T013-06
Reconciling estimates of viscoelastic mantle structure using transient rheology – Glacial Isostatic Adjustment across North America and Antarctica
Tuesday, 8 December 2020: 05:58
Virtual
Harriet C. P. Lau1, Jacqueline Austermann2, Benjamin K Holtzman3, Cameron Book4, Christopher Havlin5, Emily Hopper6 and Andrew Jason Lloyd2, (1)University of California, Berkeley, Department of Earth and Planetary Science, Berkeley, CA, United States, (2)Columbia University, Lamont-Doherty Earth Observatory, Palisades, NY, United States, (3)Lamont Doherty Earth Observatory, Columbia Univ., Palisades, NY, United States, (4)Los Alamos National Laboratory, Los Alamos, NM, United States, (5)University of Illinois at Urbana Champaign, Urbana, IL, United States, (6)Lamont -Doherty Earth Observatory, Palisades, NY, United States
Abstract:
Determining the thickness of the lithosphere in any given setting combines uncertainty in both the observational method and laboratory-derived understanding of mantle rheology. The many observational and modeling criteria across geophysical subfields for plate thickness lead to significant differences in plate thickness estimates depending on the process of interest, be it seismic wave propagation or relaxation in response to changes in loads – from earthquakes, ice sheets to volcanoes – or convection. In this talk, we present a framework in which to model and interpret upper mantle mechanical structure smoothly across the full spectrum of geophysical timescale, integrating viscous, elastic and linear anelastic constitutive models and calculate the mechanical response from convective to seismic wave timescales.
To demonstrate our approach, we focus on seemingly conflicting glacial isostatic adjustment (GIA) estimates of viscoelastic structure reported for North America and Antarctica. First, we show that the contrasting geologic (thermodynamic) settings only partially contribute to these discrepancies. The remaining contributions may result from transient (and non-linear) rheologic behavior, which give rise to frequency-dependent viscosity and lithospheric thickness.
We simultaneously consider all of these effects, with GIA processes spanning ~1-100,000 years in timescale. In doing so, asthenospheric viscosity and lithospheric thickness are predicted to vary with frequency. By adopting traditional Maxwell viscoelastic models, many GIA studies cannot reproduce such variation. Using the most up-to-date viscoelastic rheological models, we produce frequency-dependent estimates of these parameters that significantly reduce this discordance, demonstrating the importance of transient rheology within GIA processes and therefore, important solid-Earth/cryosphere/sea level feedbacks.
