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Chapter 9 – FOLDS, FAULTS & GEOLOGIC
MAPS
Rock Deformation• Stress
– 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
• Tension– Divergent boundaries– Normal faults
• Compression– Convergent
boundaries– Reverse faults
• Shear– Transform boundaries– Strike-slip faults
Rock Deformation
• Elastic 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
Rock Deformation
• 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
Rock Deformation & 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
Structural Geology
• Strike-slip fault– Movement is horizontal &
parallel to strike of fault• Right-lateral• Left-lateral• San Andreas Fault
Structural Geology
• Folds– 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
Structural Geology
Geologic Maps• Geologic map
– 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
Chapter 10 –METAMORPHISM: NEW
ROCKS FROM OLD
What is Metamorphism?• Metamorphism
– Mineralogical, textural, chemical & structural changes in rocks
– Rocks exposed to elevated temperatures &/or pressure• Rocks do NOT melt
• 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
What is Metamorphism?
stress
stress
• 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
What is Metamorphism?
• 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
What is Metamorphism?
Metamorphic Rocks
Texture Metamorphic Rock Parent Rock
Foliated
Slate Mudstone or shale
Phyllite Mudstone, shale or slateSchist 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 Basalt, gabbro or ultramafic igneous rocks
Soapstone Basalt, gabbro or ultramafic igneous rocksQuartzite Sandstone
Marble Limestone
Metaconglomerate Conglomerate
• Texture: foliation• Composition: minerals present
Metamorphic Rocks• Rocks with foliation
– Slate• Very fine grained metamorphic rock; low grade• Metamorphic product of shale
– Phyllite• Fine grained metamorphic rock; intermediate grade• Further metamorphism of slate
Metamorphic Rocks• Rocks with foliation
– Schist• Visible individual mineral grains; intermediate grade• Further metamorphism of phyllite
– Gneiss• Course grained,
high grade, strongly foliated (light/dark bands)
• Further metamorphism of schist
• Rocks without foliation– Quartzite
• Metamorphosed sandstone– Marble
• Metamorphosed limestone
Metamorphic Rocks
• 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
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
Metamorphic Processes
Metamorphic Facies• Index minerals
– Minerals that form at specific temperature & pressure conditions
• Isograds– Lines of equal grade– Used to map index minerals