The origin of anisotropic structure of the Earth's inner core from mineralogical model to dynamic mechanism
Seismological observations suggested that Earth's inner core presents complex heterogeneity and anisotropic structure.The key to understand the structure of Earth's inner core is to study the mineralogical composition and dynamic mechanism of the anisotropic structure of Earth's inner core.Hexagonal close-packed(hcp)and body centered cubic(bcc)Fe alloys both have seismically anisotropic features under temperature and pressure conditions of the Earth's inner core.When the fast axis can be oriented along the Earth's rotation axis,the anisotropic characteristics of the Earth's inner core,which is fast in the north-south direction and slow in the equatorial direction,can be explained.The input of light elements into Fe alloys significantly changed the anisotropy of Fe alloys.Particularly,the fast axis orientation of superionic Fe-H alloys had changed inversively with the increase of H contents in those alloys.Under There are 3 kinds of dynamic mechanisms of the Earth's inner core.(1)The lattice preferred orientation(LPO)during the solidification period.The LPO texture and structure formed in the solidification process cannot be maintained at the temperature of Earth's inner core for a long time,therefore the LPO is not the main reason resulted in the anisotropic structure of the Earth's inner core;(2)The LPO due to the external stress:The directional arrangement driven by external stress needs to consider the rheological mechanism of the material in the Earth's inner core,while the current model is mainly established based on the assumption of a rigid inner core of the Earth.It is required that the dislocation creep mainly occurred in the Earth's inner core with the viscosity of its material exceeding to 1018 Pa·s.(3)The LPO due to the diffusion induced stress:If the Earth's inner core was under the superionic condition,the directional diffusion of light elements driven by the geomagnetic field could result in the presence of the lattice internal stress which would then result in the LPO.The driving forces of the above mechanisms(chemical convection,thermal convection,and geomagnetic field)are all sourced from the Earth's outer core.In this case,understanding the interaction mechanism between the Earth's outer core dynamics and the Earth's inner core dynamics is the key for understanding the composition and structure of the Earth's inner core.
Earth's inner coreanisotropyhigh temperature and high pressureiron alloyslattice preferred orientation
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