Michael and Ernie
The argument is very simple.
It is well known that the continental crust is permeable to great
depths. (See CE Manning & SE Ingebritsen 'Permeability of the
Continental Crust: Implications of Geothermal Data and Metamorphic
Systems in Reviews of Geophysics 37,1 Feb 1999. Also same authors in
Geology 27, 12. 1107-1110 Dec. 1999.)
The phase diagram for water shows the Critical Point to be at
temperature 374 deg. K and pressure 22.064 MPa.
This critical point is affected by the presence of CO2 and NaCl in
varying concentrations.
The normal lithostatic pressure and temperature gradients will enter
this supercritical realm at about 10 kilometers depth, close to the
postulated brittle-ductile transition zone. Therefore it is a
reasonable thought that the presence of supercritical water is a
possible cause of that transition.
It has been experimentally proved that NaCl in solution alters the
critical point of water, ionises it and results in a vigorous
supercritical fluid solvent action almost as potent as HF.
As brine gets buried to depths in excess of 10 km. it will enter the
supercritical domain and affect the rock components it is in contact
with.
This relationship deserves experimental investigation by those with
access to the appropriate equipment.
Regards
Malcolm.
On 30 Jul 2010, at 17:40, Michael Stipp wrote:
> Malcolm,
> I have also no idea, how the brittle-ductile transition could
> coincide with the phase change to super-critical water. Let me know
> what you find out about it.
>
> Ernie, thank you for the very quick answer for me!
>
> Michael
>
>
>
> Malcolm McClure schrieb:
>> Ernie
>>
>> Take a look at Robert O Fournier's paper 'Hydrothermal Processes
>> related to Movement of Fluid From Plastic into Brittle Rock in the
>> Magmatic Epithermal Environment' in Economic Geology 94 : 8 1193
>> - 1210 December 1999.
>>
>> I'll get back on how this relates to supercritical water.
>>
>> Regards
>>
>> Malcolm.
>>
>>
>>
>> On 30 Jul 2010, at 16:23, Ernest Rutter wrote:
>>
>>> There is absolutely no reason why such a correlation could exist,
>>> neither is there an evidence for it.
>>> Ernie Rutter
>>>
>>> -----Original Message-----
>>> From: Tectonics & structural geology discussion list [mailto:[log in to unmask]
>>> ] On Behalf Of Malcolm McClure
>>> Sent: 30 July 2010 16:15
>>> To: [log in to unmask]
>>> Subject: Re: Ductilitis
>>>
>>> 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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