Folds, Faults, and Joints

1. A fold is a bend in rock. Folds show up best in layered rock, but also occur in unlayered rock such as granite.

Image scanned from Thompson & Turk, (1992). Earth Science and the Environment. 1992, Orlando, Florida: Harcourt & Brace, p. 191.

2. A fault is a fracture along which rock on one side has moved relative to rock on the other side. A joint is a fracture without movement of rock. Joints and faults often occur as sets of many parallel fractures.

Image scanned from Thompson & Turk, (1992). Earth Science and the Environment. 1992, Orlando, Florida: Harcourt & Brace, p. 192.

3. An anticline is a fold arching upward, a syncline is a fold arching downward. The sides of these folds are called limbs. Where the two limbs meet is called the axis.

Image scanned from ESU class handout.

4. A non-plunging fold is a fold where the axis does not tilt at an angle.

Image scanned from ESU class handout.

5. A plunging fold is a fold where the axis tilts at an angle.

6. A monocline is a special kind of fold with only one limb.

Image scanned from ESU class handout.

7. A circular or elipticle anticline resembling an inverted bowl is called a dome. Sedimentary layering dips away from the center of a dome in all directions. A similarly shaped syncline is called a basin. Domes and basins can be small structures a few kilometers in diameter or less, but commonly are much larger. Large domes and basins result from regional warping of the entire continental crust.

Image scanned from Thompson & Turk, (1992). Earth Science and the Environment. 1992, Orlando, Florida: Harcourt & Brace, p. 194.


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