HR: 16:00h
AN: V32G-01 INVITED     [PDF]
TI: Experimental and Theoretical Mineral Physics Challenges Posed by Core Formation and Evolution Models
AU: * Stevenson, D J
EM: djs@gps.caltech.edu
AF: Caltech, 150-21, Pasadena, CA 91125
AB: The current state of Earth's core is a legacy of its formation and evolution. It is likely that many of our notions of this are simplistic and arise from an ignorance of what took place, but this does not reduce the merit of considering the relevant experiments and calculations that are motivated by current ideas. The perspective I will adopt is that Earth's core is an ensemble of different sources: A source that may have formed in precursor bodies and thus reflects relatively low temperature, low pressure equilibration at a very early stage; a source that experienced high T and maybe P created immediately after a giant impact, a source that arises from equilibration at the base of a magma ocean (the most popular current idea) and perhaps a source that arises from core-mantle boundary interactions. I will accordingly focus on three kinds of challenges: (1) What is the behavior of metallic iron-liquid silicate mixing and equilibration under extreme temperature? This may be needed to understand some aspects of what happens during the prompt Rayleigh-Taylor instabilities that follow giant impacts. On general thermodynamic grounds, we expect immiscibility to decrease at high temperature. I will discuss likely estimates of critical temperature and how solubility should scale as temperature decreases.(2) What is the nature and consequences of dissolution from the core as the outer core cools? On quite general thermodynamic grounds, we can expect that the least soluble mantle constituent (probably MgO but not really known) is also the one most likely to become saturated in the outer core as the core cools. Silica or the combination with MgO (Mg perovskite) may also become saturated. I will discuss how this would show up in earth properties (e.g., seismology, geodesy) and how this would be important for the energy source for the dynamo. (3) How is the siderophile pattern of residual mantle affected by the likely equilibration between mostly solidified mantle and core-forming melt? This is relevant to the bottom of a magma ocean and the last equilibration of core forming liquid with mantle. The "bottom" of the magma ocean is rheologically defined and is therefore mostly solid, not liquid. In each of these cases I will describe what kind of experiments or calculations are needed to make progress.
DE: 1015 Composition of the core
DE: 3924 High-pressure behavior
DE: 5455 Origin and evolution
DE: 8124 Earth's interior--composition and state (old 8105)
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting