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Tadashi Yamasaki, VU University Amsterdam (Netherlands)
Laurent Gernigon, Norges Geologiske Undersøkelse (Norway)
Carmen Gaina, Norges Geologiske Undersøkelse (Norway)
Gwenn Perron-Pinvidic, Université Louis Pasteur (France)
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The understanding of the development of continental rifts and passive margins requires a good knowledge of the processes which explain how the deformation can localized. Continental break-up is an end product of continental extension, and the break-up axis is usually extremely localized. The formation of micro-continent, which involves at least two break-up systems, is likely influenced by the migration and localization of the deformation. In this study, we investigate the influence of underplated mafic bodies (UPMB) on the style of lithospheric extension to establish a correlation between magmatism, rifting and break-up dynamics. Our main purpose is to evaluate, using a two-dimensional thermo-mechanical finite element model, the influence of the UPMB on the deformation localization. Our numerical model shows that rheological heterogeneity brought about by the UPMB is mostly influenced by two main physical effects: the UPMB material is assumed to have (1) an anomalous high temperature and (2) a mafic crustal rock composition which is intrinsically weaker than the mantle. The former effect will disappear rather quickly, but the latter still have an effect at any stage of the extension.
The UPMB strongly influences the distribution of deformation, which depends on the condition of the lithosphere at the time when the UPMB is emplaced. Since the strength contrast between the weakened and non-weakened regions is the most important factor, the UPMB works more efficiently on the strain localization for a colder uppermost mantle. Dependence of deformation localization on the temperature and thickness of the UPMB (i.e. more significant localization for the UPMB with higher temperature and greater thickness) also depends on the lithospheric conditions. However, the width of the UPMB has a strong influence on the localization for any condition of the lithosphere; a greater amount of thinning is distributed into a narrower weakened region. Such model behaviours imply that an UPMB emplaced during a drift phase has also the potential to create a new spreading centre, depending on the conditions of the lithosphere and UPMB. We discuss the results of the numerical model particularly in relation to the onset of break-up between the Jan Mayen and Møre margins.
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