Investigations and interpretations of the vertical distribution of U, TH, and K: South Africa and Canada

Schneider, Robert V.; Roy, Robert F.; Smith, Alan Р.

doi:10.1029/gl014i003p00264

Cited by 16 publications

(5 citation statements)

References 8 publications

(6 reference statements)

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“…Sclater, Jaupart & Galson (1980) conclude that for continental lithosphere older than 800 Ma the average surface heat flow, Q s , is ∼ 46 mW m − 2 , that heat flow from the mantle, Q r , averages ∼ 25 mW m − 2 and that D averages ∼ 10 km 1. These mean values have been confirmed by subsequent studies on cratonic shields in Scandinavia, South Africa and Canada (Pinet & Jaupart 1987; Schneider, Roy & Smith 1987; Pinet et al . 1991).…”

Section: Deeper Earthquakes and Crustal Rheologysupporting

confidence: 77%

Source parameters of large African earthquakes:implications for crustal rheology and regional kinematics

Foster

Jackson

1998

Geophysical Journal International

160

163

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Summary Source parameters for 38 African earthquakes have been determined using P and SH body‐waveform inversion of analogue and digital waveforms. The results of this modelling are combined with 15 other earthquakes whose source parameters are also well constrained by body‐waveform inversion. This data set shows that parts of East Africa have a seismogenic thickness of up to ∼ 35 km, and that seismicity occurs throughout the upper and lower crust. 1‐D heat‐flow calculations suggest temperatures of ∼ 325–475 ° C at 35 km depth in the Archaean and Proterozoic crust, requiring that the lower crust has a dry, mafic bulk composition in order to deform seismogenically. The slip vectors associated with these 53 earthquakes are combined with an additional 28 solutions from the Harvard CMT catalogue in order to investigate plate kinematics. In the Red Sea/Gulf of Aqaba the slip vectors agree closely with the Africa–Arabia extension direction predicted by the current best‐fit plate model of Jestin, Huchon & Gaulier (1994). In the southern East African Rift System motion is split between a southeast direction in Zambia and a northeast direction in Malaŵ i and Rukwa, which combine to achieve the predicted Africa–Somalia east–west extension. Thus the current best‐fit plate model of Jestin et al. (1994) adequately describes the active kinematics of Africa.

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Section: Deeper Earthquakes and Crustal Rheologysupporting

confidence: 77%

Source parameters of large African earthquakes:implications for crustal rheology and regional kinematics

Foster

Jackson

1998

Geophysical Journal International

160

163

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“…The heat flow values, ranging from 47 mW m -2 to 60 mW m -2 are among the highest found near the Superior Province [Jessop and Lewis, 1978]. The mean heat flow is significantly higher than in the neighboring Abitibi belt ( Table 2); it reflects the high radioactivity of basement rocks [Schneider et al, 1987].…”

Section: The Huronian Basinmentioning

confidence: 89%

Heat flow and structure of the lithosphere in the Eastern Canadian Shield

Pinet¹,

Jaupart²,

Mareschal³

et al. 1991

J. Geophys. Res.

157

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Twenty-two new determinations of heat flow and radiogenic heat production in the Superior and Grenville provinces of the Canadian Shield are presented. The new data and previously published measurements strongly constrain the thermal structure of the eastern Canadian Shield. In the Abitibi greenstone belt, heat flow gradually increases from 29 mW m -2 near the Grenville Front to 44 mW m -2 east of the Kapuskasing uplift. This heat flow variation is interpreted in terms of crustal thickening and increased thickness of a tonalitic layer with average heat production of about 1.1 m -3. This interpretation, based on estimated heat production of major rock types in the region, is consistent with crustal models derived from recent seismic reflection and refraction studies. It also leads to an estimate of about 12 mW m-2 for the mantle heat flow beneath the area. The average heat flow in the Grenville Province, 41 +-10 mW m -2, is the same as that of the Superior Province. This similarity and the lack of significant variation of heat flow across the Grenville Front indicate that the crust on both sides of the front has similar heat production and thus composition. In the western part of the Grenville Province, heat flow reaches high values in the vicinity of the boundary between the Allochtonous Polycyclic and Monocyclic belts where enriched granitic plutons are found. In the crystalline terranes in the central part of the Grenville Province, heat flow and heat production are related to each other. The parameters of the linear •eat flow-heat production relationship (Qr = 30 +_ 2 mW m -2 and D = 7.1 +_ 1.7 km) are close to those of the much younger Appalachian Province,implying that the higher Appalachian heat flow is due solely to higher heat production in the upper crust. The data provide no evidence for variation of mantle heat flow between the Superior, Grenville, and Appalachian provinces, whose tectonic ages range between 2700 and 400 Ma. The small value of the mantle heat flow, about 12 mW m -2, implies that the depth to the 450øC isotherm, which controls the effective elastic thickness of the lithosphere, is very sensitive to crustal heat production.

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“…Although the HPE abundances are expected to decrease with depth, the decrease may be highly site-dependent and non-monotonic (see [35] as an example for the Japanese crust). In some cases (e.g., Sudbury [36]) the horizontal and vertical distributions of HPE's are correlated by the fact that the crust is locally "tilted" -a situation which may represent both a complication and an opportunity.…”

Section: Horizontal and Vertical (U Th K) Distribution Uncertaintiesmentioning

confidence: 99%

Geo-Neutrinos: A Systematic Approach to Uncertainties and Correlations

et al. 2006

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Geo-neutrinos emitted by heat-producing elements (U, Th and K) represent a unique probe of the Earth interior. The characterization of their fluxes is subject, however, to rather large and highly correlated uncertainties. The geochemical covariance of the U, Th and K abundances in various Earth reservoirs induces positive correlations among the associated geo-neutrino fluxes, and between these and the radiogenic heat. Mass-balance constraints in the Bulk Silicate Earth (BSE) tend instead to anti-correlate the radiogenic element abundances in complementary reservoirs. Experimental geo-neutrino observables may be further (anti)correlated by instrumental effects. In this context, we propose a systematic approach to covariance matrices, based on the fact that all the relevant geo-neutrino observables and constraints can be expressed as linear functions of the U, Th and K abundances in the Earth's reservoirs (with relatively well-known coefficients). We briefly discuss here the construction of a tentative "geo-neutrino source model" (GNSM) for the U, Th, and K abundances in the main Earth reservoirs, based on selected geophysical and geochemical data and models (when available), on plausible hypotheses (when possible), and admittedly on arbitrary assumptions (when unavoidable). We use then the GNSM to make predictions about several experiments ("forward approach"), and to show how future data can constrain a posteriori the error matrix of the model itself ("backward approach"). The method may provide a useful statistical framework for evaluating the impact and the global consistency of prospective geo-neutrino measurements and Earth models.

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Investigations and interpretations of the vertical distribution of U, TH, and K: South Africa and Canada

Cited by 16 publications

References 8 publications

Source parameters of large African earthquakes:implications for crustal rheology and regional kinematics

Source parameters of large African earthquakes:implications for crustal rheology and regional kinematics

Heat flow and structure of the lithosphere in the Eastern Canadian Shield

Geo-Neutrinos: A Systematic Approach to Uncertainties and Correlations

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