that presented the highest susceptibility for terrain collapse and subsidence corresponded to regions where carbonate rocks outcrop, with high density of photolineaments and 2.62 sinkholes/km². Processes associated with terrain collapse and subsidence in karst areas consisted of a combination of various factors, hindering precise predictions. However, zones of different types of susceptibilities to terrain collapse and subsidence can be delimited when the relationships between these processes and their factors are understood. The Hazard Index proposed does not provide quantitative values for the probability of hazard susceptibility, but rather indicates areas that are more susceptible to terrain subsidence and collapse.  相似文献   

Effects on runoff caused by changes in land cover in a Brazilian southeast basin: evaluation by HEC-HMS and HEC-GEOHMS     

Thalita Costa de Moraes  Vitor Juste dos Santos  Maria Lúcia Calijuri  Fillipe Tamiozzo Pereira Torres 《Environmental Earth Sciences》2018,77(6):250

The Southeast Region of Brazil has undergone major changes in land cover, especially after the eighteenth century. It is currently the most populous region of the country, highly urbanized, with a high degree of industrial and agricultural development. Extensive areas of native vegetation have been replaced by pastures, crops and urban areas, which have increased runoff, causing environmental, economic and social problems related to flooding. The objective of this study was to analyze effects of land cover changes in a basin with rural and urban characteristics on the flow of its main river. Hydrological data, orbital images, soils and topographical maps were used for this purpose. Based on the land cover maps for the years of 1989, 2001 and 2015, and on the hydrological modeling performed using the Hec-HMS 4.1 software, scenarios were simulated and showed that the land cover changes in this basin significantly affect the flow behavior of the main river. The simulated runoff was calibrated using the data observed in the field during 2001, and validation was performed using data from 1989. After the calibration and validation processes, a scenario was simulated where the rainiest month of the whole series measured by the rainfall station (during December 1989) acted on the land cover of 2015. There was an increase in pasture areas and impermeable spaces in the basin, which caused a decrease in infiltration and an increase in surface runoff, and also an increase in the flow peaks and a reduction in the time of concentration. The hydrological modeling was satisfactory, since the uncertainties related to the simulation were low.  相似文献   

Influence of a Drought Event on Hydrological Characteristics of a Small Estuary on the Amazon Mangrove Coast     

Luci Cajueiro Carneiro Pereira  Ádila Kelly Rodrigues da Costa  Rauquírio Marinho da Costa  André Magalhães  Manuel de Jesus Flores-Montes  José A. Jiménez 《Estuaries and Coasts》2018,41(3):676-689

The effects of atypical climatic conditions, such as those of a drought event, are remarkably accentuated in minor estuaries filled with sediments and with reduced or sporadic freshwater input, where the salinity intrusion is pronounced. To understand these effects, hydrological and hydrodynamic parameters were evaluated during a drought period in a small estuary located on the eastern Amazon coast in northern Brazil. Five campaigns were conducted between June 2012 and June 2013. Samples were collected from the surface and bottom layer every 3 h over a 25-h period at three stations of the Taperaçu Estuary. To compare drought and post-drought periods, in terms of salinity and chlorophyll-a, data was recorded until June 2015. Taperaçu is a relatively shallow estuary of the Amazon coastal zone, which is characterized by the absence of any direct fluvial discharge, although it does receive freshwater input from adjacent wetlands, as well as less saline waters from the Caeté Estuary through the Taici Creek. Hydrological variables were controlled by rainfall levels and the tidal range, and the water became more saline and more oxygenated, with reduced dissolved nutrient and chlorophyll-a concentrations when precipitation decreased. A significant variation was found between the months of June 2012 (most intense drought) and 2013 (less intense drought). The connection to the neighboring Caeté Estuary and adjacent mangroves and wetlands contributed to the influx of nutrient-enriched waters. Overall, then, it is hoped that the results of this study can contribute to the understanding of the effects of drought events in other minor estuaries on the highly indented Amazon coast, as well as in other areas of the equatorial zone with similar environmental characteristics.  相似文献   

http://www.sciencedirect.com/science/article/pii/S1674987114000310   总被引：3，自引：0，他引：3  

M.F.Pereira  A.Castro  C.Fernández 《地学前缘(英文版)》2015,6(2):297-306

This paper presents a compilation of recent U-Pb(zircon) ages of late Carboniferous—early Permian(LCEP) calc-alkaline batholiths from Iberia,together with a petrogenetic interpretation of magma generation based on comparisons with Mesozoic and Tertiary Cordilleran batholiths and experimental melts.Zircon U-Pb ages distributed over the range ca.315—280 Ma,indicate a linkage between calc-alkaline magmatism,Iberian orocline generation and Paleotethys subduction.It is also shown that Iberian LC-EP calcalkaline batholiths present unequivocal subduction-related features comparable with typical Cordilleran batholiths of the Pacific Americas active margin,although geochemical features were partially obscured by local modifications of magmas at the level of emplacement by country rock assimilation.When and how LC-EP calc-alkaline batholiths formed in Iberia is then discussed,and a new and somewhat controversial interpretation for their sources and tectonic setting(plume-assisted relamination) is suggested.The batholiths are proposed to have formed during the subduction of the Paleotethys oceanic plate(Pangaea self-subduction) and,consequently,they are unrelated to Variscan collision.The origin of the Iberian batholiths is related to the Eurasian active margin and probably represents the inception of a Paleotethyan arc in the core of Pangaea.  相似文献   

Effect of fines content on soil freezing characteristic curve of sandy soils     

Vu  Quoc Hung  Pereira  Jean-Michel  Tang  Anh Minh 《Acta Geotechnica》2022,17(11):4921-4933

Acta Geotechnica - Soil freezing characteristic curve (SFCC) represents the relationship between soil temperature and unfrozen water content of soil during freezing and thawing processes. In this...  相似文献