Tectonic Plate

Question 1

(How tectonic plates move)
Slab Pull

Answer 1

• it occurs at convergent plate boundries, where one tectonic plate is forced under another in a process called, subduction.
• as denser, oceanic plate subducts, gravity pulls the plate deeper into the mantle
• this creates a pulling force on the rest of the olate, helping to move it away from mid oceanic ridges
• the weight of the descending slab, effectively drags the plate with it

Question 2

(How tectonic plates move)
Ridge Push

Answer 2

• it occurs at divergent plate boundries particularly at mid oceanic ridges
• at these ridges, magma rises from the mantle, creating new crust as the tectonic plates push away
• this newly formed crust is hot and elevated, creating a slope as it cools and becomes denser
• the force if gravity causes this denser, cooler crust to slide away from the elevated ridge
• this exerte a pushing force on the rest of the plate, helping to drive its movement away from the ridge

Question 3

(How tectonic plates move)
Convection currents

Answer 3

• the heat stored in the core rises due to high energy
• the heat cannot escape past the plates, so it stays beneath the tectonic plates
• the movement of the heat under the plate causes slight movement of the tectonic plate
• but eventually, heat looses energy and density, so it sinks back down to the core and repeats, like a cyle

Question 4

Tectonic plates

Answer 4

Tectonic plates are made of peices of the earth’s rigid lithosphere. The lithosphere is formed of the crust and upper mantle.

The plates sit above the asthenosphere below. The asthenosphere behaves plastically, as it is solid but with some plastic qualities. This means it can move slowly.

Question 5

Contintental crust

Answer 5

Thick, 10 - 70 KM
Over 1500 million years old
Mainly granite
Density -> 2.6 g/cm3

Question 6

Oceanic crust

Answer 6

Thin, 6 - 10 KM
Less than 200 million years old
Mainly basalt
Density -> 3.0 g/cm3

Question 7

The theory of continental drift:
Alfred Wegner

Answer 7

His evidence:
- fossil plants and animals, such as sesosaurs, a fresh-water reptile, was found in both South America and Africa
- Similar patterns of rocks on both side of the atlantic. For example, the Appalachian mountains and the Munros.

Question 8

(Evidence supporting the theory of tectonic plates)

• Paleomagnetism

Answer 8

• The polarity of the rock either side of the Mid Atlantic Ridge, alternwted in a striped pattern - symmetrical
• The oceanic crust was slowly moving away from the plate boundary
• The oceanic crush got older with distance from the Mid Atlantic Ridge

Question 9

(Evidence supporting the theory of tectonic plates)

• Sea Floor Spreading

Answer 9

• the sea floor is spreading because the atlantic ocean is getting bugger
• this means the distance between South America and Africa is increasing at a rate of a few centimetres per year
• However, the crust is also being destroyed at convergesnt plate margins in the process of subduction

Question 10

Divergeant plate margins - continental

• Rifting

Answer 10

the divergence of continental plates initiates continental rifting, where the lithosphere stretches and thins. This process forms a rift vallay, as the land subsides and stretches. Overtime, the rift can evolve into a new plate boundary.

Question 11

Divergeant plate margins - continental

• Volcanic Activity

Answer 11

the stretching and thinning of the crust allow magma from the mantle to rise, leading to volcanic eruptions. Eruptions at these margins are typically basaltic, producing shield volcanos or volcanic rift zones

Question 12

Divergeant plate margins - continental

• Ocean Formation

Answer 12

If rifting continues, it can eventually lead to the formation of a new ocean basin. As the rift widens the continental crust is replaced by oceanic crust, eventually leading to the creating of a new divergent playe boundary similar to those found at mid oceanic ridge.