Physical Geology: Chapter 19 (Plate Tectonics)

Question 1

Lithosphere

Answer 1

• rigid outer shell of Earth; more than 12 plates that mover the asthenosphere
• rigid lithosphere broken into about 12 large ridged plates in motion over surface
• note: plate extents don’t match continents

Question 2

theory of plate tectonics

Answer 2

• describes movement of plates and nature of forces
• theory explains distribution of geological features such as mountain chains, volcanos, seafloor structures, rock assemblages, and earthquakes

Question 3

divergent plate boundaries

Answer 3

• plates move in opposite directions (away from each other) and lithosphere is created
• new lithosphere is forms from upwelling magma
• normally at “mid-oceanic ridge” (chain of mountains beneath oceans)
• characterized by earthquakes and volcanism
• “seafloor spreading”: creation of new seafloor as basins widen
• a mature divergent boundary forms oceanic ridges

Question 4

convergent plate boundaries

Answer 4

• boundaries of plate collisions
• plates come together and one is usually recycled into mantle
• usually one plate sinks beneath the other: (subduction)
• sea trenches (where ocean has greatest depths) are common
• edge of overriding plate crumpled and uplifted to form mountain chain parallel to trench
• during subduction, the descending plate can add water to subsurface, producing magma; magma can rise and erupt at surface

Question 5

transform-fault boundaries

Answer 5

• plates slide horizontally past each other
• boundaries of horizontal slip across a transform fault
• rocks facing each other on two sides of fault are of different types and ages
• sliding can take place in sudden events causing severe earthquakes

Question 6

magnetic epochs

Answer 6

• major normal or reversed periods (about half a million years)

Question 7

magnetic events

Answer 7

• short lived (less than 200,000 years)
• new seafloor that is generated is magnetized in direction of Earths field at that time (allowing us to have a recored of time)

Question 8

isochrons

Answer 8

• contours that connect rocks of equal age

- more widely spaced isochrons indicate periods of faster seafloor spreading

Question 9

two primary principles used in reconstructions

Answer 9

• 1) transform boundaries: indicate directions of relative plate movement
• 2) seafloor isochrons: reveal positions of divergent boundaries in earlier times (isochrons are roughly parallel/symmetrical with boundary of plate separation at relevant time)

Question 10

classic examples of hot spots

Answer 10

• Iceland
• Island of Hawaii
• Yellowstone Park

Question 11

differentiations

Answer 11

• enough internal heat to allow partial melting and substances move down to core