The core-mantle boundary (CMB) is the interface between the liquid iron core and the silicate solid mantle, and is the most significant internal boundary of the Earth. The core and the mantle interact across the boundary through transfer of heat and material, and various coupling mechanisms. While the nature and variability of these interactions remains uncertain, they strongly affect the convection in the mantle, responsible for plate tectonics and intra-plate volcanism, as well as the much more vigorous convection in the core, responsible for the geodynamo.
Constraining the interactions at the CMB is crucial to understanding physical processes in the deep Earth and the thermal, compositional, and dynamical evolution of the Earth. The CMB interactions are strongly controlled by heterogeneous structures on or near the boundary. On the mantle side, seismological imaging has observed slow velocity layering and patches, but their physical significance remains uncertain, and it is unclear whether they represent global or local features. Turning to the core, suggestions of a stable light-element-enriched layer have been made. The estimated thickness of such a layer varies from 40 to 450 km, and the origin of the inferred light elements is heavily debated.
In ZoomDeep, I propose innovative seismic techniques to image the structure near the CMB with unprecedented resolution. One technique, dubbed ‘the Frequency Fan’, will be newly developed, while another technique has recently been successfully applied at the Earth’s surface and will be adapted to the CMB. ZoomDeep will lead to the first high-resolution maps of the structures near the CMB and will specifically focus on the roots of mantle upwellings beneath volcanic hotspots. The implications of these maps on fundamental questions impacting core and mantle dynamics will be assessed in multi-disciplinary approaches. The results of this work will transform our understanding of the dynamics and evolution of the Earth.
ERC project ZoomDeep runs from 2019-2023. We will continue update this page with significant outcomes related to the project.
The root to the mantle plume beneath the Galapagos hotspot
Sanne Cottaar and Zhi Li
The deployment of seismic stations from the Transportable Array in Alaska has provided unique resolution on the core-mantle boundary in the Eastern Pacific. We have identified and mapped a ULVZ to the west of the Galapagos Islands through scattered diffracted phases. This ULVZ be the root the mantle plume feeding the Galapagos hotspot. ULVZs of this size have so far only been identified beneath Hawaii (Cottaar and Romanowicz, 2012), Iceland (Yuan and Romanowicz, 2017), and Samoa (Thorne et al. 2012).
Kilometer-scale layering in the root to the Hawaiian mantle plume
Zhi Li, Kuangdai Leng, and Sanne Cottaar
To map the finer structure on the core-mantle boundary beneath Hawaii, we have push our data set to higher frequencies than ever used before. This allowed us to reveal that the velocities in several kilometres at the base of the Hawaiian ULVZ is much more reduced in velocity, and is possible also more widespread. These constraints provide new information on what ULVZs might be!
Presented at the AGU fall meeting 2019 and soon to be published.