On the persisting conundrum of mantle viscosity inferred from mantle convection and glacial isostatic adjustment processes

Professor Shijie Zhong

University of Colorado, Department of Physics

2024.05.17（星期五）15:10，二教311

Abstract:

The "falling sea" rate in Fennoscandia was first determined in 1731 by Sweden Astronomer/Physicist Anders Celsius who is best known for his temperature scale. With the discovery of the Ice Age about 100 years later, it was soon recognized that the "falling sea" was actually the land rebounding caused by deglaciation in Fennoscandia ~15,000 years ago. In 1935, Haskell used the land rebounding rate in Fennoscandia to offer the first determination of mantle viscosity of 10^21 Pas, thus for the first time expanding the horizon of studies of mantle convection from a purely theoretical pursuit to that with possible observational constraints. However, as studies of post-glacial rebound since 1970's suggested a more uniform mantle viscosity, mantle flow studies for long-wavelength geoid starting in 1980's indicated that mantle viscosity increase significantly with depth from the upper mantle to the lower mantle. Although in recent years some post-glacial rebound studies also proposed significant viscosity increase with depth, these models may have difficulties in explaining the GPS and GRACE data. In this presentation, I will show our recent studies to further highlight the conundrum of mantle viscosity and propose some possible solutions to resolve the difficulties.

Bio:

Shijie Zhong is a Professor of Physics and Geophysics in the Department of Physics at the University of Colorado at Boulder. His primary research interest is in the dynamics of the mantle and lithosphere of the Earth and other terrestrial planets. In recent years, he has devoted a substantial amount of time to studying the dynamic interaction between the solid Earth, ice sheets and sea level changes. He received his B.S. and M.S., both in Geophysics, from the University of Science and Technology of China in 1985 and Institute of Geophysics of Chinese Academy of Sciences in 1988, respectively. He started his PhD studies at the University of Michigan in 1990 and received his PhD degree in Geophysics and Scientific Computing in 1994. He was a post-doctoral scholar at Caltech from 1994 to 1997 and then a research scientist at MIT. In 2000, he took an assistant professor position at the University of Colorado at Boulder and has remained in Colorado since.