FOLDS FAULTS AND GEOLOGIC MAPS Objectives Define three

FOLDS, FAULTS AND GEOLOGIC MAPS

Objectives • Define three types of stress. • Describe the differences between elastic, brittle, and ductile deformation. • Define cratons and orogens. • Define strike and dip. • Define and describe synclines, anticlines, and other types of folds. • Distinguish between a topographic map and a geologic map.

Rock Deformation • Stress – The force acting on a surface, per unit area – May be greater in certain directions than in others • Pressure – A kind of stress in which the forces acting on a body are the same in all directions

Rock Deformation • Tension – A stress that acts in a direction perpendicular to and away from a surface • Compression – Stress that acts in a direction perpendicular to and toward surface

Rock Deformation • Shear – A stress that acts in a direction parallel to a surface • Strain – A change in shape or volume of a rock in response to stress • Uniform stress causes change in volume only • Differential stress may causes change in shape

Rock deformation • Elastic deformation – Temporary change in shape or volume from which a material rebounds after the stress is removed

Rock deformation • Ductile deformation – Permanent but gradual change in shape or volume of a material, caused by flowing or bending

Rock deformation • Brittle deformation – Permanent change in shape or volume, in which a material breaks or cracks

Rock Deformation • Main factors that affect rock deformation – – Temperature Confining pressure Rate of deformation Composition

Rock Deformation • Where rock deformation occurs – Craton • A region of continental crust that has remained tectonically stable for a very long time – Orogen • An elongated region of crust that has been deformed and metamorphosed through a continental collision • Isostasy – The flotational balance of the lithosphere on the asthenosphere

Rock Deformation

Structural Geology • Structural geology the study of: – Stress and strain • Processes causing stress and strain • Deformation and rock structures that result from stress and strain

Structural Geology • Strike – The compass orientation of the line of intersection between a horizontal plane and a planar feature (e. g. rock layer or fault) • Dip – The angle between the tilted surface and a horizontal plane

Structural Geology

$Structural Geology • Faults and fractures – Normal fault • The block of rock$

Structural Geology • Faults and fractures – Normal fault • The block of rock above the fault surface moves downward relative to the block below

Structural Geology

$Structural Geology • Faults and fractures – Reverse fault • The block on top$

Structural Geology • Faults and fractures – Reverse fault • The block on top of the fault surface moves up and over the block on the bottom – Thrust fault • A reverse fault with a shallow angle of dip

Structural Geology • Strike-slip fault – A fault in which the direction of the movement is mostly horizontal and parallel to the strike of the fault • San Andreas Fault

Structural Geology

Structural Geology • Folds – A bend or warp in a layered rock • Monocline – A local steepening in otherwise uniformly dipping strata • Anticline – A fold in the form of an arch, with the rock strata convex upward and the older rocks in the core

Structural Geology • Syncline • A fold in the form of a trough, with the rock strata concave upward and the younger rocks in the core • The geometry and the orientation of a fold is described by the: – – – Axial plane Flanks Limbs Axis Hinge

Structural Geology

Geologic Maps • Geologic map… – Shows the locations, kinds, and orientation of rock units – Shows structural features such as faults and folds

Geologic Maps

Geologic Maps • Making and interpreting geologic maps – Topographic maps… • Show the shape of a ground surface, as well as the location and elevation of surface features, usually by means of contour lines

Geologic Maps

The Canadian Rockies

Critical Thinking • Which orogens in North America would you expect to have the deepest roots, and how could you test your hypothesis? • In the figure below, which strata in the photograph are the oldest and how can you tell?