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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