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Phase Relationships of Gabbro-Tonalite-Granite-Water at 15

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Phase Relationships of Gabbro-Tonalite-Granite-Water at 15 American Mineralogist, Volume 71, pages 301-316, 1986 Phaserelationships of gabbro-tonalite-granite-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- pyroxene, amphibole, and plagioclase.No glassescould be analyzedin the gabbro. The data provide Ko values as a function of temperaturefor pairs of coexisting minerals 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 basalt,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 syenite. INrnooucrroN ExpnnrunNTAL METHoDs One of the major chemical trends in igneouspetrology Starting materials is given by the calc-alkaline rock seriesgabbro-tonalite- (gabbro), granodiorite-granite(basalt-andesite-rhyolite). 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 Quartz 1I. 7 472 1100 5 14 cpx+r orthoclase 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 feldspar, 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.
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