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Geology > metamorphic rocks > Flashcards

metamorphic rocks Flashcards

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1
Q

What is metamorphism?

A

The process that alters rocks through heat, pressure, and chemical fluids

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2
Q

What are the two main types of metamorphism?

A

1) Regional Metamorphism: Affects large areas due to tectonic forces
2) Contact Metamorphism: Occurs near igneous intrusions⁠

⁠

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3
Q

Describe slate and its characteristics

A
  • Fine-grained, formed from shale
  • Exhibits slaty cleavage
  • Composed of clay minerals and mica
  • Result of low-grade metamorphism
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4
Q

What are the characteristics of phyllite?

A
  • Fine-grained with silky sheen
  • Wavy or crinkled foliation
  • Contains muscovite, chlorite, and quartz
  • Low-grade metamorphism
  • Grey or pale green in color
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5
Q

Describe the key features of schist

A

Medium to coarse-grained (1-5 mm)
* Contains porphyroblasts (large crystals like garnet)
* Shows schistosity (aligned mica crystals)
* Contains muscovite, biotite, and quartz
* Medium-grade metamorphism

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6
Q

What are the characteristics of gneiss?

A
  • Coarse-grained (>5 mm)
  • Light and dark bands (gneissose banding)
  • Contains feldspar, quartz, biotite, and kyanite
  • Result of high-grade metamorphism
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7
Q

Describe marble and its properties

A
  • Composed of calcite or dolomite
  • Reacts with acid
  • White or light-colored
  • Formed from limestone
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8
Q

What are the key characteristics of metaquartzite

A

Composed of quartz
* White or grey in color
* Formed from sandstone

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9
Q

Define porphyroblasts

A

Large crystals formed during metamorphism

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10
Q

What is schistosity

A

Parallel alignment of platy minerals in medium to coarse-grained metamorphic rocks

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11
Q

Define gneissose banding

A

Alternating layers of light and dark minerals

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12
Q

What is metamorphic grade

A

A measure of the intensity of metamorphism, determined by temperature and pressure conditions.

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13
Q

What is country rock

A

Pre-existing rock that has been affected by metamorphism.

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14
Q

Define metamorphic aureole

A

The zone around an igneous intrusion where rocks have been altered by heat. Can extend up to 10 km from the intrusion.

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15
Q

What are index minerals

A

Minerals that form under specific temperature and pressure conditions, indicating metamorphic grade

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16
Q

What characterizes contact metamorphism?

A
  • High-temperature, low-pressure conditions
  • Creates metamorphic aureole
  • Forms spotted rocks with dark mineral clusters
17
Q

What are the key features of regional metamorphism?

A

Associated with high pressures and temperatures
- Typically occurs in mountain-building regions
- Metamorphic grades increase with depth

18
Q

How does thermal gradient work in metamorphic aureoles?

A

Temperature decreases with distance from the intrusion, producing a sequence of index minerals that indicate different metamorphic grades.

19
Q

What are the three grades of regional metamorphic rocks and their characteristic minerals?

A
  • Low-grade: Contains minerals like chlorite
  • Medium-grade: Contains minerals like garnet
  • High-grade: Contains minerals like sillimanite
20
Q

How do index minerals help geologists?

A

They help determine the metamorphic history of a rock because each mineral forms at a specific range of temperature and pressure.

21
Q

What is slaty cleavage?

A

Low-grade metamorphic fabric where rocks split into thin sheets due to aligned platy minerals under compression

22
Q

What characterizes schistosity?

A

Visible alignment of mica crystals creating a shiny appearance in medium-grade metamorphic rocks like phyllites and schists.

23
Q

Describe gneissose banding

A

Alternating light (quartz, feldspar) and dark (biotite, mica) bands in high-grade metamorphic rocks.

24
Q

What is porphyroblastic fabric?

A

Large crystals (porphyroblasts) surrounded by finer-grained matrix, showing evidence of metamorphic growth.

25
Q

What is granoblastic fabric?

A

Random orientation of equal-sized grains with sugary texture, typical in non-foliated rocks like marble and quartzite.

26
Q

What is crenulation cleavage?

A

Wavy or crinkled textures formed when older foliations are folded during multiple deformation events.

26
Q

what dos fabrics mean interms of classifying metamorphic rock?

A

the texture of the rock

27
Q

What are the main categories of fabric identification in metamorphic rocks?

A
  • Fine-grained (e.g., slate, phyllite)
  • Medium-coarse grained (e.g., schist, gneiss, quartzite, marble)
  • Rocks without preferred alignment (e.g., spotted rock)
28
Q

How do fabrics help geologists understand metamorphic rocks?

A

Fabrics reveal:
* Conditions of temperature and pressure during metamorphism
* History of deformation events
* Help reconstruct metamorphic histories, especially during mountain-building events

29
Q

What are the key factors that influence metamorphic fabrics?

A

Reaction Rates:
* Temperature levels
* Presence of water
* Speed of ion movement
2. Time and Deformation:
* Stress levels
* Rate of deformation
* Duration of metamorphic processes

30
Q

How do stress-related changes affect metamorphic fabrics?

A

Stress affects fabrics in two main ways:
* Rapid stress (like faulting) creates cataclasites
* Slower stress forms foliated textures
These changes help reveal the history of metamorphic pressure and temperature

31
Q

How can mineral timing be used to understand metamorphic fabrics?

A
  • Pre-kinematic: Formed before deformation
  • Syn-kinematic: Formed during deformation
  • Post-kinematic: Formed after deformation
    This timing can be determined through microscopic analysis of features like folded micas, inclusions, and mineral alignment
32
Q

What are index minerals and what do they indicate?

A

Index minerals are specific minerals that indicate metamorphic grade:
* Low-grade: Chlorite
* Medium-grade: Biotite, garnet
* High-grade: Kyanite, sillimanite

They form at specific temperature and pressure conditions, helping geologists determine metamorphic history.

33
Q

What is retrograde metamorphism?

A

Retrograde metamorphism is:
* The recrystallization of rocks during cooling
* Occurs when fluids like H₂O and CO₂ are reintroduced
* Results in hydration and oxidation reactions
* Has slower chemical reactions due to decreasing temperatures

34
Q

What are the different geothermal gradients in metamorphism?

A

Contact metamorphism
* Regional metamorphism
* Subduction zones

Each represents different temperature-pressure pathways in metamorphic environments.

Geology (2 decks)

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