DIOCTAHEDRAL MICAS IN TRIASSIC METAVOLCANIC ROCKS by dandanhuanghuang

VIEWS: 3 PAGES: 12

									Canadian Mineralogist
Vol. 23, pp. 597-608(1985)



DIOCTAHEDRAL
           MICAS IN TRIASSICMETAVOLCANICROCKSOF WESTERNGREEGE

                                       GEORGIA PE-PIPER
                  Department Geologt,SaintMary's Ilniversity,Hatifax, NovoScotiaB3H 3C3
                           of


                       ABSTRACT                           m6tamorphisme, roches
                                                                             les      dont le plagioclase €tdalbi-
                                                                                                         a
                                                          tisdproduisent   pumpellyite,       et
                                                                                      6pidote "leucoc6ladonite".
  Chemically the dioctahedral micas from low-grade Comme substitution Al d FeetMg continue, con-
                                                                    la            de                       elle
metamorphosed     mafic volcanic rocks (Triassic, western duit i la formation leucophyllite,
                                                                              de             phengite finalement,
                                                                                                     et,
Greece)can be grouped into three distinct types: (l)      muscovite.   L'augmentation Al s'observe dans
                                                                                     de             aussi     l'6pi-
celadonite, (2) compositions rangrng from an aluminous dote.La paragonite formei temp€rature 61ev6e,
                                                                                 se                    plus
celadonitetermed "leucoceladonite'n  through leucophyl- lorsque    l'albitesed6compose perdsonNa.
                                                                                        et
lite to phengite and (3) muscovite- paragonite. Celadonite
shows substitution of Fd+ for uAl beyond the celadonite                                     (Iraduit par la R6daction)
- leucophyllite - muscovite composition space. There
appears to be a natural compositional gap between               Mots-cl6s:micasdiocta6driques,
                                                                                             cdladonite,leucocdlado-
celadonite and the phengite - leucophyllite - ..leuco.                               phengite,
                                                                  nite, leucophyllite,                 roches
                                                                                             triassique,     m6ta-
celadorilte" series. Three different structural types cor-        volcaniques,Grbceoccidentale.
respond to the chemical types. Celadonite showsvariable
substitution of Fd+ for Mg. In the "leucoceladonite" -
leucophyllite - phengite series,the Mg/Fd+ rado depends                            INTRODUCTIoN
on Al content. Muscovite also showsvariable substitution
of Fe?:F,for Mg and Na for K. As to genesis,      celadonite        The externalHellenidesof westernGreececontairi
developsfrom ferromagnesian       mineralsin basic rocks in      a suiteof Triassicmafic volcanicrocks (Table l; Pe-
which phlogopite or K-rich groundmasswere originally
present. At a higher meta:morphicgrade, rocks in which           Piper 1982)that haveundergone      varying degrees of
plagioclaseis albitized develop pumpellyite, epidote and        low-grade(principally geenschist)metamorphism.
"leucoceladonite". Continued substitution ofAl for Fe and       These.metavolcanic basic rocks contain several
Mg leads to leucophyllite, phengite and, eventually, mus-       different types of K-bearing mica. The chemical
covite. There is a parallel increasein Al content of epidote.   properties and petrographicrelationshipsof these
Paragonite forms at higher temperatures,as Na is released       micas are the subject of this paper.
from albite.                                                       The Triassicvolcanicrocks of westernGreece    have
                                                                a very limited arealextent(Fig. l). Outcropsin Lako-
Keywords: droaahedral micas, celadonite,leucoceladonite,        nia @e-Piper Kotopouli l98l), Kalamae,Zarouhla
                                                                               &
   leucophyllite, phengite, muscovite, paragonite, Trias-
   sic metavolcanic rocks, western Greece,
                                                                and Tyros (Pe-Piper 1983b, 1984)are in the Phyl-
                                                                lite Series the Gawovo-Tripolitsa zone @anagos
                                                                           of
                                                                et al. lWg); the Lakmon Mountain outcrops (Pe-
                       SoMMAIRE                                 Piper 1983a)are in the tectonically overlying Pin-
                                                                dos Nappe,and the volcanicrocks of Melidoni @e-
   Chiyniquement, peut classeren trois types distincts
                    on                                          Piper et ol. 1981) and Epidawos are locatedfurther
les micas dioctaddriques des roches volcaniques mafiques
triassiques la Grdceoccidentale
            de
                                                                eastin the Pelagonianzone. All ofthese areas,ex-
                                 ayant subi un faible degr6
de mdtamorphisme, savoir: (l) cdladonite,(2) composi-
                      i                                         cept for Epidawos, consistpredominantlyof mafic
tions allant de la "leucoc€ladonite" (c€ladonite i teneur       rocks.
d'6luminium) d leucophyllite et phengite, (3) muscovite -          The metamorphic facies of the mafic volcanic
paragonite. Dans la c6ladonite, on p€ut substituer Fe3+ d       rocks are summarizedby Pe-Piper (1982) and in
vIAl au delAde I'espace compositionqui s'6tendde ia
                          de                                    Figure 2. Rocks of the Lakmon Mountains contain
c€ladonited la muscovite. Une lacune naturelle de compo-        fresh primary feldsparand pyroxene.Celadoniteand
sition semble s6parerles deux premiers types chimiques.         vermiculite are the main metamorphic phases(Pe-
Trois types structurels correspondentaux types chimiques.
                                                                Piper 1983a).The Phyllite Series  rocks are tectonized
La c€ladonite est caractdrisdepar une substitution varia-
ble de Fd+ i,Mg. Dans la deuxibmes€riechimique, le rap          and more highly metamorphosed.       Neither primary
port MglFez- est fonction de la teneur en Al. La musco-         feldspar nor orthopyroxeneis preserved,and only
vite montre la substitution variable de Fd+ i Mg, ainsi         rare clinopyroxenerelics occur. The predominant
que celle de Na d K. Quant i la gendse, c6ladonitese
                                          la                    metamorphic' assemblage from Lakonia is
forme i partir de min6raux ferromagndsiens rochesbasi-
                                            de                  chlorite + epidote t pumpellyite, together with al-
ques, dans lesquellesla phlogopite (ou une p6te riche en        bite, quartz, hematite,calcite and K-bearingmica.
K) 6tait originellement pr6sente.A un degr6plus 6lev6de         Actinolite is a rare accessory.A similar assemblage
                                                          597
598                                                                     THE CANADIAN MINERALOGIST

        1.
    TABLE          SUI.f.IART I'IINEMTOOY SAIiPLES
                           OF          OF            lN
                                                 TJSED IHIS STUDT                                          5 electron microprobe. Natural minerals and syn-
Lo@llty        Refar-    Rock        Rock         lilcas            other     lllca                        thetic standards were used in calibration, and the
                                                                    SecondsryXtallln-
               enes      f           Type
                                                                    lilnerals lty                          datawerereducedusingthe EMPADR VII program
                                                                                       (')
                                                                               (Kijbler)
                                                                                                           (Rucklidge & Gasparrini 1969).
               1,2       LK827          B         Ce]
                                                  Cel
                                                             sn€                                              Where very similar results were obtained from
                         1K831
                         1K842                    Cel        Vm                                            different crystals in the samesample, data for only
                                                  Cel         -                        4.4
                         1K847
                         LK85I                    Cel,H-C€] Ym                                             one representative   sampleare reported. This resulted
Kalanae I,3.4 KVI                       B         L-Cel,Leuc Ls,Ep,Chl,                                    in a set of about 80 compositions.Of these,25Yo
                                                             Pmp
                         w4                       Ph         Chl,Pnp'Ep                                    were rejected as having been altered by retrograde
                         KV5            B         Leuc       Chl'Ep                                        metamorphism,usingthe criterion that K + Na is less
                                                                                       4.0
Lakonla        I,5,6     D5
                         D7
                                        B
                                        s
                                                  Ph,Leuc
                                                  Lsuc
                                                             chl ,Cal,Kfs
                                                             Cal                       4.4                 than 1.65,or that the total of the microprobedeter-
                         D8
                         Dll
                                                  Ph
                                                  Cel
                                                             Chl'Pnp'Ep
                                                             chl,Ep                     3.6
                                                                                                           minations (sum of SiO2,TiO2, Al2O3,FeOl, MnO,
                         L7                       Leuc,Ph    Chl,Ep                     4.9                MgO, CaO, NarO, K2O) is less than 93t/o (i,e,'
Tyms           1 '4      T15                       ils-PS           Cht 'tp                                  >?Vo volatiles). Twelve represenlativecompositious
                         f32                       [s-Ps            Ep'ChI,Tur
                         T38            B           I               chl 'EP             3.8                 of this final set of sixty-two are shown in Table 2.
Zarcuchla I,4            ZU3            B          Leuc              Chl,Pnp                                The complete data-set is available on request from
tilefldonl 1,7           tlELlz                    L-Cel ,Ph         Chl,Pnp.Ttn,
                                                                     Cal
                                                                                                            the author.
                          llEL14                   L-Cel             Chl 'Ep'Pnp,                              Mineral separationfor an X-ray investigation was
                                                                     Cal
                          EP19A          R
                                                                                                            attempted. Unfortunately, only small samples are
Epldavrcs I,8
                          EP21           R                           cir                                    availablefor this purpose,and separates    were con-
References: I Pe-Plper(1982), 2 Pe-Plper(19834)' 3 Pe-Plper(1984)'                                          taminated with groundmass mica. As a result' no
4 Fvtrc'lakls ('1970),5 Pe-Plper& Kotopoull (1981)' 6 Pe-Plperet az.
(19b2). 7 Pe-PlDer 4L, J9811,8 Bannert& Bender(1968).
                          et                                                                                useful X-ray pattern$could be obtained.
i c r i i l e s : B i b a s a l t ) , s i o 2 . 5 3 g i A ( a n d e s l t e ) '5 3 < s l 0 2 < - 5 2 2 i
i irtrviritaclte)''slOz, 6n (*.1; AGagglmrate. lllnerals: Cal-cal-
clte, Cel celadonlte, Chl chlorlte' Ep epldote' H-Celhydrateocela-                                                           NOMENCLATURE
donlte. Kfs K-feldspar, Lwslasonlte' L-Cel "Ieucceladonlte"' Leuc
 leucoDhylllte. Na-Ph         sodlc phenglte' Pg parrgonlte' Ph phenglte' Pnp
omei]vlte, Sre smctlt€, Ttn tltEnlte, Tur touru]lne' Vm vemlcu-
 tl*.      buariz, alblte and hemtlte are almst alwayspresent' except                                         Compositionsof most natural K-bearing diocta-
 ln smies fM the Lakmn ltountalns and Epldavrcs. * Detqmlned on                                            hedral micascan be expressed terms of three com-
                                                                                                                                           in
 the < 2 m fractlon of pqdered satrples,follwlng Kubler (1968).
                                                                                                           ponents (Fig. 3): celadonite KrFer3*Mgr(SirOro)
                                                                                                           (oH)4, leucophyllite K2Al2Mg2(SirOf(OH)o and
 is present at Zarouhla (except that epidote may be                                                        muscovite K2Al4(siAl2ozoxoH)a (Deer et al. l97l'
 absent), and at Kalamae (where lawsonite is pre$ent                                                       cuidotti & Sassi1970. Velde (1965)usedthe term
 in some samples).Tyros has chlorite * epidote or                                                          celodonitefor any dioctahedralmica with the general
 chlorite + clinozoisite, with pumpellyite absent,and                                                      formula K2R23+R22*(SiEo2o)(oH)4'              naming
 paragonite in somesamples.A chlorite + epidote +                                                          individual species the R3" and Rz* ions. Thus
                                                                                                                               for
 pumpellyite assemblageis also found at Melidoni                                                           celadonite as listed above is FeMg celadonite, and
 (Pe-Piper et al. l98l).                                                                                   leucophylliteis AlMg caledonitein Velde's nomen-
     Some of the rocks studied show retrograde                                                             clature. Phengite is intermediate in composition
 metamorphism,represented local hydration of
                                 by                                                                        between  muscoviteand leucophyllite.Na may replace
  celadoniteand phengite(Pe-Piper& Kotopouli l98l)                                                         K in the muscovite structure to yield paragoqite
  and alteration of celadoniteto vermiculite @e-Piper                                                      Na2Alo(Si.AlrOzoXOFI)r, Na-for-K substitution
                                                                                                                                       but
  & Kotopouli 1981,Pe-Piper1983a).                                                                         in the other phasesis minor.
     The purpose of this investigationis l) to define                                                          Many of the samples    studiedhave compositions
 the P-T conditions under which different K-micas                                                          intermediate between celadonite, leucophyllite and
  occur in low-grademafic metavolcanicrocks, 2) to                                                         muscovite;the terms celadonite, "leucoceladonite",
  evaluate the range of solid solution and the natrue                                                      leucophylliteand phengitehavebeenusedto describe
  of atomic substitutions in the micas, and 3) to estab-                                                   the particular compositional rangesshown in Fieure
  lish the metamorphic reactions leading to the                                                             3. The boundaries between these compositional
  developmentof the micas in low-grade mafic meta-                                                          ranges :ue arbitrary. Sampleshave been located in
  volcanic rocks.                                                                                           Figure 3 on the basisof'their Si and Al content' since
                                                                                                            theseare the two elements  that showthe leastreplace-
                                            METHoDS                                                         mgnt by other elements.
                                                                                                               Becausethe oxidation state of iron is not deter-
    This study is based principally on electron-                                                            mined by electron microprobe, the partitioning of
  microprobe analysesof about 200'grains of K-                                                              iron between Fd* and Fe3+ has been estimated
  bearing mica from about 20 different samples.                                                             from Si content. For an ideal composition within the
  Almost all the crystals analyzed are at least 1C0pm                                                       celadonite - leucophyllite - muscovite composition
  across.The analyses werecarried out by wavelength'                                                        space,both Al + Fe3+and Mg + Fd+ are fixed for
  dispersionspectrometry on a Cambridge Microscan                                                           any particular value of Si. Sinceboth Al and Mg are
                        MICAS IN TRIASSIC METAVOLCANIC ROCKS. WESTERN GREECE                                s99
                                         zlc                      ??"




                                                                                              23"
Ftc. 1. Generalizedgeological map of western Greeceshowing major tectonic zonesand samplelocations (arge dots).
   E Epidavros; K Kalamae, L Lakonia, N Lakmon Mountains, M Melidoni, T Tyros, Z Zarouhla,


determined,the partitioning of Fe can be estimateei,      muscovite- paragonite) are minor. The few samples
and can be checkedagainst total Fe determined by          wherethe differencebetwsenobserved  and calculated
analysis.In almost all analyses that meetthe criteria     Fe exceed 0.22have beenomitted.
mentionedabove(K+Na>1.65; volatiles 17Vo),
calculated and observed amounts of total Fe lie                      .   CHEMICAL VARIATIoN
within the limits setby analytical precision. This sug-
gests that substitutions not within the plane of            Most analyzed samplesare chemically similar to
celadonite - leucophyllite - muscovite (except for        K-mica previously analyzed by Wise & Eugster
600                                                     THE CANADIAN MINERALOGIST


                                      K a l a m aL a k o n i a a r o u h l a y r o sE p i d a v r o s L a k m o nM e l i d o n i
                                                 e           Z              T

lawsonite
clinozoisite
epidote
pumpellyite
actinolite
              i
c eI a d o nt e
leucoceladonite
leucophyllite
phengite
phengite-paragonite
par'agonite
c hl o r i t e
K-feldspar
albite
quartz
hematite
calcite
t i t a ni t e
vermiculite


                                                    associatedwith K-bearing micas at the localities studied.
                          Frc. 2. Mineral assemblages




                          2.                                         BY      I'IICROPROBE
                                               OF!'IICAS,AS DETER}{INEDELECTRON
                                      COMPOSITIONS
                      TABLE REPRESENTATIVE
                                            L-Cel                             Cel        Pg-l'ls   Pg-l'ls   Pg-l'ls   Pg-lls    Leuc    Cel
             L-cel         Leuc Ph            '18        Ph       CeI
                                                                                                                                          73
                ?           I   16                       21       28          40          44        45        47        49        58

s.t02        55.1r         51.92 49.66      -53.97       48.07 5 6 . 7 3      57.28 54.19 47.59 46.39                  46.26     53.25 53.69
T102          0.00          0.00 0.00         0.00         0.00 0.18           0.00 0.00 0.00 0.00                      0.00      0.00 0.33
A1203        14.8s         21.L0 28.34       14.01       33.41 4.87            2.Il 29.33 3 3 . 6 9 3 5 . 1            37.63     19.59 2.80
              7.66          6.97 3.25         9.80         1.60 17.05         20.33 1.64 3.19 2.02                      1. 3 9    5.99 2r,28
Fer0,
              0.00          0.00 0.00         0.00         o,26 0.00           0.11 0.00 0.00 0.00                      0.00      0.00 0.09
liln0                                                                                                                   0.10      4.63 6.35
nSo           5.95          4.77 1.91         5.73         0.56 7.24           A.22 0.54 1.05 0.39
CaO           0.08          0.00 0.00         0.0,         o.L2 0.13           0.04 0.08 0.09 0.08                      0.20      0.00 0.50
Nazo          0.00          0.06 0.r2         0.00         0.60 . 0.00         0.05 5.06 2.26 5.38                      6.96      0.24 0.00
KzO          10.50         10.40 10.43       11.06'      . 1 01 3 1 0 . 0 0
                                                             .                10.48 6.47 8.24 4.03                      2.12     10.01 9.21
Total        94.15         95.22 93.7L       94.64        94,75 96.20         98.62 97.31 9 6 . 1 1 9 3 . 4 0          94.66     93.71 94.2s

                            7.015. .714
                                  6          7.446       a too    7.855       7.858      6.930     6.252     6.163     6.019     7.257   7.7n
sJ           7.541                                                                                                               0.000   0.036
Ti           0.000          0.000 0.000      0.000       0.000 0 . 0 1 9      0. 0 0 0   0.000     0.000     0.000     0.000
Al"*         2.396          3.361 4.517      2.279       5.?44 0.795          0.341      4.422     5.218     5.499     5.772     3.148   0.475
Fe"'         0.789          0.709 0.330      1.018       0 .160 1 . 7 7 6     2.099      0.158     0.315     0.202     0.136     0.614   2.036
             0.000          0.000 0.000      0.000       0.029 0 . 0 0 0      0.013      0.000     0.000     0.000     0.000     0.000   0.011
liln                                                              '|          'l                                       0.019     0.940   1.363
l'lg         1.213          0.961 0.385      1. 1 7 8    0 . 1 1 I .494          .681    0.103     0.206     0,077
             0.012          0.000 0.000      0.010       0.017 0.019          0.006      0.011     0.013     0.011     0.028     0.000   4.077
Ca
Na           0.000          0.016 0.031      0.000       0.155 0"000          0.013      1"255     0.576     1.386     1.756     0.063   0.000
K            1.833          1.793 1.799      L.947       1.721 1.766          1.834      1.056     1.381     0.683     0.352     L.740   r.692

IvAl                                                                                      1.07      1.75     1.84       1.98      0.74    0.27
       cut. 9.46             0.98 1.zg        0.55        r.60     0.15        0.14
vIAl                                                                                                                    3.79 2.40 0.2r
       cul. 1.94             2.38     3.23 1.73            J.Oa 0.65 0.20 3.35 3.47 3.66
 Fe3+ca1c .52
        0                    0.61     0.05 0.83          -0.04  1.50 1.94 -0.28 0.28 0.18                               0.19 0.34 2.06
                             0.05 0.33       0.27         0.29 0.36   0.18 0.83 0.05 0.09                              -0.00 0.32 0.37
 F e 2 + c a l c0 . 3 3                                                                                                -0.05 -0.04 -0.13
   A Fe -0,06                0 . 0 5 -0.05 - 0 . 0 8     -0.09 -0.08 -0.02 -0.39 -0.01 -0.06

  A Fe is dlfference betweendetermined and calculated Fe.
 rey'io'drpjeii-i,a rvr. io rvi, is Mir-iq. ir r.rsr- zs LKB5l. 40 LK842.44
                                                   lz.                     r38. 45T15.47732.4er32-
 58 17. 73 LK 842.
                         MICAS IN TRIASSIC METAVOLCANIC          ROCKS. WESTERN GREECE                          601

                                                       CELADONITE
                                                 KaFezMga[Sir0zo]
                                                             (OH)r


                                                -'
                                                                                    r Melidoni
                                                                                    . Lakmon Mountains
                                                                                    o Zarouchla
                                                                                    a Tyros
                                                                                    o Lakonia
                                                                                    o Kalamae
                                                                                    o French al.(1977)
                                                                                            et
                                                                                    ' Wise Eugster
                                                                                          &       (1964)
                                                                                    + Foster(1969)


                         Y--*



                  /,




        6                                                                            7.5                  I
        MUSCoVITE                                         skot                                LEUCIPHYLLITE
                (0H),
     K2At{SioAl202ol                                                                        KzAlzMgz[SieOzo]
                                                                                                        (OH)r
Ftc. 3.-celadonite-leucophyllite-muscovite triangular diagram, showing composition of samplesfrom westerncreece
   and samplesof celadonite and related minerals reported by French it ot. (iglz), Foster (1969)and Wise & Eugster
   (1964).Samplesplotted on,basisof Si and Al composition. Boundariesbetweengroupi of compositions
                                                                                                           thar are
   given different names zue located in compositionai gaps, but are otherwise arbitrary.-


(19&), Fosrer(1969)and Frenchet qt. (t977) (FiE.           Only a ferv of theseplots are illustrated here. Some
3). Most of the analyzed grains fall within the            plots, such as Si against (IvAl + Na + K), show a
celadonite- leucophyllite- muscovitefield. Some            reasonablestraight-line distribution with little scat-
celadonitecompositions(c/ Wise & Eugster 1964,             ter. Plots involving the element Mg, such as
Foster 1969)revealan apparentdeficiencyin total            (Si + Mg) againsttotal Al, Mg + Ti) against2 uAl,
Al + Si, so that they plot outside the muscovite-          and vIAl against Mg, also show a reasonable
 c€ladonite-leucophyllite field in Figure 3 (e.g.; com.    straight-line distribution for all micas except
position 40, Table 2). They show up to l5go substi-        cpladoniteand muscovite-paragonite,wherethere
tution of a ferrimuscovite component KrFeo3-               is considerable scatter.
sidAl2o2o(oH)4.                                               The causeof this scatter is illustrated in Figure 4,
   A variety of scatter plots of pairs of elementsor       which showstotal Al againstMg/Fe+. (The Fd*
groups of elementshave been examined in order to           is a calculatedvalue, and should therefore be treated
assesschemicalvariability and elementsubstitution.         with caution). This shows that for muscovite -
                                               THE CANADIAN MINERALOGIST


                                                             used, there is only one major compositionalgap'
                             -
                     Muscovlte paragonlto                    betweenceladoniteand "leucoceladonite".
                                                                Except for samples phengiteand muscovite,the
                                                                                    of
     lit;"-- --                                              sodium content of the micas is generallytoo small
                                                                                                0.0690Na2O. The
     Phonglto                                                to determineand never exceeds
            D!
       oo                                                    sodium content of phengite attains 0.6V0 Na2O
            !
                dq
                                                             (7.5V0paragonitecomponent)(#21' Table t). The
                                                             sodium content of the muscovite-paragonitelies
                                                         9
                                                             between 2.3 and 7.090 Na2O (between30Vo and
                                                         a
                                                             75Voparagonitecomponent). (No pure K-muscovile
                                                             hasbeenfound.) In somemuscovite-paragonite' the
                       o o Leucophyllho                                                                of
                                                             total alkalis are substantiallyin excess stoichio-
                            b
                                                             metricvalues(from 2.1 to2.4); many of thesealkali-
                                o)'                           rich compositions show poor agreementbetween
                                                              observed  and calculated (e.g., #44,Table2), and
                                                                                        Fe
                                  o+td
                                                              thus do not lie in the celadonite-leucophyllite-
                                                              muscovitecompositionplane. The paragoniteoccurs
                                               "
                                 " Loucoclladonlto
                                                              as relatively large, optically clean crystalsnso that
                                                              the excess alkalis is not likely due to a dispersed
                                                                         in
                                                              microcrystallinephase.

                                                               Souo SolurloN AND CnsMrcAL SUBSTITUTIoN

                                                                 In the absenceof X-ray data, a definitive discus-
                                                              sion of the structrue of the various micas is not pos-
                                                              sible. However, certain conclusionscan be drawn
                                                              from the detailed chemicaldata presented       here.
    01234567>10                                                  The celadonitestructure may be distinct from that
              Ms/F%                                           of the other K-rich micas; celadonitecompositions
                                                              show a distinctive behavior on various scatter-plots,
Flc. 4. Plot of Al versas       for
                         Mg/Fe2+ micasfrom western
                                                              and there is a substantialcompositional gap between
   Greece.   Symbols in Figure3 @d+ is calculated).
                      as
                                                              celadoniteand "leucoceladonite". Limited substi'
                                                              tution into the ideal celadonite  structureis possible,
                                                              of Fe3lAl for Mgsi, and of IvAl vIAl for Fe3*Si
paragoniteand for celadonitethere appearsto be                (Fig. 3). There is much greatersubstitution of F**
random substitution of Fd* for Mg, whereasin                  for Mg2+ than in the other K-micas, and this sub-
"leucoceladonite", leucophylliteand phengite,the              stitution is independentof Al content. The celadonite
extent of substitution of Fd+ for Mg is dependent             structure thus appearscapable of incorporating the
on the.Al content. The only exceptionis a small               relatively large Fe3+and Fd+ ions.
group of phengite compositions (from four differ-                Mica samplescontaining phengite, leucophyllite
ent localities)that are essentially lacking in Fd*.           and "leucoceladonite" components        appearto have
   This separation of muscovite-paragonite and                a cornmoncomposition that allows a systematicsub-
celadonite from the other micas also is illustrated in        stitution of Al for (Mg, Fd*) Si, possibly forming
a plot of total Al against Si + Mg + Mn + Fd"                 a solid-solutionseries.The substitutionof Fd* for
(Fig. 5). This figure shows muscovite-paragonite              Mg is dependent on Al content. The best-fitting
compositionslying closeto the muscovite-celadonite            linear trend through the compositions shown in
join. Kanehira & Banno (1960) and Velde (1965)                Figures 4 and 5 does not pass through any of the
demonstratedthat muscovite doesnot contain more               muscovite, leucophyllite or celadonite end-member
 thar. 25s/oceladonitesubstitution; the compositions           compositions.
reportedhereshowno more than l5q0 substilution,                   With the aluminous species,  thoe is up to 890sub-
which is shown as the "theoretical limit" by Velde             stitution of Na for K in phengite, and up to 75v/o
 (1965,his Fig. ). Similarly, celadonitecompositions           substitution in muscovite, to yield the paragonite-
lie closeto this join, although they do show rather            muscovite solid-solution series. Paragonite-
 more scatter. However, phengite, leucophyllite and            muscovite shows slight substitution of Fe3" Mg Si
 "leucoceladonite" show increasingly positive devi-            for IvAl vIAl (along the muscovite-celadonite join
 ation from the muscovile-celadonite join, although            in Figures 3 and 4), but no substitution of Mg in the
 they do not lie clo$e to the stoichiometric                   absence Fe3+(i.e., no leucophyllitecomponent).
                                                                        of
 muscovite-leucophyllite join. In all the scatterplots         Substitution of Fd" for MgF appears to be ran-
                       MICAS IN TRIASSIC METAVOLCANIC      ROCKS. WESTERN GREECE                      603
dom, in contrast to the phengitecompositions.Thus          I
the muscovite-paragonitestructuremay be differ-
ent from that of phengite-leucophyllite-,,leuco-
celadonite".
                                                           o
   In his experimentalwork, Velde (1965)recognized
a distinction between muscovite, "Fe2+Fe3i
celadonite" and the "Fe2+Al celadonite,,-
 muscoviteseries,with the latter two showingno solid       1
solution in muscovite. The ,.MgFd* celadonite"
component (i.e., the celadoniteof this paper) shows
some solid solution with muscovite, particularly at      Ea
high pressures.
   There is a small group of compositionsof phen-
gite and leucophyllite that contain essentially no
Fd+ substituting for Mg (e.g,, #8, Table 2), ,and
thus form a distinct cluster in Figure 4. The sig-
nificance of these compositions is uncertain.


          Pptnocnepny oF TI{E MrcAs

    K-bearing micas occur in four main forms: (l)
 large crystals that are an alteration product of                        $+mg+F€lL+Mn
phenocrysts of ferromagnesian minerals @e-Piper
 1983a)and possibly feldspar, or of glass in the        Ftc. 5. Plot of Al yenszs + Mg + Mn + Fd+ for micas
                                                                                Si
groundmass(Fig. 6), (2) large crystals filling amyg-       from western         Symbols in Figure Dashed
                                                                          Greece.       as        3.
 dales@igs.7, 8), (3) as large neomorphicminerals          line is trend of phengite-leucophyllite-"leuco-
 (Fig. 9), and ( ) as fine-grained groundmass. Color       celadonite"compositions.  Amount of Fe?+is calcu-
                                                           Iated.
variesaccordingto the iron contentof the minerals,
ranging from green or blue for celadonite to color-
less for phengiteand muscovite.                   i'
    In the low-grade metamorphic rocks of the              FAcroRs CoNtnolr-rNc Mlce CovposrtloN
Lakmon Mountains, clinopyroxene and plagioclase
phenocrysts are partly replaced by celadonite.          Metamorphic grade
Phlogopite in theserocks is also partly altered to
celadonite   and may thus be the sourceof potassium        Independentestimatesof metamorphicgrade of
for the celadonite.Patchesof groundmassin the           host rocks can be madefrom the mineral assemblages
Lakmon Mountain samples that are altered to             discussed  above and summarizedin Figure 2. The
celadonite may originally have been glass.              presence of unaltered pyroxene and feldspar at
    Crystalsor crystal aggregates mica are in places
                                  of                    Lakmon suggeststhat these rocks are aknost
rimmed by retrogrademetamorphicproducts,com-            unmetamorphosed.     The abundanceof paragonite
monly hydrated phyllosilicates.Hydrated celadonite      and clinozoisite at Tyros indicates higher tempera-
(Fig. O and vermiculite @e-Piper 1983a) rim             turesthan the chlorite-epidote-pumpellyite assem-
celadonite in the Lakmon Mountain samples.Ver-          blageof Lakoriia, Kalamae,Zarouhla and Metidoni.
miculite rims celadonite,and hydrated phengiterims      Degreeof crystallinity, estimatedfrom X-ray diffrac-
phengite in the Lakonia samples(illustrated in Pe-      togramsusingtle method of Kiibler (1968),increases
Piper & Kotopouli 1981,Fig. 6). Elsewhere;rrore         from the Lakmon Mountainq through Lakonia to
sodic or aluminous phasesrim the micas. Examples        Tyros (Table l).
include sodic phengite rimming phengite in the             Celadonite is found in the lowest-gade metamor-
Melidoni samplesand phengite rimming leucophyl-         phosed mafic volcanic rocks at Lakmon. It also
lite from Lakonia (Fre. 9).                             occurs in two samplesfrom Lakonia. Pumpellyite
   More complexrelationships     between mica phases    is absent in the rocks with celadonife. Muscovite-
are also illustrated in Figures 6-9. Mixed leucophyl-   paragonite is present in the highest-temperature
lite and chlorite are rimmed by a zone of chlorite      assemblages Tyros. "Leucoceladonite" is common
                                                                     at
and then an ouler rim of pure leucophyllite in a sam-   at Melidoni, and also occurs with lawsonite at
ple from Lakonia (Fig. 8). A samplefrom Kalamae         Kalamae.It is also commonin mineralsreportedby
has euhedral lawsonite and leucophyllite in a mass      Foster (1969).Phengiteand leucophyllite occur at
of "leucoceladonite" crystals (Fig. 7).                 Lakonia, Zarouhla, Kalamae and Melidoni.
604                           THE CANADIAN MINERALOGIST




      Frc. 6. Blue-green celadonite (Cel) rimmed by a dusty zone (d) of quartz and
         celadoniteand then by light greenhydro-celadonite(H-cel) replacing groundmass
         (possiblyoriginally glass).851' andesite,Lakmon Mountains. Plane-polarizedlight.
         Scalebar I mm.




      Frc. ?. Amygdale or phenocrystpseudomorphfilled with leucoceladonite  (L-Cel) with
         euhedrallawsonite (Lws) and leucophyllite (Leuc). KVI, basalt' Kalamae. Plane-
         polarized light. Scalebar I mm.
        MICAS IN TRIASSIC METAVOLCANIC ROCKS. WESTERN GREECE                        605




Flc. 8. Leucophyllire(Leuc) and chlorite (Chl) rimmed by a dusty zone of chlorite
   (Chl) and then leucophyllite(Leuc), apparently.fillingan amygdale.D5, basalt,
   Lakonia. Plane-polarized  light. Scalebar I mm.




Ftc.9,-Leucophyllite(Leuc),in part as spherules,
                                               rimmed by phengite@h), in places
   sodium-rich. L7, basalt, Lakonia. Crossedpolars. Scalebarl mm.
606                                    THE CANADIAN MINERALOGIST


   Both the regional variation of mica minerals with      the metamorphic reactions involved in the develop-
metamorphic assemblage the petrographic rela-
                           and                            ment of micas in the rocks studied. Celadonite
tionships describedabovesuggest   that there is a pro-    developsfrom ferromagnesian     minerals, particularly
grade metamorphic development of increasingly             pyroxene, with K derived from alteration of a
aluminous micas, from celadoniteto the "leuco'            potassium-bearinggroundmassor of biotite to chlo-
celadonite"-leucophyllite-phengite series and             rite. "Leucoceladoniie" developsby substitution of
finally to muscovite-paragonite. Retrograde               Al for Fe in celadonite. Al is releasedby the albiti-
metamorphismleadsto the formation of vermicu-             zation of plagioclase,
                                                                               with Ca and Fe accommodated
lite (Pe-Piper1983a) hydrated mica (Pe-Piper&
                      or                                  in pumpellyite and epidote. Continued replacement
Kotopouli l98l).                                          of Fe and Mg by Al leads to leucophyllite, phengite
                                                          and, eventually, muscovite. There is a parallel
Host-rock composition                                     developmentin epidote (Fig. l0)' which shows a
                                                          progressivebuildup in Al and decrease Fe as the
                                                                                                   in
   Within individual sample-areas,rocks that are          micasbecomemore aluminous.Sodic phengiteand
more felsic tend to contain a mica closerto musco-        paragonite develop at higher temperatures,as Na is
vite in composition. Thus, for example,at Melidoni        released  from albite. Representative  equationsfor
(Pe-Piper et al, l98l), basalts and andesitescontain      thesereactionsare given in Table 3.
"leucoceladonite" with rare phengite, whereas
dacites contain phengite zoned outward to sodic
phengite.The virtually unmetamorphosed      rocks at                           CoNcLusIoNs
Epidawos and Lakmon are of similar metamorphic
grade. They contarn vermiculite and lack epidote.             K-bearing dioctahedral micas with a wide range
The basalts and andesites at Lakmon contain                of chemicalcompositionare found in potassium-rich
celadonite; the rhyodacites at Epidawos contain            mafic rocks that haveundergonegreenschist-facies
"leucoceladonite".                                         metamorphism. The micas become progressively
                                                           more aluminouswith increasingmetamorphicgrade.
                                                           However, the key reactionsinvolve phasesof very
      RnIanToNsHTP MINERALCHEMISTRY
                 OF                                        variable composition, notably mica and epidote.
             To METAMoRPHIC      GRADE                     Thus, although representative chemical equations
                                                           can be written for the inferred reactions(e.9., Pe-
  The petrographic observations and inferred               Piper & Kotopouli 1981),they neitherprovide addi-
parageneticsequence minerals allow hrferences
                  of                         on            tional insight into the metamorphic reactions nor




                                                                      o/oFo




                                                         .Ph
                                                         Pat. ',.Ph                30    0\g


                                                             Par.
                                                                    L9UC
                                                            LeucLPh
                                                                 Cel. .L-Col
                 40                                                 'Cel

                 Fro. 10. Epidote compositions plotted on an Al-Ca-Fe triangular diagram, show-
                    ing compositionsassociated with eachtype of mica. Cel celadonite, L-Cel "leuco-
                    celadonite", Leuc leucophyllite,Par paragonite,Ph phengite.
                             MICAS     IN TRIASSIC     METAVOLCANIC         ROCKS.    WESTERN       GREECE                          607
                             TABLE RTPRESENTATIVE
                                  3.                     COMPOSITIOIII.IINERALS T}IEIXFERRED
                                                  CHEMICAL         OF         AIID
                               }IASS-BALANCE
                                          CHAIIGEs
                                                 ASSOCIA1ED II.IFERRED
                                                          UITH       I{ETAilORPHIC
                                                                                 REACTIONS
                l,lineral                                                             l'|ass-balanechanqes
                Seouence               RepresentatiE   Fomulqe               Pos't I vE-------N-e
                                                                                 t                 qa-[iG-
                Pvrc)!9ne      cus.i[g:.+F"t zA]
                                           . o.q(slz.o0z+)
                                                                            I.7( l.lFe 0.3S1    3.4Ca .lil9
                                                                                                     2
                celadon
                      tre      K.,               e:     r.roro) toH)n
                                .1e.,.rFe2lo.rreft o.ntsi
                                                                            0.2( I .gAt        0 . 1 l { g1 . 2 F e0 . 4 S i
                Leuco-         l(.. t.ils,. z Fe2lr,Fe:+sAl2.3(st7.sozo)(oH)4
                                        -t ,
                Celadonlte       t              u.   U
                                                                            2,Al                                0
                                                                                               o . l K 0 . 8 U 9 . 8 F e0 . 8 5 1
                phensite       Kr. gnso.cF"6:Al (s.t6.soz0 )
                                                        ) (0H
                                             a.s

                Plagloclaso(An50)             CaNaAl
                                                   35f50l6
                                                                            l.oNal.0Sl         1 . 0 C al . 0 A l
                Alblte                        Na2Al25l60t6


                Bloti te       (l                          (Al       (0H)
                                    .4nu0..qx94.8F"0 I
                                                 . BTio.      zsl 6020 4
                                                                 2.0t'lg .]Fel.3Al l.0Sl 1.4( 0.3Na .lTt
                                                                       1                           0
                chlorlte       N"o.1M9o.aF"t.9(A13.3s17020)(0H)16


                Pvrcxene       cu:.4ff93.qFet.zAlo.a(siz.e0za)
                                                                            0.6Ca0.8Fe 3.641      3,4l,lgl.65l
                Fe-ep dot€
                    l          CanFerAl(S1     (0H
                                     O r0.,.,)     )
                                                                            1.0A1                1.4Fe
                A1-epldote     CaOFeO.rAl(Sl    ) (0H)
                                        U r0r.,




allow calibration with experimentally determined                                                REFERENcES
phase-equilibria.Many of the micas are pseudo-
morphs of phenocrysts fill amygdales,
                          or                and mica                   BeNNenr,D. & Brxoen, H. (1968): Ziir Geologie der
type is dependent bulk-rock compositionat any
                     on                                                  Argolis-Halbinsel (Peloponnes, Griechenland).
one metamorphic grade. Theseobservationssuggest                          Geol. Polaeont, 2, 15l-162.
that local equilibria under the low-grade meta-
morphic conditionsmay be important in determin-                        CHerrsnrse, N.B. (1973): Low-temperature compati-
ing what type of mica is present.                                        bility relations of the assemblagequutz - paragonite
                                                                         and thermodynamic status of the phase rectorite.
   Someindication of the rangeof temperatureand                          Contr. Mineral. Petrologlt 42, 259-271.
pressure   conditionsis givenby Velde's(1972)deter-
mination of. 420"C as the temperature of maximum                       Drrn, W.A., Howrr, R.A. & Zussuar, J. (1971):Rock-
stability for celadonite.Chatterjee(1973)determined                       Forming Minerals. 3. Sheet Silicates (2nd edition).
that paragonite+ quartz is unstablebelow 335oCat                          Longmans, London,
2 to 7 kbar.
   Mineral chemistry suggeststhat there are three                      Fosrsn, M.D. (1969): Studies of celadonite and glau-
structurally distinct mineral phases. In both                            conite. U.S. Geol. Sum. Prof. Pap.6l4-F.
celadonite   and mqscovite,thereis a rangeof substi-
                                                                       FnsNcH, W.J., HesseN, M.D. & Wesrcorr, J.E,
tution of Fe2+ for Mg; in contrast, in the                               (1977): A celadonite-vermiculite seriesfrom the vol-
                  -             -
leucoceladonite leucophyllite phengiteseries the ,                       canic rocks of the Ochils, Stirlingshire. Mineral.
F&* /Mg ratio is dependenton the Al content. In                          Mag. 41,481485.
this series there is probably solid solution with sys-
tematic substitution of Al for (Mg, Fe2*) Si.                          Fvrnolaxn, N. (1970): Die bis heute unbekannten
Although there is limited substitution of Na for K                        palaeozoischenSchichten sud<istlichvon Kalamae.
in phengite,only in muscoviteis there extensive solid-                    Geol. Soc. GreeceBull.8. 70-81.
solution with paragonite.
                                                                       Guroorrr, C.V. & Sessr,F.P. (1976): Muscovite as a
                                                                         petrogenetic indicator mineral in pelitic schists.
              ACKNowLEDGEMENTS                                           Neues Jahrb. Mineral. Abh. 1n,97-142.

  I am grateful to Dr. D.B. Clarke and Mr. R.                          Kawesrna, K. & Bemo, S. (1960): Ferriphengite and
MacKay for useof the DalhousieUniversity electron                        aegirinejadeite from the Iunori district. Geol. Soc.
microprobe.I am alsograteful to Drs. B. Velde, H.                        Japan 66, 65+659.
Massonne,D.J.W. Piper, W. Jolly, R.F. Martin and                       K{JBlpn, B. (1968): Evaluation quantitative -du
an anonymous reviewer for critically reviewing the                        metamorphisme par la cristallinite de I'illite. Etat
manuscript. This study has been supported by an                           de progr0s r6alis6 ces dernidres ann6es. Bull. Centre
NSERC operating grant to G. Pe-Piper.                                     Rech. Pau - Soc,Nat. Pdtrole Aquitaine 2, 385-397.
608                                  THE CANADIAN MINERALOGIST

Paxecos, A.G., Pr, G.G., Ftren, D.J.W. &                     PaNecos, A.G., Prrnn,D.J.W. & Koropoult,
  Koropowr,C.N. (1979):                      sub-
                         Age and stratigraphic           C.N. (1982):
                                                                    The ? mid Triassicvolcanicrocks of
  division of the Phyllite Series,Krokee region,         Lakonia,Greece.Geol.Mag. l\9,77-85.
  Peloponnese,       NeuesJahrb. Geol.Paliiont,
               Greece.
  Monatsh,3, l8l-190.                                               & VanNavAs, (1981):The volcanic
                                                                                  S.
                                                         rocks of Melidoni (Locris, Greece).
                                                                                           NeuesJahrb.
Pn-Pppn, (1982):Geochemistry,
       G.                   tectonicsettingand           Mineral. Abh. 143, 102-lll,
  metamorphism Mid-Triassicvolcanicrocks of
               of
  Greece.           85,
         Tectonophys. 253-n2.                         Rucrr,rocs,J.C. & GaspexnNt,E.L. (1969):Specifica-
                                                        tions of a completeprogramfor processing
                                                                                               electron
-       (1983a):Triassicshoshonites andesites,
                                  and            Lak-   microprobeanalyticaldata. EMPADR VII. Dep.
    mon Mountains,western   continentalGreece:differ-   Geology, Univ. Toronto, Toronto, OnL
    encesin primary geochemistryand sheet silicate
    alterationproducts.Lithos !6, 23-33.                Verne,B. (1965):Phengite  micas:synthesis,stability
                                                          andnaturaloccurrence,  Amer, J. Sci.?.63,88G913.
        (1983b):The Triassicvolcanicrocksof Tyros,
    Zarouhla,Kalamae,    and Epidavros,Peloponnese, -(1972):         Celadonite mica:solidsolutionandsta-
    Greece. Schweiz.Mineral. Petrog.Mitt, 63,2y',9-26f,                                              ,
                                                          bility. Cont. Mineral. Petrology 37, 235-247

        (1984):Low-grademetamorphic     mineralsfrom WrsB,W.S. & Euosmn,H.P. (1964):             syn-
                                                                                       Celadonite;
    the Triassicvolcanicrocks of Tyros, Zarouhla, and                                          Amer,
                                                       thesis, thermal stability and occurrence.
    Kalamae, Peloponnese,Greece. Neues Jahrb.          Mineral,49, 1031-1083.
    Mineral.Abh, 149,163-175.

        & Koropour.l C.N. (1981):Very low grade
    metamorphism ? Triassic
                 of                  WestHellenic
                            volcanics,
    Nappes,southern  Peloponnese,
                                Greece.Geol, Soc,                          revisedmanuscriptaccepted
                                                             March 18, 1985,
                                                      Received
    Amer. Bull, 92, 1762-1806.                          June16, 1985.

								
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