Fragmentation of wall rock garnets during deep crustal earthquakes

Håkon Austrheim, Kristina G. Dunkel, Oliver Plümper, Benoit Ildefonse, Yang Liu, Bjørn Jamtveit

Research output: Contribution to journalArticleResearchpeer-review

38 Citations (Scopus)

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.

Original languageEnglish
Article numbere1602067
Number of pages7
JournalScience Advances
Volume3
Issue number2
DOIs
Publication statusPublished - 2017
Externally publishedYes

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