HR: 0800h
AN: V11A-0358    [Abstracts]
TI: Insights Into the Mechanisms of Shallow Dike Intrusions Through Particle Code Modelling
AU: * Mongrain, J C
EM: ftjcm1@uaf.edu
AF: Geophysical Institute, University of Alaska Fairbanks, 903 Koyukuk Drive, Fairbanks, AK 99775, United States
AU: Ord, A
EM: alison.ord@csiro.au
AF: CSIRO Exploration and Mining, Australian Resources Research Centre (ARRC) 26 Dick Perry Avenue Kensington, Perth, WA 6151, Austria
AB: Volcanic eruptions are assumed to result from an intruding dike reaching the surface. A conduit is simply the same dike pathway used repeatedly to transport magma over a longer time period. Consequently, understanding the mechanism of dike intrusion at shallow depths is critical to our ability to predict volcanic eruptions. Until recently it was commonly assumed that most dikes were feeders to eruptions, however, recent field based studies have suggested that many more dikes are intruded than ever reach the surface. Almost all previous dike work has focused on the problem of buoyant dike propagation through a combination of analytical studies and gelatine experiments. However, these studies are not generally applicable at shallow depths where buoyancy may play a lesser role. The few shallow depth studies have considered only the static elastic stress state of the country rock prior to intrusion and its impact on the direction of dike propagation. The critical brittle behaviour, the impact of the intrusion itself on the local stress field and the potential damage to the country rock are ignored. This study uses a particle code to investigate intrusion behaviour at shallow depths through weak sandstones and strong granites. Starting from small models calibrated with laboratory tests, an upscaled set of models with dimensions of 500x100m are used to investigate intrusion behaviour under lithostatic, compressional and extensional regimes. The model results show observed field relations such as microfracturing and dike jointing and a scale dependence to fracture toughness. In addition, the intrusions in most of the models do not readily propagate towards the surface. This study is of interest to those in volcanology and also mineral exploration as the evolving microfractures develop permeable pathways for volatile escape from the intrusion.
DE: 5104 Fracture and flow
DE: 8439 Physics and chemistry of magma bodies
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting