3 September 2016

Viewing the Sea Point migmatite through the lens of GigaPan

Posted by Callan

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It was five years ago when I first visited Sea Point, the outcrop on the coast of the Cape Peninsula where the Cape Granite (~540 Ma) intrudes the (meta-)sedimentary rocks of the Malmesbury Group. The outcrop is (a) beautiful and evocative, and (b) of historical importance, as Charles Darwin visited it while on the voyage of the Beagle, contemplating and confirming Lyell’s assertions of the validity of plutonism as he walked on these very rocks. This is a migmatite that formed due to the injection of porphyritic felsic magma between bedding planes of the sedimentary rock, cooking them thoroughly in the process. Migmatites can also form due to anatexis – the partial melting of a rock, but that’s not the case here. Rather than one rock splitting into two components (fractionating), this is two components merging to create one composite zone of swirling mixed-up rock.

I revisited the site this week during the IGC meeting in Cape Town, toting along two geologist friends who hadn’t seen it previously. I brought the GigaPan. Here are the images that resulted.

First, some still shots to give you the flavor of this classic granitic lit-par-lit injection:

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A close-up of the porphyritic texture defined by potassium feldspar megacrysts in the Cape Granite:

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Now for the GigaPans! Enjoy exploring the site from the comfort of your computer, tablet, or phone.

Link GigaPan by Callan Bentley

Link GigaPan by Callan Bentley

A relatively homogenous sill of Cape Granite located a few hundred meters away:
Link GigaPan by Callan Bentley

Here is a sample of Cape Granite (much fresher, and phaneritic rather than porphyritic)  I collected last time I was in South Africa, 5 years ago:
Link GigaPan by Callan Bentley

And, finally, one more shot of the lovely migmatitic injection textures:
Link GigaPan by Callan Bentley