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Presentation on theme: "Chapter 9 – FOLDS, FAULTS & GEOLOGIC MAPS"— Presentation transcript:


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


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

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