10:45 AM - 11:00 AM
[SIT22-19] Experimental study on penetration of molten iron alloy into the lower mantle phase
Keywords:core-mantle boundary, bridgmanite, ferropericlase, molten Fe alloy, penetration
In this study, high pressure experiments on penetration of molten iron alloy liquid into the lower mantle phases was performed in a stability field of major lower mantle phase (bridgmanite and ferropericlase) using a large volume press to understand penetration process induced by the morphological instability at the CMB. The liquid metal had penetrated into the (Mg,Fe)O aggregate along the grain boundary and formed a layer containing many metal-rich blobs. In contrast, at interface between molten iron alloy and postspinel (or bridgmanite), penetration of molten iron alloy was not observed.
Penetration of iron alloy liquid into the (Mg,Fe)O aggregate is caused by the capillary rise or Mullins-Sekerka instability. Both the capillary rise and the morphological instability did not occur at the wall of pure polycrystalline MgO, indicating that the FeO in (Mg,Fe)O plays an essential part in this phenomena. If the ultralow velocity zone (ULVZ) with low shear velocity is composed of Fe-rich periclase, penetration distance of molten iron alloy into the core-mantle boundary region by capillary rise occurs in a limited range within 20 m. However, iron-rich melt could not penetrate into silicate-rich mantle. These observations suggest that the penetration of Fr-rich melt into the base of mantle is unlikey to account for geophysical anomalies observed at the core-mantle boundary region.