Saturday, December 14, 2013

Geo 365: Dec. 14, Day 348: Sheared Breccia

Looking more closely at roughly the center of yesterday's photo, the shearing across the rock is more apparent. I can't with any confidence pick out a single clast that's been cut and offset by one of these faults, but there's one I'm suspicious about, just above the center. This is roughly equivalent to the cracked pebbles I had hoped to see at Humbug Mountain, but these aren't pebbles: they're mostly cobbles and boulders, with some finer material in the interstices. It's also much more of a monolithic source material than that of Humbug. It looks like basalt, but I didn't look carefully enough to be certain. On top of that, again like Humbug Mountain conglomerate, this material has been somewhat metamorphosed. Though it isn't terribly apparent at this scale, the stringers of secondary minerals are sticking out from the rock face, indicating they're more resistant to weathering and erosion than the host rock. As I said yesterday, I suspect it's mostly quartz.

I tried a couple of processing steps to see if I could un-muddy this, but wasn't content. Auto level was too stark, and didn't bring out any more detail. Then I darkened that substantially, which I thought was an improvement. Below are those results:
Top photo unmodified, others processed as described. May 7, 2013. FlashEarth location.

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