Storage and Evolution of Mafic and Intermediate Alkaline Magmas beneath Ross Island, Antarctica

25 Pages·2016·2.47 MB·English

JOURNAL OF
JournalofPetrology,2016,Vol.57,No.1,93–118
doi:10.1093/petrology/egv083
PETROLOGY
OriginalArticle
Storage and Evolution of Mafic and
Intermediate Alkaline Magmas beneath Ross
Island, Antarctica
D
KaylaIacovino1*,Clive Oppenheimer1,Bruno Scaillet2and PhilipKyle3 o
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1Departmentof Geography, University of Cambridge,Cambridge CB2 3EN, UK; 2Institut des Sciencesde la Terre ad
e
d’Orle´ans, Universite´ d’Orle´ans–CNRS–BRGM, 45071 Orle´ans Cedex 2, France and 3Department of Earth and d fro
EnvironmentalScience,NewMexicoInstituteofMiningandTechnology,Socorro,NM87801,USA m
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*Corresponding author. Present address: US Geological Survey, Mail Stop 910, 345 Middlefield Road, ttp
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MenloPark,CA94025,USA.Telephone:þ1(650)329-4986.E-mail:[email protected] ://a
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a
ReceivedJune9,2014;AcceptedDecember24,2015 d
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ABSTRACT .o
u
p
Wepresenttheresultsofphaseequilibriumexperimentscarriedoutonbasaniteandphonoteph- .co
m
rite lavas from Ross Island, Antarctica. Experiments were designed to reproduce the P–T–X–fO2 /p
conditionsofdeepandintermediatemagmastorageandtoplaceconstraintsonthedifferentiation etro
ofeachofthetwopredominantlavasuitesontheisland,whicharethoughttobederivedfroma lo
g
common parent melt. The Erebus Lineage (EL) consists of lava erupted from the Erebus summit y/a
andtheDryValleyDrillingProject(DVDP)lineageisrepresentedbylavassampledbydrillcoreon rtic
Hut Point Peninsula. Experiments were performed in internally heated pressure vessels over a le
-a
range of temperatures (1000–1150(cid:2)C) and pressures (200–400MPa), under oxidized conditions b
s
(NNOtoNNOþ3,whereNNOisthenickel–nickeloxidebuffer),withX oftheH O–CO mixture tra
H2O 2 2 c
added to the experimental capsule varying between zero and unity. The overall mineralogy and t/5
7
mineral compositions of the natural lavas were reproduced, suggesting oxidizing conditions for /1
/9
thedeepmagmaplumbingsystem,inmarkedcontrasttothereducingconditions(QFMtoQFM– 3
/2
1,whereQFMisthequartz–fayalite–magnetitebuffer)intheErebuslavalake.Inbasanite,crystal- 3
7
lization of spinel is followed by olivine and clinopyroxene; olivine is replaced by kaersutitic 54
0
amphibolebelow(cid:3)1050(cid:2)Catintermediatewatercontents.Inphonotephrite,theliquidusphaseis 0
b
kaersutiteexceptinrunswithlowwatercontent(XH Ofluid<0(cid:4)2)whereitisreplacedbyclinopyrox- y
2 g
ene. Experimental kaersutite compositions suggest that the amphibole-bearing DVDP lavas u
e
s
differentiated below 1050(cid:2)C at 200–400MPa and NNOþ1(cid:4)5 to NNOþ2. Olivine- and clinopyrox- t o
ene-bearing EL lavas are consistent with experiments performed above 1050(cid:2)C and pressures n 2
around200MPa.Theplagioclaseliquidusat<1–2wt%H2Osuggestsextremelydryconditionsfor 2 N
bothlineages(XH2OfluidapproachingzeroforEL,(cid:3)0(cid:4)25forDVDP),probablyfacilitatedbydehydra- ove
tioninducedbyaCO -richfluidphase.Ourresultsagreewithpreviousstudiesthatsuggestasingle m
2 b
plumbingsystembeneathRossIslandinwhichDVDPlavas(andprobablyotherperipheralvolcanic e
r 2
products)wereeruptedthroughradialfracturesassociatedwiththeascentofparentalmagmainto 0
1
thelowercrust.ThelongertraveltimeoftheDVDPlavasthroughthecrustowingtolateralmove- 8
mentalongfracturesandthelackofadirect,sustainedconnectiontothecontinuousCO -richgas
2
fluxthatcharacterizesthemaincentralErebusconduitisprobablyresponsibleforthelowertem-
peraturesandslightlywetterconditionsandhencethechangeinmineralogyobserved.
Keywords:alkalinevolcanism;basanite;CO ;phaseequilibria;phonotephrite;RossIsland
2
VCTheAuthor2016.PublishedbyOxfordUniversityPress. 93
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94 JournalofPetrology,2016,Vol.57,No.1
INTRODUCTION magma storage and differentiation processes at these
RossIsland,Antarctica(77(cid:2)32’S,167(cid:2)10’E)ispartofthe depths. Understanding the deep system at Erebus is
crucial because the constant supply of deeply derived
ErebusVolcanicProvince(EVP)andcomprisesfivepre-
CO -rich gases combined with a sustained energy and
dominant volcanic centers. The currently active and 2
mass input into the lava lake suggests a direct link be-
volumetrically dominant Erebus volcano is surrounded
by the now extinct subsidiary volcanic centers of tweenthephonoliticlavalakeandthemantlesourceof
Mts Bird, Terror, Terra Nova, and Hut Point Peninsula theparentalmagmasviaadeepmaficplumbingsystem
(Fig.1). Erebusisknownforitspersistentlyactivepho- (Kyle et al., 1992; Oppenheimer & Kyle, 2008;
nolitic lava lake, which has been at the focus of recent Oppenheimeretal.,2011).
active monitoring and petrological studies as it repre- Gas emissions from the Erebus lava lake are rich in
sentsawindowintotheshallowregionsofthealkaline CO2((cid:3)30mol%)andcomparativelylowinH2O((cid:3)65mol
D
intraplate volcanic plumbing system. Recent investiga- %;Oppenheimeretal.,2011;Burgisseretal.,2012),con- o
w
tions employing experimental petrological work sistentwiththevolatilecompositionsdeducedfrommelt nlo
(Moussallam et al., 2013) and seismic tomography inclusions for the deeper system. The longevity of the ad
e
(sZtraanindtosmoennethgehipehtysaicl.a,l2a0n1d3)pehtarovelogpiclaaclepdrotpigehrttiecsoonf- lsatvanatlafkluexiitnsgelfoifshheyaptotahnedsizCeOd2t-oricrehflfelcuti,din(Oppaprte,nthheeicmoenr- d from
the shallow plumbing system and phonolitic lava lake et al., 2011) that originates from depths greater than h
includingitsgeometry,temperature,pressure,andoxy- those recorded by the most primitive melt inclusions ttps
genfugacity.Thesestudieshavethepotentialto refine (Iacovino et al., 2013a). Indeed, many separate studies ://a
c
theresultsofnumericalmodelsdevelopedfortheshal- have concluded that various aspects of the Erebus sys- ad
e
low Erebus system, such as those of Burgisser et al. temarecontrolledbytheinfluxofheatandCO2,includ- mic
(2012) and Molina et al. (2012). The intermediate and ing polybaric fractional crystallization throughout the .o
u
deep plumbing system beneath Erebus (>8km depth) magmatic system (Oppenheimer et al., 2011), the bi- p
.c
hasbeeninvestigatedviastudyofasuiteofmeltinclu- modal eruptive behavior in the lava lake (Oppenheimer om
sions (Oppenheimer et al., 2011) and mixed volatile & Kyle, 2008), shallow magma chamber processes /p
e
solubility experiments (Iacovino et al., 2013), which (Moussallam et al., 2013), and fumarolic degassing and tro
lo
haveplacedconstraintsonthedepthsofdegassingand theformationoficecavesandicetowers(Curtis&Kyle, g
y
the equilibrium fluid contents of primitive and inter- 2011).CO flushinghasbeeninvokedtoexplainthechar- /a
mediate composition magmas. Little is known, how- acteristics2ofdegassingandmeltinclusionsatothervol- rtic
le
ever, about the specific P–T–X–fO conditions of canoes including Stromboli (Allard, 2010), Vesuvius -a
2 b
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Fig.1.MapshowingthelocationofRossIslandwithintheMcMurdoVolcanicProvince,Antarctica.Erebusvolcanoissurrounded
bytheperipheralvolcanicconesBird,TerraNova,Terror,andHutPointPeninsula.ThelocationsoftheDVDPandELsamplescol-
lectedforthisexperimentalstudyareindicated.
JournalofPetrology,2016,Vol.57,No.1 95
(Marianelli et al., 2005), Etna (Spilliaert et al., 2006; constrained to (cid:3)1000(cid:2)C by several studies (Kyle, 1977;
Shinohara et al., 2008; Tagliani et al., 2012) and volca- Caldwell & Kyle, 1994; Dunbar et al., 1994). The result-
noes in southeastern Guatemala (Walker et al., 2003) ingexperimentalchargesthusspantheentirerangeof
thatsitatoplargesedimentarycarbonatesequences,the compositions seen in the natural lavas, allowing eluci-
devolatilizationofwhichcouldprovidethenecessaryex- dationoftheevolutionaryprocessesoccurringthrough-
cess carbon (Iacono-Marziano et al., 2009). As Erebus out the Ross Island magmatic plumbing system. With
has no such shallow carbon reservoir and probably de- thisapproach,ouraimhasbeentwo-fold:(1)toexperi-
rivesallofitsvolatilesfromthesamemantlesourcere- mentally establish the conditions necessary to derive
sponsibleformagmaproduction,weproposeErebusas thedistinctErebusandDVDPlineagesfromahypothe-
thearchetype for mantle-sourcedcarbon-controlledvol- sizedsinglebasaniteparent;(2) toplaceconstraintson
canismonEarth. the intermediate Erebus and DVDP plumbing systems
Subsidiary extinct volcanic centers and cones on withrespecttopressure,temperature,oxygenfugacity, Do
1R2o0s(cid:2)sfIrsolamndeaacrheodtihsetrri.bTuhteisdsryamdimalelytraicraoludnidstrEirbeubtuiosnahtacs. andExdpoemriimnaennttsvowlaitthileHs(OH–2COOanfdluCidOc2)o.mpositionsinthe wnloa
2 2 d
bcoreneeanttheehdycbpryoutshttheesdiizpreerdecstlstyourbbeeenoetfhauethprdeMosmuoluitnnogtfmErraaednbitaullesfmr(aKacyttlueerriea&sl rHa2nOgeinocfoXnHtr2oOll¼in0g–p1hnaosteoenqlyuihlieblrpiae,lbuucitdaaltseothceonrostleraoinf ed from
the effect of CO2 on crystallization processes via melt h
Cole,1974;Kyleetal.,1992).Therareearthelementpat- dehydration.Giventhatcarbondioxideisknowntoplay ttp
terns in primary Ross Island basanitoids indicate the animportantroleinthegenesisofalkalinemagmas,in s://a
generation of a basanitic parent magma through low- both the mantle (Spera, 1984) and crust (Kaszuba & ca
degree partial melting of the mantle source (Sun & Wendlandt,2000), it is important to understand itsrole dem
Hanson,1975,1976).Majorandtraceelementmodeling atErebusthroughoutthemagmaticsystem(fromman- ic
suggests that lavas from Erebus [the Erebus Lineage tletosurface). .oup
(EL)] and the peripheral Hut Point Peninsula [the Dry .c
o
Valley Drilling Project (DVDP) lineage] both evolved m
MineralogyandpetrologyofRossIslandlavas /p
fromacommonbasaniteparentmelt,whichunderwent e
twodistinctfractionalcrystallization trends(Kyle,1981; ThemajorityoflavasonRossIslandarerepresentedby tro
two strongly undersaturated sodic differentiation lin- lo
Kyleetal.,1992).Sofarexperimentalworkhasfocused gy
on the evolved magmas (Moussallam et al., 2013) and eearugpetse:dthferomEreEbruesbuLsinevaoglcean(EoL,),anmdadtheeupDryofVlaalvleays /artic
no experimental work is available to constrain storage le
and differentiation conditions of mafic lavas at Erebus DrillingProject(DVDP)lineage,madeupoflavasonthe -ab
Hut Point Peninsula and sampled via drill coring. The s
(orIonththeirsseuxbpseirdiimareynvtaollcsatundoye,so).nelavafromeachofthe ruanrdeerrsEantruicrahteedd-IraonndScoernisetsitu(EteFSo)nllyavaassmaraelllveoslsumsileicoaf- tract/5
two Ross Island lava lineages (EL phonotephrite AW- 7
82038 and DVDP basanite KI-04) were chosen as start- RossIslandrocks.TheEFSwillnotbediscussedinthis /1/9
ingmaterialsforequilibriumcrystallizationexperiments study. The DVDP and Erebus lineages are similar in 3/2
toestablishtheP–T–X–fO2conditionsnecessarytopro- tseimrmilsarofvwarhiaotlieo-nrocink cmheamjoirstreyleamsednetmeovnoslutrtaiotendobfy tthhee 3754
duce the observed natural rock series. Phase equilib- 0
0
rium experiments are commonly used to constrain the DVDP and EL lavas with the exception of P2O5 (Fig. 2), b
y
pre-eruptive storage conditions of magmas, as well as the variation of which is probably being controlled by gu
apatitecrystallization.Majorelementmassbalanceand e
their liquid line of descent (Sack et al., 1987; Moore & s
trace element modeling of DVDP and EL rocks (Kyle, t o
Carmichael, 1998; Freise et al., 2003; Mart´ı et al., 2008; n
1981;Kyleetal.,1992)suggestsfractionalcrystallization 2
Andu´jaretal.,2010;DiCarloetal.,2010).Althoughnon- 2
equilibrium processes such as magma mixing and re- fromacommonbasaniticparentmelt,withslightdiffer- No
peated replenishment of the system are important to ences in differentiation conditions resulting in the two ve
m
consider, high pressure–temperature experimentation similaryetdistinctlineages. be
nevertheless illuminates the fundamental processes The mineralogy of the EL and DVDP lineage rocks r 2
0
that control magma evolution from mantle to surface, from Ross Island has been extensively documented by 18
allowing us to evaluate to what extent crystal–liquid Kyle et al. (1992) and Kyle (1981), respectively, whose
equilibriumhasbeenattainedormaintainedatdepth. observations are summarized below. These lineages
Experiments were performed over a range of tem- share the same assemblage with two notable excep-
peratures (1000–1150(cid:2)C) and at pressures between 200 tions. First, kaersutitic amphibole is present in almost
and 400MPa to reproduce the intermediate region of allDVDPlavas(exceptinbasaniteswhereitisrare)but
themagmaplumbingsystemwheremuchearlycrystal- isabsentinELlavas.Second,olivineispresentinallEL
lization (differentiation of a basanitic parent to form lavas and in DVDP basanites, but occurs only as xeno-
intermediate lavas) is thought to occur. A temperature crystsinmoreevolvedDVDPlavas.IntheELrocks,oliv-
of1000(cid:2)Cwaschosenasathermallowerbound,asthe ine ranges in composition from Fo in basanites to
88
temperature of the surficial lava lake, which should be Fo in phonolites. Olivine xenocrysts are rare and
51
the coolest region of the plumbing system, has been occur only in the most primitive lavas. In the DVDP
96 JournalofPetrology,2016,Vol.57,No.1
D
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Fig.2.VariationdiagramsillustratingtheevolutionoftheDVDPlineage(reddiamonds;Kyle,1981)andErebusLineage(EL;bluetri- r 2
0
angles;Kyleetal.,1992).Forwhole-rockcompositionsthemajorelementtotalsarenormalizedto100%.Onelavasamplefrom 1
8
eachofthesetwolineages(redstar:DVDPKI-04;bluestar:ELAW-82038)wasusedasthestartingmaterialfortheexperimental
work.
lavas, olivine occurs only in basanites as euhedral to Kaersutite is absent in EL lavas but is an important
subhedralphenocrystsandinthegroundmass. phaseinallDVDPlavasexceptthebasaniteswhereitis
ClinopyroxeneisubiquitousinallELandDVDPlavas rare. In some phonotephrites, kaersutite ranges from
and occurs as euhedral to subhedral phenocrysts. euhedralgrainstothoseshowingstrongresorptionand
Pyroxeneswithgreencores,whichshowirregularrims, oxidation. It was suggested by Kyle (1981), based on
possiblyowingtoresorption,areoccasionallyfoundin previous experimental work, that temperature and
DVDPlavas.IntheELlavas,clinopyroxenesshowoscil- PH Oprobablyexertastrongcontrolontheappearance
2
latory zoning in basanites and intermediate lavas, but or absence of kaersutite in DVDP and Erebus lineages,
nozoninginphonolites. respectively.
JournalofPetrology,2016,Vol.57,No.1 97
Feldspar is the modally dominant phenocryst phase Thelavaswerecrushedtoapowderandmeltedina
in EL lavas (up to 40% of the mode in anorthoclase- Pt crucible in a 1atm furnace at 1300(cid:2)C. Sample AW-
bearing phonolites) with compositions ranging from 82038 was held in the furnace for (cid:3)30min under a
An toAn inbasanites,becomingincreasinglyalbitic stream of nearly pure CO (corresponding to an oxida-
72 59 2
in the more evolved lavas. The feldspar in the EL tionstateneartheNi–NiO buffer,NNO) andthendrop-
phonolite is primarily anorthoclase. In the DVDP lava, quenchedintocoldwater[samplepreparedbyIacovino
feldspar occurs mostly as microphenocrysts or in the et al. (2013a)]. Sample KI-04 was held in furnace for
groundmass and is mainly labradorite (An ) in bas- (cid:3)1hinair(i.e.extremelyoxidizingconditions)andthen
50–60
anites, and andesine to oligoclase in all other lava removedfromthefurnaceandimmediatelyplacedinto
types. cold water to quench. The resulting glassy samples
Feldspathoids occur in the groundmass of the EL wereextractedfromtheircrucibles,re-crushed,andre-
lavas, as nepheline, which contains up to 24% norma- meltedunderidenticalconditionstoensureahomoge- Do
w
tive Ne. Microphenocrysts of apatite are common in neousandcrystal-free glass. Aportion of eachstarting n
lo
most rocks of both lineages and are often found as in- material was polished and analyzed by electron micro- a
d
clusionsinkaersutiteandmagnetiteintheDVDProcks. probe to verify that no compositional changes had ed
Pyrrhotiteispresentinallrocksfrombothlineagesand occurredduringmelting(seeTable1). fro
m
occurs as small round blebs, suggesting the presence h
of an immiscible sulfide liquid in the Ross Island mag- Experimentaltechniques ttp
s
mas. Opaque Fe–Ti oxides are common in both lava Between 30 and 60mg of glassy starting material pow- ://a
c
suitesandaretypicallytitanomagnetiteasphenocrysts der was added to Au Pd capsules with lengths of a
80 20 d
andinthegroundmass,plusrareilmenitephenocrysts. (cid:3)20mm, an outer diameter of 2(cid:4)9mm, and an inner em
diameterof2(cid:4)5mm. LiquidH2O was addedviaa micro- ic.o
EXPERIMENTALMETHODS spyorwindgeer(((cid:3)A0g–26C2mOg4),,(cid:3)a0n–d1C8Om2gw).aTshaedXdHe2dOaisnsthilveeHr2oOx–aClaOte2 up.com
Startingmaterials mixtureofpre-runchargeswasvariedatstepsbetween /p
e
ToinvestigatetheevolutionoftheRossIslandmagmas zero and unity (i.e. XH2O¼0, 0(cid:4)25, 0(cid:4)5, 0(cid:4)75, and 1), and tro
and the two dominant lava lineages, two samples were the fluid proportion in the charge was always (cid:3)10% to lo
g
chosen,onefromeachlineage(Table1):AW-82038isan ensure fluid saturation (see Supplementary Data y/a
Erebus Lineage phonotephrite lava (SiO2¼48(cid:4)01wt %; Appendix1;supplementarydataareavailablefordown- rtic
MgO¼3(cid:4)18wt %) from Turk’s Head (Kyle et al., 1992) loading at http://www.petrology.oxfordjournals.org). le-a
b
representativeofintermediateELlavas;KI-04isabasan- Once filled, capsules were weighed, crimped at their s
ite (SiO2¼43(cid:4)06wt %; MgO¼8(cid:4)92wt %) collected from openend,arcweldedshutwithagraphiteelectrode,and trac
HutPointPeninsulaforthisstudyandrepresentstheless then subsequently re-weighed to check for any mass t/5
7
evolved magmas of the DVDP lineage. Figure 3 illus- loss or gain during welding. After welding, capsules /1/9
trates our starting material compositions relative to wereplacedinanovenat110(cid:2)Cforseveralminutesand 3/2
those of a suite of melt inclusions in Erebus Lineage thenre-weighedtocheckforanyleaksinthecapsule.As 37
5
rocks, which provides a representative cross-section a third method to check for leaks, some capsules were 4
0
0
through the evolutionary chemical trend of lavas on heldinabeakerofoilat300(cid:2)Cforafewseconds.Ifbub- b
y
RossIsland(Oppenheimeretal.,2011). bles were observed escaping from the capsule, it was g
u
TheAW-82038phonotephrite[alsoreferredtoasNe considered to have leaks and was thus discarded. After e
s
hawaiite by Kyle et al. (1992)] is weakly porphyritic completionoftheexperiment,capsuleswereweighedto t o
n
(<8% phenocrysts) with a phenocryst assemblage of checkthatnofluidlossoccurredduringtherun.Anycap- 2
2
plagioclase, olivine, clinopyroxene, Fe–Ti oxides, apa- sulesthatshowedachangeinmass>0(cid:4)2mgeitherafter N
o
titeandrareaccessorynepheline.AW-82038isconsist- weldingorafterheatingwereconsideredtohaveleaked ve
m
ent with the fractionation of 12% olivine, 35% atleastpartoftheirfluidphaseandwerediscarded. b
e
clinopyroxene,7%Fe–Tioxides,and1%apatitefrom a Experimentswereruninverticallyworkinginternally r 2
0
basaniticparent,yieldinga43%residualmelt(basanite heatedpressurevessels(IHPVs;seeHolloway,1971)at 1
8
DVDP2-105.53;Kyleetal.,1992). the Institut des Sciences de la Terre Orle´ans (ISTO) at
In the KI-04 basanite, phenocrysts constitute around isothermal and isobaric conditions between 1000 and
12vol.%andincludeolivine(6vol.%),plagioclasefeld- 1150(cid:2)C andbetween200 and400MPawiththe oxygen
spar (2vol. %), augite (2vol. %), apatite (1vol. %), and fugacity of the vessel at about one log unit above
titanomagnetite(<1vol.%).Althoughkaersutiticamphi- the Ni–NiO buffer (NNOþ1; Table 2). Each run con-
bole is common in almost all DVDP lavas, it is rare in tained 5–10 sample capsules loaded into a vertically
DVDPbasanitesandisabsentinKI-04.Crystaldistribu- working IHPV equipped with a double-wound Kanthal
tionisrelativelyhomogeneousthroughoutthesample. furnace. An Ar–H gas mixture loaded sequentially at
2
This sample is consistent with 17% fractionation from room temperature was used as the pressure medium
basanitic parent DVDP 2-105.53 yielding an 83% re- withtheAr/H ratiofixedsoastoachieveanexperimen-
2
sidualmelt. tal fO in the vessel of NNOþ1 (Scaillet et al., 1992),
2
98 JournalofPetrology,2016,Vol.57,No.1
Table1:CompositionofAW-82038andKI-04startingglass,whole-rockandrepresentativeanalysesofphenocrystsandmicrophe-
nocrystsinthenaturalrock
AW- Whole- St.Gls2 Ol-6 Ol-10 Plag-5 Plag-12 Ap-1 Sp-1 gnd gnd
82038 rock1 Ol-5 Plag-5
SiO 48(cid:4)01 48(cid:4)03 38(cid:4)72 38(cid:4)47 54(cid:4)10 53(cid:4)69 0(cid:4)26 36(cid:4)27 55(cid:4)46
2
TiO 2(cid:4)77 2(cid:4)84 0(cid:4)14 0(cid:4)15 26(cid:4)18 0(cid:4)16
2
Al O 18(cid:4)56 18(cid:4)12 28(cid:4)54 29(cid:4)24 4(cid:4)34 28(cid:4)56
2 3
FeO* 9(cid:4)49 9(cid:4)59 20(cid:4)47 22(cid:4)54 0(cid:4)35 0(cid:4)31 0(cid:4)33 63(cid:4)15 29(cid:4)08 0(cid:4)39
MnO 0(cid:4)22 0(cid:4)23 0(cid:4)28 0(cid:4)45 0(cid:4)00 0(cid:4)04 0(cid:4)10 0(cid:4)80 0(cid:4)64 0(cid:4)03
MgO 3(cid:4)18 3(cid:4)08 41(cid:4)79 39(cid:4)84 0(cid:4)03 0(cid:4)03 0(cid:4)26 5(cid:4)29 35(cid:4)09 0(cid:4)05
CaO 7(cid:4)65 7(cid:4)57 0(cid:4)30 0(cid:4)30 11(cid:4)11 11(cid:4)53 55(cid:4)11 0(cid:4)04 0(cid:4)44 10(cid:4)62
Na O 5(cid:4)99 6(cid:4)04 4(cid:4)90 4(cid:4)66 0(cid:4)07 0(cid:4)04 5(cid:4)20
2
K O 2(cid:4)88 3(cid:4)07 0(cid:4)62 0(cid:4)50 0(cid:4)70
2 D
P2O5 1(cid:4)24 1(cid:4)41 42(cid:4)02 o
Total 98(cid:4)29 99(cid:4)54 101(cid:4)72 101(cid:4)80 99(cid:4)82 100(cid:4)21 98(cid:4)16 100(cid:4)04 101(cid:4)74 101(cid:4)19 w
n
Mg# 37 36 78 76 68 lo
a
Or 2(cid:4)3 1(cid:4)8 2(cid:4)6 d
e
An 69(cid:4)8 71(cid:4)9 67(cid:4)5 d
Ab 27(cid:4)9 26(cid:4)3 29(cid:4)9 fro
m
KI-04 Whole- St.Gls2 Ol-6 Ol-9 Aug-5 Aug-24 Plag-1 Plag-4 h
rock1 ttp
s
SiO 43(cid:4)06 43(cid:4)15 38(cid:4)04 37(cid:4)62 47(cid:4)09 42(cid:4)35 49(cid:4)91 50(cid:4)10 ://a
2 c
TiO 4(cid:4)26 4(cid:4)43 2(cid:4)57 4(cid:4)99 0(cid:4)23 0(cid:4)18 a
2 d
Al O 13(cid:4)80 13(cid:4)94 4(cid:4)92 9(cid:4)16 29(cid:4)95 30(cid:4)91 e
2 3 m
FeO 9(cid:4)73 12(cid:4)35* 17(cid:4)61 19(cid:4)83 7(cid:4)98* 6(cid:4)99* 0(cid:4)66 0(cid:4)53 ic
Fe2O3 2(cid:4)87 .ou
MnO 0(cid:4)19 0(cid:4)17 0(cid:4)22 0(cid:4)31 0(cid:4)25 0(cid:4)10 0(cid:4)00 0(cid:4)00 p
MgO 8(cid:4)92 8(cid:4)46 43(cid:4)56 40(cid:4)66 13(cid:4)34 12(cid:4)10 0(cid:4)10 0(cid:4)09 .co
CaO 11(cid:4)07 11(cid:4)16 0(cid:4)29 0(cid:4)39 22(cid:4)49 22(cid:4)70 14(cid:4)11 14(cid:4)62 m
KN2aO2O 13(cid:4)(cid:4)6643 31(cid:4)(cid:4)8618 0(cid:4)46 0(cid:4)45 03(cid:4)(cid:4)4315 30(cid:4)(cid:4)3219 /petro
P O 0(cid:4)83 0(cid:4)85 lo
2 5 g
Total 98(cid:4)61 97(cid:4)68 100(cid:4)00 98(cid:4)99 99(cid:4)10 99(cid:4)06 98(cid:4)72 100(cid:4)04 y/a
MOrg# 55 55 82 79 75 76 1(cid:4)2 1(cid:4)0 rticle
An 81(cid:4)1 82(cid:4)2 -a
Ab 17(cid:4)7 16(cid:4)8 bs
tra
Gorliagsisnaalnaanlyaslyessisarteotgailvseanreingwivte%n.aSnt.dGnlos,rmstaalritziendgtgola1s0s0a%ftweritvhitorirfiigcaintiaolna;nOall,ysoilsivtiontea;lsPlgaigv,epnl.aMgiioncelraaslea;nAaply,saepsaatirtee;nSopt,nsoprimneall;izgendd; ct/57
Ol,groundmassolivine;gndPlag,groundmassplagioclase. /1
*TotalirongivenasFeO;Mg#¼100[Mg/(MgþFe*)]inmol%. /93
1Whole-rockcomposition.AW-82038analyzedbyKyleetal.(1992);KI-04analyzedinthisstudy,usingX-rayfluorescence(XRF). /2
3
2Electronmicroprobe(EMP)analysesofglasscompositionaftervitrificationin1atmfurnace,butbeforeruninpressurevessel. 7
5
AW-82038vitrifiedatanoxygenfugacityofNNOþ1[analysisfromIacovinoetal.(2013)];KI-04vitrifiedinair(analysisfromthis 4
0
study). 0
b
y
g
u
although the fO2 within each experimental charge var- viscositiesofourmaficalkalicglassesfacilitatedtheat- es
iedslightlydependingonitsspecificH2O/CO2fluidmix- tainment of equilibrium even given these relatively t on
ture (see below). It is noteworthy that, because the shortruntimes.Insimilarstudiesonmaficmelts,theat- 2
2
experimental fO2 is lower than that imposed during tainmentofequilibriumwasobservedinrunsofsimilar No
melting of the sample KI-04 starting material, some duration (Di Carlo et al., 2006; Feig et al., 2010; ve
m
additional H2O was created in the capsule during KI Pichavantetal.,2014). b
e
runs via the reduction of Fe3þ. Thus, even nominally r 2
‘dry’ runs will contain some H2O (typically<1–2wt %), ANALYTICALTECHNIQUES 018
andthishasbeentakenintoaccountforthecalculation
of experimental oxygen fugacity. Pressure was meas- Fluidphasecomposition
ured with a transducer calibrated against a Heise– Forcapsulesthatdidnotleak,theconventionalweight-
Bourdon tube gauge with an accuracy of620 bars. loss methodwas employedas a first-order measure of
Temperature was measured with two chromel–alumel thecompositionoftheequilibriumH O–CO fluidphase
2 2
(TypeK)thermocouples,whichallowforprecisecontrol (seeBehrensetal.,2009).Afterthefirstpost-runweigh-
over the length of the hotspot ((cid:3)4cm) to within 65(cid:2)C. ing, the capsule was submerged in a liquid nitrogen
Experiments were run for 17–24h and then quenched bath, thus freezing any liquid water or water vapor but
bydroppingthesampleintothelower,coldpartofthe allowing the CO to remain as a gas. The capsule was
2
pressure vessel (<40(cid:2)C), which gives a quench rate of then punctured to allow for the escape of the CO gas,
2
>100(cid:2)C s–1 (Roux & Lefevre, 1992). The very low and a hissing noise and bubbles at the puncture site
JournalofPetrology,2016,Vol.57,No.1 99
SEMandelectronmicroprobe
Charges were initially studied using a JEOL WINSET
JSM6400scanningelectronmicroscope(SEM)atISTO
for preliminary phase identification, modal abundance
determinationandtexturalanalysis.Mostphasescould
be identified by visual inspection, and several crystals
from each phase were analysed using energy-disper-
sivespectrometery(EDS).TheEDSanalysesarenotre-
ported here as they were used only for mineral
identification.
RepresentativeSEMimagesfromeachsamplewere
digitallyprocessedtomeasuretotalcrystallinityandthe D
o
w
modalabundanceofallphases.Imageswereconverted n
lo
to grayscale and a threshold was applied and adjusted a
d
toisolateeachphase.Thetotalareaofeachphasewas ed
thencalculatedasapercentageofthetotalimage.Any fro
m
areas of the image that contained no sample (holes, h
cracks,etc.)werenotincludedinthetotalsamplearea. ttp
s
Electron microprobe (EMP) analyses of the major ://a
elementcompositionsoftheglassandcrystalphasesin ca
d
Fig.3.Totalalkalisvssilica(TAS)diagramshowingthecom- the natural samples, starting glasses and experimental em
positions of the starting materials (stars) relative to the frac- runproductsweremadeprimarilyusingaCamecaSX- ic
trOieoppnpraeelsnechnreytiesmdtaelrlibezyattaiola.n(2s0se1uq1itu)e]e.nocfe smeeenlt ininEclruesbiuosnsLin[edaagtae rforockms 1C0a0mbreildegcetr.oSnommeiscarmopprloebseweraetantahleyzedUnoinvearCsiatymecoaf .oup.co
m
SX-100attheUniversityofArizonaoronaCamecaSX- /p
were typically observed. After warming at room tem- e
peratureforupto1min,thecapsulewasweighedtode- 5m0eaastutrheedUunsiivnegrsaitna` dacecgelileSratutidnigdvioPlatadgoevao.fG1la5skseVw,aas trolo
g
termine the mass of CO2 lost after puncture. This was beamcurrentof3nA,adefocusedbeamsizeof10lm, y/a
then recorded as the mass of CO2 in the fluid phase. and a peak counting time of 10s, analyzing Na first to rtic
Thecapsulewasthenplacedinadryingovenat110(cid:2)C le
minimize any measurement error owing to Na migra- -a
forseveralminutestoevaporatetheremainingH Oand b
2 tion.Crystalphaseswereanalyzedwithanaccelerating s
then weighed to determine the mass of the H2O fluid. voltage of 15keV, a beam current of 10 nA, a focused trac
Duringthisstep, capsuleweightwascheckedperiodic- beamwithadiameterof1lm,andapeakcountingtime t/5
7
allyuntilitsmassremainedconstant.Itshouldbenoted of 20s. In each experimental charge, typically 20–30 /1
/9
thatthismethodisanindirectmeasureofthecompos- analyses were performed on glass and 8–12 analyses 3/2
itionofthefluidphaseinourrunsandcanbeproneto wereperformedoneachcrystalphase. 37
significanterror owingto uncertaintiesinthe weighing 54
0
ofthecapsulesbeforeandafteropening.Behrensetal. FTIRspectroscopy 0 b
a(2r0o0u9n)de6st0im(cid:4)03ateudsinagntehrisromr einthoXdH.2OThedectoemrmpionsaittiioonn ooff tWhehegnleavsesrppohsassiebleo,ftheeacHh2OexapnedriCmOe2nctoalnccehnatrrgaetiownserine y gue
s
the fluid phase was also calculated by mass balance, measured using a Thermo Scientific Nicolet iN10 MX t o
n
wherethemassofdissolvedH2OorCO2intheglass[as mapping FTIR system at the US Geological Survey in 22
measuredbyFouriertransformIR(FTIR)spectroscopy] MenloPark,California.TransmissionIRspectraofdou- N
o
is subtracted from the amount of fluid (liquid H2O or bly polishedglass chipsranging in thickness from (cid:3)20 ve
m
CO2 as silver oxalate) added to the capsule (see to 150lm were obtained in the 6000–1000cm–1 wave- b
e
SupplementaryDataAppendix1).Acomparisonoffluid numberrangeusingaKBrbeamsplitterwithavariable r 2
compositions calculated both by weight loss and by aperture size between 25 and 500lm2. The sample 01
8
massbalanceshowsreasonableagreement,withacor- stagewascontinuouslypurgedwithdryair,andaback-
relation coefficient between the two methods of ground measurement was made before the collection
R¼0(cid:4)79 and an average error in XH2O determination ofeachspectrumtominimizeandcorrectforthecontri-
betweenthetwomethodsof60(cid:4)11.Here,calculationof bution of atmospheric H O and CO . Moderately to
2 2
thefluidphasecompositionbyweightlossispreferred, highlycrystal-richchargeswerecharacterizedwithFTIR
with the mass-balance method used for sample KI-07, mappingtoidentifycrystal-freeregionsfortheanalysis
for which weight-loss data were not obtained. After ofdissolvedvolatiles.
fluidmassmeasurement,theAuPdcapsulewaspeeled TheconcentrationsofOH,H O,CO ,andCO species
2 2 3
away, and the sample was mounted in epoxy and pol- were calculated with the Beer–Lambert Law (Ihinger
ished for analysis. Selected samples were doubly pol- et al., 1994), using near-IR (4500 and 5200cm–1), total
ishedforanalysisbyFTIRspectroscopy. water (3500cm–1), molecular H O (1640cm–1), CO
2 2
100 JournalofPetrology,2016,Vol.57,No.1
Table2:Experimentalconditionsandrunproducts
Run Experiment P T XH2Oin1 XH Ofluid2 H Oglass CO glass fO Phases(vol.%)5
2 2 2 2
(MPa) ((cid:2)C) (wt%)3 (ppm)3 (DNNO)4
AW82038phonotephriteexperiments
PV-4B AW-19B 200 1000 0(cid:4)18 0(cid:4)14 0(cid:4)49 — 0(cid:4)9 Gl5,Cpx10,Plag81,Tit3,Ap1
PV-4B AW-20B 200 1000 0(cid:4)49 0(cid:4)35 1(cid:4)79 1077 1(cid:4)7 Gl81,Kaers16,Tit3
PV-4B AW-21 200 1000 0(cid:4)72 0(cid:4)56 3(cid:4)22(23) 931 2(cid:4)1 Gl87,Kaers9,Tit4
PV-4B AW-22 200 1000 0(cid:4)88 0(cid:4)74 4(cid:4)04(37) 817 2(cid:4)4 Gl87,Kaers8,Tit5
PV-4B AW-23 200 1000 1(cid:4)00 1(cid:4)00 5(cid:4)55(10) 0 2(cid:4)6 Gl96,Tit4
PV-3 AW-06 200 1050 — — 1(cid:4)42(7) 1298(137) — Gl92,Plag7,Tit<1
PV-3 AW-17 200 1050 0(cid:4)75 0(cid:4)43 3(cid:4)14(11) 443(17) 1(cid:4)2 Gl99,Tit1
PV-3 AW-18 200 1050 0(cid:4)87 0(cid:4)71 4(cid:4)006 — 1(cid:4)6 Gl99,Tit1
PV-3 AW-10 200 1050 1(cid:4)00 1(cid:4)00 5(cid:4)57(11) 0 1(cid:4)9 Gl99,Tit1,Ap<1 D
o
w
PV-2 AW-14 200 1100 0(cid:4)78 0(cid:4)20 1(cid:4)86 831 1(cid:4)2 Gl99,Tit1 n
lo
PV-2 AW-13 200 1100 0(cid:4)91 0(cid:4)68 4(cid:4)27(20) 937 2(cid:4)3 Gl99,Tit1 a
d
e
PV-8 AW-24B 250 1100 0(cid:4)21 0(cid:4)13 1(cid:4)14(1) 1700(74) 1(cid:4)0 Gl100 d
fro
PV-11 AW-42 300 1000 0(cid:4)21 0(cid:4)22 0(cid:4)73(3) 1145(107) 1(cid:4)6 Gl78,Kaers13,Plag2,Tit7 m
PV-11 AW-41 300 1000 0(cid:4)49 0(cid:4)49 1(cid:4)78 1180 2(cid:4)3 Gl80,Kaers15,Tit5 h
PV-11 AW-40 300 1000 0(cid:4)72 0(cid:4)64 2(cid:4)75(34) 1975(329) 2(cid:4)6 Gl94,Kaers2,Tit4 ttp
s
PPVV--1111 AAWW--3398 330000 11000000 01(cid:4)(cid:4)8060 01(cid:4)(cid:4)8060 47(cid:4)(cid:4)3206((1262)) 12207(366) 23(cid:4)(cid:4)80 GGll9915,,TTiitt95,Ap<1 ://ac
a
d
PV-6 AW-29 300 1050 0(cid:4)18 — 1(cid:4)01(3) 1653(150) — Gl93,Plag7 e
m
PV-6 AW-33 300 1050 0(cid:4)73 0(cid:4)71 2(cid:4)94(6) 1702(358) 1(cid:4)9 Gl99,Tit1 ic
PV-6 AW-34 300 1050 1(cid:4)00 1(cid:4)00 5(cid:4)90(78) 0 2(cid:4)2 Gl97,Tit3 .o
u
p
PV-10 AW-37 300 1100 0(cid:4)21 0(cid:4)14 0(cid:4)176 — 1(cid:4)2 Gl99,Tit1 .c
o
m
PV-5 AW-25 300 1100 0(cid:4)53 0(cid:4)25 2(cid:4)25(9) 1186(97) 1(cid:4)7 Gl99,Tit<1 /p
PV-5 AW-27 300 1100 0(cid:4)88 0(cid:4)67 3(cid:4)03(1(cid:4)13) 1622(311) 2(cid:4)6 Gl99,Tit<1 e
PV-5 AW-26 300 1100 0(cid:4)75 0(cid:4)43 3(cid:4)59(3) 982(59) 2(cid:4)2 Gl99,Tit<1 tro
lo
PV-5 AW-28 300 1100 1(cid:4)00 1(cid:4)00 6(cid:4)65(85) 0 3(cid:4)0 Gl99,Tit<1 g
y
PPVV--1155 AAWW--4434 440000 11000000 00(cid:4)(cid:4)2419 00(cid:4)(cid:4)1581 02(cid:4)(cid:4)02216 —— 12(cid:4)(cid:4)76 GGll3765,,CKpaexr2s21,9P,lTagit365,Tit7 /article
PV-15 AW-45 400 1000 0(cid:4)70 0(cid:4)71 4(cid:4)04(13) 3375(824) 2(cid:4)9 Gl80,Kaers13,Tit7 -a
PV-15 AW-46 400 1000 0(cid:4)86 0(cid:4)74 4(cid:4)76(76) 3439(134) 2(cid:4)9 Gl87,Kaers9,Tit4 bs
PV-15 AW-47 400 1000 1(cid:4)00 1(cid:4)00 6(cid:4)84(49) 0 3(cid:4)2 Gl74,Tit26 tra
c
t/5
KI-04basaniteexperiments 7
/1
PV-7 KI-09 200 1050 0(cid:4)19 0(cid:4)17 0(cid:4)73(17) 1154(271) 0(cid:4)4 Gl70,Cpx23,Tit7 /9
PPVV--77 KKII--1101 220000 11005500 00(cid:4)(cid:4)7750 00(cid:4)(cid:4)5650 12(cid:4)(cid:4)51286(11) 123—3(137) 11(cid:4)(cid:4)44 GGll6503,,KCapexr4s43,7T,iTti3tþ4rareOl 3/23
PV-7 KI-12 200 1050 0(cid:4)86 0(cid:4)78 3(cid:4)556 — 1(cid:4)7 Gl65,Ol6,Cpx25,Tit5 75
4
0
PV-2 KI-05 200 1100 1(cid:4)00 — — — — Allquench 0
b
PV-2 KI-06 200 1100 0(cid:4)89 — — — — QuenchþrareOl y
PV-2 KI-08 200 1100 0(cid:4)58 — — — — Gl86,Ol11,Tit2 gu
PV-2 KI-07 200 1100 0(cid:4)76 0(cid:4)58 2(cid:4)90(8) 1131(100) 2(cid:4)2 Gl93,Ol4,Tit3 es
PV-8 KI-14 250 1100 0(cid:4)17 0(cid:4)20 0(cid:4)456 — 1(cid:4)4 Gl52,Ol26,Cpx23 t on
PV-8 KI-15 250 1100 0(cid:4)49 0(cid:4)43 1(cid:4)91(2) 3074(627) 2(cid:4)1 Gl91,Ol9,Tit<1 22
PV-8 KI-16 250 1100 0(cid:4)69 0(cid:4)54 3(cid:4)33 4338 2(cid:4)3 Gl72,Ol27,Tit1 N
PV-8 KI-17 250 1100 0(cid:4)87 0(cid:4)77 3(cid:4)846 — 2(cid:4)6 Gl58,Ol21 ov
e
PV-8 KI-18 250 1100 1(cid:4)00 1(cid:4)00 — — 2(cid:4)8 Allquench m
b
PPVV--1100 KKII--2232 330000 11110000 00(cid:4)(cid:4)2419 00(cid:4)(cid:4)1246 12(cid:4)(cid:4)11136(4) 262—8(257) 11(cid:4)(cid:4)82 GGll9820,,OOll81,5T,Qit<51 er 20
PV-10 KI-21 300 1100 0(cid:4)70 0(cid:4)48 2(cid:4)79(58) 2798(573) 2(cid:4)3 Gl91,Ol9,Tit<1 18
PV-10 KI-20 300 1100 0(cid:4)87 0(cid:4)61 2(cid:4)21(31) 1256(364) 2(cid:4)5 Gl,QþrareOl
PV-10 KI-19 300 1100 1(cid:4)00 1(cid:4)00 — — 3(cid:4)0 Allquench
PV-12 KI-28 300 1150 0(cid:4)21 0(cid:4)21 0(cid:4)596 — 0(cid:4)9 Gl98,Ol2,Tit<1
PV-12 KI-27 300 1150 0(cid:4)49 0(cid:4)32 1(cid:4)806 — 1(cid:4)3 Gl99,Ol1,Tit<1
PV-12 KI-26 300 1150 0(cid:4)70 0(cid:4)43 — — 1(cid:4)6 Allquench
PV-12 KI-25 300 1150 0(cid:4)86 0(cid:4)83 — — 2(cid:4)2 Allquench
PV-12 KI-24 300 1150 1(cid:4)00 1(cid:4)00 — — 2(cid:4)3 Allquench
PV-13 KI-29 400 1000 0(cid:4)21 0(cid:4)13 — — 1(cid:4)4 Subsolidus
PV-13 KI-30 400 1000 0(cid:4)48 0(cid:4)31 — — 2(cid:4)1 Subsolidus
PV-13 KI-31 400 1000 0(cid:4)71 0(cid:4)59 2(cid:4)726 — 2(cid:4)7 Gl38,Kaers60,Tit2
PV-13 KI-32 400 1000 0(cid:4)85 0(cid:4)80 3(cid:4)05(5) 1601(139) 3(cid:4)0 Gl57,Kaers41,Tit2
(continued)
JournalofPetrology,2016,Vol.57,No.1 101
Table2: Continued
Run Experiment P T XH2Oin1 XH Ofluid2 H Oglass CO glass fO Phases(vol.%)5
2 2 2 2
(MPa) ((cid:2)C) (wt%)3 (ppm)3 (DNNO)4
PV-13 K1-33 400 1000 1(cid:4)00 1(cid:4)00 4(cid:4)306 0 3(cid:4)2 Gl38,Kaers59,Tit3
PV-14 KI-36 400 1100 0(cid:4)72 0(cid:4)53 3(cid:4)386 — 2(cid:4)6 Gl95,Ol5,Tit<1
PV-14 KI-37 400 1100 0(cid:4)85 0(cid:4)80 3(cid:4)566 — 3(cid:4)0 Gl29,Q51,Ol20
PV-14 KI-38 400 1100 1(cid:4)00 1(cid:4)00 — — 3(cid:4)2 Allquench
1MolefractionofH OintheH O–CO fluidaddedtotheexperimentalcapsulepriortorunningatPandT.
2 2 2
2MolefractionofH OintheequilibriumH O–CO fluidphaseduringtherun,measuredbyweight-lossmethod.SampleKI-07calcu-
2 2 2
latedbymassbalance.
3Weight per cent H O or ppm CO dissolved in the glass, measured via FTIR spectroscopy. Standard deviation shown in
2 2
parentheses. D
4CalculatedoxygenfugacityoftheexperimentintermsofDNNO(logunitsfromtheNi–NiObuffer).(Seetextfordetails.) ow
5Phaseproportionscalculatedasvolumepercent;Gl,glass;Ol,olivine;Cpx,clinopyroxene;Kaer,kaersutite;Fsp,feldspar;Ap,apa- nlo
tite;Tit,titanomagnetite;Q,quenchcrystals. a
d
6Volatile concentration calculated by mass balance using values in Table 3. Corrected values using the calibration lines in e
d
SupplementaryDataFig.A2.2arereportedhere. fro
m
h
Table3:Absorptioncoefficientsusedtodetermineconcentra- fringes in reflectance IR spectra allowed for the meas- ttps
tions of dissolved volatiles in experimental charges via FTIR urementofthesamplethicknessintheprecisespotthat ://a
spectroscopy c
a
was analyzed with transmitted light, following the d
e
Compositionand Species Coefficient Reference methodofNichols&Wysoczanski(2007,andreferences m
wavenumber(cm–1) [l(molcm)–1] ic
therein; see Supplementary Data Appendix 2 for .o
u
Phonolite details). p
1640 HO 2563 Dixonetal.,1994 .c
2345 CO2 m 890 Morizetetal.,2002 Glass densities were calculated for each sample om
2
Te31p54h03r00iphonolite HCO2O3tot 6C4al6cu8lated CDiioxonin,2&0P00an,1995 uinsginagnthHe2OmomdoellaorfvLoalnugmee&oCfa2r2m(cid:4)9icchmae3lm(19o8l–71),(Oascshusm&- /petrolo
11562450 CHO2O3m C25al6cu3lated DDiixxoonn&etPaal.n,1,9199495 Ldaenpgeen,d1o9n99g).laMssolcaormapbososirtpiotinon(Pcaonedfyfiacieenttsal.s,tr1o9n9g2l)y. gy/a
34550000 HO2HOtot 60(cid:4)4662680(cid:4)02 CBieohnrie,n2s00e0tal.,2009 Becauseofvariationinthecrystallinityofoursamples, rticle
5200 H2Om 1(cid:4)0260(cid:4)06 Behrensetal.,2009 and therefore significant variation in glass chemistry, -a
Phonotephrite b
11341565542400350000 CHHOCOO22HOO33mtot CC260(cid:4)53aa6(cid:4)ll692ccuu663llaa50tt(cid:4)(cid:4)ee40dd2 DDDBBeeiiixxxhhooorrnnneenn&&esstPPeeaaattl.nn,aa1,,ll..911,,9229940099005599 aacpinpoepsnasrtotisbtpeluremis,aeptthdetewifnmoarstohdeimsealacsodhtufedDstyaioxmaourpneslee&l.isaPAtbaelsndlo(rai1npb9ts9iToo5anr)bpwlcteioao3sen.fufWicscoeihedeenfrtftoies- stract/57/1/9
Ba5s2a0n0ite H2Om 1(cid:4)0260(cid:4)06 Behrensetal.,2009 calculatee1525ande1430(carbonateabsorption)forsin- 3/2
3
1430 CO3 375620 Fine&Stolper,1986 gle samples. This calculation can only be applied to 75
11562450 CHO2O3m 3275566320 DFiinxeon&eSttaoll.p,e1r9,914986 glasses with an Na/(NaþCa) ratio between 0(cid:4)25 and 400
34550000 HO2HOtot 60(cid:4)35(cid:4)986650(cid:4)(cid:4)402 BCeohchreenos,1e9t9a3l.,2009 0ri(cid:4)t5e(ainndouterpcharsiep,hmonoosltitgelafsaslleisnctlhaisssirfaiendgea)s.pFhoorngolatesspehs- by g
5200 H2Om 0(cid:4)5660(cid:4)04 Cocheo,1993 wweitrheNsae/l(eNcateþdCfaro)<m0t(cid:4)2h5eolirte>ra0t(cid:4)u5,ree1(5s2e5eanTdabe1le4303)v.a(lSueees uest o
n
Supplementary Data Appendix 2 for details of FTIR 22
(2345cm–1),andcarbonate(1430and1525cm–1)bands. spectral background fitting, absorbance measure- No
v
The total water 3500cm–1 band was always preferred ments, sample thicknesses, and glass density e
m
for retrieving H O concentrations; in five samples the calculations.) b
2 e
peak at this band was unusable and so near-IR bands Dissolvedvolatileconcentrationscouldnotbemeas- r 2
0
were used. The H2O concentrations in samples meas- ured in nine crystalline samples (29–75vol. % glass) 18
uredwithboththetotalwaterandnear-IRbandsagree where glass pools were too small to analyze by
well, with an average standard deviation of 0(cid:4)57wt % FTIR spectroscopy. A further six glassy samples
andanR2valueof0(cid:4)83. (95–99vol.%glass)couldnotbesuccessfullyprepared
Sample thicknesses were measured to an accuracy for FTIR analysis. For these 15 samples, H O and CO
2 2
of 62lm usinga digital tabletop micrometerequipped contents were calculated using the mass-balance
withafinetipthatallowedformeasurementatmultiple method (see Supplementary Data Appendices 3 and 4
spots on the sample surface. Additional sample thick- fordetails),andthe35samplesforwhichFTIRmeasure-
nessesforsomesampleswerealsomeasuredusingan ments were obtained were used as internal standards.
ADEPhaseshiftMicroxamsurface-mappingmicroscope The standard error for these calculations is large at
(withwhitelightinterferometer)toanaccuracyof60(cid:4)5– 61(cid:4)4wt % and 61000ppm for calculated H O and CO
2 2
2lm.Inverythinsamples,thepresenceofinterference values,respectively.
102 JournalofPetrology,2016,Vol.57,No.1
Oxygenfugacity Phaserelationships
The fO of all IHPV runs was controlled by loading the The equilibrium phase relations for the AW and KI ex-
2
pressure vessel with sufficient H to achieve an appar- periments are shown in Figs 4 and 5. In both compos-
2
atusfO of(cid:3)NNOþ1.ThefO insideeachexperimental itions, titanomagnetite is ubiquitous in nearly all
2 2
capsulewillvarydependingontheH O/CO ratioofthe experimental charges independent of P/T/H O and is
2 2 2
fluidphasecontainedtherein.AssumingthatthefH of probably stabilized owing to the relatively oxidizing
2
thepressurevesselwillbethesameasthefH insidean conditionsofourexperiments.Experimentsareplotted
2
experimental capsule owing to the very fast diffusion in terms of the mole fraction of H2O in the H2O–CO2
ratesofhydrogen,wecancalculatethefO2insideeach fluidaddedtothecapsule,XH2Oin.
capsulefollowingthemethodofIacovinoetal.(2013a). In AW, kaersutite is the liquidus phase at median to
First,becausethepartialpressureofH isfixedforeach high water contents, crystallizing below about 1025(cid:2)C.
2
experiment, we can calculate the fH2 of the pressure Amphibole is common in the AW experiments and is Dow
vesselforeachrunusingtheequation stableto meltH2Ocontentsas lowas (cid:3)1wt %.A reac- nlo
tion relationship betweenkaersutite andclinopyroxene a
where/isthefugacityfHco2e¼ffi/ciPeHn2tofhydrogenforthe(1P) iwshiinchfercrleindoptoyroexxeisnteairsouthneddXoHm2iOnfalunidt¼ca0l(cid:4)c1ic–0f(cid:4)e2r,robmelaogw- ded fro
m
and T of a given experiment (Shaw & Wones, 1964), nesian phase (experiments AW-19B and AW-43). As h
taondthPeH2IHiPsVthaetptahretiasltaprrteossfutrheeorfuhny.dIfrotgheenXgHasOaflduiddeids wabitohutka1e0r2s5u(cid:2)tCit.eP,laclginioocplaysroexfeenldespisarreissttrhiceteddrytoliqbueidlouws ttps://a
2 c
phase and is restricted to low water contents, with its a
ckanposwunle, wase can also then calculate the fH2O inside the stability field increasing with decreasing temperature. dem
Phase equilibria at 300 MPa are similar to those at ic
.o
fH2Oinside¼fH2OpureXH2Ofluid (2) 200MPa[thestabilityfieldforclinopyroxeneat300MPa up
(Fig. 4b) is inferred based on that at 200MPa (Fig. 4a)]. .co
wherefH OpureisthefugacityofpureH Ovaporatthe m
2 2 Althoughapatitewasnotalwaysdetected,itisinferred /p
experimental P and T conditions, assuming ideal mix- e
ing between H2O and CO2 in the fluid [calculated with ittoycrisysmtalolisztelybecloonwst1ra1i0n0e(cid:2)dCabtybowtahteprr-essastuurreaste.dItsesxtpaebrili-- trolo
g
the modified Redlich–Kwong equation of state of ments, but apatite is probably stable but undetectable y/a
Holloway(1977)asmodifiedbyFlowers(1979)].Now,it in drier runs (see Harrison & Watson, 1984). This hy- rtic
ispossibletocalculatetheoxygenfugacityforeachex- le
pothesis is supported by the steady decrease in the -a
perimentasfollows: b
fOi2nside¼ fHf2HO2iKnsFide!2 (3) twmPh2aaeOytn5sitnsct.ohthTneehtleiepqnrupteioodsflsuyrusberasperihdircaausnasegel,lceiftqoi2oul0lnio0dw–sa4tei0nd100pbM0hy0oP(cid:2)PnaCloaa(tmFneipdgph.hCr4ipibtcexo),leseixnhipostehwaralis-t- stract/57/1
/9
where KF is the equilibrium constant of formation for order. 3/2
H2O(Robieetal.,1979).Oxygenfugacitiesinourexperi- In KI experiments at 200MPa (Fig. 5a), olivine is the 37
5
ments arereportedin Table 2 and rangefrom a DNNO liquidus phase followed by clinopyroxene and kaersu- 4
0
ofþ0(cid:4)3toþ3(cid:4)2. tite. Although loosely constrained, the liquidus is 0 b
y
locatedabove1100(cid:2)CexceptatveryhighH2Ocontents gu
(XH Oinapproachingunity),whereitdropsto(cid:3)1075(cid:2)C. e
RESULTS 2 s
Aperitectic-like relationshipexistsatintermediatemelt t o
n
Texturalandmineralogicalobservations water contents and 1050(cid:2)C at 200MPa where olivine is 2
2
Optical and electron microscope images revealed replacedbykaersutiteatlowtemperatures.AttheseP– N
o
homogeneously distributed euhedral crystals in most T conditions, clinopyroxene replaces kaersutite as the ve
m
experimental charges, with crystals ranging in size dominant ferromagnesian phase at low and high melt b
e
from <5mm to (cid:3)80mm in length. Phases identified in- water contentswhere it coexistswith olivine, exceptat r 2
clude olivine, clinopyroxene, plagioclase, amphibole, verylowmeltwatercontents(XH Oinapproachingzero) 01
2 8
Fe–Ti oxides, apatite, glass and fluid inclusions. In the where clinopyroxene is the only stable silicate phase.
most highly crystalline charges, glass tends to collect The phase relationships observed at 400MPa (Fig. 5b)
in pools and small subhedral crystals (‘quench’ tex- are broadly similar to those at 200MPa except that the
ture)areubiquitous.Quenchtextureisespeciallycom- kaersutite stability field is enlarged towards H O-rich
2
mon in KI samples with high H2O contents, probably conditions, this mineral being in reaction relationships
owingtotheextremelylow-viscositymeltallowingfor withbotholivineandclinopyroxeneastemperaturede-
the rapid crystallization upon quench. In samples creases. The polybaric section at 1100(cid:2)C (Fig. 5c) illus-
where crystals were too small to analyze by electron tratesthatolivineistheliquidusmineralinthepressure
microprobe(<25mm2),phaseswereanalyzedquantita- range 200–400MPa, for a large range of fluid compos-
tively for identification purposes only. Those analyses itions (melt water content), followed by clinopyroxene
arenotreportedhere. atXH O <0(cid:4)25.
2 in