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 of<br/>continents, leading to the formation of new oceanic floor between the two continental<br/>plates. Although the concept of continental rifting is accepted within the scientific<br/>community, it is still debated what controls the volume and composition of igneous<br/>material generated at these constructive plate boundaries. Here I present the results<br/>of dynamic modelling of rifted margins. I have explored the consequences of margin<br/>and mantle structure on the melt generated during continental extension and breakup.<br/>The central aim is to understand how melting affects the rifting of continents, especially<br/>in the North Atlantic. In order to understand the enigmatic melt production observed<br/>around the North Atlantic various tools are developed for interpreting the model output.<br/>These are predictions of primary major element composition of the melt, rare-earth<br/>element composition of the melt, predictions of the crystallised mid-oceanic ridge basalt<br/>composition and the seismic velocity of the lower crust.<br/>The thickness of the lithosphere has a very large impact on the subsequent rifting style.<br/>Extension of a 125 km thick thermally and rheologically defined lithosphere that has no<br/>prior thinning produces little melt during breakup. The Southeast Greenland margin<br/>rifted above a pre-thinned lithosphere and at initial fast half spreading rates. Further-<br/>more, to generate the thickness, chemistry and seismic velocities observed off this margin,<br/>rifting was coincident with the arrival of a 50 km thick, 200 ?C thermal anomaly. This<br/>thermal anomaly is not a plume, rather an exhaustible thermal layer that has drained<br/>along the sub-lithospheric topography from a distal plume. The melts generated are high<br/>in MgO, and depleted in TiO. They are depleted in rare-earth elements. This would<br/>lead to high seismic velocities within the underplate being, as observed off Southeast<br/>Greenland.

Name dc:type.qualificationname

Ph.D.

Level dc:type.qualificationlevel

doctoral

Grantor dc:publisher.institution

University of Southampton

Year dc:date.issued

2008

Author dc:creator

• Armitage, John J.