Ch 11 Diversification

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Chapter 11: Diversification ofChapter 11: Diversification of

MagmasMagmas



Magmatic DifferentiationMagmatic Differentiation

Any process by which a magma is able toAny process by which a magma is able todiversify and produce a magma or rock ofdiversify and produce a magma or rock of

different compositiondifferent composition



Magmatic DifferentiationMagmatic Differentiation

Two essential processesTwo essential processes

1. Creates a compositional difference1. Creates a compositional difference in one or morein one or more

phases phases

. !reserves. !reserves the chemical difference bythe chemical difference by segregatingsegregating "or"or

fractionatingfractionating# the chemically distinct portions# the chemically distinct portions



!artial Melting!artial Melting

$eparation of a partially melted li%uid from$eparation of a partially melted li%uid from

the solid residuethe solid residue



&ffects of removing li%uid at various stages of melting&ffects of removing li%uid at various stages of melting &utectic systems&utectic systems

'irst melt'irst melt alwaysalways ( eutectic composition( eutectic composition Ma)or Ma)or element composition of eutectic melt iselement composition of eutectic melt is

constant until one of the source mineral phases isconstant until one of the source mineral phases is

consumedconsumed "trace elements differ#"trace elements differ# *nce a phase is consumed+ the ne,t increment of melt*nce a phase is consumed+ the ne,t increment of melt

will be different - and Twill be different - and T



$eparation of a partially melted li%uid from$eparation of a partially melted li%uid fromthe solid residue re%uires a critical melt the solid residue re%uires a critical melt

$ufficient melt must be produced for it to$ufficient melt must be produced for it to

'orm a continuous+ interconnected film'orm a continuous+ interconnected film

/ave enough interior volume that it is not/ave enough interior volume that it is not

all of it is adsorbed to the crystal surfacesall of it is adsorbed to the crystal surfaces



The ability to form an interconnected film is dependentThe ability to form an interconnected film is dependent

upon theupon the dihedral angle "dihedral angle "θθ## a property of the melta property of the melt

Figure 11-1Figure 11-1 Illustration of the dihedralIllustration of the dihedral

angle (angle (

) of melt droplets that typically) of melt droplets that typically

form at multiple grain junctions.form at multiple grain junctions. AfterAfter

Hunter (198)Hunter (198) In I. !arsons (ed.)" #riginsIn I. !arsons (ed.)" #rigins

of Igneous $ayering. %eidel" &ordrecht"of Igneous $ayering. %eidel" &ordrecht"

pp. '-*'.pp. '-*'.



0ravitational effects "0ravitational effects " buoyant buoyant li%uid#li%uid# 'ilter pressing'ilter pressing+ or+ or compaction+compaction+ ofof crystal mushcrystal mush

$hear $hear the 2CM! drops considerablythe 2CM! drops considerably 2CM! varies with2CM! varies with

TT

viscosityviscosity --



Dominant mechanism by which mostDominant mechanism by which most

magmas+ once formed+ differentiate3magmas+ once formed+ differentiate3

Crystal 'ractionationCrystal 'ractionation



0ravity settling0ravity settling

The differential motion of crystals and li%uidThe differential motion of crystals and li%uidunder the influence of gravity due to theirunder the influence of gravity due to their

differences in densitydifferences in density



0ravity settling0ravity settling

Cool pointCool point aa →→ olivine layer at base of plutonolivine layer at base of plutonif first olivine sinksif first olivine sinks

4e,t get ol5cp, layer 4e,t get ol5cp, layer

finally get ol5cp,5plagfinally get ol5cp,5plag

Cumulate te,ture:Cumulate te,ture:

Mutually touchingMutually touching phenocrysts with phenocrysts with

interstitial crystalli6edinterstitial crystalli6ed

residual meltresidual melt

Figure -+. After ,oen

(191)" A. . /ci." and

0orse (199')" ,asalts

and !hase &iagrams.

rieger !u2lishers.



Figure 11-+Figure 11-+ 3ariation diagram using 0g# as the a2scissa for la4as associated ith the 199 ilauea eruption in Haaii.3ariation diagram using 0g# as the a2scissa for la4as associated ith the 199 ilauea eruption in Haaii.

AAfter 0urata and %ichter" 1955 (as modified 2y ,est" 198+)fter 0urata and %ichter" 1955 (as modified 2y ,est" 198+)



$toke7s 8aw$toke7s 8aw

99 ( the settling velocity "cmsec#( the settling velocity "cmsec#

gg ( the acceleration due to gravity ";<= cmsec( the acceleration due to gravity ";<= cmsec

##r r ( the( the radiusradius of a spherical particle "cm#of a spherical particle "cm#

ρρss ( the density of the solid spherical particle "gcm( the density of the solid spherical particle "gcm>>##

ρρll

( the density of the li%uid "gcm( the density of the li%uid "gcm>>

##

ηη ( the viscosity of the li%uid "1 ccm sec ( 1 poise#( the viscosity of the li%uid "1 ccm sec ( 1 poise#

9 gr " #;

= −ρ ρ

η s l



*livine in basalt*livine in basalt

*livine "*livine "ρρss ( >.> gcm( >.> gcm>>++ r ( =.1 cmr ( =.1 cm##

?asaltic li%uid "?asaltic li%uid "ρρll ( .@ gcm( .@ gcm>>++ ηη ( 1=== poise#( 1=== poise#

9 ( B;<=B=.19 ( B;<=B=.1 ">.>.@#;B1=== (">.>.@#;B1=== ( =.==1> cmsec=.==1> cmsec



2hyolitic2hyolitic meltmelt ηη ( 1=( 1=CC poise and poise and ρρll ( .> gcm( .> gcm>>

hornblendehornblende crystal "crystal "ρρss ( >. gcm( >. gcm>>++ r ( =.1 cmr ( =.1 cm##

9 ( , 1=9 ( , 1=CC cmsec+ orcmsec+ or @ cmyear @ cmyear

feldsparsfeldspars ""ρρll ( . gcm( . gcm>>##

9 ( cmyear 9 ( cmyear (( == m in the 1=== m in the 1=DD yearsyears that a stock might coolthat a stock might cool

Ef =. cm in radius "Ef =. cm in radius "1 cm diameter 1 cm diameter # settle at# settle at =.@=.@

metersyear metersyear + or @. km in 1=+ or @. km in 1=DD

year cooling of stock year cooling of stock



$tokes7 8aw is overly simplified$tokes7 8aw is overly simplified

1. Crystals are not spherical1. Crystals are not spherical

.. *nly basaltic magmas very near their li%uidus*nly basaltic magmas very near their li%uidus

temperatures behave as 4ewtonian fluidstemperatures behave as 4ewtonian fluids



Many silicic magmas approach the ternary eutecticMany silicic magmas approach the ternary eutectic

&ither&ither fractional crystalli6ationfractional crystalli6ation does take place or theydoes take place or they

areare minimum "eutectic# meltsminimum "eutectic# melts

Figure 11-Figure 11- !osition of the H+#-saturated!osition of the H+#-saturated

ternary eutectic in the al2ite-orthoclase-ternary eutectic in the al2ite-orthoclase-

silica system at 4arious pressures. 6hesilica system at 4arious pressures. 6he

shaded portion represents theshaded portion represents the

composition of most granites. Includedcomposition of most granites. Included

are the compositions of the 6uolumneare the compositions of the 6uolumne

Intrusi4e /eries (Figure '-+)" ith theIntrusi4e /eries (Figure '-+)" ith the

arro shoing the direction of the trendarro shoing the direction of the trend

from early to late magma 2atches.from early to late magma 2atches.

7perimental data from yllie7perimental data from yllie et al et al . (195).. (195).

From inter (+**1) An Introduction toFrom inter (+**1) An Introduction to

Igneous and 0etamorphic !etrology.Igneous and 0etamorphic !etrology.

!rentice Hall!rentice Hall



!olybaric!olybaric 'ractional Crystalli6ation'ractional Crystalli6ation

1. $tability of phases changes "hi! garnet...#1. $tability of phases changes "hi! garnet...#

. $hift of the eutectic point with pressure will. $hift of the eutectic point with pressure will

cause the %uantity of the li%uidus phases to varycause the %uantity of the li%uidus phases to vary



Ol

Low-P

Pyx

Hi-P/igh! "red tieline#/igh! "red tieline#

has li% F olhas li% F ol

8ow! "yellow tie8ow! "yellow tie

line# has ol F li%uidline# has ol F li%uid

&,pansion of olivine field at low pressure causes&,pansion of olivine field at low pressure causes

an increase in the %uantity of crystalli6ed olivinean increase in the %uantity of crystalli6ed olivine



Two other mechanisms that facilitate theTwo other mechanisms that facilitate the

separation of crystals and li%uidseparation of crystals and li%uid

1. Compaction1. Compaction



Two other mechanisms that facilitate theTwo other mechanisms that facilitate the

separation of crystals and li%uidseparation of crystals and li%uid

. 'low segregation. 'low segregation

Figures 11-' and 11-Figures 11-' and 11- &re4er and ohnston (198). %oyal&re4er and ohnston (198). %oyal

/oc. 7din2urgh 6rans." 5" '9-'99./oc. 7din2urgh 6rans." 5" '9-'99.



9olatile Transport9olatile Transport

1. 9apor released by heating of hydrated or carbonated1. 9apor released by heating of hydrated or carbonated

wall rockswall rocks



9olatile Transport9olatile Transport

. As a volatilebearing. As a volatilebearing

"but undersaturated#"but undersaturated#magma rises andmagma rises and

pressure is reduced+ the pressure is reduced+ the

magma may eventuallymagma may eventually

become saturated in the become saturated in thevapor+ and a free vaporvapor+ and a free vapor

phase will be released phase will be released

Figure -++. From ,urnham and &a4is (19'). A /ci."

+'" 9*+-9'*.



>. 8atestage fractional crystalli6ation>. 8atestage fractional crystalli6ation

'ractional crystalli6ation enriches late melt in'ractional crystalli6ation enriches late melt in

incompatible+ 8E8+ and nonlithophile elementsincompatible+ 8E8+ and nonlithophile elements

Many concentrate further in the vapor Many concentrate further in the vapor

!articularly enriched with resurgent boiling "melt!articularly enriched with resurgent boiling "melt

already evolved when vapor phase released#already evolved when vapor phase released# 0et a silicatesaturated vapor 5 a vaporsaturated0et a silicatesaturated vapor 5 a vaporsaturated

late derivative silicate li%uidlate derivative silicate li%uid



9olatile release raises li%uidus temperature9olatile release raises li%uidus temperature →→

porphyritic te,ture porphyritic te,ture

May increase ! fracture the roof rocksMay increase ! fracture the roof rocks 9apor and melt escape along fractures as dikes9apor and melt escape along fractures as dikes

$ilicate melt$ilicate melt →→ %uart6 and feldspar %uart6 and feldspar

→→ small dikes ofsmall dikes of apliteaplite

9apor phase9apor phase →→ dikes or pods ofdikes or pods of pegmatite pegmatite

C i ibl lC i ibl l



Concentrate incompatible elementsConcentrate incompatible elements

Comple,: varied mineralogyComple,: varied mineralogy

May displayMay display concentric 6onationconcentric 6onation

Figure 11-5Figure 11-5 /ections of three :oned fluid-phase deposits (not at the same scale)./ections of three :oned fluid-phase deposits (not at the same scale). a.a. 0iarolitic pod in granite (se4eral cm0iarolitic pod in granite (se4eral cm

across).across). 2.2. Asymmetric :oned pegmatite di;e ith aplitic 2ase (se4eral tens of cm across).Asymmetric :oned pegmatite di;e ith aplitic 2ase (se4eral tens of cm across). c.c. Asymmetric :oned pegmatiteAsymmetric :oned pegmatite

ith granitoid outer portion (se4eral meters across).ith granitoid outer portion (se4eral meters across). From ahns and ,urnham (1959).From ahns and ,urnham (1959). Econ. Geol.Econ. Geol." 5'" 8'-85'." 5'" 8'-85'.



< cm tourmaline crystals< cm tourmaline crystals

from pegmatitefrom pegmatite

mm gold from a mm gold from ahydrothermal deposithydrothermal deposit

8i id E i ibili



8i%uid immiscibility in the 'o$i*8i%uid immiscibility in the 'o$i* systemsystem8i%uid Emmiscibility8i%uid Emmiscibility

Figure 5-1+. Iso2aric 6-< phasediagram of the system Fo-/ilica at *.1

0!a. After ,oen and Anderson (191')

and =rieg (19+). Amer. . /ci.



The effect of addingThe effect of adding

alkalis+ alumina+ etc. isalkalis+ alumina+ etc. is

toto eliminate the solvuseliminate the solvus

completelycompletely

Figure -'. Iso2aric

diagram illustrating the

cotectic and peritectic

cur4es in the system

forsterite-anorthite-silica

at *.1 0!a. After Anderson(191) A. . /ci." and Ir4ine

(19) >I ?ear2. '.



2enewed interest when 2oedder "1;1# discovered a2enewed interest when 2oedder "1;1# discovered a

second immiscibility gap in the ironrich 'a8c$i*second immiscibility gap in the ironrich 'a8c$i*

systemsystem

Figure 11-. 6o immisci2ilitygaps in the system fayalite-

leucite-silica (after %oedder"

199). ?oder (ed.)" 6he

74olution of the Igneous

%oc;s. !rinceton @ni4ersity

!ress. pp. 1-8. !rojected

into the simplified system are

the compositions of natural

immisci2le silicate pairdroplets from interstitial Fe-

rich tholeiitic glasses

(!hilpotts" 198+). >ontri2.

0ineral. !etrol." 8*" +*1-+18.



$ome &,amples$ome &,amples

8ate silicarich immiscible droplets in 'erich8ate silicarich immiscible droplets in 'erichtholeiitic basalts "as in 2oedder#tholeiitic basalts "as in 2oedder#

$ulfidesilicate immiscibility "massive sulfide$ulfidesilicate immiscibility "massive sulfide

deposits#deposits# Carbonatitenephelinite systems "Chapter 1;#Carbonatitenephelinite systems "Chapter 1;#



Tests for immiscible origin ofTests for immiscible origin of

associated rock pairsassociated rock pairs

1. The magmas must be immiscible when1. The magmas must be immiscible when

heated e,perimentally+ or they must plot onheated e,perimentally+ or they must plot on

the boundaries of a known immiscibilitythe boundaries of a known immiscibility

gap+ as in 'ig. 11gap+ as in 'ig. 11



. Emmiscible li%uids are in e%uilibrium with. Emmiscible li%uids are in e%uilibrium with

each other+ and thus they must be ineach other+ and thus they must be in

e%uilibrium with the same mineralse%uilibrium with the same minerals

Tests for immiscible origin ofTests for immiscible origin of

associated rock pairsassociated rock pairs



Compositional Convection andCompositional Convection and In In

SituSitu Differentiation !rocessesDifferentiation !rocesses In-situ: crystals don7t sinkmove

Typically involves

Diffusion

Convective separation of li%uid and crystals



The $oret &ffect andThe $oret &ffect and

Thermogravitational DiffusionThermogravitational Diffusion

Thermal diffusionThermal diffusion+ or the+ or the $oret effect$oret effect

/eavy/eavy elementsmolecules migrate toward theelementsmolecules migrate toward the

colder colder end andend and lighter lighter ones to theones to the hotter hotter end ofend ofthe gradientthe gradient



Galker and De8ong "1;<# sub)ected two basalts toGalker and De8ong "1;<# sub)ected two basalts to

thermal gradients of nearly =thermal gradients of nearly =ooCmm "H#Cmm "H#

'ound that:'ound that: $amples reached a steady$amples reached a steady

state in a few daysstate in a few days

/eavier elements/eavier elements →→ coolercoolerend and the lighterend and the lighter →→ hothot

endend

The chemical concentrationThe chemical concentrationis similar to that e,pectedis similar to that e,pected

from fractionalfrom fractional

crystalli6ationcrystalli6ation Figure -'. After al;er"

&. >. and /. 7. &e$ong

(198+). >ontri2. 0ineral.!etrol." 9" +1-+'*.



Thermogravitational diffusionThermogravitational diffusion

$table and persistent stagnant boundary layers$table and persistent stagnant boundary layers

have been shown to occur near the top andhave been shown to occur near the top and

sides of magma chamberssides of magma chambers



/ildreth "1;;# =. Ma/ildreth "1;;# =. Ma ?ishop Tuff ?ishop Tuff at 8ongat 8ong

9alley+ California9alley+ California

9ertical9ertical compositionalcompositional variation in the stratifiedvariation in the stratifiedtuff tuff

Thermal gradient in chamber Thermal gradient in chamber



ModelModel

Figure 11-11. /chematic section through a rhyolitic magma cham2er undergoing con4ection-aided in-situ differentiation. After Hildreth (199). =eol. /oc. Amer. /pecial !aper" 18*" '-.



8angmuir Model8angmuir Model Thermal gradient atThermal gradient at

wall and capwall and cap →→ variation in variation in

crystalli6edcrystalli6ed

CompositionalCompositional

convectionconvection →→

evolved magmasevolved magmas

from boundaryfrom boundary

layer to cap "or mi,layer to cap "or mi,

into interior#into interior#

Figure 11-1+Figure 11-1+ Formation of 2oundary layersFormation of 2oundary layers

along the alls and top of a magmaalong the alls and top of a magma

cham2er.cham2er. From inter (+**1) AnFrom inter (+**1) An

Introduction to Igneous and 0etamorphicIntroduction to Igneous and 0etamorphic

!etrology. !rentice Hall!etrology. !rentice Hall



Magma Mi,ingMagma Mi,ing

&nd member mi,ing&nd member mi,ing for a suite of rocksfor a suite of rocks 9ariation on /arkertype diagrams9ariation on /arkertype diagrams

should lie on a straight lineshould lie on a straight line between the between the

two most e,treme compositionstwo most e,treme compositions



Figure 11-+Figure 11-+ 3ariation diagram using 0g# as the a2scissa for la4as associated ith the 199 ilauea eruption in Haaii.3ariation diagram using 0g# as the a2scissa for la4as associated ith the 199 ilauea eruption in Haaii.AAfter 0urata and %ichter" 1955 (as modified 2y ,est" 198+)fter 0urata and %ichter" 1955 (as modified 2y ,est" 198+)



?asalt pillows?asalt pillows

accumulating at the bottomaccumulating at the bottom

of a in granitic magmaof a in granitic magma

chamber+ 9inalhavenchamber+ 9inalhaven

Esland+ MaineEsland+ Maine

Comingled basalt2hyoliteComingled basalt2hyolite

Mt. Mc8oughlin+ *regonMt. Mc8oughlin+ *regon

Figure 11-8Figure 11-8 From inter (+**1) AnFrom inter (+**1) An

Introduction to Igneous andIntroduction to Igneous and

0etamorphic !etrology. !rentice Hall0etamorphic !etrology. !rentice Hall



AssimilationAssimilation

Encorporation of wall rocks "diffusion+Encorporation of wall rocks "diffusion+,enoliths#,enoliths#

Assimilation by melting is limited byAssimilation by melting is limited by

the heat available in the magmathe heat available in the magma



Ione meltingIone melting

Crystalli6ing igneous material at theCrystalli6ing igneous material at the base e%uivalent to the amount melted base e%uivalent to the amount melted

at the topat the top

Transfer heat by convectionTransfer heat by convection

D i d i i il iD t ti d i i il ti



Detecting and assessing assimilationDetecting and assessing assimilation

EsotopesEsotopes are generally the bestare generally the best

Continental crust becomes progressively enrichedContinental crust becomes progressively enrichedinin <C<C$r$r<@<@$r and depleted in$r and depleted in 1D>1D> 4d 4d1DD1DD 4d 4d

Figure 9-1.Figure 9-1. 7stimated %2 and /r7stimated %2 and /r

isotopic e4olution ofisotopic e4olution of

the 7arths upperthe 7arths upper

mantle" assuming amantle" assuming a

large-scale meltinglarge-scale melting

e4ent producinge4ent producing

granitic-typegranitic-type

continental roc;s atcontinental roc;s at

.* =a 2.p After.* =a 2.p Afterilson (1989).ilson (1989).

IgneousIgneous

!etrogenesis. @nin!etrogenesis. @nin

HymanBluer.HymanBluer.

D t ti d i i il tiD t ti d i i il ti



;1><

J → >D

J → =@

!b "λ ( 1.1 , 1=1=

a1

#; >AJ → =C!b "λ ( ;.<< , 1=1= a1#

;> >Th → =<!b "λ ( .; , 1=11 a1#

JTh!b system as an indicator of continentalJTh!b system as an indicator of continental

contamination is particularly usefulcontamination is particularly useful

All are incompatible 8E8 elements+ so theyAll are incompatible 8E8 elements+ so they

concentrate strongly into the continental crustconcentrate strongly into the continental crust

Detecting and assessing assimilationDetecting and assessing assimilation



Mi,ed !rocessesMi,ed !rocesses May be more than coincidence: twoMay be more than coincidence: two

processes may operate in con)unction processes may operate in con)unction

"cooperation3#"cooperation3#

A'C: '- supplies the necessary heatA'C: '- supplies the necessary heatfor assimilationfor assimilation

'ractional crystalli6ation 5 recharge of'ractional crystalli6ation 5 recharge of

more primitive magmamore primitive magma



Tectonic-Igneous AssociationsTectonic-Igneous Associations

Associations on a larger scale than theAssociations on a larger scale than the

petrogenetic provinces petrogenetic provinces

An attempt to address global patternsAn attempt to address global patterns

of igneous activity by groupingof igneous activity by grouping

provinces based upon similarities in provinces based upon similarities in

occurrence and genesisoccurrence and genesis



Mid*cean 2idge 9olcanismMid*cean 2idge 9olcanism

*cean Entraplate "Esland# volcanism*cean Entraplate "Esland# volcanism

Continental !lateau ?asaltsContinental !lateau ?asalts

$ubductionrelated volcanism and plutonism$ubductionrelated volcanism and plutonism

Esland ArcsEsland Arcs

Continental ArcsContinental Arcs

0ranites "not a true TE Association#0ranites "not a true TE Association#

Mostly alkaline igneous processes of stableMostly alkaline igneous processes of stable

craton interiorscraton interiors

Anorthosite MassifsAnorthosite Massifs

Tectonic-Igneous AssociationsTectonic-Igneous Associations

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Ch 11 Diversification