Hi Michael
Have you come across any reference that supports the possibility that
the brittle-ductile transition coincides with the phase change to
super-critical water?
Regards
Malcolm
On 30 Jul 2010, at 14:53, Michael Stipp wrote:
> Hi Julian,
>
> great, many thanks! I thought about making the same comment on the
> wrong use of the term "ductile". But one word in favor of Dave
> Kohlstedt and co-workers and their great 1995-review paper: They
> clearly explain it in their text, brittle-ductile denotes the change
> in deformation mode and brittle-plastic the change in dominant
> deformation mechanism. And they refer to Ernie's paper from 1986.
> So, the use of "plastic" and "ductile" does not seem to be so
> difficult. Nevertheless, many people seem to ignore it, even when it
> is corrected in a review.
>
> I always use the term plastic shear zone as synonym for mylonite
> zone, but this will probably raise the next discussion round on
> terminology.
>
> Best wishes
> Michael
>
>
>
> Julian Mecklenburgh schrieb:
>> 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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