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Geological Society, London, Special Publications; 2007; v. 282; p. 157-172;
DOI: 10.1144/SP282.8
© 2007 Geological Society of London

The Iberia-Newfoundland continental extensional system (dynamic modelling)

A dynamic model of rifting between Galicia Bank and Flemish Cap during the opening of the North Atlantic Ocean

D. L. Harry1 & S. Grandell2

1 Department of Geosciences, Colorado State University, Fort Collins, CO 80523-1482, USA (e-mail: dharry{at}cnr.colostate.edu)
2 Department of Geology, Adams State College, Alamosa, CO 81102, USA

A finite-element model is used to simulate Late Jurassic–Early Cretaceous rifting between the Flemish Cap and Galicia Bank continental margins. The model results show that variations in the thickness of the continental crust on these margins at wavelengths greater than about 75 km can be explained as a consequence of the interaction of two pre-existing weaknesses in the lithosphere. A weakness in the crust, attributed to structural fabrics in the Variscan front, controls the location of crustal extension during the early stages of rifting in the model. This results in formation of a broad rift basin similar to the Galicia Interior Basin. A deep-seated weakness located 110 km further west, attributed to the thick crust beneath the central Variscan Orogen, controls the location of mantle necking. Extension in this region is initially diffuse, but accelerates and becomes more focused with time. Approximately 13 million years after rifting begins, the locus of crustal extension shifts from the region of pre-weakened crust into the region of pre-weakened mantle. This marks the end of subsidence in the Galicia Interior Basin and the onset of subsidence in the Flemish Cap and Galicia Bank marginal basins. Extension in these areas continues for another 12 million years before continental breakup. The asthenosphere does not ascend to depths shallow enough for decompression melting to begin until less than 5 million years before the onset of sea-floor spreading. The model predicts that all late-stage synrift magmatism during this period is limited to within 45 km of the rift axis, and production of melt thicknesses greater than 2 km is restricted to within 35 km of the rift axis. Mantle potential temperatures of 1250–1275 °C, ~5–30 °C cooler than normal, result in 3.1–4.5 km-thick oceanic crust at the time of breakup, in general agreement with the 2–4 km thick crust observed adjacent to these margins.