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 continents, leading to the formation of new oceanic floor between the two continental plates. Although the concept of continental rifting is accepted within the scientific community, it is still debated what con...
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| Format: | Thesis |
| Language: | English |
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2008
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| Online Access: | https://eprints.soton.ac.uk/66263/ https://eprints.soton.ac.uk/66263/1/Armitage_2008_PhD.pdf |
| Summary: | Rifting is the process that leads to the formation of oceans. Rifting is the break up of continents, leading to the formation of new oceanic floor between the two continental plates. Although the concept of continental rifting is accepted within the scientific community, it is still debated what controls the volume and composition of igneous material generated at these constructive plate boundaries. Here I present the results of dynamic modelling of rifted margins. I have explored the consequences of margin and mantle structure on the melt generated during continental extension and breakup. The central aim is to understand how melting affects the rifting of continents, especially in the North Atlantic. In order to understand the enigmatic melt production observed around the North Atlantic various tools are developed for interpreting the model output. These are predictions of primary major element composition of the melt, rare-earth element composition of the melt, predictions of the crystallised mid-oceanic ridge basalt composition 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 no prior thinning produces little melt during breakup. The Southeast Greenland margin rifted 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. This thermal anomaly is not a plume, rather an exhaustible thermal layer that has drained along the sub-lithospheric topography from a distal plume. The melts generated are high in MgO, and depleted in TiO. They are depleted in rare-earth elements. This would lead to high seismic velocities within the underplate being, as observed off Southeast Greenland. |
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