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

Abstract

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.

Thermal regime of the North China Craton: Implications for craton destruction

“…Archean cratons are currently characterized by low heat flow, with an average of 41 mW/m 2 (Nyblade and Pollack, 1993), much less than the global continental average (65 mW/m 2 ) (Michaut et al, 2009;Davies, 2013). For example, the average heat flow value is 42 mW/m 2 in the Archean Superior Province (Jaupart and Mareschal, 1999;Rolandone et al, 2003), 46 mW/m 2 in the Canadian Shield (Mareschal et al, 2004), 36 mW/m 2 in the Archean Dharwar cratons of the Indian landmass (Gupta et al, 1991;Roy and Rao, 2000), 47 mW/m 2 in the Kalahari Craton, Southern Africa (Nyblade et al, 1990) and 28-53 mW/m 2 in the São Francisco Craton (Alexandrino and Hamza, 2008), respectively. Generally, a craton comprises a thick, cold, low-density, melt-depleted mantle keel (Menzies et al, 2007), which makes it buoyant, rigid, and stable.…”

A Magma Accretion Model for the Formation of Oceanic Lithosphere: Implications for Global Heat Loss

“…On the other hand, unlike those derived from GDH reference models there are no discontinuities in the temperature field of the lithosphere (Hamza et al[16]). At this point it is convenient to consider the sensitivity of VBA model response to the values of the parameters listed inTable (1). For young ocean crust (with ages less than 55 Ma) the main parameter that controls bathymetry is δ , the best fit value of which is 0.6.…”

Thermomagnetic Features of Crust in Southern Parts of the Structural Provinces of Tocantins and São Francisco, Brazil

“…Also, "suture" techniques need to be employed in integration of data from several surveys in this area in obtaining a coherent analysis of the subsurface geological significance of the results and its correlations with structural features. Another parallel objective of this work has been comparison of maps of the residual anomalies of magnetic and the geothermal fields in the area of study as a means of obtaining complementary information on the thermal state of the upper crust in the study area [5].…”