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Speaker Dr Shijie Zhong Explains "Slab Stagnation" Effects on Mantle Dynamics

EES welcomes Dr. Shijie Zhong, Professor of Physics at University of Colorado Boulder.

"The Cause of Slab Stagnation in Mantle Transition Zone and Its Effects on the Dynamics of the Mantle"

The linear structures of seismically fast anomalies, often interpreted as subducted slabs, in the southern Asia and circum-Pacific lower mantle, provided strong evidence for the whole mantle convection model. However, recent high resolution seismic studies have consistently shown that subducted slabs are deflected horizontally for large distances in mantle transition zone in the western Pacific and other subduction zones, suggesting that the slabs meet significant resistance to their descending motion and become stagnant in the transition zone. This poses challenges to the whole mantle convection model and also raises the question about the origin of stagnant slabs. Here, using a global mantle convection model with realistic spinel-post-spinel phase change (-2 MPa/K Clapeyron slope) and plate motion history, we demonstrate that the observed stagnant slabs in the transition zone and other slab structures in the lower mantle can be explained by the presence of a thin, weak layer at the phase change boundary that was suggested from mineral physics and geoid modeling studies. Our studies suggest that while the phase change may affect slab and plume dynamics on time scales of tens of millions of years, it does not alter long-term mass exchange between the upper and lower mantles.

Zhong's research is focused on understanding the dynamics of planetary interiors and its relation to observations at the planetary surfaces including gravity, magnetics, topography, volcanism, and tectonics. In his work, Zhong uses methods of fluid dynamics with both numerical and theoretical models.

Join us for this dive into slab stagnation on Friday, October 5, 2018 at 12:30 PM in Room 204, Natural Science Building on the East Lansing Campus.

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