Chapter 9 – FOLDS, FAULTS & GEOLOGIC MAPS

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

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

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

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

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 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

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

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

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

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

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

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

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

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

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

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

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