MassTransportin MagmaticSystems
BjornO.Mysen
GeophysicalLaboratory, CarnegieInstitutionofWashington, Washington,DC,UnitedStates
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2.1
2.2 Meltingintervalofmantleperidotitewithoutvolatiles...........................................53 2.2.1Degreeofmelting...........................................................................................56
2.2.2Meltcompositioninthemeltinginterval......................................................60
2.2.3Uppermantlemagmagenesiswithoutvolatiles............................................63
2.3 Meltingintervalofmantleperidotitewithvolatiles................................................65
2.3.1Degreeofmelting:Peridotite H2O..............................................................65
2.3.2Meltcompositionintheperidotite H2Omeltinginterval..........................67
2.3.3UppermantlemagmagenesiswithH2O.......................................................72
2.3.4Degreeofmelting:Peridotite
2.3.5Meltcompositionintheperidotite
2.3.6Meltingofperidotitewithhalogens,CO2 and/orH2O..................................83
2.3.7Peridotite-CO2 meltinganduppermantlemagmagenesis...........................83
2.3.8Peridotite C O Hmeltingandmeltcompositions....................................84
2.4 Meltingintervalofbasalt..........................................................................................87
2.4.1Redoxvariationsatambientpressure............................................................87
2.4.2High-pressuremeltingwithoutvolatiles........................................................89
2.4.3Meltingofbasaltwithvolatiles.....................................................................90
2.5 Meltingintervalofandesite......................................................................................96
2.6 Meltingintervalofgranite......................................................................................100
2.6.1H2O-undersaturatedmelting.........................................................................102
2.6.2Meltingwithvariableredoxconditions.......................................................102
2.7 Concludingremarks................................................................................................103
References.......................................................................................................................104
CHAPTER3Elementdistributionduringmeltingandcrystallization .................
3.1 Introduction.............................................................................................................113
3.2 Principles.................................................................................................................113
3.3 Traceelementsubstitutioninmeltsandminerals..................................................115
3.3.1Traceelementsubstitutioninminerals........................................................116
3.3.2Traceelementsubstitutioninmelts.............................................................120
3.4 Elementpartitioning,intensive,andextensivevariables.......................................130
3.4.1Olivine-melt..................................................................................................130
3.4.2Plagioclase-melt...........................................................................................141
3.4.3Clinopyroxene-melt......................................................................................154
3.4.4Orthopyroxene-melt......................................................................................171
3.4.5Garnet-melt...................................................................................................182
3.4.6Amphibole-melt............................................................................................189
3.4.7Othermineral-meltpairs..............................................................................199
3.5 Mineral-meltpartitioningandigneousprocesses..................................................200
3.5.1Meltingmodels.............................................................................................200
3.5.2Variablepartitioncoefficients......................................................................200
3.6 Concludingremarks................................................................................................201 References.......................................................................................................................202
CHAPTER4Energeticsofmeltsandmeltinginmagmaticsystems
4.1 Introduction.............................................................................................................213
4.2 Energeticsofmelting..............................................................................................214
4.2.1Thermodynamicsofpremelting...................................................................214
4.2.2Enthalpyandentropyoffusion....................................................................225
4.3 Heatcontent,heatcapacity,andentropyofsilicatemeltsandmagma................233
4.3.1Heatcapacityandentropyofmagmaticliquids..........................................237
4.3.2Heatcapacity,entropy,andsilicatemeltpolymerizationinmetal oxide-SiO2 systems......................................................................................243
4.3.3HeatcapacityandentropyinAl-bearingsystems.......................................246
4.3.4HeatcapacityandentropyinFe-andTi-bearingmeltsystems..................247
4.3.5Thermodynamicsofmixingandsolution....................................................252
4.4 Thermodynamicsofmeltsandliquidusphaserelations........................................262
4.5 Concludingremarks................................................................................................266
CHAPTER5Structureofmagmaticliquids ..........................................................
5.1 Introduction.............................................................................................................275
5.2 Glassversusmeltandglasstransition....................................................................275
5.3 Silicatemeltandglassstructure.............................................................................278
5.3.1Degreeofsilicatepolymerization, NBO/T...................................................279
5.3.2Si O Albondingandcharge-balanceoftetrahedrally coordinatedAl3þ ..........................................................................................287
5.3.3Silicatespeciation(Qn-species)....................................................................292
5.3.4Al3þ substitutionforSi4þ inmagmaticsystems.........................................304
5.3.5Othertetrahedrallycoordinatedcations(P5þ andTi4þ)..............................309
5.4 Ironinmagmaticliquids.........................................................................................310
5.4.1RedoxrelationsofFe3þ andFe2þ ...............................................................311
5.4.2Structuralroleofironinmagmaticsystems................................................315
5.4.3Magmapropertiesandredoxratioofiron...................................................317
5.5 Concludingremarks................................................................................................318
CHAPTER6Structureandpropertiesoffluids
6.1 Introduction.............................................................................................................331
6.2 Fluid/meltpartitioningofvolatilecomponents......................................................332
6.2.1Fluid/meltpartitioningofH2O.....................................................................333
6.2.2Fluid/meltpartitioningofCO2 .....................................................................334
6.2.3Fluid/meltpartitioningofchlorine...............................................................336
6.2.4Fluid/meltpartitioningoffluorine...............................................................344
6.2.5Fluid/meltpartitioningofbromineandiodine............................................345
6.2.6Fluid/meltpartitioningofsulfur...................................................................347
6.3 StructureandpropertiesofH2Oinfluids..............................................................349
6.3.1StructureofliquidandsupercriticalH2O....................................................351
6.3.2PropertiesofliquidandsupercriticalH2O..................................................363
6.3.3H2O NaCl....................................................................................................375
6.3.4H2O C O H..............................................................................................383
6.3.5H2O
6.4 Solubilitybehaviorinfluid:H2O SiO2 .................................................................393
6.4.1SolubilityofSiO2 inH2O............................................................................393
6.4.2SolubilitymechanismofSiO2 inH2O.........................................................400
6.4.3PropertiesofH2O SiO2 fluid......................................................................406
6.4.4H2O SiO2 NaCl.........................................................................................410
6.5 Solubilitybehaviorinfluid:H2O SiO2 MgO.....................................................413
6.5.1SolubilityofMgO SiO2 inH2O.................................................................413
6.5.2SolubilitymechanismofMgO SiO2 inH2O.............................................415
6.5.3MgO SiO2 solubilityinsalinesolutions....................................................418
6.5.4PropertiesofMgO SiO2 H2Ofluid..........................................................421
6.6 Solubilitybehaviorinfluid:H2O Al2O3( NaCl KOH SiO2)..........................422
6.6.1Al2O3 H2Owithandwithouthalogens......................................................422
6.6.2H2O Al2O3-alkalialuminosilicatewithandwithouthalogens..................426
6.7 Minorandtraceelementsinaqueousfluid............................................................433
6.7.1Tisolubility..................................................................................................434
6.7.2Zrsolubility..................................................................................................436
6.7.3Salinityofaqueoussolutionsandtraceelementsolubility.........................440
6.7.4Sulfurinaqueoussolutionsandtraceelementsolubility............................450
6.8 Concludingremarks................................................................................................463
H2Osolubility.........................................................................................................485
7.4.1H2Osolubilityinsimplesystemmelts........................................................486
7.4.2Miscibilitybetweenhydrousmeltsandaqueousfluids...............................493
7.4.3Watersolubilityandmixedvolatiles...........................................................493
7.4.4Watersolubilityinnaturalmagmaticliquids..............................................496
7.4.5H2Osolubilitymodelsfornaturalmagma...................................................496
7.4.6Watersolutionmechanismsinmagma........................................................501
7.4.7H2Oinmagmaticliquids..............................................................................511
7.4.8Propertiesandprocessesofhydrousmagmaticliquids...............................513
7.5 Concludingremarks................................................................................................525
8.2.1SolubilityofCO2 inmagma........................................................................536
8.2.2SolubilitymechanismsofCO2 inmagma...................................................539
8.2.3Oxidizedcarbon(CO2)inmagmaticprocesses...........................................542
8.3 Reducedcarbon(CH4,CO,andcarbide)...............................................................548
8.3.1Carbonmonoxide(CO)................................................................................550
8.3.2Carbide(C)...................................................................................................551
8.3.3Methane(CH4).............................................................................................551
8.3.4MagmapropertiesandCH4-inducedmeltdepolymerization......................554
8.4 Sulfursolubility......................................................................................................555
8.4.1Oxidizedsulfur(SO2 andSO3)....................................................................558
8.4.2Reducedsulfur(S2 )....................................................................................561
8.5 Nitrogensolubilityandsolutionmechanisms........................................................567
8.5.1Oxidizednitrogen.........................................................................................568
8.5.2Reducednitrogen..........................................................................................569
8.5.3NitrogenintheEarth’sinterior....................................................................572
8.6 Hydrogensolubilityandsolutionmechanisms......................................................573
8.6.1HydrogenintheEarth’smantle...................................................................574
8.7 Halogensolubilityandsolutionmechanisms.........................................................575
8.7.1Fluorinesolubility........................................................................................575
8.7.2Fluorinesolutionmechanisms......................................................................576
8.7.3Chlorinesolubility........................................................................................579
8.7.4Chlorinesolutionmechanisms.....................................................................582
8.7.5Bromineandiodine......................................................................................582
8.7.6Halogensinmagma......................................................................................582
8.8 Noblegassolubilityandsolutionmechanisms......................................................585
8.8.1Noblegasesinfullypolymerizedsilicatemeltstructure............................585
8.8.2Noblegasesindepolymerizedsilicatemeltstructure.................................588
8.8.3Noblegasesinmagmaticsystems...............................................................589
8.9 Concludingremarks................................................................................................590
Relationshipsamongtransportproperties..............................................................606
9.3 Viscosityofmagmaticliquids................................................................................607
9.3.1Magmaviscosity,composition,andtemperature........................................608
9.3.2Viscosityandstructureofmagmaticliquids...............................................614
9.3.3Viscosity,ironcontent,andFe3þ/SFeofmagmaticliquids.......................617
9.3.4Effectofpressureonviscosityofmagma...................................................619
9.3.5Viscosityandvolatilesinmagmaticliquids................................................626
9.4 Viscosityofmodelsystemsilicatemelts...............................................................633
9.4.1Viscosityofmeltsandglassesinthe M nþ 2=n O SiO2 system......................634
9.4.2Viscosityofmeltsandglassesinthe M nþ 2=n O Al2 O3 SiO2 system.......651
9.4.3Viscosityofiron-bearingsilicatemelts.......................................................670
9.5 Modelingmeltviscosity.........................................................................................673
9.6
9.6.1Diffusion,composition,andtemperature.....................................................677
9.6.2Diffusion,composition,andpressure..........................................................684
9.6.3Volatilesanddiffusion..................................................................................694
9.7 Electricalconductivity............................................................................................717
9.7.1Electricalconductivity,composition,andtemperature...............................719
9.7.2Electricalconductivityandpressure............................................................724
9.7.3Electricalconductivityandvolatiles............................................................725
CHAPTER10Equation-of-stateofmagmaticliquids
10.2 Equation-of-state(EOS)ofglassversusmelt......................................................757
10.4 Equation-of-stateofmagmaticliquids.................................................................766
ofmagmaticliquids...............784
10.5 Equation-of-stateofsimplesystemmodelliquids...............................................799
EOS ofmeltsinthe M
10.5.3 EOS ofmeltswithTi4þ andFe3þ ............................................................807
10.6 Concludingremarks..............................................................................................810 References.......................................................................................................................811
CHAPTER11Masstransport
11.1 Introduction...........................................................................................................821
11.2 Porosity,permeability,andtransport....................................................................822
11.2.1Porosityandpermeabilityofaqueousfluidsandsilicatemelts..............822
11.2.2Equilibriumtextureandwettingangle....................................................826
11.2.3DihedralanglesandH2Odistributionintheearth..................................841
11.2.4Wettinganglesandpartialmelts..............................................................849
11.2.5Melt/mineraldihedralangle,porosity,andproperties.............................854
11.2.6Permeabilityandporosityincarbonateandsulfide-bearingsilicate systems......................................................................................................859
11.3 Concludingremarks..............................................................................................865 References.......................................................................................................................866
Preface
TheformationandevolutionoftheEarthandplanetsdependontransferofmassandenergy.Magma andfluidareintegralpartsofthetransportprocessesthatgovernthemassandenergytransfer.Mass transportpropertydataarecentraltodescribethoseprocesses.Masstransportisaccomplishedby transferoffluidsandmagmaandtypicallytakesplaceathightemperatureandpressure.Masstransport typicallyoccursalongtemperatureandpressuregradients,whichmeansthatenergytransportalsoassociateswithmasstransport,althoughinthisbook,energytransferisnotexplicitlydiscussed.A structure-basedunderstandingofhowtransportpropertiesreflectchangesincomposition,temperature, andpressuregreatlyenhancesourabilitytousepropertydatatocharacterizetransportandtransfer processes.Thisknowledgenotonlyishelpfulforthematerialscharacterizationneededtodescribe masstransportprocessesinnature,italsocontributestotheknowledgebaseofadjoiningscientificdisciplinesincludingglassandmaterialsscience.Thefocusofthisbookistodescribeanddiscusstransportpropertiesofmagmatogetherwithaspectsoftransportpropertiesoffluids,andtoemploysuch datatocharacterizemasstransportintheinteriorofEarth,itsmoon,andtheterrestrialplanets.
TheprincipalaimofthisBook,therefore,istodescribemasstransportbymagmaandfluids,what andhowmeltandfluidpropertiesgovernthoseprocesses,andhowunderstandingofthestructureof thosetransportagents,and,therefore,theirchemicalcomposition,temperature,andpressure,canbe usedtocharacterizetheproperties.Linkageoftransportpropertiestostructureofthetransportagents isimportantbecausethisunderstandingprovidesabasisforquantitativemodelingofproperty behaviorwithoutotherwisemorecomprehensiveandextensiveexperimentalstudyofeachandevery compositionandconditions.Thelattereffortsrequiremorehumanandfinancialresourcesthanoften areavailable.
Themainfocusofthisbookisontransportbymagmawithlesseremphasisonmasstransferby fluids.Someofthereasonsforthisselectionisthatfluidpropertydatasuchasdensityandviscosity, forexample,differgreatlyfromthoseofsurroundingcrystallinematerialstotheextentthatvariations ofthosepropertiesoffluidsdonotimpactgreatlyfluid-mediatedmasstransport.Ofcourse,fluidcompositions,pressures,andtemperaturesdo.Thesepropertyvariations,therefore,arethesubjectofamajorchapterofthebook,buthavenotbeenisolatedintoindividualchaptersaswasdoneforsilicatemelt andmagmaproperties.Thevariablescausingpetrogeneticallyimportantchangesinpropertiesof fluidsalsoaffectmigrationefficiency.ThesevariableshavebeendiscussedinthelastChapterof theBook(Chapter11).ThatChapteriscenteredonmasstransferbyfluidsandmagmathroughcrystallinerockmatrixtogetherwithanumberofexamplesfromnaturalobservationsthatcanbe,orhave been,interpretedintermsofthepassageofmeltsorfluidsinarockmatrix.
Thetransportpropertiesofmagmaticliquids,oftensubstantiatedwithinformationfromcompositionallysimplermodelsystem,arethemainfocusofthisBook.Forthispurpose,theBookisorganized inapetrogeneticallyevolutionarysensebeginningwithmeltingandcrystallizationofrock-forming materialstoformandevolvemagma(Chapters1and2).Withinthisevolution,whichleadstoa widevarietyofmagmacompositionsandgreatlyvariabletransportproperties,wefollowthemelting andcrystallizationbehaviorfromthemostprimitivemagmacreatedbypartialmeltingofperidotitic parentalrocksintheEarth’smantletoafinishwheremeltingandcrystallizationofthemostevolved magmaticliquids,suchasthoseofrhyoliteandgranitecomposition,arepresented.Rolesofvolatiles, inparticularH2OandCO2,wereincorporatedasappropriate.Thecompositionalvariationsofthe
magmaticliquidsinthoseenvironmentscancausetheirtransportpropertiestovaryovermanyorders ofmagnitude.
Elementdistributionamongmelts,fluids,andminerals,andhowthisdistributionisaffectedby theircompositionandstructure,iscentraltocharacterizationofmasstransportintheEarth.Bulk compositionofmagmaandcrystallinemineralstogetherwithelement,oxide,andisotopicsolubility inandpartitioningbetweenthesephasesaresensitivetotemperature,pressure,andredoxconditionsof theformationandevolutionofmagmaticliquidsandtheenvironmentinwhichpartitioningoccurs. Elementpartitioningisdescribedanddiscussedin Chapter3,whichfollownaturally,therefore, fromphaseequilibriummeltingandcrystallizationbehaviorpresentedinChapters1and2.Thefocus of Chapter4 isthermodynamicdataneededforcharacterizationofthepropertiesandprocesses discussedin Chapters1 3.Thischapterhighlightsexistingthermodynamicdataandhowsuch informationaidsourunderstandingofthebehaviorofmagmaticsystems.Thisincludesmeltingand crystallizationbehavior,elementpartitioning,andhowthermodynamicdatacanbeemployedto characterizetransportproperties(viscosity,diffusion,andelectricalconductivity)ofsilicatemelts andmagmaticliquids.Thermodynamics,therefore,notonlyhelpustounderstandmelting,crystallization,andelementdistributionbehavior,suchinformationcanbeemployeddirectlytomodel transportpropertiesofmagma.Ofcourse,ultimately,thermodynamicdataandothermeltandfluid propertydataaremanifestationsofthestructureofthematerialsofinterest.
Structuralinformationformsthebasis,therefore,forcharacterizationoftransportpropertiesof magmaticliquidsandoffluids.Structuraldataandhowthosedataarelinkedtotransportandassociatedpropertiessuchasdescribedin Chapters1 4,obtainedforthemostpartfromexperimental studies,arecontainedin Chapters5 8.Thosefourchaptersareseparatedintoabasicdescription ofstructuralprinciplesnecessarytodescribesilicatemeltstructureandcanbefoundin Chapter5 formeltandin Chapter6 forfluidstructure.
In Chapter6,inadditiontostructurediscussions,otherpropertiesoffluids,includingpartitioning ofthefluidcomponents(H2O,CO2,CH4,H2,halogen-,N-,andS-containingfluidspecies,both reducedandoxidized)betweenfluidsandmeltsfillouttheinitialsectionsofthediscussion.Thisis followedbydescriptionofsolubilitybehaviorofmajor,minor,andtracecompositionsinfluidsof variousrelevantcompositions.Thesolubilityandsolutionmechanismsofvolatilesinmagmaticliquidsandmodelsimple-systemsilicatemeltsarediscussedin Chapters7and8.Thispresentation wasintendedtofollownaturallyfromthestructuredataprovidedin Chapters5and6.Manyfacets ofmeltandfluidstructureaffecttheirtransportproperties,someofwhichalsocanbefoundinthese chapters.
Theremainingchapters(Chapters9 11),focusdirectlyonhowmasstransport(propertiesandprocessesgovernedbyproperties)bymagmaandfluidandofmagma-andfluid-bearingsystemsdepends onintensiveandextensiveparameters.Transportpropertiessuchasviscosity,diffusion,andconductivitytogetherwithhowthesemaybelinkedtogether,canbefoundin Chapter9.Thischapteralso offersseveralexamplesofhowtransportpropertiesaffectmasstransportprocessesintheEarthand terrestrialplanets.
Masstransportinplanetaryinteriorsisaffectedcriticallybytheequation-of-state(EOS)of magmaticliquidsasdiscussedinChapter10.TheEOSinformationincludesdensity,volumes,thermal expansion,andcompressibilityofchemicallycomplexmagmaticliquids.Similardatareportedforthe simplermodelsystemareemployedforamorethoroughunderstandingofEOSofmagmaand(fluid) athightemperatureandpressure.
Thelastchapter(Chapter11)dealswithactualmovementoffluidsandmagmathroughrock matricesatpressuresandtemperaturesexceedingthoseabovewhichopencrackscanbesupported bytherockstrength.Characterizationofthesepropertiesandhowtheyareaffectedbyintensive andextensiveparametersarecriticalforcharacterizationofmasstransportinplanetaryinteriors.In thischapter,therenotonlyisadiscussionofsomeofthemainvariablesgoverningfluidandmelt migration,Chapter11alsoincludesassessmentofwhichmeltandfluidpropertiescanaffectmovementofthoseliquidsthroughacrystallinematrix.Moreover,thischaptercontainssummariesof howliquiddistributionandcompositioninacrystallinematrixaffectsgeophysicallyandgeochemicallyimportantpropertiesofrocksoftenwithsmallvolumefractionsofmagmaorfluid,andhow suchknowledgehelpsinterpretationofnaturalgeochemicalandgeophysicaldata.
Thecreationofabooksuchasthisrequiresinputfromawiderangeofspecialties,manyofwhich mightnotalwayshavebeeninthecenteroftheauthor’sresearchactivities.Ithasbeenveryimportant, therefore,togarnerinputfromfriendsandcolleaguesand,perhaps,mostimportantofall,accessand helpinaccessingpublishedliteraturefromawidevarietyofscientificdisciplinesandsubdisciplines. Theassistancefromourlibraryanditstwomembers,ShaunHardyandM.O.O’Donnell,has beeninvaluableinthisregard.Thisbookcouldnothavebeenproducedwithouttheirexceptional professionalism,efficiency,andcheerfulassistance.Thisisparticularlysoasthisbookwaswritten whiletheCOVID-19pandemicwasraginghereandelsewhereintheworld.Hence,muchofthe workwascarriedoutelectronicallybecauseperson-to-personcontactwasdifficult.Moreover, COVID-19-relatedtechnicalproblemssuchas,forexample,productionofgraphicswereovercome thanksinnolittleparttotheassistanceandsupportofmywife,Susana,whoassistedinthegeneration ofmanyofthediagramsusedinthetext.
Thereis,ofcourse,muchmoredataandunderstandingneededbeforewecanclaimanunderstandingofalltransportprocessesgoverningthemassandenergytransferassociatedwiththeformationand evolutionofEarth,itsmoon,andtheterrestrialplanets.Ihope,however,thattheinformationthatis offeredinthisbookwillhelppointingnotonlytowhatwebelieveweknow,butalso,andperhaps moreimportantly,whatwedonotknow.Itprovides,therefore,anoverviewofcurrentunderstanding ofmasstransportinpetrogeneticprocesses.Amajoraimalsoistodevelopsuggestionsforwhere futureresearchactivitiesmightbethemostuseful.Thoseobjectivescanbereachednotbywhat maybethefancyoftheday,butwithconcertedandintegratedeffortsandinputsfromnaturalobservations,fromsystematiclaboratoryexperiments,andbynumericmodelingandintegration.
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MeltingintheEarth’sinterior: solidusandliquidusrelations 1
1.1Introduction
MasstransportintheEarthandterrestrialplanetsisbymagma(silicatemelts)andbyfluids compositionallyinthesystemC O H N S.Generationofmagmaisthefocusofthischapter.
Magmaexistsfromambientpressureandhightemperaturetothepressuresandtemperatures correspondingtothecore/mantleboundary(Labrosseetal.,2007; Andraultetal.,2014; Frenchand Romanowicz,2015).Magmacan,therefore,serveasamass(andenergy)transportmedium throughoutthepressurerangeofthesilicateEarth(136GPa).Detailsofmagmatransportare presentedinChapter9.
Inthischapter,wewilldiscusshowtogeneratemagmaintheEarthwithafocusonthevariables thatgovernthemelting(solidus)andcrystallization(liquidus)temperature/pressurecoordinates.The phaserelationsthatdescribeequilibriabetweenmineralsandmeltthetemperatureintervalbetween initialmeltingandcompletemeltingwillbediscussedin Chapter2.Here,afterabriefdiscussionof premeltingphenomena,wewilldescribetherelationshipsatornearthesolidusandtheliquidusofthe dominantsilicaterocksintheEarth.
1.2Premelting
Aphenomenonknownas“premelting”isdetectedbydiscontinuitiesinheatcapacityversustemperaturetrajectories(Fig.1.1).Todatepremeltinghasbeenobservedonlyinlaboratoryexperiments usingendmemberminerals(RichetandFiquet,1991; Courtialetal.,2000; Richetetal.,1996, 1998). Thelackofinformationfromchemicallycomplexnaturalsystemsmaysimplybebecausetherelevant experimentshavenotbeencarriedout.
Macroscopically,premeltingisrepresentedbyarapidincreaseoftheheatcapacityasthemelting temperatureofacrystalisapproached(Fig.1.1).Theheatcapacitydiscontinuitybeginsfrom80to 250 Cbelowactualmeltingtemperatures.Enthalpyandentropyeffectsrepresentifrom7%to22%of theenthalpiesandentropiesoffusion(RichetandFiquet,1991; Thie ´ blotetal.,1999; Courtialetal., 2000; Nera ´ detal.,2013).
Premeltinghasbeenreportedinsyntheticdiopside,CaMgSi2 O6,togetherwithothersynthetic metasilicates(Richetetal.,1996).Fordiopside,theonsetofpremeltingcoincideswithdiscontinuouschangesinpropertiessuchasCadiffusion(DimanovandIngrin,1995 )andelectricalconductivity(Bouhifdetal.,2002 ).Inthiscase,premeltinghasbeeninferredtobeareflectionof
FIGURE1.1
Meanheatcapacityofcrystallinediopside(CaMgSi2O6)andanorthite(CaAl2Si2O8)asafunctionof temperature.Shadedregionshowstemperatureintervalofactualtemperaturerangeofpremelting.
Modifiedafter Richetetal.(1996)
temperature-dependent(Ca,Mg)structuraldisord erasthestructuralmechanismforthepremelting phenomenon(Richetetal.,1996).Inothermetasilicates,incipie ntbreakupofthesilicatechain structurehasbeenproposed(Richetetal.,1998 ; Nesbittetal.,2017).Foraluminosilicatecrystals suchasanorthite(CaAl2Si2 O8),(Al,Si)disorderingaccountsforthepremeltingeffect( Richetetal., 1994 ).Possibleeffectsofsolidsolutionssuchasdiopside-hedenbergitean danorthite-albiteon premeltinghavenotbeenaddressedasyet.
1.3Meltingofperidotite
PartialmeltingofperidotiteintheEarth’smantleistheprincipalsourceofprimarymagma.Following melting,magmaaggregatesandascendstowardthesurfaceoftheEartheithertoformshallow-depth magmachambers,perhapsgovernedbytheprincipleofneutralbuoyancy(Ryan,1987),wherecrystal fractionationcanalterthemagmacomposition,ormagmaascendsdirectlyascenttoorneartheEarth’s surface.
Peridotitemeltingmaytakeplaceunderessentiallyvolatile-freeconditions(e.g., Kushiro,1969; Falloonetal.,1988; ZhangandHerzberg,1994; Walter,1998)oritoccursinthepresenceofvolatiles suchasH2O(Groveetal.,2006; KawamotoandHolloway,1997),CO2 (CanilandScarfe,1990; Brey etal.,2008),ormixturesofCO2 andH2O(MysenandBoettcher1975a,b; Wyllie,1977; Ulmerand Sweeney,2002).Underredoxconditionsequaltoormorereducingthanthatcorrespondingtothe iron-wu ¨ stite(IW)oxygenbuffer1 reducedspeciessuchasH2 andCH4 canalsoplayimportantroles
1Inthisandfollowingchapters,oxygenfugacityisoftenreferredtowithreferencetocommonoxygenbuffers.TheseareHM (hematite-magnetite),NNO(nickel-nickeloxide),QFM(quartz-fayalite-magnetite),MW(magnetite-wustite)andIW(ironwustite).
duringmelting(EgglerandBaker,1982; LuthandBoettcher,1986; TaylorandGreen,1988).Such conditionslikelyweremorecommonduringtheEarth’searlyhistory.
1.3.1Peridotitemeltingwithoutvolatiles
NotwithstandingthecommonoccurrenceofmantlemeltingwithvolatilessuchaseitherH2OorCO2, orboth,meltingofaperidotitelithospherealsotakesplacewithoutvolatiles(Herzbergetal.,1990; HiroseandKushiro,1993; Asimowetal.,2001).Earlyexperimentalstudiesonperidotitemelting usingnaturalperidotitestartingmaterialwerethoseof GreenandRingwood(1967) and Kushiroetal. (1968).Ascanbeseenin Fig.1.2,theambientpressuresolidusofatypicalperidotiteisnear1150 C. Thesolidustemperatureincreaseswithincreasingpressureatarateofabout150 C/GPa.Within experimentalerrorofthe Kushiroetal.(1968) study,thesoliduscurveislinear.However,giventhe changeofsolidusmineralassemblagefromolivine þ orthopyroxene þ clinopyroxene þ spinelto olivine þ orthopyroxene þ clinopyroxene þ garnetatpressuresbetween2and3GPa,onewould expectachangeoftheslopeofthesoliduscurve.FromtheClaussius-Clapeyronexpression
thevolumechange, DV,willchangeasthemineralassemblagechangeswithincreasingpressure.Such avolumechangewouldbeexpectednear3GPaatthesolidustemperatureshownin Fig.1.2 asthisis approximatelywherethegarnet-to-spineltransitionislocated.Evidently,thiskinkiswithin
FIGURE1.2
Pressure/temperatureofperidotitemelting(solidus)intheabsenceofvolatiles.
Modifiedafter Kushiroetal.(1968)
ol: olivine
cpx: clinopyroxene
gt: garnet
b: β-Mg SiO
g: γ-Mg SiO
gt: garnet
MgPv: Mg-perovskite
CaPv: Ca-pervskite
Mw: magnesiowüstite
FIGURE1.3
Pressure/temperaturetrajectoryofperidotitemeltingtopressuresneartheinterfaceofthetransitionzoneto thelowermantle.
Modifiedafter HerzbergandZhang(1996)
experimentalerrorintheearlydatashownin Fig.1.2.Inmorerecentexperimentalstudies,thereare distinctivekinksofthesoliduscurveasaphasetransformationisencounteredalthoughnokinksin thesoliduswerereportedwherethespinel-to-garnetislocated(Herzbergetal.,2000;seealso Fig.1.3).Theresultssummarizedin Fig.1.3 do,however,showkinksofthesolidusnear15,20,and 23GPa.Thesekinksandchangeinsolidusslopereflecttransformationfromolivineto b-spinelphase (b-Mg2SiO4),Ca-perovskite(CaSiO3),tomagnesiowustite þ Mg-perovskite(MgOandMgSiO3). Obviously,thesechangesinphaseassemblageswillalsoaffectthecompositionofthemeltsonthe solidus.Theselatterissueswillbediscussedindetailin Chapter2
Althoughthereislittledisagreementastothegeneralnatureofsolidusphaseassemblagesof peridotiteintheEarth’smantle,detailsofthesephaseassemblagesaswellasthepressure/temperature coordinatesofthesoliduscurveandofthephasechangesremainopentosomediscussion(see,for example,areviewofthosedataby Herzbergetal.,2000).Someofthedifferences,seen,forexample, inthevarioussolidustemperaturesreportedintheliterature(Fig.1.4)aretheresultofdifferent peridotitecompositions.
Themostobviouscompositionaleffectontheperidotitesolidustemperatureisfromchangesinthe Mg/(Mg þ Fe)ratiooftheperidotite.Thisratiorangesfromnear0.95tolessthan0.85inmantle peridotite.Fromacompilationof3GPadatafromvariousexperimentallydeterminedperidotite solidustemperatures, Hirschmann(2000) foundtheretobea90 100 Crangeintemperaturesasa functionofthebulkmeltMg/(Mg þ Fe)oftheperidotite(Fig.1.5).Thiseffectisnotsurprisinggiven therelationshipbetweenMg/(Mg þ Fe)andsolidustemperaturesoftheperidotitemineralphases (olivine,pyroxenes,spinel,andgarnet).TheMg/(Mg þ Fe)ratioalsoaffectsthepressureofthespinelto-garnettransformationgarnetontheperidotitesolidus(MysenandBoettcher,1975a).
Anothercompositionvariableaffectingsolidustemperaturesofterrestrialmantleperidotiteisthe alkalicontent(Na þ K)(Fig.1.6).Thisprobablyhappensbecausealkalielementsareincompatiblein peridotitemineralassemblagesand,therefore,entersthemeltphasealmostexclusively,atleastunder uppermantleconditions.IncreasingNaandK,orboth,resultsinsolidustemperaturedepression.
FIGURE1.4
HiroseandKushiro[1993]
Robinsonetal.[1998] BertkaandHolloway[1994]
Pressure/temperaturetrajectoriesofvariousperidotitesolidiiintheabsenceofvolatiles.
Modifiedafter Herzbergetal.(2000) withthesourcesofindividualcurvesindicatedonindividualsolidii.
FIGURE1.5
Solidustemperatureofvolatile-freeperidotiteasafunctionoftheirMg/(Mg þ Fe).
Modifiedafter Hirschmannetal.(2000)
FIGURE1.6
Solidustemperatureofvolatile-freeperidotiteasafunctionoftheirtotalalkalicontent.
Modifiedafter Hirschmannetal.(2000)
Takahashi[1986]
1.3.2Solidusphaseassemblageandpressure
Theperidotitesolidusmineralassemblagegovernsthecompositionofinitialmelts.Thisassemblage and,therefore,themeltcompositionontheperidotitesolidus,isafunctionofpressure(seealso Chapter2 fordiscussionofmeltingandcrystallizationmineralassemblages).Uptopressuresnear 15GPa,olivine,orthopyroxene,clinopyroxene,andoneormorealuminousphases(plagioclase, spinel,andgarnet)formthesolidusmineralassemblage.Atpressuresbelowapproximately1GPa, plagioclaseistheprincipalaluminousphaseandinitialmeltissimilartomidoceanridgebasalt(Yoder andTilley,1962; Presnalletal.,2002).Fortypicalterrestrialperidotite,aluminousspinelisonthe solidusfromnear1GPatosomewherebetween2and3GPaabovewhichpressuregarnetbecomesthe aluminousphaseonthesolidusofvolatile-freeperidotite.Garnetandaluminousspinelcancoexist overapressurerangeuptoasmuchas1.5GPaforthemostFe-richperidotites(BertkaandHolloway, 1994; Walter,1998; Groveetal.,2013).Thereisalsoapressurerangebetweenabout1and1.5GPa wherespinelandplagioclasecoexist.Inthispressurerange,plagioclasebecomesincreasingly anorthite-richaspressureincreasesuntiltheplagioclaseendmember,anorthite,finallydisappearsvia themeltingreaction(Presnalletal.,2002):
olivine þ anorthite ¼ orthopyroxene þ clinopyroxene þ spinel þ melt.(1.2)
Atpressuresnear2GPa,spinelbeginstoreactouttoformagarnet þ spinelperidotitemineral assemblagewithspinelfinallydisappearingatpressuresnear2.5GPafortypicalperidotitecompositionssuchasillustratedin Fig.1.7.Thepressurerangewithonlygarnetonthesoliduscansometimes beaswideas10GPa,whichcorrespondstothedepthrange w300kmintheuppermantle(Takahashi, 1986; HerzbergandZhang,1996).ThegarnetinthispressurerangenotonlychangesitsMg/ (Mg þ Fe)butalsoitsAl/(Al þ Si)ratiobecausetheconcentrationofthesilicateperovskite componentingarnetincreaseswithincreasingpressure(Irifune,1994; OkamotoandMaruyama, 2004).
FIGURE1.7
Walter(1998)
1.3 Meltingofperidotite
Atpressuresnear15GPa,olivineonboththesolidusandliquidusofperidotitecompositions undergoesatransformationtodenser b-(Mg,Fe)2SiO4 (Feietal.,1992).Thisphaseistransformedto g-(Mg,Fe)2SiO4 withafurtherpressureincreasebeforesilicateperovskiteisstabilizedatpressures near20GPa.Magnesiowustite[(Mg,Fe)O]becomesthesolidusphaseatevenhigherpressures (Irifune,1994; HerzbergandZhang,1996).
Thecompositionoftheinitialmeltattheselatterveryhighpressures(>20GPa)isnotwellknown. Mostlikely,thislackofinformationresultsfromchallengesassociatedwithtemperature-quenchingof meltwithoutcrystallizationofquenchphasesattheseveryhighpressures.
Asnotedearlierinthedescriptionoftheresultsin Fig.1.3,thepressure/temperaturetrajectoryof thesoliduscurveshowsadistinctivechangesorkinksinslopeaschangesinsolidusphaseassemblages takeplace.Thesekinksreflectthevolumechangeofmeltingasnewmineralphasesappearonthe solidus.
1.3.3Peridotitemeltingwithvolatiles
TheprinciplesthatdescribecongruentmeltingofanyrockinthepresenceofH2Ooranyothervolatile intheC O H N Ssystemareillustratedintheisobaric,low-pressureschematicrepresentationin Fig.1.8.Inthisfigure,thesolidustemperature, f-d,isfixedregardlessoftheamountofH2Ointhe systemunlessalltheH2Oisboundinhydratedmineralssuchaschloritephases,amphiboles,mica minerals,orepidote.Thesolidusterminatesat d becausethereisafinitesolubilityofrockmaterialsin theH2Ofluid(seeChapter6).Theliquidustopology,ontheotherhand,dependsontheamountofH2O
H2O fluid
vapor
H2O-saturated liquidus
Rock+melt+H2O vapor
Solidus: Rock+H2O
Subsolidus: Rock+H2O vapor
CompositionH
FIGURE1.8
Schematicrepresentationofrock-H2Ophaserelationsfromtemperaturesabovetheirvaporoustosubsolidus conditionsatlowpressure(seetextfordetaileddiscussion).
presentinthesystem.Foranybulkcompositionbetween f and b,theinitialmeltisat b.Thismeltis saturatedwithH2O.Byincreasingtemperatureabovetheundersaturatedliquidus, a-b,anH2Oundersaturatedmeltwillform.Asdrawnin Fig.1.8,itisassumedthattheH2Osolubilityinthe meltdecreaseswithincreasingtemperature,afeaturecommonlyobservedinexperiments(Holtzetal., 1995;seealso Chapter7 fordiscussionofH2Osolubilitybehaviorinmagmaticliquids).Thismeans thatbyincreasingthetemperatureuntiltheH2O-saturatedliquidus, c-b,isreached,H2Owillexsolve. ItisevenpossibletoreachaconditionbelowtheH2O-saturatedliquiduswherethemeltwillexsolve H2Oandwillalsopartiallycrystallize.Afurtherincreasewilleventuallyreachthevaporous.Details onsolubilityofsilicate(rock)inthevapor(orfluid)canbefoundinChapter6.
1.3.3.1Peridotite-H2O
MeltingofperidotiteinthepresenceofH2Oathighpressuresuchasthedeepcrust,uppermantle,and beyondoccursatlowertemperaturethanmeltingofperidotiteintheabsenceofH2O(Fig.1.9).When thereisexcessH2Ooverthatwhichmaybeboundinhydrousminerals(amphibole,phlogopite,and chlorite,forexample)oriftemperaturesandpressuresareoutsidethestabilityfieldofhydrousphases inaperidotite-H2Osystem(MysenandBoettcher,1975a; Groveetal.,2006; Tilletal.,2012),the isobarichydroussolidustemperatureisthesameregardlessoftotalH2Ocontent.
AsisalwaysthecaseformeltingofrocksinthepresenceofH2O,itssolidustemperaturedecreases fromitscoincidencewithH2O-freemeltingatambientpressuretominimumtemperatureatpressures
FIGURE1.9
Soliduspressure/temperaturetrajectoriesofdifferentperidotitecompositionsinthepresenceofexcessH2O. TheindividualcurvesarefromperidotitewithvaryingMg/(Mg þ Fe)andtotalalkalicontent.
Modifiedafter MysenandBoettcher(1975a) and Groveetal.(2006).Alsoshowninthesolidustrajectoryofvolatile-freeperidotite from Kushiroetal.(1968)
Groveetal.(2006)
anhydrous
peridotite solidus
[Kushiro et al. (1968)
Mysen and Boettcher (1975a)
peridotite-H2
inthe2 4GParange(Fig.1.9).ThecoincidenceatambientpressureoccursbecausetheH2Osolubilityinmagmaatambientpressureisonlyasmallfractionofwt%(see Chapter7)anddoes,therefore, havenodiscernibleeffectsonthesolidustemperature.Theexactpressure/temperaturetrajectoryofthe H2O-saturatedsolidusdependsontheparticularbulkcompositionoftheperidotite. Mysenand Boettcher(1975a) found,forexample,thatdependingofMg/(Mg þ Fe)ratioandalkalicontent,the hydrousperidotitetemperaturecanvarybyasmuchas150 Catpressuresnear3GPa(Fig.1.9).
Thetemperature/pressuretrajectoryofthehydrousperidotitedifferssignificantlyamongvarious publishedexperimentalstudies.Attheminimumtemperaturebetween2and4GPa,solidustemperatureshavebeenreportedtobefrom1000 C(HiroseandKawamoto,1995; KawamotoandHolloway, 1997)tolessthan800 C(MysenandBoettcher,1975a; Groveetal.,2006; Tilletal.,2012).The reasonforsuchalargevariationinexperimentallydeterminedsolidustemperaturesisnotclear.Itis evenfurtherpuzzlinginlightofthefactthatforotherrocktypesrangingfrombasalt/gabbro þ H2Oto granite/rhyolite þ H2O,thereislittledisagreementbetweenthepublishedexperimentaldata(see discussionofthoseexperimentaldatabelow).A w200 Cdifferenceinreportedsolidustemperatures forhydrousperidotiteisimportantasthisaffectsthedepthinthemantlewheremeltingofhydrous peridotitemaytakeplacebyperhaps25kmdependingonthegeotherm.
Themineralassemblagesonthehydrousperidotitesolidusinthecontinentallithospherearethe sameasforanhydrousperidotiteexceptthatthepressuresatwhichthetransformationofplagioclaseto spinelandspinel-to-garnetoccursontheH2O-saturatedsolidusislowerbecausethepressuresand temperaturesofthehydroussolidusislowerthanforanhydrousperidotiteandthespinel-to-garnet transformationasapositivedT/dPslope(see Fig.1.9,forexample).Garnetappearsnearandbelow 2GPa,forexample(TaylorandGreen,1988),whereasforanhydrousmelting,garnetontheperidotite solidusappearsabove2.5 3.0GPa(Takahashietal.,1993; Walter,1998).
Thestabilityrelationsofhydrousphasesincontinentallithosphereareprofoundlydifferentfrom theirstabilityrelationsintheperidotitewedgeinsubductionzones.Thisdifferenceisgovernedbythe releaseofhydrousfluidssaturatedinsilicatecomponentsfromthedescendingslabinsubduction zones,whereasnosuchsourceofH2Oandsilicatecomponentscanbefoundinlithosphericmantle. Hydrousphasessuchasamphibole,mica,andchloriteonthehydrousperidotitesoliduswedgein subductionzonescanoccuroverarangeofpressuresandtemperatures(MysenandBoettcher,1975a; Groveetal.,2006; Tilletal.,2012).Duringmeltingofcontinentallithosphere,ontheotherhand,the nearabsenceofH2Ointhemeltingregionresultsinlackofsignificantcontributionofhydrousphases totheperidotitemelting.
Itisgenerallyagreedthatatleasttopressuresnear2GPa,theinitialmeltonthesolidusofhydrous peridotiteisquartznormativeandresemblesandesiticcompositions(Kushiro,1972; Groveetal., 2006).Itislesswellknownhowthatmeltcompositionmaychangeathigherpressures.Itseems reasonabletoassumethatthemeltcompositionsmayeventuallytakeonanolivinenormativecharacter (Condamineetal.,2016).
1.3.3.2Dehydrationontheperidotitesolidus
WheneverthetotalH2Oofhydrousperidotiteiscontainedinhydrousphases,initialmeltinginlimited pressurerangescouldbecontrolledbythedehydrationofthehydrousmineral(s).Thismaybethe situationinthecontinentallithospherewheretheH2Ocontentsareontheorderofhundredsofppm (Jambon,1994).ThisH2Olikelyiscontainedinafewhydrousphasesandinnominallyanhydrous phases.Amongthesehydrousphases,theirdetailedstabilityfielddependsontheperidotite
FIGURE1.10
Exampleofsoliduspressure/temperaturetrajectorywithallH2Oboundinhydrousphases(amphiboleand chlorite)intheirstabilityrangeonthesolidus.
Modifiedafter Fig.1.5:Solidustemperatureofvolatile-freeperidotiteasafunctionoftheirMg/(Mg þ Fe)(Modifiedafter Tilletal. (2012)
composition.Forthe HartandZindler(1986) primitiveperidotiteusedintheexperimentsby Tilletal. (2012),therelationshipsbetweenhydrousphasestabilityanddehydrationmeltingareshownin Fig.1.10
TheMg/(Mg þ Fe)ofmantleperidotiteisintherange0.85 0.94andtotalalkaliconcentrations rangingbetween,0.1and0.9wt%.Arangeinamphibolestabilityoverabout75 Cand0.3 0.4GPa temperatureandpressurerangeistheresult(Fig.1.11).Thealkaliconcentration,whichisimportant fortheamphibolestability(Allenetal.,1975),isuncertainintheperidotitewedgeabovedescending platesinsubductionzonesasdehydrationoftheplatematerialslikelywillreleaseanaqueousfluid enrichedinalkalimetals(Mysen,2002; Manning,2004).
AlkalimetalconcentrationalsoisimportantindefiningmicastabilityfieldasaK-richphasesuch asphengitecanbestabletopressuresnear10GPa,forexample(PoliandSchmidt,1998; Tronnes, 2002).K-richamphiboleshavebeenreportedstabletonear10GPaattemperaturesnearthehydrous peridotitesolidus(SudoandTatsumi,1990; Tronnes,2002).Suchamphibolesandmicasmaynotbe foundintypicaluppermantle,butcanbestableinmetasomatizedperidotitewedgeabovesubducting slabs.Inthedeepermantleofsubductionzones,theH2OcontentlikelyissolowthatallH2Oisbound insuchhydrousphases.Theperidotitesolidusunderthiscircumstancescanthenbegovernedby dehydrationofthesephases(Fig.1.12).
Green [1973]
Mysen and Boettcher (1975a)
FIGURE1.11
Pressure/temperaturetrajectoriesofamphiboledehydrationsolidiofperidotitewithallH2Oboundin amphibolewhenstableonthesolidus.
Modifiedafter Green(1973) and MysenandBoettcher(1975a)
FIGURE1.12
Pressure/temperaturetrajectoryofdehydrationsolidusofperidotitewithK-richteriteandphlogopiteas dehydrationphases.
Modifiedafter Tronnes(2002).H2O-saturatedsoliduswithextrapolationtohighpressurein dashedlines from Mysenand Boettcher(1975a)
