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1st International Congress of the Brazilian Geophysical Society
- Conference date: 20 Nov 1989 - 24 Nov 1989
- Location: Rio de Janeiro, Brazil
- Published: 20 November 1989
81 - 100 of 208 results
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MODELADO GRAVIMETRICO DEL TAFROGENO CUYANO
More LessSe analiza en base a perfiles de anomalias de Bouguer la Cuenca Cuyana (Provincia de Mendoza, Argentina) que representa a un tafrógeno. Se calculó en los perfiles el efecto gravimétrico del relleno sedimenta rio de la cuenca, que alcanza valores de -55 mGal.
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SECCION GRAVIMETRICA DESDE ARGENTINA CENTRAL HASTA PORTO ALEGRE Y COSTA AFUERA, EN LATITUDE 30° SOUTH
More LessCon datos de Argentina, Uruguay y Brasil fue completado en la latitud 300 S un perfil transcontinental, cuyos resultados en el segmento Occidental: Oceano Pacifico-Argentina central fueron ya analizados (ver Introcaso A., 1988).
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MAPA GRAVIMETRICO DO BRASIL I: REPRESENTAÇĂO DAS ANOMALIAS AR-LlVRE E BOUGUER
Authors Nelsi C. de Sa, Naomi Ussami, Eder Molina and Denizar BlitzkowAs aplicaçőes do método gravimétrico em Geocięncias visam basicamente detectar massas anômalas. A representaçăo de anomalias gravimétricas em easis regional é necessária na determinaçăo das ondulasçőes geoidais e das componentes do desvio da vertical, utilizadas no apoio cartográfico em geral e no posicionamento geodésico em particular.
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MAPA GRAVIMETRICO DO BRASIL II: ANOMALIAS ISOSTATICAS E SEU SIGNIFICADO GEOLOGICO RESIDUAlS
Authors Naomi Ussami, Nelsi de Sa, Eder Molina and Denizar BlitzkowO mapa medias de 1° gravimetrico do Brasil, obtido a partir de anomalias 1 x 1° ,mostra anomalias gravimetricas de carater regional sue apresentam correlaçăo com as principais provincias tectónicas 2 A resoluçăo do mapa permite detectar fontes cujas anomalias gravimetricas tem comprimento de onda maior que 200 km. A correlaçăo entre feiçőes topograficas e anomalias Bouguer de longo comprimento de onda indica que estas devem estar associadas a distribuiçăo de massas compensatorias.
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THE SOUTH AMERICAN GRAVITY PROJECT
More LessThe South American Gravity Project (SAGP 1988-1991) is designed to bring together into a single database all available proprietary and public domain land and marine gravity data. The land and marine gravity data are reprocessed tD a common datum and resampled onto a S'xS' grid approximately 10km x 10km). This grid is used to construct colour contour maps at a range of scales. The five minute grid prevents gravity anomalies less than 20km in wavelength from being seen thus preserving the commercial value of proprietary data used in the project. The gravity maps do however provide sufficient detail to resolve the spatial configuration of sedimentary basins and delineate their tectonic control. The talk will focus on how the delineation of the regional gravity anomaly field associated with the Cretaceous rift basins of West and North Africa provides a key to the understanding of their mode of origin and their tectonic linkage with the opening of the South Atlantic Ocean.
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INTERPRETAÇĂO DE ANOMALIAS MAGNETICAS REGIONAIS ATRAVES DA INTEGRAL VERTICAL DO CAMPO
More LessO metodo magnetico tern sido amplamente empregado no estudo de bacias sedimentares, com o objetivo de determinar profundidades do embasamento. No entanto, é bem conhecida a dificuldade fundamental de tais interpretaçőes: a presença de fontes magneticas rasas, em geral intrusőes sob as formas de dique ou soleira.
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AVALIAÇĂO E AUTOMATIZAÇĂO DAS TECNICAS EMPIRICAS PARA ESTIMATIVAS DE PROFUNDIDADES A CORPOS MAGNETICOS, QUANDO USADAS EM BAIXAS LATITUDES
More LessAs tecnicas empiricas, utilizadas na interpretaçăo quantitativa de dados magneticos, săo aquelas que, sem apresentarem fundamentaçăo matematica, pennitem uma estimativa proximada da profundidade, a partir da observaçao de certos parametres da curva da ananalia magnetica. Tais tecnicas sao suportadas por intmeras experiencias praticas e tem tido extensa utilizaçăo em grande numero de trabalhos de interpretaçăo de dados magneticos.
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UMA ANOMALIA MAGNETICA DE CARATER REGIONAL NO SERIDO (RN-PB) E UMA DISCUSSĂO DE SUA ORIGEM
More LessUma anomalia magnetica (A.M.) foi identificada na porçăo sul da Faixa Serido, em torno da cidade de Santa Luzia (PB) (Fig. 1). Sua direçăo geral e NE-SW, vergindo no sul para E-W, acompanhando o lineamento Patos. A cobertura gravimetrica constatou (Fig. 2) a presença de anomalias negativas correlacionadas com a AM. Será discutida a origem desta AM, tendo como condicionantes dados potenciais, medidas densidade (e) e susceptibilidade magnética (X) em rochas da área.
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AEROMAGNETIC GRADIOMETRY - THE STATE OF THE ART
More LessThere has been speculation in recent years regarding the advantages of airborne magnetic gradiometry for enhancing the detail in magnetic maps made by the conventional method of measuring the total field. However, it is only recently that the necessary instrumentation has been refined to the point that some of these advantages can be demonstrated. This paper outlines briefly the advantages of gradiometry and gives an overview of the instrumentation required. Particular emphasis is placed on the magnetic compensation subsystem because in gradiometry, where total field- measurements are differenced to a resolution of several parts in 10 7, the demands on magnetic interference compensation are very stringent. The NRC Convair-SSO's three-axis gradiometer system is used to illustrate gradiometer instrumentation. In recent surveys flown by the Convair 580, the lateral gradient was used to enhance detail in the direction perpendicular to the survey lines. Some results from this work are shown.
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COMPARACION DEL MODELADO DIRECTO E INVERSO DE ANOMALIAS MAGNET/CAS
More LessSe comparan resultados de los modelos obtenidos por una metodologi a de interpretación directa con el metodo inverso. Se obtienen profundidades, formas y parametros de los bloques componentes modelados para la anomali a magrletica de la zona de Las Armas (Provincia de Buenos Aires, Argentina) que pertenece al borde Sur de la Cuenca del Salado.
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EVOLUCION TEMPORAL DE UNA ANOMALIA DE BORDE DE CUENCA
Authors Iris R. Cabassi, Julio L. GianibeIli, O. Sidoti, E. Suarez S. Weiss, F.F. Rios and L. PetcoffLas caraoteristicas geotectónioas de una cuenca sedimentaria están dadas por su evoluoión de subsidencia y efectos de acumulacion de tensiones en la parte superior de la corteza. Los relevamientos geomagneticos locales en los bordes de dicha cuenca permiten observar estos efectos con el fin de conocer particularidades de la evoluoión de las anomalias.
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PROJECT EQUANT CORRECTING OPEN-OCEAN MARINE MAGNETICS DATA FOR DIURNAL FIELD VARIA TIONS
Authors Gordon E. Ness, Michael G. Kelsay and Robert T. OMalleyMagnetic data from open-ocean marine surveys are seldom, if ever, corrected for diurnal field variations. It is also characteristic of marine surveys that data are obtained continuously regardless of the occurrence of magnetic storms and disturbances. This is unlike the practice in aeromagnetic surveys, where the plane simply is not flown during disturbances. Moreover, survey ships typically operate quite distant from magnetic observatories or temporary base stations. The questions arise: Can marine magnetics data be significantly improved by directly using nearby base station or observatory data? Can synthetic diurnal variation models be effectively used in lieu of real base station data when such real data are either unavailable, too distant from the survey area, or simply too inconvenient to obtain and process? Can real base station data be projected to some distance after modification using synthetic models of field behavior? Can synthetic data be conveniently modified to accommodate large field disturbances using very distant observatory data?
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RESULTADOS DOS LEVANTAMENTOS AEROMAGNETOMETRICOS "OFF-SHORE" NO LITORAL BRASILEIRO ENTRE SALVADOR E JOĂO PESSOA
More LessUm fator importsnte para a pesquisa de hidrocarbonetos, pelo menos numa perspectiva de longo prazo, reside na distançia do limite entre a crosta continental e a crosts oceânica em relaçăo litoral. Existe um consenso entre as geológos de que a crosta continental, quando coberta par sedimentos, e bem mais favoravel a geraçăo e acumulaçăo de reservas de hidrocarbonetos que a crosta oceânica.
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MODELADO DE ANOMALIAS GEOFISICAS EN BORDES DE UN AULACOGENO
Authors Liliana Barrio, Julio L. Gianibelli and Francisco F. RiosSe da una descripción de los aulacógencs presentes en la Provincia de Buenos Aires, Argentina. Utilizando dos perfiles gravimagneticos. se analizan las anomali as de aire libre y las de campo magnetico total detectadas en la zona. Por medio de la fórmula de Demenistkaya se calcula la profundidad de la discontinuidad de. Mohorovicic.
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NEW DEVELOPMENTS IN AIRBORNE ELECTRO-MAGNETICS
More LessThe first airborne electromagnetic (AEM) systems were developed in Canada in the early 1950s. By the late 1970s, AEM instrument development focused in two directions: multifrequency, multicoil helicopter systems and timedomain, towed-bird systems. Modern helicopter AEM systems typically operate with two coil configurations (vertical coaxial and horizontal coplanar) and 4-7 frequencies ranging from 700 Hz to 70 kHz. High-density data acquisition permits removal of sferic noise by post-flight processing. Products that can be compiled from modern helicopter AEM surveys include composite profiles, profile maps, and color conductivity maps. Examples will be shown from Monts Stoke, Quebec. Time-domain, towed-bird AEM systems have been redesigned in the mid 1980s. Both INPUT® and GEOTEM® are presently operated with digital receivers, which are self-calibrating and permit a removal of sferics in real time. As examples of GEOTEM survey results, conductivity maps and composite profiles from Lynn Lake, Manitoba, will be shown. AEM systems have been used in systematic surveying in Canada; Ontario and Quebec have close to 1 million line km, mostly acquired with time-domain, towed-bird systems.
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EFEITOS DO MANTO SOBRE ANOMALIAS EM NO DOMINIO DO TEMPO OBTIDOS DE DADOS EM MULTIFREQUENCIA
Authors Joaquim Carlos Barbosa Queiroz and Om Prakesh VermaUma das grandes dificuldades na aplicaçăo de metodos indutivos de prospec9ao EM em regioes tropicais e semi-ari dase causada pela presença do manto de intemperismo comumente encontrado nestas regioes. Uma maneira de estudar a influencia do manto sobre a resposta de um corpo condutivo e utilizar medidas em uma larga escala de frequencias.
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THE USE OF RESISTIVITY AND INDUCED RECONNAISSANCE FOR GOLD BEARING (NORTH-EAST MASSIF CENTRAL, FRANCE)
Authors C. Boulanger, A. Bouvier and B. DeBacqueAt Varennes (Creuse) , sulfides (pyrite and arsenopyrite with gold) were found in the vicinity of faults (shear zones) which divide a volcano-sedimentary basin into metric to decametric compartments formed mainly by rhyolitic tuffs and breccias. Resistivity measurements carried out using the gradient array mode with two different spacings and directions contributed to the definition of the local structural scheme, based on two normal faulting systems. Induced polarization readings taken using the same array showed stronger anomalies at the fault junctions and along discrete subvertical faults striking N15 00, which channelled hydrothermal fluids, the source of the ore mineralization.
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CONTORNO AUTOMATICO DE DADOS GEOELETRICOS
Authors Jorge Kazuo Yamamoto and Carlos Alberto BirelliOs dados geoeletricos obtidos a partir dos levantamentos de Polarizaçăo Induzida e Resistividade sao normalmente aprsentados sob a forma de pseudo-segees e/ou mapas de cargablidade e resistividade aparente; onde sao contornadas cur vas de isovalores dos parametros citados.
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MAGNETOTELLURICS FOR MINERAL EXPLORATION
Authors Edward Nichols and H. Frank MorrisonThe development of portable broadband MT systems has led to new applications of this method in mineral exploration surveys. A test of a new profiling tecnnique for mapping resistivity to a depth of 1.0 km has been carried out in the Carlin Gold District in Nevada. The goal of geophysical exploration in this region is to map physical properties which may be related to rock alteration brought about by mineralizing fluids. This mineralization has been controlled by faults and fracture zones that cross mapped contacts between different rock units. A generalized cross section perpendicular to regional strike for the area of this study is presented in Figure 1.
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SONDAGENS MAGNETOTELÚRICAS NA REGIĂO NORDESTE DA BACIA DO PARANA
Authors A.L. Padilha, N.B. Trivedi, Icaro Vitorello and J.M. da CostaAs margens da Bacia do Parana exibem caracteristicas estruturais e geotectonicas importantes que tem sido pouco investigadas. Observa-se que, de modo geral, os dados geologicos e geofisicos disponiveis na bacia concentram-se em sua parte central. Em particular, na regiao NE da bacia, os resultados publicados referem-se apenas a dados gravimetricos (1) e sondagens eletricas (2).
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