Metamorphism 9-11

Question 1

Metamorphism

Answer 1

Recrystallisation without melting under heat and/or pressure

Question 2

Thermal or Contact metamorphism

Answer 2

• High-temperature low pressure

- Rocks near an igneous intrusion will be heated and recrystallized; metamorphic ‘aureole’

Question 3

Metastability

Answer 3

Rocks brought out of their regions of stability where they are formed take a long time to break down as will not have the activation energy to recrystallize

Question 4

Regional metamorphism

Answer 4

Metamorphism formed due to conditions in a region under the earth
Burial at depths

Question 5

Low-temperature high-pressure metamorphism

Answer 5

Formed in subduction when the rock does not have time to heat up but is exposed to great pressures

Question 6

Paired metamorphic belts

Answer 6

Igneous intrusions above subduction zones and belts formed by high pressure subduction often come together

Question 7

Facies

Answer 7

Formed under identical conditions with different minerals

Question 8

Idioblastic (or Idiomorphic)

Answer 8

Crystals completely bounded by their own crystal faces; the metamorphic equivalent of euhedral.

Question 9

Metapsammitic

Answer 9

Describes rocks formed by the metamorphism of sandstones

Question 10

Dynamic metamorphism

Answer 10

Dominant processes involve deformation and recrystallisation rather than temperature change

Question 11

Migmatitic

Answer 11

Partly metamorphic and partly igneous in appearance, commonly formed by partial melting in metamorphism

Question 12

Metasomatic

Answer 12

Describes a metamorphic process involving mass transfer and change of bulk chemical composition

Question 13

Protolith

Answer 13

Original rock changed by metamorphism

Question 14

Lithostatic load

Answer 14

Pressure on rocks caused by the weight of rocks above it

Question 15

3 agents of metamorphism

Answer 15

Temperature
Pressure
Fluids

Question 16

Cataclasitic

Answer 16

Rock ground and crushed during faulting

Question 17

Prograde vs Retrograde

Answer 17

Prograde metamorphism is when minerals adapt to more extreme conditions
Retrograde metamorphism is when minerals adapt to less extreme conditions

Question 18

Isochemical metamorphism

Answer 18

New minerals are formed from others without large-scale migration of chemicals

Question 19

Recrystalisation of strained minerals

Answer 19

Same mineral recrystallises in a different way to allow it to unstrain e.g. quartz

Question 20

Formation of new textures / Foliation

Answer 20

Minerals are realligned in response to deformarion and form in a pattern

Question 21

Low grade Regional Metamorphism

Answer 21

Rock types: Slate
Temperatures: 200-350
Pressures: 2-3 kbar (6-10km)
Index minerals: Muscovite, Chlorite (250-325), Biotite (325-375)

Question 22

Medium grade Regional Metamorphism

Answer 22

Rock types: Schist
Temperatures: 350-550
Pressures: 3-4 kbar (10-15km)
Index minerals: Garnet (425-550), Staurolite (525-600)

Question 23

High grade Regional Metamorphism

Answer 23

Rock types: Gneiss
Temperatures: >550
Pressures: >4kbar (>15km)
Index minerals: Sillimanite (>550), Kyanite (>4kbar)

Question 24

Pellitic Protolith

Answer 24

Protolith fine grained sedimentary rock e.g. mudstone

Question 25

Garnet colour for composition in metamorphism

Answer 25

Red - Almandine IRON Dark - Pyrope MAGNESIUM Green - Grossular CALCIUM-ALUMINUM

Question 26

Change in texture through regional metamorphic grade

Answer 26

Slatey: strong cleavage and foliation Schistosity: prominant foliations and banding with minerals visible to the naked eye Gneiss: diffuse bands with segraegated different compositions and larger coarse minerals

Question 27

Index minerals

Answer 27

Cholrite-Biotite-Garnet-Staurolite-Sillimanite/Kyanite | Staurolite only forms if there is iron!

Question 28

Aluminum Silicates triple point

Answer 28

514 C, 4kbars

Question 29

Low temperature low pressure facies

Answer 29

Zeolite

Question 30

High temperature low pressure facies (e.g. Contact metamorphism)

Answer 30

Hornfels

Question 31

Low temperature High pressure facies (e.g. subduction)

Answer 31

Blueschist

Question 32

Very High temperature (some pressure) facies

Answer 32

Granulite

Question 33

Very high pressure (some heat) facies

Answer 33

Eclogite

Question 34

2 middle facies in order of increasing temperature

Answer 34

Greenschist | Amphibolite

Question 35

Quartzite

Answer 35

Metamorphosed sandstone

Question 36

Marble

Answer 36

Metamorphosed limestone

Question 37

Metamorphic aureole factors:

Answer 37

Size of intrusion - will take longer to cool Magma temperature - hotter magmas (more mafic usually) will affect the area more Depth of intrusion - shallow intrusions will cause more change as the rocks around will be cool

Question 38

Metamorphic zones in conact metamorphism of pelites

Answer 38

1) Inner Hornfels Zone (C) a granoblastic texture completly recrystalised with interlocking quartz, corderite and biotite surrounding the intrusion (A) and the chilled margin (B). 2) Intermediate Porphyroblastic zone (D) Large andalusite porphyroblasts, and cordierite in slate 3) Outer Spotted slate zone (E) Small spots of metamorphic minerals form. This is surrounted by unaffected mudstone (F)