Previous page     Contents     Next page

3. Research Projects

In this section an overview of the most important on-going projects is given. Information concerning recently-completed projects can be obtained from the publication lists of sections 4.1 and 4.2. Please note that the following contributions should not be cited.

3.1 Phase Transformations, Deformation and Properties of Mantle Minerals

The Earth's mantle has a layered structure as a consequence of high-pressure phase transformations between the constituent silicate and oxide minerals. For example, (Mg,Fe)2SiO4 olivine, the most common mineral in the upper mantle, transforms to the higher-density polymorphs wadsleyite at 410 km depth and ringwoodite at 520 km depth; at 660 km ringwoodite reacts to (Mg,Fe)SiO3 perovskite + (Mg,Fe)O. Likewise, phase transformations also occur in other minerals of the upper mantle, such as pyroxenes and garnet, with increasing depth. However, the proportions of the various minerals and their chemistry as a function of depth in the mantle are still uncertain.

The primary information pertaining to the chemical composition, mineralogy and temperature of the Earth's interior consists of geophysical estimates of density, elastic properties and electrical conductivity as a function of depth. In order to derive mineralogical and geochemical models of the Earth's mantle from such estimates, the elastic and electrical properties of potential mantle minerals must be measured in the laboratory as a function of pressure, temperature and composition. The results of such measurements are the topic of the first three contributions in this section.

Large-scale solid-state convection in the mantle is the driving force for the motion of lithospheric plates and for many near-surface geological phenomena such as earthquakes and volcanism. Although rheology is one of the most important physical properties that control mantle convection, the rheological properties of most mantle minerals and their dependence on pressure are very poorly known. Therefore, in the last 2-3 years, new and innovative experimental methods have been developed at the Bayerisches Geoinstitut with the aim of studying the rheology of materials under the pressures and temperatures of the Earth's mantle. The results of several such studies are reported here. The deformation mechanisms in a number of important mantle minerals have also been investigated by transmission electron microscopy because these ultimately control the rheological behaviour.

Bayerisches Geoinstitut, Universität Bayreuth, 95440 Bayreuth, Deutschland
Tel: +49-(0) 921 55 3700 / 3766, Fax: +49-(0) 921 55 3769, E-mail: bayerisches.geoinstitut(at)