Here’s another sight at the Eocene dikes site in Bluegrass Valley, Virginia, mentioned yesterday:
That’s a gorgeous fault breccia, emplaced parallel to bedding, and parallel to the felsic dike (which can be found a few feet to the west / right of these photos):
It was very poorly lithified, shockingly crumbly to the touch, considering the big slab of rock downhill (to the right) of it.
Here’s a link to the site on Google Maps if you want to visit it yourself.
I once visited a weathered kimberlite dike that looked something like this. Are you sure it is not an intrusive breccia, perhaps powered by volatiles related to the local igneous dikes?
Totally possible. I am not sure about anything. I like your idea a lot – it’s literally five feet away from the felsite sill.