Chap 14/15: Metamorphic rocks

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1

metamorphism definition

changes in minerology and texture in the (usually) solid state due to changing external conditions (Pressure and temperature) after 200C

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2

how are new minerals formed in metamorphism without melting

atoms are moved one by one along grain boundaries to form a new mineral

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3

diagenesis meaning

chemical, physical, and biological changes that affect sediment after initial deposition up to 200C (after 200C is metamorphism)

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4

melting temperature occurance

600-800C, bound after metamorphism where igneous processes typically lie

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5

protolith meaning

starting material for a rock ie parent rock

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6

order of metamorphic progression with increasing temperature and pressure

  • shale

  • slate

  • phyllite

  • schist

  • gneiss

  • migmatite (partially melted)

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7

what happens along the metamorphic progression

  • new or different minerals appear

  • folliation appears

  • increased grain size

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8

driving forces of metamorphism?

  • heat

  • pressure

  • fluids

  • deformation

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9

lithostatic pressure meaning

pressure induced from rocks

(at deep levels, pressure is equal due to flowing rock)

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10

hydrostatic pressure meaning

pressure induced from liquids

(pressure is equally distributed)

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11

typical geothermal gradient

15C/km

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12

regional metamorphism

metamorphism that occurs over a large scale

  • heat transfer occurs when rocks heat after thrusting on top of each other which causes lower rocks to heat

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13

contact metamorphism

metamorphism that occurs over small region

  • magma intrusion heats an area

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14

contact heat transfer is controlled by (3)

  • size of intrusion

  • temperature of magma

  • fluid circulation

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15

heat capacity

adding the same amount of heat and energy to different materials will lead to different increases in temperature

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16

aureole

region of metamorphism surrounding an intrusion

  • larger intrusion = larger aureole

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17

what affects the size of an aureole (5)

  • temperature difference btwn intrusion and host

  • composition of intrusion and host

  • speed of emplacement

  • fluid interactions (ground water and magmatic fluids)

  • shape of intrusion

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18

amount of water as metamorphic progress occurs?

weight precent of water decreases due to dehydration reactions

  • shale (12-15%) to gneiss (0-1%)

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19

regional deformation

rock texture will changed due to differential stress which produces folliation

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20

contact deformation

since the metamorphism is static, there’s no metamorphic stress and no foliation

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21

fabric definition

the combined effects of mineral reactions and deformation throughout the metamorphic event and the subsequent return of the rock to the terrestrial surface

  • foliation is a type

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22

crystal settling

early formed crystals piling up at the bottom of a magma chamber

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23

what structure does quartz form in rocks like quartzite in thin section

triple grain bonds

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24

can calcite foliate?

calcite cannot since it does not have a long axis

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25

undulous extinction

texture resulting from a deformed crystal which causes the extinction to be wavy and irregular

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26

when does the reduction of grain size occur

extreme deformity that occurs when lots of heat is applied (mylonites)

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27

what metamorphic rock form is most useful when wanting to know about the temperature and pressure of the area

regional shales/pelites (marine origin)

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28

what metamorphic rock form is most useful when wanting to know about the metabasic rock

basaltic rocks

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29

pelite definition

alumina-rich rock that is sensitive to the metamorphic conditions

can define the general increasing metamorphic grade trend

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30

if a rock is on the border of having either kyanite and silimanite but one has a higher Gibbs energy and the other is lower, which form is taken?

Form with the lower gibbs energy

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31

pelite prograde minerals in order (7)

  • chlorite

  • biotite

  • garnet

  • staurolite

  • kyanite

  • silimanite

  • k-feldspar

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32

prograde meaning

the grade changes in order from low to high temperature

  • more common since energy is more available

  • loss of volatiles occurs here

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33

metabasic rock prograde minerals in order (5)

  • chlorite

  • epidote

  • amphibole

  • garnet

  • pyroxene

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34

retrograde meaning

the grade changes in order from high to low temperature

  • needed stuff for the minerals to revert are gone such as H2O and CO2 during peak metamorphism

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35

what conditions make plagioclase more calcium rich?

increased temperature and pressure

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36

how is the kinetics of the rocks shown?

via texture

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37

metamorphic facies

metamorphic rocks that form under the same pressure and temperature but different protoliths

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38

minerals in amphibolite shale facies

quartz, biotite, muscovite, and garnet

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39

minerals in amphibolite limestone facies

calcite

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40

minerals in amphibolite basalt facies

amphibole, plagioclase, quartz

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41

isograds meaning

lines of constant metamorphic grade where new minerals are seen

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42

metamorphic zone naming

named after highest grade metamorphic mineral between the isograds

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43

metasomatism

fluids passing through rock that bring new elements to replace old ones, changes bulk composition of the rock

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44

porphyroblasts

crystal in metamorphic rock that is significantly larger than other minerals in the rock

garnet and staurolite are common

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45

metamorphic grade

loosely states intensity of metamorphism using the formation of minerals at each stage (ie slate, phyllite…)

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46

conditions needed to form greenschist

  • regional metamorphism

  • mid temp and pressure

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47

conditions needed to form blueschist

  • mid to high pressure

  • low temp

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48

conditions needed to form zeolite

  • low temp

  • low pressure

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49

conditions needed to form eclogite

  • high pressure

  • mid to high temp

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50

conditions needed to form hornfels

  • low pressure

  • mid to high temp

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51

conditions needed to form amphibolite

  • mid pressure

  • mid to high temp

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52

conditions needed to form granulite

  • mid to high pressure

  • high temperature

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53

geothermometer meaning

metamorphic reactions that are sensitive to temperature changes so can be used to determine metamorphic temperatures

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54

geobarometers

metamorphic reactions that are sensitive to pressure changes so can be used to determine metamorphic pressures but much less common

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55

skarns

calcsilicate rich rocks that can form Fe-ore deposits

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56

soapstone

mixture of serpentine and talc from the metamorphism of ultramafic igneous rocks

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57

index mineral

a mineral that forms in a metamorphized rock that indicates the minimum pressure and temperature in which the rock forms

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