On lateral viscosity contrast in the mantle and the rheology of low-frequency geodynamics
Mantle-wide heterogeneity is largely controlled by deeply penetrating thermal convective currents. These thermal currents are likely to produce significant lateral variation in rheology, and this can profoundly influence overall material behaviour. How thermally related lateral viscosity variations...
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Oxford University Press
1995
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fthighwire:oai:open-archive.highwire.org:gji:123/2/305 2023-05-15T16:35:30+02:00 On lateral viscosity contrast in the mantle and the rheology of low-frequency geodynamics Ivins, Erik R. Sammis, Charles G. 1995-11-01 00:00:00.0 text/html http://gji.oxfordjournals.org/cgi/content/short/123/2/305 https://doi.org/10.1111/j.1365-246X.1995.tb06856.x en eng Oxford University Press http://gji.oxfordjournals.org/cgi/content/short/123/2/305 http://dx.doi.org/10.1111/j.1365-246X.1995.tb06856.x Copyright (C) 1995, Oxford University Press Articles TEXT 1995 fthighwire https://doi.org/10.1111/j.1365-246X.1995.tb06856.x 2012-11-23T22:11:15Z Mantle-wide heterogeneity is largely controlled by deeply penetrating thermal convective currents. These thermal currents are likely to produce significant lateral variation in rheology, and this can profoundly influence overall material behaviour. How thermally related lateral viscosity variations impact models of glacio-isostatic and tidal deformation is largely unknown. An important step towards model improvement is to quantify, or bound, the actual viscosity variations that characterize the mantle. Simple scaling of viscosity to shear-wave velocity fluctuations yields map-views of long-wavelength viscosity variation. These give a general quantitative description and aid in estimating the depth dependence of rheological heterogeneity throughout the mantle. The upper mantle is probably characterized by two to four orders of magnitude variation (peak-to-peak). Discrepant time-scales for rebounding Holocene shorelines of Hudson Bay and southern Iceland are consistent with this characterization. Results are given in terms of a local average viscosity ratio, Δη¯ 1 , of volumetric concentration, φ i . For the upper mantle deeper than 340 km the following reasonable limits are estimated for Δη¯ 1 ≈10−2:0.01≤φ≤0.15. A spectrum of ratios Δη¯ 1 <0.1 at concentration level φ i ≈ 10−6−10−1 in the lower mantle implies a spectrum of shorter time-scale deformational response modes for second-degree spherical harmonic deformations of the Earth. Although highly uncertain, this spectrum of spatial variation allows a purely Maxwellian viscoelastic rheology simultaneously to explain all solid tidal dispersion phenomena and long-term rebound-related mantle viscosity. Composite theory of multiphase viscoelastic media is used to demonstrate this effect. Text Hudson Bay Iceland HighWire Press (Stanford University) Hudson Bay Hudson Geophysical Journal International 123 2 305 322 |
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English |
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Articles |
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Articles Ivins, Erik R. Sammis, Charles G. On lateral viscosity contrast in the mantle and the rheology of low-frequency geodynamics |
topic_facet |
Articles |
description |
Mantle-wide heterogeneity is largely controlled by deeply penetrating thermal convective currents. These thermal currents are likely to produce significant lateral variation in rheology, and this can profoundly influence overall material behaviour. How thermally related lateral viscosity variations impact models of glacio-isostatic and tidal deformation is largely unknown. An important step towards model improvement is to quantify, or bound, the actual viscosity variations that characterize the mantle. Simple scaling of viscosity to shear-wave velocity fluctuations yields map-views of long-wavelength viscosity variation. These give a general quantitative description and aid in estimating the depth dependence of rheological heterogeneity throughout the mantle. The upper mantle is probably characterized by two to four orders of magnitude variation (peak-to-peak). Discrepant time-scales for rebounding Holocene shorelines of Hudson Bay and southern Iceland are consistent with this characterization. Results are given in terms of a local average viscosity ratio, Δη¯ 1 , of volumetric concentration, φ i . For the upper mantle deeper than 340 km the following reasonable limits are estimated for Δη¯ 1 ≈10−2:0.01≤φ≤0.15. A spectrum of ratios Δη¯ 1 <0.1 at concentration level φ i ≈ 10−6−10−1 in the lower mantle implies a spectrum of shorter time-scale deformational response modes for second-degree spherical harmonic deformations of the Earth. Although highly uncertain, this spectrum of spatial variation allows a purely Maxwellian viscoelastic rheology simultaneously to explain all solid tidal dispersion phenomena and long-term rebound-related mantle viscosity. Composite theory of multiphase viscoelastic media is used to demonstrate this effect. |
format |
Text |
author |
Ivins, Erik R. Sammis, Charles G. |
author_facet |
Ivins, Erik R. Sammis, Charles G. |
author_sort |
Ivins, Erik R. |
title |
On lateral viscosity contrast in the mantle and the rheology of low-frequency geodynamics |
title_short |
On lateral viscosity contrast in the mantle and the rheology of low-frequency geodynamics |
title_full |
On lateral viscosity contrast in the mantle and the rheology of low-frequency geodynamics |
title_fullStr |
On lateral viscosity contrast in the mantle and the rheology of low-frequency geodynamics |
title_full_unstemmed |
On lateral viscosity contrast in the mantle and the rheology of low-frequency geodynamics |
title_sort |
on lateral viscosity contrast in the mantle and the rheology of low-frequency geodynamics |
publisher |
Oxford University Press |
publishDate |
1995 |
url |
http://gji.oxfordjournals.org/cgi/content/short/123/2/305 https://doi.org/10.1111/j.1365-246X.1995.tb06856.x |
geographic |
Hudson Bay Hudson |
geographic_facet |
Hudson Bay Hudson |
genre |
Hudson Bay Iceland |
genre_facet |
Hudson Bay Iceland |
op_relation |
http://gji.oxfordjournals.org/cgi/content/short/123/2/305 http://dx.doi.org/10.1111/j.1365-246X.1995.tb06856.x |
op_rights |
Copyright (C) 1995, Oxford University Press |
op_doi |
https://doi.org/10.1111/j.1365-246X.1995.tb06856.x |
container_title |
Geophysical Journal International |
container_volume |
123 |
container_issue |
2 |
container_start_page |
305 |
op_container_end_page |
322 |
_version_ |
1766025736193310720 |