Plate Tectonics

Question 1

Who proposed Continental Drift?
-Evidence? And why was the theory rejected

Answer 1

Alfred Wegener; proposed in 1915

Evidence:
1.) Geometric fit of continents
2.) Ancient Glaciations
3.) Climate Belts
4.) Fossil Distribution ->match across oceans
5.) Geological Unit Match
-Proterozoic Mountain Belts
-Archean Crust

Wegener explained the existence of continental drift, but failed to explain how or why. As a results his peers rejected the theory. Additionally, he was a meteorologist rather than a geologist,

Question 2

Three types of Plate Boundaries

Answer 2

Divergent, Convergent, Transform

Question 3

Divergent
(2 types)

Answer 3

1.) Oceanic Rifting : Mid-Ocean Ridges
2.) Continental Rifting The East African Rift, or Basin and Range (United States)

Question 4

what does depth of seafloor signify?

Mid-Ocean Ridges

Answer 4

depth of seafloor reflects progressive cooling of new oceanic crusts + upper mantle
-depth depends on age of lithosphere
-depth=a function of cooling. The cooler: the more dense, which drive the lithosphere to sink further down

Question 5

Why?Which is closer the equator?

Which ridge has a faster spreading rate? (East-Pacific vs. Mid-Atlantic)

Answer 5

East-Pacific = faster spreading rate; Hot, high melt supply by being closer to the equator) 10 knots S

Mid-Atlantic= slower spreading rate; Cooler, lower melt supply) 25 Knots N

Question 6

Continental Rifting ; Continental Extension

Answer 6

1.) East African Rift
2.) Basin and Range : extension and volcanism

Question 7

Convergent
(3)

Answer 7

1.) Continental-Continental: Mountain Ranges
ex: Himalayas, Alps
2.) Continental-Oceanic: Trenches, Volcanoes
ex: Andes, Cascades, Japan
3.) Oceanic-Oceanic
ex: Aleutians, Western Pacific

Question 8

At Oceanic-Continental Convergent Boundaries, which plate is subducted?
-> why?

Answer 8

Oceanic

-Oceanic crust has a thinner crust + lithosphere that is younger and less complex compared to the continental crust
-Oceanic Crust is also more dense

Question 9

What makes oceanic crust more dense than continental crust?

Answer 9

The oceanic crust is mainly composed of basalt (which comes from magma melt-lower levels of the earths layers)
->Mafic rock is denser than felsic (Basalt denser than Granite)

Question 10

Formation of the Himalayas?

Answer 10

Continent-Continent Collisions
-> lead to large mountain ranges and thick continental crust
(Himalayan Crust up to 70km thick)

Question 11

Where does the Continental Crust Form?

Answer 11

At Subduction Zones

Question 12

Tectonic Evolution of CA -San Andres Fault

Answer 12

~30 Ma : Farallon Plate consumed by subduction causing Pacific & North American plates to be in contact (San Andreas Transform Boundary)

Question 13

Paleomagnetic Evidence of Continental Drift
(4)

Answer 13

1.) Apparent Polar Wander Path:
-Polar wander paths differ between continents
-Continents move while magnetic field remains relatively fixed
2.) Maps of Ocean-Floor
3.) Earth quakes:
-occur at boundaries of tectonic plates (specifically divergent and convergent boundaries)
-supports idea plates move with respect to one another.
4.) symmetry of magnetic stripes on sea-floor confirms sea-floor spreading and therefore separation of continents/continental drift.

Question 14

(T/F) Polarity of Earth’s Magnetic Field flips periodically

Answer 14

True

Question 15

Magnetic Inclination

Answer 15

Latitudinal distance from the pole

Question 16

Magnetic Declination

Answer 16

Direction of the Pole

Question 17

(three)

Magnetic Sea-Floor Anomalies (“Stripes” of the Sea-Floor) result from:

Answer 17

-Sea-floor spreading
-Reversal’s in Earth’s Magnetic Field
-Basaltic Volcanism

Question 18

Magnetic anomalies on the sea floor run ___ to mid-ocean ridges

Answer 18

parallel

Question 19

Which Plate does Santa Barbara sit on?

Answer 19

Pacific Plate

Question 20

Subduction doesn’t occur at latitudes present?

Answer 20

True

Question 21

Which locations sit over hot-spots?

Answer 21

Yellowstone and Iceland

Question 22

The Ring of Fire

Answer 22

Subduction zones that encircle the Pacific Ocean; prone to seismic and volcanic activity

Question 23

1.) The Youngest Hawaiian Islands are those in the ____
2.) Oldest in the _____

Answer 23

1.) Southeast
2.) Northwest

Question 24

San Andreas Fault represents a _____ plate boundary between which two plates?

Answer 24

Transform
Pacific and North American Plate

Question 25

Hotspot

Answer 25

A location at the base of the lithosphere where temps can cause melting and igneous activity

Question 26

mantle-plume

Answer 26

Core-mantle boundary
buoyant -> Magma melt rises to the surface

Question 27

Why is the oceanic crust young?

Answer 27

continually subducted/ returned to mantle