Micromechanisms of shear zone propagation at the brittle-viscous transition

Florian Fusseis*, Mark Handy

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract / Description of output

Our investigation of progressively strained rock samples from the margins of greenschist-facies shear zones utilizes a space-for-time approach to reveal how the mylonitic overprint of metapsammitic and -pelitic host rocks at the Cap de Creus involved brittle fracturing. We present a set of microscale observations indicating that microfractures formed immediately prior to or coevally with a fine-grained mylonite. Microfracturing dominated early stages of strain localization on the scale of the shear zones. On the microscale, centimeter-long fractures facilitated strain softening by allowing enhanced fluid access, thereby accelerating the dynamic recrystallization of quartz and a metamorphic reaction of biotite. As these two processes produce a polyphase matrix of small, dislocation-poor grains that eventually form an interconnected, rheologically weak phase, fractures become inactive. This represents a strain-dependent brittle–viscous transition. We outline this transition in a conceptual model for the rheological evolution of mid-crustal shear zones.
Original languageEnglish
Pages (from-to)1242-1253
Number of pages12
JournalJournal of Structural Geology
Volume30
Issue number10
DOIs
Publication statusPublished - 1 Oct 2008

Keywords / Materials (for Non-textual outputs)

  • Brittle-Ductile
  • Brittle-Viscous
  • Cap de Creus
  • Shear zone propagation
  • Shear zones
  • Strain localization

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