Final Metamorphic

Question 0

Cataclasis

Answer 0

Crushing or breaking of mineral grains associated with deformation

Question 1

Textural changes without mineralogical changes

Answer 1

Recrystallization

Cataclasis

Question 2

Mineralogical changes

Answer 2

Neocrystallization: formation of new minerals involving chemical reactions

Question 3

Evidence of metamorphism

Answer 3

1. Different textures

2. New minerals

Question 4

Physical agents of metamorphism

Answer 4

Pressure temp and directed stress

Question 5

Chemical agents of metamorphism

Answer 5

Chemically actives fluids: water and stuff

Question 6

Temperature (lower limit upper limit and most common temp range)

Answer 6

100-200 degrees
750-800
150-750

Question 7

Main sources of heat

Answer 7

1. Heat flowing within the base of the earths crust from the mantle
2. Radioactive decay within the crust
3. Migrating Magmas
4. Minor/local sources: friction fluids etc

Question 8

Evidence for a fluid phase

Answer 8

Fluid inclusions
Formation of a hydrous or carbonate mineral
Whole rock analysis
Isotopic studies
Prescence of a vein in metamorphic rocks
Active metamorphism in modern geothermal fluids
Common dehydration and decarbanation reactions

Question 9

Nomenclature and fabric of metamorphic rocks

Answer 9

1. Nature of the protolith (limestone to marble or basalt to metabasite)
2. Mineralogy (named for the most abundant mineral within that rock)
3. Rocks textures
4. Special names

Question 10

Greenschists

Answer 10

Predominantly of actinolite, epidote, chlorite

Question 11

Blueschists

Answer 11

Glaucophane (why it’s a blue)

Question 12

Amphibolites

Answer 12

Hornblende and plagioclase

Question 13

Serpentines

Answer 13

Predominantly of Serpentine group minerals

Question 14

Eclogites

Answer 14

Clinopyroxene and garnet (Christmas tree)

Question 15

Granulites

Answer 15

Very high temperature metamorphism

Question 16

Migmatites

Answer 16

Mixed rocks

Question 17

Skarns

Answer 17

Predominantly composed of calc silicate minerals

Question 18

Isograd

Answer 18

Plane of constant metamorphic grade marked by the first appearance of index minerals

Question 19

Classic barrovian zones

Answer 19

Chlorite 
Biotite 
Garnet 
Staurolite 
Kyanite 
Silimanite

Question 20

Metamorphic facies # 1

Answer 20

Facies of high p/t ratios
Blueschist: areas of low t/p gradients: subduction zones
Eclogite: stable under normal geothermal conditions: deep crustal chambers or dikes, sub crustal magmatic underplates

Question 21

Metamorphic facies #2

Answer 21

Medium p/t ratios
Most exposed metamorphic rocks: greenschist, amphibolite, Granulite
Greenschist and amphibolite conform to the “typical” geothermal gradient

Question 22

Metamorphic facies #3

Answer 22

Low p/t ratios
Albite-epidote hornfels, hornblende hornfels, pyroxene hornfels facies: contact metamorphic terranes and regional terranes with very high geothermal gradient
Sanidinite: rate limited to xenoliths in basic Magmas

Question 23

Factors that influence development of aureole

Answer 23

Temp of magma 
Size of magma 
Depth of magma 
Chemical activity of the fluids from inclusions 
Character of country rock 
Mode of emplacement 
Stoping develops static aureole 
Forceful emplacement causes deformation

Question 24

Skarns: contact metasomatism in limestones

Answer 24

Develop along contact between granite and limestone or dolomite
Coarse grained
Consist of calc silicate minerals

Question 25

Contact metamorphism (pelite) 
Intrusion 
Country rock 
Aureole 
Zones

Answer 25

Intrusion: Devonian grandiorite 
Country rock: slate
Aureole: .5-2.5 km wide 
Outer zone: hornblende hornfel
Inner zone: pyroxene hornfel

Question 26

Contact metamorphism (skarn) 
Intrusions
Country rock 
Aureole 
Zones

Answer 26

INtrustions: Quartz monzonite 
Country rock: limestone 
Aureole: up to 15 m 
Zones: 
Marble 
Montecellite 
Vesuvianite 
Garnet, wollastonite, diopside

Question 27

Regional metamorphism (pelites)

Answer 27

Low p/tmtype: and-sil
Zonal sequence: chl-bt-cord-and-sila
High p/t: blueschist- ecologite

Question 28

Ocean to ocean

Ocean to continent convergence

Answer 28

Dewatering of the subducting plate causes hydration of the surrounding asthenosphere which in turn causes partial melting forming mafic Magmas

Question 29

Gravity settling

Answer 29

The differential motion of crystals and liquids under the influence of gravity due to the differences in density

Question 30

Greenschist to amphibolite facies transition has 2 major mineralogical changes

Answer 30

Albite- oligoclase: increase ca content across the peristerite gap
Actinolite to hornblende: amphibole accepts increase in aluminum and alkalis at higher temperature

Question 31

Origin of Granulite rocks is controversial there are however agreements on 2 points

Answer 31

1. Represent unusually hot conditions
   Temp >700
   Average geotherm is in the vicinity of 500, suggesting granulites are the products of crustal thickening or excess heating
2. Granulites are dry
   Rocks don’t melt due to lack of available water
   Fluid inclusions in Granulite facies rocks of s Norway are co2 rich whereas amphibolite facies rocks are h2o rich
   This suggests that the co2 replaced the h2o and that there wasn’t an elimination of fluids altogether

Question 32

Metamorphic belts

Answer 32

In Japan 
Pair of parallel metamorphic belts exposed along a ne sw axis parallel to the active subduction zone 
Inner: high temp low pressure 
Granitic plutons common
Outer: high pressure low temp 
Blueschists common