Agpaitic and Miaskitic Nepheline Syenites of The

Canadian Minelalogist Vol. 28, pp.25l-266 (1990)

AGPAITIC AND MIASKITIC NEPHELINESYENITES OF THE MCGERRIGLEPLUTONIC COMPLEX. GASPE, OUEBEG: AN UNUSUAL PETROLOGICALASSOCIATION*

GRAEME M. WALLACE Depaftmentof GeologicalSciences, McGill University,3450 UniversityStreet, Montreal, QuebecH3A 2A7 JOSEPH B. WHALEN GeologicalSumey of Canado,601 Booth Strcet, Ottawa,Ontario KIA 0E8

ROBERT F. MARTIN Department of Geological Sciencesand Mineral Exploration ResearchInstitute, McGill University, 3450 UniversityStreet, Montreal, QuebecH3A 2A7

ABSTRAcT dansun r€servoircrustal pourrait avoir fourni le flux de chaleurrequis pour une fusion partielle du protolithedes The dominantly granitic Early Devonian McGerrigle plu- rochesgranitiques. Cette hypothbse explique Ia miseen place tonic complex, in the Gasp6region of Quebec,contains demagmas contemporains sous-satur6 et sursaturden silice minor volumesof 1) miaskitic and 2) sodalite- aenigma- dansle massifde McGerrigle. Ce sch6ma requiert une cham- tite - astrophyllite - arfvedsonite-bearingagpaitic nephe- bre magmatiquetrCs stable, donc un milieu en extension line syenites. Significant mineralogical variations in these le long d'un rift ou d'unefaille transformante. rocks principally reflect the aepaitic index andflO) of the magma,These geochemically highly evolvedundersaturated Mots-clds:sy6nite n6ph6linique, miaskitique, agpaitique, rocks probably representthe products of fractionation of granite,contamination crustale, complexe de McGer- mildly alkaline mafic magma(s). Isotopic data imply that rigle,Gaspdsie, Qu€bec. batchesof juvenile syenitic magma were variably contami- nated by minor volumes of crustal material. Fractionation of mafic magmasin a crustal reservoir could have supplied INTRODUCTION heat to partially melt the protolith of the granitic rocks. This proposal accounts for the contemporaneoussupply The nephelinesyenites of the generallygranitic of silica-undersaturatedand silica-oversaturatedrock-types McGerrigle plutonic complex, Gasp6 Peninsula, in the McGerrigleplutonic complex.Our proposalis con- (Fig. l; Whalen 1987)constitute the only with a very stable magma chamber, as would be Quebec sistent known exampleof silica-undersaturatedfelsic mag- expectedin a tensional environment, possibly associated with rifting or strike-slip faulting. matism of Devonian age in the Canadian Ap- palachians(Currie 1976,Woolley 1987).The associ- Keywords: nepheline syenite, miaskitic, agpaitic, granite, ation in the McGerrigle complex of small volumes crustal cont.rmination, McGerrigle complex, Gasp6, of both agpaitic and miaskitic nephelinesyenite with Quebec. largevolumes of granite and lesservolumes of gabbro (Whalen 1987)is petrologicallyhighly unusual. SOMMAIRE In this paper, we present new mineralogical and geochemicaldata bearing on the nature and petro- plutonique Mccerrigle, en Gasp6- Le complexe de situ6 genesisof theserocks. Where usedwithout a quali- sie (Qudbec),d'6ge d6vonienpr€coce et i cardctbresurtout granitique, contient de petites quantit€s de sy6nitesn€ph6- fier, "nepheline syenite" will refer to both agpaitic liniques miaskitique et agpaitique (association de sodalite and miaskitic varietiesof nephelinesyenite. + aenigmatite + astrophyllite + arfvedsonite). Lesvaria- tions min6ralogiquesimportantes dans cesroches reflbtent surtout I'indice d'agpaicitd et la fugacit6 d'oxygbne du GsNsRAr GeoLocY AND PETRocRAPHY magma. Cesroches sous-satur6s fortement 6volu€esr6sul- teraient du fractionnement de magma(s) mafique(s) l6gb- The McGerrigle plutonic complex, which intrudes rement alcalin(s). Les donn€esisotopiques t6moipent aussi the Cambro-Ordovician Shickshock and Quebec d'une contamination locale du magma sydnitique juvdnil groups (de Rdmer 1977),hasbeen subdivided into par la cro0te. Le fractionnement de magma(s) mafique(s) two suites, a predominantly northern hybrid suite *GeologicalSurvey of CanadaContribution Number 34789. (Fig. 1), with which the undersaturatedrock$ are Mineral Exploration ResearchInstitute contribution num- associated,andagranitic suitein the southernpart ber A9031. (Whalen1985, 1987). The hybrid suiteexhibits a het- 251

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FIG. l. Location of the McGerrigle Plutonic Complex, GaspdPeninsula, and a generalizedgeological map of the area giving locations of the nephelinesyenite samples studied in detail (closedcircles). Sample 16 (WXMGI6) consists of miaskitic nephelinesyenite, whereas the others consistof agpaitic nephelinesyenite, exposed as dykes or sills. The triangles correspondto the main peaks in the McGerrigle Mountains.

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TABLE 1. !,{INERTIO€Y AND IdODAI, CO{POSIf,XON OT SAUPLES OF erogeneousappearance on both the outcrop and NEPHSLINE SYENITE FROM XllE UCGERRIGI.E PLUTON regional scale;xenoliths of gabbro, diorite, nepheline syenite, metavolcanicrocks and hornfels are 7234567 Rock Tylp MIAS AGPA AGPA AGPA AGPA AGPA CINC found in quartz-bearingmonzodiorite, monzonite s@ple !,tc16 MG3? UG39 UG67 I{G94 l.tc98 MG98 and syenite(Whalen & Gari6py 1986).Felsic inclu- K-feldspar I 78.361.9XXXXx sions are rare. Remarkablefeatures suggestiveof AIbit6 trlrxXxXx complexinteraction and hybridization of the mafic NepheJ.in6 9.219.3XXXX sodaltte - 2.8 X ? X X and felsic magmasled Whalen (1985)and Whalen FlEoxone 3.0 11.9 X X X X X Agt Aa Ae Agt As & Gari6py (1980 to proposea magma-mixingmodel AnphLbole - 3.5 - X - X X Arf for tlte origin of the hybrid suite. On the other hand, Btott!€ 4.60.2XXXXX granitic Bt Lep UgBt I€P I€P the suite doesexhibit textural variations, but uagnqtlte 0.8 - x x x - x in generalit correspondsmineralogically and com- l1tsenLte x- A€nLgmtitE - 0.6 positionally to a homogeneoussubsolvus biotite- l'9 x rr zLxcoa 2.2 - X - X - X amphibole gratite sensustricto. Mafic inclusions are AlEtlto trtrx-XXX Aatlophyl1lte _trx rare. Fluollte -trtxx Pectollte -trx-? Radiometric data indicate that the complex is 9l6hle!1go x- Devonianin age(de R6mer L974,LaRocque 1986, I}i6och1oro x- Eudlal!rc6 -tr Whalen& Roddick 1987).A K-Ar age of 377+9 RoaenbuachLte -96rzenlte ?- Ma, determinedon biotite from a sampleof miaskitic

nephelinesyenite (WXMGIO, falls within the range litLnoralogy atrd nodal contrDsLtLon of selocted 6tup1oa ol of rock nepholLng gyenlta (whalen f, Gart6py 1986). Abbrevlatlons agesexhibited by the silica-oversaturated of rock tf'tE6! ltlAs nLaskttlc nepholiae syentte' AGPA types in the pluton (Whalen & Roddick 1987).U- [email protected] nephelLte syonit€, cINc J,eucoclatLc cognat€ tiiluslon tn-wxMG98 (;orlm 6). stdbolsr Ao aegLrlno Pb agesfrom the samesample of nephelinesyenite, (UG3?, lfc39 also cootaln tltml.an aeqLrlne)' Agt aegLr- Lne-auglte, Arf arfvedaon.tio. Bt biotlto, l4gBt ug-rlch a sampleof gabbro and one of granite all overlap biotlte, I€p lapLdonelanei X proaont, tr lraca tuounts, - abgont, r altsred to aecondaty ninerals, *r lDsstbly at about 390Ma, which suggeststhat all components aocondary. Tho full 6dple nu&ber contalns tho prafia tlx of the pluton are contemporaneous(J.B. Whalen and J. Mortenson, unpubl. data). Equilibrium assemblagesof mineralsin a 1.5- to 3-km contactaureole ofthe complexindicate a con- indicated by mapping. fining pressureof lessthan 2 kbars (de Rdmer 1977, Gabbro, which occursas inclusionsup to 1500m Van Bosse& Williams-Jones1988). The aureolehas in length or as thin dykes(Whalen 1987)in the hybrid a much broader extent than 3 km, as revealedby suite, is the only other silica-undersaturatedrock type regional contact-relatedgradients in illite crystallinity in the complex.The gabbroscontain up to 6 wt.9o and reflectanceof organic matter in the enclosing normative nepheline and exhibit a chemistry and Cambro-Ordovician flysch sequence(Islam et al. mineralogy (e.g., presenceof titaniferous diopside 1982).The extent of the aureolesuggests that the plu- and kaersutite)consistent with an alkaline charac- ton flares out at a shallow depth. ter (Whalen & Gari6py 1986,Wallace 1986). The agpaitic nephelinesyenite is exposedin dykes Inclusions are present in the nephelinesyenite. and sills up to 3 m thick that cut syenite and other Someare mafic to intermediate,angular to irregu- rocks of the hybrid suitein the northern half of the larly shaped,metasomatized xenoliths up to 10 cm complex (Fig. l) The dyke rocks are fine grained, across. The more strongly agpaitic samples(e.9., grey to dark green,and porphyritic. A chilled mar- WXMG37, WXMG39) contain rare polymineralic gin commonly is observed,with little or no evidence clots @igs.2a,b) that may representpseudomorphs of metasomatismof the host rock at the contact. The after, or remnantsof, xenocryststhat werepossibly miaskitic nephelinesyenite, texturally similar to the' derived from such xenoliths. A\o presentare ovoid, agpaitic variants, appearsas grey pods or ovoid bod- equigranular to porphyritic cognateinclusions up to ies about 100by 20 m that cut syeniteof the hybrid 10 cm acrossthat havea mineralogysimilar to that suite northeast of Mont Jacques-Cartier(Fig. l). of their host rock. The larger cognateinclusions may Leucocraticaplitic veinscommonly cross-cutor are exhibit disaggregationfeatures. associatedwith the miaskitic nephelinesyenite, and the host rocks may exhibit local evidenceof alkali Mnnnelocv oF THE NEpHELINESvsNtrss metasomatism(c/. Wallace 1988).Modal and mineralogical data for the nepheline syenite are summa- Feldspars ond feldspathoids rized in Table 1. Owing to the sporadic nature of the outcrop, the fields of felsenmeer,and the similar- K-feldspar, the dominant mineral in the nepheline iry betweenthe weatherednepheline syenite and other syenite,occurs as anhedralto euhedral,pristine to membersof the hybrid suite, the actual volume of strongly turbid laths or phenocrystsof perthite that nephelinesyenite probably exceedsthe abundance commonly exhibit a trachytic texture. Minor

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Hc. 2. a. Pseudomorph after an amphibole (xenocryst?)consisting of arfvedsonite (A), aegirine (Ae), pectolite (p) and minor fluorite. Long dimension of pseudomorph: l.l mm. Agpaitic nephelinesyenite sample WXMG37. b. Regrystal- lized remnants @) of feldspar (xenocrystic plagioclase?)at the core of a perthitic K-feldspar phenocryst. Crossed polars. Width of field of view: 2,6 mm. Agpaitic nephelinesyenite sample WXMC39. c. A phenocrystof turbid pefihitic K-feldspar (K) has been albitized, principally along its margin. The phenocryst is characterizedby a very patchy extinction. Width of field of view: 8 mm. Agpaitic nepheline syenite sample 8+105. d. Euhedral zoned aegirine crystal (Ae) containing a gxass-gxeencore and a blue-green titanian rim. Grain is cross-cut by fluorite. Long dimensionof zonedcrystal: 0.3 mm. Agpaitic nephelinesyenite sample WXMG37. e. Euhedralphenocryst of arfvedsonite (A) coexisting with a phenocryst of aegirine (Ae). Width of field of view: 2 mm. Agpaitic nepheline syenite sampleWXMG37. f. Remnantsof Mg-rich biotite (b) at the core of an aegirinephenocryst (Ae). The phenocrysf is 0.3 mm across.Agpaitic nephelinesyenite sample WXMG39.

amounts of discretegrains of anhedral to subhedral common in strongly agpaitic samples (e.9., albite are found in the groundmass. Nepheline is WXMG37), in which it forms interstitial grains or anhedral, and predominantly interstitial. Sodalite is anhedral to subhedralphenocrysts.

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TABLE 2. COIdPOSIIIION AND DEGRSE OF AI-31 ORDSR IN All K-feldspar samplesare monoclinic to X rays, ORTTI@I,ASE IN XIIE NEPHELINE SYENIEE but a small volume of microcline also is present, accordingto the powder-diffraction pattern (Table Stuple R@k fiTB u* e.o+t-o c-o-t-o 2; Guinier-Hiigg camera, CuKa, radiation). The K- wtl.rct6 MrAS 1.014 0.893 0,45 feldspar in the miaskitic nephelinesyenite consists n5r.rc37 AGPA 0.956 0.739 0.37 : WXI.'G94 AGPA of orthoclaseQ4 0.89; nomenclatureof Ribbe phenocryst 0.960 o.724 0.36 1983),whereas the agpaitic nephelinesyenite con- @t!Ix 0.93a 0.?89 0.40 tains low sanidineto orthoclase(0.72 < 2^ < 0.79) comwsLtiotr N- ls eapr€sBod io rcl g or, and Ia calculatsd (Wallace 1988).In agpaitic sampleWXMG94, the uetirg the eqr*f,tlon oi rroll & Rtbbe (1983) that relatee the unit:cell volue to coElpsi.tLon tn a lEttly dlsordergd K- phenocrysticorthoclase is lesswell orderedthan the rich f,eldspar. Ibgree of A-I-Si ordor, expressed by g1O, ls caLculated using ths cell trDlueters (relprted ln warrace matrix orthoclase,an illustration of the grain-size 1988) and the equatlons of, Blaal (1977). Tho erlor In q. effect on degreeof Al-Si order (Martin 1973).The and !,o is estl@ted co b€ t0'015. Ths rock typea ar€ dea- cltboa tn fable 1. greater degreeof disorder of the K-feldspar in the agpaitic nephelinesyenite is consistentwith more rapid cooling of the narrow dykesand sills than of OF &ItrOPNOW Itr M MPMIM SMXE the larger bodies of miaskitic nephelinesyenite. TM 3. CMSITIOtrS The K-feldspar in the perthite rangesfrom Orro r23 5574 RoCK NN AEPA AEA AGPA ACPA A@A A@A AGPA to Orlss; such a K-rich composition indicatesthat ryp€ Av(ro) Av(4) Av(l) Ae(1) Av(r) Av(1) Av(1) Av(2) subsolidusequilibration continuedto low tempera- s.to, 5L.08 52.72 52.39 53.31 52.17 52.41 52.80 50.31 tures, in the range 300 - <200'C, vio the exsolu- Ar"o. 1.54 r.36 1,L2 2.29 L.22 7.32 1.02 L.29 Fe;o. rt.54 26.47 21.25 2L.OO 22.34 25.59 23.07 L4.42 tion of albite. Thereis a high proportion of diffrac- Tl0"- 0.48 1.70 3.54 1.07 3.4A 0.64 L.54 0.42 MqO- 6.50 0.21 O.37 2.33 0,29 0.41 O.44 2.43 tion lines in the powder pattern that is assigned Fd 6.39 2.75 5.52 2.96 4.06 4.43 4.93 9'18 ron r6.i7 26.s7 24.6q 2L.e6 24.16 27.45 25.7L 22'L5 unambiguouslyto the albite componentof the per- ho 1.60 0.39 0.57 t.74 0.55 0.55 0.s0 2.34 zfr- 0.29, 0.o2 1.83 o.L2 n.d. 0,14 n.d. 0.70 thite. Petrographicevidence (e.9., Fig. 2c) suggests cao' 16.64 1.59 0.98 4.80 2.54 2.77 3.L3 L2.L9 tra2o 4.44 I2.7I 12.70 LO.73 L2.29 11.66 11.66 6.35 that this enrichmentin sodium may in part reflect Eolal 100.60 99.91 Loo.27 100.34 99.00 99.91 99.49 99.53 postexsolution Na-metasomatism(e.g., White & st x.945 2.010 2.004 2.011 2.008 2.013 2.033 1.973 Martin 1980).Such interaction with a fluid medium "at 0.055 o.o0o 0.000 0.0o0 0.000 0.000 0.000 0.027 *Al o.or4 0.061 0.050 0.r0r 0.055 0.050 0.046 0.033 must have occurred above the stability field of Fs'' 0.33I 0.750 o.612 0.595 0.647 0.?40 0.668 0.426 (>400oC), Tl 0.014 0.049 0.102 0.030 0.100 0.018 0,045 0.0r? microcline asthe conversionof orthoclase uc 0.375 0.015 0.02x 0.131 0.017 0.023 0.025 0.14? 16" 0.203 o.o88 0.176 0.093 0.131 0,142 0.159 0.301 to microclineis incipient only in thesesamples. The h 0.052 0.013 0.018 0.056 0.02r 0.018 0.026 0.078 probably zt 0.005 0.000 0.034 0.002 0.000 0.003 0,000 0.013 conversion involved deutericfluids gener- & 0.579 0.065 0.040 0.194 0.105 0.114 0.129 0.512 ated during crystallizationof the nephelinesyenite. Na 0.328 0.940 o.942 0.785 0.917 0.060 0.859 0.483

The nephelinein theseassemblages (Wallace 1988, k* 0.413 0.017 0,025 0.160 0.021 0.025 0.029 0.153 il6l (Mq+F€?') Table A5.4) contains low concentrations of Ca 0.648 0.149 0.107 0.584 0.r13 0. I42 0.13? 0.320 (0-0.24 wt.Yo CaO) and Fe (0.19-0.72 wt.tlo Fs"/Fe" 0.620 0.a96 o.771 0.865 0.832 0.839 0.808 0.586 FerO). Its averagebulk composition approaches Coop€llions f,sle obtalnd uslng a Cd*a Ceebax €lectton dcto_ NetoKsrrQtzo,which is typical for plutonic nephe- prob equtplEd eIlh f,ou savolor.gth_dlaFlalod aqsntial aIPc- i!o@!er€, Accolerattf,g rcltag€: L5 kv, h@ cutten!: 7 d, line 1984). wallaco (1988) llstd coutlng il@a ud atan&da usd' fre plo_ @dgar F*ton 6f *e total Fe that lE F€.o. and ths stnctural fomula ;ers celdlatd by norultzlnq to a tatlons and th€n bv adJustt ng Lhe Fe" content;o that the total ntrr of orygon atoE eSals Clinopyroxene slx, f,ollorlng th€ r4@endallona of, Robinson ( 1980) . No@n- claiu€ after ioltdoco (1989). Rock tiTbs als dof,lnd tn Tsle 1. Avln)r av€ra@ lesu]t of n analyBesi l: total F6t r average of foG'd€tsmlmtron]t vq* a Mgl(Mg + Fe'), n'd' not detetulned' Clinopyroxeneoccurs as green pleochroic anhedral tuptssr I aeqirtno-auglts, ffi15,2 a€gltln€ (core), WG37-la, 3 tltanlan ireglrlns (r1o of th€ aee gain aE 2), 4 aeglrhs grains or phenocrystsof aegirine-augiteor aegirine (lale-stag€ !41; blom rld), WC37, 5 tltulan aeglllne, wG39, a aqtrtie lcore of phen;ryst), wG39-36' 7 aegltlno (tlE of (Table 1). Zoning is rare, but in some samplesof lhe s;@ phenocryt as 5), I aoglrln€-augtto, wG94-24. agpaiticnepheline syenite, grains have a blue-green rim of titanian aegirine @ig. 2d, Table 3, no. 3). Pyroxenecompositions (Table 3) resemblethose in (Larsen L976), The lowest concentrations of Zr nepheline syenite from other alkaline complexes (<0.1 wt.9o ZrO) are found in the core of both (e.g.,Gomes et al.1970,Larsen l976,Brooks et al. groundmassand phenocrysticaegirine. Owing to the 1982,Brousse & Ranqon1984). high solubility of Zr it peralkaline melts (Watson In the agpaiticnepheline syenite, the sodicpyrox- 1979),enrichment in Zr is only observedwhere a ene is essentially silica-saturated, with the greatest sodic pyroxene crystallizes from a late-stage Zr' proportion of the jadeitecomponent, l0.l mol.9o, enrichedresidual liquid. occurring in pale brown, late-stage(possibly post- A plot of Na-Mg-(Fe2+ +Mn) (Fie. 3) doesnot magmatic)overgrowth pf aegirine(Table 3, no. 4). display a single continuoustrend, the existenceof Both Ti and Zr are concentratedin the blue-green which usually is interpretedin terms of consanguinity titanian aegirineof the agpaitic nephelinesyenites, of batches of alkaline magma in a fractionating even though both cations compete for the Ml site sequence(e.g., Stephenson lW2, NielsenlW9).Lack

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observedvariation among pyroxenecompositions in Na the McGerrigle nephelinesyenites.

Amphibole

Amphibole, which occurs only in some samples of agpaiticnepheline syenite (Table l), forms interstitial or poikilitic, unzoned grains or phenocrysts that exhibit a yellow-brown or brownish green to black or deep blue-green pleochroism. Whereas amphibole and pyroxeneappear to be at equilibrium in some samples(Fig. 2e), a replacementrelation- ' ship is observedin others. SampleWXMG37 con- ,, 1/ l\. tains manganoanpotassian arfvedsonite (Table 4) .rtrtl\ \ ." .t' 31-t which, relative to the arfvedsonite in nepheline /---' 4) syenitesfrom other complexes(e.9., Lasen 1976, " :------'3'- -'/ Ferguson1978, Brooks et ol.1982), is characterized by high Mn (2.5-3.4wt.9o MnO) and K (2.1-3.3 wt.9o K2O),and low Al (0.9-1.5wt.9o Al2O), Mg Ms Fez++Mn(l.l-2.4 wt.9oMgO) and Ca (0.7-1.7wt.9o CaO). Arfvedsonite is characteristicof the most highly Frc. 3. SelectedpYroxene cornpositions plotted in terms of evolvedperalkaline rocks of undersaturatedsuites Na-Mg-Fe'- +Mn (molar). Filled circle: miaskitic (Mitchell & Plau 1982). nephelinesyenite, open circle: agpaitic nephelinesyenite. Compositional trends of pyroxene from other silica- undersaturatedalkaline suites: l) Itapirapud: Gomeset Biotite ol. (1970),2)Uganda: Tyler & King (1967),3) South Q6roq: Stephenson (1972), 4) Coldwell nepheline Biotite, the dominant mafic mineral in the syenites:Mitchell & Platt (1982),5) Ilimaussaq:Lar- miaskitic nephelinesyenite, occurs as anhedral or sen (1976). poikilitic flakes. It rangesin composition from man- ganiferous titaniferous biotite in miaskitic nepheline

' syeniteto manganiferoustitaniferous lepidomelane IIABI.E 4. COUPOSITION OF AUPIIIBOITE TlI AGPAITIC !{EPTIELINE ATENITE IIX}TG37 or Mg-rich biotite in the agpaitic nephelinesyenite (Table 5). Biotite in the nephelinesyenites of the IP 8t s.011 8.121 McGerrigle complex is characterizedby hieh Mn Av(6) Av(5) "ll o.24L 0.180 Tt 0.117 0.109 (1.6-4.8fi.90 MnO), moderateTi (1.4-4.0wt.9o Fe2' 3.803 3.438 TiO) and low Na (0.03-0.18wt.9o Na2O)relative sio, rt.l 50.57 50.96 Fe3' 0.114 0.289 At"o. L.29 0.95 ltn 0.42t 0.359 to compositionsreported from other suitesof nephe- Tt0-- 0.98 0.91 ug 0.293 0.504 Feot 29.57 27,97 ca 0.25L 0.140 line syenite(e.9., Rock 1978,Mitchell &Plart 1982, FeO 28.7 25.A L.749 1.850 Brooks et al,1982). Fe-O- 1.0 2.4 iltu 0.659 0.522 l.tn6' 3.14 2.66 K- 0.501 0.650 ugo t,24 2.L2 CaO 1.48 0.42 F 0,446 0.534 Aenigmatite and oxide minerals !|a"O 7.44 7.7L 0.005 0.003 Kd 2.48 3.20 F 0.89 1.06 The aenigmatite in aegirine-bearingnepheline 0.02 0.01 ug7.1ug+pe"1O.ozr 0.128 Fe'-,/ ( Fe'-+Mq) syenite approachesthe end-membercomposition ost'rCI 0.38 0.i15 0.930 0.881 Total 99.25 98.15 FE"/Fso 0.029 o.o78 (Na2F{*TiSi6O26;Table 6). However, its extreme enrichmentin Mn (4.6-5.9 wt.oloMnO) exceedsthe ConcsntrctLon of F€,O" calculated by the nethod of lalld 4.4 wt.olo MnO reported by Marsh (1975). E Alb€€ (198I), ualird a coDput€r progrm Ettt€n by A.J. pased Blmea . Fomla '3 on 23 61,oru. Av(g) 3 averag€ result Fe3*-poor aenigmatiteis typical of an association of E ual-yseg. total lron, 6ap!€aaed aa fe o! as FeO. I mgaou tDtaeElu ufvedaonlte (lnt€rstLttat) , P with arfvedsoniteand aegirine,whereas Ca- and Al- mgu@ tDtasglu dlvedBonlte (phen@ryst8). N@n- poor aenigmatitemay reflect a relatively low tem- clatu€ af,ter t€ake (1978). Frotrprtion of, F and Cl in a f,omla unit u€ caldlated aasunLng a stoLchlonetry of perature of primary crystallization (Larsen 1977). (og+F+cr)-2. The observedabsence of a coexistingFe-Ti oxide mineralis consistentwith the exislenceof a no-oxide field in which sodicpyroxene and aenigmatitecoex- of a smooth trend may indicate that processesor fac- ist (Marsh 1975). tors otherthan closed-systemfractionation (e.g.,var- Magnetite is the only primary oxide observedin iations in intrinsic /(O) and in alkali conten! c/. the miaskitic nepheline syenite. Aegirine-bearing Woolley & Platt 1988)are partly responsiblefor the nepheline syenite WXMG39 contains magnetite

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rll m TABLE 5. SELECTED COMPOSITIONS OF BIOTITE IN jcNN rM 6. Comsrrrotrs oF AccEssoRYurmws AGPAITIC MPMLIM SNNITE NEPIIEI.INE SYENITE

I 23 A5 7 34s ga[plo uc3?a uc3?b r4c37c uc37d uc94a uG94b UGg4c Rock I\|18 !{IAS AcPe AGPA AGPA CINC Av({) Av(5) Av(2) Av(3) Av(2) Av(2) Av(2) smple MG16 ualli+ Mc39-81 !,1c94 MG98-1 Av(4) Av(4) Av(4) Av(3) Av(5) slo" sl.g 42.49 35.87 56.79 52.91 0.0 30,41 3r.2L Ar d- 0.34 1.1,9 0.08 0.01 0.0 0.01 0.0 116,' 9,r7 11.05 o.sl 0.01 a.22 1.12 7.79 SiO, wt.8 tr 10 11 1< 41.88 35.67 37.77 zfi- 0.0 0.34 L2,69 0.0 0.34 13,96 7.49 A1d. L2.82 10.6r 12.58 11.50 10.35 Nb.d. 0.23 L.23 1.03 0.0 43.54 11.19 1.36 - 0.0 Tt0-- 2.71. 2.06 2.56 3.74 3.42 uqo 0.29 0.60 0.01 0.01 0.01 0.07 treO 34.34 26.42 5.57 1.14 0.19 0.39 0.1{ Fooe 22.2A 30.10 9 . 10 30.37 26.79 0.09 L.24 0.75 21,30 ho 5.23 7.97 2,50 4.29 I'eO 16.34 23.94 9.10 24.L6 CaO 0.05 r.89 12.20 26.19 L6.94 26.12 24.92 Fe,O.- 5.5 6.8 0.0 6.9 na"o 7.63 2.O4 2.94 8.71 4.9S 7.94 8.35 Mno r.77 3.17 4,20 3.07 4.45 K^d 0.0 6.64 0.31 0.04 0.04 0.04 0.03 ugo 9,46 2.50 14.90 2,s0 3.30 La"o, n.d. tr.d. n.d. O.02 0.66 0.05 0.35 0.87 CaO 0.01 0.0 0.01 0.0 0.01 ce:o: n.d. n.d. n.d. 0.06 1.55 0.22 n.d. n.d. 0.0r 0.09 0.12 0.15 Na,o 0.06 0. 16 0. 10 0. 08 P-6.'' n.d. 0.13 F 0.01 7.47 0.22 n.d. n.d. n.d. n.d. K,0 t. ru t.oa 9.34 9.75 10.17 ct 0.10 0.02 0.?5 tr.d. n.d. n.d. n.d. L.25 0.15 3. 17 0. 13 o.23 0.02 0.02 0.01 0.o2 0.0 cF,cl 0.03 0.62 0.26 !otal 99.85 96.11 95.31 93.40 ,r]eu 0.53 0.0? x.34 0.05 0.10 "rlrt "rl"t 6.050 7,7t9 6.992 3.095 0.0 2.068 2.090 Tota!. 96.26 96.57 91.4A 97,08 s1 9?.15 0.057 0.303 0.012 0.001 o:o o:o o:o 0.0 st 2,852 3.001 3,085 2.445 2.990 TT 0.982 1.795 0.047 0.0 0.449 0.057 0.362 AI. 1. 148 0. 999 0.915 1.081 zt 0.0 0.036 0.761 0.0 0.012 0.463 0.257 0.041 Fe" 0.0 0.0 0.0 0.074 0.044 s 0.015 0.120 0.05? 0.0 1.431 o.344 Ug 0.062 0.193 0.001 0.00r 0.001 0.007 0.0 4.773 0,573 0.056 0.011 o.022 0.008 tl 0.0 F6i 0.004 0.006 0,L77 0.0 4.089 T1.- 0. r55 0.124 0.t42 0.224 o,204 h 0.63X 1.459 0.260 0.272 0.006 0.071 0.043 Fe- 0.379 0.4r.1 0.0 0.340 0.319 @ 0.008 0.436 1.608 r.641 1.319 1.904 2.O74 YI 0.538 0.541 0.319 0.564 0.523 trq 2.106 0,856 0.700 0.989 0.702 1.047 1.08{ !.lg 1.0?5 0.299 1.536 0.297 0.389 K 0.0 1.830 0.049 0.003 0.004 0.003 0.003 0.018 0.002 0.009 FE L.042 L.6L2 0.551 1.611 1.410 0.001 ce 0.001 0.041 0.00s 0.021 l.an 0. 114 0.216 0.262 0.207 0 .298 0.006 0.007 0.008 t{a 0.0 0.0 0.0 0.007 0.012 F oloos 1.002 0.086 z2 2.23L 2.L27 2. X09 c1 0.02i1 0.008 0. x58 K 0 .893 0.986 0.878 0.992 L.027 Na 0.019 0.009 0.023 0.008 0.0 Rock tws def lnd tn TSIo l. Av(I) t avelage corysltlon tEad Ca 0.001 0.0 0.001 0.0 0.001 ;;-; ;;iw;;t n.d. not d€temLnd:- 1 aonlg@ttte (basts of- the x 0.913 0.995 0.902 1.000 1.028 i*if*fuifo"i 14 catloE sd 20 atoM of, oxygen), 2 asrophvr- iiG-ize o! orygen), 3 €udlaf,yte (r8.5 atoE of ory-gen), (4 cattoM)' 6 wonrer- 0.738 0.033 0,058 a witoltte"ro@ 16 callom), 3 Fdhlore 0.302 0.041 it"- ii *tr"*1, z ro66nuuechtte-gdtzenlt€(?) (5 cattoE)' m€ 0.003 0.0 wero 0. 003 0.003 0.001 full ;@DIe-out nuber contalre th€ prefla ffi. k the salysed cafiled uslnq tsavsl€nqth dlstrpBlonr lh€ls lg no Intorutlon on ifie-""ncottitlon oi ninor el@nts ltko Ta' sn, Bi, ro11(Fej+Mq) 0. s69 0,871 0.255 0.872 0.820 il,"""fi.lt" whlch de oxtrFcted tn Bore of, thes€ nln€lals (atld hencs Fe"/Fe' 0.267 0.203 - 0,204 0.205 rhe I6F"i1., aml](tcal tobls). Mgl (ti,tgr!'e") O.508 0. 157 0..745 0.155 0.21.6

' A11 re tr€atsd as FeO. !'or othor conPosltlonB' Fs,ol ,a€ obtalnsd by tltratton (Wallace 1988). Fomula bdsad on 11 atore of, oxygen' Proporilons of F and Cl ln a for- = mula unl! aaaue a-slolchlonetry of (OH + F + c1") 2' pyrophanite. It is, however, also Ti-depleted trcea deflned tn Table 1. Av(4)! average re6ul-tE of Rock r: (0.06-0.16 wt.9o TiO) and anomalously Mn- n analieee. cotal .lron, expressed as Fa or F6o' 1 tanqanlierous tltanlferous btotLie (nonenclature after enriched(S.3-9.3 wt.9o MnO), which suggeststhat Rocli (1982), 2 Mnqanlfsroug tltanlferoua lepldonelane' 3 reriqanlioroue Mq:rLch btotite (lncluslon i.n aagLrinei the magnetitewas initially hiehly Ti-depleted (c/. Ftd. 2i). 4 mnqanlferous tltanLf€rous lepldomelane, 5 miqaniierous tieanlfarous lspldonalane (lncluslon tn Wallace1988). aegirtne phonocryst).' Tho f,ulL 6@pte nuober containg th€ pref,lx wx. Other accessoryminerals

Severalaccessory minerals have been identified in instead of aenigmatite,and both primary ilmenite the nepheline syenites(Tables l, 6). In aegirine- and magnetite occur in aegirine-augite-bearing bearingnepheline Syenite WXMG37, a Na-Zr silicate, interpreted to be a member of the eudialyte nephelinesyenite WXMG94. As is the casein other *,Mn,Y) felsic undersaturatedcomplexes (Neumann 1974, group Na.(Ca, REE) r(F e2 (Zr,Ti) (Si8O2t Brooks et al.1982), the oxide mineralsare charac- (OH,CI)2 (Table 6, no. 3) occurs as interstitial, terized by high Mn contents(Table 7). A low con- colorless to pale pink-brown, low-birefringence centration of the ulvOspinelcomponent and the grains. The presenceof zircon in WXMG39 rather presenceof pyrophanite lamellaein the magnetite than the Na-Zr silicate of WXMG37 may appear indicate that "oxidation-exsolution" (Buddington & anomaloussince both samplesare characterizedby Lindsley 1964)has occrured. The pyrophanite lamel- the same agpaitic index (1.09) and near-identical lae in magnetitereflect the preferenceof Mn for the whole-rock compositions(Table 8). The formation rhombohedral over the spinel phaseunder conditions of Na-Zr minerals dependson ,Loexcess of alkalis of subsolidus"oxidation-exsolution" (e.g,, Hag}erty at the stageof their crystallization (Currie 1976)and 1976).Only magnetitein an aegirine-bearingnephe- on the Fe3+/Fe2*value of the melt (Watson 1979). line syenite (WXMG39) lacks visible lamellae of The presenceof zircon in WXMG39 is probably

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TABLE 7. CO!4POSIIIONS OF OXIDE PHASES IN IIHE TABITE 8. E[rL( CO{POBITIOI OF SSLE0IED SN,iPIAS OF NEPHELINE STENITE IEPHELINE 8YENIIE 8'ROI IrtsE [email protected] COI{PI.ET

!2 34 nek type lllAg ACPA AGPA ACPA ACPA AGPA Rock l'!TE UIAS MIAS AGPA AGPA AGPA AGPA Eaqrle 11616 l,tc37 uG39 uG67 I{C94 r{G98 Seple ucl6 !1G16-2 uG39 lr!G39 r.1G94 MG94-4 Av(8) Av(3) Av(6) Av( 1) Av(3) Av(3) SIO- wt.t 50.80 59.20 59.50 58.90 59.90 59.10 rro: 0.59 0.31 0.3r 0.3r 0.33 0.32 A1,O.*.8 0.11 0.50 0.05 0.0 0.06 0.0 Al-0- 19.30 19.50 19.60 19.60 20.00 19.60 Tlo,- 0.29 49.85 0. tt 52.65 0.74 50.?8 Fe:o: 1.65 2.?L 3.38 3.00 2.3L 2.67 roo- (total) 91.36 5.23 83.38 3.40 90.94 32.28 Fe6' 1.39 0.89 0.40 0.59 1.40 1.09 I.lnO L,23 41.40 a.77 4t.s3 0.72 14.45 t{no 0.17 o.2a 0.24 o.2a 0.26 0.27 ugo 0.01 0.0r 0.05 0.10 0.01 0.03 l'So 0.54 0.14 0.13 o.25 0.12 0.L2 Nio 0.05 0.02 0.0 0.0 0.03 0.02 CaO 1.30 0.90 0.78 0.96 0.8r 0.93 v,o. 0.20 0.34 0.08 0.0 0.02 0.34 I{a-O 7.48 9.61 9.62 8.49 9.2L 9,2L ci,or 0.02 0.0 0.0 0.0 0.0 0.0 x-d s.67 5.10 5.20 5.07 5.09 5.06 P:o- o.l4 0.03 0.04 0.04 0.04 0.04 Fe,O,- 68.15 2.72 68.10 0.0 66.93 r.47 do' 0.53 o.74 0.50 1.30 0.29 1.03 FeO 30.04 2.79 22.03 3.40 30.72 30.95 c6-' o.ro 0.08 0.09 0.07 0.03 0.04 E o.o4 0.05 0.05 0.06 0.03 0.07 fotal 100.10 97.72 .6A 99.27 97 99.23 98.04 cl 0.01 0.19 0. t5 0.10 0.01 0.10 0.005 0.015 0.002 0.0 0.003 0.0 tttaces O,24 0.36 0.3{ 0.36 0.28 0.3t Tt.. 0.008 0.963 0.003 1.012 0.022 0.983 1.973 0.053 1.989 0.0 1.954 0.029 sotal 100.15 100.19 100.37 99.{8 100.11 99.96 iJ. 0.060 0.7L4 0.073 0.996 0.666 I'ln 0.040 0.903 0.246 0.899 0.024 0.315 trt pBo 7A 84 58 140 29 27 Mg 0.001. 0.0 0.003 0.004 0.001 0.001 Ba 3ll 45 28 43 6t 38 N1 0.002 0.0 0.0 0.0 0.001 0.0 Rb L52 188 L75 t8? r58 156 0.005 0.006 0.002 0.0 0.0 0.005 g! 300 23 65 r49 7 48 C! 0.001 0.0 0.0 0.0 0.0 0.0 432 62 57 64 t9 59 zt 845 L979 1917 2009 LA74 lSrl Fe,TIO. wt.t 0.0 - 0.0 0.86 - nb 202 362 335 396 305 ,?o Fe-O- 96.27 70.78 97.04 PD 15 31 30 -22 unjrlo, 0.70 1.13 - - v38 87 <1 IilnF6,o; 2.54 27.97 0.0 ft8 78 87 8 Cu4 34 54 fetto" 5.88 10.78 65.38 zn 6t 134 95 137 85 115 Ii.tnTto" 88.20 88.31 l.{g!,rO: 0.03 0 .30 0.09 ca 24 32 34 34 3l gc 1.6 0.8 0.8 Cr

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