A constraint to thermal conductivity of Earth’s core and CMB heat flow by assessment on a stable region of Earth’s core

<p>It is still controversial for an emergence of a stable region at the top of Earth&#8217;s core in theoretical modeling because both thermal conductivity of Earth&#8217;s core and heat flow across the core-mantle boundary (CMB) have not been clearly constrained from mineral physics and geophysical observations, ranging 20 to 220 W/m/K for the thermal conductivity (denoted as ) and 5 to 20 TW for the present-day CMB heat flow (denoted as Q^P_CMB). In this study, in order to resolve these uncertainties, we try to constrain the values of thermal conductivity of Earth&#8217;s core and the present-day CMB heat flow by requiring continuous generation of geomagnetic field in addition to existence of a stable region at the top of present Earth&#8217;s core using a one-dimensional thermal and compositional evolution model. &#160;</p><p>Numerical experiments for various values of &#160;and Q^P_CMB show that the solutions satisfying both long-term magnetic field generation and emergence of a stable region is possible only when &#160;is larger than 40 W/m/K and Q^P_CMB is less than 18.5 TW. The specific required value of depends on Q^P_CMB. If the expected CMB heat flow would be as large value as 17.5 TW, which is suggested by the recent studies on the core evolution theory (e.g., Labrosse, 2015), &#160;should be a high value such as about 212 W/m/K to satisfy our requirements. The thickness of an expected stable region would be about 30 km in this case. In contrast, when Q^P_CMB is as small as that derived from numerical mantle convection models (e.g., 10 TW; Nakagawa and Tackley, 2010), the required value of &#160;decreases to 110 W/m/K. In this case, a stable region extends about 75 km thickness below CMB.</p><p>If the requirements assumed in this study is confirmed by certain geophysical observations and/or Q^P_CMB can be restricted more precisely with some methods, our assessment scheme would be useful for evaluations of the radial convective structure of Earth&#8217;s core and for further constraint of the value of thermal conductivity of Earth&#8217;s core.</p>