Folding – The process by which crustal forces deform an area of crust so that layers of rock are pushed into folds.
Faulting – The process by which crustal forces cause a rock formation to break and slip along a fault.
Fold – A bent or warped stratum or sequence of strata that was originally horizontal, or neatly so.
Fault – A planar or gently curved fracture in the earth's crust across which there has been relative displacement of the two blocks of rock parallel to the fracture.
· It takes 2 measurements to describe the orientation of a layer of rock exposed at a given location:
· Strike – The direction of the intersection of a rock layer with a horizontal surface.
· Dip – Measured at right angles to the strike, is simply the amount of tilting – the angle at which the inclines from the horizontal.
Constructing a Geological Map and Cross Section
o The dips and strikes of inclined layers
· 3 types of tectonic forces:
o Compressive forces – squeeze and shorten a body
o Tensional forces – stretch a body and tend to pull it apart
o Shearing forces – push two sides of a body in opposite directions
What Determines Whether a Rock Bends or Breaks?
· If subject to tectonic forces near surface, where confining pressure is low it would tend to deform by fracturing and faulting.
· If deeper than few Km's it would change shape by gradually folding.(also if hot)
· Brittle rocks – little change, then breaks
· Ductile rocks – smooth and continuous plastic deformation.
· Igneous rocks are more brittle (stronger) than sedimentary rocks
· Basement rocks more brittle than overlaying sedimentar
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