7) Plate Tectonics

Question 0

Type of earths crust

Answer 0

-oceanic
-continental
Most tectonic plate contain both types of crust but some only have oceanic crust

Question 1

Alfred Wegener (1880-1930)
Coined term "continental drift"

Answer 1

In 1915 wrote the origins of continents and oceans
Basis of hypothesis:
-shape of 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 continent is a plate boundary

- passive: margin of a 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 the mantle, source of basalts

Question 4

Divergent plate 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 mantles asthenosphere

Question 5

Feature of convergent 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: subduction of ocean crust under ocean crust
• Andean-type subduction: subduction of ocean crust under continental crust
• continent-continent collusion

Question 7

Features of ocean crust subduction

Answer 7

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

Question 8

Benioff zone -> earthquake generating zone

Answer 8

Earthquakes that are associated with subduction are causes by friction between the subducting plate and the overlying crust or mantle

Question 9

Featured of continental collisions

Answer 9

• Produce long, talk mountain belts

- can produce large earthquakes

Question 10

Features of transform fault boundaries

Answer 10

• 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 11

Evidence for active plate tectonics

Answer 11

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

Question 12

Evidence for past plate tectonics

Answer 12

• fits continental margin
• match of geological belts on different continents
• volcanic hot-spot traces
• flora and fauna at “wrong” latitudes
• geomagnetic record
• age of ocean floor

Question 13

Magnetic “stripes” at mid-ocean ridges

Answer 13

• 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