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Understanding Earth’s mantle dynamics requires bridging insights from the present-day deep
mantle with the tectonic regimes that may have operated on the early Earth. In the first part of this
talk, I present 3-D regional and global geodynamic models that investigate mantle plume
generation from Large Low-Shear-Velocity Provinces (LLSVPs) and the resulting shear wave
radial anisotropy in the lowermost mantle. Using ASPECT (mantle convection code) coupled with
ECOMAN (mantle fabric simulation code), we test a range of LLSVP density and viscosity
contrasts and examine their influence on mantle flow, plume formation, and resulting deformation
mechanisms of key lower mantle minerals. The models reproduce key seismic features, such as
fast vertically polarized shear wave in plume conduits and anisotropy concentrated at LLSVP
margins and predict plume locations consistent with present-day observations. These results
demonstrate how modern plate motions and subduction patterns shape deep-mantle flow and
resulting seismic anisotropy.
However, the present-day convection regime is strongly driven by plate velocities and organized
subduction, conditions that did not exist on the early Earth. This raises a fundamental question:
how did mantle flow and crust–mantle interaction operate when plate tectonics had not yet
developed? In the second part of this talk, I explore this using 2-D ASPECT models of Archean
sagduction dynamics, where dense lower crust sinks into a hotter, weaker mantle. By varying
thermal and rheological structure, we show how sagduction could control the long-term evolution
of the lower crust and the mantle lithosphere beneath it. The findings provide new insight into the
dynamics of Archean lithosphere and the mechanisms that may have governed early continental differentiation. |