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Strain quantifications in different tectonic scales using numerical modelling
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Mineralogy Petrology and Tectonics.
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis focuses on calculation of finite and progressive deformation in different tectonic scales using 2D numerical models with application to natural cases. Essentially, two major tectonic areas have been covered: a) salt tectonics and b) upper mantle deformation due to interaction between the lithosphere and asthenosphere.

The focus in salt tectonics lies on deformation within down-built diapirs consisting of a source layer feeding a vertical stem. Three deformation regimes have been identified within the salt: (I) a squeezing channel flow underneath the overburden, (II) a corner flow underneath the stem, and (III) a pure channel flow within the stem. The results of the model show that the deformation pattern within the stem of a diapir (e.g. symmetric or asymmetric) can reveal information on different rates of salt supplies from the source layer (e.g. observed in Klodowa-diapir, Poland). Composite rock salt rheology results in strong localization and amplification of the strain along the salt layer boundaries in comparison to Newtonian rock salt. Flow and fold structures of passive marker lines are directly correlated to natural folds within a salt diapir.

In case of the upper mantle, focus lies on deformation and resulting lattice preferred orientation (LPO) underneath an oceanic plate. Sensitivity of deformation and seismic anisotropy on rheology, grain size (d), temperature (T), and kinematics (v) has been investigated. The results of the model show that the mechanical lithosphere-asthenosphere boundary is strongly controlled by T and less so by v or d. A higher strain concentration within the asthenosphere (e.g. for smaller potential mantle temperatures, higher plate velocities, or smaller d) indicates a weaker coupling between the plate and the underlying mantle, which becomes stronger with the age of the plate. A Poiseuille flow within the asthenosphere, significantly affects the deformation and LPO in the upper mantle. The results of the model show, that deformation in the upper mantle at a certain distance away from the ridge depends on the absolute velocity in the asthenosphere. However, only in cases of a driving upper mantle base does the seismic anisotropy and delay times reach values within the range of natural data.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2016. , 58 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1354
Keyword [en]
Deformation modelling, progressive and finite deformation, salt tectonics, down-built diapir, upper mantle, lithosphere-asthenosphere boundary, seismic anisotropy, plate-mantle (de)coupling
National Category
Geology Geosciences, Multidisciplinary
Research subject
Earth Science with specialization in Mineral Chemistry, Petrology and Tectonics
Identifiers
URN: urn:nbn:se:uu:diva-280759ISBN: 978-91-554-9513-8 (print)OAI: oai:DiVA.org:uu-280759DiVA: diva2:911946
Public defence
2016-05-04, Hambergsalen, Geocentrum, Villavägen 16, Uppsala, 10:00 (English)
Opponent
Supervisors
Available from: 2016-04-11 Created: 2016-03-15 Last updated: 2016-04-12
List of papers
1. Numerical modeling on progressive internal deformation indown-built diapirs
Open this publication in new window or tab >>Numerical modeling on progressive internal deformation indown-built diapirs
2014 (English)In: Tectonophysics, ISSN 0040-1951, E-ISSN 1879-3266, Vol. 632, 111-122 p.Article in journal (Refereed) Published
Abstract [en]

A two-dimensional finite difference code (FDCON) is used to estimate the finite deformationwithin a down-builtdiapir. The geometry of the down-built diapir is fixed by using two rigid rectangular overburden unitswhich sinkinto a source layer of a constant viscosity. Thus, the model refers to diapirs consisting of a source layerfeeding a vertical stem, and not to other salt structures (e.g. salt sheets or pillows). With this setup westudy the progressive strain in three different deformation regimes within the “salt” material: (I) a squeezedchannel-flow deformation regime and (II) a corner-flow deformation regime within the source layer, and(III) a pure channel-flow deformation regime within the stem. We analyze the evolution of finite deformationin each regime individually, progressive strain for particles passing all three regimes, and total 2Dfinite deformationwithin the salt layer. Model results show that the material which enters the stem bears inherited strainaccumulated from the other two domains. Therefore, finite deformation in the stem differs from the expectedchannel-flow deformation, due to the deformation accumulated within the source layer. The stem displays ahigh deformation zone within its center and areas of decreasing progressive strain between its center and itsboundaries.High deformation zoneswithin the stemcould also be observedwithin natural diapirs (e.g. Klodowa,Polen). The location and structure of the high deformation zone (e.g. symmetric or asymmetric) could revealinformation about different rates of salt supplies from the source layer. Thus, deformation pattern could directlybe correlated to the evolution of the diapir.

Place, publisher, year, edition, pages
Elsevier, 2014
Keyword
Numerical modeling, Salt tectonics, Progressive and finite deformation, Differential loading
National Category
Geosciences, Multidisciplinary Geology
Research subject
Earth Science with specialization in Mineral Chemistry, Petrology and Tectonics
Identifiers
urn:nbn:se:uu:diva-237448 (URN)10.1016/j.tecto.2014.06.005 (DOI)000343378500009 ()
Available from: 2014-12-02 Created: 2014-12-02 Last updated: 2017-12-05Bibliographically approved
2. Numerical modeling of the effect of composite rheology on internal deformation in down-built diapirs.
Open this publication in new window or tab >>Numerical modeling of the effect of composite rheology on internal deformation in down-built diapirs.
2015 (English)In: Tectonophysics, ISSN 0040-1951, E-ISSN 1879-3266, Vol. 646, 79-95 p.Article in journal (Refereed) Published
Abstract [en]

A two-dimensional finite difference code (FDCON) is used to estimate the progressive deformation and the effect of a composite rheology, i.e., Newtonian combined with non-Newtonian, on finite deformation patterns within a down-built diapir. The geometry of the diapir is fixed using two rigid rectangular overburden units which sink into a source layer of a certain viscosity. We have analyzed the progressive deformation within the entire salt layer for a composite rheology and compared them to a standard model with Newtonian rheology (ηs = 1018 Pa s). The composite rheology models show a more complex deformation patterns in comparison to the standard model. Deformation is more localized within the source layer, leaving a broader less deformed zone within the middle of the source layer. In comparison to the standard model, ellipticity (R) of the strain ellipse is amplified by a factor of up to three in high deformation regions with a finite deformation f larger than two (f = log10(R)). Initially vertical and horizontal passive marker-lines within the salt layer, are folded during salt movement. Initially horizontally-oriented marker-lines in the source layer show upright folds within the middle of the stem. Within the source layer, initially vertical marker-lines form recumbent folds, which are refolded during their flow from the source layer into the stem. During their refolding, the hinge of the fold migrates outward towards the flank of the diapir. A temporal and spatial hinge migration is observed for sub-horizontal folds that originated in the source layer as they are refolded. We have also studied both the effect of curved versus sharp corners between the source layer and the stem on strain evolution within both the feeding source layer and the down-built diapir. Strain evolution and hinge migration are strongly influenced by the geometry of the corner between the source layer and the stem.

Keyword
Numerical modeling; Salt tectonics; Composite rheology; Newtonian and non-Newtonian rheologies; Progressive and finite deformations; Differential loading
National Category
Geosciences, Multidisciplinary
Research subject
Earth Science with specialization in Mineral Chemistry, Petrology and Tectonics
Identifiers
urn:nbn:se:uu:diva-240805 (URN)10.1016/j.tecto.2015.01.014 (DOI)000352184200006 ()
Available from: 2015-01-08 Created: 2015-01-08 Last updated: 2017-12-05Bibliographically approved
3. Thermo-mechanical modelling of progressive deformation and seismic anisotropy at the lithosphere-asthenosphere boundary
Open this publication in new window or tab >>Thermo-mechanical modelling of progressive deformation and seismic anisotropy at the lithosphere-asthenosphere boundary
(English)In: Geophysical Journal International, ISSN 0956-540X, E-ISSN 1365-246XArticle in journal (Other academic) Submitted
Abstract [en]

   Deformation at the lithosphere-asthenosphere boundary is strongly governed by its effective viscosity, which depends on temperature, strain rate, and grain size. Moreover, deformation can cause lattice preferred orientation resulting in seismic anisotropy and shear wave splitting. We used a 1D model approach to calculate shear strain and characteristic depths for an oceanic plate as a function of age. We assume a composite rheology (dislocation and diffusion creep) in combination with a half-space cooling model temperature field for constant and variable thermal parameters, and different potential mantle temperatures. Systematically, sensitivity of characteristic depths, deformation pattern, and seismic delay times δt on temperature, plate velocity, steady state grain size, and rheology have been analyzed. Model results show that the characteristic depths are only affected by local variations in the temperature field or a shift in the dominant deformation mechanism. The other parameters, however, do strongly affect the maximum total shear strain. Due to a continuous simple shear of the upper mantle governed by the motion of the plate, anisotropy, thickness of the anisotropic layer, and δt reach relatively large values in comparison to observed data. However, a small amount of dislocation creep (25-40 %), due to a modified rheology or small grain sizes, leads to a significantly thinner anisotropic layer. As a result, δt is reduced by 50 % or more. The change of the characteristics of the anisotropic layer and degree of its anisotropy may reflect and be of significance for the viscous (de)coupling between the lithosphere and asthenosphere.

National Category
Geology Geosciences, Multidisciplinary
Research subject
Earth Science with specialization in Mineral Chemistry, Petrology and Tectonics
Identifiers
urn:nbn:se:uu:diva-280694 (URN)
Available from: 2016-03-14 Created: 2016-03-14 Last updated: 2017-11-30
4. Thermo-mechanical modelling of progressive deformation at the lithosphere-asthenosphere boundary: The effect of a horizontal pressure gradient
Open this publication in new window or tab >>Thermo-mechanical modelling of progressive deformation at the lithosphere-asthenosphere boundary: The effect of a horizontal pressure gradient
(English)Manuscript (preprint) (Other academic)
National Category
Geology Geosciences, Multidisciplinary
Research subject
Earth Science with specialization in Mineral Chemistry, Petrology and Tectonics
Identifiers
urn:nbn:se:uu:diva-280695 (URN)
Available from: 2016-03-14 Created: 2016-03-14 Last updated: 2016-04-11

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