Heat-flow density across the Central Andean subduction zone

Abstract

New and revised heat-flow density determinations for the Central Andes in Chile and Bolivia between 60° and 75°W and between 15° and 30°S are presented. Heat flow was determined from temperature logs obtained from fourteen boreholes in northern Chile and from a large Bottom-Hole Temperature (BHT) data set in Bolivia. Thermal data were corrected for perturbations resulting from drilling, topography, and fluid circulation, and effects of porosity and temperature were considered in adjusting thermal conductivity for in-situ conditions. Thus, the 74 reliable heat-flow values available were used to interpret heat flow in the context of lithospheric conditions. The heat flow in the Andean orogen shows a strong dependence on the different tectono-morphologic units. Clusters of heat-flow values projected onto a W-E profile reflect significant changes from the Nazca Plate in the west to the Chaco Basin in the east. Heat-flow density is low (20 mW/m 2) in the area of the Coastal Cordillera and high (50–180 mW/m 2) in the active magmatic arc and the Altiplano. The back-arc region is characterized by a comparably high heat flow (80 mW/m 2) whereas the Andean foreland has a heat flow of 40 mW/m 2, which is slightly lower than the heat flow in the adjacent Brazilian Shield farther east. The Central Andean subduction zone shows a heat-flow pattern similar to the active margin of the North American continent, but differs in the subduction parameters. Consequently, this results in different lithospheric thermal conditions.