Planetary Core Formation

Early-stage core-mantle differentiation and core formation represent pivotal geological events that defined the major geochemical and geophysical signatures of Earth. In order to test potential mechanisms and hypotheses of core formation, we need textural information on the interaction and separation of the solid and liquid phases. Previous experiments have been mostly limited to upper mantle conditions, though the actual events may have occurred at much higher pressures and temperatures.  DAC can achieve the necessary pressure and temperature conditions of this region, but textural study of a 100 µm-sized sample requires nanoscale in-situ probes that do not currently exist.

We have been working todevelop nanoscale x-ray computed tomography (nanoXCT) within a laser-heated diamond anvil cell.  Pilot studies we conducted this year have revealed the exciting potential for using nanoXCT as a powerful 3D petrographic probe for non-destructive, nanoscale (<40nm) resolution of multiple minerals and amorphous phases (including melts).  This will extend measurements of the texture, shape, porosity, dihedral angle, and other characteristics of molten iron-rich alloys coexisting with silicates and oxides to the relevant high pressure and high temperature conditions.  NanoXCT can also be used to investigate grain shape, intergrowth, orientation, and foliation -- as well as mineral chemistry and crystallography -- to understand whether shape-preferred orientation is a primary source of the observed seismic anisotropy in Earth’s D” layer and to determine the textures and shapes of the melt pockets and channels formed by the putative partial melt which may exist in ULVZs.