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

The formation mechanism of terrestrial planetary cores is still poorly unde rstood, and has been the subject of numerous experimental studies(1-3). Sev eral mechanisms have been proposed by which metal-mainly iron with some nic kel-could have been extracted from a silicate mantle to form the core. Most recent models involve gravitational sinking of molten metal or metal sulph ide through a partially or fully molten mantle(4,5) that is often referred to as a 'magma ocean'. Alternative models invoke percolation of molten meta l along an interconnected network (that is, porous flow) through a solid si licate matrix(6,7). But experimental studies performed at high pressures(1- 3) have shown that, under hydrostatic conditions, these melts do not form a n interconnected network, leading to the widespread assumption that formati on of metallic cores requires a magma ocean. In contrast, here we present e xperiments which demonstrate that shear deformation to large strains can in terconnect a significant fraction of initially isolated pockets of metal an d metal sulphide melts in a solid matrix of polycrystalline olivine. Theref ore, in a dynamic (nonhydrostatic) environment, percolation remains a viabl e mechanism for the segregation and migration of core-forming melts in a so lid silicate mantle.