Building Continents

Question 1

continents include all areas underlain by continental crust, including….

Answer 1

Continental land areas

Margins: shelf, slope (below sea level)

Question 2

why are continents elevated?

Answer 2

Gravity -> denser material “sinks” lower (less buoyant)
Oceanic plates: more dense -> stand low, sink
Continental plates: less dense -> “float”, stand high

Question 3

what do plates float/sink on?

Answer 3

mantle rock, behaving as fluid on long time scales

Question 4

Why are some parts of continents higher than other parts?

Answer 4

Mountains -> thicker crust
Thicker crust sinks deeper, but sits higher
Mountains are supported by crustal root

Question 5

what is Isostasy?

Iso(equal) stasy(standing)

Answer 5

Plates float on the mantle at a height that maintains gravitational equilibrium

Question 6

what is isostatic adjustment

Answer 6

Loading of mass (increases load) -> subsidence
then,
Erosion/removal of mass (lightens load) -> uplift

Question 7

How are continents built?

Answer 7

(1) Add volcanic material (flux melting produces magma at volcanic arcs)
(2) Accrete (add) material to the edge of continents (scrape sediments, volcanic seamounts off subducting plate)
(3) Collision & orogenesis (mountain building)

Question 8

what is a Wilson cycle?

Answer 8

ocean basin opens then closes
Divergent margin: continental rift -> mid-ocean ridge
Convergent margin: subduction zone -> continental collision

Question 9

how do continents grow?

Answer 9

they collide

Question 10

how do continents come apart?

Answer 10

they rift