Plate Techtonics Flashcards
(31 cards)
Asthenosphere
A layer of softer, almost plastic-like rock which moves very slowly and carries the lithosphere on top
Collision plate margin
A type of destructive margin where two continental plates moves towards each other.
Conservative plate margins
When two plates slide past each other and crust is not destroyed by subduction. They are associated with powerful earthquakes but no volcanic activity
Constructive plate margin
When two plates separate or diverge. They can create sea-floor spreading in oceanic areas and rift valleys in continental areas
Continental crust
Thicker (35km) and older than oceanic crust. It is also less dense than the oceanic crust and is mainly composed of granite.
Convection currents
Circular movements of magma driven by heat from the inner core.
Core
The widest section of the Earth, where the mainly silicate rocks are in a thick, liquid state, which become denser with depth.
Crust
The Earth’s outer shell, made up of oceanic crust and continental crust.
Destructive plate margins
When two plates collide or converge. This can occur when an oceanic plate meets a continental plate; when an oceanic plate meets an oceanic plate; or when a continental plate meets a continental plate.
Gravitational sliding
The movement of tectonic plates as a result of gravity.
Hot spot
An area where radioactive decay within the Earth’s core is concentrated, generating very hot temperatures and heating the lower mantle. This creates localised thermal currents where magma plumes rise.
Island arcs
Volcanoes arranged in an arc pattern in the ocean, formed when an oceanic plate subducts beneath another oceanic plate.
Island chains
A line of volcanoes in the ocean formed above a hotspot.
Lithosphere
The outermost solid layer of the Earth, approximately 100km thick, comprising the crust and upper mantle.
Magma
Molten rock, gases and liquids from the mantle accumulating in vast chambers at great pressures deep within the lithosphere.
Magma plume
A rising column of hot rock created by hot spots heating the lower mantle, creating localised thermal currents. Although usually found close to plate margins, these plumes occasionally rise within the centre of plates and then ‘burn’ through the lithosphere to create volcanic activity on the surface.
Mantle
The layer of the Earth between the crust and the core, composed of mainly silicate rocks.
Mid-ocean ridges
Chains of submarine mountain ridges that extend for thousands of kilometres across the ocean floor, caused by oceanic divergence.
Oceanic crust
Found beneath the world’s oceans and is formed at spreading centres on oceanic ridges at constructive plate margins. It is composed of basalt and is approximately 6km thick.
Ocean ridges
When oceanic plates rise at a constructive plate boundary due to upwelling magma in the mantle to form a ridge under the ocean.
Ocean trenches
Long narrow depressions on the sea floor where subduction is taking place.
Plate tectonic theory
The theory that explains the landforms and hazards that occur as a result of the Earth’s tectonic movement.
Primordial heat
Heat left over from the Earth’s formation. This is one reason the core’s temperature can exceed 5000°C.
Radiogenic heat
Radiogenic heat produced by the radioactive decay of isotopes, particularly Uranium-238, Thorium-232 and Potassium-40. This is one reason the core’s temperature can exceed 5000°c.
