JpGU-AGU Joint Meeting 2017

Presentation information

[EE] Oral

S (Solid Earth Sciences) » S-IT Science of the Earth's Interior & Tectonophysics

[S-IT23] [EE] Structure and Dynamics of Earth and Planetary Mantles

Mon. May 22, 2017 1:45 PM - 3:15 PM A05 (Tokyo Bay Makuhari Hall)

convener:Takashi Nakagawa(JAMSTEC/MAT), Dapeng Zhao(Department of Geophysics, Tohoku University), Takashi Yoshino(Institute for Planetary Materials, Okayama University), Chairperson:Takashi Yoshino(Institute for Planetary Materials, Okayama University), Chairperson:Hiroko Watanabe(Tohoku University)

2:30 PM - 2:45 PM

[SIT23-22] Defining the deep Earth with the OBK detector

*William F McDonough1 (1.RCNS & Earth Sciences, Tohoku University, Sendai, Japan)

Keywords:geoneutrino, mantle, heat flow, radiogenic power, thermal evolution

The global surface heat flow reflects the combine contributions of primordial and radiogenic heat, with the former comprised of accretion and core formation sources. The continental crust contributes 7 TW of radiogenic power and a sub-MOHO flux of 10 to 30 mW/m^2 for a total surface flux of 65 mW/m^2. The continents contribute about 1/3 of the total power lost from the Earth. At its present spreading rate, the oceans contribute 2/3 of this flux, but we do not know how much of this flux is primordial versus radiogenic contributions. Earth models collectively allow up to a factor of 30 in the spread of estimates of the present-day mantle’s radiogenic power. Moreover, the surface heat flux is likely to be a relative constant over the continents, whereas in the oceans it is unlikely to remain a constant over the last few billion years given variations in spreading rates. Our understanding of the Earth’s thermal evolution history is intimately linked to knowing the total radiogenic power of the mantle.

OBK (Ocean Bottom KamLAND) is the next generation underwater geoneutrino detector designed to measure the Earth’s abundance and distribution of Th and U inside the mantle. We have shown that such a detector is capable of identifying and mapping out large deep Earth structures (e.g., LLSVP), where they have enrichments in these elements relative to the ambient mantle.

Following on from the successes of the existing detectors in Japan and Italy, we propose an international effort, with Japanese geoscientists and particle physicists leading, to construct and deploy an ocean-going detector (OBK) to (1) map out structures in the mantle, (2) constraint the cooling history of the planet, (3) distinguish continental and mantle Th/U ratios, which documents the Earth’s biological imprint on the mantle, and (4) define the power driving plate tectonics. Beyond these goals in Earth Sciences, this instrument will have spinoffs for particle physics and astroparticle physics. This field of science has been richly acknowledged by Nobel prizes; the science proposed here has the potential to continue this great tradition.