The Duke Quarry
The Duke Quarry in 1928, three years after its purchase. Image: Duke University Archives.
Duke University is a private university with a strong reputation. It is located in Durham, North Carolina. The campus has a distinctive "Old World" look with its gothic architecture, and many movies and television series have filmed there. Duke gets all its exterior building stone from a quarry near Hillsborough in Orange County, NC, that they purchased 85 years ago. Here's a Duke Magazine feature on the quarry: "By the numbers." This seems like a pretty clever move to me: they end up owning the source of their own stone, and that allows them to "brand" the rock used as unique to Duke. The university has found brick to be six times as cost-effective for modern campus additions, though they're still finding ways to integrate "Duke Stone" in those buildings too, as this nice little video explains (RealPlayer video).
After checking out other metavolcanics in the North Carolina Piedmont, Rob took us to see the Duke Quarry. It's pretty cool: a big operation, with lots of interesting rock about. Here's a view from one of the active walls, looking out over the semi-vegetated quarry (with Rob in the middle distance):
Piles of the rock await Duke architects and stonemasons:
The rock itself is a meta-volcanic assemblage, metamorphosed to phyllite. Original volcanic clasts can be seen, stretched out parallel to the foliation:
So the deal here is that these are ~andesitic island arc volcanics, originally erupted out in the Iapetus Ocean somewhere. Later, they were accreted to the edge of the Laurentian continent (ancestral North America). There, they were squished and squeezed during Appalachian mountain-building during the Paleozoic. I don't know any ages for this particular unit: if anyone can supply either a crystalization age or a metamorphic age, I'd be interested to hear it. Please leave it in the comments section below, along with any published references I should read.
The color of the clasts and the matrix varies quite a bit from one area of the quarry to another.
In a couple of places, I was delighted to find bedding/foliation relationships exposed. Here, you can see bedding as ~horizontal layers in the photo (look for the grain size change):
And here it is again, a bit more explicitly (you're looking at the plane of foliation):
A lovely rock. I want to learn more about it...