5 April 2019

Friday fold: Angel Island “I”

Posted by Callan Bentley

As mentioned last week, I’m part of a team updating the beloved “Streetcar to Subduction” field guide to San Francisco geology in time for AGU’s Centennial year and the return of the AGU Fall Meeting to San Francisco. Today I’d like to share another fold we saw in our Bay Area field work last month. This shows metalliferous cherts (perhaps due to nearby deep-sea black smokers?) that have undergone deformation (folding, faulting) and blueschist-facies metamorphism as a result of subduction and accretion to the western edge of the North American continent during the late Mesozoic:

I love the super-high contrast of these layers; it really helps the visiting geologist lock on to the deformational patterns.

A few close-ups:

I hope this gorgeous outcrop gets your Friday off to a great start! Have a terrific weekend!