Deformations of the Crust

Chapter 5.1

DEFORMATION OF THE CRUST

1.Deformation of the Crusta.Deformation

i.The bending, tilting, and breaking of the Earth’s crust.

b.While plate tectonics is the major cause of the deformation of the crust, it is not the only cause.

ISOSTASY

1.Isostasya.The balancing of the forces pressing up and

down on the Earth’s crust.b.Since the crust “rides” on top of the mantle,

when parts of the crust become thicker and heavier they will sink deeper into the mantle, and when it becomes thinner and lighter it will rise higher on the mantle.

ISOSTASY

i.This causes two forces which causes the up and down movement of the crust.

1.The crust presses down on the mantle.

2.The mantle presses up on the crust.

ISOSTASY

a.When these two forces are balanced crust doesn’t move up and down.

b.Isostatic adjustments is the up and down movement of the crust to reach isostasy.i.During Isostatic adjustment, pressure

created by this bending of the crust causes the land in those areas to deform.

ISOSTATIC ADJUSTMENT

a.Isostatic adjustment is constantly occurring all over the globe.i.In areas where mountain ranges are

being weathered.ii.In areas where minerals are

deposited (deltas).iii.In areas of retreating glaciers.

GEOLOGIC STRESS

1.Geologic Stressa.Stress is the amount of force per unit area that is

placed on a given material.b.Stress is caused by isostatic adjustment and plate

tectonics. c.Stress can also cause strain on lithospheric rocks.

i. Strain is a change in the shape or volume of rocks that results from the stress of being squeezed, twisted, or pulled apart.

GEOLOGIC STRESS

a.There are three main types of stress: i.Compression occurs when crustal rocks

are squeezed together.ii.Tension occurs when crustal rocks are

pulled apart.iii.Shearing occurs when crustal rocks

slide past each other.