| 521. |
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| 522. |
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| 523. |
- Fuchs, Lukas
(författare)
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Strain quantifications in different tectonic scales using numerical modelling
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 524. |
- Fuchs, Lukas, et al.
(författare)
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Thermo-mechanical modelling of progressive deformation and seismic anisotropy at the lithosphere-asthenosphere boundary
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Ingår i: Geophysical Journal International. - 0956-540X .- 1365-246X.
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 525. |
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| 526. |
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| 527. |
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| 528. |
- Ismail, Nazli, 1971-
(författare)
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Controlled Source Radiomagnetotelluric (CSRMT) Applications in Environmental and Resource Exploration
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- An integrated use of radio magnetotelluric (RMT) and controlled source tensor magnetotelluric (CSTMT) measurements, the so-called CSRMT method, has been employed in environmental and resource exploration studies. A number of case histories, including a groundwater investigation in glacial deposits, a study of fracture zones for geotechnical purposes and a mining exploration study of a copper deposit, are presented in this thesis in order to illustrate the usefulness and capability of the CSRMT method. The resolutions of the estimated models using various types of data are studied. Magnetotelluric transfer functions are used to analyze the dimensionality, the near surface resistivity distortions and the near field effects in the case of CSTMT data analysis. The near field effects in CSTMT data have also been identified by performing 2½D forward modelling. Data analysis, dimensionality tests and forward modelling show that at the lowest frequencies used the CSTMT transfer functions are generally distorted by source effects, except when the source-receiver distances are sufficient large compared with the penetration depth. Regarding CSTMT transfer functions, apparent resistivities are generally less distorted than phases. TM mode transfer functions are more affected by the sources than TE mode, while tipper vectors generally contain source signatures at all frequencies. Based on the analysis of dimensionality and source effects 2D inverse modelling of CSTMT and RMT data, as well as their combination, have been performed under the plane wave assumption. The RMT method proved to be a powerful tool for imaging the upper 50 m near-surface, but their penetration depth reduces as a conductive layer structures cover the targets at depth. The penetration depth can be increased by including the CSTMT data in the modelling if the measurements are in the far field range. The resolution of the deeper parts of the models may be improved by performing a joint inversion of TE and TM modes, if the strike direction is well-defined. Alternatively, inversion of determinant data can be performed, since the determinant data are less affected by 3D structures and source effects. However the resolution of the determinant models is somewhat degraded compared to the models inverted from combined TE and TM modes.
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| 529. |
- Mukhina, Elena, 1991-
(författare)
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Deep generated methane in the global methane budget
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Methane is a significant part of the global carbon cycle. The distribution of methane above and below the Earth’s surface suggests that atmospheric methane might be related to methane originating from the deep mantle.The purpose of the present study is to identify this relationship between methane emissions to the atmosphere and methane, which can be abiogenically generated within the Earth’s interior. Methane hydrates within the Earth’s surface sediments might be among the possible hosts of migrated deep methane.In this thesis, experimental work is presented, which aimed to reveal the depth at which methane and other hydrocarbons in the upper mantle are abiogenically generated, considering pT and redox conditions of the surrounding environment. High-pressure, high-temperature experiments were conducted using a large reactive volume device with a toroid-type chamber in specially prepared sample containers.The present study evaluates the formation of methane and other hydrocarbons at temperatures higher than 300 °C at pressures of 2.5-6.5 GPa despite the redox conditions of the surroundings. These conditions correspond to a depth below 70 km on the surface of a cold subducting slab.The proposed hypothesis claims that the deep-mantle-generated methane can contribute to the formation of methane hydrates and accumulation of free gas below hydrates.
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| 530. |
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