A Hybrid Mechanism for Enhanced Core‐Mantle Boundary Chemical Interaction

• Published in: Geophysical research letters Vol. 48; no. 23
• Main Authors: Lim, Kang Wei, Bonati, Irene, Hernlund, John W.
• Format: Journal Article
• Language: English
• Published: 16.12.2021
• Subjects: core composition; core‐mantle boundary; core‐mantle interaction; dynamic topography; lubrication theory; mantle dynamics
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2021GL094456

Detection of chemical signatures from the core‐mantle boundary (CMB) could provide an unprecedented glimpse into our planet's deep interior and ancient past. Several isotopic and elemental anomalies in ocean island basalts (OIBs) have been proposed as core tracers. However, the process(es) by which particular chemical signatures from the core are conveyed into the mantle remain uncertain. Here, we propose a hybrid mechanism that results from a collaborative feedback between dynamic topography, porous infiltration of liquid metal into submerged rock, gravitational collapse of weakened metal‐silicate mush, and draw‐down of additional rocks from above in the induced small‐scale mantle circulation. Using a mantle convection model coupled to gravitational spreading of a thin layer, we show that induced mantle circulation due to the gravitational collapse of the layer becomes comparable to buoyancy‐driven mantle flow when the viscosity of the mushy layer is reduced to values ∼105 times smaller than the overlying mantle. Plain Language Summary The core and mantle may be able to exchange matter by the build up of inverted mountains and valleys at their boundary, and the erosion of this terrain driven by gravity can significantly enhance mantle circulation through this region, allowing metals and rocks to mix more extensively than previously thought. Key Points Mixing in a metal‐rock mushy layer offers a promising mechanism to explain some geochemical observations linked to core‐mantle interaction A mushy layer produced by core‐mantle boundary topography may become weak and collapse due to gravity, enhancing mantle circulation Our models show that this “soft CMB” mechanism becomes dominant for viscosity contrasts of 105 or more, influencing deep mantle dynamics