Heat flow map of South America

Abstract

The results of geothermal investigations carried out in South America have been compiled with the purpose of preparing regional maps of terrestrial heat flow. The compilation revealed that 655 heat flow values had been determined, giving an overall data density of 37 10 6 km 2 and a representative mean heat flow of 63+-36 mW/m 2. The quality of the data set is variable, depending on the nature of the primary geothermal data, and the geographic distribution of the data set is also non-uniform. In spite of such difficulties a careful analysis of the data set, following suitable priority schemes, has allowed not only the determination of reliable mean heat flow values for a large number of major geological structures in South America, but also the preparation of mosaics of regional heat flow variations. Heat flow is extremely variable in the Cordilleran regions, with the eastern and southern parts having relatively high values compared to the western and northern parts. The general trend of increasing heat flow from the western coastal regions towards inland areas is interrupted by a N-S trending low heat flow belt in the Pre-Cordilleran basins. In the eastern part of the continent heat flow is low to normal (<75 mW/m 2) but there are indications that in the Patagonian Platform it is higher than in the Brazilian Platform. There are, however, several isolated localities of high heat flow in the northeastern and south-central parts of Brazil. The Mesozoic rift basins (Potiguar, Recôncavo and Taubaté) are also characterized by relatively high values. In order to examine the tectonic significance of variations in the regional geothermal regime, heat flow maps have been prepared using manual and automatic contouring methods. The comparative study of automatic contour maps generated by means of a variety of data interpolation and gridding schemes has led to the identification of some geothermal features that are believed to be related to tectonic processes affecting the South American continent. Prominent among these are E-W trending belts of low heat flow in northern Peru and in central Chile (extending into the Sierras Pampeans in Argentina), as well as high heat flow belts in northern Chile (extending into the Altiplano in Bolivia) and southern Chile (extending into western Argentina). The low heat flow belts coincide approximately with zones of sub-horizontal subduction, while the high heat flow belts are situated in regions of high-angle subduction. Some of these features correlate well with the results of studies on anelastic attenuation, electrical resistivity distribution and some patterns of global seismic tomography. On the other hand, many of these features are not evident in the recent spherical harmonic analysis of global heat flow, which suggests that the use of empirical predictors based on a heat flow-age relation in devising global heat flow maps should be restricted to tectonically stable areas.