Tectonics: Earth's Structure + Plate Movement Theoretical Framework Flashcards
Describe the continent lithosphere 
Up to 70 km, thick, solid, less dense 2.8 g/cm³ Granite
O and S waves thro
Describe oceanic lithosphere
Up to 7 km, thick solid denser 3.3 g/cm³. Basalt, P and S waves pass through 
Describe the mantle
Solid but plastic with different densities made of periodite silica, rich Rock
P and S waves pass through a variable rates due to changes in density
Describe outer core
Liquid, dense, 12% sulphur, 88% iron only P-waves past thro high temperature
Describe inner core
Solid densest, hottest 20% nickel, 80% iron
only P waves reach the inner core and pass thro
What heats up the inner core?
Residual heat and radioactive decay
What three mechanisms move plates?
Convection current slab, pull ridge push
How to convection currents occur
Core is hot and heats up surrounding magma which makes it less dense. This causes the rock or magma to rise as it rises it cools down, gets denser- as sinks it pushes against the plates, helping them move.
What is slab pull?
As a plate subducts its weight pulls, the rest of plate along - the more that is subducting the greater the force of the pull
What is ridge push?
As magma make its way to the surface and pushes through it separates and pushes against the surrounding plate
evidence for continental drift - biological
fossil remains across continents e.g. mesosaurus fresh water species fossil remains in south afric and brazil - can’t have swam across salt sea
evidence for continental drift -climatological
carboniferous limestone pennines and uk coal deposists need high temp and wet - fast decomp - suggests Eng was in tropics
evidence for continental drift - geological
mount ranges across continents - Appalachian (NA) and Caledonian (Scandenavia and UK)
what is the plate tectonic theory
earths surface is made up of plates which move relative to each other at diff speeds or directions. The boundaries btw plates are zone of tectonic activity like seismicity, vulcanity and mountain building
Wadatti Benioff
Date
Idea
Significance
1920
EQ at Wadatti Benioff due to subduction - zone where plates no longer exist
Explains EQs
Mantle Convection Current
Evidence for seafloor spreading
Magnetic properties of the erupted basalt
earths magnetic field have been shown to flip occasionally so north and south pole swap
salts contains minute magnetic minerals and this changes directions depending on the earths magnetic field at the time of eruption 
magnetic stripes
Polarity reversal from rock formations at the, mid-Atlantic ridge 
Arthur Holmes, date, hypothesis and critique
1927 British geologist, he suggested convection currents. As a reason for continental drift. He suggest a radioactive decay generate enough heat for convection currents. As mantle is not exact same temperature throughout. Heat not evenly distributed, causing a magma to sink and rise
Holmes taken seriously as he had no real evidence.
Harry Hess theory, date, evidence and hypothesis and critique
1961 seafloor spreading hypothesis
Using naval submarine detection technology recorded young age is four pieces on or near ridges are much older ages for ocean rock near the continental masses began to theorise that made ocean ridges. Mark structurally weak spots are in the ocean floor is being pushed to either side, new magma from deep within the Earth rises easily for this weak spots and eventually creates new seafloor
Critique is if new ocean floor is continually being made, why has earth not expanded
Frederick, Vine and Drummond, Matthews, date, theory and significance
1963 theory of palaeomagnetism repeated reversals of earths magnetic field
as underwater volcanic, eruption occurred and the basaltic lava entries intrudes crust during the cooling process process. Particles of iron oxide align themselves along the earths magnetic field, which provides a permanent record of the polarity at the time which alternates approximately every 200,000 400,000 years creating a series of magnetic stripes with rocks aligned. this can be used to age the rocks
deep ocean trenches cut across existing magnetic anomalies. The boundary between the ages of lithosphere suggest that older or denser oceanic crust subducts, which provides an explanation to Hess’s greatest critique.
Tuzo Wilson, date, theory and significance
Propose the Conservative plate Boundry - fault slips, horizontally, connecting oceanic ridges divergent plate, boundaries to ocean trenches of convergent boundaries. They were consider the last puzzle of the tectonic theory .
Explained the earthquakes and tectonic activity is that occur around these plate boundaries.
Dan McKenzie year and contribution
Professor Vidya, physics and University of Cambridge, 1966,
use mathematical evidence to back up the theory
McKenzie modeled generation of magma at both mid ocean ridges and mantle plumes and helped us understand factors controlling partial, melting and
used knowledge of math physics and thermodynamics to understand the mechanisms for Earth cast movement.
