10 June 2016

Friday fold: Mesoscopic structures in the Lightning Creek Schist

Posted by Callan

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There are some structural goodies here at the confluence of the Rapid River and the Salmon River in west-central Idaho. I visited these outcrops three weeks ago on a field trip after the Rocky Mountain section meeting of GSA. The rocks are the Lightning Creek Schist, a schist that’s part of the Wallowa Terrane, an accreted chunk of crust that docked with western North America during the Mesozoic.

Here is the trace of foliation:

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And here it is folded, with a few veins thrown in for good measure:

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Folded vein at center:

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This next one has a lot of structure going on…

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Now let’s zoom in to three areas of that image for some close-ups:

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Nearby, there was some sweet boudinage to be seen with a vein segment:

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Note the blocky bottom margin of the vein and the way the foliation warps upward into the boudin neck:

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Two views of a fold expressed partly in 3D:

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A small squidge’um nearby:

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Next up, a big vein catches the attention, but then let’s zoom in to the recess just above it…

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And let’s close with this lovely isoclinal fold…

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That should satisfy your appetite for deformation for at least an hour or so. Happy Friday!