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Features & processes at plate boundaries - Coggle Diagram
Features & processes at plate boundaries
The Wilson Cycle
explains the formation to extermination of oceans
1) Embryonic
uplift
complex system with linear rift valleys on continent
East African rift valleys
2) Juvenile
divergence (spreading)
narrow seas with matching coasts
Red Seas
3) Mature
divergence (spreading)
ocean basin with continental margins
Atlantic and Arctic oceans
4) Declining
convergence (subduction)
island arcs and trenches around basin edge
Pacific Oceans
5) Terminal
convergence (collision) and uplift
narrow, irregular seas with young mountains
Meditterean Sea
6) Suturing
convergence and uplift
young to mature mountain belts
Himalayan mountains
Conservative plate margins
conservative motion is where 2 plates are sliding (shearing) past eachother
strike-slip or transform faults
any plate
where 2 plates slide past eachother, often at acute angles
friction between plates causes earthquakes
few volcanoes are formed
1) plates try slide past eachother
2) plates stick or jam together
3) huge amount of pressure build up
4) pressure release causes violent earthquake
5) plates move on a few mm
6) no volcanic activity
Alpine fault, New Zealand:
a major plate boundary with a segment where plates slide past eachother
Australian & Pacific moving southwards, difference in speeds
San Andres Fault:
Pacific plate & N.American plate
pacific plate is faster
San Fransisco & Los Angeles both sit on the fault
Conservative:
-strike-slip or transform faults
(San Andreas Fault)
Physical features:
fault line, fractured rocks
Magmatism (type & cause):
no volcanic activity
Earthquake (location & cause):
frictional resistance of movement along boundary causes pressure build up
rocks fracture releasing energy as earthquakes
Driving mechanism:
plates slide past each other or in a shearing motion
Convergent plate boundaries
convergent margins are where plates are moving towards eachother under compression
island arcs (ocean-ocean)
andean type subduction zones (ocean-continent)
continent collision zones (continent-continent); orogeny-fold mountains
move towards eachother; earthquakes, volcanoes, deep trenches
oceanic lithosphere is more dense so subjects e.g. oceanic Nazca plate
older oceanic goes under the younger oceanic
two continental, neither subjects
Pacific Ring of Fire:
island arcs on the West side
andean types on the East side
Island arcs:
oceanic crust is subjected beneath other oceanic crust
the subjected slab dehydrates & releases fluids that melt the overlying mantle wedge
the magma rise to form magma chambers beneath volcanic islands
volcanism is explosive
volcanism forms new crust, the erosion of these forms new sedimentary rocks creating new land
Example:
Lesser Antilles Island Arc
Haiti (earthquakes) & Monsterrat (volcanoes)
Caribbean plate & N.American plate; N.American plate subjects beneath the Caribbean plate
an arc of volcanic islands are formed
magmas are andesite and rhyolites & highly explosive
trench -> fore-arc ridge -> fore-arc basin -> volcanic arc & mountain range -> back-arc basin
oceanic crust -> <- continental crust
Andean type subduction zone:
oceanic crust subjects beneath continental crust
slab melting generates magmas that rise to form volcanoes
volcanism is explosive, magmas are andesite or rhyolites
Slab pull:
a driving force for plate motion
the mass of the cold dense downing slab pulls the rest of the oceanic lithosphere with it
mineral transformation to denser structures add to the density contrast and pull effect
mid oceanic ridge, ridge pull
subduction zones, slab pull
The Benioff Zone:
occurs at any subduction zone
the line of earthquakes along the top of the slab is called the Benioff Zone
these earthquakes are caused by: faulting in compression, blending of the brittle plate, friction between the plates, back compression in denser mantle
Continent-continent margins:
the arrival of another continent at an island arc causes continent collison
one continent subjects beneath another, yet as both are warm & buoyant, crust material is squeezed vertically forming a mountain range with a deep root
deep melting gives rise to instrusion of magma
Forming the Himalayas:
the collision of India with Eurasia formed the Himalayan mountain range, since 40m years, India rapid northward 46mm/yr, plates can be locked for 10s-100s years
as India subducts northwards a series of thick slices of crust pile up or are scrapped off eachother
these slices are serpated by major faults along which earthquakes occur as they move
Features:
Benioff zone (oceanic-oceanic) (oceanic-continent)
island arc (oceanic-oceanic)
granite batholiths (oceanic-oceanic) (oceanic-continent) (continent-continent)
fold mountain chains (oceanic-continent) (continent-continent)
ocean trench (oceanic-oceanic) (oceanic-continent)
reverse faults (oceanic-oceanic) (oceanic-continent) (continent-continent)
Features of an active island arc (Sumatra, Indonesia):
trench, formed by downbending (dragging down) of the subjected ocean plate
fore arc basin, a depression formed in front of the arc and behind the outer arc ridge, volcanic materials and erosion of the arc forms sediment that fills the basin
accretionary prism, formed by off scraping of sediment & ocean crust, reverse faults pile up material to form an emergent ridge
subduction zone, formed by convergence of plates as cold dense ocean crust is forced downward, density drags the plat deeper (slab pull)
volcanic arc, formed by rise of magma, buoyancy of magma forces crust up & addition of volcanic products builds up mountain range
partial melting, dehydration & melting of the slab forms magma that rises upwards & forms intrusions
back-arc basin, convection causes tension / extension leading to a shallow basin, erosion of the ride causes deposition of sediment that fills the basin
Features of an Andean-Type plate boundary:
accretionary prism
trench
volcanic chain / arc
explosive magmaatism
magma chamber
dehydration & melting
slab pull
Benioff zone
ocean crust & lithosphere with continental crust & lithosphere
Features of a continent-continent collision zone:
example of Indian plate -> <- Eurasian plate
frontal mountain ranges
faults, reverse faults, thrust belts
major earthquakes
slices of ocean crust, ophiolites
metamorphism melting zone
thrust suture zone (boundary)
Himalayan mountain range
tibetan plateau
granite intrusion
Oceanic-continental "Andean Type":
(Nazca-S.America)
Physical features:
trench, sediments, accretionary prism, mountain chains, fold mountains, volcanoes
Magmatism (type & cause):
plutons rise to surface and batholiths form due to melting of oceanic plate subducting beneath continental plate
Earthquake (location & cause):
Benioff zone, both shallow and deep earthquakes along the subduction zone
Driving mechanism:
difference in density between the plates force oceanic plate to subduct
convection currents as well as "ridge push" and "slab pull" processes move the plates
Oceanic-oceanic "Island Arc":
(N.America-Caribbean)
Physical features:
trench, sediments, island arc, accretionary prism, fore arc basin, back arc basin, volcanic islands
Magmatism (type & cause):
partial melting: dehydration & melting of slab forms magma that rises upward, volcanic arc formed by rise of magma
Earthquake (location & cause):
occur along the top of the slab
caused by friction, compression and bending
Driving mechanism:
older oceanic crust is more dense so subducts beneath the other
convection currents as well as "ridge push" and "slab pull" processes move the plates
Continental-continental "Orogeny":
(India-Eurasia)
Physical features:
mountain ranges, reverse faults, plateaus, thrust suture zone
Magmatism (type & cause):
minimal volcanic activity
Earthquake (location & cause):
intense convergence causes build up of extreme pressure, this causes major earthquakes
Driving mechanism:
plates have similar densities reducing the amount of subduction, warm buoyant plates squeezed vertically
Divergent plate boundaries
plates moving away from each other, produced by tensional forces (stretching of the crust)
mid-ocean ridges
continental rift zones
Continental rift zones:
a spreading centre below continental crust causes a massive tear in the continents
tension & rise of magma leads to thermal expansion of rocks and buoyant warping of the crust
the crust stretches and collapses inwards on faults forming a rift valley
East African Rift Valley:
a major tectonic crack tearing Africa apart, various African rift zones
Mid-Ocean Ridge:
next stage: continued tension leads to influx of the ocean forming a linear sea (The Red Sea)
finally, a mature ocean is formed with a Mid-ocean ridge
What happens at mid-ocean ridges?
1) the hot mantle rises on the top of a convection current
2) heat causes the crust to become warm & buoyant, forming a ridge, tension forms cracks
3) magma is injected along tension cracks or fractures along dykes giving rise to basalt lava flows on the surface
4) magma injection pushes the plates apart
Transform faults & mid-ocean ridges:
mapping of the ocean floor by sonar revealed a curious pattern of fractures which offset the ridges
these fractures offset the ridge and allow movement away from the ridge
shallow earthquakes occur as magma is emplaced & faults move
transform faults (lie orthogonal to the ridge, 90) accommodate differential spreading rates (between 2-5cm/yr) parallel to the poles
on a globe, this means faster rates at the Equator, and slower rates towards the poles
Iceland: Mid Atlantic Ridge:
the MOR is above sea level
Continental rift zone features:
linear fault block mountain ranges & basins
rift valley
ribbon lakes sedimentation
faults & fissures pathway for magma
volcanoes, lavas & hot springs
rising mantle, forms crustal up-warping or doming partially melting
Surface features of a mid-ocean ridge:
canyon
continental slope
volcanic islands
mountain range (ridge)
atoll
continental shelf
guyot
fault/fracture
abyssal plain
rift (axial)
continental rise
coastline
Features:
mantle uprise & melting, magma injection
axial rift zon
Process and landforms:
currents are caused by heating of the mantle by the Earth's core leading to up-flow of more buoyant (lighter) asthenosphere
as the currents spread laterally away from the ridge they cause divergent plate motion and tensional stresses
when the plates move apart melting of the upper mantle peridotite occurs and basalt in injected into the crust and extrudes as lava (pillow lavas)
thermal expansion of the lithosphere and rise of magma forms an elevated ridge (mountain chain)
expansion and tension leads to formation of fractures and faults.
basalt intrudes along these faults along the ridge axis and pushes apart the crust (lateral spreading), a process called seafloor spreading
the forceful rise of magma also leads to earthquakes along the ridge
at the centre of the rift zone faults form as a result of tensional stress release leading to shallow level earthquakes
earthquakes also occur along transform faults which lie orthogonal (at 90° to the ridge and accommodate differential spreading rates (between 2-5cm/yr)
as the lithosphere spreads it cools, contracts and sinks; the increase in density of the ridge causes gravitational collapse pushing crust away from the ridge, down the slope towards the abyssal plain; a process called ridge push
inward collapse of the axial zone along normal faults leads to formation of an axial rift zone with elevated rift shoulders forming small ridges
Divergent:
rift zone or MOR
Physical features:
ridge, axial rift, abyssal plain, faults (transform and normal), sediments, volcanoes and lava flows
Magmatism (type & cause):
volcanoes and fissure eruption, lava flows, basalts, effusive, pillow lavas, black smokers
cause: mantle rise and melting
Earthquake (location & cause):
shallow along faults parallel to ridge axis and along transform faults, occur during magma emplacement
cause: tension due to spreading
Driving mechanism:
rising convection currents by mantle melting leads to magma injection along faults, ridge push mechanism, gravity driven collapse of ridge