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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.

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Presentation on theme: "Chapter 9 – FOLDS, FAULTS & GEOLOGIC MAPS. Rock Deformation Stress –Force acting on surface, per unit area Pressure –Confining (uniform) Stress is equal."— Presentation transcript:

1 Chapter 9 – FOLDS, FAULTS & GEOLOGIC MAPS

2 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

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

4 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

5 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

6 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

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

8 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

9 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

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 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

13 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?

14 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?

15 Metamorphic Rocks Texture: foliation Composition: minerals present

16 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

17 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

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

19 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

20 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

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


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