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Emplacement of laboratory igneous sheets and fingers influenced by the Mohr-Coulomb properties of the host
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  • Frank Bo Buster Guldstrand,
  • Alban Souche,
  • Håvard Svanes Bertelsen,
  • Alain Zanella,
  • Olivier Galland
Frank Bo Buster Guldstrand
The NJORD Center
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Alban Souche
Physics of Geological Processes, The NJORD Center, Geosciences Department, University of Oslo, Norway
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Håvard Svanes Bertelsen
Physics of Geological Processes, The NJORD Center, Geosciences Department, University of Oslo, Norway
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Alain Zanella
Le Mans Université, Géosciences Le Mans, France
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Olivier Galland
The NJORD Center, Physics of Geological Processes

Corresponding Author:[email protected]

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Planar magma intrusions such as dykes and sills are major magma transport features and the main feeders of volcanic eruptions. Among planar intrusions, sheet intrusions are fracture-like continuous conduits, which are assumed to form by tensile opening and dominantly elastic deformation of the host. However, numerous planar intrusions are not continuous, and consist of aligned finger-shaped or more lobate conduits. Field observations show that the emplacement of these fingers is associated with inelastic, shear failure of the host rock, suggesting that the Mohr-Coulomb properties of crustal rocks play a significant role in the emplacement of fingers. In this study, we test the effects of the Mohr-Coulomb properties of crustal rocks on the emplacement of sheet-shaped and finger-shaped intrusions through quantitative 2-dimensional laboratory experiments. The model magma is viscous Golden Syrup, and the model rock is made of mixtures of dry granular materials of variable cohesion. A sideview camera allows monitoring the shape of the propagating intrusions and the associated deformation in the host, and a pressure sensor monitors the pressure of the syrup. Our experiments show that sheet intrusions form in high-cohesion hosts whereas finger-shaped intrusions form in low-cohesion hosts. Deformation analysis of the host and pressure data show that the sheets and fingers result from drastically distinct dynamics: sheets dominantly propagate as a fracture, whereas fingers are emplaced as viscous indenters. All in all, our experiments highlight that the cohesion of the Earth’s crust and the associated shear damage play a major role on planar intrusion emplacement.