Theoretical Frameworks to explain Plate Movements

There are 2 different types of crusts given below:

• Oceanic (high density, mainly basalt)
• Continental (low density, mainly granite)

Structure of the Earth:

Structure of the Earth

	Temperature	Distance	Composition
Crust	400oC at base	7-70km	Granite/basalt Solid Less dense
Mantle ↳ Has a temp gradient	870oC	2890km	Peridotite Mixed density layers Solid & liquid layers
Outer core	4400oC to 6100oC	5150km	88% Iron Dense Liquid
Inner core	7000oC		80% Iron Dense Solid

Plate Tectonic Theory:

The following evidence supports the theory:

1. Mantle Convection:

• The heat derived from the Earth's core rises within the mantle to drive the convection currents ∴ moving the tectonic plates.
• Heat radiating from the inner core through the mantle material causes it to convect as it behaves like a viscous liquid.
• The convection cells make contact with the base of the crust, causing friction, and so drag the crust along in the general direction.

2. Palaeomagnetism:

• The outer core is mostly liquid iron & it convects.
• This movement creates a magnetic field for the earth (direction changes every 100000 yrs).
• When new igneous rocks, inc lavas, cool to form solid rock, they trap in the magnetic field direction of the time.
• Geological records of magnetic directions are symmetrical either side of constructive plate boundaries, proving that the oceanic crust has been moving apart in places for a very long time.

3. Subduction and Slab Pull:

• At destructive plate boundaries, the denser oceanic plate is subducted under the less dense continental plate.

• As the slab of the oceanic plate descents, it pulls the rest of the plate with it. The Benioff zone:

• An area of seismicity corresponding with the slap being thrust downwards in a subduction zone.

• The different speeds and movement of rock at this point produces numerous earthquakes.

  

Seafloor spreading:

• Occurs at divergent boundaries under the oceans.
• Seafloor spreading is a continuous input of magma forming a mid-ocean ridge.