19 April 2019

Friday fold: Angel Island “III”

Posted by Callan Bentley

It’s Friday, and that means it’s time for us to return to Angel Island, in northern San Francisco Bay, California, for more folded rocks.

Today we clamber down to Perles Beach. The rocks there are varied: serpentinite, blueschist, and meta-chert.

Here are some of the outcrops and boulders exposed there featuring folds:

The coolest thing about Perles Beach was these thoroughly recrystallized meta-cherts, with coarse reaction rims to be seen at the contact between the chert and shale protolith lithologies:

Unfortunately, I can’t speak to the identities of the various minerals involved, but if anyone is interested in querying these rocks more deeply, now you know where to find them!