Transcript Isostatic Adjustments

Crust Deformation:
Forces, Faults and Folds
Deformation
• The bending, tilting, and
breaking of the earth’s crust
• major cause of deformation
= plate tectonics
Isostasy
• There are two forces involved
in changing the earth’s crust:
• 1. The force of the crust
pressing down on the
mantle
Isostasy
• 2. The force of the mantle
pressing up on the crust.
• The balancing of these forces
is termed Isostasy!
Isostatic Adjustments
• The up and down
movements of the crust to
reach isostasy are called
Isostatic Adjustments
Isostatic Adjustments
• Isostatic Adjustments create
pressure causing rocks in that
particular area to bend and
deform.
• Common cause of
earthquakes!
Stress
• Both isostatic adjustments &
plate mov’t cause stress in
rocks that make up the
crust.
• Stress = the force that
applies pressure to the rocks
in the crust
Three types of Stress or
Forces
• Compression: occurs when
crustal rock is squeezed
together
Three types of Stress or
Forces
• Tension: occurs when rocks
are pulled apart
Three types of Stress or
Forces
• Shearing:
occurs when
rocks are being
pushed in two
opposite
directions
What happens because
of stress???
• Folding & Faulting occurs.
• When rock responds to stress
by becoming permanently
deformed w/o breaking, the
result is folding.
Faulting
• Because of cooler
temperatures & lower
pressure near earth’s surface
rocks respond to stress by
breaking.
Faulting
• When there is no movement
in the rocks along a break it
is called fracture.
• When rocks do move at a
break it is called a fault.
So what’s the REAL
difference between
folding (bending) and
faulting (breaking)?
folding
faulting
Fault terminology
• Fault plane: the actual break
in the rock
Hanging
wall
Foot
wall
Fault terminology
• Hanging wall: rock above fault
plane that moves relative to
rocks below the fault plane
• Footwall: rock below the fault
plane
Three types of Faults
• Normal fault: hanging wall
moves down relative to fault
plane
Three types of Faults
• Reverse fault: compression
causes the hanging wall to
move up relative to the foot
wall
Three types of Faults
• Strike-slip fault: rock on either
side of fault plane move
horizontally; usually occur at
transform fault boundaries.