title: Fragmentation of wall rock garnets during deep crustal earthquakes.
abstract: Fractures and faults riddle the Earth's crust on all scales, and the deformation associated with them is presumed to have had significant effects on its petrological and structural evolution. However, despite the abundance of directly observable earthquake activity, unequivocal evidence for seismic slip rates along ancient faults is rare and usually related to frictional melting and the formation of pseudotachylites. We report novel microstructures from garnet crystals in the immediate vicinity of seismic slip planes that transected lower crustal granulites during intermediate-depth earthquakes in the Bergen Arcs area, western Norway, some 420 million years ago. Seismic loading caused massive dislocation formations and fragmentation of wall rock garnets. Microfracturing and the injection of sulfide melts occurred during an early stage of loading. Subsequent dilation caused pervasive transport of fluids into the garnets along a network of microfractures, dislocations, and subgrain and grain boundaries, leading to the growth of abundant mineral inclusions inside the fragmented garnets. Recrystallization by grain boundary migration closed most of the pores and fractures generated by the seismic event. This wall rock alteration represents the initial stages of an earthquake-triggered metamorphic transformation process that ultimately led to reworking of the lower crust on a regional scale.
authors.affiliation: Physics of Geological Processes, Department of Geosciences, University of Oslo, P. O. Box 1048 Blindern, N-0316 Oslo, Norway.
authors.forename: Håkon
authors.identifier: 0000-0002-8521-4547
authors.initials: H
authors.lastname: Austrheim
authors.affiliation: Physics of Geological Processes, Department of Geosciences, University of Oslo, P. O. Box 1048 Blindern, N-0316 Oslo, Norway.
authors.forename: Kristina G
authors.identifier: 0000-0002-4100-381X
authors.initials: KG
authors.lastname: Dunkel
authors.affiliation: Department of Earth Sciences, Utrecht University, Budapestlaan 4, NL-3584 CD Utrecht, Netherlands.
authors.forename: Oliver
authors.initials: O
authors.lastname: Plümper
authors.affiliation: Géosciences Montpellier, UMR CNRS-UM2 5243, CC 60, Université de Montpellier, 34095 Montpellier Cedex 05, France.
authors.forename: Benoit
authors.identifier: 0000-0001-7635-9288
authors.initials: B
authors.lastname: Ildefonse
authors.affiliation: Department of Earth Sciences, Utrecht University, Budapestlaan 4, NL-3584 CD Utrecht, Netherlands.; Debye Institute for Nanomaterials Science, Utrecht University, Princetonplein 1, 3584 CC Utrecht, Netherlands.
authors.forename: Yang
authors.identifier: 0000-0002-0750-7571
authors.initials: Y
authors.lastname: Liu
authors.affiliation: Physics of Geological Processes, Department of Geosciences, University of Oslo, P. O. Box 1048 Blindern, N-0316 Oslo, Norway.
authors.forename: Bjørn
authors.initials: B
authors.lastname: Jamtveit
keywords: Earthquake; crystal-plastic deformation; mass transfer; wall-rock damage