Please enable JavaScript.
Coggle requires JavaScript to display documents.
Geology AS - Continental drift, sea floor spreading and plate tectonics…
Geology AS - Continental drift, sea floor spreading and plate tectonics
-
-
-
Patterns of earthquakes
Mid-ocean areas:
- Mid-ocean ridges (MORs): shallow-focus earthquakes.
- Axial rift system: shallow-focus earthquakes.
- Transform fault: shallow-focus earthquakes
Subduction zones:
- Deep-ocean trench and fold mountains.
- Collision zones.
Depth of focus:
The depth of focus is related to the plate boundaries.
- Shallow-focus: 0-70km deep.
- Intermediate: 70-300km deep.
- Deep-focus: 300-700km deep.
- Earthquakes do not originate at depths greater than 720km, because deeper rocks are not brittle enough to fracture.
Plate tectonics
The moving Earth
Types of plates:
- Ocean plate.
- Continental plate.
Plate tectonics theory
- Uppermost layer divided into a umber of sections, which are constantly in motion relative to each other, carried by moving material beneath.
- The sections are the rigid lithosphere plates.
- The moving material is the plastic asthenosphere, which is partially melted and acts as a rheid (a solid that can flow).
- The plate boundaries or margins between the lithospheric plates are zones of geological activity along which the relative motion is taken up.
- By comparison, areas within the plates are geologically inactive (aseismic).
-
Plate margins
Divergent plate margins
At all mature divergent plate boundaries, oceanic plates move apart and create new crust.
Evidence:
- Dating of the basalts, sediments and magnetic anomalies on the ocean floor.
- The MORs are among the largest mountain ranges in the world.
- Heat flow is higher than average across the rift.
- Occurrence of shallow-focus earthquakes as the magma moves or displacement along transform faults occur.
- Fissure volcanic eruptions often form basalt pillow lava.
-
-
-