Optical Study of Thermal conductivity of Deep Earth's Materials at High Pressure and Temperature

Carnegie Institution Of Washington, Washington DC

Investigators

Abstract

Knowledge of thermal conductivity and thermal diffusivity of the Earth's minerals under extreme conditions is important for understanding the physical and chemical processes and their evolution in the Earth. The rate of the heat transport through the mantle is crucial for the existence and stability of the Earth's magnetic field. The temperature distribution inside the Earth's mantle depends on the rate of heat transfer by convection, conduction, and radiation. An understanding of these processes requires knowledge of the thermal conductivity as a function of pressure and temperature. In this project, we propose to determine the thermal conductivity of the Earth's key minerals under high P-T conditions by using optical spectroscopy in DACs (Diamond Anvil Cells) including pump-probe pulsed laser techniques. To determine the lattice thermal conductivity, we will measure the heat fluxes across the sample and their time history using time- and spatially resolved spectroradiometry and/or time-domain thermoreflectance (TDTR). Both continuous and pulsed laser techniques will be employed to access the thermal conductivity and diffusivity. To infer the radiative thermal conductivity, we will study the optical spectra of these mantle minerals in the ultraviolet-to-infrared spectral range at high P-T conditions (up to 130 GPa and 4000 K). Silicate perovskite and ferropericlase, the two dominant phases of the Earth's lower mantle, will be studied. Single crystals grown from pre-synthesized materials with a composition close to that in the Earth's mantle will be used as samples. We will also study the thermal conductivity of the postperovskite phase, synthesized by laser heating. To better understand the thermal transport and Earth's temperature profile near the Core-Mantle Boundary (CMB), we will measure the thermal conductivity of iron (using also electrical and optical conductivity methods). These experimental data will give a direct estimate of the radiative and conduction parts of the thermal conductivity, so they can be utilized in model calculations of the thermal processes in the Earth, thus providing a crucial test of these models and our current understanding of the Earth's interior. This work will advance discovery and understanding by including graduate and undergraduate students as participants in the proposed research. A range of students, including area high school students, undergraduates, graduate students, and postdoctoral associates, will benefit from the scientific training at Carnegie that will be provided by participation in cutting-edge science that will be developed in the course of this work. We have developed collaborations with US and foreign Universities that allow us to train and incorporate graduate student research into our project. Moreover, we broaden participation of under-represented groups by establishing collaborations with Universities serving such groups and by including women and foreign postdoctoral associates (using exchange programs) into the research. Our project enhances infrastructure for research and education through several fruitful collaborations with the US and foreign Universities. We offer the use of our Carnegie optical facilities for our collaborators (and also NSF-supported programs such as COMPRES and the Carnegie Summer Intern Program, as well as the DOE-supported CDAC high-pressure center, headquartered at Carnegie).