Lecture 3// Plate Tectonics Part 1

Question 1

Earth’s Composition of Layers

Answer 1

-Different mixtures of elements which makes up the layer.

Question 2

Earth’s Physical Properties of Layers

Answer 2

-Temperature, density and viscosity (ability to flow) of the layers.

Question 3

Composition:

-Inner Core & Outer Core

Answer 3

• Inner part of the Earth (2900km below surface).
• Dense ball composed by 90% iron and 10% nickel, oxygen sulfur.
• Inner core: solid (1220 km thick)
• Outer core: liquid (2260 km thick)

Question 4

Composition:

-Mantle

Answer 4

• Composed mainly by peridotite.
• Layer beneath the crust.
• 4000°C (near the outer core) - 850°C (rigid portion of Lithosphere).
• Solid rock but slowly flows due to high pressure and temperature.

Question 5

Composition:

Oceanic Crust & Continental Crust

Answer 5

-Solid outer shell, composed by granite, andesite and basalt.

Oceanic Crust:
-Magma emerges from the mantle, it cools and crystallize to create new sea floor.

Continental Crust:

• Composed by lighter elements than oceanic crust (Silicon, Sodium, Potassium, etc.).
• Floats on the denser Mantle.

Question 6

Mechanical Properties

• Lithosphere
• Asthenosphere
• Mesosphere
• Outer Core
• Inner Core

Answer 6

Lithosphere:

• Rigid, rocker outer layer.
• Consists of the crust and solid outermost layer of the upper mantle. (0-100 km)

Asthenosphere:
-Plastic (deformable) zone of the mantle lying beneath the lithosphere. (100-660 km)

Mesosphere:
-Solid part of the mantle below the lithosphere and the asthenosphere, but above the outer core. (660-2900 km)

Outer Core:
-Liquid zone below the mesosphere about 2260 km thick. (2900-5150 km)

Inner Core:
-Solid zone below the outer core about 1220 km thick. (5151-6371 km)

Question 7

Plate Tectonic Theory

Answer 7

-Lithosphere is broken into tectonic plates of various sizes, which continents are embedded in.
-Plates pushed by seafloor spreading at MORs.
-Plates pushing continental lithosphere are slower than those pushing oceanic plate alone.
(Mid-Atlantic Ridge (avg 2.5cm/yr, East-Pacific Rise (15-20 cm/yr, Central Indian Ridge (3-5 cm/yr))

Question 8

3 Movements along plate boundaries

Answer 8

• Diverge (divergent plate boundary).
• Converge (convergent plate boundary).
• Slide past each other laterally (transform plate boundary).

Question 9

Deep sea trenches

Answer 9

-Long and liner locations where oceanic plates subduct beneath oceanic or continental plates.

Question 10

Mid-ocean ridges (MORs)

Answer 10

• Wide, expansive ridges created by newly formed oceanic plate.
• Occurs in areas of uprising in mantle convection cells. As mantle rises, come minerals melt under decreased pressure (decompression melting).

Question 11

Mantle Convection

Answer 11

Hot mantle rock rises as cold rocks submerges.

Question 12

4 stages of divergent margin

Present-day example of continental rift

Answer 12

1) Mantle plume:
- Partial melting occurs in areas where heat/rocks in the mantle are rising towards the surface; causing gentle upwarping.
2) Rift Valley
- Lowland region that forms where Earth’s tectonic plates move apart, or “rift.”
3) Narrow seaway:
- A narrow sea or ocean channel between two bodies of land.
4) Wide ocean & expansive MOR:
- Mid-oceanic ridge is an underwater mountain range.

-Present-day example of continental rift is the East African Rift System (EARS) been Nubian part and Somalian part of the African Plate.

Question 13

3 evidences of seafloor spreading

Answer 13

1) Age of oceanic crust beneath the seafloor:
- Oceanic crust is found to be youngest at the ridge, and it gets progressively older as one moves away from MOR.

2) Thickness of sediments:
- Seafloor sedminets are thinnest at the ridge and thicken with distance.

3) Paleomagnetic record of oceanic crust:
- Cooling the ridge crest locks in the polarity at that time of its production creating a pattern of positive and negative magnetic anomalies.
- Lava cooling below 768°C allows iron to align itself with the existing polarity.