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Title: The thermomechanical evolution of transform continental margins
Author: Gadd, Sandra Anne
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1995
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Transform continental margins form as a result of sea floor spreading and new ocean basin formation. Their evolution can be divided into four distinct phases (continent-continent shearing; continent-ocean shearing; ridge passing; and continent-ocean passive), the early phases involving active shearing, while in the final phase, oceanic and continental lithosphere are in passive contact across the transform boundary. Different thermal and mechanical factors influence the margin evolution in each of these phases. Transform continental margins have been much less well studied and are consequently less well understood than either rifted continental margins or oceanic fracture zones, related tectonic features, and the development of models to describe their evolution is in its infancy. The further development of evolutionary models is therefore essential to gain a more complete understanding of the margin forming processes involved. A 2D numerical thermomechanical model for transform continental margin evolution, which significantly improves upon previous models, is presented. The model can be used to calculate the evolution of the thermal structure and topography at any point along a margin of any length, with any spreading rate. The resultant uplift and subsidence across the margin, in response to thermal expansion and contractions, is calculated throughout the margin evolution assuming both local and regional isostasy for a variety of different lithospheric strengths (represented by Te, the effective elastic thickness of the lithosphere). The effects of sub-aerial erosion of the continental lithosphere are considered, and the continent-ocean boundary is modelled as being mechanically decoupled during the active shearing phases, and as either mechanically coupled or mechanically decoupled during the passive phase. The appropriate differential equations are solved numerically using the finite difference method. The model results have been compared to preliminary interpretations of geophysical data from a section of the Ivory Coast-Ghana margin and to previously published observations from other margins. Results are presented for five points along a margin of length L=900km for both slow (v=1cm/yr) and moderate (v=4cm/yr) spreading rates. The evolution of the topography at each of these points is investigated for a variety of different values of Te. Significant continental thermal uplift is calculated to occur as a result of the phases of continent-ocean shearing and ridge passing. Lateral variations in the magnitude and lateral extent of continental uplift along the margin length are predicted for each set of model parameters.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available