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3.2 Geochemistry at Extreme Pressures and Temperatures

The present-day chemistry of the Earth is a product of the many processes that have occurred since its formation from the solar nebula. A sample from the Earth's interior may therefore reflect such diverse processes as accretion, differentiation including core formation, volcanism, metasomatism and convection. In our research we seek to quantify not only the static properties of the Earth such as its bulk chemistry, but also these past and present dynamic processes that define many of the physical and chemical properties of the Earth. We are confined to measurements on the Earth's surface, and to some extent our knowledge is inversely proportional to depth since we can effectively sample the Earth's interior only near the surface. One exception is the core, however, whose chemistry is relatively well established as consisting of an iron-nickel alloy with a moderate amount of light element(s) mixed into the liquid outer core and perhaps also a smaller amount in the solid inner core. Further basic knowledge about the core, for example temperature profiles, must be obtained indirectly through either experiments in the laboratory or theoretical models. The formation of the core was one of the major events during Earth history, some aspects of which were recorded in samples that we observe today from the mantle. In particular, the "siderophile element anomaly" remains a challenge to reconcile present-day observations with core-mantle equilibrium. Samples from the mantle show a siderophile element abundance (that is, elements that preferably partition into the metal phase) that is too high to be explained by conventional models for core formation. One resolution of the problem may come from the effect of pressure, temperature or composition on the partitioning behaviour of siderophile elements, and research at Bayerisches Geoinstitut continues to focus on this problem through state-of-the-art experiments using the multianvil presses to explore these variables. Oxygen fugacity, in particular, is an often neglected variable, and efforts are being focused on both the measure and control of this parameter.

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)