Radioactive element distribution in the Archean granulite terrane of Jequi� ? Bahia, Brazil

Iyer, Brijesh; Choudhuri, Asit; Vasconcellos, M. B. A.; Cordani, Umberto G.

doi:10.1007/bf00380226

Cited by 45 publications

(13 citation statements)

References 34 publications

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“…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: 89%

Airborne geophysical surveys in the north-central region of Goias (Brazil): implications for radiometric characterization of tropical soils

Guimarães

Hamza

Silva

2013

Journal of Environmental Radioactivity

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Section: Airborne Gamma Surveysupporting

confidence: 89%

Airborne geophysical surveys in the north-central region of Goias (Brazil): implications for radiometric characterization of tropical soils

Guimarães

Hamza

Silva

2013

Journal of Environmental Radioactivity

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“…Even for Archaean granulites, cases of depletion as well as nondepletion have been reported. The Lewisian granulites of northwestern Scotland are strongly depleted [ Drury , 1973] while those of Jequie and Itaberaba complexes in the Brazilian shield are not [ Sighinolfi and Sakai , 1977; Sighinolfi et al , 1981; Iyer et al , 1984]. Where there is depletion, the resulting abundances are a function of the composition of the protolith, the nature of the fluid phase, specifically its H 2 O, CO 2 and halogen contents, the amount of fluid phase passing through the rock, and the pressure and the temperature [ Rollinson and Windley , 1980].…”

Section: Radioelemental Distribution and Heat Productionmentioning

confidence: 99%

High mantle heat flow in a Precambrian granulite province: Evidence from southern India

et al. 2003

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[1] Twelve new heat flow values determined at nine sites and heat production estimated from radioelemental measurements at 330 sites in the southern granulite province (SGP) bring out contrasting crustal and subcrustal thermal characteristics between the SGP and the adjacent Archaean Dharwar greenstone-granite-gneiss province (DP) in south India. A twolayer granulitic crust of Late Archaean charnockites and gneisses characterizes the northern block (NB), north of the Palghat-Cauvery lineament (PCL). The heat production of the upper, 7-10 km thick, metasomatized granulitic layer ranges between 0.2 and 0.75 mW m À3 (mean 0.5 ± 0.3 (SD) mW m À3 ). This layer overlies radioelement-depleted granulites characterized by very low heat production ranging from 0.14 to 0.2 mW m À3 (mean 0.16 ± 0.07(SD) mW m À3). In a large sector of the NB, erosion of the upper metasomatized granulite layer has laid bare the depleted granulitic rocks, which represent one of the lowest heat-producing crustal sections. The mean heat flow in the NB is 36 ± 4 mW m À2 (N = 10). The southern block (SB), south of PCL, in contrast to the NB, comprises complexly interlayered charnockites, gneisses, granites, khondalites, and leptynites, which have variable and much higher levels of heat production ranging between 1.11 and 2.63 mW m À3 . The heat flow in the SB is 47 ± 8 mW m À2 (N = 3). Overall, the range of heat flow values in the SGP is within the range for the DP. Mantle heat flow in the NB, both from the lowest heat-producing sector and other areas, is deduced in the light of heat production and heat flow data, at 23-32 mW m À2 , whose values are distinctly higher than 11-16 mW m À2for the adjacent DP. The higher mantle heat flow in the NB appears to be a consequence of higher heat production in the subjacent mantle.

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“…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.…”

Section: Radiogenic Heat Productionmentioning

confidence: 97%

Estimates of heat flow and heat production and a thermal model of the São Francisco craton

Alexandrino

Hamza

2008

Int J Earth Sci (Geol Rundsch)

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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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Radioactive element distribution in the Archean granulite terrane of Jequi� ? Bahia, Brazil

Cited by 45 publications

References 34 publications

Airborne geophysical surveys in the north-central region of Goias (Brazil): implications for radiometric characterization of tropical soils

Airborne geophysical surveys in the north-central region of Goias (Brazil): implications for radiometric characterization of tropical soils

High mantle heat flow in a Precambrian granulite province: Evidence from southern India

Estimates of heat flow and heat production and a thermal model of the São Francisco craton

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