Today’s list____________ Ch15: Rock Deformation Mapping geologic structures

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?

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

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.

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

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: 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

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 - circulardownwarping (synclinal structure) Fig 11.19

Today’s list____________ Ch15: Rock Deformation Mapping geologic structures