Metamorphic Rocks (Part 1 - Metamorphism and Metamorphic Textures)

Question 1

The process of change or transformation of a pre-existing rock, in the solid state, into another rock due to heat, pressure and chemically active fluids.

Answer 1

Metamorphism

Question 2

A form of metamorphism due to hydrothermal fluids exchanging constituents with an external source.

Answer 2

Metasomatism

Question 3

Increase in temperature and pressure

Answer 3

Prograde Metamorphism

Question 4

Decrease in temperature and pressure

Answer 4

Retrogade Metamorphism

Question 5

Metamorphism that affects areas with less than 100km²

Answer 5

Local Metamorphism

Question 6

Metamorphism that affects areas greater than 100km² and is commonly associated with convergent and divergent plate boundaries.

Answer 6

Regional Metamorphism

Question 7

Also known as Protoliths

Answer 7

Parent Rocks

Question 8

The original rocks from where the produced metamorphic rocks transformed from.

Answer 8

Protoliths

Question 9

3 Agents of Metamorphism

Answer 9

Heat
Pressure
Chemically Active Fluids

Question 10

Provides energy for chemical reactions and recrystallization of minerals.

Answer 10

Heat

Question 11

Provides stress in equal directions or varying amounts in different directions.

Answer 11

Pressure

Question 12

Provides and enhances mobility of ions present.

Answer 12

Chemically Active Fluids

Question 13

Low Temperature Range and Pressure Range

Answer 13

200-300°C , 300-600 MPa; 0-6 km depth

Question 14

Intermediate Temperature Range and Pressure Range

Answer 14

300-500°C, 600-1000 MPa; 2-20 km depth

Question 15

High Temperature Range and Pressure Range

Answer 15

> 500°C, >1000 MPa; >20 km depth

Question 16

2 Types of Pressure

Answer 16

Hydrostatic Pressure
Lithostatic Stress

Question 17

also called as confining pressure

Answer 17

Hydrostatic Pressure

Question 18

A uniform or isotropic form of pressure, where pressure is equal in all directions, which usually produces equant grains and non-foliated texture of metamorphic rocks.

Answer 18

Hydrostatic Pressure

Question 19

also called as burying pressure

Answer 19

Lithostatic Stress

Question 20

A non-uniform or anisotropic form of pressure, where pressure is unequal in all directions, which usually produces inequant grains and foliated texture of metamorphic rocks.

Answer 20

Lithostatic Stress

Question 21

6 Types of Metamorphism

Answer 21

(CHDBID)
Contact Metamorphism
Hydrothermal Metamorphism
Dynamothermal Metamorphism
Burial Metamorphism
Impact Metamorphism
Dynamic Metamorphism

Question 22

A variable temperature, low pressure metamorphism that develops locally where hot magma intrudes relatively cold, upper crustal country rock. (give a product)

Answer 22

Contact Metamorphism (Hornfels, Metaquartzite, Skarn)

Question 23

Chemical alteration from circulating fluids within cracks and fissures. Pervasive at ocean spreading ridges
that experience tension, thinning and uplift, causes metasomatism. (give a product)

Answer 23

Hydrothermal Metamorphism (Alteration Products, Metallic ore deposits)

Question 24

Name all major types of Hydrothermal Alteration

Answer 24

(AAACPPPSSSSZ)
Albitic - Albite
Alunitic - Alunite
Argillic - Kaolinite, Smectite, Illite
Carbonatization - Carbonate Minerals (Calcite, etc.)
Phyllic - Sericite, Quartz, Pyrite
Potassic - Biotite, Potassium Feldspar
Propylitic - Chlorite, Epidote, Actinolite, Tremolite
Sericitic - Sericite
Serpentinization - Serpentine
Silication - Quartz, Chert
Spilitization - Albite
Zeolitic - Zeolite Minerals

Question 25

A regional metamorphism induced by increase in pressure and temperature with non-uniform stress which produces foliated textures, mostly aerially extensive, and dominates convergent margins and associated fold and thrust belts. (give a product)

Answer 25

Dynamothermal Metamorphism (Greenschist, amphibolite, granulite, blueschist, eclogite)

Question 26

Metamorphism that results from increase in lithostatic stress caused by deep burial of rocks and produces non-foliated textures, affects regional subsiding basins that accumulate thick sequences of sediments and volcanic debris, and usually starts at temperatures 150 °C to 300 °C and gradational with diagenesis at depths of about 8 km. (give a product)

Answer 26

Burial Metamorphism (Non-foliated rocks with low temp. mineral assemblages)

Question 27

A local form of metamorphism generated by explosive volcanic eruptions or relatively rare collisions of extraterrestrial objects with Earth, causing a high strain rate. (give a product)

Answer 27

Impact Metamorphism (Impactites)

Question 28

Induced primarily by non-uniform stress in fault zones and shear zones, where the high strain rate is mostly local but extend to a regional scale in large faults or shear zones, and most likely recur in the same fault or shear zone. (Give a product)

Answer 28

Dynamic Metamorphism (Cataclasites, pseudotachylites, mylonites)

Question 29

A low temperature, brittle grain-fracturing process that involves grain size reduction through the mechanical grinding, rotation and crushing of rock.

Answer 29

Cataclasis

Question 30

A fine-trained, non-foliated, clastic metamorphic rock produced by cataclastic processes.

Answer 30

Cataclasite

Question 31

A ductile grain reduction process that produces oriented grains of smaller diameter.

Answer 31

Mylonitization

Question 32

A product of mylonitization characterized by grain size reduction via macroscopic scale cataclisis, plastic stretching and thinning associated with ductile deformation.

Answer 32

Mylonite

Question 33

Occurs in metamorphic rocks where individual atoms or molecules can migrate in gaseous, liquid or solid phases from one location in a rock body to a new location.

Answer 33

Diffusion

Question 34

Involves the dissolution of solid grains under high compressive stress conditions.

Answer 34

Pressolution

Question 35

An insoluble seam that accumulates as soluble minerals dissolve.

Answer 35

Stylolite

Question 36

Occurs when existing minerals are transformed under higher temperature and/or pressure conditions, without experiencing a significant change in chemical composition.

Answer 36

Recrystallization

Question 37

The nucleation and growth of new minerals as pre-existing minerals become unstable due to temperature or pressure changes.

Answer 37

Neocrystallization

Question 38

Newly formed minerals that are distinctly larger than the minerals in the surrounding matrix.

Answer 38

Porphyroblasts

Question 39

The segregation of minerals in an initially homogenous rock due to different physical or chemical characteristics such as solubility, ductility, mineral growth or crystallization temperature.

Answer 39

Differentiation

Question 40

Partially melted rocks that form by quenching under high strain rates in shear zone fractures.

Answer 40

Pseudotachylites

Question 41

A metamorphic halo in the contact zone that surrounds it, produced from the heat of the igneous intrusion, and can range from centimeters to hundreds of qmeters in diameter.

Answer 41

Aureole

Question 42

The size, shape, orientation and intergranular relationships of metamorphic rocks' constituents that were influenced by temperature and pressure conditions or relict textures.

Answer 42

Metamorphic Textures

Question 43

Metamorphic textures based on the sizes of the notable grains in metamorphic rocks.

Answer 43

According to Grain Size

Question 44

Metamorphic textures based on the orientation of the grains in a metamorphic rock.

Answer 44

According to Grain Orientation

Question 45

Texture defined by large relict grains

Answer 45

Porphyroclasts

Question 46

Texture defined by large relict grains from the protolith that have experienced deformation but retained its composition.

Answer 46

Porphyroclastic

Question 47

Oval-shaped feldspar porphyroclasts that are particularly common in gneiss.

Answer 47

Augen

Question 48

Oval shaped quartz porphyroclasts that are particularly common in gneiss.

Answer 48

Flaser

Question 49

Texture defined by large grains

Answer 49

Porphyroblasts

Question 50

Texture defined by large grains that experienced neocrystallization and growth in response to favorable temperature and pressure conditions due to metamorphism.

Answer 50

Porphyroblastic

Question 51

A texture of metamorphic rocks that exhibit planar arrangement of mineral grains or structural features of a rock.

Answer 51

Foliated

Question 52

A texture of metamorphic rocks that exhibit linear arrangement of mineral grains or structural features of a rock.

Answer 52

Lineation

Question 53

A texture of metamorphic rocks that lack the planar arrangement of mineral grains or structural features of a rock.

Answer 53

Non-Foliated