04 Jan 2022

04 Jan 2022

Review status: this preprint is currently under review for the journal SE.

Regional mantle viscosity constraints for North America reveal upper mantle strength differences across the continent

Anthony Osei Tutu and Christopher Harig Anthony Osei Tutu and Christopher Harig
  • Department of Geosciences, University of Arizona, Tucson

Abstract. We present regional constraints of mantle viscosity for North America using a local Bayesian joint inversion of mantle flow and glacial isostatic adjustment (GIA) models. Our localized mantle flow model uses new local geoid kernels created via spatio-spectral localization using Slepain basis functions, convolved with seismically derived mantle density to calculate and constrain against the regional free-air gravity field. The joint inversion with GIA uses two deglaciation of ice sheet models (GLAC1D-NA and ICE-6G-NA) and surface relative sea level data. We solve for the local 1D mantle viscosity structure for the entire North America (NA) region, the eastern region including Hudson Bay, and the western region of North America extending into the Pacific plate.

Our results for the entire NA region show one order of magnitude viscosity jump at the 670 km boundary using a high seismic density scaling parameter (e.g., δlnp/δlnvs = 0.3). Seismic scaling parameter demonstrates significant influence on the resulting viscosity profile. However, when the NA region is further localized into eastern and western parts, the scaling factor becomes much less important for dictating the resulting upper mantle viscosity characteristics. Rather the respective local mantle density heterogeneities provide the dominate control on the upper mantle viscosity. We infer local 1D viscosity profiles that reflect the respective tectonic settings of each region's upper mantle, including a weak and shallow asthenosphere layer in the west, and deep sharp viscosity jumps in the eastern transition zone, below the suggested/proposed depth range of the eastern continental root.

Anthony Osei Tutu and Christopher Harig

Status: open (until 19 Feb 2022)

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Anthony Osei Tutu and Christopher Harig

Anthony Osei Tutu and Christopher Harig


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Short summary
The Earth’s surface deforms due to surface mass load such as ice sheets and subsurface dynamics. Sea level and GPS data show North America (NA) is undergoing surface deformation, due to past ice loads and/or Earth’s interior pull by dense material. We employ mathematical methods and computer simulations to study the region viscosity/strength as a function of depth using a localization technique. Our results show the east of NA has a stiff interface compared to the western part.