Tectonics of the Argentine and Chilean Andes: An introduction

Abstract

The aim of this work is to quantify variations in heat flow and thermal gradient patterns at the latitude of central Chile and to evaluate the role of thermal properties of macro-geological units within the lithosphere. We developed a numerical thermal model for a continental-scale cross section at 33∘S latitude, integrating available and new data on geometry and dynamics of subduction, as well as thermal and mechanical properties for the continental and oceanic lithosphere, and asthenosphere. The model compares heat flow and thermal gradient curves against homogeneous inputs for radiogenic heat production (RHP) and thermal conductivity. The results of 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 the regional 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 it reaches up to values in the range between 20 and 28∘C/km. Model results indicate that thermal gradient increases eastward up to ∼25∘C/km in the easternmost foreland, which is a stable domain. The consistency of the model with respect to seismic record is discussed. Variation in composition and thermal properties is common at subduction zones due to dynamic petrologic processes. The RHP of the exposed upper crust units was obtained from more than 1000 in-situ measurements, whereas thermal conductivity, specific heat capacity and density of samples were obtained in the laboratory. The calculated RHP of upper crust is ∼2.0 μW/m3, which is responsible for ∼15–40% of the heat flow that reaches the surface.