Structural geology
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structural geology & mountain building. key terms. Deformation – change in the original form, size or shape of a rock unit Stress – amount of force applied to a given area Differential stress – stress applied unequally in different directions

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Structural geology mountain building

structural geology&mountain building


Key terms

key terms

  • Deformation – change in the original form, size or shape of a rock unit

  • Stress – amount of force applied to a given area

  • Differential stress – stress applied unequally in different directions

  • Strain – causes irreversible changes in the shape, size or orientation of a rock unit

  • Elastic deformation – recoverable stress, when stress is removed rock returns to its original shape & size

  • Ductile deformation – elastic limit of rock is exceeded, the rock flows into a new shape, size or orientation

  • Brittle deformation – elastic limit and ductile limit of rock is surpassed, failure occurs, the rock breaks

  • Joint – a crack along which there is no motion


Stress strain deformation

Stress,strain &deformation

  • When does failure occur?

  • How is deformation in a stick like deformation of a rock unit?


Effects of directional stress

effects of directional stress

  • Compress ional stress – causes rock units to shorten horizontally & thicken vertically

  • Tensional stress – causes rock units to lengthen horizontally & thin vertically

  • Shear stress – causes horizontal displacement along fault zones


Strike dip

strike & dip

  • Strike – compass direction of a line where a rock layer intersects the horizontal

  • Dip – angle of inclination or tilt of a rock layer from the horizontal


Terminology of folds

Terminologyof folds

  • Limb – sides of a fold

  • Axial plane – imaginary plane that divides a fold as symmetrically as possible

  • Axis – intersection of axial plane with the surface

  • Symmetrical – limbs are mirror images of each other

  • Asymmetrical – limbs are not mirror images of each other

  • Overturned – a fold in which one limb is tilted beyond the vertical

  • Recumbent – a fold folded over on itself

  • Plunge – a fold in which the axis is tilted from the horizontal


Types of folds

types of folds

  • Syncline – downwarping of strata, older strata are found on limbs, younger strata in the axial region


Types of folds1

types of folds

  • Anticline – upwarping of strata, older strata are found in axial region, younger strata on the limbs


Types of folds2

types of folds

  • Asymmetrical – either an anticline or syncline in which one limb is tilted at a different angle than the other


Types of folds3

types of folds

  • Recumbent – a fold which is folded over on itself


Fault terminology

fault terminology

  • Fault – fracture in rock along which there has been displacement

  • Hanging wall – rock surface above the fault

  • Footwall – rock surface below the fault

  • Fault scarp – exposed fault surface


Types of faults

types of faults

  • Normal fault – a fault in which the hanging wall moves down relative to the footwall


Types of faults1

types of faults

  • Reverse fault – a fault in which the hanging wall moves up relative to the footwall


Types of faults2

types of faults

  • Strike-slip fault – a fault in which the motion is in the horizontal plane, also a transform fault


Types of faults3

types of faults

  • Thrust fault – hanging wall moves up and thrusts over the footwall, the dip is less than 45 degrees, low angle fault


Domes basins

domes & basins

  • Basin – circular or elongated structure caused by downwarping of sedimentary rock

  • Youngest rock found in the center of the basin, older on the flanks

  • Dome – circular or elongated structure caused by upwarping of sedimentary rock, usually overlying igneous or metamorphic rock

  • Youngest rock found on the flanks of the dome, oldest in the center


Hogbacks

Hogbacks

  • Ridges of steeply dipping strata

  • Highly resistant sedimentary layers remain exposed along the edge of an uplifted block


Orogenesis

orogenesis

  • Orogenesis – processes by which mountain belts are created

  • Oros – mountain, genesis – to come into being


Types of mountains

Types of mountains

  • Fault block mountains – mountain belts formed by extensional forces

  • Mountains are associated with high angle normal faulting

  • Examples include: Sierra Nevada, Grand Tetons, “Basin & Range province


Types of mountains1

Types of mountains

  • Folded mountains – result from large scale compressional forces

  • Rock units are shortened and thickened as a series of synclines and anticlines forms a mountain belt

  • Examples include: the Appalachians Valley and Ridge Province


Terrane accretion

Terrane accretion

  • Small crustal fragments collide and merge with larger continental masses

  • Accreted crustal blocks are called terranes

  • Accretion of larger fragments may result in formation of a mountain range

  • Examples include: the western coast of North America


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