HR: 08:30h
AN: V51B-03    [PDF]
TI: Fault textures in a volcanic conduit
AU: * Tuffen, H
EM: tuffen@min.uni-muenchen.de
AF: Department of Earth and Environmental Sciences, University of Munich, Theresienstraáe 41, Munich, 80333 Germany
AU: Dingwell, D B
EM: dingwell@lmu.de
AF: Department of Earth and Environmental Sciences, University of Munich, Theresienstraáe 41, Munich, 80333 Germany
AB: Fault textures in the obsidian walls of a dissected rhyolitic conduit in Iceland record a history of fracture and healing in rising magma, and may represent fossilised hybrid and long-period volcanic earthquakes [1]. In this contribution we highlight the striking similarities between micro- and meso-scale fault textures in obsidian and those found in seismogenic tectonic faults [2,3]. The conduit walls contain networks of angular shear fractures, which are typically 0.1-2 m in length and filled with banded cataclasites generated by corner abrasion and wear on the fracture surfaces [2]. During continued flow of magma and shear deformation, these networks coalesce [4] and mature into near-planar shear bands parallel to the flow direction. Shear bands are up to 4.8 m long and several centimetres across, and slip is accommodated by distributed deformation in cohesive cataclasites and pseudotachylites. Due to the increasing cohesion of fracture-filling material during displacement, which is attributed to viscous and frictional heating, each fracture system heals, and thus has a limited seismogenic lifetime. The combination of localised slip and distributed flow textures are typical of the repetitive deformation sequences that are characteristic of seismic cycling [2,5]. Earthquakes occurring in highly-viscous magma and elsewhere in the crust are governed by similar physical processes. The material properties of the fractured medium, such as ductile-brittle behaviour, temperature-dependent viscosity and strength, are key to linking field observations and failure theory to recorded seismic events[1,6]. 1. Tuffen, H., Dingwell, D.B, Pinkerton H. (2003) Geology, in press. 2. Chester FM, Chester JS (1998) Tectonophysics 295:199-221. 3. Lin AM (1996) Eng Geol 43: 213-224. 4. Kilburn CRJ (2003) J Volcanol Geotherm Res 125:271-289. 5. Beeler NM et al. (2001) Bull Seis Soc Am 91:1797-1804. 6. Neuberg J, Tuffen H, Jolly A, Green D (2003) Abstract, Fall AGU 2003.
DE: 5104 Fracture and flow
DE: 7209 Earthquake dynamics and mechanics
DE: 7280 Volcano seismology (8419)
DE: 8419 Eruption monitoring (7280)
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting