Working Group E

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Experimental Programme Working Group E:

Why magma moves through the crust and mantle (dynamics)

Modelling of dyke intrusions will explore the reasons behind dyke geometry and the repeat timing of the intrusions. To investigate dyking in a rift environment like Afar, fluid will be injected into gelatine and the gelatine subjected to extensional deformations (pulled apart in different directions). The increase in density with depth in the Earth's crust can be modelled by adding salt to the gelatine layers. The lab experiments will also be compared with information from the field and numerical models.

Thermal modelling of the crust and mantle will determine the conditions of magma creation and evolution. The results from groups A–D will be used to test and develop a model of magma creation and movement in the crust in an extensional environment. An aim of this modelling will be to calculate the variations in density, composition and temperature in the crust and the compositions of magmas that erupt.

Numerical modelling of rift segmentation will explore the reasons why rift segmentation occurs and what it tells us about the physical nature of the crust. When the crust is extended (pulled apart), it does so by faulting near the surface and by ductile flow at greater depth (a similar effect can be seen when pulling a Mars Bar apart - the chocolate breaks, whilst the caramel stretches). When the crust is extended a lot, partial melting occurs. This melt separates from the surrounding rocks and, because it is lighter, rises up through the crust. Computer modelling can be used to see how, in 3D how deformation is localised in the processes of melt segregation and dyking. The models will be constrained with and tested against results from the other working groups.

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Small silicic cones at northern end of the Dabbahu segment. Dabbahu itself is the hill in the distance. Photograph by Tim Wright, January 2006.