Awesome Dug!
At 01:46 AM 01/06/03 -0400, you wrote:
>At 09:23 PM 2001/06/01 +0100, John Milsom wrote:
>>...
>>There IS an asymmetry. East facing subduction zones (western Pacific,
>>Caribbean, Scotia) seem to have a tendency to migrate outwards
>>('roll-back'). West facing zones (Pacific coasts of the Americas) seem to
>>be locked to their continental margins. First working hypothesis would be
>>that the asymmetry in the Earth's rotation (it goes one way, not the other)
>>has something to do with it.
>
>At 09:22 PM 2001/06/02 +0100, John Milsom wrote:
>>... I can't believe that no-one has looked at this,
>>perhaps back as far as when they were rubbishing Wegener. ...
>
>Sir Harold Jeffreys, in the several editions of his influential textbook
>"The Earth", was the chief rubbisher of Wegener's idea of "Westwanderung" -
>westward drift of continents due to tidal drag by the moon and sun.
>Jeffreys argued that the force of tidal drag (calculated from the rate of
>slowing of the earth's rotation) was much too small to cause shearing
>strain within the upper mantle. But his value for mantle viscosity was much
>too large - it was based on a false premise that the
>larger-than-hydrostatic part of the earth's measured ellipticity was due to
>a lag time (~10 million years) in readjusting its shape to the slowing of
>its rate of rotation (and consequent lessening of centripetal force).
> In the 1970's Robert Bostrom, George Moore and others revived the idea of
>tidal drag as an important driving force of plate tectonics. This time Tom
>Jordan was the chief rubbisher - he calculated that in order for a rigid
>lithosphere to be tidally dragged westward at typical plate-tectonic
>velocity the asthenosphere would have to be no more viscous than honey.
>Moore and others countered that the asthenosphere does not shear at
>constant velocity - instead the plates wriggle westward like caterpillars
>as the tidal bulges propagate through them twice every day from east to
>west. But leading geodynamicists were not persuaded, and the prevailing
>geodynamic consensus does not explain why so-called "slab roll-back" is
>most prevalent on west-dipping slabs, nor why earthquakes are virtually
>absent in polar regions, nor why deep-focus earthquakes are concentrated at
>low latitude, nor why the Antarctic Plate is bounded by so many
>left-lateral transform faults, nor why east-dipping slabs dip so shallowly
>under North and South America.
>
>Dugald M Carmichael Phone/V-mail: 613-533-6182
>Dept of Geological Sciences and Geological Engineering
>Queen's University FAX: 613-533-6592
>Kingston ON K7L3N6 E-mail: [log in to unmask]
>
David R.M. Pattison, Department of Geology and Geophysics,
University of Calgary, Calgary, Alberta, T2N 1N4, Canada.
Phone: 403-220-3263 (my office); 403-220-5841 (dept. office)
Fax: 403-284-0074 email: [log in to unmask]
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