Plate Tectonics Flashcards
Inner core
Can reach over 6000°C. In spite of heat and pressure, inner core is solid and contains iron with around 20% nickel content.
Outer core
Found at depth of 2900 km and can reach up to 5500°C. It is semi molten and is composed of mostly iron. We know it is semi molten as seismic waves cannot pass through it.
Mantle
Thickest later at around 2300 km thick. Consists of silicate materials that are rich in iron and magnesium. The upper part is rigid and is welded to the overlying crust. Most of the mantle is semi molten with temperatures reaching 5000°C.
Crust
Thinnest layer composed of tectonic plates.
Oceanic crust
Covers 65% of the earth's surface 6 km thick average. Denser 2.9g/cm3 Newer 200 million years old Contains Basalt, gabbro and sima.
Core
6350 km down and is the densest part of the planet.
Continental Crust
Thicker 30-70km average
Less dense 2.7g/cm3
Older 3.7 billion years old
Contains granite and sial
Lithosphere
The crust and the upper part of the mantle
Asthenosphere
Partial liquid layer in mantle below lithosphere. Part of mantle which lithosphere floats on.
Mohorovicic discontinuity
Division between mantle and crust in lithosphere.
Gutenburg discontinuity
Division between mantle and core.
Tectonic Plate
A section of the lithosphere which moves due to convection currents in the mantle.
The theory of plate tectonics
Idea that the earth’s lithosphere is made up of many plates that are moved around by convection currents.
Continental Drift
In 1912, Alfred Wegener suggested that all continents were pervasively joined to form a super continent (pangea) before drifting apart to form Laurasia and Gondwanaland and then eventually the continents we have today.
Constructive Plate Margin
Where two plates diverge
Eurasian plate and North American plate.
Mid-Ocean Ridges (when underwater), Rift valleys (when under land)
Seismically and volcanically active.
Destructive plate margin
Where two plates converge.
Oceanic-continental destructive margin
Nazca plate and South American plate.
Deep sea trenches, young volcanoes
Seismically and volcanically active
Oceanic-oceanic destructive margin
Pacific plate and Philippine plate
Deep sea trenches, island arcs
Seismically and volcanically active
Continental-continental destructive margin
Indo-Austrailian plate and Eurasian plate.
Fold mountains
Seismically active
Conservative plate margin
When two plates move past each other.
North American plate and Pacific plate.
Low ridges, fault lines
Seismically active
Hotspot
Areas of intense volcanic activity where heat is very localised underneath the earth’s crust that aren’t near to any plate margins.
Intrusive volcanic activity
Takes place beneath the earth’s surface where magma forced into the crust doesn’t break through. Typically composed of granite and dolerite
Extrusive volcanic activity
Takes place on the earth’s surface when magma forced into the crust breaks through.
Dykes
Intrusive volcanic feature. A vertical wall-like intrusion of igneous rock.
Sills
Intrusive volcanic feature. Horizontal intrusions of igneous rock.
Batholiths
Intrusive volcanic feature. Gigantic mass of igneous rock such as granite.
Laccolith
Intrusive volcanic feature. A mass of igneous rock that has been intruded between rock strata causing uplift in the shape of a dome.
Pyroclastic flows
High-density mixtures of hot, dry rock fragments and hot gases that move away from the vent that erupted them at high speeds. Most pyroclastic flows consist of two parts: a basal flow of coarse fragments that moves along the ground, and a turbulent cloud of ash that rises above the basal flow.
Lahars
Hot or cold mixture of water and rock fragments flowing down the slopes of a volcano and (or) river valleys.
Geyser
Minor form of extrusive activity. A type of hot spring where hot water and steam are ejected from the surface in a fountain. Form in areas of intense volcanic activity.
Fumaroles
Minor form of extrusive activity. Low pressure outlets of steam and gas. Emit steam, carbon dioxide but also CO. HCl and sulphur gases.
Hot springs and boiling mud
Minor form of extrusive activity. Source of stream flows near to area of recent intrusive volcanic activity so water is heated. Groundwater heated below surface may contain minerals dissolved from contact with hot rocks that build up on surface as colourful boiling mud deposits.
Seismic waves
Waves of energy that travel through the Earth’s layers, and are a result of an earthquake, explosion, or a volcano that gives out low-frequency acoustic energy.
Richter scale
Measure magnitude of an earthquake. Its a logarithmic scale where each unit represents a 10 fold increase in amplitude (strength) and a 30 fold increase in energy. Magnitude proportional to energy released.
Mercalli scale
Measures the intensity of the event and its impact. 12 point subjective scale based on eyewitness accounts where 1 is detected only by instruments and 12 is complete destruction. 8.5 on Richter scale = 12 on Mercalli.
Primary waves
Fastest waves that reach surface first. 330m/s in air, 1450m/s in water.
Push and pull earth in direction of travel
Compressional, hig frequency waves
Travel through any material.
Secondary waves
Slower than P waves (half as fast)
Waves move earth at right angles to direction of travel
High frequency transverse waves- very damaging
Travel through solids but not liquids (core) so can;t be measured at point opposite focus.
Surface waves
Slowest of seismic waves and come in two varieties
Love waves and Raleigh waves.
Love waves
Travel slowest on earth’s surface but do most damage
Side to side motion with shearing effect
Strength drops with increasing depth of earthquake.
Only travel through solids.
Raleigh waves
Radiate from epicentre at low frequency
Travel through liquids and solids
Rolling motion similar to a wave that cause shaking.
Benioff zone
Zone of melting of a subducted plate. 100km-700km. Melting caused by extreme heat and friction
