Folds, Alaska - Interpreted

The small asymmetric folds (asymmetric because the fold limbs are of different length) are the most obvious feature here. However, it may have struck you that the layering being folded is rather irregular. A close look finds the isoclinal fold hinges, and some thought then suggests that these belong to earlier folds with a different style of deformation - i.e. these are refolded folds, and the degree of deformation here rather severe. Do not be disheartened if you did not find these isoclinal folds or recognize their significance - seasoned geologists have missed such field clues. The blue lines trace out a weakly developed and spaced new tectonic foliation that was likely produced during the later folding phase (more on tectonic foliation development later in the course). The tectonic setting here is one of past subduction and terrane accretion, a setting where sedimentary rocks often have a polyphase and severe deformation history.

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