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American Mineralogist, Volume 71, pages 301-316, 1986

Phaserelationships of -tonalite--waterat 15 kbar with applicationsto differentiation and anatexis

Wuu-LrlNc HuaNc Exxon Production ResearchCompany, Houston, Texas 77001 Pprnn J. Wrr-r-rn Division of Geologicaland Planetary Sciences,California Institute of Technology,Pasadena, California 9 1I 25

Ansrnncr Phase relationships have been determined at 15 kbar with variable HrO contents for three rocks-a gabbro,a tonalite, and a muscovite granite-representing the compositional trend of the calc-alkalinerock series.Experiments were conducted in 0.5-in. piston-cylinder apparatususing Ag-Pd or Pt capsules.The results obtained are acceptablerepresentations ofthe phaserelationships for elucidation ofpetrological processes.Selected runs with 5olo HrO were completed using Au capsulesto overcome the problem of iron loss, up to the temperature limit of Au, for reliable electron microprobe analysesof glass,garnet, clino- , , and .No glassescould be analyzedin the gabbro. The data provide Ko values as a function of temperaturefor pairs of coexisting and liquid. The chemical variations are usedto evaluate(l) the fractionation trends in hydrous magmasat 55 km in thickened continental crust or uppermost mantle and(2) the products ofanatexis ofthe thickened crust. At this depth, fractionation ofhydrous ,or anatexis of gabbro and tonalite or their metamorphosed equivalents, appearsto produce liquids diverging from the calc-alkalinetrend. Anatexis ofgranite producesa liquid less siliceous than itself, with some chemical characteristicsof .

INrnooucrroN ExpnnrunNTAL METHoDs One of the major chemical trends in igneouspetrology Starting materials is given by the calc-alkaline seriesgabbro-tonalite- (gabbro), -granite(basalt--). The phase Natural olivine tholeiitic basalt tonalite, and mus- covite granite were usedas startingmaterials. The chemicalcom- relationships of specific rocks in this series have been positions,clrw norms, and approximatemodes are listed in Table studied under a variety of conditions by many investi- l. The tholeiite is from a fino-grained basaltic sill in Scotland gators, commonly with applications to particular petro- (Lambert and Wyllie,1972). The tonalite from the SierraNevada geneticproblems related to the specificrocks. The exper- batholith was kindly provided by P. C. Batemanand F. C. Dodge imental resultsfor three rocks at l5 kbar are presentedin (tonalite 101, or M 127 in Piwinskii, 1973b). Field and petro- this paper in T-Xrro phase diagrams,together with a set graphic descriptionsofthe tonalite have been given by Bateman of reliable analysesof minerals and glasses. et al. (1963). The granite collected from Harney Peak, South The more general construction of the phase relation- Dakota, was kindly provided by T. T. Norton and R. T. Mc- ships for the complete rock series,representing a com- Laughlin of the U.S. GeologicalSurvey (Huang and Wyllie, 1973, rocks positional line through the componentsof igneousrocks, 1981). The chemistry of major elements in these corre- sponds closely to the calc-alkaline trend (although the granite is hasbeen addressed by Piwinskii and Wyllie (1968, 1970) of S-type). and Piwinskii (1968, 1973a, 1973b, 1975) with excess HrO at 2 and l0 kbar, by Green and Ringwood (1968) Apparatus and procedures for the anhydrous seriesat 18,27, and 36 kbar [seealso Green (1972), Green and Ringwood (1972) for the effect Experimentswere performed in a single-stagepiston-cylinder of HrO on the liquidus at high pressuresl,by Stern and apparatussimilar to that describedby Boyd and England(1960), Wyllie (1973,1978) at 30 kbar with HrO contentsfrom using a 0.5-in.-diameterpiston and chamber with hardenedsteel liner. The was calibrated for pressure and temperature 5oloto excess,and by Green ( I 982) at I 5 and 30 kbar from apparatus asdescribed by Boettcherand Wyllie (1968).Temperatures, mea- dry to excessHrO. An important petrogeneticquestion is suredwith chromel-alumel(below 850€) and Pt-PtroRh,o(above to what extent the liquid compositions within the crys- 850"C) thermocouples, were precise to +5"C and accurate to tallization intervals of gabbro and tonalite parallel the + l5'C. Furnaceassemblies were constructedfrom graphite and calc-alkalinecomposition trend, for a variety of pressures talc for mns up to 850'C, but for higher temperatures,the talc and water contents. rods were replaced by pyrex glass to avoid talc dehydration and

0003{04xi8610304{30I $02.00 301 302 HUANG AND WYLLIE: GABBRO-TONALITE-GRANITE-WATERAT l5 kbar

Table 1. Chemical analyses,crpw nonns and approximate Table 2. Results of quenchingexperiments modes for whole rocks in the present study for gabbro (DW-l) at l5-kbar pressure

cabbro, Dw-1 Tonafite I01 cranite L26

(1) Cheni@L a@L!6ea

45-91 59. 14 14-66 800 30 30 Ti02 o.94 o.79 0-03 825 4-4 23 Cpx, Hb, I A1203 17,19 18.23 15.55 4A4 a25 30 22 Lpx, rc, L Fe2O3 2. 33 2.32 0.17 451 850 30 1l Cpx, Hb, I Fe0 o.42 480 Cpx' Hb' Gt(?) + L ho o .22 0.I1 0.07 4s4 900 30 23-5 cPx, b, I '7 ugo .4A 2.50 0.02 453 925 5 34 cpx, ft, I r3. 54 5.92 o.42 452 975 23 cpx, Hb, I Na2O 1.63 3.81 4-29 456 1000 30 23.5 CPx, ft, I Kzo 0.14 2. r9 3.08 455 rO25 Cpx, ft, I Hzo+ 1.78 0.82 0.66 451 1050 30 12 Cpx, Hb(tr), L 0.04 0,04 463 1050 40 12 cpx, Hb(tr), I Pzos 0.04 0,30 0.15 461 1075 20 Lr Cpx(tr) + L cQz 0.01 o.02 46a I075 25 1l cpx(tr) + L 470 I075 25 I0 CPx(tr) + L ( 2) CfPW Mome 46I 1075 3014L 469 1075 4013L 1I. 7 472 1100 5 14 cpx+r 0.83 12.9 18. 20 476 1100 1022L AIbite 13.78 32-2 36.24 47r 1100 1523L horthite 39.14 26.2 o.98 459 1100 3072L Diopside 22.59 0.9 462 Cpx(tr), L 5-95 9.4 514L olivine 8.55 458 1200 s 1r L 3. 39 3.4 Ilmenite 0.78 1.5 0.06 488 IOOO 5 3 CPr' Hb' Ga, L Apatite 0.10 o-7 4a6 llOO 5 I cpx, Hb(?), L Corudw 4.80 485 1150 5 1 Cpx(tr), L 4811200511 (3) App"aeimate l4ade6 '7 473 1150 40 I3 Quartz ] 1020 40 22 Cpx, S(?), L a1 Lal i F-l Ac^:r 4.5 I "t.t 466 1150 40 7 PIagj-oclase 4'7 59 1040 40 25 cpx, L Augite 41 475 1200 5 9 Biotite 12.5 0.1 1050 5 25 cpx, L Horhblende 9 411 1150 15 2r Olivine 3 r050 15 24 cpx, Eb(?), L Opaques 3 2 I 47a rr50 20 6 krnet l 0.9 1050 20 cPx, L Apatite ) 479 l]so 30 9 Muscovite 1050 30 24L 414 1200 5 11 1075 23L 'l 465 r200 5 embrittlement. All runs were brought to final pressure with the "piston-out" proceduresas describedby Boyd et al. (1967).Pres- sures listed are nominal, incorporate no corrections for friction, and are consideredaccurate to +590. Crystalline rock sampleswere used in the experiments. Oxygen fugacity was not controlled. The oxidation state of the sample Identification of phases during the mn conditions should be close to the Ni-NiO buffer quenched (Allen et al., 1975). Water and (dry) powdered rock sample were Phasespresent in runs were identified using standard powder-diffraction in weighed into capsules in the required proportions, sealed, and optical and X-ray techniques, described in run at 15 kbar and selectedtemperatures. The run tableslist the previous papers on these rocks. Phases encountered include garnet,liq- HrO weighed into the capsules.The actual HrO present in a the gabbro-watersystem, amphibole, clinopyroxene, garnet, capsule during a mn was thus the total of HrO stored in the uid, and vapor deposits; in the tonalite-water system, plagioclase, quartz, vapor de- hydrous minerals of the rock, plus the HrO added. Two types of clinopyroxene, biotite, liquid, and quartz, plagioclase, runs were made to determine the phaseboundaries: (l) "single- posits; in the granite-water system, alkali- garnet, liq- stage" runs in which the crystalline rock samples were brought , muscovite, kyanite, sillimanite, corundum, directly to the desired temperatures and (2) "two-stage" runs in uid, and vapor deposits. Opaque minerals, although of interest, which the crystalline samples were held above the liquidus until were too sparse for confrdent identification. completely melted and then the temperature was reduced to the Expnnrlvrmlur, REsULTS AT 15 KBAR desired value. The first type was prevalently used in the present study while the secondwas made as a test for equilibrium. One major uncertainty in the interpretation of experimental Electron-microprobe analyses were performed on quenched results is the absorption of iron from samples by the noble-metal charges at two intervals during the present study. Early recon- capsules(Merrill and Wyllie, 1973;Stern and Wyllie, 1975;Neh- naissanceanalyses were made on an ARr-/EMxelectron-micro- ru and Wyllie, 1975). Experimentsfor the gabbro-watersystem probe analyzer at 15 kV,0.02 pA sample current, for l0 s per were first performed using Pt capsules. In order to test the effect element. The beam size was about 2 pm. The microprobe ana- of iron loss on the liquidus boundary, some additional runs with lyzer was then automated. Most of the analysesfor the present 5% HrO were performed, using AgrrPd25capsules to determine study were performed on the computerized .ornr-/er'.rxanalper, the liquidus temperature. Most runs for the tonalite-water system using standard procedures for the J. V. Smith laboratory at the were made using Ag3oPd?ocapsules. Runs for the low-iron gran- University ofChicago. The accuracyofanalyses is -r2% ofthe ite-water system were performed using Pt capsules. When the amount of major elementspresent. phase diagrams had been determined, selected runs lvere com- HUANG AND WYLLIE: GABBRO-TONALITE-GRANITE-WATERAT 15 kbar 303

I I

t I

I I

I I ll LI r200

i Hb-ouTv t I CJ roI 1000 Hb cc i\o lr + = r\ cpx O + lGal CL + = t

Hb+Cpx+02+lcal+l+v

Hb+Gpx+Pl+(L+lGal Hb+CpxaPl+(lz+lGal+U

WATERWT. % Fig. |. Phase relations of gabbro Oasal| at l5 kbar with varylng HrO contents. For definitive runs and abbreviations, see Table 2. Squaresindicate runs oflambert and Wyllie (1972). Seetext for other data sources.HrO bound in the original rock is indicated by the arrow. Only for 090 HrO is assemblagedevoid of Hb + Bi. (Ga) indicates garnet, which should be stable, but failed to nucleateexcept in Au capsules(see text). pleted in Au capsulesfor analysis of minerals and glasseswith mated from Green and Ringwood (1968). For a vapor-absent minimum iron loss, up to the temperature limit of Au. rock, with all HrO stored in amphibole, the solidus corresponds to the reaction temperature of amphibole in this assemblage, extrapolated from runs with HrO added. This temperature was Phase relationships for gabbrewater not determined, but it is probably between 1000 and ll00"C. Figure I shows the experimental results at 15 kbar for the For a rock with a free vapor phase, the solidus is at 635qC. melting relations of gabbro with 5-400/0HrO added. The H,O Plagioclase and quartz disappear, respectively, at I 5 and 40€ structurally bound in the original rock is shown by the arrow. above the solidus in the presence of excess water. The upper Near-solidus runs with excessHrO are from I-ambert and Wyllie stability boundaries for plagioclase and quartz are estimated by (1972). The definitive mns are listed in Table 2. The liquidus interpolation between the anhydrous melting relations of similar temperature of an anhydrous rock of similar composition was rock compositions (Green and Ringwood, 1968; Ito and Ken- determined by Green and fungwood (1968). The solubility of nedy, 1968)and the melting boundariesin the presenceof excess HrO in gabbro liquid at 15 kbar and 1080"C,which should be H,O. The boundaries fall steeply with increasing HrO in the given by the change of the slope of liquidus boundary, is not vapor-absent region. The runs do not define the position of the constrained. dashed boundary separating the phase fields with vapor present The subsolidus mineral assemblageat this pressurewith excess or absent. water is Ga + Hb + Cpx + Pl + Qz + V according to the results Amphibole is present from subsotdus temperature to near- of Lambert and Wyllie (1972). There are three solidus temper- liquidus temperature (1070"C) with excess HrO. In the vapor- atures, depending upon the amount of water present. For a de- absent region, lve expect the upper stability temperature of hydrated rock, the solidus temperature is about 1200€, esti- amphibole to increase slighfly with decreasingHrO content (Hol- 304 HUANG AND WYLLIE: GABBRO-TONALITE-GRANITE-WATER AT 15 kbar

1200

s0u0us

oo lllllll llt G

Hb+Cpx+Ky+[+v G .,' EI G = H 800

Hb+clx +(Ga)+ BiaKY+ t+ v 'fQrr," \<*, D (Gal+[,,'--- fil* Co,+ 0r* (G.]* Bi+ xy+ [+ V[ tr

Hb+ Gpx+ Pl+ 0z + (Gal+Bi Hb+ Cpx+ Pl+ 0z + (Ga)+Bi + V

WATERWT % Fig. 2. Phaserelations of tonalite at 15 kbar with varying HrO contents. For definitive runs and abbreviations, see Table 3. Squaresindicate runs from Lambert and Wyllie (1974). Seetext for subsoliduschanges, other data sources,and seelegend for Fig- ure 1. loway, 1973). No garnet was observedin run products using h runs with excessHrO are from Lambert and Wyllie (1974). The and Ag-Pd capsules,except in a single run (#R488) at 1000t definitive runs are listed in Table 3. The liquidus temperature with 5% HrO (Ag^Pd.). Yet garnets occur in runs from Au for anhydrous tonalite is near l250qC as estimatedfrom Green's capsuleswith 50/oHrO between 700 and 1000qC(Table 5). The (1972) study of a rock of similar composition. The liquidus tem- failure ofgarnet to nucleateunder theseconditions is well known perature drops to about 1 140"C for the vapor-absent rock (with and much reviewed (Lambert and Wyllie, 1972, 1974; Green, HrO releasedfrom amphibole and biotite), and down to 940qC 1972). The nucleation ofgarnet in Au capsulesmay be due to with excessH,O. The solubility of H,O in tonalite liquid at 15 retention of iron in the sample. (Ga) indicates regions where kbar and 950qC,which should be grven by the changein slope of garnet should be stable, despite its failure to nucleate in Pt and the liquidus boundary, is not constrained. Clinopyroxene and Ag-Pd capsules. amphibole are liquidus or nearJiquidus phaseswith excessHrO. Clinopyroxene and garnet are the near-liquidus phases for all Clinopyroxene occurs only in minor amounts except near the HrO contents (separate boundaries not distinguished). They are liquidus. In the vapor-absent region, the upper stability temper- joined by amphibole just below the liquidus with excessHrO. ature of amphibole changes little with decreasing HrO content Through more than 350{, liquid coexistswith amphibole, cli- and thereforediverges from the liquidus. Amphibole is the dom- nopyroxene,and garnet for HrO contents at least down to 5olo. inant phase down to the solidus region. The biotite-out curve rises to somewhat higher temperatures in the vapor-absent re- gion. Precisedetermination of rhe amphibole-out and biotite-out Phase relationships for tonalite-water curves at low HrO contents is highly desirable, but experimentally Figure 2 shows the experimental results at 15 kbar for the difficult. melting relations of tonalite with 5-35 wt% HrO added.The HrO The solidus at 15 kbar is within the garnet stability field and structurally bound in the rock is shown by the arrow. Near-solidus in the region of the reaction of plagioclase to jadeitic pyroxene. HUANG AND WYLLIE: GABBRO-TONALITE-GRANITE-WATERAT15 kbar 305

According to Lambert and Wyllie (1974), the subsolidusassem- Table 3. Results of quenchingexperiments for tonalite (l0l) blage with excessHrO is Pl + Qz + Hb + Bi, u.ith a trace of at l5-kbar Pressure Cpx and possible Ky, and with Ga, which failed to nucleate. ----:------Hzo Plagioclase should be replaced completely by clinopyroxene and Rm Results* garnet within a short temperature interval below the solidus. This is not indicated in Figure 2, and no nrns were completed to 444 800 5 f5 Hb, Cpx, PL Bio, KYr L generalpicture (Lambert 441** 425 5 9,6 &, cpx, P], Bio' L establish this, but the is clear and Wyllie, 4r9 850 5 24 b, cpx, Ca(tr), Pr, Bio(?)' KY(?), L 1974, Fig. l). There are three different solidus reactions and 442 475 5 9 S, cpx, @, PI' KY(?), r 4I3 925 5 12 &, cpx, G, Pl, KY(tr), L temperatures, depending on HrO content, as discussed for gab- 44r 925 5 3 6, cpx, Ga, Pl, Ky(tr), L 403 925 33 13 Eb, cPx(tr), KY' L bro-HrO. 422 940 32.7 1l I Plagioclasedisappears within 5'C above the solidus with excess 420 94A 50 1 L 429 950 20 20 6(tr), CPx, KY, I HrO, but is stable to considerably higher temperature, 950eC, 404 950 20 2l b, cpx, KY(tr), L 423 950 28 18.5 L with 50/oHrO added, and is stable to almost 1350€ in a dehy- 4I2 975 5 1 ft(?). cpx' c, I drated rock (Green, 1972).For a dehydratedandesite, quartz is 4L6 975 L4 7 2I-S cpx, I 421 975 stable to about I 150'C, 50'C below the liquidus (Green, 1972), 4L1 1000 L2I4L 402 1000 33 5 L but addition of 50/oHrO is sufrcient to lower its upper stability 4r4 1025 5 25 cpx, L temperatureto about 775'C. disappearsabout 50€ above 445*r rO25 5 3 cpx,@,l Quartz 435 102s s 3 cpx, Ga, a the solidus with excessHrO. The dashed boundary separating 410 to50 40a rloo vapor-absent from vapor-present fields is only estimated. How- 424 Lr25 0 5 cpx,l its estimated position constrains the low-temperature ends 4ra 1150 05L ever, 431 1150 0 t2 L and the curvaturesofthe plagioclase-outand quartz-out bound- 407 1150 5lal 5 18 A aries. The latter boundary has the normal concave-upward cur- 405 1200 vature (see Figs. I and 3). The unusual, retrograde shape for the 430 rooo 33 5 915 33 I7 s(tr), cpx, r plagioclase-outcurve is a consequenceof the plagioclase-clino- 43A rO50 339 pyroxene reaction near the solidus, which can be modeled in the 925 33 22 Cpx, L 42a 1050 235 systemNaAlSiO4-SiOr-HrO. 950 23lAL 425 1050 204 10 In the presenceofexcess vapor, trace amounts ofgarnet were 96s 2o,4 35 cpx(?), r observed at 15 kbar between 725 all.d 875"tCby Lambert and 433 lO50 13 11 975 13 24 Cpx' L Wyllie (1972). In the presentexperiments with Ag-Pd capsules, 432 1100 52r 1000 5 25 cPx, r garnetswere observeddown to 850qCwith 5% HrO added. The 42r 1100 amount of garnet increaseswith temperature, and near the liqui- 1025 514L phases. = dus, garnet and clinopyroxene become the dominant For ahbpetiatian see Table 2 Addi-tional abb?eoiatians: 0a However, garnet appearsin runs down to 700qCin Au capsules gonet; PL = plagioc1'ase; Bio = biotitej 4i = kAmite. with 50/oHrO (Table 5). The failure of gamet to nucleateat lower temperatures where it should be stable, denoted in Figure 2 by (Ga), was alreadydiscussed in connectionwith the gabbro-water systemand by I-ambert and Wyllie (1972). to higher temperatures. Metastable corundum forms from the breakdown ofmuscovite at 15 kbar, instead ofthe anticipated Phase relationships for granite-water AlrSiO, polymorph. Corundum, once formed metastably, per- sists indefinitely in this system, as well as in parts of the synthetic Figure 3 shows the experimental results at 15 kbar for the muscovite system (Huang and Wyllie, 1974). melting relationships of muscovite-granite with and without water added, and the results are extrapolated toward the anhydrous Phase relationships for gabbretonalite-granite-water rock composition (Huang and Wyllie, 1973, l98l). The HrO structurally bound in the muscovite granite is shown by the arrow Figure 4 comparesand combines the phase relationships for at0.66o/o.The definitive runs arelisted in Table 4. The subsolidus the rock seriesat 15 kbar with 5qoHrO. The phaseboundaries assemblage at this pressure corresponds to that of the natural have been drawn through points transferred from Figures 1, 2, rock, two ,quartz, and muscovite, with just a trace of and 3. The data of Green and fungwood (1972) on a rhyodacite garnet. with 690loSiO, were included in constnrction ofthe diagram. The The phase-boundarybetween vapor-absent and vapor-present diagram shows two liquidus piercing points bounding the garnet fields is determined by runs in Figure 3, in contrast to Figures 1 liquidus between about 60 arrd 700/oSiOr, with lowest liquidus and 2, and this gives a better estimate of HrO solubility in the temperaturenear 700/oSiOr. The effectof pressureand HrO con- liquid at about 77 5C. ln the vapor-absentregion, upper bound- tent on the liquidus profile for the calc-alkaline rock series has aries for quartz, feldspars, and garnet decreaseconsiderably with been discussedby Green and Ringwood (1968) and Stern and increasing HrO content. The muscovite-out temperature in- Wyllie (1973,1978). creasessomewhat with decreasingHrO content, as anticipated Test of equilibrium from phase relationships in synthetic mica systems (Yoder and Kushiro, 1969;Huang and Wyllie, 1974).The vapor-absentsoli- The phase diagrams in Figures l, 2, and 3 are reaction dia- dus for the beginning of reaction of Na-bearing muscovite in this grams, with phase boundaries drawn on the basis of single-stage assemblagehas been measured(Huang and Wyllie, 1981). runs using capsulesofPt and AgrrPd' for gabbro, AgroPdrofor Quartz was the liquidus phase for the biotite-granite studied tonalite, and Pt for granite. Tests for continuation or completion by Stern and Wyllie (1973, l98l), and the correspondingbound- of reaction and for the attainment of equilibrium include in- ary is shown by the heavy line in Figure 3. For the aluminous creasingrun duration and making two-stage nrns (also necessarily granite used in the present study, traces ofcorundum persisted oflonger duration) to reversethe reactions.The longer durations 306 HUANG AND WYLLIE: GABBRO-TONALITE-GRANITE-WATER AT 15 kbar

I t I I I I I I I I CJ o 1000 I trt CE I I oc ltt \l 4 = ll,l e\ o \% 0z+Ms+L 0z+Ms+[+V tu Pl+02+Ga+Ms+L+V

Pl*0r+02+Ga+Ms+[*V Pl+0r+02+Ga+Ms+V

30 WATERWT % Fig. 3. Phase relations ofgranite at 15 kbar with varying HrO contents. For definitive runs and abbreviations, see Table 4. Modified after Huang and Wyllie (1973). for enhancing the degree of reaction and testing reversibility in- excesswater (runs 240 and242 in Table 4) and with 9.5% water troduce other problems, such as increased iron loss from the addedat 25kbar (runs2l5 and2I7; HuangandWyllie,l98l). sarnple and contamination of thermocouple junctions, causing The granite-water system is notorious for its sluggish reaction drift of temperature. rates. dthough the results in Figures 1, 2, and 3 must be regarded The liquidus boundaries for gabbro-water were determined in as provisional, for the reasons stated above (similar statements three groups of runs: (l) ft capsulesin single-stage,(2) AgrrPd* could be made for most published rock-HrO studies), the results capsules in single-stage, and (3) Pt capsules in two-stage runs. with Au capsules (50/oHrO) are broadly consistent (Table 5). The definitive runs are listed in Table 2. The liquidus boundary Therefore, the diagrams are considered to be acceptable repre- determined by the first group is at 1080.,Cwith excesswater. sentationsof the phase relationships,with respectto major as- With 5oloH,O, the liquidus boundary is I l3OC, identical to that semblagesand geometricalsequences. from the second group of runs. However, the liquidus boundary The etrect of iron loss from the sample in changing the phase determined by two-stageruns is 55"C lower with 590HrO and assemblage,in addition to changingthe compositions of phases, 30"C lower with excessHrO. For the tonalite-water system, the can be seen by comparison of the results listed in Table 4 for liquidus boundaries for clinopyroxene were reversed successfrrlly selectedruns in Au capsules,with the results plotted in Figures in two-stage runs within a 25 and 50"C bracket, respectively, for I, 2, and 3. For gabbro with 5% H,O, the use of Au capsules 33 and 50/owatercontents; butno amphibole orgarnetcrystallized between 700 and l00OC produced garnet where none nucleated in these two runs in contrast with their presence in the single- with Pt capsules;garnet was also present in the 1000t run using stage runs. The diference between liquidus temperatures deter- Ag-Pd. A similar difference occurred with tonalite-5% HrO. With mined by single-stage and two-stage runs for both gabbro and Ag-Pd capsules,garnet formed only at 850€ and above,whereas tonalite is tentatively attributed to the nucleation problem, but in Au, it occurred down to 700C, the lowest-temperature run. also to the iron loss ofbulk composition from charge to capsules. No quartz occurred in the 700qCrun with Au, whereas with Ag- For the granite-water system, the upper boundary ofquartz was Pd capsules it should be present. No kyanite occurred in runs experimentally determined with a 25"C bracket at 15 kbar with \4'ith Au, whereasit was presentup to 925qCin Ag-Pd capsules. HUANG AND WYLLIE: GABBRO-TONALITE-GRANITE-WATERAT I 5 kbar 307

Table 4. Resultsof quenchingexperiments for muscovite Table 5. Selectedruns for microanalysesat l5-kbar pressure granite (L26) at 15-kbar pressure and 5oloH"O

- TemDerature H,0 added Time Ru kbbro Dw-1 *at hous 10000c 5 h Au 493 G+cpx+6+L 950.C 15 h Au 494 G+Cpx+b+L 226 600 9 Qz, M, Or, Ms, Ga 36 h Au 4A9 Ga+CPx+&+i 227 610 29 9 S, Or(tr), Ms, e, L 900'c 92, 800'c 3 days Au 49o Ga+cPx+6+L 20 Qz, Ab, re, Co(?), Ga{tr), L ?oo'c 53.5h Au 492 6+cPx+b+L 3a 16 Qz, Ab, re, Ga(tr) , t Tanalitu lAj 351 660 9 22 Qz, Ab, re, L 12 re, I Qz, I025.C AqTsPd2s 445 Ga + CFx + L 21r 660 l6 re' I Qz, 975.C A93oPd7o 4I2 G+cpx+&(?) +L 374 700 1 M, Or, re, G, I Qz, 9500C Au 609 G+CPx+L 307 700 5 4I Ab, b, Ga, I Qz, 9250C A930Pd70 44I G+S+cpx+Pl+Ky(t!) +L 3r0 700 LO 21 w, L Qz, 900'c Au 606 fr+&+Cpx+P1+L 240 425 36.3 6 I e750c AgroPdTo 442 6+S+cpx+P1+(Y(?J +L i 7oo 36. 3 16 re, L QZ, a50ec A9!0Pd?0 4a9 Ga(tr) +S+cpx+Pl+Bio(?) +Kv+L 23I 725 26 MS, L Qz, aoo.c 15 A93oPd7o 444 6+Cp*+P1+Bio+Ky+l 242 t a25 6 a000c 30 Au 602 &+ft+cPx+PI+Blo+L | 125 ls Qz, re(tr), ! 700.c 40 au 603 e+e+CPx+P1+Bio+L 2a2 750 20 re, Co(tr), I Qz, 7OO'c 63h au 610 Ga+b+cPx+P]+Bio+L 299 750 24 Qz, Ms, Co(tr), I 3a6 750 24 l2 92, re, Co, I t h Au 506 301 750 25 22 Qz, b(tr), co, f, 10000c Qz+Co+L 229 150 40 24 Ky(tr), Co, L 9500c 7 h Au 509 Qz+Co+L 395 750 43 I2 Ky(tr), Co, L 900"c 25 h Au 505 Qz+co+L 800"c 48 h Au 507 re+Pl+Qz+Co+L 293 715 22 Qz, Co, L 700"c 90 h Au 508 Ms+PI+Qz+ Ga+L 337 715 20 22 Qz{tr), Co, L Ga+L 21 Ky, Co, L 650'c 5 days + 21 h Au 5to b+P]+Qz+ 2r9 715 46 2! Ky(tr), Co, L 303 195 5 20 02, Ab, re, Co, I 257 800 0 23 Qz, Ab, Or, Ms, k 2A3 800 l5 20 Qz, co(tr), L 223 aOO 2T Co(tr), L 302 820 5 20 Qz, Ab, re(?), co, L were discard- 306 520 9 22 Qz, Co, L at different rates. Therefore, theseanalyses o Qz, I$t Ot, re(tr) ' Co(tr), Ga, L(tr) ed. 2ro 425 45 Co(tr), L 292 425 15 Qz, Co, L Runs using Au capsuleswith 50/oHrO added are listed 38a 850 3.2 18 Qz, t\b, Co, e{?), L 2AO 850 l4 20 co, I in Table 5 for gabbro, tonalite, and granite compositions 230 475 0 25 qz, Fsp, Co, Ga, L 390 875 2.7 ro.5 Qz, Fsp,6, e, L at temperaturesof 650, 700, 800, 900, 950, 1000, and 3€2 475 5 l0 Qz, Co, L 1025'C. The phase results are broadly consistent with 289 | 94O 9.5 9 { 87s 9.5 11 Qz, Co, L those shown in Figures 1,2, and 3, with the differences 2ea 900 9.5 11 Q2, Co, L 219 900 20 co, L described in the preceding section. Electron-microprobe 284 925 9.5 9 si(?), co, L 354 950 Qz, si(?), co(tr), L analyseswere performed for l0 elements(Si, Ti, Al, Cr, 241 1000 3 Qz, FsP, Co, G, L Fe, Mn, Mg, Ca, Na, and K) for garnet, clinopyroxene, 269 1000 43 Qz, Fsp, Co, I 363 1000 5 Qz, co, L amphibole, plagioclase,muscovite, and glass. For most 266 1050 42 92, Fsp, Ky(tr), Co, L 265 1100 0 47 Qz, Kyl?), Co(tr), I runs, there is considerablescatter of analysesfrom one 50r 1125 r.6 23 Qz, Co, L grain with less variation from center 502 1175 r.6 Co, L mineral to another, 263 1200 o Qz, si, L to margin of individual grains. Rangesof values and av- 1315 296 | o + 12OO 0 Co(tr?) ' I eragecompositions are plotted in Figures 6 through 10. 247 1250 0 Qz(t!) 0 Glass compositions plotted are averagesof 4 to l0 anal- 254| 1315 + r24O 0 si(tr), Co(tr), L yses. unfortunately, 249 1300 0 Co(tr), I We have eight tablesof analysesthat, cannot be fitted into this paper. Spacelimitations also Abb\eoiation,: Qz = qu@tz; Ab = albite; Ar = orthocLase; precludedetailed comparison of our analyseswith related Me = Mcaotte; Ga = gffiet; lsp = alkaLi-feldepd" eoL;'d soLution; Co = cowdn; KA = kAnite; Si = siLlimite' resultsby Green and Ringwood ( 1972),Allen and Boettcher (1978, 1983),Allen et al. (1975),and Stern and Wyllie (l 978).

Amphibole-out occurredbetween 900 and 950"Cin Au capsules, Garnet whereasa trace of amphibole may remain in the 975'C run with are plotted in Figure 64' Note the range an Ag-Pd capsule. In the granite-water system, results in Au Garnet analyses capsulesbetween 650 and 1000{ were the same as those in Pt ofresults at each temperature. Garnet synthesizedat 950qC capsules,probably becauseofthe smaller Fe content ofthe gran- contains less gtossular component in the center than in rte. the margin. Garnet synthesizedat 800€ exhibits lesszon- ing. The averagevalues in Figure 68 define a trend show- AN.ql-yrrcAr- RESULTS FRoM GoLD cApsuLE RUNS ing significant decreasein pyrope component with de- Several runs made in Pt and Ag-Pd capsules were orig- creasingtemperatures for both gabbro and tonalite. There inally selected for microprobe analyses. Figure 5A shows is also a decreaseof grossular components in garnet as the percentage ofiron loss (forglass) quenched from above rock composition becomesmore silicic from gabbro to the liquidus as a function of time. Figure 58 shows the tonalite to rhyodacite. Data for rhyodacite with 50/oHrO difference in Mg/(Mg + 2Fe) values for coexisting garnet, at 13.5kbar werereported by Greenand Ringwood(1972), clinopyroxene, and glass using Ag.oPdro and AgrrPd* cap- with garnet compositions located on the upper right-hand sules under the same conditions. Diferent phases lose iron side of the tonalite curve in Figure 68. 308 HUANG AND WYLLIE: GABBRO-TONALITE-GRANITE-WATERAT 15kbar

1400

rSKb 5WT.%r{20

GABBRO TONATITE GRANITE I t200 t t

1000 qt

E

CE u IL = F 8oo --t--- , t,

600 r, Hb+ Cpx Fsp+ 0z Pl+ oz Hb+cpr+Fsp+oz+ca+Mica+ v ! IrJ, Ga*V I +{i 40 50 60 70 80 slucAwT % Fig.4. Phaserelations of the calc-alkalinerock seriesas a function of SiO, at 15 kbar and with 50/oHrO. Rectanglesindicate the temperaturesofphase boundaries from Figures I,2, ald 3. The vapor-out boundary is situated a few degreesabove the solidus. For abbreviations, seeTables 2, 3, and,4.

0 1025c 15Kb,3h 5WlYoH20

1234 Ago As$ Pd70 As75Pd25 A9100 TIMEH()URS % As lN AsPdCAPSUTES Fig. 5. Absorption ofiron by AgroPdroand AgrrPd- capsules.(A) Percentageofiron lossin glassquenched from liquid oftonalite composition as function of time. (B) Comparison of Mgl(Mg + Fe) values for coexistinggarnet, clinopyroxene,and glassquenched from two runs differing only in capsules,AgroPdro and AgrrPdrr. HUANG AND WYLLIE: GABBRO-TONALITE-GRANITE-WATER AT 15 kbar 309

GARNET 15Kb 5%H,O Alm 60

Alm 20 Py 80 ALMANDINE Alm 60 { + SPESSARTINE) Alm 60 Gr 40; \Py 40 An 6O

PLAGIOCLASE (TONALITE} Alm 20 o Grt AsPd\\Au Py 80 u GROSSULAR MOLE% PYROPE P soo 15Kb Fig. 6. Garnetcompositions from gabbroand tonalite,par- EXCESSWATER H.O u 5 Yo tially meltedat 15kbar in Au capsules,with 50/oH,O added.(A) o- Range (B) = of analysesin eachsample. Trendlines as a function u of temperatureshown by averageanalyses. F 7oo

RIM CORE I-----l Clinopyroxene and amphibole 600 30 40 50 60 70 Clinopyroxene compositions for each run with gabbro MOLE% AnCONTENT are plotted in Figure 7. There is considerableoverlap of Fig. 8. Plagioclasecompositions from partly melted tonalite resultsfrom 700 to 1000"c. The averagecompositions for and granite with 50/oHrO at 15 kbar. (A) Individual analysesfrom each temperature are closely clustered, with no defined runs in Au capsules.(B) Average analysesfrom tonalite as a variation as a function of temperature.The averagecom- function of temperature, compared with the zoned plagioclase in position of clinopyroxene in tonalite at 1025'C has a original tonalite. Results of Piwinskii (1968) on the same rock somewhat lower Mg/(Mg + ZFe) value than that in gab- at 2 kbar with excessHrO are shown for comparison. bro. Average amphibole analysesfor gabbro and tonalite, plotted in Figure 7, are very similar. According to the Plagioclase and muscovite classificationof kake (1978), the lie closeto Plagioclase analyses for granite and tonalite runs are the boundary between magnesio-hornblendeand tscher- plotted in Figure 8A. Results for granite at 650 and 700"C makitic hornblende. remain similar to the 50/oAn in the original plagioclase

Ca2O Ca2Q 'M920 MsSO MOLE PERCENT Fe60 Fig. 7. Clinopyroxene and amphibole compositions in partly melted gabbro and tonalite in Au capsules,with 5% HrO at 15 kbar. The closedsymbols indicate the composition of amphibole in gabbro. 310 HUANG AND WYLLIE: GABBRO-TONALITE-GRANITE-WATERAT l5 kbar

Fe0 r TONAIITE 1/4Si02 1sKb5%H,O t\\ A GABNET O AMPHIBOIE ailo"l . GLASS O PTAGIOCTASE s00''i I I O GLASS I (AsPd) 9500. i t I t2- I I a-"gsoo I .."4 .{o (!'r*'o ' " 8000 o o

Na20+ l(20 Ga0 MgO+ FeO A WETGHTPER CENT B Fig. 9. Compositions of glass and crystals quenched from partially melted tonalite at l5 kbar with 50/oHrO added. All runs rvere in Au capsules, except for the open circles for glassesfrom Ag-Pd capsules. The dashed lines show the average calc-alkaline rock trend.

(Huang and Wyllie, 1973). For the tonalite, the average Glass in tonalite plagioclasecompositions (closeto clusteredanalyses de- The composition of glassesquenched from the melting spite broad ranges)show increaseofAn between900 and interval for the tonalite were measuredat 950, 900, and 800'C, and decreaseof An between 800 and 700"C (Fig. 800'C, with resultscompared with mineral analysesin the 8B). This is probably related to changesresulting from AMF and CMS diagramsof Figure 9. The glassesat 800- proximity to the albite-jadeite reaction and the retrograde 900'C contain 7 1.6-72o/o SiO 2, 3.2-4.290NarO, and 2.8- curvature ofplagioclase-out in Figure 2. Piwinskii (1968) 3.10/oKrO (cf. Table l). The runs in Au capsulesfollow determined the composition of plagioclasein the same the calc-alkalinecomposition trend quite well in the AMF tonalite at 2 kbar with excesswater and found the expected diagram, but deviate somewhat from this trend in the increase of An content with increasing temperature, as CMS diagram. The loss of iron from samplesrun in Ag- shown in Figure 8B. There is a decreaseof l-2o/o An Pd capsulesis obvious in Figure 9A. component in plagioclasefrom tonalite run in Ag-Pd cap- Ifthe differencebetween the total ofeach analysisand sules,compared with Au capsules. 1000/ois equatedto the dissolved HrO in the glasses,and Muscovite was analyzedin two granite nrns. The parag- thus to that dissolved in the original HrO-undersaturated onite componentsat 700 and 650'C were,respectively 5.9 liquid, the results indicate l2-l5o/o HrO between800 and and3.7 molo/0,in contrast to 6.7 molo/oparagonitein mus- 950"C, compared with an estimated saturation value at covite of the original granite (Huang and Wyllie, 1973). 15 kbar of l9o/o(poorly constrained in Fig. 2).

r GRANITE

15 Kb 5% H,O . GLASS O MICA O PLAGIOCLASE

Na20+ K20 Mgo Ga0 Mso WEIGHT PERCENT Fig. 10. Compositions of glass and crystals quenchedfrom partially melted granite in Au capsulesat 15 kbar with 5% HrO added. The dashed lines show the average calc-alkaline rock trend. HUANG AND WYLLIE: GABBRO-TONALITE-GRANITE-WATERAT l5 kbar 3l I

1/4.SiO2 r GABBBO 1sKb 5% H,o

A GARNET O CI.INOPYROXENE O AMPHIBOTE

MgO+ FeO WEIGHTPER CENT B Fig. 11. Compositions of crystals coexisting with liquid in partially melted gabbro in Au capsuleswith 5% HrO at 15 kbar. Gamet compositions at 1000 and 700'C are extrapolated from data measured at other temperatures (Fig. 6). The dashed lines show the average calc-alkaline rock trend.

Glass in granite in the original granite, and NarO is somewhatlower. The The compositions of glassesquenched from the melting glasscomposition has similarities with syenite. Between interval for the granite were measuredat six temperatures. 700 and 900'C, SiO, increasesto the 750lolevel, and AlrO, The analyseswere publishedby Huangand Wyllie (1981), and KrO reachgranitic levels.The NarO content increases and results are plotted in Figure 10. The glasscomposi- to the granitic level between 800 and 900"C, where the tions change fairly regularly with increasing temperature plagioclasedissolves. If the difference between the total (although the 800'C glassdeparts from the main trend). analysesand 1000/ois equated to the HrO content of the At 650 and 700"C,SiO, is in the range61.4-65.50/0, AlrO, glasses,and thus to that of the original HrO-undersatu- in the range 22.6-26.70/o(considerably higher than in the rated liquids, the results indicate that dissolved HrO original granite; Table l), KrO is about twice as high as changedfrom about I 1-130/obetween 650 and 800oC,with

BULKMItrERAL coMx)stTtoN

l[61[ * KrO MgO CaO A WEIGHT PER CENT Fig. 12. The dashed lines show the average calc-alkaline rock trend. (A) Ifliquids are assumed to lie on the dashed trend line, the bulk mineral composition must be as shown. (B) From partial modal analyses of partially melted gabbro in Au capsules at 15 kbar with 50/oadded HrO, the analyzed minerals from Figure 11 yield by calculation the bulk mineral compositions plotted as a function of temperature. The plotted liquid compositions in equilibrium with these calculated mineral assemblagesdiverge signif- icantly from the calc-alkaline trend. 3t2 HUANG AND WYLLIE: GABBRO-TONALITE-GRANITE-WATERAT 15kbar

15Kblr ci--$.q?19- -TONAL 5o/oH.O 1000 o o uJ PLAGIOCLASE ul 5 eoo k cck E uJ u o- = u 8oo o F E \. AMPHIBOLE

700 TONALITE o.5 1.O 1.5 2.O Log Na/K (ATOMICRATIO) 1OOMg/Mg + Fe (ATOM;CRATTO) Fig. 14. Variationof Na/K for coexistingliquids and crystals Au 15 kbar with HrO. The dashedand solid Fig. I 3. Variation of Mil (Me + Fe)for coexistingliquids and in capsulesat 50/o linesrepresent results for gabbroand tonalite,respectively. Ar- crystalsin Au capsulesat l5 kbarwith 5oloHrO. The dashed lines for rock and solidlines represent results for gabbroand tonalite,respec- rows showlog(Na/K) the compositions. tively.Arrows show Mg/Mg + Fe)for the rock compositions.

used to calculatethe averagemodal percentageof crystals a decreaseto about 7-80loassociated with the increased through the melting interval. Finally, these modal per- melting where plagioclaseand muscovite disappear be- centagesof the crystals and their compositions (Fig. I l) tween 800 and 900"C. According to Figure 3, aboul 22o/o were used to calculatethe liquid compositions plotted in HrO is required for saturation of the liquid at 15 kbkar. Figure l2B. The results diverge from the calc-alkaline trend in Figure l28. The maximum liquid variation that Liquid in gabbro could be produced from the calculated mineral assem- The presenceof quenchcrystals precluded reliable mea- blageslies betweenthe pair of arrows. Similaily, if it was surementof liquid composition for the gabbro.However, assumedthat the liquids lay on the calc-alkalinetrend line a mass-balancecalculation was made to determine if the in Figure I 28, the correspondingcalculation showedthat liquid compositions were close to the averagecalc-alka- the liquids could not lie on the trend in Figure l2A,. Thus, line-rock trend line. The compositions of averagegarnets, althouglr the liquid compositions are not known, it is clinopyroxenes,and amphiboles transferredfrom Figures demonstratedthat the liquid path doesnot follow the calc- 6 and 7 to Figure I I were used in the calculations. The alkaline trend. first assumptionis that the liquid compositions follow the calc-alkalinetrend in terms of the (NarO + KrOlMgO- DrsrnrnurloN oF ELEMENTSAS FUNcrroN oF FeO, as illustrated in Figure 12A; then, a seriesof cal- TEMPERATURE culations were made to determine whether the same liq- Two chemical parametersof significancein magmatic uids would also follow the trend in terms ofCaO{MgO + history are the Mg-number, representedin Figure 13 as FeOfSiO, in Figure l2B. the atomic ratio Mg/(Mg * Fe), and Na/K, represented The percentagesof liquid producedthrough the melting in Figure 14 as the log of the atomic ratio. Figures 13 and interval were point counted petrographically from the run 14 compare the values of these parametersfor the bulk products. The results are 25, 40, 52, 60, and 800/oby rock compositions of gabbro and tonalite with the values volume with 5olouncertainty, respectively, at 700, 800, derived from the analysesof minerals and glasses(plotted '7, 900, 950, and 1000"C.The percentagesofgarnet, clino- in Figs. 6, 8, and 9) through the melting intervals of pyroxene, and amphiboles could only be roughly esti- gabbro and tonalite. mated from the polished sections.The percentagesof the The Mg-numbersofgarnet (Fig. l3) arelower than those minerals in Figure I I required to keep the liquids on the of coexisting amphibole, clinopyroxene, and liquid, but calc-alkaline trend in Figure l2A, were calculated. The at high temperaturesthey are similar to or slightly lower bulk crystal composition required to yield the liquids fol- than those of the rocks; they decreaserapidly with de- lowing the trend is indicated by the open circle in Figure creasing temperature in both gabbro and tonalite. The l2A; the shaded area indicates the limited range of the variation of Mg-numbers of clinopyroxene with temper- bulk crystal composition when the maximum variation ature is small, but the Mg-numbers are much higher than ofthe trend is taken into account,giving the rangebetween the coexisting garnet and amphibole, and higher than those the pair of arrows. The bulk crystal composition was then ofthe rocks. HUANG AND WYLLIE: GABBRO-TONALITE-GRANITE-WATERAT l5 kbar JIJ

TEMPERATUREOC TEMPERATUREAC 1100 900 2.5 900 800 10 30 2.O 20 3.0 5 1.5 4 3 2.O t'o KP KD2 tn*o LnKp 0.5 1.0 1 -.--- GABBRO o.o - TONALITE """" R&c(1974) -0.5 0.5 GREEN(1977} -.-"--E&c(1979) 0 o 9.0 9.5 10.0 10.5 7.O 8.O 9.0 10.O 11.0 1/T oKxlOo 1fi oKx10a Fig. 16. The partition coefrcieRtsof Na/K and CalNa be- Fig. 15. The partition coefrcientsof Mg/Febetween coex- tweencoexisting minerals and glass as a functionof temperature istingminerals and glass as a functionof temperaturewith 50/o with 50/oHrO at 15 kbar. The dashedand solid lines are for HrO at 15 kbar.The gabbro dashedand solidlines are for and gabbroand tonalite, respectively. tonalitecompositions, respectively. The dotted and dash{ouble dot lines grve Ko valuesbetween clinopyroxene and garnetin anhydroustholeiite at 15 kbar, interpolatedfrom Raheimand partition coefrciont (K") for coexisting garnet and clino- Green(1974) and Ellis and Green (1979). The dash-dot line gives pyroxene. Our results on basaltic composition for Ko vs. Ko valuesbetween glass and garnetfrom a pelitecomposition temperatureare in good agreementwith theirs, as shown (Green,1977). in Figure 15. Note that the definition of Ko used in our study, (Mg/Fe).o./(Mg/Fe)"",is different from theirs, (Fe/ The compositions of amphibole in both gabbro and Mg)""/(Fe/Mg)"o.,but the actualK" value is the same.Ellis tonalite are similar in terms of Mg-number, which is close and Green (1979) redetermined the coefrcient by taking to the value for the gabbro, but higher than that for the the effect of Ca on the garnet-clinopyroxeneFe-Mg equi- tonalite (Fie. l3). Figures13 and 14 also show that am- librium into consideration.They derived a new empirical phibole variations in Mg-number and Na/K with tem- equation by incorporating the effectofthe Ca component perature are small. The Mg-number of the amphibole ap- in garnet. When the equation was applied to calculateKo pears to be nearly independent of bulk composition, as by using the Ca component in garnetsat 800, 900, and well as temperature. Na/K ratio, on the contrary, is sig- 950"C from our experiments, the Ko values are signifi- nificantly controlled by bulk composition. The Na/K for cantly higher than our experimentally determined data. amphibole in tonalite is slightly lower than that of the This suggeststhat some other parameter that was not tonalite, whereas amphibole in gabbro changes from identified by Ellis and Green (1979) may significantly af- slightly lower to slightly higher than that of the gabbro fect the Ko value. These unknown parameterscause the between800 and 700'C. The Na/K ratio of plagioclasein inconsistency between our data and results calculated from gabbro, considerably higher than that in tonalite, shows Ellis and Green( I 979). However, we are unableto explain little variation with temperature. why our data are consistent with those of Raheim and The Mg-numbers of successiveliquids are lower than Green(1974). the coexisting amphiboles but higher than the coexisting The partition coefficients of Mg/Fe between hydrous garnet. The Na/K ratio of liquids increasesslightly with glassand garnet of a model pelite composition at l5 kbar degreeof partial melting. (Green, 1977)also show closeagreement with our tonalite data, in spite of different bulk composition. However, the Partition coefficientsamong coexisting phases same coefrcient for Mt. Hood andesite determined by Figure l5 showsthe partition coefficientsof Mg/Fe ratio Allen and Boettcher(1983) at 900"Cand 19 kbar is sig- as a function of temperaturefor gabbro and tonalite com- nificantlylower (0.8) than ours(1.4 at 900C1andl5 kbar). positions. For gabbro, the partition coefficientsof Mg/Fe Figure 16 showsthe partition coefficientsof Na/K and betweencoexisting clinopyroxene and garnet,K": (M9 CalNa ratios as a function of temperature. The different Fe)""./(MglFe)o",and betweenclinopyroxene and amphi- partitioning of Na/K and CalNa betweencoexisting pla- bole decreasewith increasing temperature. For tonalite, gioclaseand liquid is evident. The Na/K ratio in plagro- the KD values betweenamphibole and garnet, amphibole clase is much higher than that in glass, but the CalNa and glass,and glassand garnet decreasewith increasing ratio is lower in plagioclasethan in glass.The K" of Na/K temperature. betweenplagioclase and glassand that of CalNa between Raheim and Green (1974) experimentally determined glass and plagioclasedecrease with increasing tempera- the temperature and pressuredependence of the Fe-Mg ture. In contrast to plagioclase,amphibole in tonalite has 314 HUANG AND WYLLIE: GABBRO-TONALITE-GRANITE-WATERAT 15 kbar lower Na/K and higher CalNa than the coexistingliquid. compositional range,with overall higher Mg-numbers than The K" of Na/K betweenamphibole and glassdecreases ours (Fig. l3), and on this basis they concluded that am- with increasing temperature whereas the Ko of CalNa phibole fractionation could cause iron-enrichment in between amphibole and glass increaseswith increasing magmas. However, this contradiction now appears less temperature. pronounced, since the new data of Allen and Boettcher (1983) on the samesamples, with lessiron loss,gives Mg/ Pnrnor,ocrcAr, AppLrcATroNS (Mg + Fe) values for amphibole closer to our results in The generationof magmasby differentiation of a parent Figure 13. or by partial fusion is complex and probably intermediate The variety of amphibole compositions determined in betweenequilibrium and fractional conditions. However, experimental studies, and especially those of Allen and equilibrium experimental results are required as a starting Boettcher(1978, 1983)under a variety of experimental point. Our experimentally determined phase diagrams, conditions, implies that many factors including pressure, although not representingperfect equilibrium, neverthe- water content, noble-metal capsule,and oxygen fugacity, lessdefine the phaserelationships well enoughto elucidate as well as liquid composition and temperature,may affect processes.The resultson liquid compositionsand the dis- amphibole composition. Similarly, many factors will in- tribution of elementsbetween coexisting crystals and liq- fluence amphibole composition in natural magmas. In uids are reliable, having beenmeasured for runs complete order to evaluate the actual role of amphibole fraction- in Au capsules.They provide some basis for prediction ation during magma differentiation, a detailed and sys- of the differentiation trends of hydrous basaltic and an- tematic experimental program for determination of am- desitic magmas in the deep crust or uppermost mantle phibole composition as a function of the variables is and for the products of anatexis of deep crustal rocks required. composed of gabbro, tonalite, and granite or their meta- morphic equivalents.A pressureof l5 kbar is attained at Magma differentiation at 55-km depth a depth of about 55 km in thickened crust of orogenic Although fractionation of amphibole from basaltic belts. magmamay be capableofproducing differentiatedliquids with Mg/Fe correspondingto those of the calc-alkaline Amphibole fractionation at 55-km depth trend at leastduring the early stagesofdifferentiation, our It has been suggestedthat amphibole fractionation ex- results indicate that it is not the dominant process in erts a major control on the formation and differentiation hydrous at 55-km depth. Fractionation of clino- of the calc-alkalinerock suite (e.g.,Boettcher, 1973;C,aw- pyroxene and garnet togetheris the main processcausing thorn and O'Hara, 1976).Figure l3 showsthat Mg-num- changesin composition ofhydrous basalt, becausethese bers of amphibole in gabbro (basalt)and tonalite (andes- two minerals are the liquidus phases,with subordinate ite) lie in a small range from 56 to 60 and are nearly amphibole joining them below the liquidus; these three independent of temperature and bulk composition. The minerals are coprecipitated through several hundred de- amphiboles have Mg-numbers close to those of basalt, grees (Fig. l). The analysesand calculations plotted in but much higher than those of andesite,as well as of the Figures I I and I 2 confirm that the differentiating hydrous liquids in the crystallization interval of andesite. These basalticliquid doesnot follow the calc-alkalinetrend. The Mg-numbers are in good agreementwith the values be- crystallization of clinopyroxene with high Mg-numbers tween 59 and 62 reported by Holloway and Burnham averaging70 tends to produce a liquid with high Fe/Mg, (1972) for amphibole in basalt of similar composition at but this effect is offset at least at the lower temperatures 5 and 8 kbar. by the low Mg-numbers of garnet(Fig. l3). Crystallization Ringwood (1974) usedthe data of Holloway and Burn- of amphibole controls Na/K in liquids until the low tem- ham (1972) to support his proposal that fractionation of peratureswhere plagioclasebegins to crystallize. amphibole from basaltic magmas may not cause iron- Garnet and subordinate clinopyroxeneare also the liq- enrichment in diferentiating basalt.Our resultsfor gabbro uidus minerals in crystallization of hydrous andesite(Fig. are consistentwith this conclusionas illustrated in Figures 2), joined within a small temperatureinterval by amphi- I lA and 13. However, our data demonstratein addition bole and plagioclase,with biotite and quartz appearingat that precipitation of amphibole from hydrous andesitic lower temperatures.Precipitation of clinopyroxene and magma at this depth may contribute to iron-enrichment amphibole, with Mg-numbers much higher than that of of liquids (Fig. l3). The latter conclusion is contradicted the liquids, tends to causeiron-enrichment of the liquids, by the data reported by Green (1972) on amphiboles in but garnetoperates in the other direction (Fig. 9), asshown andesite(Mg-number: 48) with 2o/otolDo/oHrO between by values of K" for Hb/glass and glass/Ga in Figure 15. 5 and 15 kbar. He reported Mg-numbers for amphibole The glassanalyses plotted in Figure 9 indicate that liquid lower than thoseplotted in Figure 13.Allen et al. (1975) compositions in the middle-temperature range approxi- and Allen and Boettcher (1978) also reported amphibole mate the calc-alkalinetrend, with slight divergencetoward analysesfrom basaltsand andesitesthrough pressureranges higher CaOl(MgO + FeO) with decreasingtemperature. including 15 kbar with H,O-CO, mixtures giving varia- The Na/K is mainly controlled by the relative amount of tions in X"ro. Their amphibole analysescovered a wide amphibole and plagioclaseprecipitating. Becauseof the HUANG AND WYLLIE: GABBRO-TONALITE-GRANITE-WATERAT 15kbar 315 very high K" for PVglass(Fig. 16), we expectthe effect of seriesof liquids with chemical variation correspondingto plagioclaseto dominate, causingdecrease of Na/K in the the calc-alkalinerock series.The glassanalyses from par- liquid with decreasingtemperature, which is consistent tially melted tonalite indicate a liquid trend with CaO/ with the glassanalyses in Figure 14. (MgO + FeO) somewhat higher than the calc-alkaline We do not expect to find granite or rhyolite magma trend. At 900'C, with a generousallowance of 50/oHrO, differentiating at a depth of 55 km, but Figures 3 and l0 the residual mineral assemblageHb + Ga + Cpx + Pl illustrate the controls on suchbehavior. Hydrous rhyolite coexistswith liquid containingT2o/oSiOr, 4.2010NarO, and liquid would precipitatequartz alone (excludingthe meta- 3.10/oKrO. Despite its high SiO, content, this does not stablecorundum) through 100"Cor more, causingdeple- correspondto a granite becausegranite under these con- tion of the liquid in SiOr, as illustrated by the glasscom- ditions would precipitate only quartz through a wide tem- positions plotted in Figure l0B. With subsequent perature interval below its hydrous liquidus (seeFig. 3). coprecipitation of plagioclase,the depletion of the liquid The evidence indicates that if magmas are generatedby in SiO, continues,with the formation of liquid similar in partial fusion of gabbro and tonalite in thickened conti- composition to syenite (Huang and Wyllie, 198l). nental crust, they do not correspond to the rocks com- posing the calc-alkaline batholiths, nor do they give rise Anatexis of lower crust, thickened to 60 km to the batholiths by fractional crystallization. It is generallyassumed that the baseof the continental The partial melting of deep granite proceedsalong a crust is composeddominantly of the metamorphic equiv- path quite different from that for tonalite and gabbro.The alentsofgabbro and tonalite, hydrated to greateror lesser alkali feldspar dissolves first, yielding a potassic liquid, extent. At compressiveplate boundaries with thickened and subsequentfusion is controlled essentially by the crust, or during the Archean when localized subduction quartz-plagioclaseboundary. The quartz volume expands might have been more prevalent, we consider also the considerablyat high water pressures,and the liquid com- prospect that granitic rocks could be carried as deep as positions coexistingwith quartz and feldspar are thus forced 55-60 km. The mineral assemblagesfor theserocks at 55- to lower SiO, contents (Huang and Wyllie, 1975).This is km depth are given in the subsolidusregions ofFigures indicated in Figure l0B. The relatively low-SiOr, high- 1,2,3, and, in combination,in Figure 4. Wyllie (1977) KrO liquids at 650 and 700'C have some characteristics reviewed the conditions for anatexisof the samerange of of syenite. rock compositions at l0 kbar, correspondingto crustal is an important component of Archean thickness of 35-40 km, concluding that HrO-undersatu- igneous activity and of some more recent calc-alkaline rated granite or rhyolite magma was the normal product batholiths. The data in this paper do not provide evidence of progressive metamorphism of many crustal rocks at for the conditions ofgeneration oftrondhjemites, but they moderate depths and that the generationof magmasless do demonstratesome conditions unsuitable for their for- siliceous required the addition of heat or magmatic ma- mation. Na/K ratios as high as 2-4 are characteristicof terial or both from the underlying mantle. . None of the hydrous glassesanalyzed in The mineralogy in a thickened crust differs from that the tonalite (Fig. la) or granite approachedthis value, and in the normal crust by the addition of the high-pressure extrapolation from the analyzedglasses through other parts minerals garnet and clinopyroxene in the gabbro and to- of the determined phaserelationships (Figs. 2 and 3) sug- nalite, but the muscovite granite retains essentially the gest that trondhjemites are not simply related to either same mineral assemblage.Wyllie (1977) reviewed the or tonalites at 15 kbar. We have no analysesof conditions for partial fusion of the rocks both with pore glassesfrom the gabbro,but within the phaserelationships fluid and without. In this paper, we consider only the at 15 kbar (Fig. l), there appearsto be a prospect that anatexisofthe rocks in the presenceofaqueous pore fluid, liquids of appropriate composition might be found at using compositions of glassesmeasured in runs with 50/o moderate HrO contents near the plagioclase-out and HrO as a possible guide to liquid paths. Unfortunately, quartz-out boundaries. Holloway and Burnham (1972) we have no glasscompositions for the gabbro, and it was and Helz (1976) analyzedglasses from partially melted difficult to obtain reliable glass measurementsnear the hydrous basaltsat lower pressures,reporting trondhjem- solidus with small fractions of melting. itic to tonalitic compositions with l5-300/omelting, 850 Anatexis ofgabbro and tonalite under theseconditions to 1000'C. involves similar minerals, with a quartz field-boundary AcxNowr,nocMENTS controlling the composition of the first liquid. The first liquids developedfrom either rock are thereforesiliceous, This researchwas supportedby the Earth ScienceSection of and probably similar in composition. Successiveliquids, the National ScienceFoundation, NSF grant EAR 84-07115. however, will follow different paths becausequartz and ExxonProduction Research Company contributed to manuscript plagioclase(with biotite) remain among the residual min- preparationcosts. erals through a wider temperature in the progressivefu- RnrnnrNcns sion oftonalite than ofgabbro. The analysesand calcu- Allen, J.C.,and Boettcher,A.L. (1978)Amphiboles in andesite lations based on Figures I I and 12 indicate that partial andbasalt: II. Stabilityas a function of P-T-f',o-for. American fusion of hydrous gabbro at this depth does not yield a Mineralogist,63, 1074-1087. 316 HUANG AND WYLLIE: GABBRO-TONALITE-GRANITE-WATERAT15 kbar

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