Modelling the controls on melt generation during continental extension and breakup

Rifting is the process that leads to the formation of oceans. Rifting is the break up ofcontinents, leading to the formation of new oceanic floor between the two continentalplates. Although the concept of continental rifting is accepted within the scientificcommunity, it is still debated what controls the volume and composition of igneousmaterial generated at these constructive plate boundaries. Here I present the resultsof dynamic modelling of rifted margins. I have explored the consequences of marginand mantle structure on the melt generated during continental extension and breakup.The central aim is to understand how melting affects the rifting of continents, especiallyin the North Atlantic. In order to understand the enigmatic melt production observedaround the North Atlantic various tools are developed for interpreting the model output.These are predictions of primary major element composition of the melt, rare-earthelement composition of the melt, predictions of the crystallised mid-oceanic ridge basaltcomposition and the seismic velocity of the lower crust.The thickness of the lithosphere has a very large impact on the subsequent rifting style.Extension of a 125 km thick thermally and rheologically defined lithosphere that has noprior thinning produces little melt during breakup. The Southeast Greenland marginrifted above a pre-thinned lithosphere and at initial fast half spreading rates. Further-more, to generate the thickness, chemistry and seismic velocities observed off this margin,rifting was coincident with the arrival of a 50 km thick, 200 ?C thermal anomaly. Thisthermal anomaly is not a plume, rather an exhaustible thermal layer that has drainedalong the sub-lithospheric topography from a distal plume. The melts generated are highin MgO, and depleted in TiO. They are depleted in rare-earth elements. This wouldlead to high seismic velocities within the underplate being, as observed off SoutheastGreenland