A model for thermal gradient and heat flow in central Chile: the role of thermal properties

Abstract

The aim of this work is to quantify variations in heat flow and thermal gradient patterns at the latitude of centralChile and to evaluate the role of thermal properties of macro-geological units within the lithosphere. We developeda numerical thermal model for a continental-scale cross section at 33 S latitude, integrating availableand new data on geometry and dynamics of subduction, as well as thermal and mechanical properties for thecontinental and oceanic lithosphere, and asthenosphere. The model compares heat flow and thermal gradientcurves against homogeneous inputs for radiogenic heat production (RHP) and thermal conductivity. The resultsof this model were calibrated with results of thermal gradient measurements at different morpho-tectonic domains.The results show that both, cold slab subduction and mantle wedge advection, play major roles in theregional thermal structure. Variations with respect to regional tendency are due to changes in thermal properties.The fore-arc has an average thermal gradient from 12 to 16 C/km, whereas in the High Andes Cordillera itreaches up to values in the range between 20 and 28 C/km. Model results indicate that thermal gradient increaseseastward up to 25 C/km in the easternmost foreland, which is a stable domain. The consistency of themodel with respect to seismic record is discussed. Variation in composition and thermal properties is common atsubduction zones due to dynamic petrologic processes. The RHP of the exposed upper crust units was obtainedfrom more than 1000 in-situ measurements, whereas thermal conductivity, specific heat capacity and density ofsamples were obtained in the laboratory. The calculated RHP of upper crust is ∼2.0 μW/m3, which is responsiblefor ∼15–40% of the heat flow that reaches the surface.