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 language | English |
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Pages (from-to) | 1242-1253 |
Number of pages | 12 |
Journal | Journal of Structural Geology |
Volume | 30 |
Issue number | 10 |
DOIs | |
Publication status | Published - 1 Oct 2008 |
Keywords / Materials (for Non-textual outputs)
- Brittle-Ductile
- Brittle-Viscous
- Cap de Creus
- Shear zone propagation
- Shear zones
- Strain localization