11 January 2013

Friday fold: Hoerikwaggo Trail 5

Posted by Callan

And so now it’s Friday, and our Hoerikwaggo Trail series comes to a close in the only way it appropriately can: with a look at the folds of Table Mountain.

Table Mountain is in the Cape Fold Belt. Here’s a Google Map “terrain view” wherein I’ve highlighted the strike of strata (or maybe it’s the trend of the fold axes; same orientation):

Note the two distinct orientations: a roughly north-south trend on the west, and then a roughly east-west trend in the south.

Cape Town is at the “corner” where these two trends meet.

Based on this, and based on the mesa-like appearance of Table Mountain, I didn’t expect to see any deformation on our hike. A local geologist informed me that there was much less deformation in the Table Mountain area because it was underlain by the strong pluton of the Cape Granite, and that protected the overlying strata like an undercarriage.

And, indeed, as we walked along, at first everything seemed more or less horizontal and undisturbed. But then I began noticing anomalies…

This photo shows the scene looking south along the western shore of False Bay, back towards Cape Point. There’s a subtle, open fold there. See it?

Then I saw this…

Whoa….

That’s some serious folding, and the presence of flat-lying strata above suggests a drag fold below a thrust fault, or perhaps a duplex structure.

Here’s another one, seen later that same day. This looks like a fold at the tip of a small thrust fault…

You know, the classic “ramp and flat” structure we see in fold and thrust belts the world over, including the one where I live.

Here’s another one, close by:

This was the largest-scale fold I saw. Two perspectives: first, looking north towards Table Mountain…

Second, the next day, from the ridge above Orangekloof, looking back to the south:

Thanks for hiking along with me this week. Happy Friday, and put the Hoerikwaggo Trail on your bucket list!