metamorphic rocks

Question 1

What is metamorphism?

Answer 1

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

Question 2

What are the two main types of metamorphism?

Answer 2

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

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Question 3

Describe slate and its characteristics

Answer 3

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

Question 4

What are the characteristics of phyllite?

Answer 4

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

Question 5

Describe the key features of schist

Answer 5

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

Question 6

What are the characteristics of gneiss?

Answer 6

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

Question 7

Describe marble and its properties

Answer 7

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

Question 8

What are the key characteristics of metaquartzite

Answer 8

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

Question 9

Define porphyroblasts

Answer 9

Large crystals formed during metamorphism

Question 10

What is schistosity

Answer 10

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

Question 11

Define gneissose banding

Answer 11

Alternating layers of light and dark minerals

Question 12

What is metamorphic grade

Answer 12

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

Question 13

What is country rock

Answer 13

Pre-existing rock that has been affected by metamorphism.

Question 14

Define metamorphic aureole

Answer 14

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

Question 15

What are index minerals

Answer 15

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

Question 16

What characterizes contact metamorphism?

Answer 16

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

Question 17

What are the key features of regional metamorphism?

Answer 17

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

Question 18

How does thermal gradient work in metamorphic aureoles?

Answer 18

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

Question 19

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

Answer 19

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

Question 20

How do index minerals help geologists?

Answer 20

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

Question 21

What is slaty cleavage?

Answer 21

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

Question 22

What characterizes schistosity?

Answer 22

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

Question 23

Describe gneissose banding

Answer 23

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

Question 24

What is porphyroblastic fabric?

Answer 24

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

Question 25

What is granoblastic fabric?

Answer 25

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

Question 26

What is crenulation cleavage?

Answer 26

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

Question 26

what dos fabrics mean interms of classifying metamorphic rock?

Answer 26

the texture of the rock

Question 27

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

Answer 27

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

Question 28

How do fabrics help geologists understand metamorphic rocks?

Answer 28

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

Question 29

What are the key factors that influence metamorphic fabrics?

Answer 29

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

Question 30

How do stress-related changes affect metamorphic fabrics?

Answer 30

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

Question 31

How can mineral timing be used to understand metamorphic fabrics?

Answer 31

* 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

Question 32

What are index minerals and what do they indicate?

Answer 32

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.

Question 33

What is retrograde metamorphism?

Answer 33

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

Question 34

What are the different geothermal gradients in metamorphism?

Answer 34

Contact metamorphism * Regional metamorphism * Subduction zones Each represents different temperature-pressure pathways in metamorphic environments.