tectonics Flashcards
who proposed the idea of continental drift
Alfred Wegener, 1912 Pangaea
- Asserted Pangaea had broken into pieces were still moving apart - related to the spinning Earth
what is density
mass per unit volume
what is the density stratification like on earth
denser substances towards the center
what kind of waves do earthquakes generate
seismic waves
2 types of seismic waves
surface waves - travel along Earth’s surface
body waves - travel through Earth
2 types of body waves
- P wave - compressional wave – refracted at density boundaries (travel 2x as fast as S waves in solids )
- S wave – shear wave – cannot pass through liquids
what is used to detect and record arrival times and intensity of seismic waves
seismograph
what did Oldham discover
“shadow zones” - different waves bend different ways in dense and less dense zones – able to get an idea of planet structure
crust characteristics
Earth’s rocky shell ~ 2-75 miles
- form shifting slabs of rock called tectonic plates
2 types of crust
Oceanic – basalt
Continental – granite
upper mantle characteristics
~400 miles thick
- The rigid top ~40 miles
lower mantle characteristics
~ 1400 miles thick
- extends to core – similar composition to asthenosphere, but does not melt due to rapid pressure increase – increases melting point
mantle characteristics
Oxygen, iron, magnesium, silicon - ~68% of Earth’s mass, 83% of volume
outer core characteristics
~1,400 miles thick
- Mostly iron and nickel
inner core characteristics
~ 1,500 miles in diameter
- Mostly iron
what factors determine the behaviour of the rock
temperature, pressure, rate at which stress is applied
Lithosphere characteristics
~ 44-125 miles depth
- crust + uppermost cool and rigid portion of mantle
- floats on (and is supported by) the denser deformable asthenosphere
Asthenosphere characteristics
~ 400 miles depth
- hot, partially melted, slowly flowing
upper core characteristics
dense, viscous liquid
inner core characteritics
solid, ~6 times denser than crust
what is earths internal heat maintained by
radioactive decay
- Heat transfer occurs via conduction (solid materials) + convection (fluids like the mantle)
what is buoyancy
Things sink until the same proportion of their volume is submerged – continents do this
what is Isostatic equilibrium
erosion of a top of a mountain causes their roots to rise to get equilibrium – cause continental crust to get thinner
crustal rock vs asthenosphere differences
- crustal rock is rigid and does not flow at surface temperatures
- Ships adjust to weight changes via buoyancy, but crustal rock cannot
what is a fault
When the force of uplift/down-bending exceeds mechanical strength of adjacent rock – the rock will fracture - adjacent rock fragments move vertically toward each other
what are the 3 historical debates over Earth’s age
- James Hutton – uniformitarianism
- Controversy with biblical school of thought – catastrophism
- Darwin and Wallace – biological evolution
Some interesting observations that led to the sea floor spreading hypothesis
- Many earthquake lines correspond with ocean ridges
- Seismographs indicated non-rigid layer in North Atlantic upper mantle - shows how tectonic plates can move
- Radiometric dating shows ocean floor is about 200 million years old - very young compared to Earth’s age
- Ocean floor sediments thickest at edge of Atlantic, thinnest near ‘Mid-Atlantic Ridge’
what are Mid-ocean ridges
spreading centers where oceanic crust forms
what are Subduction zones
areas where oceanic crust recycled into mantle
what is the sea floor spreading hypothesis and the key observations that support it
explains how new oceanic crust forms and moves across the ocean floor
- Spreading centers were hot
- New oceanic crust cooled and so shrunk in volume and become denser as move from center
- The ocean was thus deeper father from the spreading center
what are plate tectonics a combination of
Seafloor spreading + continental drift = plate tectonics
who proposed the idea of continental drift
Wilson, 1965
what are tectonic plates and how are they formed
- Earth’s lithosphere is divided into separate plates that float on the asthenosphere
- they move over the semi-fluid, deformable asthenosphere
- Heat from Earth’s interior causes the asthenosphere to expand, become less dense, and rise
- Rising material lifts and cracks the crust, creating the edges of tectonic plates.
3 ways that tectonic plates interact at plate boundaries
- Divergent
- Convergent
- Transform
divergent plate interaction
plates move apart
- where ocean basins are formed (mid-ocean ridge systems)
- can also get continental divergence (rift valley)
Convergent plate interaction and its 3 types
plates collide and one moves underneath the other
- Ocean to ocean convergence = Trench, Island arc systems
- Ocean to continent convergence = Trench, Volcanoes
- Continent to continent convergence = Mountains, Earthquakes
Transform plate interaction
plates move aside each other
what are mantle plumes
continent-sized columns of superheated mantle e.g. Deccan Traps, India; Pacific Northwest
- remain relatively stationary under moving plates
what are Hotspots
relatively narrow plumes of magma e.g. Hawai’i; Yellowstone
- remain relatively stationary under moving plates
what happens when an oceanic plate moves over a hot spot
Formation of a volcanic island chain
