Numerical and functional representations of regional heat flow in South America

Abstract

A summary of heat flow data acquired over recent years in several areas in the eastern (Brazil and Paraguay) and western (Bolivia, Chile, Colombia and Ecuador) parts of South American continent are presented. The improvements in the database have allowed numerical representations of heat flow for southeastern and central segments of the Precambrian fold belts in Brazil, Central Andean cordilleras in Chile and Bolivia, Southern Volcanic arc in Peru, Neuquén Province in southwestern Argentina, Chaco basin in Paraguay, Oriente basin in Ecuador and the system of pericratonic basins in north central Colombia. The maps reveal considerable variability in heat flow, not only between the main tectonic units but also within them. The intra-regional variations seem to originate mainly from complexities in local geologic structures while the inter-regional ones seem to point to action of deep-seated tectonic processes. The cordilleran regions are, in general, characterized by relatively high heat flow (>70 mW/m 2), compared with the coastal regions to the west and the Pre-cordilleran basins to the east. In the eastern part of the continent, heat flow is low to normal (<60 mW/m 2), the exceptions being the Mesozoic rift basins, areas of Cenozoic alkaline intrusions and some isolated belts of overthrust tectonics in the central parts of Brazil. There are indications that heat flow is high in the Patagonian Platform relative to that found in the Brazilian Platform. In addition, polynomial methods were employed for examining large-scale variations of heat flow over the continent. Specifically, a general-purpose least square solution was used to determine the coefficients of up to fourth order in latitude and longitude. Some of the large-scale trends seen in low order polynomial representations seem to be indicative of the nature of deep-seated heat transfer processes. The systematic increase in regional heat flow in the north-south direction is an example. It is considered as the consequence of thermal blanketing effect of the continental segment of the South American lithosphere. Trends seen in higher order polynomials seem to be associated with regional tectonic patterns and subduction-related magmatism. Prominent among these are east-west trending belts of low heat flow in northern Peru and in central Chile, as well as the high heat flow belts in northern Chile, Altiplano of Bolivia and northwestern Argentina. Limitations arising from low data density and uneven geographic distribution warrant higher degree polynomial representations.