Week 2: Plate tectonics Flashcards
What is meant by plate tectonics?
Plate tectonics is a theory that Earth’s lithosphere consists of ~20 distinct pieces (plates) that slowly move relative to one another.
Describe and identify the three types of tectonic plate boundaries and state examples in the world.
(From the video lectures)
Divergent - [Constructive] Two plates move apart. [The Mid-Atlantic ridge]
Convergent - [Destructive] Two plates move towards one another, one subducts.
- oceanic-continental: Andes
- oceanic oceanic: Japan
- continental continental: Himalayas
Transform - Where 1 plate slips along the side of another plate. [San Andreas fault]
Describe and identify pillow lava.
Lava that spills from the mid-ocean ridge axis and cools quickly to form a layer of basalt blobs (that looks like
cushions) on the sea floor. (As plates diverge)
Describe and identify subduction zones.
Subduction is when two plates converge and the denser plate (oceanic plate) sinks below the other into the mantle. (As plates converge)
Describe and identify Wadati-Benioff zone.
The Wadati-Benioff zone is a band of
deep earthquakes that occur in subducted oceanic lithosphere. (As plates converge)
Describe and identify Accretionary prism.
An accretionary prism is a wedge-shaped mass, including sediment, that has settled on the surface of the subducting plate that gets scraped up during the subduction process. (As plates converge)
Describe and identify continental volcanic arc.
A volcanic arc that developed on a continent and caused mountains to rise.
Describe and identify island arc.
A volcanic arc that developed on the ocean floor.
Describe and identify transform faults that occur between segments of diverging mid-ocean ridges.
Fracture zone – narrow belts of broken and irregular sea floor between the short segments of the mid-oceanic ridges.
Oceanic transform faults - the portion of a fracture zone along which movement occurs at mid ocean ridges.
3 main transform boundaries along Pacific plate.
Describe triple junctions
and give examples.
Places where three plate boundaries intersect at a point.
E.g. Australian-Indian plate; African plate; Antarctic plate.
Describe hot spots and give examples.
When a plume of hot mantle rock rises from just above the core-mantle boundary and causes volcanic action at an isolated volcano.
As a plate moves over the mantle plume, the volcano moves off the hot spot and dies, and a new volcano forms over the hot spot. (Seamount chains are formed.)
E.g. Hawaii! Iceland.
Continental drift hypothesis?
The idea that the Earth’s continents move relative to each other by appearing to drift across the ocean bed. Ain’t that cool.
What is sea-floor spreading?
The process where new sea floor is always forming.
What are four features of an ocean floor?
- Mid-ocean ridges - elongated submarine mountain ridges. (Not very deep.)
- Deep-ocean trenches - The trench 8-12km deep and borders volcanic arcs.
- Seamount chains - A row of submarine mountains where only the last is an active volcano.
- Fractured zones - Narrow
bands of vertical fractures at roughly right angles to mid-ocean ridges.
What is heat flow?
The rate at which heat rises up from the Earth’s interior through the floor of the ocean.
What do earthquakes show?
The movement of the crust. So an earthquake belt defines the position of plate boundaries.
The youngest oceanic crust is
presently being formed at mid-oceanic ridges. The oldest is about 150 to 200 million years old. This older material is the farthest from the spreading centers and is going to be subducted next.
Craaaazy.
What is the difference between the two continental margins active and passive plate boundaries?
Active - [Divergent, Convergent, Transform] Marked by earthquakes, volcanoes, mountain formation and deep ocean trenches. (e.g. West Coast of South America.)
Passive - Plates move away from seafloor spreading. Very little activity. Marked by a continental shelf. (e.g. East and West coast of Africa.)
What is the difference between magma and lava?
Magma is molten rock when it’s underground.
Lava is molten rock when it breaks through Earths surface.
