Plate Tectonics

Question 1

Why do we have tectonic plates?

Answer 1

1. Many asteroids smash into each other over time
   become one big ball (protoplanet)
   2.All the collisions have caused much heat and radioactive decay
2. Because asteroid has become so big, the heat can no longer escape out of the mass as fast, which causes melting
3. This now lava ball allows the movement of elements (called differentiation): heavier ones sink to the core while lighter ones float up

Question 2

Elements found in core

Answer 2

Mg, Fe

Question 3

Elements found closer to surface

Answer 3

Li, O, C

Question 4

Importance of water for plate tectonics

Answer 4

1. Lowers melting point of mantle
2. Lowers viscosity
   So greater flow of lava and better convection (allows heat to distribute itself, circulating up from earths core)

Question 5

Venus stagnant lid

Answer 5

Closer to the sun
May once have had water but now it has all evaporated
Internal heat cannot escape (no help from water) so venus remains very hot and crusts remelts ever couple thousand years

Question 6

Mars stagnant lid

Answer 6

Smaller mass, so cooling occurs faster
Probably had liquid water but because cooling occured to quickly, it froze
Mantle lacks convection and flow (too solid/viscous), internal heat engine no longer functional –> heat production drives convection in earths mantle

Question 7

Where does the heat for the convection in the Earths natnel come from?

Answer 7

1. primordial heat: Heat from when Earth was forming (asteroids smashing etc)–> Earth is still releasing this heat
2. Radiogenic heat: TRadioactive decay of elements such as Uranium, Potassium and Thorium decaying into diferent elements release heat as by product

Question 8

Earths structure

Answer 8

1. Crust
2. MOHO
   3.Lithosphere (Mantle)
3. Asthenosphere (Mantle)
4. Transition zone (Mantle)
   6.Outer and inner core

Question 9

MOHO

Answer 9

Crust and mantle boundary
Depth varies depending on thickness of crust
Densite change above and below this boundary (S and P waves travel faster below this boundary so easy to detect)

Question 10

Lithosphere

Answer 10

RIGID upper mantle

Question 11

Asthenosphere

Answer 11

DUCTILE/plastic
Lithosphere- asthenosphere boundary (LAB) found at isotherm aka constant temp of 1280°

Question 12

Trabsition zone

Answer 12

Found between upeper and lower mantle
Seismic wave behaviour change because of olivine structure change at this pressure (increase pressure, atmons more tighlty packed)

Question 13

Outer and inner core

Answer 13

Outer = LIQUID
Inner = SOLID (because high pressure)
Spin of Earth causes turbulent convection in outer core producing magnetic field

Question 14

Composition of Earths crust

Answer 14

Silicon
Oxygen
Aluminum
Iron
Calcium
Potassium

Question 15

Oceanic crust general info

Answer 15

Formed by divergent plate boundaries

Esentially solidifed mantle, mnantle exposed to surface and cools (to form mid atlantic ocean ridges MORB)

Thinner (7-10km)

Consists of heavier elements such as Fe and Mg

Question 16

Continental crust general info

Answer 16

Formed by converging or subducting plates

Thicker

Less dense

Question 17

Continental Shield

Answer 17

-Large stable areas in the middle of areas of continental crust
-low relief
-Extremely old rocks (composed of precambrian crystalline rocks, some as old as 2-3 billion years old–> anything older has already been “reclycled”)
-continetal “nuclei”, surrounded by belts of folded, younger rocks

Question 18

Oceanic Crust structure

Answer 18

“Simple”, layered structure

1.Sediment

2.Pillow basalts
in rift zones, molten lava erupts from cracks and cools very fast as it comes into contact with the water

3.Basalt dykes
underground plumbing system that brings magma from mantle onto ocean floor, essentially fractures caused by the extensional environment.

4.Gabbro
Same composition as basalt, just bigger crystals cause slower cooling)

5.Peridotite

Question 19

Continental Crust structure

Answer 19

Because continental crust is less dense and hot, it doesn’t get subducted, instead it folds and crumples getting thicker and thicker

It consists of:

-intensley deformed metamosphic rock, typically more granitic/felsic than its mafic counterpart (oceanic crust)

-rocks near the center are geenrally the oldest: protliths consisting of basalt and andesite and volcanic derived deiments such as the black sand in the canary islands (erosions of volcanoes)

Question 20

Continental accretion

Answer 20

Belts/layers of younger rock have undergone intense deformation (episodes of mountain building)
They become welded against pre-existing shields. This accumulates and crumples further. Since it is also more felsic in composition, it is less dense and is even less likely to be subducted, so it will keep getting bigger and bigger

Question 21

Is oceanic crust keeps getting subducted and continental crust keeps forming, why isnt all of Earths crust continental? And shouldn’t mountains keep growing?

Answer 21

Mountains don’t keep growing because erosion occurs. And also: ISOSTASY

Question 22

Isostasy

Answer 22

The lithosphere (rigid), weighs the asthenosphere (ductile) down –> where lithosphere is thick, asthenisohere is thin (MOHO is lowered)
When erosion occurs, the load of the lithosphere lightens. Then asthenosphere is ductile, so asthenosphere can bounce/move back. The crust is ISOSTATICALLY UPLIFTED

Question 23

Contour lines and bedding

Answer 23

Contour lines are parallel to geological boundaries of rock: HORIZONTAL BEDS

Dipping boundaries that cut across contour lines, smoothing or accentuating contour lines: DIPPING BEDS

Boundaries cuz straight across topography: VERTICAL BEDS