Paul
Doesn't the very shape of a boudin preclude pure shear in the strict sense,
be it chocolate tablet or otherwise?
Brett
-----Original Message-----
From: Paul Evins <[log in to unmask]>
To: [log in to unmask] <[log in to unmask]>
Date: Wednesday, 1 September 1999 6:28
Subject: another vote for quasipurish shear
>Hi all,
>I do not think metamorphic rocks should always exhibit a lineation by
>default. I couldn't find more than 20 or so mineral lineations in my old,
>400 km2, granulite/upper amphibolite facies study area in the Superior
>province. These were confined to a special, 3km2 unit. Instead,
>mesostructures in the area are dominantly boudinage. These boudinage are
>practically equidimensional in the xy plane (ie. nice chocolate
>tablets).Check out the attached photo of Pierre Robin admiring a larger
>wavelength boudin mold with internal casts of smaller wavelength boudins.
>Furthermore, assymetric folds are absent. The only way I can envisage this
>group of structures forming is by dominant pure shear. As with Juergen, I
>admit that nothing in nature is ever pure except nature itself, so I
suppose
>there is some simple shear going on there. I just can't see it. Once again,
>this all depends on scale. This area may just represent a patch dominated
>by pure shear. Any comments from the photo?
>
>Paul M. Evins W tele# +358 8 553 1481
>University of Oulu FAX# +358 8 5531484
>Dept. of Geology
>PL 3000 email: [log in to unmask]
>
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