9(f) Fig 9.1 Folds and Faults caused by tectonic activity - plate movement
an anticline near Mizen Head, West Cork, Ireland
Fig 9.1
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Folding shows the compression of layers due to plate tectonic movement as plates
meet head on! Along the various layers of rock a curve down is called a syncline, a
curve in an upwards is called an anticline.
Sometimes large sections of rock layers are tilted at extreme angles by the
tectonic forces.
Fault lines are huge 'cracks' down through layers of rocks. They are caused by
earthquake activity and for subsequence earthquakes, the rock movement is often
along these fault lines.
In the diagram the sequence might be interpreted as follows from 10 up to 1:
o layers from 10 up to 4 laid down in that order with 10 first
o the folding occurs later, since newer layers of sedimentary rock would tend
to be laid on top and fill up the fold.
o the faulting occurred after the folding because all the folds are uniformly
displaced
o the left folds have been displaced downwards with respect to the middle
section (or middle folds upwards with respect to left folds)
o the more right linear sections may have been moved upwards with respect to
the middle section or the middle section has slipped down.
layers 3, 2 and 1 could be the most recent sedimentary rock layers laid down
later on top of the eroded layers 4-6 (by weather or glaciations) and have
not been subjected to major tectonic forces since there is no evidence of
folding or faulting.
Folding and faulting can give information on the magnitude and direction of the
tectonic forces involved.
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