An interconnected network of core-forming melts produced by shear deformation

Abstract

The formation mechanism of terrestrial planetary cores is still poorly understood, and has been the subject of numerous experimental studies^1,2,3. Several mechanisms have been proposed by which metal—mainly iron with some nickel—could have been extracted from a silicate mantle to form the core. Most recent models involve gravitational sinking of molten metal or metal sulphide through a partially or fully molten mantle^4,5 that is often referred to as a ‘magma ocean’. Alternative models invoke percolation of molten metal along an interconnected network (that is, porous flow) through a solid silicate matrix^6,7. But experimental studies performed at high pressures^1,2,3 have shown that, under hydrostatic conditions, these melts do not form an interconnected network, leading to the widespread assumption that formation of metallic cores requires a magma ocean. In contrast, here we present experiments which demonstrate that shear deformation to large strains can interconnect a significant fraction of initially isolated pockets of metal and metal sulphide melts in a solid matrix of polycrystalline olivine. Therefore, in a dynamic (non-hydrostatic) environment, percolation remains a viable mechanism for the segregation and migration of core-forming melts in a solid silicate mantle.