Metamorphic rocks and processes

Question 1

Protolith

Answer 1

• parent rock to metamorphic rock
• can be virtually any rock

Question 2

What is the phase present dependent on?

Answer 2

the PT conditions

Question 2

Prograde metamorphism

Answer 2

• rocks change mineral composition + texture according to increasing temp and pressure

Question 3

Retrograde metamorphism

Answer 3

• exhuming the rock
• decompression and cooling

Question 4

Metamorphic grade

Answer 4

• corresponds to degree of metamorphism
  low grade: low temp, low pressure
  high grade: high temp, high pressure
• can be determined based on minerals present in the rock

Question 5

Burial process

Answer 5

• new layers of sediment accumulate, old rocks get pushed down
• lithostatic pressure
• metamorphic processes begin ~2km

Question 6

Tectonic pressure

Answer 6

• during large collisions of
  crustal blocks rocks
  are dragged deeper into earth
• more directed pressure and sheer stress, also lithostatic pressure

Question 7

Geothermal gradient

Answer 7

• naturally, increasing pressure towards earth, temp increases
• ~25-30°C per kilometer

Question 8

Magma intrusion

Answer 8

• when magma intrudes into cooler surrounding rocks it transfers heat into them
• aureole = zone surrounding an intrusion

Question 9

Foliated texture

Answer 9

• crystals are somehow aligned (some sort of cleavage etc.)
• mostly by directed pressure
• atoms migrate into
  area of lesser pressure and reform bond with other atoms
• causes rock to look layered
  Examples: slate, phyllite

Question 10

Foliation examples

Answer 10

• slaty cleavage
• phyllitic
• schistose
• gneissic

Question 11

Non-foliated texture

Answer 11

• result of recrystallization
• ## pressure is not directed

Question 12

Metapelitic rocks
(mudstone protolith)

Answer 12

1. mudstone (sedimentary)
2. shale (sedimentary)
3. slate (low grade)
4. phyllite (low grade)
5. schist (medium grade)
6. (para)gneiss (high grade)
7. Migmatite (partially molten rock)

Question 13

Metapsamitic rocks
(sandstone protolith)

Answer 13

1. sandstone (sedimentary)
2. quartzite (metamorphic)

Question 14

Metacalcareous rocks
(limestone protolith)

Answer 14

1. limestone (sedimentary)
2. marble (metamorphic)

Question 15

Facies

Answer 15

• objective description based on mineral assemblage
• reflects certain set of PT values

Question 16

Series

Answer 16

• trend of metamorphism characteristic for a specific geological environment

Question 17

Contact metamorphism

Answer 17

• low P/T
• magma pushes up into the crust
• cooked area = aureole
  hornfels

Question 18

Regional metamorphism

Answer 18

• medium P/T
• typically mountain-forming areas
  greenschist–amphibolite–
  granulite

Question 19

Subduction-zone
metamorphism

Answer 19

• high P/T
• one plate sliding under another, causes super high pressure
  blueschist, eclogite

Question 20

Metagranitic

Answer 20

• granite,
  granotiorite, or
  tonalite
• ortho gneiss

Question 21

Metarhyolitic rocks

Answer 21

1. rhyolite, dacite (igneous)
2. metarhyolite, metadacite (low-grade)
3. Felsic schist (medium-grade)
4. Felsic gneiss (high-grade)

Question 22

Metaultramafic rocks

Answer 22

1. peridotite (igneous)
2. serpentinite (metamorphic)

Question 23

the rock cycle

Answer 23

your time has come

Question 24

Slate

Answer 24

• Protolith: Mudstone or Shale • Grade: Low • Texture: Foliated, slaty cleavage • Minerals: Mica, chlorite, quartz, feldspar

Question 25

Phyllite

Answer 25

• Protolith: Shale or mudstone • Grade: Low to medium • Texture: Foliated, phyllitic sheen • Minerals: Mica, chlorite, quartz, feldspar

Question 26

Schist

Answer 26

• Protolith: Shale or mudstone • Grade: Medium • Texture: Foliated, schistosity • Minerals: Mica, quartz, feldspar, garnet Met

Question 27

Paragneiss

Answer 27

Protolith: Shale or mudstone • Grade: High • Texture: Foliated, banded • Minerals: Quartz, feldspar, mica, amphibole

Question 28

Quartzite

Answer 28

Protolith: Sandstone • Grade: Low to High • Texture: Non-foliated, crystalline • Minerals: Quartz

Question 29

Marble

Answer 29

Protolith: Limestone or dolostone • Grade: Low to High • Texture: Non-foliated, crystalline • Minerals: Calcite, dolomite

Question 30

Orthogneiss

Answer 30

Protolith: Granite, granodiorite, tonalite • Grade: High • Texture: Foliated, banded • Minerals: Quartz, feldspar, mica, amphibole

Question 31

Green schist

Answer 31

Protolith: Basalt • Grade: Low to Medium • Texture: Foliated, slaty or schistose • Minerals: Chlorite, actinolite (green amphibole), epidote, albite (Na-plagioclase)

Question 32

Amphibolite

Answer 32

Protolith: Basalt or gabbro • Grade: Medium to High • Texture: Foliated, banded • Minerals: Amphibole, plagioclase, epidote, garnet

Question 33

Eclogite

Answer 33

Protolith: Basalt or gabbro • Grade: High (high- pressure) • Texture: Granoblastic • Minerals: Garnet, omphacite (green pyroxene)