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divergent plate boundaries - Coggle Diagram
divergent plate boundaries
🔀 PLATE MOVEMENT
Plates move away from each other
Usually occurs at mid-ocean ridges
Can also occur within continents → continental rifting
Driven by processes including:
Mantle convection
Ridge push
Slab pull elsewhere in the plate system
2. MID-OCEAN RIDGES
Example: Mid-Atlantic Ridge
Long underwater mountain chains
Form where oceanic plates diverge
Magma rises through fractures
Magma cools → new basaltic oceanic crust
Older crust moves away from the ridge
Example
North American Plate ↔ Eurasian Plate
South American Plate ↔ African Plate
at the Mid-Atlantic Ridge.
3. MAGMA & VOLCANISM
As plates separate:
Pressure decreases in the mantle↓Partial melting occurs↓Magma rises↓Magma erupts / intrudes↓New oceanic crust forms
Volcanic activity
Usually basaltic magma
Relatively low viscosity
Can produce effusive eruptions
Lava flows build new crust
→ Divergent boundaries are associated with frequent volcanic activity.
4. EARTHQUAKES
Movement along faults produces earthquakes
Usually shallow-focus
Generally less powerful than major subduction-zone earthquakes
Earthquakes occur as the crust fractures and adjusts to spreading
Key point:Divergent boundary → shallow earthquakes + volcanic activity
5. SEAFLOOR SPREADING
New crust forms at the ridge
New crust moves away from ridge
Ocean becomes wider
PALEOMAGNETISM
This is an important A-level evidence point.
When basaltic lava cools:
Iron-bearing minerals align with Earth's magnetic field
The magnetic orientation becomes preserved in the rock
Earth's magnetic field has reversed many times
This produces:
Alternating magnetic stripes on either side of the mid-ocean ridge.
7. AGE OF OCEANIC CRUST
Closest to ridge = youngest
Further from ridge = older
8. CONTINENTAL RIFTING
Divergence can begin within a continent.
Process:
Upwelling mantle↓Heating + uplift↓Crust stretches↓Normal faults develop↓Rift valley forms↓Crust becomes thinner↓Magma rises↓Eventually → new ocean basin
Example: 🌍 East African Rift
African Plate is undergoing continental rifting
Crust is being stretched and faulted
Volcanic activity occurs
Represents an early stage of continental breakup
. EXAMPLE — MID-ATLANTIC RIDGE
Location: Atlantic Ocean
Plates:
North American ↔ Eurasian
South American ↔ African
Processes:
Plates diverge
Magma rises
New basaltic crust forms
Seafloor spreads
Shallow earthquakes
Volcanic activity
Evidence:
Symmetrical magnetic stripes
Increasing age of crust away from ridge
High heat flow
Direct observation of seafloor spreading