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Modelling sea floor spreading initiation and rifted continental margin formation V Tymms (1) & iSIMM Team (1) Department of Earth Sciences, Liverpool University, 4 Brownlow Street, Liverpool L69 3GP, UK [email protected] Recent observations of depth dependent (heterogeneous) stretching where upper crustal extension is much less than that of the lower crust and lithospheric mantle at both non-volcanic and volcanic margins plus the discovery of broad domains of exhumed continental mantle at non-volcanic rifted margins are not predicted by existing quantitative models of rifted margin formation which are usually based on intra-continental rift models subjected to very large stretching factors. New conceptual and quantitative models of rifted margin formation are required. Observations and continuum mechanics suggest that the dominant process responsible for rifted continental margin formation is sea-floor spreading of the young ocean ridge, rather than pre-breakup intra-continental rifting. Simple fluid flow models of ocean ridge processes using analytical iso-viscous corner-flow demonstrate that the divergent motion of the upwelling mantle beneath the ocean ridge, when viewed in the reference frame of the young continental margin, shows oceanward flow of the lower continental crust and lithospheric mantle of the young rifted margin giving rise to depth dependent stretching as observed. Single-phase fluid-models have been developed to model the initiation of sea-floor spreading and the thermal, stretching and thinning evolution of the young rifted continental margin. Finite element fluid-flow modelling incorporating the evolving temperature dependent viscosity field on the fluid flow also show depth dependent stretching of the young continental margin. Two-phase flow models of ocean ridges incorporating the transport of both solid matrix and melt fluid (Spiegelman & Reynolds 1999) predict the divergent motion of the asthenosphere and lithosphere matrix, and the focusing of basaltic melt into the narrow axial zone spreading centre at ocean ridges. We are adapting two-phase flow models for application to the initiation of sea-floor spreading and rifted continental margin formation. iSIMM investigators are V Tymms, NJ Kusznir, RS White, AM Roberts, PAF Christie, N Hurst, Z Lunnon, CJ Parkin, AW Roberts, LK Smith, R Spitzer, A. Davies and A. Surendra, with funding from NERC, DTI, Agip UK, BP, Amerada Hess Ltd., Anadarko, Conoco, Phillips, Shell, Statoil, and WesternGeco. V Tymms1, NJ Kusznir1, RS White2, AM Roberts3, PAF Christie4, N Hurst1, Z Lunnon2, CJ Parkin2, AW Roberts2, LK Smith2, R Spitzer2 1 Department of Earth Sciences, Liverpool University, 4 Brownlow Street, Liverpool L69 3GP 2 Bullard Laboratories, Cambridge University, Madingley Rd, Cambridge CB3 0EZ 3 Badleys,,North Beck House, Hundleby, Spilsby, Lincs. PE23 5NB. 4 Schlumberger Cambridge Research, High Cross, Madingley Road, Cambridge CB3 0EL