Dan J. Bower

Dynamic structure of the large low shear velocity provinces (LLSVPs).

Collaborating with Michael Gurnis^a and Eh Tan^b.

^aSeismological Laboratory, Caltech, Pasadena, CA, USA; ^bCIG, Caltech, Pasadena, CA, USA.

The dynamic structure of the large low shear velocity provinces (LLSVPs) beneath Africa and the Pacific Ocean remains enigmatic. Several lines of evidence imply that the structure is chemically distinct, although it is unclear if the material is primordial or generated by processes occuring on the present-day Earth (e.g. subduction), or maybe a combination of both. These structures appear to be long-lived and therefore have remained stable in the Deep Earth for at least several hundreds of millions of years, and maybe much longer.

Numerical simulations demonstrate that it is difficult to dynamically generate a LLSVP-esque structure satisfying the necessary geodynamic, mineralogical, and seismic constraints. In particular, several seismic studies have identified sharp edges to the African structure and suggest that it stands 1500 km above the core-mantle boundary. Conventional thermochemical simulations have not convincingly created such a morphology.

We are continuing to investigate and test the metastable superplume (AKA high bulk modulus structure) proposed by Tan and Gurnis (2005) as a plausible model for the LLSVPs.

References