HR: 13:40h
AN: V23C-01    [Abstracts]
TI: An Experimental Investigation of Sill Formation and Propagation in Layered Elastic Media
AU: Kavanagh, J L
EM: Janine.Kavanagh@bristol.ac.uk
AF: University of Bristol, Centre for Environmental and Geophysical Flows, Department of Earth Sciences, Bristol, BS8 1RJ United Kingdom
AU: * Menand, T
EM: T.Menand@bristol.ac.uk
AF: University of Bristol, Centre for Environmental and Geophysical Flows, Department of Earth Sciences, Bristol, BS8 1RJ United Kingdom
AU: Sparks, S
EM: Steve.Sparks@bristol.ac.uk
AF: University of Bristol, Centre for Environmental and Geophysical Flows, Department of Earth Sciences, Bristol, BS8 1RJ United Kingdom
AB: A series of experiments were conducted in which dyed water (a magma analogue) was intruded into solid gelatine (a crustal analogue) to investigate the formation of sills. We considered a layered gelatine system with adjacent layers having contrasting properties. By varying the density and rigidity of the gelatine we found that density variations did not control sill emplacement. Instead sills form when the upper layer is more rigid than the lower layer with intrusion in a plane directly below the interface. Dykes were observed to propagate to the surface when the Young's Modulus ratio of upper to lower gelatine layers was less than one. We observed two varieties of sill to form when the upper layer is more rigid than the lower layer, the form of the intrusion depending on the balance of driving pressures and Young's Modulus ratio of contrasting adjacent layers. When the rigidity ratio is high and there is a large driving pressure the feeder dyke completely converts to propagate as a sill. However, when the rigidity ratio and driving pressure are both close to one a dyke-sill hybrid forms. Under these conditions the sill formation is accompanied by contemporaneous dyke intrusion into the overlying more rigid layer. During sill propagation deformation structures are formed into the lower layer. Sill propagation dynamics are controlled by viscous dissipation along the length of the sill; causing acceleration with increasing length. Our study suggests that rigidity contrasts may play a major role in the location of sills and development of igneous complexes. In ancient cratonic areas the moho is a suitable site for the preferential formation of sills with higher rigidity continental crust overlying weaker mantle. Mantle plumes impacting ancient continents provide a situation in which large sills can form to fractionate prior to eruption on flood basalts. The boundary between the upper and lower crust (Conrad discontinuity) may provide a preferential focus for the emplacement of granite sills and sheets at continental arcs where the lower crust is weakened by prolonged heating and possible hydration.
DE: 8137 Hotspots, large igneous provinces, and flood basalt volcanism
DE: 8145 Physics of magma and magma bodies
DE: 8434 Magma migration and fragmentation
DE: 8445 Experimental volcanism
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005