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 shalePhyllite Mudstone, shale or slateSchist Mudstone, shale, slate or phylliteGneiss Mudstone, shale, slate, phyllite, schist, granite, or diorite

Foliated or Nonfoliated Amphibolite Basalt, gabbro or ultramafic igneous rocks

Nonfoliated

Anthracite Coal Peat, lignite, bituminous coalHornfels Any type of rockSerpentinite Basalt, gabbro or ultramafic igneous rocksSoapstone Basalt, gabbro or ultramafic igneous rocksQuartzite SandstoneMarble LimestoneMetaconglomerate 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