Minor-element abundances in obsidian, perlite, and felsite of calc-alkalic rhyolites

12 Pages·2007·1.02 MB·English

American Mineralogisl, Volume 62, pages 426437, 1977
Minor-elemenat bundanceins obsidianp, erlite,
andf elsiteo f calc-alkalicr hyolites
Rosnnr A. ZtsI-tNsrI,P ntnn W. LtpueN eNn Hucu T. Mtlu,Rn, JR.
tJ.S.G eologicaSl uruey,D enuerF ederalC enter
DenuerC. olorado8 0255
Abstract
Evaluationo f differencesin minor-elemenct ompositionb etweenc oexistingo bsidian,p er-
lite, and felsitef rom four Cenozoicr hyolitel avaf lowsi n the Rocky Mountain regioni ndicates
that significanet rrorsc anb e madei n estimatingth e originalc ompositiono f rhyolitico bsidian
simplyb y relyingo n abundanceosf elementsin associatedp erlite and,/orf elsite.
Perlitesh avel ow Li, highS r and Ba,a nd variableF relativeto obsidianV. ariationso f Li,
Sr, and Ba in perlitesa re controlledb y low-temperaturieo n exchangew ith groundwater.
Felsitesh avel ow Li, Cs, U, Mo, and F, and high Sr, Ba, and Eu relativet o obsidian.
Variationso f elementaal bundanceisn felsitesr esultf rom a combinationo f high-temperature
(crystal-meltf ractionationa nd volatile transport) and low-temperaturep rocesses(l on ex-
changed, ifferentiasl olution,a nd absorptionb y secondarpyh ases)F. or rhyoliticr ockst hat
evolveb y major feldsparf ractionation,t he rare-earthe lements(R EE), and particularlyE u,
are useful for evaluatinga bundancev ariations produced by magmatic heterogeneityo f
feldspar.T he componento f Sr and Ba variationsc ausedb y magmatic heterogeneityo f
feldsparm ay be estimatedu sing the Eu data. Young felsitesh ave significantlyd ifferent
abundanceosf F, REE, Cs,a nd Li thanc oexistinogb sidiana, ndt hisi ndicatetsh atv ariations
are producedb y either crystal-meltf ractionationo r processeasc tived uring or shortly after
eruption.C omparedt o obsidian,f elsitese xhibitr elatived epletionso f U and Mo that increase
with age,w hichi ndicatesth at lossesa rec ausedb y weathering.
Introduction During eruption and emplacements, ilicic lava
This study evaluatesm inor-elementv ariations flows are typically quencheda t their margins to a
within differentp arts of individual rhyolitic lava glassye nvelopeo f obsidian,w hile the more slowly
flows. The reportede lementsr epresenta variety of cooled interiors undergo primary crystallizationt o
chemicalg roups of different geochemicaal ffinities. densef elsite.R hyolitic felsitei s typicallyc omposedo f
The purposeo f sucha studyi s to providea dditional alkali feldspar and cristobalitew ith minor iron
datao n (l) the extentt o whichh ydratedo r crystal- oxides.S ubsequentto emplacementt,h e quenched
lizedg lassr epresentcsh emicael quivalentosf original glassg raduallyh ydratest o grey perlite (Rossa nd
non-hydratedg lass(, 2) the mechanismasn d rateso f Smith, 1955;F riedman and Smith, 1958;N oble,
elementaml obilityr elatedt o hydrationa ndc rystalli- 1968)c, ontainingu p to 5 weightp ercentw ater.
zalion of rhyolitic glass. Previouss tudiesh aved ocumenteds everacl hanges
The four flows studieda re from the Rocky Moun- accompanyingh ydrationa nd crystallizationo f acidic
tain region and range in age from Pleistoceneto volcanicg lass.H ydration causeso xidationo f iron,
OligoceneA. n obsidian,o ne or more felsitesa, nd, losso f Na, and increaseo f K (Lipman. 1965;A ra-
generally,a secondarily-hydratepde rlite were ana- maki and Lipman, 1965;T ruesdell,1 966;N oble,
lyzed from each flow. Obsidiana nd perlite were in 1967).A lkali contentso f crystallizedc alc-alkalic
intimate contact,a nd felsitesw erec ollectedw ithin a rhyolitesa re very similar to thoseo f coexistingo bsi-
few meterso f glassys amplesT. he sames amplews ere dian (Lipman et al., 1969),b ut peralkalinev olcanic
earlieru tilized for a study of the retentiono f alkalis rocks in which molar alkalis exceeda luminat end to
and halogens(L ipmane t a|.,1969). loseN a during crystallization(N oble, 1965;N oble,
ZIELINSKI ET AL.: MINOR.ELEMENT ABI]NDANCES
1970).E wart (1971)r eporteds mall-scalem igration of thorium, and oxygen were applied. Sample transfers
Na and K within spherulitesc ontained in rhyolite and data collection and reduction were computer-
glass. Other elementsr eported depleted in crystal- controlled.
lized rhyolites relative to glassy portions include The remaining analysesw ere performed by a num-
halogens (Noble et al., 1967;L ipman et al., 1969), ber of standard proceduresi ncluding atomic absorp-
Mo (Haffty and Noble, 1972), U (Rosholt and tion, X-ray fluorescencee, missions pectrometrica nd
Noble, 1969; Rosholt et al., l97l; Shatkov et al., isotope dilution (analysisp erformed by C. E. Hedge)
1970),C s (Shatkov, l97l), and Be (Shatkov er c/., mass spectrometict echniques.
1970; Steven et al., 1973, p. 92-98). Sr has been
reported to be enriched in crystallized rhyolites rela- Results and discussion
tive to glassyp ortions (Noble and Hedge, 1969). Elemental concentrations are expresseda s parts
per million (ppm) by weight (Table l) along with
Analytical techniques
estimated analytical precision. Of note are the ex-
Approximately 100g aliquots of hand-sizes amples tremely low concentrationso f Ba and Sr comparedt o
were ground in ceramic plates to -100 mesh. Splits averagea cidic crustal rocks and the low concentra-
were distributed for analysis of 38 elements by a tions of elements normally concentrated in mafic
variety of analytical techniquesc hosen to optimize phases( Co, Cu, Cr, Sc). Thesea bundancesa, sw ell as
accuracy and precision for each element. those of the rare earth elements (Fig. l), indicate
Twenty-four elements( Na, K, Cs, Cr, Mn, Fe, Co, origin of the rhyolitic magmas by large degreeso f
Sc,L a, Ce, Nd, Sm, Eu, Gd, Tb, Dy, Tm, Yb,Lu,Zr, fractional crystallizationa nd/or small degreeso f par-
Hf, Ta, Sb, and Th) were determinedb y instrumental tial melting involving equilibration of melt and a
neutron activation analysis( Gordon et al., 1969;Gij- feldspar residuum (Noble et al., 1969;Z ielinski and
bels and Hertogen, l97l). Splitso f 1.5 g were irra- Frey, 1970).
diated with standards for 30 minutes in the USGS Concentrations of 29 selectedm inor elementsi n
TRIGA reactor in a neutron flux of 3 X perlite and felsitea re normalizedt o concentrationsi n
l0lon/cm2/sec.T he standards were USGS standard closely coexisting obsidians (Fig. 2). Elements
rock G-2 and synthetic standards (CQS-l and -2) omitted from Figure 2 include major elements ob-
prepared by adding the elementso f interest to high- tained by neutron activation (Na, K, Fe) but dis-
purity quartz powder. Following this short irradia- cussed elsewhere (Lipman et al., 1969), and minor
tion, the samplesa nd standardsw ere counted over an elements with consistently large analytical errors
interval of decay of 4 hours using coaxial Ge(Li) (Tm, Gd, Sb, Cu, As, Se). No correction was made
detectors( resolution 2.0 keV FWHM at 1333 keV, for density differences between samples. This could
efficiency- l0 percent). The samplesa nd standards introduce small systematice rrors in some of the nor-
were then irradiated for 8 hours in a neutron flux of 3 malized ratios, but inspection of Figure 2 indicates
X l}t2n/cm2/seca nd counted on the coaxial Ge(Li) that such effects are not a major problem. Perlites of
detectorsa s well as planar Ge(Li) detectors( resolu- this study contain up to 3 weight percentH rO (Lip-
tion -500eV FWHM at l22keY) after decayt imes of man et al., 1969), resulting in a density decreaseo f
7, 14, and 60 days. The spectra of induced 7-ray less than 5 percent. Density corrections should be
activitesw ere stored on magnetict ape and areasu n- more important for glassesu ndergoing extensived is-
der the photopeaksc alculateda nd comparedb y com- solution and secondarya lteration to zeolite and clay
puter. (Hoover, 1968).
Uranium abundancesw ere determined by a de- Conclusions regarding elemental variability are
layed-neutron counting technique (Millard, 1976). drawn only when measuredd ifferencesa re large rela-
Splits of 8 grams of samplesa nd standards( U-doped tive to analytical uncertaintiesa nd when consistent
dunite) were irradiated for I minute in the USGS trends appear in more than one sample suite. The
TRIGA reactor in a neutron flux of 6 X l0t1n/ general validity of the observed trends can only be
cm2/sec and transferred by pneumatic tube to documented through additional studies of this na-
an array of BF, neutron detectors. After a 20-second ture.
period of decay the samples and standards were
Minor-element differencesb etweeno bsidiana nd perlite
counted for I minute. This procedure was repeated
but with irradiation in a Cd-lined terminus to deter- All three perlites show large relative depletion of
mine thorium. Corrections for detector dead-time. Li, and two show enrichment in Sr compared to
428 ZIELINSKI ET AL.: MINOR-ELEMENT ABUNDANCES
Table l. Compositionso f somer hyoliteo bsidiansp, erlites,a nd felsitesfr om the Rocky Mountain region
uDsldlan ullrr rtog
Yellosstone Park,
Rhy(ocllltteg oceonfe ,N ath2roep-2, 9 CEo,lyo.r)a do Rj|yoltte o(fM toBceeanveer, C22re emk.,y .)Colorado Rhyolire( Plroofc eNnoe , Aqu4a ,n .yN.)es Mexico (PWleytsot[olnc8ene)
obstdtan Perllte FelBtte Obsldlan Perllre Felslte 1 Felslte 2 Obsidien Perllle Felslte 1 Felslte 2 Felslte 3 Obdtdian Felslte
66L-230A 66L-230D d6l--230c 65L-161A G5l,-t6lc 65L-l6tB 65L-t6tD 66L-zi4D 66l-23ra 66L-234c 66L-234D 66L-2348 6yc-64 6yc-153
Anal. C.v. (Z)r
Technlque
47. 51. 77. 30. 33. 2L. 133. 88, 105. 75. 63. 63. A.A. 10
Ne 33000. 25100. 32900. 30000. 25300. 30900. 30900, 34800. 32500. 34400. 35800. 33900. 27800. 2E800. INAA I-2
K 39700. 43000. 39E00. 38500. 41300. 39500. 40100, 35200. 36700. 35000. 37800. 37300. 39400. 41500. lNM 1-7
Rb 304, 310. 295 225. 2r2. 227. 230. 280. 278. 252. 273. 294. 222. 238. XRF IO
Cs 7.8 7. 4 7.4 6.3 6.8 6.4 5.5 6.2 5.3 3.4 INAA 4-7
Be 10. 9. E. 6. 6. 10. 13. 10, E.S . 15
SE 1.3 4.7 3.r E.7 8.3 8,5 8.7 2.5 3.0 3.2 3.2 2.5 2.7 I.D. 5
Ba 2. 2A. lE, 12. 4. 24. 1. 12. 34. 37. xRr 10-30
Cr 11. 7 11. 12. 12. 12. 8. 9. 4. 11. r0. 8, 13. 13, INAA 2-45
h 731. 700. 407. 376. 353. 261. 1220. rr50. 1180 1210. 1510. r90. L47. INAA I-3
4270. 3790. 4190. 5640, 5080. s380. 5440. 4490, 4070. 3950. 4190. 4180. E660. 8830. INAA 1-5
Co 0.1 0.05 0.09 o.2 0.2 o.2 0.7 0. 09 0.1 0,4 0,3 0.4 0,3 0.3 INM 1-41
Cu <.3 0.4 <.1 0,3 0.3 0.4 0.9 <.3 0.4 0.3 0.4 1. E,S , 50
Sc 3.67 4.01 L.52 1.53 r.38 1.41 7.69 7.52 7. 21 7. 89 1. 28 1.13 1.14 INAA 1-2
Le 20.0 18.8 16.3 33.5 32.7 32.4 32.8 10.6 ro.7 10,6 10.8 56.8 5E.7 rNAA r-4
ce 51..4 46.3 46.1 52,5 51.4 52.7 49.1 27.6 30,0 21. 3 28.6 33.7 11E.0 727.O rNAA 2-E
Nd 26.3 22.2 13.7 19.3 19.5 11.7 16.9 18.9 15.9 L4.9 11. 9 56.9 6L.2 INAA 1-36
Sb 5.9 4.9 3.3 z-3 2.r 5.9 5.3 s.2 5.8 12.3 13,5 rNAA 1-9
Eu 0.1E 0. 17 0.lE 0.20 0.22 0.20 0.29 0.r4 0.14 0,19 0.18 o.26 0.r8 0.r5 rNAA r-8
Gd 2.9 6.3 0.6 2.2 2.6 6.r 3.8 4.6 8,1 6.1 9.4 6.0 9.3 I2.I INAA
Tb 0.9 o.7 0.6 0.3 0.3 0.3 0.2 L.2 r,3 1) 1' I.B L.7 II{AA
Dy 3.6 3.6 2.4 1t 7.O r0.5 10,1 rNAA
Tn O.7 0.5 0.2 1.2 0.5 0.2 0.8 0.7 0.9 0.9 0.6 0.7 0.9 0.9 rNAA 2-46
Y! 3.0 1.0 1.0 6,0 5.8 3.6 5.E 7,I 6.5 INAA
Lu 0,34 0.30 0.35 0.r5 0.17 0.13 0.r5 0.67 0.68 0.54 0.98 0.91 0.75 rNAA
2t6. 1E7. tt9. 207. 182. I73. 178. I90, 200. 7a7 IE5. 272. 27L. rNAA 1-5
Nb 83, 74. 16. 50. 55. 28, 49, 110. 120. 130. r30. 99. 58. 63. E.S, 15
b 3. 2. 9. 6. 2. 2. 2- 4. 5. E.S. 20
Hf 4.4 3.8 4.2 4.8 4.8 4.9 4.9 5,9 s.4 5.2 5.8 5,4 1.6 7. E INAA 1-13
Ta 4. 3 4.5 3.5 1.3 E,l 7.9 7.2 8.3 7.7 3.7 3.9 rNM 1-5
30. 30, 30. 30. 30. 30. 30. 30. 30. 70. 50. 30. 20. <20. E.S.
Pb 43. 46. 38. 19. 31. 31. 29. 50. 46. 46. 43. 40. 42. 4r. E,S. 15
Sb 0, 3 0.5 1,1 1.1 0.E 1.1 1.0 2.0 0.9 0.6 0.6 rNM 5-92
<1. <1, 1. <1, r, <1. 1. <1, <1. 1. 1. 5. <1. 2. Specrr.10
0.3 <0,1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.r <0.r <0.1 1.2 <0.1 <0.1 xrt 50
F 1700. 1700. 700. 1200. 1500. 500. <400, 1900. 2500. 2100. rr00, 400. L600. 1200, ELectrode L0
Th 34.0 30.2 33.6 22.8 26.l 24.3 23.4 24,3 24.L 26.4 27. O rNAA 1-r2
U 16.2 !4.7 6,3 r0.8 tr.o v.) t.6 8,3 8.4 7.7 8.4 7.3 6.6 D.N. 5
A.A. - atonlc abaorptlon, INAA - instruhental neutton actlvatlon, XRF - x-ray fluorescense, I.D. - isotope dllutlon Msa apectometry'
E.S. - quantltatlve enisslon spectrometry, Spectr. - spectrophotonetric, Electrode - speclfic 1on electrode, D.N, - delayed neutron technlque,
i BstlMted coefficl.ent of varlatlon (percent)
obsidian.B a abundanceasr ev ariable,s howingr ela- H*, K*, Ba2+,S r2+s Na+, Li+ are actived uring
tive enrichmenta nd depletion.I f Na and K abun- hydration.
dancesi n perlite are controlledb y low-temperature Two of three perlitesh ave higher fluorine abun-
ion-exchangper ocessews ith groundwater( Lipman, dancesth an coexistingo bsidiansB. asedo n analyses
1965;L ipman et al., 1969),t he chemicallys imilar of natural glassesf,l uorine concentrationsa re also
alkali and alkaline-eartehl ementsp robablya re sus- reportedt o show no change( Friedmana nd Harris,
ceptibleto the samee xchangem echanismsT.h e rate l96l) or depletion(N oblee t al., 1967\d uringh ydra-
of suche xchangeis probablyc ontrolledb y the speed tion. Documentationo f fluorine homogenity in
at which ions can diffuse through glass.T ruesdell obsidian must precedei nterpretationo f relative
(1966)m easuredio n-exchangceo nstantsin l2 natu- changesd uring hydration.O bsidiansfr om the same
ral glassesa t 25"C and documentedi ncreasesi n flow are reportedt o be remarkablyh omogeneousin
K'O/NarO ratios during glassh ydration.H e also major elementsa nd mostt racee lementso f this study,
reported increaseds electivityo f alkaline-earth-rich with respectiveco efficientos f variationo f t 5 percent
glassesf or alkaline-earthi ons. Measuredd iffusion and * 15p ercent( Borchardet t al.,l97l; Condiea nd
coefficientsfo r alkalisi n glassd ecreasien the order Li Hayslip,1 975;L aidleya nd McKay,l97l; Gorduse t
) Na ) K (Sipple,1 963;Y uskeshiraa nd Antonev, al., 1968)b, ut halogenhs aven ot beene xaminedE. llis
1967R; ybacka ndL aves,1967)R. eportedre sultsa nd and Mahon (1963,1 967)s tatet hat muchf luorinei n
the data of this paper suggeset xchangeos f the type rhyoliteg lasso ccursa s surficialc oatings.
ZIELINSKI ET AL.: MINOR-ELEMENT ABUNDANCES 429
BeoverC eek
. Obsidion
x Perlite
o Felsife I
A Felsile 2
o
lrJ
F
(l
o
z
o
I
()l
F
z Nothrop No Aguo
U
=
. Obsidion
lrl
J x Perlite
lrj
o Felsife
. Obsidion
x Perlile
o Felsile 1
A Felsite 2
o Felsile 3
Ho Er Tm Yb Lu Lo Ce Pr Nd Pm Sm Eu Gtt Tb Dy Ho Er Tm yb Lu
Fig. L Chondrite-normalized rare-earth concentrations of calc-alkalic obsidians, perlites, and felsites of this study. Bars represent
typical estimateda nalyticalp recisionf or obsidian values( 1 lo).
430 ZIELINSKI ET AL.,' MINOR-ELEMENT ABUNDANCES
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IVrOrSaO/Zt ltSllJ lrvrorsao|/ 3lrs13J
Fig. 2. Minor-element compositions of perlites and felsitesn ormalized to coexisting obsidian. Shaded areas equal to typical analytical
precision of * 10VoC. ircled points have estimated errors )3070
ZIELINSKI ET AL.: MINOR.ELEMENT ABUNDANCES 431
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Fig 2. continued.
ZIELINSKI ET AL: MINOR-ELEMENT ABUNDANCES
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Fig. 2. continued.
ZIELINSKI ET AL: MINOR.ELEMENT ABUNDANCES
+JJ
Although analytically marginally significant, Mo assimilationo f 20 percentf eldsparc an changeE u
shows relative depletions in all three perlites. Inter- abundancebsy 30p ercen(tf eldspar/meldt istribution
pretation is subject to the same restrictions as fluor- coefficien:t 2.5).T he samplea reaa t No Aqua,N ew
ine. Mexico,s howst heg reatesvta riabilityi n Eu andc on-
The variable content of Cu, Co, and Cr in perlites tains the most widely-spacesda mplingl ocalitiesI.f
and felsitesr elativet o obsidian cannot be interpreted eruption is in the sequenceo bsidian-felsitet,h e rare
becauseo f (l) increaseda nalyticalu ncertaintyd ue to eartha bundanceisn dicatet hat the moste volved( Eu
extremely low concentrations in the rhyolites, (2) depleted)l iquid eruptedf irst. The obsidian-felsite
possible inhomogeneity in the analyzeds plits for ele- suitea t No Aqua may reflectt he compositionahl eter-
ments highly concentratedi n minor phases,( 3) pos- ogeneityo f a stratifiedm agmac hamber.
siblec ontamination during crushingi n steelj aws (the One may uset he variationso f Eu to predictc om-
samples were originally prepared for other work, plementarym agmaticv ariabilityo f Sr andB a caused
without minor-elements tudiesi n mind). by feldsparf ractionationB. oth Sr and Ba are also
stronglyi ncorporatedi n feldspar,w ith typical re-
Minor-element differencesb etweeno bsidiana nd felsite
ported feldspar/rhyolitic-melt distribution coeffi-
The felsitess how consistente nrichmentso f Ba and cients( D.C.) rangingf rom 3 to 6 (Arth andH anson,
Sr, depletion of Li and Mo, and increasedv ariability 1975).M inor-elemenat bundanceisn coexistingso lid
of Cu, Co, and Cr concentrationsr elative to obsid- and liquid phasesre lativet o originalm elt arec alcu-
ians. In contrast to perlites,s ix of sevenf elsitesh ave latedf or variablev alueso f crystallizatioann d distri-
lower F contents than the correspondingo bsidians. butionc oefficient(sF ig.3 ). Onem ayc onsidevr ertical
Properties peculiar to felsites are higher concentra- tie linesc onnectintgw o curveso f similarD .C. to give
tions of Eu and consistentlyl ower concentrationso f relativea bundanceisn solid and liquid for a given
Cs and U. percentc rystallizationF.o r D.C. <5, magmaticp ro-
The minor-element variations in felsitesa re more cessesle adingt o efficients eparationo f crystalsa nd
complex than in glasses,b ecauseo f the combined melta t a givenp ercenct rystallizatiocna nnotp roduce
effects on a multiphase assemblageo f high-temper- new assemblagedsif feringf rom the originalb ulk con-
ature processes( crystal-melt fractionation,l volatile centration Co by greatert han a factor of 5. Sucha
transport) and low-temperature processes( ion ex- mechanismca ne xplaino bservedE u abundancvea ri-
change,d ifferentials olubility, absorption on second- ations,b ut valueso f percenct rystallizatiorne quired
ary phases). for Eu (D.C. : 2.5) areo ftenm arginaol r insufficient
Elemental variability causedb y crystal-melt frac- to explaino bservedr elativeS r and Ba abundance
tionation can be reflectedi n crystallines amplesf rom (D.C. : 3-6) within the sames ampleO. therp ossible
the same flow collectedo ver distancesa s small as a mechanismasf fectingB a and Sr mobilityi ncludei on
few meters (Watkins et al., 1970). The rare earth exchangeo f the type observedin perliteso r selective
elements( REE) provide a sensitivem easuremento f uptakeb y alterationp roductss ucha sc lays,z eolites,
the elemental variability caused by magmatic pro- or Ba-richm anganesoex ides( observed).
cessesT. he immobility of REE during weatheringa nd In spite of the unresolvedp roblem of fluorine
metamorphism has been documented by numerous homogeneitiyn obsidianf,l uorinei s stronglyd epleted
studies of natural suites (Frey,1969; Cullers et al., in mostf elsitesin, agreemenwt ith previouss tudieso f
1974; Philpotts et al., 1969).t nspection of Figure I crystallizedrh yolites( Noble et al., 1967 Rosholte t
shows that some felsitesh ave analytically significant al., l97l; Lipmane t al., 1969).L osso f fluorinea s a
differencesin REE, and especiallyin Eu, comparedt o gasp hased uringe ruptioni sw ell-knownf rom studies
obsidian. Eu variations can be explainedb y attribut- of volcanice manationsa nd F metasomatismn ear
ing some felsite to different eruptive episodesw hose fumaroles.L oss of halogensd uring interactiono f
compositionsr eflecte volution of the magma via ad- rhyolitea ndh ot waterw asd emonstratebdy Ellisa nd
dition or subtraction of feldspar,a major phaset hat Mahon( 1963,1967)w, ho removed3 .5p ercenot f the
shows high preference for Eu. Crystallization of 20 F and 13p ercento f the Cl from a partly crystallized
percent of a rhyolitic magma as alkali feldspar, or flow rhyolite after exposuret o aqueousv apor at
300"Cf or 24h ours.P ercentageosfh alogensre moved
I Variability of composition caused by partitioning of elements from rhyolitic pumicew eree veng reater.T he relative
betweens ilicate melt and growing crystals and crystal-melt redistri- F concentrationisn coexistingfe lsitesa nd obsidians
bution prior to and during eruption. of variablea ge( Fig. 4a) showl ittle correlationw ith
ZIELINSKI ET AL.: MINOR.ELEMENT ABUNDANCES
ro
9
6
7
TOTAL EOUILIBRIUMM ODEL
c"/co
-o'c.,:. s
I
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.;
|
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D.C .: ,.0
o.7
o4
ct
/co
o.,
o 09 08 07 0.6 03 0.4 0l 02 0.1 o
FRACTIONO F LIOUID REMAINING( F')
Fig. 3. Calculateda bundanceos f a minor elementi n solid (C") and liquid (C) phaseSre lativet o a startingc omposition( C"), as a
functiono f degreeo f crystallization(F ), for variousl arged istributionc oefficient(sD .C.). One may considerv erticalt ie linesc onnecting
C"/Co andC rlCoc urvesf or a constantD .C. to giver elativea bundanceisn solid and liquid phasesfo r a givenp ercentc rystallization.
ZIELINSKI ET AL,: MINOR.ELE]IENT ABUNDANCES
t
x
5?6
a Thi3 sludy
x Rotholl ond ofhcrt, l97l
to 20
AGE, IN MILLIONSOF YEARS
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AGEI.N TILLIONSO F YEARS
Fig. 4. Relativef luorinea nd uraniumc oncentrationisn coexistingp airso f felsitea nd obsidiano fvariousa gesa nd compositionatly pes,
(a) Fluorine( b) Uranium.