Flashcards in Plate Boundries Deck (32)
What two crusts are present at a destructive plate margin?
Oceanic and continental
When labelling a diagram of a destructive boundary, what key aspects should be included?
-arrows showing direction of play movement
-two plates, the oceanic plate being sub-ducted beneath the continental
-earthquake and Benioff zone
-convection currents in mantle
-magma chamber, composet cone and fold mountains
-a ocean trench with subduction zone
What is a real life example of a destructive margin?
Nazca crust and the South American plate
Peru- chile trench
The Andes as fold mountains
Give an explanation of a destructive boundary
-plates collide at a destructive boundary
-younger, denser oceanic crust sinks as it is forced beneath older permanent continental crust
-as the plate is submerged friction melts the oceanic crust and this contributed to the magma chamber as it melts and creates pressure so a volcano can form also, due to the immense pressure exerted, earthquakes can be triggered in the Benioff zone
-fold mountains occur as the collision occurs and the plate buckles upwards
-obduction could occur resulting in a mid ocean ridge
-ocean trench is formed
What crusts are present at a continental oceanic collision?
Oceanic and continental
When labelling a diagram for a continental- oceanic collision margin, what aspects would you include?
-direction of the two plates movement
-ocean, trench and a volcanic arc mountain range
-oceanic crust subducting beneath the continental crust
-a volcano with magma chamber going to the asthenosphere
-firstly add a lithosphere layer subducting then a asthenosphere
What is an example of a real life continental- oceanic collision boundary?
Nazca crust and South American plate
Give an explanation of a continental-oceanic collision boundary
-As the plates meet the denser lithosphere is forced down under the continental lithosphere and it descends by the process of subduction
-this can be made clear by a ocean trench at the surface
-as the oceanic plate descends, shallow focus earthquakes can be triggered by friction in the Benioff zone
-as subduction continues, sediment accumulated on the ocean floor is scraped off and forced onto the continental plate, this is called obduction this contributes to the continents size
-continual plate buckles forming fold mountains
-sea water enters the mantle, causing water to be liberated lowering the mantles melting point which produces magma which rises and can be erupted in the surface
What two crusts are involved in oceanic-oceanic collision?
Both oceanic crusts
When labelling a diagram of oceanic-oceanic collision, what key aspects would you label?
-direction of plate movement
-understand it's underwater
-trench thought one side and a island arc with a volcano
-one overriding plate and one subducting
-magma rising from the asthenosphere, through the lithosphere to the surface
What is a real life example of oceanic-oceanic collision?
The South American plate moving increasingly westwards until it meets the Caribbean plate
Give and explanation of a oceanic-oceanic collision boundary
When two oceanic plates collide one oceanic plate is eventually subducted under the other.
As the subducting plate descends into the mantle where it is being gradually heated a benioff zone is formed. This benioff zone is a zone of shallow,intermediate and deep focused earthquakes. Some deep focused earthquakes that occur at ocean ocean- collision boundaries
As the subducted plate descends into the mantle it is gradually heated allowing the formation of magma.
The magma that forms is andesitic in composition and begins to form when the subducted plate reaches a depth of 100 kilometres
This andesitic magma is formed from the partial melting of the asthenosphere just above the subduction zone.
This partial melting of the subducting plate is due to the loss of water as it descends into the mantle. The andesitic magma is now less dense than the surrounding material so it rises through the crust and erupts to form an arc of volcanoes called an island arc.
What crusts are involved in continental-continental collision (collision boundary)?
Continental and continental
What key aspects would you label on a diagram?
-one side subducting
-separate diagram with geosynclines and anticlines and synclines
-lithosphere and asthenosphere
What is a real life example of a continental-continental collision boundary?
Himalayas, Indian plate and Eurasian plate
Began moving 50 million years ago and is still moving
225 million years ago after Pangea broke up India began to migrate to wars the Asian continent at 9-16 cm per year
Continents then collided and the ocean was closed
Explain what happens at a continental-continental collision boundary
-ancient rivers once flowed in to ancient seas, geosynclines which over time, layers of sediment built up and compressed in the geosyncline
-as the plates move together, the sediment begins to buckle upwards as it is compressed by the moving plates
When the plates collide a fold mountain has been created with anticlines and sync lines as neither crusts can be subducted due to their low density
What crusts are involved in a constructive plate margin?
Oceanic and oceanic crusts
On a diagram for a constructive plate margin, what key aspects would be labelled?
-mid Atlantic ridge a range of submarine mountains and volcanoes
-fissure, volcanic vent
Asthenosphere and convection currents
What is a real life example of a constructive plate margin?
Mid Atlantic ridge is made up of the Eurasian plate and the North American plate pulling away from each other's
Explain a constructive plate margin
-played pull apart in opposite directions
-as they move apart they leave cracks and fissures, lines of weakness, which allow magma to filter up and escape in the gap
-the magma eventually erupts and cools to form new land which can create huge ridges of undersea land (mountains and volcanoes)
-the process of sea floor spreading is developed as the lave which erupts is andesitic so, it can travel long distances as it is less viscous and cools to form new land
What crusts are involved at a conservative plate margin?
Continental and continental crust or oceanic and oceanic
On a diagram of a conservative margin, what key aspects would be labelled?
-direction of plates
-a focus and epicentre
-crust, lithosphere and asthenosphere
Name an example of a real life conservative plate margin
San Andreas fault Pacific plate and North American plate
Explain a conservative plate margin
-movement of these plates is horizontal and they slide past one another
-movement is classed as either sinistral (left) or dextral (right)
-lithosphere is neither created or subducted
-no volcanic activity as they are sites of extensive shallow earthquakes of a high magnitude
-it is a real lease of pressure built up over thousands of years
Who came up with the hotspot theory and in what year?
J Tuzo Wilson in 1963
What did Wilson note firstly about hotspots?
Wilson noted that in certain locations around the world, such as Hawaii, volcanism has been active for very long periods of time. This could only happen if relatively small, long-lasting, and exceptionally hot regions called hotspots existed below the plates that would provide localized sources of high heat energy (thermal plumes) to sustain volcanism
What did Wilson hypothesise?
linear shape of the Hawaiian Island-Emperor Seamounts chain resulted from the Pacific Plate moving over a deep, stationary hotspot in the mantle, located beneath the present-day position of the Island of Hawaii. Heat from this hotspot produced a persistent source of magma by partly melting the overriding Pacific Plate. The magma, which is lighter than the surrounding solid rock, then rises through the mantle and crust to erupt onto the seafloor, forming an active seamount. Over time, countless eruptions cause the seamount to grow until it finally emerges above sea level to form an island volcano. Wilson suggested that continuing plate movement eventually carries the island beyond the hotspot, cutting it off from the magma source, and volcanism ceases. As one island volcano becomes extinct, another develops over the hotspot, and the cycle is repeated.
What evidence is there to suggest the Hawaiian chain get progressively older?
Ancient Hawaiians during voyages noticed differences of erosion, soil formation and vegetation
Islands to north west (niihau and kauai) were older then the southeast (maui and Hawaii)
What is a mid ocean ridge?
Contains volcanoes and mountains, longest continuous uplifted feature of the surface of the planet
Ocean crust is pulling apart and new crust is made
Magma rises and cools to form new crust