Heat flow in terrestrial-type bodies from high P,T electrical resistivity measurements of Au, Fe-Si and Fe-Ni-Si solid and liquid alloys
Abstract
The source of the fluid stirring mechanism that powers the dynamo of terrestrial-type bodies during their active magnetic field era is debated. Prior to the formation of a solid inner core, thermal convection may cause enough mechanical stirring of the core fluid to generate a magnetic field through dynamo action. After inner core formation, compositional convection in the liquid outer core becomes the main source of fluid stirring mechanism to power a dynamo. Constraints on the likelihood and duration of these convection mechanisms may be obtained by the experimental determination of the thermal properties of core materials. These cores consist of complex Fe-alloys and the effects of impurities have not yet been established under high pressures and temperatures. The first objective of this thesis was to investigate the behavior of electrical resistivity along the melting boundary of metals by measurements in large volume presses (1000 ton, 3000 ton) using the 4-wire method. Unprecedented measurements on Au up to liquid temperatures from 2-5 GPa show a decrease in resistivity along the melting boundary, conflicting with the prediction of invariant behavior. In contrast, the first measurements on Fe-8.5wt%Si revealed a constant behavior of resistivity along the melting boundary from 10-24 GPa. The second objective of this thesis was to investigate the effect of impurities on the resistivity via measurements on Fe-xSi (x is 2, 8.5, 17 wt%) and Fe-10wt%Ni-10wt%Si from 2-24 GPa and up to liquid temperatures. The similarity in Fe-8.5wt%Si and Fe-10wt%Ni-10wt%Si measurements indicate a negligible effect of Ni. Finally, the estimated heat flow at the top of an Fe-10wt%Ni-10wt%Si Earth core is estimated to be 14 TW. The results of an Fe-Si lunar core date the end of the high magnetic field dynamo to be in the range of 3.32-3.80 Gyr. A similar analysis of an Fe-8.5wt%Si Mercurian core suggests a thermally driven dynamo up to 4.28-4.42 Gyr. However, an Fe-10wt%Ni-10wt%Si Mercurian core indicates a thermally driven dynamo up to 4.29-4.48 Gyr. Lastly, measurements of Fe-10wt%Ni-10wt%Si suggest the lack of dynamo in Venus can be explained by a solid inner core and at least partially liquid outer core.