1. Chapter 9 – FOLDS, FAULTS & GEOLOGIC MAPS

2. Rock Deformation Stress Pressure Strain
Force acting on surface, per unit area
Pressure
Confining (uniform)
Stress is equal from all directions
Differential stress
Stress is stronger from some directions
Strain
Change in rock shape or volume in response to stress

3. Rock Deformation Tension Compression Shear Divergent boundaries
Normal faults
Compression
Convergent boundaries
Reverse faults
Shear
Transform boundaries
Strike-slip faults

4. Rock Deformation Elastic deformation Ductile deformation
Temporary change; rebounds when stress is gone
Elastic limit (AKA yield point)
Ductile deformation
Permanent, gradual change; folds or bends
AKA Plastic deformation
Brittle deformation
Permanent change; breaks or cracks

5. Rock Deformation & Structural Geology
Factors affecting rock deformation
Temperature
Confining pressure
Rate of deformation
Composition
Structural geology
Study of stress & strain
Strike
Compass orientation of line of intersection between horizontal plane & planar feature
Dip
Angle between tilted surface & horizontal plane

6. Structural Geology Faults & fractures: Dip-slip faults Normal fault
Hanging wall moves downward relative to footwall below
Reverse fault
Hanging wall moves up & over footwall below
Thrust fault
Reverse fault with shallow dip angle

7. Structural Geology Strike-slip fault
Movement is horizontal & parallel to strike of fault
Right-lateral
Left-lateral
San Andreas Fault

8. Structural Geology Folds Monocline Anticline Syncline Dome Basin
Bend or warp in layered rock
Monocline
1-sided fold
Anticline
Layers fold upward (arch)
Older rocks in core
Syncline
Layers fold downward (trough)
Younger rocks in core
Dome
Broad area of up-warping
Basin
Broad area of down-warping

9. Geologic Maps Geologic map Topographic maps Geologic cross section
Shows locations, kinds, & orientation of rock units
Shows structural features
Topographic maps
Shows shape of ground surface, as well as location & elevation of surface features
Relief
Contour lines
Geologic cross section
Diagram of geologic features underground

10. Chapter 10 –METAMORPHISM: NEW ROCKS FROM OLD

11. What is Metamorphism? Metamorphism
Mineralogical, textural, chemical & structural changes in rocks
Rocks exposed to elevated temperatures &/or pressure
Rocks do NOT melt

12. What is Metamorphism? Factors that influence metamorphism Temperature
150°C = “official” boundary between diagenesis & metamorphism
Pressure
Composition
Pore fluids
Pores
Open spaces in rocks
Migmatite
Transition between metamorphic & igneous rocks
stress
stress

13. What is Metamorphism? Factors that influence metamorphism (cont’d)
Stress
Foliation
Planar arrangement of textural features in metamorphic rock
Gives rock layered or banded appearance
Duration
Rate of metamorphism

14. What is Metamorphism? Grade Low-grade High-grade
Degree of temperature & pressure a rock is exposed to during metamorphism
Low-grade
Low temperature & pressure conditions; minimal rock changes
High-grade
High temperature & pressure conditions; significant rock changes

15. Foliated or Nonfoliated
Metamorphic Rocks
Texture: foliation
Composition: minerals present
Texture
Metamorphic Rock
Parent Rock
Foliated
Slate
Mudstone or shale
Phyllite
Mudstone, shale or slate
Schist
Mudstone, shale, slate or phyllite
Gneiss
Mudstone, shale, slate, phyllite, schist, granite, or diorite
Foliated or Nonfoliated
Amphibolite
Basalt, gabbro or ultramafic igneous rocks
Nonfoliated
Anthracite Coal
Peat, lignite, bituminous coal
Hornfels
Any type of rock
Serpentinite
Soapstone
Quartzite
Sandstone
Marble
Limestone
Metaconglomerate
Conglomerate

16. Metamorphic Rocks Rocks with foliation Slate Phyllite
Very fine grained metamorphic rock; low grade
Metamorphic product of shale
Phyllite
Fine grained metamorphic rock; intermediate grade
Further metamorphism of slate

17. Metamorphic Rocks Rocks with foliation Schist Gneiss
Visible individual mineral grains; intermediate grade
Further metamorphism of phyllite
Gneiss
Course grained, high grade, strongly foliated (light/dark bands)
Further metamorphism of schist

18. Metamorphic Rocks Rocks without foliation Quartzite Marble
Metamorphosed sandstone
Marble
Metamorphosed limestone

19. Metamorphic Processes
Type of metamorphism
Contact metamorphism
Rocks heated & chemically changed adjacent to magma intrusion
Aureole
Burial metamorphism
Occurs after diagenesis
Due to burial of sediments in deep sedimentary basins

20. Metamorphic Processes
Type of metamorphism
Regional metamorphism
Metamorphism of extensive area of crust
Plate convergence, collision, subduction
Other types of metamorphism
Fault zone
Shock
Pyro-metamorphism

21. Metamorphic Facies Index minerals Isograds
Minerals that form at specific temperature & pressure conditions
Isograds
Lines of equal grade
Used to map index minerals