Plate tectonics Flashcards
who came up with the continental drift theory
Alfred Wegener
Continental Drift Theory
that the continents used to form one supercontinent but began to drift a part into their current positions
when was continental drift widely accepted
1950
why was the theory of continental drift NOT taken seriously at first
because there was no mechanism that could be explained
what were the two large portions that made up Pangaea
- Laurasia
- Gondwanaland
what happened to the continents 135 MYA
separated to more present shape WITHOUT separating too much
what did the continents look like 65 MYA
began to break apart from each other to be located in the present day locations
polar position
focused on the latitudinal position as a cause of the glaciation of continents = ice sheets should appear on continents when they are located at polar or near-polar latitudes.
describe polar position of the continents 440 MYA
polar position - yes
ice sheets - yes
describe polar position of the continents 390 MYA
polar position - yes
ice sheets - no
describe polar position of the continents 300 MYA
polar position - yes
ice sheets - yes
describe polar position of the continents 260 MYA
polar position - yes
ice sheets - yes
do the location of continents and whether they are together or separate affect weather
YES
where is slow flow
in the upper mantle
what drives slow flow and continent movements
convection cells
steps within the convection cells
- heating of the material in the mantle
- the hot material rises
- begins to move outwards
- cools
- eventually there will be collisions and subduction
how does the gravity push/pull affect plate tectonics
lava is pushed up while the weight of thickening plate is pushed down
curst formation steps
- material from the asthenosphere upwells along the sea floor and becomes extrusive igneous rock
- the oceanic crust is subducted under the lighter continental crust
- the subducted oceanic crust begins to melt
- melting generates magma = forms igneous intrusion rock and extrusive explosions
what is the range of speed for the movement of continents
from 1 to 12cm per year
how can the movement of continents differ
- in their speed
- in their direction
- in their orientation
what is the Wilson cycle focused on
the different formations of supercontinents in the past
how many supercontinents were expected to have been formed in 3 billion years (Wilsons cycle)
5
supercontinents act as
insulators - their mass traps geothermal heat in earth
what are the 4 steps in the Wilson cycle
- assembly
- stability
- splitting
- reassembly
average Wilson cycle takes ____ years
500 Million
does assembly in the Wilsons cycle have to be complete
NO- it can be incomplete
3 main types of plate boundaries
- convergent
- divergent
- transform
divergent plate boundary
plates move AWAY from each other
convergent plate boundary
plates move TOWARDS each other
transform plate boundary
plates move in OPPOSITE directions but they REMAIN together
types of convergent plates
- convergent oceanic plates
- convergent continental plates
- convergent oceanic AND continental plates
convergent plates results in _____
subduction
convergent OCEANIC plates results in
volcanic expression
convergent CONTINENTAL plates results in
formation of mountains (such as the Himalayas)
convergent of OCEANIC AND CONTINENTAL plates results in
volcanic activity
divergent CONTINENTAL plates results in
rift valleys and sometimes divots
TRANSFORM plates can be identified by
- ridges not lining up
3 main STRESS types of crust deformation
- tension
- compression
- shear
crust deformation
tension AKA
stretching
crust deformation
compression AKA
shortening
crust deformation
shear AKA
twisting
the stress of curst deformation results in
STRAIN
two examples of strains caused by crust deformation stress
- folding (bending)
- faulting (breaking)
what causes folding
compression at convergent plates
what are examples of the result of folding
basins and domes
anticlines and synclines in folding
the up and down folds that usually occur together and are caused by compressional stress
anticlines vs synclines of folding
Anticlines
folds in which each half of the fold dips away from the crest.
Synclines
folds in which each half of the fold dips toward the trough of the fold.
shear stress
shear stress results in
fault and bending horizontally
compression
compression results in ____ surface expression(s)
- folding
- faulting
tension
tension results in _____ surface expression
thining crust
what causes faulting
forces on both sides of a plate that causes fracture of material (break)
what are three examples of faulting
- normal fault
- thrust fault
- strike-slip fault
what causes a normal fault
tension
how do identify a normal fault
when the hanging-wall side is displaced DOWNWARDS
what causes a thrust fault
compression