Wednesday, October 12, 2011

Mt Baker

In my previous post, I mentioned that on a Rodeo Holiday we went up to Heather Meadows on the Mt. Baker Highway. While we were there, we ran into a High School Geology class and the instructor pointed out to me that even though we couldn't see any mountains, there was some notable geology under foot.

Basically the canyon that forms drains Bagley Lake is a fault. On the west side of the lake is the Chilliwack River Terrane an accreted island arc, and on the east side are Mt. Baker Andesites. The Bagley Lakes trail parallels this drainage and crosses over a small dam, where you can see the difference in rocks from one side to the other.

Sam Looking at Mt. Baker Andesites

Sam Looking at Chilliwack Terrrane
  According to the USGS website on the Chilliwack Terrain, it is mostly phyllites and Greenstones that are thrust over the younger Nooksack Terrane.

Before the Chilliwack River terrane was thrust over the Nooksack terrane, its beds were folded upside down.
From: Terranes of the North Cascades: Chilliwack River Terrane
We saw a couple of nice metamorphic rocks on our hike. Admittedly the weather wasn't conducive to finding the best examples (and I am not great at identifying metamorphic rocks), but there were three areas that had distinctly different outcrops

Greenstone with quarts veins
Not sure with this one, originally thought it was a different metaconglomerate, but then thought about a fault Breccia, didn't know if that made sense. Help?
Though I certainly saw the difference between the rocks, I was in "Look at the Mountain and Glacial Features mode" so I'm not sure if I would have put together the drainage was a contact between terranes. So thank you to the unnamed HS teacher I met. It certainly made more sense to look at rocks than mountains on that foggy day.

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