571

Canodian MineralogistVol. 30, pp. 571-585 (1992)

A DYNAMIC MODEL FOR GRAPHIC OUARTZ_FELDSPARINTERGROWTHS IN GRANITIC PEGMATITES

IN THE SOUTHWESTERN GRENVILLE PROVINCE

DAVID R. LENTZ. AND ANTHONY D. FOWLER

Ottawo-Carleton Geoscience Centre, and Department of Earth Sciences,The University of Ottowa, Ottowa, Ontario KIN 6Ns

ABSTRACT

During the formation of U-, Th-, Mo-, R.EE-, and Nb-bearing granitic pegmatites in the Grenville Province,conditions of crystallization were such that widespread graphic quartz-feldspar intergrowths were formed. The alkalifeldspar - quartz intergrowth is characterized by angular rods of quartz that have an irregular inner interface and aplanar outer interface with the host alkali feldspar. The quartz is interpreted to have nucleated epitactically on roughedges and corners ofalkali feldspar crystals. Rapid growth, at or near volatile-saturated conditions, resulted in quartzsaturation along the irregular melt-feldspar interface. Slow diffusion of Si and Al species (network formers) in theboundary-layer melt was likely the rate-controlling step for quartz saturation, which occurred along corners and edges,where the feldspar grew most rapidly. Diffusion-limited growth resulted in SiO2 buildup at the interface, producingoscillations from quartz-oversaturated to quartz-undersaturated conditions and thus the rhythmic quartz-feldsparintergrowths. The transition from planar, to edge, to cellular growth, and changes in the lobate inner feldspar-quartzboundary occurred in response to changes caused by crystallization that affect rates of Si-Al diffusion. Evidence ofsaturation in a volatile phase in these pegmatites indicates that water was a catalyst for feldspar growth and thatlower activities of H2O in the melt decrease Si diffusivity at the crystal interface.

Keywords: graphic texture, granophyric, growth kinetics, diffusion, granitic pegmatite, quartz, feldspar, GrenvilleProvince, Ontario, Quebec.

SOMMAIRE

Au cours de la formation de pegmatites granitiques enrichies en U, Th, Mo, Nb et les terres rares dans la provincedu Grenville dans le sud-est de I'Ontario, les conditions de cristallisation ont favorise une intercroissance graphiquede quartz et feldspath alcalin. L'intercroissance est faite de bitonnets angulaires de quartz poss6dant des interfacesinterne irr€gulilre et externe planaire par rapport au feldspath alcalin h0te. Une nucl6ation 6pitactique du quartzaurait favorisd les ar6tes rugueuses et les coins des cristaux de feldspath alcalin. Une croissance rapide, sous conditionsde saturation, ou de quasi-saturation, en phase aqueuse, aurait causd une saturation en quartz le long de I'interfaceirrdgulidre entre bain fondu et feldspath. Une diffusion lente des espbces porteuses de Si et Al, composants de latrame, d fravers la couche de liquide prds de l'interface, aurait r6gi le taux de saturation en quartz. Cette saturationa eu lieu aux coins et le long d'ar6tes, oir le feldspath a pu croitre le plus rapidement. La croissance limit6e par letaux de diffusion a men€ i un enrichissement en SiO2 A I'interface, causant des oscillations entre conditions desaturation et de sous-saturation en quartz, et donc une intercroissance rythmique de quartz et de feldspath alcalin.La transition d'une croissance le long de plans, ir une croissance le long d'arOtes, i une croissance cellulaire, et leschangements dans la morphologie de l'interface interne entre feldspath et quafiz, ont eu lieu suite ir des changementsqui ont influenc€ les taux de diffusion de Al et Si. Des signes de saturation en phase volatile dans ces pegmatitesindiquent que l'eau a agi comme catalyste pour la croissance du feldspath, et qu'une faible activit6 de I'eau dans lemagma mbne ir une diminution de la diffusivitd du Si A l'interface magma-cristal,

(Traduit par la R6daction)

Mots-cbs:texture graphique, granophyrique, cin6tique de croissance, diffusion, pegmatite granitique, quartz, feldspathalcalin, province du Grenville, Ontario, Qu6bec.

'Present address: Geological Survey of Canada, P.O. Box 50, Bathurst, New Brunswick EzA3Zl,

572 THE CANADIAN MINERALOCIST

INTRODUCTION

The graphic texture refers to the regularcuneiform intergrowth of two mineral phases,typically quartz and alkali feldspar. Thegranophyric texture is the irregular finer-grainedcounterpart of the graphic texture. Detailed tex-tural, petrographic, and chemical examination oftwenty-five samples of graphic granite pegmatitesfrom ten localities in the southwestern GrenvilleProvince has provided insight into their formation.

Numerous hypotheses have been proposed forthe formation of the graphic texture, but simul-taneous growth of quartz and feldspar near thethermal minimum, originally proposed by Vogt(1931), is considered to Qp the controllingmechanism (e.g., Barker I 970, Cern!' 197 l, Hughesl97l). Replacement of feldspar by quartz-saturatedsolutions (Wahlstrom 1939, Drescher-Kaden 1948,Augustithis 1962, Seclaman & Constantinescu1972) and, vapor-phase crystallization (Simpson1962) also have been proposed. Schloemer (1964)produced the texture by hydrothermal coprecipita-tion of quartz and feldspar. Lofgren (1971) alsoobserved the texture by devitrification of rhyoliticglass in experimental charges. Maalde (1974), Smith(1974), Walker (1976), Carstens (1983), Fenn(1986), and London et al. (L989) have proposedthat the textures are formed near the cotectic oreutectic for the system but are not necessarily anequilibrium phenomenon. Fenn (1986) and Londonet al. (1989) experimentally produced the texturefrom granitic bulk compositions within the primaryfield of K-feldspar and concluded that the textureis related to the interplay of diffusion and growthkinetics.

Graphic and granophyric textures have beeninterpreted to result from rapid crystallization atvolatile-saturated conditions (Mehnert 1968,Barker 1970, Smith 1974, Hibbard 1980, Martin1982, Shannon et al. 1982, Cernj' & Meintzer 1988,Kirkham & Sinclair 1988). Both these textures occurwithin marginal facies of pegmatite, pegmatitepods, miarolitic cavities, aplites, and are alsoassociated with hydrothermal mineralization.

This paper identifies morphological and com-positional features of the intergrowths that supporta diffusion-controlled model of growth. However,the grofih dynamics differ from those proposedby Carstens (1983) and Fenn (1986) for granophyreand the graphic texture, respectively. Theirmechanism involves short-range continuous dif-fusion of quartz- and feldspar-forming componentsto a crystallizing surface containing both minerals.Observation and interpretation of the lobategrowth-boundaries between feldspar and quartzsuggest that quartz nucleated on feldspar growth-surfaces. The effects of a dissolved and free volatile

phase are examined because there is an empiricalrelationship between the development of thegraphic texture and evidence of volatile saturationin these pegmatites.

GgoLoctceL Ssrrll.{c

The U-, Th-, Mo-, REE- and M-bearing graniticpegmatites in the southwestern Grenville Provincecontain abundant examples of a well-developedgraphic texture. In general, granitic pegmatitesform both concordant and discordant dykes in thegneisses, marbles, and amphibolites. They canattain widths of tens of meters to hundreds ofmeters and have lengths up to several kilometers.Some of the larger pegmatites are associated withmineral deposits, for example the Faradayuraniferous granitic pegmatite in Bancroft, On-tario. Figure I illustrates the distribution of samplelocalities within the Central Metasedimentary Beltof the Grenville Province. Several of the santplesof graphic granite pegmatites studied are hosted bymixed marbles, calc-silicate rocks, and paragneis-ses (samples 26, 43, 49, 52, 108 and 122), as thisstudy forms part of a larger investigation ofpegmatite-related skarns (LerLtz 1992). The remain-ing samples (57, 105, 109 and ll8) are fromdiscordant pegmatites that cut biotite-bearingquartzofeldspathic gneisses. The local geology andsetting of eight of these occurrences may be foundin Lentz (l99lb), and a brief description of themineralogy and geology of the Blue Sea Lakepegmatit;i\22) and the Perth Quarry (l 18) may befound in Sabina (1987).

The granitic pegmatites under consideratiolr arelate tectonic (1020 to 1060 Ma, U-Pb zircon;Rimsaite 1982, Easton 1986) with respect to theGrenville Orogeny (ca. 1090 Ma; Easton 1986) andwere emplaced into the Grenville rocks at pressuresand temperatures less than peak metamorphicconditions (Lentz l99lb), which is compatible withtheir generally undeformed nature (Fowler & Doig1983). 4oArl3eAr cooling curves for the Bancroftterrane of the Central Metasedimentary Belt (CMB)suggest that the pegmatites were emplaced whiletemperatures remained between 500o and 550'C(Berger & York 1981), which is consistent with thedevelopment of mineral assemblages in the ex-ogranitic skarns (Lentz l99lb, 1992). Pressureshave been estimated to be between 300 and 500MPa based on fluid-inclusion studies on theMacDonald zoned pegmatite (Peach l95l), and areconsistent with the pressure - temperature - timepaths presented by Martignole (1986). Theseconditions differ from those inferred for the peakof metamorphism (upper amphibolite facies; 650'Cand 600 to 700 MPa) for the host rocks (Davidson1986).

CRAPHIC QUARTZ-FELDSPAR INTERGROWTHS

O tu'"oto'"

Grenville ProvinceCentralMetasedimentarYBelt

Central GneissBelt

Central GranuliteTerrane

CMB bundary

a)6--\\F + t

@r.- e*tqi-t boundary

,tJ F"rrnoboundary

o Sample Numb€r

. City\town

& Lake\river

Frc. 1. Sample localities of granitic pegmatite displaying the graphic texture within the Central Metasedimentary Belt(CMB) of the southwestern Grenville Province (after Davidson 1986). BT Bancroft terrane, ET Elzevir terrane, FTFrontenac terrane, MT Mont Laurier terrane, CMBBZ Central Metasedimentary Belt Boundary Zone, C-CMZColton-Carthage Mylonite Zone, LSZ Labelle Shear Zone. Sample numbers and names: 26 MacDonald U-REE-Mopegmatite,43 Liedke Mo pegmatite,4g Legris U-REE pegmatite, 52 Belanger's Corner granite, 57 Goshen "B"U-REE pegmatite, 105 McCormack U pegmatite, 108 Armac Mo pegmatite, 109 Genesse U pegmatite, 118 PerthU pegmatite, and 122 Blue Sea Lake amazonite pegmatite. Within the inset, the black square outlines the map;CH Churchill Province, AP Appalachians.

573

GnaNttIc PEGMATITES

Granitic pegmatites are composed essentially ofqtrartz, microcline and plagioclase, with lesseramounts of biotite, amphibole, calcic pyroxene,tiianite, magnetite, zircon, allanite, calcite andfluorite. Field evidence suggests that some of theferromagnesian phases, locally concentrated alongthe contact zone, originated by a complex processof hybridization or skarnification (Satterly 1956,Shaw 1958, Masson & Gordon 1981, Haynes 1986,Lentz l99la, b). Partial melting of rocks in theCentral Gneiss Belt during post-tectonic upliftproduced H2O-undersaturated, anatectic meltsdeep within the crust (Lentz l99lb); an origin inthe lower crust or upper mantle for these melts hasalso been proposed on the basis of radiogenicisotope evidence (Fowler & Doig 1983). Fractionalcrystallization of anhydrous silicates (quartz andfeldspar) during the ascent of these melts within

the crust caused their enrichment in rare metal andvolatile components, to the point of saturation(Lentz l99lb). In addition to H2o, HF (< I wt.vo),HCI, and alkali chlorides also were constituents ofthe melt and vapor phase, based on the presenceof micas, fluorite and scapolite in and around thepegmatites (Lentz l99lb, 1992). Goad (1990) foundthat the feldspars in many of these pegmatites havetrace-element abundances characteristic of rare-metal-bearing pegmatites. These feldspars crystal-lized at temperatures above 600" to 650oC, basedon two-feldspar geothermometry (Sempels 1971,Pride 1974) and trace-element (Rb) partitioningbetween biotite and K-feldspar (Lentz & Kretz1989). This temperature is consistent with that ofthe thermal minima in the haplogranite system; thephase relations are quite comparable to those forthe Spruce Pine pegmatite at a pressure of 500 MPa(Fenn 1986, Strong 1988), although biotite is moreprevalent than muscovite in the samples studied.

574 THE CANADIAN MINERALOGIST

Pegmatite textures

Numerous textural variations occur within Gren-ville pegmatites, indicative of the variable condi-tions of crystallization. The pegmatites occur asboth zoned and unzoned types (Hewitt 1967). Mostbodies are unzoned and contain fine-grained aplitic( I m). Ferromag-nesian silicates are euhedral, whereas quartz andthe feldspar are subhedral to anhedral, except inthe core zone. Perthitic microcline is ubiquituous.Feldspar exsolution postdated the formation of thegraphic texture, as the traces of exsolution lamellaeintersect the intergrown quartz.

Description of graphic granite pegmatites

Storey & Vos (1981) have described the occur-rence of the graphic texture in 40 of the 50pegmatite deposits examined in the Bancroft-Renfrew area of Ontario. De Schmid (1916) andSpence (1932) noted that the mining of feldsparand quartz from many zoned pegmatites ceasedafter coarse- to fine-grained graphic granite peg-

matite was encountered at depth. The graphictexture is extremely variable even on outcrop scale;grain sizes range from 2 mm to greater than l0 cm(Spence 1932, Hewitt 1967, Storey & Vos 1981).The reported grain-size of the graphic texture, theaverage distance between adjacent quartz domains,varies from fine (0.25 to I mm) to coarse (greaterthan l0 mm).

The quartz forms discontinuous plates, trian-gular rods, and angular corners (arrows), whichimpart the characteristic cuneiform texture in twodimensions (Figs. 2, 3). The graphic quartz has ananhedral (irregular) inner boundary, whereas theouter boundary is euhedral (planar). This observa-lion indicates that quartz nucleated on the anhedralboundaries of the host feldspar and grew to a moreeuhedral form @ig. 3). The cuspate protuberancesare particularly obvious in the coarser-grainedvarieties of the graphic texture (Fig. 3b). In thefiner-grained samples, quartz has a saw-tooth-shaped inner surface (Fig. 3e).

Surprisingly, the irregular nature of the innersurface of the quartz does not seem to have beendocumented. This may be in part due to the lackof preservation of the irregular interface (e.9.,Smith 1974). This relationship indicates that quartznucleated onto an irregular feldspar interface andgrew to a more regular (prismatic) outer surface.The formation of feldspar protuberances into the

.

Frc. 2. Coarse-grained graphic granite pegmatite (unknown Grenville locality; 35 cmwide; GSC photo #204994).

i1,\t'-l \ R:o--j"t \ \

GRAPHIC QUARTZ-FELDSPAR INTERGROWTHS

.(

Ftc. 3. A. Tracings of coarse-grained graphic texture with irregular lobate quartz-feldspar interface (parallel to edge)(sample #105-l). B. Sketch of coarse-grained graphic texture with faceted quartz-feldspar outer interface andirregular interface (perpendicular to edge or at corner (sample #57F). C. Sketch of coarse-grained graphic granitepegmatite from Hybla pegmatite field near Bancrofr, Ontario (perpendicular to edge; Figure 10.81, Hurlbut &Klein 1977). D. Sketch of coarse-grained lobate-textured graphic granite pegmatite from Topsham, Maine (no scale)(Appalachian) (after de Schmid 1916). E. Sketch of medium-grained graphic granite pegmatite with safiooth andbarbed shaped inner quartz-feldspar margin (after de Schmid 1916).

h::H,ffffi'ffiffi

melt is a result of a change from planar(equilibrium) to cellular growth (nonequilibrium;e.9., Fenn 1986). The hook-shaped protuberancesat the feldspar-melt interface (irregular innerQtz-Kfs surface) have the appear:rnce of screw-dis-location growth in side view. Quartz saturation didnot occur until the outermost portion of thefeldspar protuberances crystallized. The bulboustips of the protuberances suggest that either l)quartz nucleated in the embayments and overgrewthe protuberances, or 2) the feldspar protuberances

extended beyond the silica-enriched zone but wereovergrown upon quartz saturation. Note added inproof: Stel (1992) documented the existence ofrugose inner feldspar-quaftz boundaries andeuhedral outer boundaries as evidence that thegraphic texture is a primary magmatic feature.

Composition of graphic granitic pegmatites

A comprehensive compilation of the chemicalcompositions of Grenville pegmatites and aplites

576 THE cANADIAN MINERALocIST

TAttLE 1. ColllPOgIlXIOn OI'GRAPEIC GRAI{ITE PES{ATITES Itt IIIIE SotlftrllEsllErur GRElnllLLE PROVII|CE

sspleTextureS1O2 f,f.STlO2A1AF€glrsocaONa2OK'ollnoPP:aotal

Bq pp0srRb

q w t . Corab&

Sepl€TextureSl,O, wt.8

"r02Al2orF'€AugocaoNe2OKrOIltnoPfrtotal

n9 n97 3 . 3 7 2 . 6

o . 0 1 0 . 0 1L4.24 14 .38

o . 0 7 0 . 1 0o . 2 4 0 . 2 L0 . 1 7 0 . 0 92 . 2 4 L . 7 99 . 6 0 1 0 . 2 80 . 0 2 0 . o 0

1 0 0 . 0 9 9 . 5

26C 438 49-I 49-2 49-3 49-4 49-5 49-6 49-7 57F 105-1ng tg cg tg og e9 ng Bg n9 ca nS7 6 . L 7 4 . 3 7 4 . 2 7 5 . 2 7 5 . 5 7 3 . 7 7 5 . 7 7 4 . 5 7 4 . 4 ? 5 . 5 7 L . 5

0 . 0 0 0 . 0 1 0 . 0 1 0 . 0 0 0 . 0 0 0 . 0 1 0 . 0 1 0 . 0 1 0 . o 0 0 . 0 0 0 . o oL4.46 13 .75 14 .00 13 .48 13 .59 ] .4 .46 13 .3A 13.33 13 .57 L2 .7A 14.10

0 . 1 7 0 . L 2 0 . 1 8 0 . 2 0 0 . 1 4 0 . 1 5 0 . 1 4 0 . 1 9 0 . 2 r 0 . 2 3 0 . 4 00 . 1 0 . 1 4 0 . 0 0 0 . 0 1 0 . t 2 0 . o 7 0 . 0 6 0 . 0 8 0 . 2 r 0 . 1 4 0 . 2 41 . 6 4 0 . 1 9 0 . 1 1 0 . 1 0 0 . 0 ? 0 . 0 9 0 . 0 9 0 . 0 9 0 . 0 7 0 . 6 5 0 . 1 16 . 2 3 2 . A 6 2 . 7 2 2 . 7 3 3 . 0 1 3 . 2 4 2 . A 9 2 . A ! 2 . 9 4 2 . 7 r 2 . s O0 . 8 5 8 . 1 1 7 . 8 8 7 . 6 7 7 . 7 1 8 . 3 1 7 . 6 1 1 . 5 7 7 . 9 2 7 . 1 1 8 . 8 2o . o o o . o o 0 . 0 0 0 . 0 0 0 . 0 1 0 . 0 0 0 . 0 1 0 . 0 0 0 . 0 1 0 . 0 1 0 . 0 10 . 0 0 0 . 0 1 0 . o 2 0 . 0 2 0 . 0 1 0 . o 0 0 . 0 1 0 : 0 3 0 . o 0 0 . 0 0 0 . 0 1

9 9 . 7 9 9 . 5 9 9 . 1 9 9 . 3 1 0 0 . 1 1 0 0 . 0 9 9 . 9 9 5 . 7 9 9 . 6 9 9 . 1 9 4 . O

22.43 22 .30 33 .54 26 .24 2a .2A 30.19 2A.O4 22.74 29 .s1 28 .94 26 .52 31 .21 22 .5456.73 50 .75 5 .08 48 .16 47 .O4 45.27 45 .56 49 .11 44 .97 44 .74 46 .81 42 .O2 52.L21S.95 15 .15 52 .21 24 .29 23 .27 23 .27 25 .47 27 .42 24 .45 23 .7A 24.A5 22 .93 2L . r5

0 . 5 5 0 . 4 5 B . I 2 0 . 7 6 0 . 4 2 0 . 3 7 0 . 2 A 0 . 3 7 0 . 3 8 0 . 2 5 0 . 3 5 1 . 7 1 0 . 4 8

105-2 108-1 LOA-2 108-3 10S-4 109-X 109-2 11S-l Lre-2 L22-L L22-2 !22-3f,g a9 cg cg ng cg cg BS ca cg cg ng7 4 . 5 7 5 . 1 7 5 . 8 7 4 . A 7 3 . 9 7 7 . O 7 4 . 7 7 2 . a 7 2 . 3 7 5 . 7 7 2 . 5 7 3 . 3

o . o o o . o 1 0 . 0 1 0 . o o 0 , 0 1 0 . 0 0 0 . 0 3 0 . 0 1 0 . 0 0 0 . o o o . o 0 0 . 0 013.70 !3 .26 13 .16 IX .74 14 .00 12 .4A 14.13 13 .90 14 .51 12 .A0 14 .33 14 .10

0 . 1 9 0 . 1 ? O . 2 0 0 . 1 5 0 . 2 4 0 . 1 6 0 . 3 2 0 . 1 8 0 . 1 2 0 . 1 1 0 . L 2 0 . O Ao . o 0 0 . 1 6 0 . 1 8 0 . 1 3 0 . L 2 0 . 0 5 0 . 2 L 0 . 0 5 0 . 1 1 0 . 0 0 0 . o o 0 . 0 00 . 2 L 0 . 4 2 0 . 7 2 0 . 1 1 0 . X 9 0 . 0 8 1 . L 7 0 . 1 5 0 . 2 6 0 . 0 9 0 . 0 6 0 . 1 82 . 2 5 3 . 6 0 3 . 7 6 4 . 1 3 3 . 9 3 1 . 8 4 s . 7 4 1 . . 8 9 2 . O O 1 . 9 4 L . 9 7 2 . O A8 . 3 6 6 . 2 7 6 . 2 L 6 . 4 9 6 . 6 5 A . 3 1 2 . O 9 9 . 8 3 1 0 . 3 0 8 . 3 0 9 . 5 5 9 . 3 90 . o 1 0 . 0 x 0 . 0 0 0 . o 0 0 . 0 L 0 . 0 1 0 . o 2 0 . 0 1 0 . 0 1 0 . 0 1 0 . o l 0 . 0 1o . o 2 0 . 0 2 0 . 0 1 0 . 0 1 0 . 0 1 0 . o o o . o o 0 . o 1 0 . 0 1 0 . o o 0 . 0 0 0 . 0 2

9 9 . 2 9 9 . 1 9 9 . 5 9 9 . 5 9 9 . 1 9 9 . 9 9 a . 4 9 8 . 8 9 9 . 6 9 S . 9 9 8 . 8 9 9 . 0

70 80 90 480 490 430 440 460 460 440 330 1380 1050L7 61 234 !77 3A3 319 344 383 351 373 350 848 49L

567 501 33 296 614 508 517 573 497 509 s38 351 6L2

180 590159 136L44 305

490 ?10 710 760 690294 506 480 49s 3969s5 22I 22L 2L9 237

Ba pp6srRb

q wt .8orabu

29.67 29 .s I 29 .A5 25 .S5 25 .2A49.4L 37 .4L 36 .88 3S-47 39 .551 9 . 0 4 3 0 . 7 2 3 1 . 9 9 3 4 . 6 9 3 3 . 5 9

0 . 9 1 t . s s o . s 3 0 . 0 0 0 . 8 8

580 140 L20 110145 30 37 32318 1247 1533 1518

3X.02 24 .L2 20 .44 33 .05 24 .50 25 .L9x2.53 5A.AO 51.34 49 .54 57 .40 56 .O249.33 16 .16 17 .31 16 .25 15 .84 L7 .77

5 . 9 0 0 . 4 3 0 . 0 0 0 . 4 5 0 . 3 0 0 . 7 6

34.2649.L71 5 . 5 7

0 . 4 0

* lfot€s: fg: fl.ne-gral.ned, mg: medlum-graLned, cg! coarse-graLned graphlc teature. Ilhe x-rayfluoregcence (Phtltps PYf 1410t atralyaea for malor- and trace el€Bents rr€re psrformed on fuseddLska at the UaLverstty of ottawa. GA and gl-2 were used as lntelaral. standards to dgternlneaccuracy, and several duplicates were used to determl.ng precLsLon. Edtlnated pteclsl.on formaJor elements: IeEs than 2t, except for na.O (3t), for trace el€B€nta, prsclslon ls lessthan 5t .

indicates an average composition near the volatile-saturated minimum or eutectic in the haplogranitesystem at approximately 400 MPa (Lentz & Kretz1989). Results of twenty-five chemical analyses ofgraphic granitic pegmatite from l0 localities (Tablel) are presented in Figure 4a. Representativesamples consisting of single feldspar crystals andtheir contained quartz intergrowths were analyzed.The samples varied from 2 to 5 kg depending onthe grain size. They contain less than I vol.9o ofadditional phases. This was confirmed by thenormative mineralogy (>99 wt.qo quartz, or-thoclase, albite, and anorthite in the norm; Tablel). The low abundance of anorthite (0 to 1.7 wt.9o)in the norm is a result of the analysis of perthiticmicrocline. Therefore, a separate plagioclase phasewas not incorporated into the graphic texture. Thesystem quartz - albite - orthoclase - HzO (Fig. 4b)is used to illustrate the phase relations because ofthe considerable experimental work published on

equilibria in the haplogranitic system. The quartz- K-feldspar intergrowths consistently fall on thefeldspar side of the cotectic. This would alsoinclude the two samples of quartz-plagioclaseintergrowths that are located in the qtrattz-saturated field if the calcic component ofplagioclase were considered. There is no obviousrelationship between the grain size of the graphictexture and composition with respect to theeutectic. The quartz-microcline intergrowths havean average quartz content of 27.0 + 1.5 wt. Vo (n: 23).

Phas e- e qui I i b r ia co n s id e ro t io ns

The transition from a granitic melt saturated inquartz and feldspar to one saturated in feldsparalone is problematic. In order for the graphictexture to grorr, it is necessary that equilibriumsaturation in quartz not occur throughout the melt;

GRAPHIC QUARTZ-FELDSPAR INTERGROWTHS 577

Frc. 4. A. The pseudoternary system quartz (Qtz) - albite (Ab) - K-feldspar (Or), showing the normative mineralogyof 23 samples of graphic granite pegmatite (this study). The squares represent coarse-grained, circles,medium-grained, and triangles, fine-grained samples. B. The estimated pseudoternary quartz (Qtz) - albite (Ab) -

K-feldspar (Or) diagram with the phase boundaries for the haplogranite system at 400 MPa P(H2O). The dotrepresents the approximate composition of the melt. The dashed-dotted line indicates the integrated evolution ofthe liquid over the course of crystallization of the graphic texture. The jagged line represents the composition ofthe boundaryJayer melt at the crystal-melt interface.

therefore, the appropriate phase-equilibriumrelationships must be considered.

At the approximate pressures and temperaturescorre$ponding to pegmatite crystallization (H2O-saturated), the quartz and alkali feldspar cotecticat 500 MPa (Luth e/ al. 1964) is located at 280/oQtz (eutectic, (650'C) to 36t/o Qtz (Qtz-Orpseudobinary eutectic, 735"C). At 300 MPa, thecotectic lies between 33i/o QIz (eutectic, 665'C) to42t/o Qtz (Qtz-Or pseudobinary eutectic, 745"C)(Tuttle & Bowen 1958). By interpolation, an alkalifeldspar composition of 0176 at 400 MPa cor-responds to 35Vo quartz along the cotectic. Theminor amount of fluorine inferred to be present,based mainly on fluorite in the associated skarnsand fluorine-rich biotite in the pegmatites, wouldreduce the liquidus and solidus temperatures in theQtz - Or - Ab system and expand the primary fieldof quartz. At a pressure of. 775 MPa, Wyllie &Tuttle (1961) noted a decrease in the volatile-saturated thermal minimum from 675o to 595'Cwith the addition of 4 wt.9o fluorine. Manning(1981) reported a substantial shift to higherproportions of feldspar with the addition offluorine at 100 MPa (volatile-saturated system).These observations suggest that similar shifts in thequartz-feldspar equilibria would occur at 4@ MPapressure with the addition of fluorine. The inferredconcentration of fluorine in the granitic melts thatcrystallized to form the Grenville pegmatites isvariable but is estimated to be less than I wt.9o.

The maximum effect on the solidus is, by analogy,on the order of 30'C, yielding a 6@'C eutectictemperature, thus enhancing the stability field ofquartz, mainly at the expense of albite.

In contrast, a decrease in the confining pressurecan displace the quartz-orthoclase cotectic, enhanc-ing the primary field of feldspar with respect tothat of q\artz. The occurrence of large alkalifeldspar phenocrysts only does not preclude quartzsaturation elsewhere in the granitic melt; however,the phase equilibria indicate that crystallization inthe feldspar field is possible under specificconditions.

A Monsl oF DyNAMIC CnvsralltzertonFOR GRAPHIC INTERGROWTHS

The observation of lobate inner boundaries onfeldspar-hosted quartz is critical @igs. 2, 3). Roughboundaries arise during conditions of high super-cooling (Woodruff 1973), when the supply ofgrowth atoms is restricted by low diffusivities ordepletion of crystallizing constituents in the bound-ary layer. This results in nonequilibrium growtt.Protuberances on the crystal face become stabilizedand grow (e.9., Nittmann & Stanley 1986). Weinterpret the appearance of the lobate innerboundary as the onset of diffusion-limited condi-tions during feldspar grofih. Feldspar-hostedquartz in graphic intergrowths has characteristicprism, arrow, and rod morphologies. Fenn (1977)

Awwre

578 THE CANADIAN MINERALOGIST

Frc. 5. Schematic three-dimensional drawings of feldspar showing three quartz intergrowths and illustrating possibletwo-dimensional morphologies of graphic texture (cross-hatched) A. Simple three-dimensional view of quartz(angles) inside host feldspar (space) B. and C. Oblique sections through quartz-feldspar intergrowth withtwo-dimensional view (cross-hatched) D. Two-dimensional view (ll0) of A wirh two-dimensional section(cross-hatched).

found that the growth morphology of feldsparchanges from equilibrium planar to skeletal growthas a function of the degree of undercooling. Crystalcorners and edges subtend a greater angle in themelt than planar crystal faces and preferentiallygrow because they have access to a greater volumeof melt. The striking patterns of the graphic textureare the result of consistent angular relationshipsbetween the intergrown quartz and the hostfeldspar crystal imposed during growth. Weinterpret them to be due to preferential nucleationand growth of quartz along corners, edges and, toa lesser extent, faces of the alkali feldspar. Theobserved narrow arrows and prisms of quartz aretwo-dimensional sections of quartz that grew alongedges of the feldspar, whereas rods represent

two-dimensional slices of edge or surface growthof quartz on the host feldspar. Figure 5 is aschematic threedimensional image of a graphicintergrofih of quartz and feldspar that illustfatesthe geometrical aspects of the grofih. Forsimplicity of design, we used a cubic rather than amonoclinic feldspar host. Note that qtJafiz(hachured) occurs along corners and edges of thefeldspar; Figure 5 illustrates a few of the possiblegeometries of quartz in feldspar. The spacingbet$,een the three sequential episodes of quartzgrowth is exaggerated in order to exemplify thethree-dimensional nature of the texture; it portraysonly the large-scale morphologies and leaves outdetails on the irregular (inner) and regular (outer)surfaces.

CRAPHIC QUARTZ-FELDSPAR INTERGROWTHS

B

579

c

BLM

4ttt

YOr Bu'lk 11elt

. - - - l>

f (H20)

+---

! a(Slo^)a zaa

tt

Flc. 6. A. Growth of alkali feldspar crystal. Shown schematically are the diffusion of rejected Si-species and H2O(solid vectors) and the diffusion of Al-species added to the crystal (hachured vectors). B. Magnification of crystaledge at corner of (A), showing grofih of protuberances (displaced diagonal hachure) to form rough boundary.The relative fugacity of water tllHzO)l and activity of silica ta(Siorl are shown in the boundary-layer melt (BLM)and bulk melt. C. Crystallization of quartz has reduced a(SiO), so that alkali feldspar crystallizes next.

II

As shown previously, grofih of the graphictexture in pegmatites of the Grenville Provinceoccurred at an approximate pressure of 4@ MPaand a rninimum melt temperature near 600oC, closeto H2O-saturated conditions. Figures 4b and 6illustrate the dynamics of growth. Alkali feldsparwas the first mineral on the liquidus. Growth ofthe feldspar in this melt required the rejection ofH2O and excess silica. An increase in dissolvedvolatiles alone should increase slightly the dif-fusivity of all feldspar components by decreasingthe degree of polymerization of the melt (Dingwell1986, Scarfe 1986). This has the effect ofincreasingrates of crystal growth. Fenn (1986) proposed thatincreased grofih occurred in response to theincreasing activity of rilater at the melt interface.Thus the net effect of the rejected H2O is to catalyzefeldspar growth in the immediate vicinity of thecrystal. Initially, this process is self-propagating,because growth will cause rejection of H2O, whichincreases the rate of growth, and so on. Depletionof Al-bearing species in the boundary layer (i.e.,Si enrichment) results from more rapid growth offeldspar and slow diffusion of Al-bearing speciesfrom the bulk melt into the boundary layer.Therefore, diffusion-limited growth of feldspararises (Fig. 6). Thus edges and corners become silesof preferred grofih, and the feldspar faces becomerough. Eventually, SiO2 builds up to saturation at

these sites, and quartz is epitactically nucleated andgrown on the feldspar structure. The growth ofquartz depletes the boundary layer in Si (Fig. 6c)relative to Al, resulting in renewed crystallizationof alkali feldspar.

Drscussror.r

The shape of quartz in graphic intergrowths ofquartz and feldspar is a function of orientation ofthe feldspar (Fersman 1928, Simpson 1962, Smith1974), as is observed here. Consistent orientationsalso have been observed by Fersman (1928),Simpson (1962) and Smith (1974). The detailedwork by Heritsch & Holler (1960) and Simpson(1962) shows that quartz rods change shape alongtheir length. Surprisingly, the irregular nature ofthe inner surface of the rod quartz had notpreviously been documented. This may be in partdue to the lack of preservation of the irregularinterface (e.9., Smith 1974). Fersman (1928) founda 42" angle between the c axes of quartz andfeldspar. Using X-ray and optical techniques,Wahlstrom (1939) found no particular orientation.However, using both X-ray and optical techniques,Heritsch (1953a, b), Heritsch & Holler (1960),Heritsch et al. (1962), choudhury et al. (1965) andBakumenko (1966a, b) confirmed several angularrelationships.

580 THE CANADIAN MINERALOGIST

We found consistent proportions of quartz tofeldspar (28 wt.7o normative quartz) in graphicpegmatites from the southwestern GrenvilleProvince (Table l). Similarly, Erdmannsdorfer(1942) found an average of 27 vol.Vo quartz and arange of l0 to 65 vol.9o quartz in quartz-microclineintergrowths. Vogt (1931) found 25 vol.Vo, whereasde Schmid (1916) determined an average 28.9 wt.Voguartz for the Lower St. Lawrence pegmatites.Cernf (1971) found similar proportions of quartzto feldspar in a study of graphic pegmatites fromCzechoslovakia. Mehnert (1968) areued that aquartz-to-feldspar ratio of. 27:73 was not com-patible with a melt on the quartz-feldspar cotectic.Within each data $et, the volume propoftion ofquartz is approximately constant, indicative of arecurrent process.

The dynamics of the proposed model are drivenby an interplay between crystal growth anddiffusion rates of rejected solutes. The diffusivityof Si- and Al-bearing species is very low inlow-temperature granitic systems (Hofmann 1980,Dunn 1986); however, the depolymerization of themelt by network modifiers (H2O and HF) reducesviscosity and increases diffusion in volatile-richgranitic melts (Scarfe 1986). The diffusivity of H2Oin obsidian and granitic melt is between l0-8 andl0-e cm2ls at temperatures between 600"C and800'C (Shaw 1974, Arzi 1978, Karsten et al.1982).The effect of depolymerization of the network ofS(AI)-O tetrahedra and coordination with OH-could considerably reduce the diffusivity of OH-in the melt and increase the diffusivity of Si andAl because of their coherent behavior. Thenucleation and growth of either quartz or feldsparat the interface may be too rapid for the rejectedHrO to diffuse into the volatile-undersaturatedmelt, and may create locally volatile-saturatedconditions at the interface. Evidence of volatilesaturation was found by Fenn & Luth (1973), whoreported the presence of fluid inclusions in quartz,in experiments at H2O-undersaturated conditions.The limiting factor in diffusion-controlled crystalgrowth is most likely the diffusion of Si away fromthe feldspar and diffusion of Al toward the feldsparinterface, since the diffusivity of potassium andsodium is considerably greater (Hofmann 1980,Dunn 1986).

Swanson (1977), Fenn (1977) and Dowty (1980)have shown that nucleation and growth curves forfeldspar shift toward the liquidus at higher volatilecontents in the melt. The formation of epitacticquartz on feldspar may be indicative of a relativelylow density of nuclei for quartz, which is expectedat very low undercoolings. Heterogeneous nuclea-tion in pegmatites, particularly along the walls, willinitiate crystal growth at low degrees of supercool-

. ing. This inference was substantiated by Fenn

(1986) and London et al. (1989), who found thegraphic texture along the walls of their reactionvessels.

Perhaps the most unusual feature of theproposed model is its oscillatory nature. Therefore,the liquid line of descent @ig. b) is distinctlydifferent from the familiar equilibrium case. Thegraphic intergrowths are a nonequilibriumphenomenon. If the crystallization were equi-librium (i.e., if the system was well mixed), onewould observe a granitic texture produced by thecrystallization of discrete crystals of alkali feldsparand quartz. It is now known that systems drivenfar from equilibrium may have an oscillatorybehavior (e.g., Nicolis & Prigogine 1989). Chemicaloscillators produce striking spatial or temporalpatterns that, in the opinion of Gray & Scott (1990),are due to an interaction of autocatalytic or thermalfeedback with the diffusive transport of moleculesin the system. The proposed model for graphicintergrowths identifies H2O as the catalyst thatchanges the diffusion properties of the melt withcrystallization. The corner and edge habit, andinner lobate boundaries of quartz, indicate that thegrowth of feldspar was diffusionJimited. Conver-sely, the euhedral outer boundaries of the quartzwith the feldspar are indicative of a return to anequilibrium style of growth (Fenn 1977). Oscilla-tions in far-from-equilibrium growth commonly arecharacterized by such growth, involving a transitionfrom stable to unstable growth of one phasefollowed by an abrupt and stable growth of adifferent phase (e.9,, Gray & Scott 1990).

The common association of graphic andgranophyric textures in granites and pegmatitesindicates that understanding the nature of themagmatic-hydrothermal transition is key to theformation of these textures. There is an increasingbody of experimental information on the phaserelations in volatile-bearing granitic magmas (melt+ crystals + vapor) (Luth & Tuttle 1969, Maalde& Wyllie 1975, Whitney 1975, L977, Naney 1983'Huang & Wyllie 1986, London et al. 1989). Thecrystallization history of granitic magmas may besignificantly affected by the original volatilecontents (amount and species).

Figure 7 illustrates in a qualitative mannet' thenature of the vapor-saturation surface in terms ofpressure, temperature, and amount of H2O for amelt of granitic composition. The crystallization ofanhydrous silicates in the melt enriches theremainder of the melt in that component bydiffusion of the volatile component away from thecrystal-melt interface (Jahns & Burnham 1969,Fenn 1977; Fig. 7, curve A), to the point ofachieving saturation in a volatile phase. Water-saturated conditions at the interface enhancefeldspar growth and result in progressively decreas-

CRAPHIC QUARTZ-FELDSPAR INTERGROWTHS581

L*V

4OO MPa

Or+LtV

o1o

E=

Eoo.EoF

800

OrrAb.e:L

ing activities of H2O in the melt away fromfeldspar-melt interface. This in turn leads to adecrease in the diffusivity of cations away from thecrystal. Therefore, factors affecting saturation andseparation of a volatile phase in the melt areimportant, in particular geostatic changes inpressure arising from emplacement of the pegmatiteand hydrofracturing associated with separation ofthe volatile phase (Fig. 7, curve B).

If the fluid is retained within the pegmatitebecause the competency ofthe rocks is not exceeded(Fig. 7, curve C), internal replacement of primaryminerals and textures would occur (London et al.1989).

Or+9tz+Ab+V

HrO wt.o6Frc. 7. Schematic representation of crystallization of a granitic melt and conditio.ns

of saturation in tire haplogranite system at 400 MPa similar to the experimentallyderived equilibria (Fenn t9SO1. fne sequence of crystallization has been modified

so that orthoclase apears on the liquidus before quartz, as explained in the text.

Curve A is the bulkJiquid line of descent at volatile-undersaturated conditionsdue to crystallization of orthoclase and intermittent saturation of quartz; curve

B is the iath of crystallization at volatile-saturated conditions, with separationof the vapor phase, and curve c is the path of volatile-saturated crystallizationfor a fluii paitially retained in the pegmatite into subsolidus conditions. within

the pegmatite, plagioclase compositions in the system are variable between albite

and oligoclase.

CoNct-usIol.ts

The physical conditions within the [J-, Mo-,REE-, ar,rd Nb-bearing granitic pegmatites ot theGrenville Province were responsible for the forma-tion of graphic quartz-feldspar intergrowths. Thespatial distribution of the graphic texture in thesepegmatite bodies, near the contact with the hostioiks, suggests that the saturation of a volatilephase during crystallization is important to under-standing their formation. The available whole-rockgeochemical data, the volume propoltions ofquartz to K-feldspar, and phase-equilibrium datain the fluorine-bearing haplogranite system favor

582 THE CANADIAN MINERALOGIST

nearly simultaneous crystallization of quartz andK-feldspar from a melt approaching the cotectictoward quartz saturation. Close observation ofthetextures reveals an irregular qvartz - K-feldsparboundary and indicates that quartz preferentiallygrew on the corners and edges of the feldspar.During feldspar growth, the area immediatelysurrounding alkali feldspar crystals becamedepleted in Al and enriched in Si. This resulted ingrofih being concentrated at crystal edges andcorners and the production of rough crystal faces(feldspar protuberances). The buildup of rejectedsilica resulted in quafiz saturation and epitacticnucleation. Growth of quartz depleted the silicaconcentrated in the boundary layer melt andrestored feldspar-saturated growth. This processrepeated and resulted in the oscillation of the meltcomposition in the boundary layer from quartz-oversaturated to quartz-undersaturated conditions,producing rhythmic quartz-feldspar intergrowths.The saturation of a volatile phase (H2O) at thefeldspar-melt interface may increase undercoolingand further reduce diffusion of Si away from thefeldspar.

AcKNowLEDGEMENTS

This work was supported by a postgraduateNSERC scholarship to D. Lentz and NSERCoperating grants to Anthony Fowler and RalphKretz. We thank Don Lentz for the computer-as-sisted drawing of the graphic texture. We acknow-Iedge the help of R. Hartree and discussions withE. Maclellan. Comments on the manuscript by P.Cernj', A.E. Lalonde and R.F. Martin, andconstructive reviews by P. Fenn and an anonymousreviewer, were particularly helpful.

RSFERENceS

ARzl, A.A. (1978): Fusion kinetics, water pressure, waterdiffusion and electrical conductivity in melting rock,interrelated. J. Petrol. 19, 153-169.

AucusrrrHls, S.S. (1962): Non-eutectic, graphic,micrographic, and graphic-like .,myrmekitic,' struc-tures and texturcs, Beitr. Mineral. Petrogr. 8,491498.

BAKUmerKo, I.T. (1966a): Regulor Quartz-FetdsparIntergrowths in Pegmatites and their Genesis. Nauka,Moscow (in Russ.).

- (1966b): Structural relation in induction graphicpegmatites. Zap. Vses. Mineral. Obshchest. 95,441447 (in Russ.).

BARKER, D.S. (1970): Compositions of granophyre,myrmekite, and eraphic granite. Geol. Soc. Am. Bull.El, 3339-3350.

BERGER, c.W. & YoRK, D. (1981): 4Arl3eAr dating ofthe Thanet gabbro, Ontario: looking through theGrenvillian metamorphic veil and implications forpaleomagnetism. Can. J. Earth Sci, 18,266-n3.

CinsrnNs, H. (1983): Simultaneous crystallization ofquartz-feldspar intergrowths from granitic magmas.Geology ll, 339-341.

6rnNV, p. (1971): Graphic intergrofihs of feldspar andquartz in some Czechoslovak pegmatites. Contrib.Mineral. Petro l. 30, 343-355.

- & MErNrzER, R.E. (1988): Fertile granites in theArchean and Proterozoic fields of rare-elementpegmatites: crustal environment, geochemistry andpetrogenetic relationships..In Recent Advances in theGeology of Granite-Related Mineral Deposits (R.P.Taylor & D.F. Strong, eds.). Can. Inst. Min. Metoll.,Spec. Vol. 39,170-207.

CHoUDHURY, J.M., Reo, M.N. & Buanracuenwa, B.K.(1965): A study of graphic granite occurring nearGolpara Town, Assam. Quart. J, Geol. Min, Metall.Soc. India 37. 9-14.

DAvIDsoN, A. (1986): New interpretations in the south-western Grenville Province.,ln The Grenville Province(J.M. Moore, A. Davidson & A.J. Baer, eds.). Geol.Assoc. Can., Spec. Pap. 31,6l-74,

or Scurrato, H.S. (1916): Feldspar in Canada. Con. Dep.Mines, Rep. 401.

DrNcwrlr-, D.B. (1986): Volatile solubiliries in silicatemelts. /n Silicate Melts (C.M, Scarfe, ed.). Mineral.Assoc. Can., Short-Course Handbook 12, 93-129.

Dowry, E. (1980): Crystal growth and nucleation theoryand the numerical simulation of igneous crystal-lization. ^In Physics of Magmatic Processes (R.B.Hargraves, ed.). Princeton University Press, Prin-ceton, New Jersey (419-485).

DnrscHrn-Kaorn, F.K. (1948): Die Feldspat-Quarz-Reaktionsgefilge der Cranite nund Gneise und ihregenetische Bedeutung. Springer-Verlag, Berlin.

DuNN, T. (1986): Diffusion in silicate melts: anintroduction and literature review. .Ir Silicate Melts(C.M. Scarfe, ed.). Mineral. Assoc. Can., Short-Course Handbook 12, 57-92.

EAsroN, R.M. (1986): Geochronology of the GrenvilleProvince. ft The Grenville Province (J.M. Moore, A.Davidson & A.J. Baer, eds.). Geol. Assoc. Can., Spec.Pop. 31, 127-173.

EnppreNNsoonFER, O.R. (1942): Studien im Gneisgebirgedes Schwarzwaldes. XIII. Uber Granitstrukturerr.Sitzb. Heidelberg Akad. Wiss. Math,-naturw. K\.2.Abh.

FrNN, P.M. (1977): The nuclearion and growth of alkali

GRAPHIC QUARTZ-FELDSPAR INTERGROWTHS 583

feldspars from hydrous melts. Can. Mineral. 15,135-161.

- (1986): On the origin of graphic granite. Am.Mineral.7l, 325-330.

- & Lu"rH, W.C. (1973) Hazards in the interpreta-tion of primary fluid inclusions in magmatic minerals.Geol, Soc, Am,, Abstr. Programs 5, 617.

FERsMAN, A.E. (1928): Die Schriftstruker der GranitPegmatite, und ihre Entstehung, Z. Kristallogr. 69,77-tM.

FowlEn, A.D. & Dorc, R. (1983): The age and origin ofGrenville Province uraniferous granites and peg-matites. Can. J. Earth Sci. 20,92-104.

Goao, B. (1990): Granitic pegmatites of the Bancroftarea, southeastern Ontario. Ont, Geol. Sum., Open-File Rep.57L7.

Cnev, P. & Scott, S.K. (1990): Chemical Oscillationsand Instabilities: Non-Linear Chemical Kinetics.Oxford University Press, Oxford, England.

HAvNEs, S.J. (1986): Metallogenesis of U-Th, GrenvilleSupergroup, Peterborough County, Ontario. /n TheGrenville Province (J.M. Moore, A. Davidson & A.J.Baer, eds.). Geol. Assoc. Can., Spec, Pap, 31,27t-280.

HemrscH, H. (1953a): Die Verteilung von Rechts- undLinksquarzen Schriftgraniten. Tschermaks Mineral.Petrogr. Mitt. 3, l15-125.

(1953b): Rcintgenuntersuchungen anSchriftgraniten, Tschermoks Minerol. Petrogr. Mitt.3, tzat4t.

- & Holrcn, H. (1960): Untersuchungen anstengeligem Quarz eines Schriftgranites von Zwiesel,Bayern. Tschermaks Mineral. Petrogr. Mitt.7,200-203.

Peul-rrscH, P. & Hdlrcn, H. (1962): UberSchriftgranitquarze. Tschermaks Mineral, Petrogr,Miu. E, 152-165.

HEwrrr, D.F. (l%7): Pegmatite mineral resources ofOntario, Ont. Dep, Mines, Indwt. Mineral Rep.2l.

Hraaeno, M.J. (1980): Indigenous source of late-stagedikes and veins in granitic plutons. Econ. Geol.75,4t0423.

HoFMANN, A.W. (1980): Diffusion in natural silicatemelts: a critical review. ft Physics of MagmaticProcesses (R.8. Hargraves, ed.). Princeton UniversityPress, Princeton, New Jersey (385417).

HUANG, W, & Wvllre, P.J. (1986): Phase relationshipsof gabbro-tonalite-granite-water at 15 kbar with

application to differentiations and anatexis. Am.Mineral.71, 301-316.

HucuEs, C.J. (19?l): Anatomy of a granophyre intrusion.Lithos 4, &3415.

Hunrsur, C.S., Jn. & KlerN, C. (1977\: Manual ofMineralogy (l9th ed.). John Wiley and Sons, NewYork.

JeHNs, R.H. & BunNuau, C.W. (l%9): Experimentalstudies of pegmatite genesis. I. A model for thederivation and crystallization of granitic pegmatites.Econ. Geol. A,843-864.

KARSTEN, J.L., HoLLowAv, J.R. & DeLeNBv, J.R. (1982):Ion microprobe studies of water in silicate melts:temperature-dependent water diffusion in obsidian.Earth Planet. Sci. Lett. 59,420428.

KTRKHAM, R.V. & Stucretn, W.D. (1988): Comb quartzlayers in felsic intrusions and their relationship toporphyry deposits. ft, Recent Advances in the Geologyof Granite-Related Mineral Deposits (R.P. Taylor &D.F. Strong, eds.). Can. Inst. Min. Metall., Spec. Vol.39, 50-71.

LENrz, D. (l99la): Radioelement distribudon in U-Th-Mo, and rare-earth element pegmatites, skarns andveins of the Grenville Province, Ontario and Quebec.Can. J. Earth Sci.2E, l-12.

(l99lb): U-, Mo, and REE-bearing pegmatites,skarns, and veins of the Central Metasedimentary Belt,Grenville Province, Ontario. Geol. Assoc. Can. -

Mineral Assoc. Can., Field Trip Guidebook A9.

- (1992\. Petogenesis of U-, Th-, Mo-, andREE-Beorins Pegmatites, Skarns, and Veins in theCentral Metosedimentary Beh of the GrenvilleProvince, Ontario ond Qtebec. Ph.D. thesis, Univ'of Ottawa, Ottawa, Ontario,

- & Knr-rz, R. (1989): Preliminary study of thepetrogenesis of uranium-, molybdenum-, RdE-bearinggranite pegmatites in the CMB of the GrenvilleProvince. Geol. Assoc. Con. - Mineral. Assoc. Can.,Progrom Abstr. 14, 434.

LoFcREN, G.E. (1971): Experimentally produceddevitrification textures in rhyolitic glass. Geol. Soc.Am. Bull. 82, lll-124.

LoNooN, D,, MoRcAN, G.8., VI, & Henvtc, R.L. (1989):Vapor-undersaturated experiments with Macusaniglass + H2O at 2@ MPa, and the internaldifferentiation of granitic pegmatites. Contrib,Mineral. Petrol. 102, l-17.

LurH, W.C., JenNs, R.H. & T'trrnE, O.F. (1964): Thegranite system at pressures of 4 to l0 kilobars. ,/.Geophys. Ras. 69, 759-773.

& Turrre, O.F. (1969): The hydrous vapour phase

584 THE CANADIAN MINERALOGIST

in equilibrium with granite and granite magmas. /rIgneous and Metamorphic Ceology (L.H. Larsen, M.Prinz & V. Manson, eds,). Geol. Soc. Am., Mem.115, 513-548.

MAAL@E, S. (1974): The crystallization of simplepegmatites in the Moss area, southern Norway. Nors/<Geol. Tidsskr. 54, 149-167 .

- (1985): Principles oflgneous Petrology. Springer-Verlag, New York.

& Wvrur, P.J. (1975): Water content of a granitemagma deduced from the sequence of crystallizationdetermined experimentally with water-saturated con-drtions. Contrib, Mineral. Petrol. 52, 175-191.

MANNINc, D.A.C. (1981): The effect of fluorine onliquidus phase relationships in the system Qz-Ab-Orwith excess water at 1 kb. Contrib. Minerol. Petrol.76,206-2t5.

MARTIGNoLE, J. (1986): Some questions about crustalthickening in the central part of the GrenvilleProvince. ft The Grenville Provine (J.M. Moore, A.Davidson & A.J. Baer, eds.). Geol. Assoc. Can., Spec.Pap. 31,328-339.

MARrlN, R.F. (1982): Quanz and feldspars...In GraniticPegmatites in Science and Industry G. ternf, ed.).Mineral. Assoc, Can,, Short Course Handbook I,4t-62.

MAssoN, S.L. & GoRDoN, J.B. (1981): Radioactivemineral deposits of the Pembroke-Renfrew arca. Ont.Geol. Surv., Mineral. Dep. Circ, 23.

MEHNERT, K.R. (1968): Migmotites and the Origin ofGranitic Rocks. Elsevier, New York.

NANEv, M.T, (1983): Phase equilibria of rock-formingferromagnesian silicates in granitic systems. Am. J.Sci. 2E3,993-1033.

Ntcorrs, G. & PRrcoclNr, I. (1989): Exploring Com-plexity: An Introdu$ion. W.H. Freeman and Com-pany, New York.

NrrrMANN, J, & SraNlrv, H.E. (1986): Tip splittingwithout interfacial tension and dendritic growthpattems arising from molecular anisotropy. Nalare32r,663-668.

PEACH, P.A. (1951): Geothermometry of some pegmatiteminerals of Hybla, Ontario. J. Geol. 59, 32-38.

PRTDE, C. (1974): Geology of Goldwin, Pontiac County,P.Q. B.Sc. thesis, Univ. Ottawa, Ottawa, Ontario.

RIMSAITE, J. (1982): Mineralogical and petrochemicalproperties of heterogeneous granitoid rocks fromradioactive occurrences in the Grenville StructuralProvince, Ontario and Quebec. 1n Uranium in

Granites (Y.T. Maurice, ed.). Geol. Sun. Con., Pap.81-23, 19-30.

SABTNA, A.P. (1987): Rocks and minerals for thecollector, Hull-Maniwaki, Quebec; Ottawa-Peter-borough, Ontario. Geol. Surv, Con., Misc. Rep. 41.

Serrrnlv, J. (1956): Radioactive mineral occurrences inthe Bancroft area. Ontario Dep. Min, LXV(6).

SCARFE, C.M. (1986): Viscosity and density of silicatemelts. /n Silicate Melts (C.M. Scarfe, ed.). Mineral.Assoc. Can,, Short Course Hondbook 12,36-56.

ScHroeven, H. (1964): Synthetic hydrothermal cocrystal-lization of orthoclase and quartz. IL lnvestigation inthe system K2O-AI2O3-SiO2-H2O. Geochem. Int.,599-612.

Srclauau, M. & CoNsraNrrurscu, E. (1972):Metasomatic origin of some micrographic inter-growths. Am. Mineral. 57, 932-940.

Seurrrs, J. (1971): Geology and Mineralogy of theLachaine Granite pegmotite, Wakefield Twp.,Quebec, B.Sc. thesis, Univ. Ottawa, Ottawa, Ontario.

SHANNoN, J.R., Warren, B.M., CARTEN, R.B. &cERAcHry, E.P. (1982): Unidirectional solidificationtextures and their significance in determining relativeages of intrusions at the Henderson mine, Colorado.Geology 10,293-297.

SHew, D.M. (1958): Radioactive mineral occurrences ofthe Province of Quebec. Quebec Dep. Min., Geol.Rep. 80.

SHAw, H.R. (1974): Diffusion of H2O in granitic liquids.1. Experimental Data, In Geochemical Transport andKinetics (A.W. Hofmann, B.J. Giletti, H.S. Yoder,Jr. & R.A. Yund, eds.). Carnegie Inst. Washington,Publ. 634,139-170.

Srursor, D.R. (1962): Graphic granite from the Ramonapegmatite district, California. Am. Mineral, 41,I 123-l 138.

Surru, J.V. (1974): Feldspar Minerals. 2. Chemicat andTextural Properties. Springer-Verlag, New York.

SpENcE, E. (1945): Myrmekite in graphic granite and invein perthite. Mineral. Mag tl,79-98.

:SrbNcr, H.S. (1932): Feldspar. Can. Dep. Mines, Mines

Branch Publ. 731.

SrEr, H. (1992): Diagnostic microstructures for primaryand deformational quartz rods in graphic granite. Am.Mineral. 77, 329-335.

SroREy, C.C. & Vos, M.A. (1981): Industrial mineralsof the Pembroke-Renfrew Area 2. Ontario Geol.Sun., Mineral. Dep. Circ, 22.

GRAPHIC QUARTZ-FELDSPAR INTERGROWTHS 585

SrRoNo, D.F. (1988): A review and model for granite-re-lated mineral deposits. /rc Recent Advances in theGeology of Granite-Related Mineral Deposits (R.P.Taylor & D.F. Srrong, eds.). Car. Inst. Min. Metall.,Spec. Vol. 39,424445.

SweNsoN, S.E. (1977): Relation of nucleation andcrystal-growth rate to the development of granitictextures. Am, Mineral, 62,96G918.

Turu-E, O.F. & BowEN, N.L. (1958): Origin of granitein light of experimental studies in the systemNaAlSi3Os - KAlSi3O8 - SiO2 - H2O. Geol. Soc. Am.,Mem.74.

Vocr, J.H.L. (1931): Die Genesis der Granitephysikochemisch Gedeutet. Z. deutsche Geol. Ges. E3,t93-2t4.

WeuLsrnou, E.E. (1939): Graphic granite. Am. Minerol.u,68t-698.

WALKER, R. (1976): The Origin of Quartz-Feldspar

Grophic Intergrowths. Ph.D. thesis, Michigan StateUniv,, East Lansing, Michigan.

WHrrNEy, J.A, (1975): The effects of pressure, tempera-ture and Xg26 on phase assemblage in four syntheticrock compositions. J, Geol, E3, l-32.

- (1977): A synthetic model for vapour generationin tonalite magmas and its economic ramifications.Econ. Geol. 72,68G690.

WooDRUFF, D.P. (1973): The Solid-Liquid Interfoce.Cambridge University Press, Cambridge' U.K.

WyLLrE, P.J. & TurrLE, O.F. (1961): Experimentalinvestigation of silicate systems containing two volatilecomponents. II. The effects of NH3 and HF, inaddition to H2O, on the melting temperatures of albiteand granite. Am. J, Sci, 259, 128-143.

Received January 29, 1991, revised manuscript occeptedFebruary 7, 1992.