Litho: Global Structural Landforms Flashcards
What are the types of divergent plate boundaries?
O-O
C-C
What are the types of convergent plate boundaries?
O-O
O-C
C-C
What landforms can be found at C-C divergence? (Hint: East African Rift Valley)
Rift valleys, faults, volcanoes, lakes
How does C-C divergence occur?
A cause of tensional stress is mantle plumes. These are localised regions of the mantle where heat flow is well above the surrounding average. They unwrap the overlying crust, resulting in doming and three-armed rifting.
How are rift valleys formed at C-C divergent boundaries?
Hor rising plume results in crustal stretching, forming tensional cracks. Broken Slabs (graben) are displaced downwards, creating rift valleys. Horsts are left upstanding.
What type of faults can be found in C-C divergent boundaries?
Step faulting - taller; cliff like
Grid faulting - floor is broken by small scale faults
How are volcanoes formed at C-C divergent boundaries?
Volcanism here is supplied by a mixture of decompression melting near the top of the upwelling zone and partial melting of the lower crust. Eg. Volcano Longonot
Flood basalt a formed from massive outpouring of lava from volcanoes along valley floor.
How do lakes at C-C divergent boundaries form?
Formed when the floor of the Rift Valley drops below water table. Types of lakes include soda lakes eg. Lake Natron
How does O-O divergence occur?
When viscous drag of the mantle convection currents exerted on the overlying plate causes it to be torn apart, resulting in sea floor spreading.
What landforms can be found in O-O divergent plate boundaries?
Mid-oceanic ridge (eg. Mid Atlantic ridge)
Volcanic islands
What are the features of mid-oceanic ridges at O-O boundaries? (Hint: There are 3)
1) thousands of km long and hundreds of I’m wide
2) a central Rift Valley runs down the middle of most mid-oceanic ridges. High geothermal heat flow increases temps due to underwater extrusion of pillow lava
3) transformed faults gives ridges a staggered path perpendicular to main ridge
How are volcanic islands at O-O divergent boundaries formed?
Iceland is a tholeitic basaltic plateau which is a part of the mid-oceanic ridge that appears above sea level. It sits directly on a mantle plume. Decompression melting produces basaltic magma. Iceland grows outwards and is constantly pulled apart by sea floor spreading.
What landforms can be found at O-O convergent boundaries?
Ocean trenches and volcanic island arcs
Describe ocean trenches in O-O convergent boundaries
Ocean trenches are long narrow troughs that usually mark zones of subduction. Most seismic activity takes place under the island arc.
How are volcanic island arcs in O-O convergent boundaries formed?
Partial melting if the descending plate and upper mantle which forms andesitic lava
Hydration melting of upper mantle as water is forced upwards
(More silica more explosive)
What landforms can be found in O-C convergent boundaries?
Ocean trenches, continental volcanic arc (strato volcanoes), Andean type fold mountains/mountain chains
Describe ocean trenches and what happens at ocean trenches at O-C convergent boundaries?
Ocean trenches are somewhat parallel to the coastline and fold mountains. More seismic activity under fold mountains.
How are continental volcanic arcs formed at O-C convergent boundaries?
Partial melting of upper mantle and hydration melting due to water rich oceanic crust. Magma formed is less dense than surrounding rocks and rises, giving rise to volcanic activity
- intrusive volcanism: rising andesitic magma cools and crystallises, forming batholiths
- extrusive volcanism: strato volcano chains that have explosive eruptions
How are Andean type fold mountains formed? (O-C convergence)
Orogenesis
Thick sequences of sediment that has accumulated along continental margins are compressed and deformed, causing folding. Faults occur when brittle rocks rupture.
How are Himalayan type fold mountain formed (C-C convergence)
Orogenesis
When two continents collide, the continental crust is too buoyant to be dragged downward. The collisions sweeps up any sediment accumulated along the margins of the continents, causing folding and faulting. Eg. Himalayas
Describe transform boundaries (hint: San Andreas Fault)
Zones of shearing where plates slide past each other horizontally. Marked by zones of intensely shattered rock. Strike slip faults found here
