Teores de potássio, urânio, tório e taxa de produção de calor radiogênico no embasamento adjacente às bacias sedimentares de Camamu e Almada, Bahia, Brasil
Abstract:ABSTRACT.The bedrock adjacent to Camamu and Almada sedimentary basins is characterized mainly by rocks of granulite and amphibolite facies, with archean and paleoproterozoic ages, which belong to orogen Itabuna-Salvador-Curaçá. The units in major proportion in this context are the metatonalites associated with basic and metamonzonites belonging to Itabuna belt. In smaller area occur the Teolândia granite and the Moenda granodiorite associated with the Ipiaú band amphibolites, the charnockites and charnoenderbi… Show more
“…The relatively large values of standard deviations of the mean values are considered as indicative of the compound effects of variations related to soil types and lithologic units. These values are in reasonable agreement with results of laboratory measurements on borehole samples of Proterozoic sedimentary sequences reported by Roque and Ribeiro (1997), lead isotope studies in some localities of the São Francisco structural province reported by Iyer et al (1984) and gamma spectrometric measurements of basement rock samples of the Atlantic coastal basins by Sapucaia et al (2005).…”
Section: Airborne Gamma Surveysupporting
confidence: 91%
“…It has also been used for mapping area extent of geologic rock formations associated with such radioactive elements. Examples of such studies carried out in Brazil include the works of Blum et al (2003) and Sapucaia et al (2005). Measurements of gamma radiation at ground level provide information on the abundances of radioactive elements in the top soil layers.…”
“…The relatively large values of standard deviations of the mean values are considered as indicative of the compound effects of variations related to soil types and lithologic units. These values are in reasonable agreement with results of laboratory measurements on borehole samples of Proterozoic sedimentary sequences reported by Roque and Ribeiro (1997), lead isotope studies in some localities of the São Francisco structural province reported by Iyer et al (1984) and gamma spectrometric measurements of basement rock samples of the Atlantic coastal basins by Sapucaia et al (2005).…”
Section: Airborne Gamma Surveysupporting
confidence: 91%
“…It has also been used for mapping area extent of geologic rock formations associated with such radioactive elements. Examples of such studies carried out in Brazil include the works of Blum et al (2003) and Sapucaia et al (2005). Measurements of gamma radiation at ground level provide information on the abundances of radioactive elements in the top soil layers.…”
“…Rochas de composição mineralógica caracterizada essencialmente por quartzo e plagioclásio apresentam baixas concentrações de K, U e Th, enquanto que as rochas compostas por micas, feldspatos e minerais acessórios como o zircão, a apatita e a monazita, contêm teores maiores desses elementos (SAPUCAIA et al, 2005). Alguns minerais acessórios portadores de Th e U podem ser citados, como zircão, titanita, epidoto primário, monazita, apatita, xenotima e allanita (ULBRICH, 2009).…”
“…Sighinolfi and Sakai 1977;Ferreira et al 1979Ferreira et al , 1992Hamza 1980;Iyer et al 1984;Vitorello et al 1980;Roque and Ribeiro 1997;Sapucaia et al 2005). The experimental techniques employed include both gamma ray spectrometry as well as isotope mass spectrometry.…”
An updated analysis of geothermal data from the highland area of eastern Brazil has been carried out and the characteristics of regional variations in geothermal gradients and heat flow examined. The database employed includes results of geothermal measurements at 45 localities. The results indicate that the Salvador craton and the adjacent metamorphic fold belts northeastern parts of the study area are characterized by geothermal gradients in the range of 6-17°C/km. The estimated heat flow values fall in the range of 28-53 mW/m 2 , with low values in the cratonic area relative to the fold belts. On the other hand, the São Francisco craton and the intracratonic São Francisco sedimentary basin in the southwestern parts are characterized by relatively higher gradient values, in the range of 14-42°C/km, with the corresponding heat flow values falling in the range of 36-89 mW/m 2 . Maps of regional variations indicate that high heat flow anomaly in the São Francisco craton is limited to areas of sedimentary cover, to the west of the Espinhaço mountain belt. Crustal thermal models have been developed to examine the implications of the observed intracratonic variations in heat flow. The thermal models take into consideration variation of thermal conductivity with temperature as well as change of radiogenic heat generation with depth. Vertical distributions of seismic velocities were used in obtaining estimates of radiogenic heat production in crustal layers. Crustal temperatures are calculated based on a procedure that makes simultaneous use of the Kirchoff and Generalized Integral Transforms, providing thereby analytical solutions in 2D and 3D geometry. The results point to temperature variations of up to 300°C at the Moho depth, between the northern Salvador and southern São Francisco cratons. There are indications that differences in rheological properties, related to thermal field, are responsible for the contrasting styles of deformation patterns in the adjacent metamorphic fold belts.
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