Flow Strength and Acoustic Emissions of Earth Materials at High Pressures

点击翻译按钮获取中文摘要

Dynamic mantle processes in the Earth that drive tectonic plate motions have shaped our planet into one that is unique in the solar system. Despite breakthroughs in laboratory rock-deformation studies, our understanding of the mechanisms behind plate motions, within the framework known as plate tectonics, are still quite primitive due principally to experimental limitations. Experimental measurements on high temperature flow of crustal and mantle rocks commenced in the 1960s, but highly accurate stress-strain measurements could only be made at crustal conditions. A second major development occurred in the 2000s when multianvil technology was combined with in situ synchrotron X-ray diffraction techniques to estimate sample stresses during controlled deformation at high pressures. However, due to a poor theoretical understanding and measurement limitations, stress estimates still have unacceptable uncertainties of up to 1 GPa. This lack in accuracy prevents robust measurements on the flow, i.e. viscosity, of mantle rocks from being made.A third breakthrough in the field of high pressure rock physics is necessary to progress further. In this project an internal piezoelectric stress sensor for large volume, high pressure devices will be developed and the viscosity of olivine will be precisely determined at high pressures. In addition, the stress sensor will be used as an application for stress measurements in conjunction with acoustic emissions detection and localization during rock deformation. Preliminary work has shown the clear feasibility and superiority of this technology over other methods. Using the developed apparatus, two principal outstanding issues will be experimentally addressed. 1) The cause and magnitude of viscosity changes responsible for the transition in rheological properties between the lithosphere and asthenosphere will be gauged. 2) The origin of subduction-zone earthquakes by means of in situ acoustic emissions recordings will be studied. Achievement of the objectives above enables future collaborations with geodynamicists (e.g. at the Bayerisches Geoinstitut) to scale up processes in the laboratory to the Earth using numerical models. The expected outcomes of the Flac project are therefore crucial towards building up a sound understanding of the inner workings of the Earth.