Abstract
There exist two large (~1000 km) dome-like structures
rising from the base of the mantle in global tomographic models that
exhibit low seismic wave-speeds, known as “Large Low Velocity
Provinces” (LLVPs). The LLVP beneath Africa is also known as Tuzo,
while the LLVP beneath the Pacific Ocean is known as Jason – two early
pioneers of plate tectonics and plume theory (Wilson and Morgan,
respectively). The source of these anomalously low wave-speeds is
debated as both thermal and chemical heterogeneities can lower
wave-speeds. These heterogeneities, however, lead to dynamically
different modes of convection, where the former results in buoyant LLVPs
and the latter relatively dense LLVPs. Recent studies that include
dynamical modeling, Stoneley modes, and body tide constraints, are
beginning to converge towards a picture where dense, chemical
heterogeneities may be stored in the deepest part of the LLVPs. Many of
these analyses, however, have not treated each LLVP distinctly.
Considering the interdisciplinary focus of this session, we combine the
unique geodetic observation of Earth’s solid body tide with methods that
combine Backus-Gilbert estimation with theoretical advances in adjoint
methodology, to constrain the density of each LLVP separately. This
process results in the enhancement of the combined data sensitivity to a
chosen region (e.g., one LLVP) while diminishing the combined data
sensitivity elsewhere. We discuss the results in the context of
geochemical observations unique to Tuzo and Jason and implications for
the dynamics of mantle evolution.