8 September 2016

Tension gashes in Malmesbury metasediments near Sea Point Contact

Posted by Callan

While en route to the Sea Point migmatite contact last week, I saw some lovely quartz-filled tension gashes in the Malmesbury Group metasediments adjacent to the contact with the Cape Granite. These en echelon tension gash arrays speak of tremendous stresses ripping and stretching these rocks, often in complicated patterns where blocks moved relative to their neighbors, and the strain was taken up in these brittle/ductile arrays of ‘stretch marks’. Here are three examples, worthy of inclusion in a structural geology textbook:

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Annotated versions of the same three photos:

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Nothing like a little structural geology to get the blood flowing on a Thursday morning, amiright? Enjoy!