Plate Tectonics

Question 0

Type of earths crust

Answer 0

-oceanic
-continental
Most tectonic plates contain both types of crust but some only ocean crust

Question 1

Basis for Wegeners hypothesis

Answer 1

• the shape of the Atlantic Ocean
• similarities of fossils and rock sequences on opposite sides of the Atlantic
• fossils of tropical plants in the arctic

Question 2

Types of continental margins

Answer 2

• active: margin of a continent is a plat boundary

- passive: margin of continent does not include a plate boundary

Question 3

Earths upper mantle and crust

Answer 3

• lithosphere: rigid crust + top of mantle

- asthenosphere: partially-molten part of mantle -> source of basalts

Question 4

Divergent boundaries

Answer 4

• mid-ocean ridges
• continental rifts
• in both, new ocean crust is created by basalts and gabbros that originate as magmas in the mantle’s asthenosphere

Question 5

Features of divergent boundaries

Answer 5

• new ocean crust is created
• earthquakes are typically small
• very active basalt volcanism

Question 6

Convergent boundaries

Answer 6

• island-arc subduction
• Andean-type subduction
• continent-continent collision

Question 7

Island arc subduction

Answer 7

Subduction of ocean crust under ocean crust

Question 8

Andean type subduction

Answer 8

Subduction of ocean crust under continental zone

Question 9

Benioff zone -> earthquake generating zone

Answer 9

Earthquakes that are associated with subduction are caused by friction between the sub-ducting plate and the overlying crust or mantle

Question 10

Features of ocean crust subduction

Answer 10

• consumption of ocean floor
• large earthquakes
• explosive volcanism dominated by dacite and andesite lavas

Question 11

Features of continental collisions

Answer 11

• produce tall, mountain belts

- can produce large earthquakes

Question 12

Features of transform fault boundaries

Answer 12

• they are offsets in crustal plate boundaries, especially mid-ocean ridges
• can occur on land
• no crust is created or consumed
• can produce large earthquakes
• volcanism is very rare

Question 13

Model of a hot spot

Answer 13

In the 1960’s J Tuzo Wilson propose the “hot spot” hypothesis
-mantle plumes (hot spots)

Question 14

Evidence for active plate tectonics

Answer 14

• earthquake distribution
• volcanic activity
• direct measurements (GPS, ground-based)

Question 15

Evidence for past plate tectonics

Answer 15

• fits continental margin
• match of geological belts in different continents
• volcanic hot-spot traces
• flora and fauna at “wrong” latitudes
• geomagnetic record (paleomagnetism)
• age of oceanic floor

Question 16

Magnetic polarity in mid-ocean ridge basalts

Answer 16

• discovered in 1962, explain in 1963

- reversals in magnetic field are recoded by magnetite within MORB’s!

Question 17

Magnetic “stripes” at mid-ocean ridges

Answer 17

• magnetic reversals are mirror images in both sides of ridge
• rocks are progressively older away from ridge
• > demonstrate the existence of divergent plate tectonic boundary
• > demonstrate past reversals in the earth’s magnetic field

Question 18

Paleomagnetic measurements

Answer 18

-paleodip (paleoinclination): dip of magnetic field along the surface of the earth
-paleodeclination: apparent angle of magnetic field direction N->S (“polar wander”)
This tells us about past rotation of land mass

Question 19

Some plate tectonics influences in climate and evolution

Answer 19

• shifting of continents influences patterns of ocean currents
• mountain ranges influence weather patterns
• flora and fauna can take different evolutionary paths on separated continents
• new continental bridges allow for exchange on species