Folds II

Advanced Tectonics
James S. Aber


Folds in Crystalline Rocks

Tight, near isoclinal folds with small crenulations. Surface displays glacial grooves. Manhattan Schist, Central Park, New York City. Keys for scale.
Strong shearing and stretching of folds leads to foliated banding, Manhattan Schist, Central Park, New York City.
Folds in Ordovician phyllite, Highway 17, southeastern New York.
Complex, irregular folding is evident in these rocks of the Hudson Highlands, I-84, eastern New York.
Multiple phases of deformation create such refolded structures in the Hudson Highlands, I-84, eastern New York.
Extremely stretched folds and foliation. Notice the "hook" structure (just below sunglasses); this is all that remains of a strongly sheared fold. Hudson Highlands, I-84, eastern New York.
Notice the small folds either side of the fault that runs through the center of view. These are "drag" folds created by movement along the fault. Hudson Highlands, I-84, eastern New York.
Another example of drag folds next to a fault, which is marked by a pegmatite zone. Hudson Highlands, I-84, eastern New York.
Folded dike (dark rock) in schist. Knitting needle marks fold axix. Appalachian piedmont "basement" strata, Lake Murray spillway, South Carolina.
Folded dike (dark rock) in schist. Dike is broken by quartz veins filling gash (tension) fractures. Scale is 6 inches (15 cm) long.
Style of folds varies from layer to layer. Thin layers display much smaller, irregular folds compared to thicker layers. Silva compass for scale. Crystalline bedrock, island of Herdla, near Bergen, western Norway.
Overturned folds with thinning and detachment of the lower limb. Notice differences in fold size depending on layer thickness. Silva compass for scale. Crystalline bedrock, island of Herdla, near Bergen, western Norway.
Thinner layers display overturned kink folds; whereas thick layers are offset by small faults. Silva compass for scale. Crystalline bedrock, island of Herdla, near Bergen, western Norway.
Intensely folded amphibolite (dark) with light colored layers and boudins. Scale pole is 2 m long. Near Haugesund, western Norway.
Huge boudins (light-colored bodies) formed by intensive folding and stretching of the rock mass. Paleozoic schist, near Mérida, Andes Mountains, Venezuela.

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Notice: Advanced tectonics is presented for the use and benefit of students enrolled at Emporia State University. Others are welcome to view the course webpages. Any other use of text, imagery or curriculum materials is prohibited without permission of the instructor. All text and images © J.S. Aber (2014).