HR: 0800h
AN: V11A-0374    [Abstracts]
TI: Experimental Modeling of the Formation of Saucer-Shaped sills
AU: * Galland, O
EM: olivier.galland@fys.uio.no
AF: Physics of Geological Processes, University of Oslo, Sem Selands vei 24, Oslo, NO-0316, Norway
AU: Planke, S
EM: planke@vbpr.no
AF: Physics of Geological Processes, University of Oslo, Sem Selands vei 24, Oslo, NO-0316, Norway
AU: Planke, S
EM: planke@vbpr.no
AF: Volcanic basin Petroleum Research, Gaustadalléen 21, Oslo, NO-0349, Norway
AU: Malthe-Sorenssen, A
EM: malthe@fys.uio.no
AF: Physics of Geological Processes, University of Oslo, Sem Selands vei 24, Oslo, NO-0316, Norway
AB: Many magma intrusions in sedimentary basins are sills, and especially saucer-shaped sills. These features are observed in many places (i.e. South Africa; the Norwegian and North Sea; Siberia; Argentina). Sand injectites exhibit similar geometries. The occurrence of such features in so various settings suggests that their emplacement results from fundamental processes in sedimentary basins. To understand such processes, we performed experimental modeling of saucer-shaped sill emplacement. The experiments consist of injecting a molten low viscosity vegetable oil (model magma) at a constant flow rate into a fine-grained Coulomb silica flour (model rock). When the oil starts intruding, the initially flat surface of the model inflates and forms a smooth dome. At the end of the experiment, the oil erupts at the edge of the dome. After the experiment, the oil cools and solidifies, the resulting solid intrusion is unburied and exposed, and its upper surface digitalized. For our purpose, we did our experiments without external deformation. We performed two series of experiments with varying depth of injection. The first series consisted of injection into a homogeneous medium. The resulting intrusions were cone-sheets and dykes. The second series consisted of heterogeneous models where the heterogeneity was a weak layer made of a flexible net. The resulting intrusions were made of (1) a horizontal basal sill emplaced along the weakness, and (2) inclined sheets nucleating at the edges of the basal sill and propagating upward and outward. The inclined sheets exhibited a convex shape, i.e. a decreasing slope outward. In addition, the deeper the sills emplaced, the larger they were. Our experimental results are consistent with saucer-shaped features in nature. We infer from our results that the transition between the basal sills and the inclined sheets results from a transition of emplacement processes. We suggest that the basal sill emplace by open (mode I) fracturing, whereas the inclined sheets result from shear (mode II) fracturing, i.e. along faults at the edge of the dome.
DE: 8020 Mechanics, theory, and modeling
DE: 8145 Physics of magma and magma bodies
DE: 8445 Experimental volcanism
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting