High-resolution lithosphere viscosity and dynamics revealed by magnetotelluric imaging.

Lijun Liu,Derrick Hasterok

doi:10.1126/science.aaf6542

Lijun Liu, Derrick Hasterok

Open Access

https://doi.org/10.1126/science.aaf6542

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Abstract

An accurate viscosity structure is critical to truthfully modeling lithosphere dynamics. Here, we report an attempt to infer the effective lithospheric viscosity from a high-resolution magnetotelluric (MT) survey across the western United States. The high sensitivity of MT fields to the presence of electrically conductive fluids makes it a promising proxy for determining mechanical strength variations throughout the lithosphere. We demonstrate how a viscosity structure, approximated from electrical resistivity, results in a geodynamic model that successfully predicts short-wavelength surface topography, lithospheric deformation, and mantle upwelling beneath recent volcanism. We further show that this viscosity is physically consistent with and better constrained than that derived from laboratory-based rheology. We conclude that MT imaging provides a practical observational constraint for quantifying the dynamic evolution of the continental lithosphere.

Highlights

An accurate viscosity structure is critical to truthfully modeling lithosphere dynamics
Previous conceptual models of rifting that highlight variations in strain appear to mimic patterns seen in the midcrustal electrical conductivity under similar circumstances [25]. We propose that these high-conductivity patterns (Fig. 1, A and B) represent low-viscosity regions owing to consequences of past deformation of the continental lithosphere
We looked for an effective lithospheric viscosity structure resembling the spatial pattern of the MT image that satisfies the available constraints

Summary

EÃ þ PV RT

Ð1Þ where d is grain size; COH, water fugacity; E* and V *, activation energy and activation volume, respectively; P and T, pressure and temperature, respectively; R, the ideal gas constant; and A, m, n, and r, all laboratory-derived parameters [23]

The electrical resistivity model takes a similar form r

AND NOTES

Findings

Spiral density waves in a young protoplanetary disk