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9th International Congress of the Brazilian Geophysical Society
- Conference date: 11 Sep 2005 - 14 Sep 2005
- Location: Salvador, Bahia, Brazil
- Published: 11 September 2005
151 - 200 of 462 results
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DADOS AEROMAGNÉTICOS APLICADOS NA INTERPRETAÇÃO DO ARCABOUÇO ESTRUTURAL DA PORÇÃO NORDESTE DA PROVÍNICA BORBOREMA, NE BRASIL
This paper reports processing techniques applied to airborne magnetic data to generate themes that could be used as a tool do delimitate the boundaries and the tectonic framework in the northeastern portion of the Borborema Province in NE Brazil. Data processing result in the generation of anomalous magnetic map, residual magnetic field, allowing to generate the horizontal gradient zero order, amplitude and inclination of the analytical signal (zero order), and Euler deconvolution for different structural index. Preliminary results show enhancement of main tectonic structures and boundaries of crustal blocks present in the region. Also, was able to quantify the major shear zones that define the framework of the Borborema Province, and to identify important features not present on actual maps. Magnetic anomalies correlated to different crustal blocks indicate the depth extension of the archean nuclei São José do Campestre to S-SW. Also, it was shown different magnetic signature as for the paleoproterozoic rocks, low magnetic response for the Seridó Belt and also distinct signatures for the pre- and syn-brasiliano granites compared to the pos-tectonic granites.
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DECONVOLUÇÃO DE EULER: NOVA PERSPECTIVA PARA A INTERPRETAÇÃO 3D DE ESTRUTURAS GEOLÓGICAS
This paper deals with a 3D magnetic data (Seridó Project, 1973) interpretation of regional geologic structures (Patos Lineament and João Câmara-Picuí Shear Zone) in Northeast Brazil based on horizontal position and depth for magnetic sources given by Euler deconvolution. Best parameters for Euler deconvolutions were found from different combinations of structural index, window sizes, and error tolerances. Best product yelded solutions for the structural trends with depth through 5 km. The Patos Lineament (E-W) and João Câmara-Picuí Shear Zone (NE-SW) showed maximum depth in the order of 3 km and 2 km, respectively. Deeper magnetic sources (> 5 km) were found under supracrustal sequence of the Seridó Belt, in the portions Southwest of Currais Novos city. 3D plots proved to be useful to get a glimpse on the geometry and distribution of magnetic material within these structures.
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Contribuição da Aerogeofísica nos Levantamentos Geológicos Regionais
More LessThis work consists of a qualitative airborne geophysical interpretation (magnetometry and gammaspectrometry) of an area of 35,450 km² of the Trombetas Aerogeophysical Project, which is located in the north portion of the the State of Pará, Brazil. The study aims at stressing the importance of the aerogeophysical surveys to the planning of the geological mapping, mainly in the regions of difficult access like this project area, whose geology is not well known but of great metalogenetic importance to the country.
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Gravity inversion of a complex interface in the presence of interfering sources
More LessWe present a new semi-automatic gravity interpretation method for estimating a complex interface separating two media containing heterogeneities produced by the existence of interfering sources. The method combines a robust fitting procedure and the constraint that the interface is very smooth near the interfering sources whose approximate horizontal coordinates are defined by the user. The proposed method differs from the regionalresidual techniques by using no spectral content assumption about the interface to be estimated, i.e., the interface can produce a gravity response containing both low- and high-wavenumber features. As a result, it may be applied to map the relief of a complex interface in a geological setting containing either shallow- or deepseated interfering sources. Tests with synthetic data have shown that the method can be of utility in estimating the basement relief of a sedimentary basin in the presence of salt layers and domes or in the presence of mafic intrusions in the basement and/or in both basement and sediments. The method was applied to real gravity data from two geological setting having different kind of interfering sources and interface to be interpreted: 1) the anorthositie-tonalite interface over the outcrop East Bull gabbro anorthosite complex, Ontario, Canada; and 2) the sediments-basement interface over Algarve Basin, south Portugal. The results showed good agreement with the corresponding known geological features, even when the estimated interface and the interfering sources present highly overlapping spectral contents.
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Delineamento crosta continental-crosta oceânica através da magnetometria
More LessWe present a method to delineate the boundary separating the oceanic and continent crusts using magnetic data. The method maps magnetic lineaments, which happen to occur solely in the continental crust. To this end, the magnetic signal is amplified by downward continuing the magnetic anomaly to a surface defined by the bathymetry of the continental shelf, continental slope, and part of the continental rise. The purpose is to locate the seaward end of the lineaments. The downward continuation if formulated using the equivalent layer principle, leading to a large-scale system of linear equations, that was solved via a conjugate gradient method. To stabilize the solutions we used the first-order Tikhonov regularization functional (global smoothness constraint). Examples with synthetic data showed that, in contrast with the plain visual inspection of the original aeromagnetic data, which leads to an erroneous delineation of the boundary separating the oceanic and continent crusts, the continued magnetic anomaly delineates this boundary with excellent resolution. The method has also been applied to real aeromagnetic data from a Brazilian coastal area, evidencing that the data window is located above the continental shelf, or, possibly
above a transitional crust.
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Towards evidences of a threshold system as the source for magnetic storms detected on Earth’s surface
Authors Ney A. B. Seixas, Luiz M. Barreto and Andrés R. R. PapaIn this work we present evidences that point to a threshold system as the source for magnetic storms detected on the Earth. We based our analysis on series of data acquired during many years in the network of magnetic observatories of the National Observatory (Brazil). In particular we focused our attention on October 2000 month of the Vassouras Observatory, which have been active since 1915. The data was appropriately processed using classical Fourier formalisms. The analysis of statistical distribution of amplitudes, periods of calm and storms was implemented on the difference resulting from the processed and unprocessed data.
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Integração de métodos geofísicos na modelagem crustal na Bacia de Santos
Authors Eduardo de Mio and Hung K. Chang e Fernando S. CorrêaThe Santos Basin is a passive margin basin generated during the Neocominian, associated with Gondwana breakup event. The thickness of the sedimentary package reach 15 km, including rift sequence deposited over a thinned crust which originally was 35 km thick. Crustal modeling was performed over 8 lines aiming to recognize the rift phase geometry and estimate the amount of crustal stretching. The database used was: four depth converted seismic horizons, magnetic and gravimetric grids and depth to magnetic basement data. The modeling results demand thick and widespreading volcanic layers to fit the model. These wedge shaped volcanic fill, bordered with normal faults, are a common feature in rift basins. Four volcanic provinces have been defined, based on structural compartmentalization and regional occurrence of the basal rift layer, so called Sin-Rift I phase.
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Evaluación del estado isostático del valle de La Rioja, La Rioja - Argentina
Authors Mario Gimenez, Gabriela Bustos, P. Martínez, A. Introcaso and T. JordanWe carry out a study isostatic 3D in the Valley of the east of La Rioja city in Argentina, considering a system of compensation isostática of the type Airy in stretched crustal.
The chart of Bouguer anomalies of gravimetric effects of the sedimentary column and of isostatic corrections, was used to prepare a chart of isostatic anomalies (or of residual isostatic anomaly) including the whole extension of the studied basin.
Our results point out that the isostatic anomalies are negative in the domain of the basin, with an evident deficit of antiroot. These values indicate us that in the future; 1) the crust underlying this basin, will ascend to reach the hydrostatic balance or 2) the strong crust could support the sedimentary deposit, without deformation.
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Análise de feições anômalas do modelo EGM96 na América do Sul utilizando dados da<br>missão GRACE
Authors Marcelo Augusto de V. Lopes and Eder Cassola Molinaof the Earth’s gravity field obtained by the EGM96 geopotential model in the brazilian territory, in order to evaluate if these features reveal the reality of the gravity field in the region or if they are result of the imprecision of the models used to elaborated the EGM96 model. To calculate the EGM96 coefficients, several types of data were used, such as satellite altimetry, land gravity observations, and the JGP95E topographic model. The fact that the gravity data in some regions of Brazil were not available when the coefficients of EGM96 were calculated, and that the topographic model over these regions were unavailable in that occasion, led to the possibility that the detected structures of the gravity field in such regions may be generated by the lack of data. These features were investigated by the analysis of the topographic model JGP95E compared with the topographic data obtained of the new highly precise model of SRTM, and the gravity anomaly of the EGM96 in comparison with a recent gravity field model calculated by GRACE mission and land gravity data. This analysis showed that there is no evidence that the investigated features have been originated by the filling up process of the areas where no gravity data was available to calculate the EGM96.
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Geoelectrical characterization of the Hydrogeological System in the part west of the Potiguar Basin applying the Vertical Electric Sounding method
More LessThis work presents a the results of a research project that it had as motivation to obtain a better knowledge of the Hydrogeological System of the Chapada do Apodi, which is an area in the which the federal and state governments are implementing important irrigation projects whose the viability and success are directly related with the considerable volumes exploitation warranty of physicalchemistry good quality groundwater. It has been intensive the increasing of drinking water supply coming from the regional aquifers Alluvium, Jandaira and Açu, This continuous withdraw has resulted in such problems as the decline of the groundwater levels in the regional aquifers. It is known based on previous hydrogeological studies in the Potiguar Basin that the Açu Formation presents outstanding lithologic and hydrologic heterogeneities that should be taken in account in groundwater exploitation for domestic, agricultural or industrial uses. Previous geophysical studies in others areas of the Potiguar Basin used the Electrical Resistivity method, however in the area studied in this work that corresponds to the Medio-Baixo Jaguaribe where the Açu Formation recovers an area of 1.100 km2 they were not still accomplished geophysical studies and consequently one doesn't know your thickness. Due to this fact the research project had as objective to obtain a geoelectrical model of the subsurface that describes in depth the stratigraphic sequence and its lateral variation along some profiles, identifying the Açu and Jandaira Formation’s thickness in the Medio-Baixo Jaguaribe's central portion that is localized in the west part of the Potiguar Basin. As it intended to map in depth the stratigraphic sequence the electrical resistivity survey was carried out using the Schlumberger configuration array. In the study area the crystalline basement is at the depth that varies from -100 m to –300 m in relation to the sea level, consequently the 23 vertical electric soundings (VES) stations were made and interpreted using the array of current electrode up to a maximum spacing AB/2 of 1 km. For the computational processing of the field data it was applied “ridge regression” inversion outline and used as priore information a lithostratigraphic log profile of a 250 m deep well. The results obtained by the geophysical investigation are analyzed and interpreted in terms of a hydrogeologic model of the deep regional Açu Aquifer.
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Análise Geofísica das Características Hidráulicas da Falha de Salvador na Região de Arembepe - Bahia
More LessThe hydraulic characteristics of the Salvador fault zone along the eastern boundary of the Recôncavo basin were inferred from sub-surface geologic and geophysical data. This fault put in direct contact the shaly sandstones of the São Sebastião Formation and the metamorphics rocks of the crystalline basement. The studied area is part the coastal zone of Salvador, included in the Camaçari country and extending from the Jauá beach to the Arembepe village.
Two geophysical methods were employed to evaluate the waters resources of the area. A total field magnetic map allows to recognize the underground fresh crystalline basement, whereas resistivity soundings were used to define a geo-structural model for the whole area. Sixteen magnetometric profiles and fifty two vertical electrical soundings were distributed in the area. The results allows to map the aquifer geometry and to infer some of their hydraulic characteristics, as well as to define the depth of the water level, and the presence of a fresh water - salt water interface close to the beach.
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Composição Isotópica e Hidroquímica de águas superficiais e subterrâneas da bacia do rio Salitre - Bahia
Hydrogen isotopes and major ion chemistry of waters from 24 wells and 5 superficial samples were used to study the recharge and flux of the aquifer system in the Salitre River Basin. Deuterium compositions varied in a range of 26‰, with the samples from wells varying from -19 to -36‰ (VSMOW). The more negative samples in the range of –36 to -31‰ are located in the southwestern border and characterize precipitations from the Morro do Chapéu region. The groundwaters samples in the range –24 to -19‰ are located in the eastern border of the basin, and characterize precipitations from the Jacobina região. These compositons were used to identify the trend of flux of groundwater in the basin. The hidrochemical data showed the enrichment in dissolved salts of groundwaters along the flux. Water from the Ourolândia Reservoir showed a big enrichment in deuterium and dissolved salts due to losses by evaporation. There was no conection between the reservoir and the sampled wells.
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O método eletromagnético HLEM na prospecção de água subterrânea em terrenos cristalinos
More LessO município de São Raimundo Nonato está localizado no estado do Piauí, Brasil. Em uma região denominada de polígono da seca, por ser dominada fundamentalmente por secas contínuas, e seu arcabouço geológico é constituído na sua maioria (cerca de 70%) por rochas cristalinas (granitos , gnaisses). Estruturalmente verificam-se algumas feições do tipo grabem, estruturas circulares, sistemas de fendas, fraturas interconectadas, descontínuas e com extensão limitada, além de lineamentos favoráveis a ocorrência de água subterrânea.
Uma conjugação de métodos foi utilizada pelo Observatório Nacional com o intuito de obter a localização mais provável de água subterrâneo. Os levantamentos geofísicos se caracterizaram por métodos eletromagnéticos, em particular o método eletromagnético HLEM (horizontal loop eletromagnetic).
Os dados gerados pelo método HLEM foram interpretados para identificação e localização de prováveis pontos de ocorrência de água subterrânea. Apresentando um bom resultado, da ordem de 90 %. Entretanto, a inversão unidimensional destes dados utilizando o programa EM1DFM mostrou-se uma ferramenta ainda mais poderosa para a indicação de água subterrânea.
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Teófilo A. R. Chifunga e Irineu Figueiredo
More LessGeophysical methods, particularlyelectroresistivity, are becoming a major tool in subsurface water exploration as their use diminishes costs by detecting precisely the exitence of water-prone structures and thus optimizing well location. This paper brings some technical and theoretical aspects of the electroresistivity method and details the procedures for the acquisition, processing and interpretation of data from crystalline basement aquifers. Results of a real case study are presented, from an area in the municipality of Sao José do Rio Pardo/SP.
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A sísmica de refração e o GPR no mapeamento do nível freático de aqüífero não<br>confinado. Uma análise comparativa a partir de um estudo na cidade de São<br>Paulo/Brasil
Authors Manuelle Santos Góis Paixão and Renato Luiz PradoThe work had as objective the water table mapping with GPR (Ground Penetrating Radar) method, and seismic refraction with a comparative analysis between both results, once both answers to the presence of interstitial water of vadosa zone are distinct. Geophysical data were acquired in São Paulo city, in
Brazil. Both methods revealed uncertainties in the determination of water table, but for the studied case, the most common errors were associated to the results of seismic refraction due to the uncertainty in the seismic wave velocity determination in the first layer. Considering the studied case, we find out the integration of the worked methods, always possible, can give rise to decrease related to inversion ambiguities of the data, and contribute to better accuracy in water table mapping.
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Prospecção Geoelétrica em Aqüíferos Fissurais, Estudo de Caso em São José do Ubá<br>(RJ)
In the crystalline system groundwater circulate through fractures and fissures. Geophysical methods are commonly used to investigate. In this paper we present the preliminary results of a geoelectrical survey conducted at Barro Branco sub basin, São José do Ubá county. We collected geoelectrical data at 3 profiles. Data were processed and interpreted with a 1D inversion scheme. Two main aquifer system were identified: sedimentary and cristalline.
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Prospecção de água subterrânea no Novo Repartimemto-Pa aplicando métodos elétricos e eletromagnéticos
Authors Lair da silva Freitas Filho and Om Prakash VermaThis geophysical study was carried out in the municipility of Novo Repatimento,localized in SW of the Pará state, with the objetive to detect fracture zones in the Pre-Cambrian basement to exploit groundwater. For this purpose were employed Vertical Eletrical Soundings (VES), Radial Soundings (RVES), Eletrical profiling, Very Low Frequency EM(VLF) and Horizontal Loop Eletromagnetic (HLEM) methods. Two types of aquifers were identified as a result of this study. (1) the fracture zones in the crystaline basement and, (2) the unconfined aquifer in the overbunden sediments. This unconfined aquifer is very limited in groundwater resounces due to its limited thickness, generally less than 4m. The fracture directions in the crystalline basement were inicially determined by RSEV and subsequently the condutor axes were localized by the HLEM profilings. Three of these HLEM profililes were run by VLF and eletric profilings. Eight conductor axes are identified which are probabely related to the fracture zones.The fracture zones are potentially a good groundwater supplier zones in this geological context.
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Aeromagnetic and Magnetotelluric Studies in Guaribas Region of Parnaiba Basin in North East Brazil for Groundwater Assessment
Authors E. Chandrasekhar, Mita Rajaram, S.P. Anand, Sergio L. Fontes and Jean Marie FlexorAeromagnetic and Magnetotelluric (MT) surveys have been conducted over the intra cratonic sedimentary Parnaiba basin located in the semi-arid northeastern part of Brazil for sub-surface structural mapping and ground water resource investigation. From aeromagnetic data several faults in the sub-surface have been identified that are conducive to be potential groundwater resource regions. Broad band (0.001sec – 1000sec) MT soundings along a profile within the area surveyed aeromagnetically, mapped two localized high conductivity zones (of resistivities <10 Ω-m) representing sedimentary aquifer zones. These zones lie close to the faults identified from the aeromagnetic survey whose top lies at depth of 150m.
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Sprites and the influence of the atmospheric density on their initiation mechanism
More LessSprites are transient optical signatures of mesospheric electrical breakdown in response to lightning discharges. Multiple sprites are often observed to occur simultaneously, laterally displaced from the underlying causative cloud-to-ground (CG) lightning discharge. The causes of this lateral displacement are presently not understood. We investigated the role of neutral density perturbations in determining the locations of sprite initiation by performing Computer simulations of the temporal-spatial evolution of lightning-induced electric fields in a turbulent upper atmosphere were performed. The modeled turbulence in the simulations spanned the amplitude range 10% to 40% of the ambient background neutral density, with characteristic scale sizes of 2 km and 5 km, respectively. The results indicate that neutral density spatial structure, similar to observed turbulence in the mesosphere, facilitates electrical breakdown in isolated regions of density depletions at sprite initiation altitudes. These spatially distributed breakdown regions provide the seed electrons necessary for sprite generation, and may account for the observed sprite offsets.
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2.5 - D Finite Element Algorithm for MCSEM Modeling
By Luiz RijoRecently a new and very important geophysical method for detection of oil-filled reservoir in deep-water areas has been introducing in the petroleum industry. The method, called Marine Controlled Source Electromagnetic (MCSEM), also known as Sea Bed Logging (SBL), maps the contrast between the electrical resistivity of an oilfilled reservoir and that of the sedimentary host strata. Usually the resistivity of the former is greater than that of the latter. The MCSEM method is based on the diffusion of electromagnetic energy at low frequency generated by a mobile horizontal electrical dipole and detected by an array of receivers distributed on seafloor. In this paper we present a finite element algorithm for 2.5-D MCSEM modeling. The performance of the algorithm is illustrated by means of some selected examples.
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Constrained 1-D inversion of MCSEM data on resistive oil reservoir
Authors Luiz Rijo and Frayzer L. AlmeidaRecently a new and very important geophysical method for detection of oil-filled layers in deep-water areas has been introduced to the petroleum industry. The method, called Marine Controlled Source Electromagnetic (MCSEM) maps the contrast of electrical resistivity between the reservoir and the host sedimentary layers. Usually the resistivity of the former is greater than that of the latter. The method is based on the diffusion of electromagnetic energy at low frequency generated by a mobile horizontal electrical dipole and detected by an array of receivers distributed on seafloor. In this paper an efficient algorithm is proposed for inversion of 1-D MCSEM in-line electrical field data. The bathymetry and the seawater resistivity, usually knowing a priori, are used as constrains for regularization of the algorithm. The efficiency of the algorithm was tested with three models with good results. The resolution of the inversion scheme improves greatly if one uses normalized data. The information of the background resistivity distribution for the normalization process can be obtained via well logging or through MMT surveys.
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High resolution geophysical survey performed at submarine slope area in Jubarte Field, Espírito Santo Basin
Authors Glória S. Cezar, Paola O. Pellizzari and Mário Ricardo CwikThe article presents partial result of high resolution geophysical survey, performed to provide information to support the design of marine installations, by the Engineering group of Petrobras.
The study area is located in Jubarte Field, Espírito Santo Basin and the survey comprised the acquisition of bathymetric data, sub-bottom profile (SBP) and sonar data. CTD’s profile were also performed in order to obtain sound velocity propagation in sea water and thus correct the depth values obtained from bathymetry. Only the sonar and SBP data will be discussed in this article.
The acquired data was processed and interpreted. The result consists of a map of submarine local features. The main features identified are presented in this article. A better characterization of the sea bottom features and sediments will be completed after the acquisition of sediments samples, which will be performed in a next phase of the survey.
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Caracterização dos Processos Sedimentares no cânion Almirante Câmara, Bacia de Campos
More LessThe Almirante Câmara canyon was first identify by Brehme (1984) and this is located on the slope at the northeast of the Campos Basin. This paper is a study of the main sedimentary processes identified on the Almirante Câmara canyon to contribute for a better understanding of its mechanisms of formation. The metodology apllied in the study of the canyon was: analysis of the local bathymetry, analysis of the 24 seismic profiles and correlations with the papers of Viana (1998) and the Site 515 of the Deep-Sea Drilling Project (DSDP). In this were identified five seismic units on the Campos slope. A major erosional unconformity was identified at the upper Mioceno, recognized as the Grey Marker of the basin.
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MAJOR TECTONIC FEATURES IN THE SOUTHEASTERN BRAZILIAN MARGIN
Authors Mohriak U. Webster and Paula B. OsniA regional geophysical and geological dataset has been integrated to analyse the major tectonic elements along the southeastern Brazilian margin, from the Espírito Santo towards the Santos basins, the most prolific oil provinces offshore Brazil. The diverse tectono-sedimentary domains identified along the continental margin are related to the Mesozoic-Cenozoic tectonic reactivations, particularly the syn-rift extensional processes associated with the separation of the West African and South American plates in the Late Jurassic – Early Cretaceous. These processes are responsible for synthetic and antithetic normal faults that formed half-grabens and grabens within the mainland and offshore, which were filled by continental volcanics and siliciclastic rocks in the Neocomian - Barremian. Subsequent to this syn-rift phase, the transitional phase (Aptian age) is associated with siliciclastic and carbonate sediments deposited above a regional unconformity (breakup unconformity) that heralds the continental drift phase and forms a sag basin that underlies the Aptian evaporites. The regionally extensive, thick evaporite layers that occur both along the Eastern Brazilian and West African margins suggest the occurrence of an elongated and shallow gulf that was periodically invaded by sea waters during the first marine ingressions of the nascent Atlantic Ocean. The presence of a highly mobile evaporite layer resulted in the development of a characteristic tectonic style marked by salt diapirs and salt walls associated with extensional and compressional structures. The outermost boundary of the salt layers seem to correlate with the feather edge of seaward-dipping reflectors that correspond to volcanic wedges formed during the inception of oceanic crust, which is related to propagators that advanced northwards by rupturing the crust and upper mantle. Several major tectonic features are associated with syn-rift and post-rift magmatic episodes, particularly in the southern Santos Basin (Florianópolis platform), in the northern Santos and southern Campos basins (Cabo Frio region), and in the Abrolhos region of the Espirito Santo Basin.
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Morfologia da calha principal do estuário Curimataú/RN, Nordeste, Brasil
O estuário do rio Curimataú é o mais proeminente da porção sul do litoral oriental do Rio Grande do Norte. Em suas margens se dá o desenvolvimento de importantes atividades econômicas como a carcinicultura e a indústria canavieira. A batimetria é uma das ferramentas básicas para compreensão de muitos processos estuarinos. Objetivando analisar a geometria e a morfologia da calha principal do estuário Curimataú, foram realizados perfis batimétricos longitudinais e tranversais à calha. A eco-sonda utilizada foi a da marca Odom modelo Hydrotrac, operando na freqüência de 200 kHz. A geração do Modelo Digital Batimétrico (MDB) foi obtida através de interpolação pelo método de krigagem. A malha de pontos interpolados ainda sofreu prévia correção da variação de maré. Com o fim de realçar a morfologia da calha do estuário produziram-se blocos-diagramas permitindo assim a compartimentação geomorfológica a partir do MDB gerado. A calha principal do estuário Curimataú possui largura entre 250 m e 500 m e profundidade média de 7 m. As principais morfologias encontradas consistiram em bancos, barras, canais de marés e franjas.
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Behavior of Martim Vaz Fracture Zone, from Mid Atlantic Ridge to Brazilian Coast
Authors Eliane da Costa Alves, Marcia Maia and Susanna Eleonora SichelMartim Vaz Fracture Zone (MVFZ), located at 20°10'S in the Mid-Atlantic Ridge (MAR), was defined by seismic register, gravity and magnetic isochrones. Today, this FZ show a second-order discontinuity, with offset 15 km corresponding to 1 My. However, in both sides of MAR, the MVFZ, two fossils FZ can be observed. If these fossils FZs were part of MVFZ, then MV was a double FZ during 5-20 My, and triple FZ between 20-80 My, with a width of 130km. Prior this time the tectonic network seemed to be more complex. The MVFZ was tectonic active, observed in seismic data set, with reactivations of old faults, strikeslip tectonics which has up lift the sedimentary column (Medium Oligocene), and beyond structure related the lithospheric flexure. All of these observation attested by a rich fractured oceanic crust and the overlaying sedimentation, with alternations of comprehensive and distensile stress associated with volcanism and normal faulting. Geological and geophysical studies, in addition earthquake epicenters, suggest that the continuation of ZFMV is related to the Cabo Frio High and to the tectonic and volcanic activity, which is express by the Poços de Caldas / Cabo Frio / Montes Submarinos Almirante Saldanha e São Tomé Alkalic Magmatic Seismic Lineament. All these observation let us to believe that MVFZ acts as a path way for the magma generated in the Tristão da Cunha Mantle Plume.
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Fatores condicionantes do arcabouço estrutural da tectônica gravitacional do Cone do Amazonas
More LessThe Amazon Cone, part of the Amazon Mouth Basin, is intensely affected by gravity-driven tectonics. In this work, approximately 9000 km of multichannel seismic reflection lines were analysed, which enabled us to create a structural map, as well as a map of the the morphology of detachment surface and isopach of Neomiocen–Recen sedimentary covert. Three main structural domains were identified in the region: a proximal extensive domain, which extends since the edge of the shelf to the depth of 500 m, an intermediate domain that translate in a rigid way and a contractional domain which covers an area of approximately 1000 m to 1500 m in depth. The extensive domain is characterised as having synthetic listric faults and rollovers. On the other hand, the contractional domain is characterised as having thrust faults. The Amazon Cone thin-skinned extension system, whose detachment surface is located at the base of the Neomiocene sequence, is divided in two main compartments, which are: the South-eastern
Compartment and the North-western Compartment. The South-eastern Compartment is characterised as a narrow gravitational system (115 km wide), geographically limited to the continental slope and its extension can reach up to 1500 m in depth. However, the North-western Compartment is characterised as a wider gravitational system (152 km wide), which reaches up to 2500 m in depth. The morphology of the surface detachment (base of the shale layer under pressure) seems to represent an important role in the development of the structural framework of the area. Extensional faults are located in the region of higher gradient of the detachment surface, while the thrust faults are in the region of lower gradient. The mechanism of differential sedimentary overload is another important factor of development of the structural framework in the region, because the extensive structures are located in the thickest part of the depocentres and the thrust faults are located on the boarders of the depocentres.
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Arquitetura sedimentar dos principais depocentros da seqüência pliocênica da Margem Catalano-Languedociana, Golfo de Lion, Mediterrâneo Ocidental
More LessOur study aims to assess the role of salt tectonics on the architecture of Pliocene sequence of the Catalano- Languedocian margin. The study is based on seismic and chronostratigraphic interpretation of multichannel seismic profiling and boreholes. Sediment thickness distribution illustrated by an isopach map reveals at how salt deformation has influenced the development of the identified depocenters. Subsidence of the Pliocene cover into the salt evacuation horizon and diapirisms are the mechanisms of salt tectonics that influenced the sedimentary architecture of the Pliocene sequence along the Catalano-Languedocian margin. The abrupt thickening of the Pliocene series along the present-day - 2200 isobath reflects the influence of the subsidence mechanism in creating depocenters in this region. In the south portion of the deep margin, halocknetic deformations create local accommodation space between salt pillows, with implications on the organization of the turbidite deposition in the area. Seismic facies analysis shows no evidence of canyons activity along the proximal Catalano-Languedocian margin during the Pliocene. Facies analysis suggests, on the other hand, that the source of siliciclastic input to the adjacent margin comes from the rhodanian canyons (Marti and Petit-Rhône Canyons), located to the east, on the Rhodanian margin.
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Análise da propagação das ondas compressionais (P) em sedimentos marinhos e sua aplicação na caracterização das propriedades acústicas do ambiente
The physical properties of marine sediments have been systematically acquired and studied in various parts of the world. However, several theories have proved that sedimentological parameters such as grain size, bulk density, porosity and water content cause relevant dispersion in models of measuring wave propagation. The aim of this study is the investigation of the relationship between a relative broad spectrum of these physical properties and geoacustic parameters. Two different physical properties have been investigated: velocity and the attenuation of compressional waves. An apparatus was constructed to measure these physical properties using ultrasonic waves (2,25 MHz). Some experiments have demonstrated good results with this approach in terms of resolution and penetration rate. The first laboratory results were performed in cores collected on the continental shelf offshore the city of Arraial do Cabo, in Rio de Janeiro state. The preliminary experiments indicate that fine-grain sediments display distinguishable properties in terms of acoustic wave speed. More measures are being done in those cores. The propagation and dispersion will be also compared with extensive data sets taken from literature. The results obtained are encouraging and indicate a feasible method to analyze the relationships between compressional wave propagation and sedimentological parameters.
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Qualitative Slope Stability Evaluation for a Pipeline Route Off Espirito Santo State, SE Brazil
Authors P.O. Pellizzari, P.O. Pellizzari, A. Ayres, C.G. Gallea, C. Gallea, G.X.O. Castańos, G. Castańos and P.O.V. PiauilinoIn order to select a pipeline route a geophysical, geological and geotechnical survey has been conducted at the continental slope off Espirito Santo state. The survey comprised an area of approximately 470 km² between the 60 m and 1.380 m isobath with a total of more than 5.700 km of geophysical data and 70 geological and geotechnical piston-cores. An integrated interpretation of the data showed the presence of several obstacles that should be avoided allowing the selection of an optimal route to the planned 12” export gas pipeline determining areas associated to erosional and depositional events. Moreover, a qualitative stability analysis showed that the area is stable under the actual geological conditions and that the instability features observed were generated during the pleistocene when the area was dominated by a shelf-edge delta associated to the Doce river.
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NW-trending lineaments across Brazilian margin: a discussion upon their origin and implications for the Albian-Maastrichtian paleobiogeography and paleoecology of the South Atlantic
Authors Claudio Lima and Dimas Dias-BritoSince the eighties, several groups of NW-trending lineaments running from the coast up to the Mid Ocean Ridge have been recognized across the South Atlantic Brazilian margin from analyses of gravity SEASAT data (Bostrom, 1989). The direction of sea floor spreading has remained remarkably constant around a ENE-trending since 84 m.y B.P. (Nurnberg & Muller, 1991; Mello & Dias, 1996). Therefore, at least for the time elapsed between the Upper Cretaceous and the Present, these features can not be straightly attributed to the divergence between South America and Africa plate since they show remarkable cross cutting relation with the EW- trending fractures zones. In this paper we briefly discuss some ideas concerning the origin of such features and some implications for the Upper Cretaceous paleobiogeography and paleoecology of the South Atlantic.
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Bacia Dove [Mar de Scotia – Antártica]. Processamento e Interpretação de Novos Dados de Sísmica 2D.
The structure of the transcurrent limit between the Scotia and Antarctica plates, and the development of small oceanic basins along the South Scotia Ridge is poorly known. New 2D reflection seismic data from the Dove Basin in the southeastern portion of the Scotia Sea, acquired during SCAN 2004 cruise, has being processed and interpreted. A preliminary interpretation suggests that the tectonic development of the Dove basin agrees with the others small oceanic basin near round and show particular asymmetric development of the spreading axis, indicating a complex setting of stress, displacement and rotation of the continental blocks.
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ASSOCIAÇÃO ENTRE A ANÁLISE PALEOAMBIENTAL DA FORMAÇÃO MACACU, GRÁBEN DA GUANABARA (RJ), E A SEDIMENTAÇÃO CENOZÓICA NA MARGEM CONTINENTAL ADJACENTE (PARTE NOTE DA BACIA DE SANTOS)
Authors Fábio de O. Costa and André L. FerrariThis paper aims to analyze the relationship between Paleogene offshore sedimentation from Macacu Basin (Guanabara Graben, RJ - Brazil) and the intense synchronous progradation at offshore Santos Basin. Guanabara Graben system is divided in three main environments: distal alluvial fan (facies association I); debris flow influenced braided river (facies association II); and braided river with episodic over flow (facies association III) in the axial of this system. The analyze of ten multichannel 2D seismic section (6 dip, 4 strike) from contiguous continental margin at the southwester-most Macacu Basin edge shows the development of three depositonal sequences since Paloegene. The second sequence is characterized by an oblique progradational prism near the continental border related to the onshore graben. This correlation is supported by paleocurrent data from faices association III.
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Seaward dipping reflectors na Margem Continental Brasileira
More LessThis study displays the occurrence of seaward dipping reflectors (SDRs) along the Brazilian Continental Margin, which were probably formed during the initiation of the margin. It is based on the interpretation of multichannel seismic lines collected during the Leplac Project, developed to establish the limits of the Brazilian Extended Legal Continental Shelf. The occurrence of the SDRs is quite extensive along the southern Brazilian Margin from Pelotas to Espírito Santo basins. But, apparently, the SDRs are not related to the oceanic-continental crust boundary at the Brazilian Margin, since earlier studies locate this boundary to the west of the SDRs.
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Sidney Luiz de Matos Mello e Cleverson Guizan Silva
Authors Maitê F. de Medeiros, Gilberto T. M. Dias and Marcelo SperleIlha Grande bay is located in the southern coast of Rio de Janeiro state, Brazil, and is characterized by a rocky coast with numerous islands, being Ilha Grande the main one with 193km2 of area. This region represents nowadays an important and strategic economic area both because of its touristic attractive and its position in the oil and gas scenario because of its proximity of the Santos Basin. In this work the west portion on the Ilha Grande Bay was priorized. The mean depth in this area is 20m with shallower areas occurring inside small bays and enseadas. Baía da Ribeira and Enseada de Parati, for example, show depths of less than 10m. A recent shallow seismic survey has been made in the area, with the acquisition of over 130km of high resolution seismic data in the frequency of 10 kHz, totalizing 6 profiles. The goal of this paper is to present the preliminary results of a project that has as the main objective the study of the holocenic sedimentary evolution of this area.
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Space-Time Evolution of the Marine Depocenters at the Pelotas Basin, Southern Brazilian Continental Margin
Authors Thiago B. S. Corrêa, Cleverson G. Silva and A. T. dos ReisThis study aims to investigate space and time evolution of the marine sequences at the Pelotas basin - southern Brazilian margin, based on interpretation of about 10.000 Km of multichannel seismic lines. This work was based on the association of depth to basement map and a series of isopach maps of marine sequences (Lower Cretaceous -Recent). It revealed that the sedimentary distribution pattern changed radically from the Lower Cretaceous to the Oligocene. Through time the main depocenters shifted seawards and backwards again under the influence of a series of processes. The configuration of depocenters was primarily conditioned by basement topographic features, while depocenter segmentation occurred under the influence of dynamic processes.
Since the end of the Oligocene a high sedimentary accumulation rate took place, giving rise to the onset of the Rio Grande Cone. This depos ition feature corresponds to the main depocenter at the south Brazilian Margin and its evolution is not related only to thermal-mechanical but also to dynamic processes such as bottom currents.
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Analysis of seafloor depth anomalies arround the south Ascension Island, South Atlantic
Authors Marisa Makler and Sidney L. M. MelloObserved seafloor depths from 12 kHz bathymetry coupled with seafloor spreading magnetic anomalies are used to derive depth anomalies across the Mid-Atlantic ridge axis between 2oS and 18oS. Theoretical seafloor depths are based on the plate cooling model and crustal ages depicted from magnetic anomalies between the zero age to 25 Ma. The magnetic anomalies are symmetric with respect to the ridge axis in the region, but the depth anomalies are quite asymmetric. The east side of the ridge axis is shallower (~ 1,000 meters) than the west side, probably as a result of an upwelling of thermal structure of the lithosphere. This type of thermal anomaly may be caused by a mantle plume located on the African Plate, which could well represent a larger swell linked to St. Helena Island and Fernando Pó-Annobon Volcanic Lineament as well.
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Radial gliding evinced by subsalt relief and salt-related structures: the example of the Gulf of Lions, Western Mediterranean
Authors A.T. Reis, C. Gorini, A. Mauffret, W.W. Weibul, M. Mepen and Di Lello M. and Stratievsky C.The young Messinian salt offshore the Gulf of Lions is a shallow décollement layer that permits direct correlation of gravity-driven structures with those predicted by analogue models. Sub-salt relief is cleary depicted by high resolution seismic data. Subsalt relief and salt isopach maps indicate the occurrence of radial gliding at the scale of the entire Gulf of Lions. This pattern of gravity gliding is also indicated by the occurrence of salt-related structures of smaller scale (families of transverse faults). Transverse faults strike parallel to the regional dip direction, indicating strike-parallel extension. As well as that, our results also permit correlation between categories of residual subsalt relief (local irregularities) and rooting of faults along with, depending on their directions, there has been either strike-slip mouvement or weld-parallel slip.
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Taxa de produção do calor radiogênico do embasamento cristalino das bacias de Camamu e Almada
More LessThe crystalline bedrock of the Camamu and Almada basins is characterized preferentially by metamorphic rocks of granulites facies and amphibolite, with archean and paleoproterozoics ages. The main litho logic units of this context are: (i) the metatonalites associates to basic granulites and metamonzonites; (ii) the granite of Teolândia and the granodiorite of Moenda associated with amphibolites;e (iii) the mafic dikes and the neoproterozoics sienites. Among these rocks, the metamonzonites, the granite of Teolândia, the granodiorite of Moenda and the sienitos are those ones that present greaters values of radiogenic heat volumetric production rates; the metatonalites present intermediate values and the basic granulites very low values. For the Camamu basin, the metatonalites are the rocks that probably more contribute for the radiogenic heat production rate in the area. Already for the Almada basin, the contribution includes also the neoproterozoics sienites.
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Estudo acerca das variações sazonais da condutividade térmica
More LessThe conductivity study was monitored in the period of un year. In order to do that, the measurements were performed on samples collected monthly, at 5,0cm depth. The selected site is representative of sandy. The moisture content of the collected samples changed significantly, that may be attributed to the seasonal variation of the local pluviometric precipitation. The thermal conductivities of the sandy samples varied from 0,12 to 2,38 W/m.oC, with an average value of 0,78 ± 0,57 W/m.oC. The variability observed from the above results indicates that the thermal conductivity values of materials existing in the aeration zone were significantly altered by physical variables. The thermal conductivity changes significantly between its extreme values, measured on field samples at natural conditions. The precautions should be taken when uses thermal conductivity values, for estimates in shallow geothermics.
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Gradiente e Fluxo Geotérmico do Estado de Santa Catarina
Authors Antonio Jorge de Lima Gomes and Valiya M. HamzaEste trabalho apresenta uma análise quantitativa de dados geotérmicos de 49 localidades do Estado de Santa Catarina distribuídos em 34 municípios. Os resultados obtidos indicam que a maior parte do Estado é caracterizada por gradientes geotérmicos no intervalo de 26 a 400C/km sendo que o valor médio é de 32 ± 8,6 ºC/km. Foram efetuadas medições de condutividade térmica em 19 amostras de rochas da Serra da Cambirela, Pântano do Sul e Ilha de Santa Catarina e uma reavaliação dos dados de condutividade térmica já existentes. As formações sedimentares de Estrada Nova, Serra Alta e Tatuí apresentaram valores de condutividade térmica relativamente baixa (menor que 2 W/m.K). Os valores mais altos (maior que 3,5 W/m.K) foram encontrados em amostras de arenitos da formação Botucatu e de rochas do embasamento (metamórficas e granitos porfíriticos da Serra da Cambirela). As demais formações sedimentares da bacia do Paraná apresentarem valores intermediários. As estimativas de fluxo geotérmico se encontram na faixa de 50 a 95 mW/m2 com valor médio de 75 ± 15 mW/m2. A elaboração de mapas geotermais permitiu avaliações de gradiente e de fluxo geotérmico em escala regional. Os mapas indicam fluxo geotérmico relativamente baixo (na faixa de 50 a 80mW/m2) na parte oeste do Estado. Contudo, a presença de aqüíferos confinados de grande porte, em profundidades entre 500 e 3000 metros, permite que várias regiões desta parte do Estado contenham recursos de energia geotérmica de baixa entalpia, passíveis de explotação econômica. Por outro lado, há indícios da existência de uma região de fluxo geotérmico elevado (valores superiores a 80 mW/m2) na parte leste, que compreende os municípios situados entre Gravatal, Águas Mornas e Caldas da Imperatriz. As características geológicas estruturais e ocorrências das fontes termais apontam para a existência de reservatórios geotermais também nesta região. Contudo, aquisição de dados de perfurações com profundidades maiores que mil metros são necessários para determinar a natureza de circulação hidrotermal e avaliação de potencial geotérmico das camadas profundas.
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Gradientes Geotérmicos nas Bacias Tafrogênicas da Região Sudeste
Authors Iran Ferreira Rodrigues and Valiya M. HamzaResultados de estudos geotérmicos realizados a partir da década de 1970 foram utilizados numa avaliação detalhada dos gradientes geotérmicos das bacias tafrogênicas da região sudeste do Brasil. O estágio atual da compilação engloba medidas experimentais em 28 locais distribuídos em 15 municípios. Os gradientes térmicos ficaram distribuídos no intervalo compreendido entre 16 a 57 ºC/km com valores médios de 23 ± 2,1 ºC/km para a bacia de Taubaté, de 20 ± 1,2 ºC/km para a bacia de São Paulo e de 38 ± 2,6 ºC/km para Resende. Esta faixa é típica de áreas continentais, tectonicamente estáveis. Contudo, foram encontradas áreas com gradientes térmicos acima de 35 ºC/km ao longo da borda norte, na parte central da bacia Taubaté, na região próxima de Jacareí e também na Bacia de Resende.
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Um critério para escolha da direção de linhas de vôo em aeromagnetometria no Brasil
More LessO presente trabalho visa estabelecer um critério para a escolha da direção de linhas de vôo em baixas latitudes magnéticas (como as do Brasil). Parte-se do princípio que, considerando apenas a componente induzida do campo, as anomalias alinham-se
paralelamente à declinação magnética. Desta forma, aplicamos o critério em simulações com linhas paralelas e perpendiculares à direção da declinação magnética, respectivamente as supostas melhores e piores direções de vôo possíveis, e comparamos os
resultados. Conclui-se que para o método magnetométrico, segundo os critérios adotados, a escolha pela direção de linhas de vôo paralelas à declinação magnética é significantemente melhor do que a escolha de linhas de vôo com direção perpendicular à declinação magnética.
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On the use of geothermal data for climate studies: a case study from Portugal
Authors António Correia and Jan SafandaPortugal using geothermal data has started in 1996. Reconstruction of ground surface temperature (GST) history from temperature logs measured in a 200 m deep borehole (TGQC-1), located near the town of Evora in Portugal, indicates warming of 1K since the second half of the nineteenth century to the middle of the 90s of the twentieth century, increasing considerably in the last 10 years. Results of the reconstruction (based on the functional space inversion (FSI) method) are compared with air temperatures recorded at the Lisbon meteorological station since 1856. The series display a warming trend with the amplitude about 1K for the same period. The coupling of the air and ground temperature changes and their downward propagation by heat conduction was confirmed by repeated logging in November 2003, 6.7 years after obtaining the first temperature log.
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A Reappraisal of Global Heat Flow Data
More Lessin an attempt to understand the characteristic features of global thermal field. The initial effort was directed at verifying the overall structure, quality and internal consistency of the database. Thus the present system of intercalating tables and references was transformed into a coherent and organized database that is amenable for scientific analysis. Subsequently, the format employed for geographic coordinates has been replaced by a consistent decimal degree system that allows implementation of automatic computer based processing facilities. At present, a detailed verification of the entire data set is being carried out to minimize problems arising from typographic errors.
The restructured database has been used in calculating mean values of heat flow for a regular grid system composed of 50 x 50 surface area elements. Spherical harmonic analysis of this system of regular grid values have allowed calculation of a new set of fully normalized Legendre coefficients (169 coefficients for a 12 degree expansion). Maps based on the new set of coefficients have lead to identification of several new features in the conductive component of global heat flow. Comparison with results of previous studies indicates discrepancies in several regions. There are indications that some of the major high heat flow anomalies identified in previous studies are artifacts of interpolation procedures. The reason appears to be widespread use of synthetic values instead of experimental data.
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Evolução Termotectônica da Parte Oeste da Bacia de Campos
Authors Roberta A. Cardoso and Valiya M. HamzaApresenta-se neste trabalho resultados de estudos sobre a evolução termotectônica da parte oeste da Bacia de Campos, na região Sudeste. Na primeira etapa deste estudo os dados de temperatura do fundo do mar e de temperaturas de poços de exploração foram utilizados na determinação do campo térmico atual da bacia, em 97 localidades. Na segunda etapa os perfis litológicos de seis poços e as idades das principais formações geológicas foram utilizados na reconstrução das seqüências evolutivas da bacia (subsidência tectônica) desde a sua formação, há 130 Ma. A elaboração das curvas de subsidência termal foi efetuada com base no procedimento conhecido como “backstripping”, no qual foi incorporado o processo de descompactação seqüencial dos sedimentos. Os resultados desta etapa foram ajustados aos modelos térmicos de subsidência, permitindo a determinação das condições paleotermais e o grau de estiramento da litosfera local. Há indícios de que a evolução da bacia ocorreu em duas fases distintas: a primeira entre 130 a 68 Ma e a segunda entre 68 Ma e o presente. Os graus de estiramento da litosfera variam de 1,4 a 1.9 para o primeiro estágio de subsidência e de 1,2 a 1,5 para o segundo estágio. Os resultados indicam fluxo térmico na faixa de 75 a 95mW/m2 no primeiro estágio, que é cerca de 30 a 50% superior aos valores atuais. As variações no fluxo geotérmico foram menos significativas no segundo estágio. Contudo, as avaliações da maturação térmica indicam que a geração de petróleo e gás ocorreu na fase final do segundo estágio, como conseqüência de soterramentos progressivos maiores.
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Um exemplo da utilização de gradiente transversal medido no aumento da resolução de imagens aeromagnéticas em baixas latitudes magnéticas
More LessThe present work was designed to evaluate if it is possible to observe an increase on the resolution of airborne magnetometry images when using measured lateral gradient during interpolation of total magnetic field data. Images were enhanced using pseudo-line method. The used sample dataset was collected at low magnetic latitudes, specifically in the Brazilian territory. The result for the specific dataset was clear, the enhanced image has a resolution much superior than the original image. Furthermore, its resolution can be compared with a resolution of a single sensor survey with half of line spacing of the original gradiometer survey.
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Análisis térmico de la Cuenca Oriental de Venezuela a partir de información de pozos
More LessThe Guárico Sub-basin, located within the Eastern Venezuelan Basin, forms an important region for oil exploitation, with an important number of oil producing wells and significant gas reserves. The geochemical well data and bore hole temperature values clearly shows an anomalous thermic behaviour in the northern region of the Guárico Sub-basin, represented by a high heat follow zone. The well selection and the quality control of their temperature data, allowed the elaboration of a series of thermal sections across the northern zone of the Subbasin where the data is concentrated. With these profiles it is possible to identify high temperature characteristics in the thick layer of the Miocene sediments and elaborate a series of heat flow maps corresponding to different geologic times. With these maps, a high heat flow has been recognized in the northern region of the Eastern Basin, with values between 60 and 75 mW/m2. The high temperature gradients to the north of the Guárico Subbasin and in the proximities of the Maturín Sub-basin are associated to Miocene sediments located between 2000 and 3500 meters depth. This high temperature gradient may be caused locally by the adiabatic compression of gases due to the compressive process associated with the Guárico Deformation Front. The regional cause of the high heat flow values in north-western Venezuela may be related to the subduction of the Caribbean Plate under the South American Plate. Under subduction melted material forms an asthenospheric wedge that erodes thermally the base of the Southamerican lithosphere producing a temperature high in the northwest and northcentral areas of Venezuela.
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Modelo de Circulação Hidrotermal em Meios Fraturados: Aplicação para Estudo do Intercâmbio Térmico das Áreas Geotermais
Authors Carlos H. Alexandrino and Valiya M. HamzaIn the present work we consider a simple semi-analytic model of heat transfer in fluid flow through subsurface conduits with impermeable walls as a means of investigating the temperature fields in geothermal areas. Results of numerical simulations based on finite difference methods are compared with results of generalized integral transform methods. The model is sufficiently flexible allowing determination of temperatures along the conduits in recharge and discharge zones as well as the intermediate zone of hydrothermal reservoirs. The success of the model however depends on the availability of complementary information on the structural and hydrogeological characteristics of the geothermal area. A number of tests were carried out for evaluating the effects of critical parameters such as temperature gradient, flow rate, dip angle of the fault zone and depth of the aquifer. As an example of application the model was employed for calculating the temperature field in the geothermal area of Cachoeira Dourada (GO). The model is also potentially useful in investigating paleothermal conditions of hydrothermal ore deposits.
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Gradiometria fluxgate no sítio Guarani Piracanjuba, Piraju-SP
We present fluxgate gradiometric maps obtained at the Piracanjuba archaeological site. Our geophysical study allowed the identification of an ancient fire hearth place that was important to site understanding and coal sampling for C14 dating.
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