structural geology & mountain building
description
Transcript of structural geology & mountain building
structural geology&mountain building
key termsDeformation – change in the original form, size or
shape of a rock unitStress – amount of force applied to a given areaDifferential stress – stress applied unequally in
different directionsStrain – causes irreversible changes in the shape,
size or orientation of a rock unitElastic 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
When does failure occur?
How is deformation in a stick like deformation of a rock unit?
effects of directional stressCompress 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 – 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
Terminologyof folds
Limb – sides of a foldAxial plane – imaginary plane that divides a fold as
symmetrically as possibleAxis – intersection of axial plane with the surfaceSymmetrical – limbs are mirror images of each otherAsymmetrical – limbs are not mirror images of each
otherOverturned – a fold in which one limb is tilted
beyond the verticalRecumbent – a fold folded over on itselfPlunge – a fold in which the axis is tilted from the
horizontal
types of foldsSyncline –
downwarping of strata, older strata are found on limbs, younger strata in the axial region
types of foldsAnticline – upwarping
of strata, older strata are found in axial region, younger strata on the limbs
types of foldsAsymmetrical – either
an anticline or syncline in which one limb is tilted at a different angle than the other
types of foldsRecumbent – a fold
which is folded over on itself
fault terminology
Fault – fracture in rock along which there has been displacement
Hanging wall – rock surface above the faultFootwall – rock surface below the faultFault scarp – exposed fault surface
types of faultsNormal fault – a fault
in which the hanging wall moves down relative to the footwall
types of faultsReverse fault – a fault in
which the hanging wall moves up relative to the footwall
types of faultsStrike-slip fault – a
fault in which the motion is in the horizontal plane, also a transform fault
types of faultsThrust fault – hanging
wall moves up and thrusts over the footwall, the dip is less than 45 degrees, low angle fault
domes & basins
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
•Basin – circular or elongated structure caused by downwarping of sedimentary rock•Youngest rock found in the center of the basin, older on the flanks
Hogbacks Ridges of steeply dipping
strataHighly resistant
sedimentary layers remain exposed along the edge of an uplifted block
orogenesis
Orogenesis – processes by which mountain belts are createdOros – mountain, genesis – to come into being
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 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 accretionSmall 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