Magee, Craig (2011)
Ph.D. thesis, University of Birmingham.
Sub-volcanic intrusive networks, of which cone sheets are recognised as a major constituent, control volcano growth and eruption style. The accepted cone sheet model is that these confocally dipping intrusions originate from an unexposed central magma chamber through dip-parallel magma flow. However, the emplacement mechanism of cone sheets has remained poorly understood. The classic ~58 Ma cone sheet swarm of Ardnamurchan, NW Scotland, offers an excellent opportunity to further resolve the emplacement dynamics of cone sheets through studying their magma flow. Structural measurements and anisotropy of magnetic susceptibility (AMS) analyses have constrained a lateral magma flow regime, consistently oriented NW-SE, in the majority of the Ardnamurchan cone sheets. This is not consistent with previous emplacement models. In this thesis, it is suggested that emplacement of the Ardnamurchan cone sheets occurred through the deflection of laterally propagating, NW-SE trending regional dykes, sourced from laterally adjacent magmatic systems (likely the Palaeogene Mull central complex). Field observations highlight the importance of host rock structure and interference between locally compressional and regional extensional stress fields in controlling intrusion geometry. Implicitly, edifice construction and potential eruption precursors observed at a volcano may instigate, or result from, magmatic activity in laterally adjacent volcanic systems.
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