1. Minerals

Question 1

Why does temperature have a profound effect on metamorphism?

Answer 1

Temperature controls the stabilities of minerals and mineral assemblages

(Temp is more important than pressure)

Question 2

Name and describe the three responses to heat

Answer 2

Recrystallisation

of existing minerals - changing texture

Neomineralisation

Formation of new minerals, due to chemical exchange between reacting minerals (no change in bulk comp except H2O and CO2)

Metasomatism

a special type of metamorphism involving reaction with infiltrating fluids (H2O plus dissolved species) -change in bulk composition

Question 3

What is Stress?

Answer 3

Force per unit area, Pascal(Pa), bar, kbar

Question 4

What is Load Pressure?

Answer 4

‘lithostatic pressure’ P, or confining pressure

acts uniformly in every direction

results from the weight of overlying rock

Question 5

What is Deviatoric Stress

Answer 5

The part of the stress that is different in different directions

‘directed’ or ‘differential stress’

caused by lateral transmission of tectonic forces through the solid Earth’s crust

results in fracturing(faulting) in cold, brittle upper crust

results in plastic deformation in warm, ductile middle & lower crust

Question 6

Describe the effects of heating due to intrusion of magma

Answer 6

contact metamorphism, in thermal aureoles around igneous intrusions

Usually no directed pressure, so foliation not developed

Question 7

Describe regional metamorphism

Answer 7

heating, pressure increase and deformation

due to tectonic processes at convergent plate margins

• pressure increase due to burial
• temp increase due to geothermal gradient
• Deformation due to directed stress field

Question 8

Describe dislocation(dynamic) metamorphism

Answer 8

deformation in fault zones

lithostatic pressure and temp not usually important

Question 9

Describe shock metamorphism

Answer 9

Intense, short lived shock pressures due to meteorite impacts

Question 10

Describe Slaty Cleavage

Answer 10

defined by aligned muscovites, oblique to bedding in a metamorphosed mudstone

Question 11

Mudstones are composed mainly of:

Answer 11

• Detrital quartz
• Clay minerals (K,Mg,Al-rich silicates)
• Fe³⁺ oxides/hydroxides

Question 12

Pelites contain:

Answer 12

• Quartz
• Micas and/or K-feldspar
• +-Al₂SiO₅ minerals, i.e. kyanite or sillimanite or andalusite
• (Fe,Mg) Al-Silicates e.g. garnet, chlorite, staurolite, cordierite, chloritoid