Fold in Franciscan Melange, California Coast

The small veins within the chert layer suggest brittle layer-parallel extension occurred in this layer. The intervening lithic arenites change their thickness, as can be seen in the one hinge area traced in blue, and this suggests that material is behaving more ductilely. The two different layers are mechanically different. The smaller folds in the thinner beds also suggests bedding thickness is also playing a role here in the specific structural development. The overall tectonic setting here was that of a subduction zone, and this is actually quite mild deformation for this area.

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