Strain-induced permeability increase in volcanic rock

Jamie Farquharson (1) , Michael Heap (1) , Patrick Baud (1)

1 IPGS-GE - Géophysique expérimentale (IPGS)

The extrusion of dense, viscous magma typically occurs along pronounced conduit-parallel faults. To better understand the evolution of fault permeability with increasing strain, we measured the permeability of low-porosity volcanic rock samples (basalt and andesite) that were deformed in the brittle regime to various levels of inelastic strain. We observed a progressive increase in sample permeability with increasing inelastic strain (i.e., with continued sliding on the fault plane). At the maximum imposed inelastic strain (0.11), sample permeability had increased by 3 orders of magnitude or more for all sample sets. Microstructural observations show that narrow shear fractures evolve into more complex fracture systems characterized by thick zones of friction-induced cataclasis (gouge) with increasing inelastic strain. These data suggest that the permeability of conduit-parallel faults hosted in the rock at the conduit-wall rock interface will increase during lava extrusion, thus facilitating outgassing and hindering the transition to explosive behavior.

Domaines: Géophysique [physics.geo-ph]

Jamie Farquharson, Michael Heap, Patrick Baud. Strain-induced permeability increase in volcanic rock. Geophysical Research Letters, 2016, 43, pp.doi:10.1002/2016GL071540. ⟨hal-01473635⟩