Plate Tectonics

1
Plate Tectonics

• A Unifying Theory
• Responsible for Mtn. Building, Earthquakes,
  Volcanism, and Seafloor Spreading
• Rigid plates of lithosphere slide over plastic
  layer of the asthenosphere

2

• Position of the continents over the past 750
  million years
• Plate Tectonics Animation

3

• Earths lithosphere is broken into about 12 major
  plates

Also on page 26 in your manual
4

• Plates move over the partially molten
  asthenosphere. There are 3 types of plate
  boundaries
• Divergent Boundaries - plates move away from
  each other
• Convergent Boundaries - plates move towards one
  another
• Transform Boundaries - plates slide past each
  other

5

• Divergent Boundaries
• As plates move away from each other, partially
  molten lava rises and is added onto the edge of
  the plates. This process is responsible for the
  formation of oceanic crust.

6

• Development of an ocean basin along a divergent
  plate margin

7

• Convergent Boundaries
• Plates move toward one another and can either
  result in subduction or collision.
• Subduction The sinking of one lithospheric
  plate beneath another one. Deep-sea trenches,
  volcanic belts, and shallow and deep-focus
  earthquakes often result from subduction.
• (a) example of ocean/continent subduction.

8

• (b) example of ocean/ocean subduction.
• (c) animation of a subduction zone

9

• Collision - Occurs when one lithospheric plate
  can not subduct beneath another one. A
  continent/continent collision results in
  thrusting, folding, and uplift of large mountain
  belts.

10

• Transform Boundaries
• As plates slide past each other, lithosphere is
  neither created nor destroyed. These plate
  margins are associated with strike-slip faults
  and shallow-focus earthquakes.

11

• Faulting occurs at all three types of plate
  boundaries. The three types of faults are
• Normal Hanging wall (top surface) moves down
  relative to the footwall (bottom surface), caused
  by tension (divergence).

12

• Reverse Hanging wall moves up relative to the
  footwall, caused by compression (convergence).

13

• Strike-Slip Movement along the fault is
  horizontal, parallel to the strike of the fault
  plane. If, standing on one side of the fault,
  the block on the other side is displaced to the
  right, the fault is termed right-lateral. If the
  block on the other side is displaced to the left,
  the fault is termed left-lateral (transform).

Is this fault right-lateral or left-lateral?
Left-lateral
14
Determining rate and direction of plate motion

• As magma is extruded, and cooled along a
  Mid-Ocean Ridge, it becomes magnetized in the
  direction of the Earths magnetic field.
• Rates of plate motion are obtained using magnetic
  anomalies in the rocks of the ocean floor.

15
Formation of Magnetic Stripes
16

• Anomalies are detected using a magnetometer.

17

• Hot spots
• Locations of intraplate volcanism.

18

• At each type of plate boundary characteristic
  rock assemblages are observed
• Typical ophiolite suite at a divergent plate
  margin.

19

• Rock assemblages associated with ocean/ocean
  subduction.

20

• Rock assemblages associated with ocean/continent
  subduction.

21

• Rock assemblages associated with
  continent/continent collision.