Other
Scientific paper
May 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agusm.u51a..02v&link_type=abstract
American Geophysical Union, Spring Meeting 2002, abstract #U51A-02
Other
3630 Experimental Mineralogy And Petrology, 8115 Core Processes (1507), 1015 Composition Of The Core, 1060 Planetary Geochemistry (5405, 5410, 5704, 5709, 6005, 6008)
Scientific paper
Potassium as a radiogenic heat source in the Earth's core has been suggested over 30 years ago but several attempts at experimental confirmation have only yielded ambiguous results. This may have been in part due to severe experimental difficulties caused by volatility of K at high temperature and the ubiquitous solubility of K not only in water but also in "water-free" hydrocarbon oils used in polishing and other organic solvents. We report here on experiments performed under conditions in which the above difficulties have been overcome by using a double capsule technique to contain the sample and by new methods of polishing without the use of liquids. We have taken a two-level approach in our experiments - first to establish that K is in fact soluble in sulfide melts at low pressure and temperature and then to determine the effect of pressure and temperature on solubility of K in systems similar to Bulk Silicate Earth. In synthetic systems composed of K-silicate, Fe-metal, and FeS, potassium is readily soluble in the Fe-S melts at 2 GPa and magmatic temperatures at fO2 close to IW. The sulfide-silicate distribution coefficient DK is 0.03 at 1200° C but increases by a factor of 7 to 0.2 at 1600° C showing a perfect correlation in a plot of ln DK vs. 1/T. These experiments indicate a significant temperature-dependent solubility of K in Fe-S melts and provide clues to the formation of K-bearing sulfide minerals in some meteorites. If the Earth's core formed by segregation of metallic liquids in the Fe-FeS system, even the level of solubility observed at these low temperatures suggests that a significant amount of potassium will be present in the core and will serve as a radiogenic heat source in the core. For example, using the DK at 1600° C, we calculate that the present heat production due to K in the core to be ~3x1012 W for a Chondritic Earth Model and 1x1012 W for a potassium poor Bulk Earth Model. The estimate for the present day heat flux from the CMB of 3-12 x1012 W shows that the radiogenic heat due to 40 K in the core can be a significant fraction of the CMB heat flux. The presence of radiogenic heat in the core has important implications for the time of formation of the inner core, convection in the outer core, the geomagnetic field and the lower mantle geochemistry and dynamics.
Fei Yingwei
Murthy V.
van Westrenen Willem
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