Today’s list____________ Ch15: Rock Deformation Mapping geologic structures How rocks get deformed 3) Folds

Study questions____________ Ch15: 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 Strike and dip TSP 15.8

1) Mapping geologic structures Strike and dip Compass bearing of a rock layer relative to North Angle of tilt of a bed from a horizontal plane Strike Dip 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 3. Ductile deformation rocks flow Shallow in crust 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

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

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

3) Folds Synclines fold downward… Anticlines fold upward… Fig. Story 11.16

horizontal and plunging anticline 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 Types of folds Other deformations Symmetrical, asymmetrical, overturning, plunging….. dome - circular upwarping (anticlinal structure) basin - circular downwarping (synclinal structure) Fig 11.19