Abstract
We conducted a series of experiments on granitoid cataclasites under mid-crustal conditions (Pc~500MPa, T=300°C) and slow displacement rates (10-8ms-1<d<10-7ms-1) i.e. within an order of magnitude of plate tectonic velocities. The samples reach high peak strength (1250<1375MPa) then weaken slightly (by ~40MPa) and continue to deform without any abrupt stress drops up to a γ of ~4. Microstructural observations show, that at peak strength nanocrystalline (mean grain size ~34nm, smallest crystalline particles ~8nm) to partly-amorphous material develops. Weakening occurs once this material is abundant enough to form through going anastomozing slip zones where the strain partitions. During higher strain deformation, deformation localizes further and 1 to 2 multiply connected layers of fragment loaded amorphous material develop. This material shares many similarities with naturally occurring pseudotachylites, however was formed at velocities up to 8 orders of magnitude slower than those calculated for earthquakes (~1ms-1). We conclude that the use of pseudotachylites as indicators for paleoseismic events should be reconsidered.
Original language | English (US) |
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Pages (from-to) | 299-310 |
Number of pages | 12 |
Journal | Earth and Planetary Science Letters |
Volume | 355-356 |
DOIs | |
State | Published - 2012 |
Bibliographical note
Funding Information:Funding by the Swiss National Foundation Grant no. 200020-129976 is thankfully acknowledged.
Keywords
- Brittle-plastic transition
- Experimental rock deformation
- Fault rocks
- Microstructures
- Pseudotachylite
- Semi-brittle flow