Model of Blobs in Earth’s Interior Explains Unusual Pacific Volcanism

Deep inside the Earth are two huge blobs of dense rock splayed across the core-mantle boundary. One of the underground structures sits under the South Pacific and the other is underneath Africa. 

Plumes rising from these deep masses feed some of the planet’s most spectacular volcanic island chains, such as the Hawaiian Islands. Because the volcanoes fed by the plumes have an unusual chemical fingerprint, scientists think the blobs are made of rock different from the rest of Earth’s mantle. Scientists also know these continent-size structures are not like typical mantle rock because seismic waves pass through the structures more slowly than in the surrounding mantle. This observation gives the two large blobs their jargony name — “large low shear velocity provinces” or LLSVPs.

A computer model from UC Davis project scientists Juliane Dannberg and Rene Gassmoeller, members of the Department of Earth and Planetary Sciences in the College of Letters and Science, offers new insights into the relationship between the mantle blobs and the lava erupted at some Pacific islands. The model provides a possible cause for the geochemical trends present in some of these volcanic island chains. 

The computer model simulates the actual movement of tectonic plates on the surface and in the mantle for the past 250 million years. The researchers were especially interested in what happens below subduction zones, where pieces of oceanic plates, or slabs, descend into the mantle. The model shows that sinking slabs of oceanic crust can snowplow into the dense blobs, creating bulges along the edge of the LLSVPs. These lumps and bulges then spawn plumes that travel toward the surface, feeding volcanic eruptions. The plumes produced in the model recreated the unique chemical fingerprint seen at Pacific island chains.

The findings were published April 9 in the journal Proceedings of the National Academy of Sciences.

The computational resources were provided by the North German Supercomputing Alliance (HLRN) as part of the project “Plume-Plate interaction in 3D mantle flow – Revealing the role of internal plume dynamics on global hot spot volcanism.” Both authors were partially supported by the Computational Infrastructure for Geodynamicsinitiative through the National Science Foundation.

— Becky Oskin, content strategist in the College of Letters and Science