Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Petrology > W8 Metamorphism: Crystal Growth and Textures > Flashcards

W8 Metamorphism: Crystal Growth and Textures Flashcards

1
Q

Metamorphic reactions occur

A

in the solid state

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Metamorphic Reactions involve

A

no change in the bulk chemistry of a rock (they are isochemica

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Metamorphic reactions result

A

in the crystallisation of new minerlas

neoblasts

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Metamorphic reactions texture

A 
result in the formation of new textures and fabrics
foliation
banding
preferered grain orientations
usually cause change in colour
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Protolith Sandstone

A

LG: Phylite
MG_ schist
HG: gneiss

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Protolith Limestone

A

LG MG and HG marble!

persistent

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Protolith: Basalt

A 
LG  greenschist
MG amphibolite
 HG eclogite
protholiths → low grad of that stone → medium grade of that stone → high grade of that stone
with pressure and temperature increasing
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Protolith Granite

A

LG metagranite
MG metagranite
HG gneiss

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Metamorphism of a Limestone

A 
Metamorphism of a Limestone
CaCO3 CaCO3
• recrystallisation means all
sedimentary textures are lost
• a marble is produced - harder,
denser, lower porosity rock
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

metamorphic reactions proceed as direct result of

A

incerasing
heat
pressure / applied stress

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

this increase results from

A

burial
proximity to igneaous intrusions (High temp, low pressure)
Deformation
Impacts

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

pressure and tempth reelated to depth

A

pressure and temp increase with deepth
30 degrees Cper km depth
so if D= 1km T= 30 C
D= 3km T= 90C

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Effects of Heat on crystal

A

As solids are heated …
• there is an increase in molecular motion
> ions can migrate
> defects can relocate

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Effects of Pressure

A

Increase in pressure favours the formation of denser
crystal forms (& usually with a decrease in volume)
Eclogites form only at the highest possible pressures …
… they are the densest of all rocks (specific gravity around 3.5)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Effects of Deformation / Deviatoric Stress

A

changes the shape of rocks & minerals (strain)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Deformation at high pressure

A

at high pressures - ductile deformation

> crystals will ‘flow

17
Q

Deformation at low pressure

A

brittle deformation
> rocks will fracture
Mylonite - an example of extreme brittle deformation, Dynamic Metamorphism associated with faults

18
Q

Speed of process

A

Recrystallisation of minerals during metamorphic reactions is a very slow process - requires millions of years
EXCEPT for
• meteorite impact related metamorphism
• seismic fault movement dynamic metamorphism

19
Q

Crystal growth in Metamorphic Rocks

A

atoms approach metamorphic crystal nucleii by diffusion through the solid (slow process)
• large grains grow at the expense of smaller ones
• for monomineralic rocks (marble, quartzite) - large
grains grow easily (and relatively quickly)
> atoms only have to diffuse short distances

20
Q

grains with large surface areas

A

recrystallise more quickly

21
Q

grains with many inclusions

A

recrystallise more quickly

22
Q

Bubbles in Crystals

A

Bubbles in a foam as a proxy for crystal growth in metamorphic rocks

23
Q

Ostwald Ripening

A

Large grains consuming smaller ones
A very stable structure with minimum surface energy results
creates granoblastic texture in a marble
NB granoblastic texture is common only in monomineralic rocks and M-H P&T rocks. Once formed, it is very stable.

24
Q

Porphyroblastst

A

equivalents of phenocrysts in igneous rocks
ex. snowball garnet rotated during formation
not always equal sizes, also can be different shapes

25
Q

Cleave results from

A

Cleavage results from alignment of platey minerals + deformation (in fine grained rocks)
i.e. slate, slatey cleavage with signs of compression and deformation

26
Q

Grain size increases

A

with an increase in T and P

27
Q

Foliation

A

All these rocks have a ‘foliation’ defined by elongate or platey minerals

28
Q

Foliation definition

A

Foliation in geology refers to repetitive layering in metamorphic rocks. Each layer can be as thin as a sheet of paper, or over a meter in thickness

29
Q

Pattern

A

banding in a gneiss- mineral segregations

does not follow banding in protolith

30
Q

Microfolds

A

Crennulation in fibrous talc crystals - microfolds

31
Q

Deformation can cause

A

twins to form in crystal

ex. calcite

Petrology (16 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions