Tectonics 1.2 Flashcards
What speed do Earth’s tectonic plates move per year?
2-5 cm
How many main tectonic plates are there?
Seven
Other than large tectonic plates, what else is there?
Micro plates
How thick is each plate?
Approximately 100km
Who proposed Continental Drift hypothesis in 1912?
Alfred Wegener;
What year was Continental Drift hypothesis in suggested?
1912
What is the name of theory Alfred Wegener suggested?
Continental Drift Hypothesis;
What did Alfred Wegener’s Continental Drift hypothesis in 1912 postulate?
Separate continents had once been joined;
What is the name of the single landmass that was present before drifting to present locations proposed by Alfred Wegener?
Pangaea;
What notion did Arthur Holmes (1930s) suggest?
Mantle Convection moved tectonics
What does mantle convection suggest about what drives movement of plate tectonics?
Earth’s radioactive heat;
When was the asthenosphere discovered?
1960;
The asthenosphere can be described as what?
Weak; Deformable;
Where is the asthenosphere in comparison to lithosphere?
Beneath
What does the asthenosphere cause the lithosphere to do?
Move;
When was magnetic strips in the oceanic crust of the sea bed discovered?
1960s
What is the name of magnetic strips in the oceanic crust of the sea bed?
palaemagnetic signals;
Where are palaemagnetic signals from?
Past reversals; Earth’s magnetic field;
What do palaemagnetic signals prove?
New ocean crust; Sea-Floor Spreading;
At what type of ridge does Sea-Floor Spreading occur?
Mid-ocean ridges;
At what type of plate boundary do seafloor spreading and palaeomagnetism occur?
Divergent;
At what type of plate boundary do seafloor spreading and palaeomagnetism occur?
Divergent;
Who proposed transform faults which were recognised in 1965?
Tuzo Wilson;
Who suggested sea-floor spreading?
Harry Hess;
What type of plate boundary does subduction of one plate under another plate occur?
Convergent;
What is the range of focal depths in subduction zones?
10km to 400km;
What is the range of focal points at subduction zones?
10km to 400km;
What line do focal points follow?
Line of subducting plate;
What type of plate margin has gravitational sliding?
Divergent margins;
What type of altitudes do constructive margins have?
Elevated altitudes;
Why do divergent margins have elevated altitudes?
Rising heat between them;
What does rising heat between divergent margins create?
‘Slope’ down;
Which plate margin does oceanic plates slide due to gravitational sliding?
Convergent;
What is gravitational sliding also known as?
Ridge Push;
What is the name of the plate that is subducted?
Oceanic;
What is the name of plate that does not subduct?
Continental;
What are the features of the subducting oceanic plate?
Colder; more dense;
Is the continental plate more or less dense than the oceanic plate?
Less dense;
Slab pull is when what type of oceanic plate is subducted beneath what type of continental plate?
Colder; more dense
Less dense
What causes the oceanic plate to pull itself into the mantle?
Its density;
What type of plate margin does slab pull occur at?
Convergent;
What are all tectonic hazards caused by?
Earth’s tectonic heat engine;
What do radioactive isotopes do in the Earth’s core?
Generate heat;
What are two examples of radioactive isotopes?
Uranium-238; Thorium-232
What do heat currents generate in the plastic mantle?
Convection Currents;
Is the interior of the Earth dynamic or static?
Dynamic;
What are the main categories of the Earth’s structure?
Crust
Mantle
Inner Core
Outer Core
Is the Mantle solid or liquid?
Solid;
Is the Outer Core solid or liquid?
Liquid;
Is the Inner Core solid of liquid?
Solid;
Despite being a solid, what is the mantle capable of doing because of high temperatures?
Slow flow; Deformable;
What type of faults do conservative plate boundaries consist of?
Transform faults;
What do faults do to sections of constructive plate boundary as they traverse the Earth’s surface
‘Join up’;
What type of pattern do these faults traverse the Earth’s surface in?
A zig-zag pattern;
What do long transform faults act like in their own right?
Boundary;
What type of focal depths do earthquakes along conservative boundaries often have?
Shallow;
What do shallow focus depths mean for earthquakes?
High magnitude; destructive;
Is there any volcanic activity at conservative zones?
No;Absent;
What are eruptions like at constructive plate margins?
Small; Effusive;
Why are eruptions small and effusive at constructive margins?
Basalt lava;
What are the features of erupted basalt?
Low gas content; High Viscosity;
Are earthquakes shallow or deep at constructive margins?
Shallow;
What is the depth of earthquakes at constructive margins?
Less than 60km;
What are the magnitudes of Constructive margin earthquakes?
Low; 5.0<
What type of earthquakes do Oceanic- Oceanic Constructive Margins create?
Minor; Shallow Earthquakes;
What type of earthquakes do Continent-Continent Constructive margins create?
Minor;
What type of volcanoes do Continent-Continent Constructive margins create?
Basaltic volcanoes;
What is the Benioff Zone?
A z of s w e are p by the i of a d g o c p i a s z.
What is a Benioff Zone?
A zone of seismicity where earthquakes are produced by the interaction of a down going oceanic crustal plate in a subduction zone.
What type of earthquakes can yield from Benioff Zone?
Large; 9.0;
What focal depths does the Benioff Zone occur in?
10km-400km;
What type of margin do Benioff Zones occur?
Convergent Margins;
What is the name of the process that the descending plate begins to melt at depth in Benioff Zone?
Wet partial melting;
What type of magma does wet partial melting generate?
High gas; silica content
What does high gas and silica content mean for volcanoes?
Explosive;
What are collision zones cut by?
Huge thrust faults;
What do huge thrust points generate?
shallow, high-magnitude earthquakes
What type of earthquakes form at Oceanic-Oceanic convergent margins?
Frequent;
What type of volcanoes form at Oceanic-Oceanic convergent margins?
violent; curving chain; volcanic islands
What type of earthquakes do Continent-Continent at convergent plates form?
Infrequent; major;
What type do earthquakes form at Oceanic-Continent convergent plates?
Frequent; large
What type do volcanoes form at Oceanic-Continent convergent plates?
Violent;
What type of focal depth do earthquakes along conservative boundaries often have?
Shallow focal depths;
What do shallow focal depths mean for earthquakes?
Destructive;
What do shallow focal depths mean for volcanoes?
Absent;
What type of earthquakes are at Oceanic-Continent conservative margins?
Frequent; Shallow;
What type of volcanoes are at Oceanic-Continent conservative margins?
No Volcanic Activity;