On the ability of rocks to conduct heat in the Lithosphere

Abstract

This work focuses on creating a model for the conductive thermal transport properties of rocks using measured thermal diffusivity (D) with the Laser Flash Analysis (LFA) method, which eliminates common errors associated with physical contacts and spurious ballistic radiative transfer. Using a suite of 122 samples of 55 Rocks, we develop a new approach to understanding D of rocks by direct, careful, and thorough characterization of the disks used in measurements, and improving our understanding of the minerals that compose samples. Using a newly-developed plagioclase interpolation model, and new measurements for the D of common carbonate minerals, we compare measured to calculated D at ambient and elevated temperature (T). For most samples, D at all Ts is best reproduced using the geometric mixing model, but some samples with clear anisotropy mix according to the series or parallel models. However, many high-temperature measurements are clouded by previously unidentified experimental errors, which typically lower reported D. For application in Earth science, we created a Microsoft Excel spreadsheet which will automatically calculate D(T) of rocks using inputs of temperature, and the relative abundances of phases. Given the random errors found in measurements of rock D, the cost and time required to directly measure thermal transport properties of rocks, and the complex and unpredictable variations in rock characteristics on the scale of samples used to measure D, we recommend using calculated D rather than measured D for modeling thermal conduction in the lithosphere.