Fractures & Faults I

Advanced Tectonics
James S. Aber


Fractures, Fissures, and Joints

Pegmatite vein (center) fills a fracture in the Svaneke granite, island of Bornholm, Denmark.
Pegmatite vein in Hammer granite, Dalegård quarry, island of Bornholm, Denmark (Jørgart 1977). Notice the large quartz and feldspar crystals of the pegmatite (right of staff).
Basaltic dike (left) and granite (right), island of Bornholm, Denmark. The basalt intruded a fracture in the granite--see closeup views below.
Closeup view of dike/granite contact. Rapid cooling of magma in the dike margin led to quick crystallization and a fine-grained (aphanitic) texture.
Closeup view of dike center. Slow cooling allowed growth of large crystals to create a phaneritic texture.
Joh's Chapel, a deep cleft on the sea cliff, island of Bornholm, Denmark. The cleft has formed by erosion and removal of mafic dike rock from between walls of granite (Jørgart 1977).
Vertical sea cliff marks one side of the eroded dike at Joh's Chapel, island of Bornholm, Denmark.
Tiny fissure (joint) in granite, island of Bornholm, Denmark. The fissure is filled with sandstone that represents marine transgression over the basement surface. The sandstone in fissure is equivalent to overlying lower Cambrian Balka sandstone (Jørgart 1977).
Closeup view of sandstone filling small fissure in granite, island of Bornholm, Denmark.
Nexø arkosic sandstone, basal Cambrian strata, Gadeby, island of Bornholm, Denmark (Bruun-Petersen 1977). Well-defined joints are utilized to quarry the rock for building stone.
Vertical joints (columnar joints) formed during cooling of Tertiary intrusion in the Basin, Chisos Mountains, Big Bend National Park, western Texas.
The "window" is the drainage outlet for the the Basin, Chisos Mountains, Big Bend National Park, western Texas. Erosion of a fault zone has created the cleft with a 100-foot dropoff on the far side.

Microstructures

Clockwise shearing of a mafic (dark) body in gneiss. Note stretched out "tails" and the pods of white crystals formed in pressure "shadows" adjacent to tails. Coin is approx. 1 inch (2½ cm) in diameter. Geological Survey of Canada, Paper 90-17, Fig. 48.
Clockwise shearing of felsic (light) pod in gneiss. Note thin tails rotated out of the pod. Coin is approx. 1 inch (2½ cm) in diameter. Geological Survey of Canada, Paper 90-17, Fig. 46.
Clockwise shearing of small (red) pod within gneiss with pressure shadows (white) on either side. Coin is approx. 1 inch (2½ cm) in diameter. Geological Survey of Canada, Paper 90-17, Fig. 62b.
Clockwise shearing produced overturned and stacked small folds in gneiss. Coin is approx. 1 inch (2½ cm) in diameter. Geological Survey of Canada, Paper 90-17, Fig. 77b.

Landslides and Slumps

Police Point landslide, Cypress Hills, southeastern Alberta, Canada. This landslide developed on a north-facing slope in the 1960s. This view shows the top, still undisturbed surface, above the landslide.
Police Point landslide. Slumped and rotated blocks to left; undisturbed surface to right. Trees are tilted but still growing in the upper portion of the landslide.
Lower portion of the landslide displays more extensive disruption of the surface with ridges of exposed bedrock (cobble gravel).
Old (mid-Holocene) landslide surface at Nine Mile Creek, Cypress Hills, southeastern Alberta, Canada. The distinctly ridged surface of a landslide is clearly visible.
Tilted ledges of sandstone bedrock are exposed in an old landslide in Medicine Lodge Coulee, Cypress Hills, southeastern Alberta, Canada. Silva compass indicates moderate angle of dip.
Frank landslide in the Canadian Rocky Mts. front range, southwestern Alberta. A large mass of rock failed suddenly from the mountain side on April 29, 1903. The resulting landslide buried the town of Frank at the valley bottom, and killed 70 people.
View toward the source and upper portion of the Frank landslide. The landslide tumbled downward with such speed that it flowed across the valley and up onto the opposite side of the valley.
Landslide debris flowed up the opposite side of the valley (to left) and deposited mounds of jagged boulders across the scene.

References

Faults--part II.
Return to advanced tectonics schedule.

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 imagery © J.S. Aber (2012).