CHPTR 7 Metamorphic Rocks

Question 1

protolith

Answer 1

parent rock

Question 2

metamorphism

Answer 2

transformation of rocks as the result of heat, pressure, or fluid activities

• below melting point BUT higher pressure and temp. than lithification

Question 3

lithostatic pressure

Answer 3

uniform stress/confining pressure
uniform field of pressure experienced by most rocks beneath Earth’s surface

Question 4

directed pressure (differential stress

Answer 4

pushes mineral grains into one direction

Question 5

geothermal gradient

Answer 5

25-30 degrees C

the rate at which the Earth’s temperature increases with depth

Question 6

what can provide heat for the metamorphic process + how

Answer 6

burial increases temp. - the deeper you go, the hotter it is

volcanoes - heat from intrusions and lava flow heats underlying rocks

Question 7

confining pressure + example

Answer 7

uniform stress in all direction - lithostatic stress

Question 8

lithostatic stress

Answer 8

pressure experienced by rocks under the Earth’s surface

Question 9

pressure due to 1km of rock

Answer 9

25 - 30 MPa

Question 10

directed pressure

Answer 10

differential stress - pushes mineral grains into one direction

Question 11

metastomatism

Answer 11

metamorphism due to fluid activity

Question 12

how does fluid activity affect metamorphism

Answer 12

accelerate chemical change which can cause new minerals to form

Question 13

origins of fluids that influence metamorphic activity (4)

Answer 13

1. trapped in pore space in rocks
2. released by magma
3. dehydration reactions
4. hydrothermal circulation

Question 14

metamorphic processes (7)

Answer 14

1. orientation of mineral grains
2. recrystallization of existing minerals
3. growth of new minerals
4. segregation of minerals
5. baking
6. shearing
7. partial melting

Question 15

controlling factors in metamorphism

Answer 15

heat, pressure, fluids

Question 16

index minerals for metamorphism grade

Answer 16

low to high
chlorite
muscovite
biotite
garnet / kyanite
staurolite
sillimanite

Question 17

3 horrible index minerals for metamorphism

Answer 17

andalusite, quartz, feldspar

Question 18

what do andalusite, kyanite and sillimanite have in common

Answer 18

polymorphs

Question 19

what causes kyanite vs sillimanite

+ why don’t i care about andalusite

Answer 19

kyanite - high pressure
sillimanite - high temperature

andalusite is a bad index mineral

Question 20

foliated texture

Answer 20

stripes - produced by the preferred orientation of platy minerals

Question 21

non-foliated texture

Answer 21

do not exhibit preferred orientation of minerals

Question 22

burial metamorphism

Answer 22

low temp, low pressure, just rocks underground

Question 23

contact metamorphism

Answer 23

high temp, low pressure
near a magma chamber and the surface

Question 24

aureoles

Answer 24

metamorphosed zones that surround plutons or other intrusions - its from contact metamorphism

Question 25

how does distance from a pluton affect metamorphic grade

Answer 25

- high grade metamorphism close to pluton, low grade farther away

Question 26

regional metamorphism

Answer 26

most common metamorphism occurs during subduction or continent-continent collision

Question 27

Barrovian metamorphism protolith

Answer 27

shale

Question 28

pelitic protolith

Answer 28

shale protolith

Question 29

Barrovian metamorphic process

Answer 29

shale slate phyllite shist gneiss

Question 30

what metamorphic grade does biotite and garnet signify

Answer 30

intermediate

Question 31

what metamorphic grade does chlorite signify

Answer 31

low grade

Question 32

economic significance of plutons/contact metamorphism

Answer 32

as pluton cools, hydrothermal circulation occurs by the fluids released from crystallizing rock and groundwater. This fluid concentrate minerals and form deposits of economic minerals

Question 33

slate features?

Answer 33

- foliated - created through grain reorientation

Question 34

phyllite features?

Answer 34

foliated - platy minerals cannot be seen by eye - identified by glossy, lustrous sheen - recrystallization; results in coarser grains

Question 35

what metamorphic grade does sillimanite signify

Answer 35

high grade

Question 36

slate foliated?

Answer 36

foliated

Question 37

schist features + what's unique about it at a higher grade

Answer 37

foliated - schistocity >50% platy material garnet and staurolite porphyroblasts appear at higher grade

Question 38

most common metamorphic rock formed by regional metamorphism

Answer 38

schist

Question 39

porphyroblasts

Answer 39

large mineral crystal that disrupts the mineral grain in metamorphic rocks

Question 40

gneiss features

Answer 40

foliated banding - bandss of black and white rock more granular minerals than platy minerals

Question 41

minerals present in the light colour in gneiss

Answer 41

quartz, feldspar

Question 42

minerals present in the dark colour in gneiss

Answer 42

biotite, amphibole

Question 43

oldest dated rock

Answer 43

Acasta Gneiss

Question 44

migmatite

Answer 44

has a mixture of apparently igneous and metamorphic components. Like liquid stripes - signifies partial melting

Question 45

prograde metamorphism

Answer 45

increasing grade

Question 46

retrograde metamorphism

Answer 46

decreasing grade

Question 47

metamorphic zone

Answer 47

area with same degree of metamorphism

Question 48

is marble foliated

Answer 48

nope

Question 49

marble's predominant minerals

Answer 49

calcite/dolomite

Question 50

what does limestone metamorphise into

Answer 50

marble

Question 51

what does quartz metamorphise into

Answer 51

quartzite

Question 52

what does mafic igneous rocks metamorphise into

Answer 52

greenstone, amphibolite, granulite eclogite

Question 53

eclogite features

Answer 53

- often contains pink garnet - stable at mantle pressures - high density

Question 54

what does felsic rocks metamorphis into

Answer 54

gneiss

Question 55

impact metamorphism

Answer 55

asteroid hit Earth/underground nuclear explosions - lots of pressure

Question 56

when the Earth was hit by an asteroid what rocks were formed

Answer 56

- shocked quartz - coesite - stishovite

Question 57

dynamic metamorphism

Answer 57

formed in fault zones due to high strains

Question 58

cataclasites

Answer 58

forms in shallow part of faults

Question 59

what causes cataclastic texture

Answer 59

shallow faults which result in crushing and grinding of rocks

Question 60

mylonites

Answer 60

forms in deeper part of faults (10-20km)

Question 61

hydrothermal metamorphism - mid ocean ridges process

Answer 61

- freshly erupted basalt and gabbro are erupted from ocean volcano and still hot - salt water percolates into the rocks. it cools into a new oceanic crust - mineral reaction occurs: olivine into serpentine

Question 62

hydrothermal metamorphism - plutons

Answer 62

- plutons cools, releasing water from the magma - water invades surrounding rocks creating pegmatite

Question 63

blueschist facies

Answer 63

low T, high P - the upper part of a subduction zone

Question 64

zeolite facies

Answer 64

burial metamorphism

Question 65

eclogite facies

Answer 65

high T, high P. the lower part of a subduction zone

Question 66

shield

Answer 66

area where pre-Cambrian igneous and metamorphic rocks are exposed at the surface

Question 67

platform

Answer 67

area where igneous-metamorphic basement overlain by sedimentary rocks

Question 68

cratons

Answer 68

formed by a combination of shield and platform

Question 69

distribution of metamorphic rock

Answer 69

1. shields 2. cores of mountain ranges - (continent continent collision)