Dear All:
I'd like to make it clear that tectonic overpressure results from flow
(strain rate) and viscosity of the material. A higher tectonic
overpressure does not necessarily mean a higher differential
stress. Rock strength will limit the magnitude of the differential
stress the rock can support. Rock can support any overpressure.
In fact the rock doesn't know if the pressure is due to overburden or
due to flow and viscosity.
Dazhi
On 4 Nov 99, at 17:05, Eric Essene wrote:
> All,
> Mancktelow is the person who asserted to me that the coesite bearing
> metamorphic rocks all formed under high deviatoric stresses and therefore
> not at 90 km depths. However, I mentioned to him that coesite has been
> found in dolomitic marbles at Dabie Shan, and that these rocks could not
> support significant tectonic overpressures, so that argument cannot be
> incorrect.
> Eric
>
>
>
> Dear All:
> >
> >Thank you for the feedback. I particularly thank Robert Schmid
> >who introduced me to Mancktelow (1993, J. Metamorphic Geol).
> >The question I asked was raised by Mancktelow in that paper. I
> >quote the following from the paper:
> >
> >"Although the influence of deviatoric stress on the effective
> >pressure during metamorphic reaction was much discussed prior to
> >the 1970s, the potential implications have been almost totally
> >ignored since that time. The implicit assumption has been made
> >that pressure estimated from geobarometry can be converted
> >directly to depth according to P=density*g*depth ......"
> >
> >So we need independent ways to estimate the depth of a
> >tectonometamorphic event to demonstrate the significance or
> >insignificance of tectonic overpressure.
> >
> >Dazhi
>
>
>
>
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