Chapter 2: Plate Techtonics

Question 1

Earth’s “puzzle” pieces

Answer 1

Crustal plate boundaries

Question 2

What were Alfred Wegener’s ideas about continental drift?

What was the problem with his ideas?

Answer 2

Came up with idea that continents had “drifted” apart in 1915. They were thought to slide across a stable and ancient oceam floor. Suggested there was once a “supercontinent” that he termed “Pangaea” (all lands).

Problem: Wegener had no mechanism for “drift of the continents”.

Question 3

Pangaea

Answer 3

“Supercontinent” that existed ~200 million years ago

Question 4

What are the units/terminogoly used for age?

Answer 4

a = annum (100 = 1 year) .
ka = Thousand years (103=1,000)
Ma = Million years (106=1,000,000)
Ga = Billion years (109=1,000,000,000)
____________________________________________

kya = Thousand years ago
Mya = Million years ago
Gya = Billion years ago

Question 5

What was the primary evidence Wegener noted for Pangaea’s existence?

Answer 5

The following features matched on all continents, now separated:

• Fossils (ex. Mesosaurus fossils, see image attached)
• Rock types/ages
• Similar geologic structures
• glacial deposits

Question 6

What kind of trace to glaciers leave, if any?

Answer 6

They scour the landscape leaving evidence of their existence and path.

Glacial deposits indicate ide flow away from a central location (south pole).

Question 7

Who created the first profiles of the seafloor in the pacific and how?

Answer 7

Harry Hess when he left echo sounder on during WWII transits.

Question 8

What does magnetic mapping do?

Answer 8

Measures the rate of seafloor spreading.

Question 9

Where on the ocean floor are the youngest and oldest points located?

Answer 9

Youngest points (0 Ma) are at very long topographic highs.

Oldest are at the edges, frequently at trenches (oldest ocean floor is ~200 Ma).

Continental rocks up to 4 Ga (billion years)

Question 10

How many major plates is the Earth’s outer shell made up of?

Answer 10

13

Question 11

Where is the Ring of Fire and what is it’s significance?

Answer 11

IT is between the Indo-Australian Plate, Eurasian Plate, North American Plate, Cocos Plate, and Pacific Plate.

It’s an area where a large number of earthquakes and volcanic eruptions occur in the basin of the Pacific Ocean. Home to over 75% of world’s active and dormant volcanoes.

Question 12

What are the keys for convection?

Answer 12

Heat source at one end

Thermally expansive

Gravity

Fluid response (viscous)

Question 13

What are the driving mechanisms for plate motions?

Answer 13

Destructive margins, or “subduction zones”

Constructive margins, or “mid-ocean ridges”

Question 14

What are the 3 major types of plate boundaries?

Answer 14

Divergent or Constructive (mid-ocean ridges)

Convergent or Destructive (subduction zones)

Conservation or Transform margins (tranform faults)

Question 15

What happens during ocean-ocean convergence and what usually forms after?

Answer 15

Two oceanic slabs converge and one descends beneath the other, often forming volcanoes on the ocean floor then volcanic island arcs.

Example: Aleutian, Mariana, Tonga Islands.

Question 16

What is ocean-contingent convergence and what results?

Answer 16

Collision between an ocean and continent. Oceanic plate will subduct beneath the continents and volcanic arcs form on continents.

Exampls: Pacific NW, Andes, Japan.

Question 17

What is continent-continent convergence and what results?

Answer 17

Collision between two continents (one subducts beneath the other) and produces large mountain ranges.

Ex: Himalayas (collision of India and Asia) and Appalachians.

Question 18

What do diverging oceanic plates produce?

Answer 18

Oceanic ridges along well-developped boundaries, forming from mantle upwelling. Along ridges seafloor spreding creates new seafloor.

Question 19

What are divergent continental plate boundaries and what is an example of an area that is currently experincing this?

Answer 19

Continental rifts form at spreading centers within a continent. Rio Grande Rift is opening.

Ex: East African Rift

Question 20

Define Transform plate boundaries and give example

Answer 20

Plate slide past one another, no new crust is formed/destoyed, most join two segments of a mid-ocean ridge.

Roughly parallel the direction of plate movement.

Ex: San Andreas Fault in CA

Question 21

Define Mantle Plume.

Answer 21

Mantle plumes originate deep within the asthenosphere as molten rock which rises and melts through the lithospheric plate forming a large volcanic mass at a “hot spot”.

Question 22

Coral Reefs and Atoll formation.

Answer 22

Question 23

How do we measure present-day plate motion?

Answer 23

Global Positioning Systems (GPS).