Schofield, Nick (2009)
Ph.D. thesis, University of Birmingham.
Mafic sill complexes are increasingly being shown to play a major role in the movement of magma around the upper crust in volcanic terranes and to have a role in mass extinction events in Earth history. Most of the current models of sill emplacement assume that brittle fracture operates at all points of sill emplacement. Within this thesis, a series of observations are presented from sheet intrusions in South Africa, USA and the UK showing that in certain situations, dependent on host rock lithology, the propagation of magma through normal brittle fracture can cease. In this circumstance a prevalent fluid/fluid or fluid/ductile relationship between host rock and intruding magma is often developed. Once this occurs, the evolution of a given sheet intrusion becomes distinctly different from that produced by normal brittle fracture alone. The break down in brittle fracture often leads to the development of magma fingers, which accelerate ahead of the main sheet of magma. It is important to note that it is ultimately the host rock lithology and its coupled response to intrusion of magma that dictates the ongoing evolution of the morphology of sheet intrusions in high-level magmatic systems.
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