Strain-induced permeability increase in volcanic rock

Jamie I. Farquharson (1, 2) , Michael J. Heap (1, 2) , Patrick Baud (1, 2)

1 EOST - Ecole et Observatoire des Sciences de la Terre
2 IPGS - Institut de physique du globe de Strasbourg

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.

Mots clés: permeability; triaxial deformation; outgassing; lava domes; gouge; fault generation

Domaines: Planète et Univers [physics]

Jamie I. Farquharson, Michael J. Heap, Patrick Baud. Strain-induced permeability increase in volcanic rock. Geophysical Research Letters, 2016, 43, pp.11,603-11,610. ⟨10.1002/2016GL071540⟩. ⟨insu-03707560⟩