Dear All,
Prompted by the recent emails about Shear Zones. I am always surprised
about how much incorrect use words such as ductile is about in the
literature.
<rant>
Ductile is a non-localised distributed deformation it says nothing about
the deformation mechanism
Brittle to ductile transition is the transition from localised to
distributed deformation with an increase in pressure.
The transition from Cataclatic deformation to thermally activated
deformation with depth in the Earth is not the brittle to ductile
transition. But cataclatic to thermally activated transition is a bit of
a mouthful so what about other options. The suggestion of the
seismogenic transition is ok what about brittle-plastic transition or
brittle-viscous transition. There is no consensus on this apart from
that most people incorrectly use the brittle-ductile transition. Even
Kohstedt et al. (1995) get it wrong (see fig1).
Ernie published a paper on this in the 80's but everybody seems to
ignore it. See Rutter (1986).
I do not like the term ductile shear zone as it is an oxymoron ductile
implies distributed deformation but shear zone implies localised. A much
better term would be plastic shear zones.
</rant>
All the best
Julian
KOHLSTEDT, D. L., EVANS, B. & MACKWELL, S. J. 1995. Strength of the
lithosphere: constraints imposed by laboratory experiments. Journal of
Geophysical Research 100(B9), 17,587-17,602.
RUTTER, E. H. 1986. On the Nomenclature of Mode of Failure Transitions
in Rocks. Tectonophysics 122(3-4), 381-387.
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