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Glacial isostatic adjustment constrains dehydration stiffening beneath Iceland
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
Nordic Volcanological Center, Institute of Earth Sciences, University of Iceland, Reykjavík, Iceland.
Institute of Earth Sciences, Section Geophysics, J. W. Goethe-University, Frankfurt am Main, Germany.
2012 (English)In: Earth and Planetary Science Letters, ISSN 0012-821X, E-ISSN 1385-013X, Vol. 359-360, 152-161 p.Article in journal (Refereed) Published
Abstract [en]

During melting in the upper mantle the preferred partitioning of water into the melt will effectively dehydrate the solid residue. Linear extrapolation of laboratory experiments suggests that dehydration can produce a sharp viscosity contrast (increase) of a factor 500 across the dry solidus. In this study we show that the suggested magnitude of dehydration stiffening in a plume–ridge setting is incompatible with the present glacial isostatic adjustment (GIA) in Iceland. Using GPS observations of current GIA in Iceland, we find that the data are best fit by a viscosity contrast over the dry solidus in the range 0.5–3. A viscosity contrast higher than 10 requires a mantle viscosity below the dry solidus lower than , depending on the thickness of the dehydrated layer. A viscosity contrast of 100 or more demands a mantle viscosity of or less. However, we show here that a non-linear extrapolation of the laboratory data predicts a viscosity contrast as low as a factor 3–29, assuming conditions of constant strain rate to constant viscous dissipation rate. This is compatible with our GIA results and suggests that the plume–ridge interaction beneath Iceland is governed by a non-linear rheology and controlled by a combination of kinematic and dynamic boundary conditions rather than buoyant forces alone.

Place, publisher, year, edition, pages
2012. Vol. 359-360, 152-161 p.
Keyword [en]
glacial isostatic adjustment, Iceland, dehydration stiffening, rheology, viscosity
National Category
Geophysics
Identifiers
URN: urn:nbn:se:uu:diva-169787DOI: 10.1016/j.epsl.2012.10.015ISI: 000312924200016OAI: oai:DiVA.org:uu-169787DiVA: diva2:507694
Available from: 2012-03-06 Created: 2012-03-06 Last updated: 2017-12-07Bibliographically approved
In thesis
1. Glacial Isostatic Adjustment: Inferences on properties and processes in the upper mantle from 3D dynamical modeling
Open this publication in new window or tab >>Glacial Isostatic Adjustment: Inferences on properties and processes in the upper mantle from 3D dynamical modeling
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Observations of glacial isostatic adjustment (GIA) offers a powerful window into the properties of the Earth's interior. Combined with dynamical modeling of the GIA process we can use the observations to infer properties such as the elastic structure of the lithosphere, the rheology of the mantle and changes in the stress conditions in the Earth. This information aids our understanding of the long term evolution of the Earth, e.g. mantle convection, but also illuminates short term processes such as magma generation, earthquakes and shoreline migration. As present day warming trends causes glacier retreat world wide, GIA offers the opportunity to gain local insight into the Earth.

In this thesis I develop an implementation of the pre-stress advection term in finite element modeling. I apply this to current GIA in Iceland, and conclude that local variations in the elastic thickness of the lithosphere can potentially be detected close to the largest ice cap. I study the magnitude of dehydration stiffening in the uppermost Icelandic mantle. The results indicate that the increase in viscosity over the dry solidus is of small magnitude, implying a non-linear rheology in the uppermost mantle beneath Iceland. The present deglaciation in Iceland causes additional melting of the mantle. I find an increased melt production rate of 100-140% at present, although the melt supply rate at the base of the lithosphere is found to be delayed, with estimated present day perturbations ranging from neglible up to 120%.

In the last section of the thesis I focus on the role of ice sheet reconstructions in GIA modeling. I compare three reconstruction of the Weichselian ice sheet and discuss similarities and difference as well as the fit to present day uplift rates in Fennoscandia. The results provide input to improvements in the ice sheet models.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2012. 83 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 906
National Category
Geophysics
Identifiers
urn:nbn:se:uu:diva-169790 (URN)978-91-554-8294-7 (ISBN)
Public defence
2012-04-20, Hamberg, Geocentrum, Villavägen 16, Uppsala, 10:00 (English)
Opponent
Supervisors
Available from: 2012-03-29 Created: 2012-03-06 Last updated: 2012-04-19Bibliographically approved

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Schmidt, PeterLund, Björn

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