Todays list Ch 15 Rock Deformation 1Mapping geologic

Today’s list______ Ch 15: Rock Deformation 1)Mapping geologic structures 2)How rocks get deformed 3) Folds

Study questions______ Ch 15: Rock Deformation · What type of tectonic forces makes a normal fault? A reverse fault? A strike slip fault? What is the difference between brittle and ductile deformation? What are the strike and dip angle of a deformation? What is the shape of an anticline, syncline, and what is the relative age of rocks exposed? What type of deformation is the San Andreas Fault? The mid-ocean ridge?

1) Mapping geologic structures Deformational processes create faults, folds, joints rock structures Visible when rock beds are exposed at surface out crops

1) Mapping geologic structures F Strike and dip TSP 15. 8

1) Mapping geologic structures F Strike and dip Strike Compass bearing of a rock layer relative to North Dip Angle of tilt of a bed from a horizontal plane Fig. 11. 4

1) Mapping geologic structures N 75 E

2) How rocks become deformed Confining pressure: force equal in all directions Differential stress: force not equal in all directions

2) How rocks become deformed Response to differential stress 1. Elastic deformation – the rock returns to nearly its original size and shape when the stress is removed 2. Brittle deformation rocks crack/fracture Shallow in crust 3. Ductile deformation rocks flow Deeper down

2) How rocks become deformed Fault definition: a fracture where displacement has occurred: rocks on either side of fault have moved relative to each other.

2) How rocks become deformed Fault definition: a fracture where displacement has occurred: rocks on either side of fault have moved relative to each other.

Joints Fractures where no slip has occurred Not same as a fault! Why? Slip happens on faults!

2) How rocks become deformed- brittle materials Differential stress: force not equal in all directions Compressive forces: shortening

2) How rocks become deformed- brittle materials Differential stress: force not equal in all directions Tensional forces: stretching

2) How rocks become deformed- brittle materials Differential stress: force not equal in all directions Shearing forces: shearing

2) How rocks become deformed - brittle materials

2) How rocks become deformed - brittle materials Fig. 11. 13 Rift valleys are the result of tensional forces in the crust, creating a series of normal faults. The downfaulted blocks result in a Rift Valley.

2) How rocks become deformed - brittle materials St. Andreas fault is an example for a strike-slip fault Because it is a plate boundary, it is also a transform fault Fig. 11. 10

Fault System Example : San Andreas

2) How rocks become deformed- ductile materials Differential stress: force not equal in all directions Compressive forces: Tensional forces: shortening stretching Shearing forces: Shearing/bending

3) How rocks fold u series of wavelike undulations of once-flat rock layers u many sizes: microscopic to 100’s of meters ucompressive stresses: shorten+thicken crust

3) Folds Anticlines fold upward… Synclines fold downward… Fig. Story 11. 16

3) Folds horizontal and plunging anticline Plunging fold: axis of fold penetrates into the ground Fig. 11. 16

Plunging anticlines and synclines See Fig. 11. 17

3) Folds F Types of folds Symmetrical, asymmetrical, overturning, plunging…. . F Other deformations dome - circular upwarping (anticlinal structure) basin - circular downwarping (synclinal structure) Fig 11. 19