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The effect of the salt viscosity on future evolution of the Gorleben salt diapir, Germany
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
Institute of Earth Sciences, Section Geophysics J. W. Goethe-University, Frankfurt am Main, Germany.
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
2009 (English)In: Tectonophysics, ISSN 0040-1951, E-ISSN 1879-3266, Vol. 473, no 3-4, 446-456 p.Article in journal (Refereed) Published
Abstract [en]

The Gorleben diapir, which has been targeted for radioactive waste disposal, contains large blocks of anhydrite. Numerical models that   depict the geometrical configuration of the Gorleben diapir are used to understand internal structure of diapir caused by movement of the anhydrite blocks for various salt rheologies. It is shown that the   theology of the salt plays a significant role in how and at which rate   the anhydrite blocks sink within the diapir. The mobility of anhydrite   blocks depends on the effective viscosity of salt which has to be lower   than threshold value of around 10(18)-10(19) Pa s. Decreasing salt   viscosity allows the previously "stationary" anhydrite blocks to sink.   If the effective viscosity of salt in post-depositional stage of the Gorleben diapir falls below this threshold value, induced internal flow   due to the present anhydrite layer might disturb any repository within the diapir.

Place, publisher, year, edition, pages
2009. Vol. 473, no 3-4, 446-456 p.
Keyword [en]
Salt, Diapir, Anhydrite, Gorleben, Deformation, Rheology
National Category
Earth and Related Environmental Sciences
Identifiers
URN: urn:nbn:se:uu:diva-97537DOI: 10.1016/j.tecto.2009.03.027ISI: 000269287000012OAI: oai:DiVA.org:uu-97537DiVA: diva2:172523
Available from: 2008-09-03 Created: 2008-09-03 Last updated: 2017-12-14Bibliographically approved
In thesis
1. Modeling internal deformation of salt structures targeted for radioactive waste disposal
Open this publication in new window or tab >>Modeling internal deformation of salt structures targeted for radioactive waste disposal
2008 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis uses results of systematic numerical models to argue that externally inactive salt structures, which are potential targets for radioactive waste disposal, might be internally active due to the presence of dense layers or blocks within a salt layer.

The three papers that support this thesis use the Gorleben salt diapir (NW Germany), which was targeted as a future final repository for high-grade radioactive waste, as a general guideline.

The first two papers present systematic studies of the parameters that control the development of a salt diapir and how it entrains a dense anhydrite layer. Results from these numerical models show that the entrainment of a dense anhydrite layer within a salt diapir depends on four parameters: sedimentation rate, viscosity of salt, perturbation width and the stratigraphic location of the dense layer. The combined effect of these four parameters, which has a direct impact on the rate of salt supply (volume/area of the salt that is supplied to the diapir with time), shape a diapir and the mode of entrainment. Salt diapirs down-built with sedimentary units of high viscosity can potentially grow with an embedded anhydrite layer and deplete their source layer (salt supply ceases). However, when salt supply decreases dramatically or ceases entirely, the entrained anhydrite layer/segments start to sink within the diapir. In inactive diapirs, sinking of the entrained anhydrite layer is inevitable and strongly depends on the rheology of the salt, which is in direct contact with the anhydrite layer. During the post-depositional stage, if the effective viscosity of salt falls below the threshold value of around 1018-1019 Pa s, the mobility of anhydrite blocks might influence any repository within the diapir. However, the internal deformation of the salt diapir by the descending blocks decreases with increase in effective viscosity of salt.

The results presented in this thesis suggest that it is highly likely that salt structures where dense and viscous layer/blocks are present undergo an internal deformation processes when these dense blocks start sinking within the diapir. Depending on size and orientation of these blocks, deformation pattern is significantly different within the diapir. Furthermore, model results applied to the Gorleben diapir show that the rate of descent of the entrained anhydrite blocks differs on different sides of the diapir. This suggests that if the anhydrite blocks descent within the Gorleben diapir, they initiate an asymmetric internal flow within it.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2008. 48 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 551Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 551
Keyword
salt, diapir, anhydrite, deformation, entrainment, numerical modeling, rheology, sinking, Gorleben
Identifiers
urn:nbn:se:uu:diva-9279 (URN)978-91-554-7281-8 (ISBN)
Public defence
2008-09-30, Axel Hambergsalen, Geocentrum, Villavägen 16, Uppsala, 10:00
Opponent
Supervisors
Available from: 2008-09-03 Created: 2008-09-03Bibliographically approved

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