Energetics of the earth derived from the Kamland observation and radiogenic heat source in the core

Details Energetics of the earth derived from the Kamland observation and radiogenic heat source in the core Energetics of the earth derived from the Kamland observation and radiogenic heat source in the core

May 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agusm.u41e..01o&link_type=abstract

American Geophysical Union, Fall Meeting 2007, abstract #U41E-01

Other

3610 Geochemical Modeling (1009, 8410), 3929 Nmr, Mossbauer Spectroscopy, And Other Magnetic Techniques, 8125 Evolution Of The Earth (0325), 8130 Heat Generation And Transport, 9800 General Or Miscellaneous

Scientific paper

Geoneutrinos generated by the beta decay of uranium, thorium, and potassium are the unique tool to clarify the distribution of radiogenic elements in the Earth. The observation of geoneutrinos from uranium and thorium is now available by the Kamland detector at Kamioka, and they observed the neutrino events consistent with the uranium and thorium abundance in the Earth estimated by the bulk silicate Earth model [1,2]. In order to study the Earth's energetics, estimation of the radiogenic heat source in the deep lower mantle and core is one of the most important topics since it could affect the age of the earth's inner core, and the history of the magnetic field of the earth. Earth's core contains light elements and they are controlling its thermal structure that drives geodynamo and heat flow from the core to the mantle. Solubilities of Si and O in liquid iron coexisting with (Mg,Fe)SiO3- perovskite or post-perovskite are essential to estimate the amounts of these elements in the core. Takafuji et al.[3] and Kawazoe and Ohtani [4] showed that the density deficit in the core due to light elements can be explained by dissolution of Si and O into molten iron under the deep lower mantle conditions by the reaction with the surrounding silicate. A possible presence of radiogenic elements such as potassium, uranium, and thorium in the core would have important for the thermal history of the mantle and core, the time of inner core formation, the heat flux at the core-mantle boundary which related to operation of geodynamo. Recent core-energetics calculations propose radiogenic elements such as potassium in the core as an additional power source necessary for sustaining the magnetic field of the Earth. Recent experiments on the partitioning of these radiogenic elements between metallic iron and silicate revealed that entry of uranium and thorium into the core is negligible even at high pressure (e.g., Wheeler et al., [5]). Whereas, Hirao et al. [6] revealed a dissolution of potassium up to 0.8 wt.percents into molten iron at the condition of 134 GPa and 3,500 K, indicating that the partition coefficient of potassium between iron and silicate is 0.15 at the core-mantle boundary. This result indicates that the core can contain 35 ppm total potassium, which could serve as a heat source in the core for driving the geodynamo. It could be possible to detect the distribution of these elements in the lower mantle and core if we can construct the detector in the oceanic regions such as Hawaii islands far from the continental crust. The development of lower energy neutrino detector is also essential to detect geoneutrinos originated from the decay of radiogenic potassium. [1] T. Araki et al., Nature, 436, 2005; [2] S. Enomoto et al., Earth Planet. Sci. Lett., Submitted, 2006, [3] N. Takafuji et al, [4] T. Kawazoe and E. Ohtani, Phys. Chem. Mineral., 2006 in press; [5] K.T. Wheeler et al., Geochim.Cosmochim. Acta, 2006 in press, [6] N. Hirao et al., G.R.L., in press, 2006.

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