Posts Tagged ‘structural’

Answer Tuesday #3

(Sorry today’s post is so late–I was working on a few other things and time just ran away from me.)

The EQ&V #3 post depicted Iceland, whose volcanism is due to both spreading at the Mid-Atlantic Ridge and a hotspot.   I’ve labeled the various bodies on land on the GoogleEarth image:

For Structure #2, the fold is comprised of two main lithologies: a sandstone and a shale.   The sandstone is distinctly more competent than the shale layer (its the lighter colored layer on the image & the one that stands out because the shale weathers more easily).   I’ve marked a section of it with a yellow X.   As for how many strike & dip measurements a geologist would need to determine the fold axis orientation, there’s the minimum answer (2) and what I would consider the “enough to compensate for error” answer (6).   If only two measurements are taken, they should be on the two different limbs (if six, three per limb would be good).   I’ve marked on the image in yellow with strike & dip symbols where I would likely take the six measurements.   In this case, it was much easier to take measurements on the competent sandstone then the very fissable shale.

Once you have the measurements, you would then plot them on a stereonet and where the traces intersect, that would be the fold axis.

(taken from: http://www.chipr.sunysb.edu/eserc/summereducationalinterns/linda/foldstereo.gif)

(I would have plotted up actual data from the fold itself, but magically, I can’t find my original data at the moment.)


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