Deformation of the lithopshere during the formation of continental rifted margins



Jeanniot, Ludovic
Deformation of the lithopshere during the formation of continental rifted margins. PhD thesis, University of Liverpool.

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Abstract

This thesis investigates lithosphere and asthenosphere deformation during intracontinental rifting leading to breakup and seafloor spreading initiation. Continental rifted margins results from the separation of a continental crust after lithosphere stretching and thinning, but their observations are poorly related to lithosphere and asthenosphere deformation. The strategy of my thesis is to use a kinematic modelling approach to examine the formation of magma-poor rifted margins. Decompressional melting is also predicted. The kinematic model consisting of pure-shear for the 15km upper brittle seismogenic lithosphere above buoyancy driven upwelling divergent flow (UDF) is used to advect temperature and material. A series of numerical experiments using this hybrid deformation model explores the conditions under which mantle exhumation is possible within the Ocean-Continent Transition (OCT) of magma-poor rifted margins. Mantle exhumation is possible and can persist over a long period of time by using a combination of shallow decoupling depth between pure-shear and UDF, narrow pure-shear region, slow spreading rate, no buoyancy and low asthenosphere temperature. However, the application of this hybrid deformation model to specific rifted margins cannot explain their thermal and subsidence evolution and complex architecture if the mode of lithosphere deformation does not evolve. A kinematic finite element model is therefore used to generate a sequence of lithosphere deformation events. The lithosphere deformation mode is similar to the previous hybrid mode but consists of (1) pure-shear induced passive upwelling and (2) buoyancy induced upwelling which is used to speed up lithosphere thinning. Each lithosphere deformation event has specific event timing, pure-shear width, half-spreading rate, buoyancy upwelling rate and lateral deformation migration. This kinematic model is applied to the present-day Iberia-Newfoundland and the fossil analogue Alpine Tethys rifted margins. Pure-shear widths and lateral deformation migration are constrained by the crustal architecture of the observed rifted margin. Lateral migration of deformation produce an asymmetry of their conjugate. Conversely, the event timing, half-spreading and buoyancy rates are constrained by the subsidence and melting generation histories and observed mantle exhumation. The pure-shear width evolves from wide to narrow and the half-spreading rate increases during rifting leading to continental breakup. Buoyancy upwelling plays an important role at the beginning of rifting. Melt retention is required to permit mantle exhumation.

Item Type: Thesis (PhD)
Additional Information: Date: 2014-10 (completed)
Depositing User: Symplectic Admin
Date Deposited: 03 Sep 2015 15:04
Last Modified: 19 Sep 2022 10:53
DOI: 10.17638/02014504
URI: https://livrepository.liverpool.ac.uk/id/eprint/2014504