lecture 2- the earth and the rock cycle

Question 1

what is decompression melting?

Answer 1

melting point of rock varies with pressure, lower near the surface due to lower pressure

Question 2

continental crust is…

Answer 2

less dense than oceanic crust yet thicker

Question 3

the crust is made of…?

Answer 3

igneous rock known as basalts and gabbros

Question 4

ocean crust density?

Answer 4

3.0g/cm3

Question 5

continental crust density?

Answer 5

2.7g/cm3

Question 6

how long until oceanic crust is fully recycled?

Answer 6

100 million years

Question 7

what is an accretionary wedge?

Answer 7

a mass of sedimentary material scraped off oceanic crust during subduction and piled up at the edge of a continental crust plate

Question 8

what drives the motion of plates?

Answer 8

thermal convection and ‘slab and pull’

Question 9

where are oceanic rocks recycled?

Answer 9

subduction margins

Question 10

why does continental crust thicken and buckle rather than be subducted at subduction margins?

Answer 10

because it is too buoyant to be subducted

Question 11

why does regional metamorphism occur?

Answer 11

due to intense pressure and heat

Question 12

how does contact metamorphism occur?

Answer 12

contact with intrusions

Question 13

why does the lithosphere float on the asthenosphere?

Answer 13

because it is less dense

Question 14

what influences the differences in density and composition of oceanic and continental rock?

Answer 14

partial melting

Question 15

what creates oceanic rock?

Answer 15

mid ocean spreading / divergent boundaries

Question 16

what creates continental rock?

Answer 16

subduction

Question 17

which characteristics of the crust vary spatially?

Answer 17

• thickness and density
• loading (e.g. sediment and ice)
• flexural rigidity