2 April 2010

Baked fanglomerate

Posted by Callan Bentley

A quick post to share a few images of an outcrop I visited last September out in California’s Owens Valley. This is a spot where alluvial fans coming off the eastern Sierra Nevada were overrun by a basaltic lava flow (Jeff, Kim, Fred, and Kurt for scale):

contact_meta_sub_lavaflow02

The unofficial term for these conglomerates deposited by alluvial fans is “fanglomerate,” and it’s pretty cool to see the contact metamorphism at the top of the fanglomerate. There’s also some weakly-developed columnar jointing in the basalt. Here’s an annotated version, in case the contact wasn’t quite obvious enough:

contact_meta_sub_lavaflow02_anno

Here’s a close up (Doug for scale), showing the orange zone of thermal metamorphism at the top of the fanglomerate as the lava flow above baked the hell out of it:

contact_meta_sub_lavaflow01

Groovy, eh? Where’s your favorite example of contact metamorphism?