HR: 1340h
AN: MR43A-0867    [Abstracts]
TI: Potassium as a Radioactive Heat Source in the Core? A High Pressure Experimental Study
AU: * Corgne, A
EM: a.corgne@gl.ciw.edu
AF: Geophysical Laboratory, 5251 Broad Branch Road, Washington, DC 20015 United States
AU: Keshav, S
EM: s.keshav@gl.cwi.edu
AF: Geophysical Laboratory, 5251 Broad Branch Road, Washington, DC 20015 United States
AU: Fei, Y
EM: y.fei@gl.cwi.edu
AF: Geophysical Laboratory, 5251 Broad Branch Road, Washington, DC 20015 United States
AB: The presence of potassium (K) in the core as a significant heat source was suggested over three decades ago. Experimental studies on K partitioning between metal and silicate have provided ambiguous results, because of experimental and analytical artefacts. It has been recognized that polishing of a run product for chemical analysis using water or oil lubricants results in substantial K loss from the metallic phase [Murthy et al., 2003, Nature 423]. Using a dry polishing technique, Murthy et al showed that K enters sulfide-rich metallic liquids with a strong dependence on temperature and silicate melt composition, but without a significant dependence on pressure over the range of their study (1-3 GPa). Extrapolating their data to conditions of pressure, temperature and melt structure, appropriate to core segregation, Murthy et al concluded that K is a substantial radioactive heat source in planetary cores. Their extrapolation technique is debatable, however, notably concerning the effects of composition and pressure on the partitioning. The aim of our study is therefore to reexamine the factors that can affect K partitioning between metallic liquid and silicate melt. We have performed multi-anvil experiments on a relatively wide pressure range, between 3 and 8 GPa, using graphite capsule. In contrast to Murthy et al who used compositions with high S and K contents, we used a CI-chondrite model composition (containing about 4000 ppm K) as starting material in order to obtain partitioning data directly applicable to planetary differentiation processes. Run products were analyzed by electron microprobe. Time-series experiments at 8 GPa reveal that equilibrium conditions are reached rapidly, within 10 s. The effect of temperature was investigated at 8 GPa on the 2000-2200 C temperature range. Results shows that over this temperature range, partition coefficients for K (DK) remain almost identical. The influence of pressure was investigated at 2000 C (3-8 GPa range). Results reveal that DK slightly increase from 3 to 8 GPa, with values of 0.074 and 0.082 respectively. However, this trend could be due to the increase of the S content of the metallic phase with pressure. Further experiments are currently underway to separate the effect of pressure from the effect of composition, and to extend the pressure range of the study.
DE: 8147 Planetary interiors (5430, 5724)
DE: 1060 Planetary geochemistry (5405, 5410, 5704, 5709, 6005, 6008)
DE: 1065 Trace elements (3670)
DE: 1015 Composition of the core
SC: Mineral and Rock Physics [MR]
MN: 2004 AGU Fall Meeting