REND/CONT/ Socio:td Itallana dl Mlneralo"la e Po:trolollla, JI (2): pp. 617-621

COmunlCllzlone presentata all.. Rlunlone della SIMP In Abano (Padoya) 1\ 3 gluino 1982

MONTICELLITE-CLINTONITEBEARING ASSEMBLAGES AT THE SOUTHERN BORDER

OF THE ADAMELLO-MASSIF

PETER ULMER

lnstitut Hit Ktistallographie und Petrographie, ETH·Zentrum, CH..a092 Zurich

ABSTRACT. - Some lenses of matly dolomites arelocalized in the contact zone between gabbroiccumulates and the intermediate intrusions of theRe di Castdlo Pluton at the southern border of theTertiary, ca!calkaline Adamdlo Massif. The followingmineral assemblages formed in these lenses as aresult of a high temperature contact metamorphism:monticdlite-forsterite-clintonite (near the contactwith the gabbroic cumul,ues) and forsterite.diopside.dintonite (away from the conlact).

A later intrusion of intermooiate plutonic rockslocally produced retrograde overprinting with theformation of chlorite and serpentine, as wdl as thebreakdown of monticellite. Calculated phase dia·grams show that the first contact m.etamorphismtook place under monticdlite facies conditions anda high value of Xoo. in the fluid. The second phase,on the contrary, took place at about 550· C anda low value of Xoo2 ,

In the case of coexistence of monticellite andforsterite grains, the substitution of forsterite in thestruclUre of monticdlite and vice versa has beenused as a gcothermometer. Chemical profiles throughmonticdlite and forsterite.grains show homogeneousdistribution palterns for a temperature around850· C in cases where no retrograde overprintingis obvious. Assemblages affected by retrograde over·printing result in a division of the temperaturedistribution pattern into the cores of the grainswith temperatures between 800 and 90lY C andinto a border zone with"" 550·650" C.

These twO metamorphic events in the same car·bonate rocks suggest that the gabbroic cumulates,as wdl as the intermediate intrusions, have crystal­lized in situ at a very shallow cnlSlal levd (max.overburden 2 km).

RIASSUNTO. - Nella zona di comano tra i cumu·lad gabbrid e le intrusioni intermediarie del plutonedi Re di Castello al bordo meridionale dell'Adamelloappaiono lenti di dolomia argillosa. In queste ul·time, come conseguenza del metamorfismo di con·tallO di alto grado dovuto all'intrusione dei gabbri,si formarono le seguenti paragenesi: monticellite­forsterite·dintonite (xamhofitlite) (vicino al contalto)e forsterite-<liopside·dintonite (lontano dal conlano).

Una seguente intrusione di rocce intermed.iarie

porta localmente ad una metamorfosi retrogradasovrapposta con formazione di dorite e serpemino,(osl come i1 .. breakdown 1O della monticellite. Dia·grammi di fase (a!colati mOSlrano che la primametamorfosi di contatto si sia svolra ad un valoredi Xco.. alto e ad ahe temperature.

La Seconda fase raggiunse invece circa 550· Coon un valore di Xoo. basso.

Nd caso di coesistenza tra forsterite e monticel·lite, si pub usare la sostituzionc: ddla forstedtenella struttura ddla momicdlite e viceveru, comemisura della temperatura. Profili di temperaturamisurati in grani di momicdlite e fOTSterite nelleparagenesi che non hanno subito una metamorfosiretrograda, mostrano una distrihuzione omogeneaoon temperatute che si aggirano ua gli 850 e i90lY C. Nelle paragenesi marcate da metamorfosiretrograda le misurazioni diedero una divisione ddlatemperatura in due parti. Un settore centrale contemperature di 800-9OlY C e un bordo di 550-650G C.

Questi due differenti metamorfismi negli stessiC1Irbonati dimostrano che sia i cumulati gabbricicosl come le intrusioni intermediarie cristallizzaronoin situ in un Jivdlo crostale moho alto (caperturamassima 2 km).

1. Introduction

In the Lago della Vacca area, at thesouthern border of the Tertiary, southernAlpine, calcalkaline Adamello intrusion (AlpiBresciane, Northern Italy) occur some lensesof high temperature contact metamorphic,siliceous, argillitic marbles. The area lieswithin the Re di Castello Pluton, thesouthernmost intrusion of the Adamello mas­sif, which intruded the southern Alpine ba­sement and the Permian and Lower to MiddleTriassic sedimentary pile 47 to 40 m.y. ago.

The igneous rocks in this area have beenstudied and described by different authors(e.g. G.B. DAL PIAZ, A. BlANCHI, E. CAL-

618 P. ULMER

Lago detla Vacca Area30001

Legend

GJ Re di Castello Tonalites

~ Re d; Castello Oior;tes

t-:;~l Gabbroic Cumulates

• Contact Metamorphic Sediments

I:·..:::'!l Quarternary

loo! Pso Croce Domini

X

xX

X

x X

X X

X

x

[±J Re d; Coll$tello Pluton

00 Adamello Pluton

B Crystal;ne Basement

D Sedimentary Cover

Geological

Map

,.'

.: .....

Cntdi Blumone

Fig. I. _ Geological map of the Lago della Vacal area at the southern botder of the Adamello massif(RI:' di Castello Pluton).

MONTICELLlTE-CLlNTONITE BEARING ASSEMBLAGES ETC. 619

LEGARI, D. COLBERTALDO, R. MALARODA).In the western and northern part of the

studied area the rocks mainly consist of in­termediate plutOnic rocks with the localname Re di Castello-Tonalite (fig. 1). Theronalite corresponds to a fine- to medium­grained biotite·hornblende tonalite with alarge number of femic, endogenic xenoliths.The tonalites are internally heterogeneous andshow transitions to diorites along fluidallyoriented zones (e.g. near the Rifugio Ga­briella Rosa). Lenses of gabbroic rocks(cumulates) or clusters of hornblende andplagioclase crystals with clear affinities tothe nearby cumulates of the Cornone diBlumone are locally concentrated along moreor less straight zones.

The eastern part of. the atea is composedof gabhroic rocks of the Cornone di Blumone.This complex mainly consists of coarse­grai ned ti tanomagneti te -cl inopyroxene -horn­blende-plagioclase (An 80-90)-gabbros whichdisplay cumulate structures. Olivine-chromi­ferous spinel-cpx-opx-hbl-cumulates occur atthe base of this complex or isolated in thetonalites. The whole complex has been af­fected by a post-accumulation event of brec­dation and hornblenditisation which hasalso produced pegmatitic dikes consistingof enormous hornblende and plagioclasecrystals. The cumulates are clearly olderthan the tonalites as indicated by stOppingphenomena at the contact as well as intrusioninto the cumulates from the side and below.In addition, the tonalites cross-cut the maficcomplex in large dikes.

The sedimentary carbonate lenses are lo­calized in the northeastern part near PassoBlumone between the cumulates and thetonalites. To the southwest, the more or lessstraight zone of lenses intersects the tonalitesand are accompanied by cumulate lenses andthe so-called «diorite a tozze» containingquadratic hornblende. These diorites containabundant hornblende and plagioclase crystalscoming from the cumulates. The southernpart of the sedimentary lenses seems to fol­low the old contact with the cumulates.However, these cumulates are broken up andhave been intruded by the tonalites, resultingin « diorite a tone» and some lenses of lessaffected cumulates. The sedimentary carbo­nate lenses have dimensions ranging from

a few dm to 300 m long at the Passo Blu­mone.

In this large lens, an old sedimentarylayering can be observed. Layers consistingof clinopyroxene and clintonite, partiallywith boudinage structures, alternate withforsterite-monticellite layers, each approxima­tely 5 cm thick. This layering correspondsto primary argillitic and dolomitic layers.A 5 m thick layer of Predazzite (calcite­hrucite rock), corresponding to a dolomite,is found at the Passo Blumone. D. COLDER­TALDO and R. MALARODA have placed theserocks in the Lower Anisian (Formazione diAngolo inferiore). However, in the author'sopinion due to total overprinting of theprimary mineral assemblages and the lack offossils or direct contact to the sediments inthe Alta Valle del Caffaro (R. MALARODA,1955; U. ROESLI and P. ULMER, 1982) nodefinite age can be determined. Based onlithological aspeCts, both Lower Anisian andLower Ladinian (Form. di Livinalongolo) orUpper Anisian to Lower Carnian (Form. diEsino s.l.) ages can be postulated.

2. Some mineralogical a8pect8

The mineral determinations have beenmade by thin section observations, XRD andelectron microprobe analyses of the mineralspeCies.

The following minerals have been found:

I. Fassaitic pyroxene (diopside series)2. Olivine (forsterite content 92-95 %)3. Calcite .4. Hen;ynitic spinel5. Chlorite (c1inochlore composition)6. Andraditic garnet (always accompaing

monticellite as an inclusion)7. Clintonite or xanthophyllite

Clintonite was discovered and has al­ready been described from this area andfrom nearby (Costone di Valbona) byA. BIANCHI, O. HIEKE and E. SANERO (1940,45, 46). Clintonite is a green, calcium brittlemica with a phlogopite structure (niocta­hedral) with the approximate formulaCa(Mg,Alh(AI,Si)~OH~OHh. Clintonite is arelatively rare mineral. This is more theconsequence of the spedfic bulk composition

620 P. ULMER

of the rock which permits the formation ofthis mica rather than thermodynamic con·ditions, as clintonite has a large stabilityfield (J. RICE, 1979, and this work). Clin­lonite will only be formed if enough ma·gnesium, calcium and alumina is available andonly a minimal amount of potassium ispresent, otherwise the farmalian of phlogo­pile would be preferred. These conditionsare: fulfilled by an argillitic dolomite withkaolinitic or montmorillonitic clay mineralsinstead of ilIilic clay.

1450r-r--.-/~~~-.,.-,-.\-,

1\"Cl

1200

P,2kb

1000

Fig. 3. - Experimental solvus Ixtwcen forslttite.md mOl'llioe.llile al 2 kbars in a lemperature venus;Ktivity (of forslc:rite}-diagnm. (From R. WAIIND:and W. LUTH, 1972).

FeMo

800

ta,n;1CQ2SiO,

CaMgSiO{ ",-ot~in._~c,Q",F. $iO,

-"1fjfj::-...,c------Oli~ill. '

Ns2siO, F·2SiO,Fo,sttril Fay"lil

Fig. 2. - Composition diagram of the olivioes Indc..()livinc:s in the system Mg.SiO,.FcoSiO•.c..,siO•.

8. Monticellite

As yet this mineral has not been describedfrom the Adamello aurrole. Monticellite ap­pears near the comact with the cumulates orin the middle of the lenses isolated in thetonalites. It forms only under high tempe­ratu~. Contact metamorphic conditions incarbonate rocks. Monticellite is an onhosili­cate which has the same space group (Pbnm)as olivine and a similar struCture to latter.The difference with olivine lies in the dimen­sions of the cation sites in the crystal lattice.Olivine has two similar sites for Mg andFe(lI'). Momicellite has a larger one for Caand a smaller one for Mg and Fe(II·). Thisalso explains why monticellite and olivineshow a large miscibility gap (6g. 2).

R. WARNER and W. LUTH (1973) haveexperimentally investigated this miscibilitygap. Their experiments were carried out from1-10000 bar and 800-1400° C. Fig. 3 showsthe experimental salvus for 2 kbars which ispracticaHy symmetric and attains a maximum

solubility of the components (forsterite andmonticellitel of about 18 % between 1300and 1400° C according to the existing pres­sure. In the constructed phase diagram (6g.4). it can be seen that monticellite reacts tomerwinite (Ca.Mg[Si~h) and forsterite at13200 C and 10 kbars. The solid solutionbehaviour of coexisting forsterite and mon­ticellite can be used as a geothermometer(see chapter 4l.

3, The paragenelle8

The mineral assemblages can be dividedintO twO groups. One group shows one hightemperature metamorphic event with a fewwater bearing minerals and is found near thecontact with the gabbroic cumulates in theP.so Blumone area. A second group showstwo differt'nt metamorphic events: an olderone which corresponds to group one and isoverprinted by H 20 bearing minerals of asecond retrograde evem. These rocks arelocalized in the isolated lenses in the tonalitesand near the contact zone between tonalitesand sediments.

MONTICELLlTE-CLlNTONITI:. BEARING ASSEMBLAGES ETC. 621

1300 ,Me • Mo.

Fo0.8

P=10kb

0.4 0 &alo

Me + FOJ$

0.2Mo

1100 I

1200

1400

1"('0

Fig. 4. _ Phasaelationships in the lynem mon­ticcllile-fontc:ritc: at 10 kbal'$ in a temperatufe+aclivity~iqram. (From R. WUNEl and W. LtlTH,1972).

Fig. 5. - Microsraph of diopsidc: free: dintonitc:bc:ai-ing monticdlitc: rock ~~ P.50 Blumone: ­Di == diopsidc:, Mo == monlicdlllC:, Fo = fontc:ntc:,Cbi = chloritc:. Cl:::: dintonltc:, Sp = spinet

GROUP

Mon/ialli/e, lo,s/~,iI~, ca/ciu, din/oni/e,+ d;opsid~, + spine/Fig. , shows a thin section of this rock.

Thc= spine! rims have bc=en rc=placed by c1in­tonite suggesting· that thc= following rc=action,although incomplete, has takc=n place:

monticellite + spinel =c1intonite + forsteritc= + calcite.

In order for this interpretation to be: cor­rc=ct the monticellite must have been formedbc=fore the c1intonile. This is' confirmed byIhc= prc=sc=nce of monlicellite inclusions inthe forsteritc= grnins. Morc= commonly thc= op­positc= situation is o~rved: inclusions offorsterite and diopside and/or calcite arefound in monticellitc= grnins as relicts of thereaction:

forsrerite + diopside + calcite =monticellitc=

corresponding to Ihc= formarion of monti­cdlite.

Diops;d~, lo,ste,it~, dintonite, ca/cit~,

+ spin~l

Away from the contact wilh the cumulates,in the same lens, one finds coexisting diopsi­de, forsterite and calcite rather than mond­cellite. Fig. 6 sho,¥~ another c1intonitc=­bearing reaction:

spinel + diopside + calcite = clinlonite.

In this rock no forstc=rite appears. Howe­ver, in parageneses containing forsteritec=xactly thc= same reaction tOok platt. Thisdemonstrates, that nc=ither forstc=ritc= norchloritc= is involved in this reaction, as sug­gested by J- RICE (1979). Forsteritc= andspinel coaist only if diopside is absent inthc= mineral assemblagc=.

622 P. ULMER

Fig. 6. - Micrograph from a momicellilc·forslcritcfree dimonirc bearing diopsidc rock from PsoBlumone.

GROUP 2

Chlorite, serpentine (on forsterite) and cal.cite have mainly been formed as retrogradeassemblages.

CJintonite, diopside, forstuite, calcite, chlo­rite, + spine!

This rock' sample is laken from the samelens as the those previously discussed alongthe contact with the tonalitic rocks. Fig. 7shows the formation of chlorite and calciteby the breakdown of clintonite, forsteriteand diopside after the reaction ~

clintonite + forsterite + diopside =chlorite + calcite.

In the lower right, relicts of the clintoniteforming reaction are preserved as inclusionsof consumed spinels and diopsides in din­tonite grains.

Montiullite, fOTsterite, clintonite, chlorite,calcite, + spinet

Fig. 7. - Micrograph from a momicc:l1ilc freechlorilC bearing rock from Pso Blumonc:.

This assemblage can be found in the iso­lated lenses in the tonalites. Diopside is nolonger present after formation of monticel·lite. and chlorite has been formed by thebreakdown of momicellite, forsterite andclintonite after the reaction:

clintonite + forsterite + monticellite =chlorite + calcite.

Monticel!ite, diopside, forsterite, calciteAlong veins in some monticellite rocks, at

the P.so Blumone, the breakdown of monti·cellil('~ to forsterite, diopside and calcite isobserved. All these are retrograde and fluid·consuming reactions have not attained equi·librium, as the fluid must have been con­sumed before hand. Chlorite is nOt homo­geneous under the microprobe and showsstrong chemical gradients towards thebordering mineral species.

4. GeothermomelryWhen forsterite and monticeIlite coexist,

the substitution of the forsterite component

MONTICELLITE-CLINTONITE BEARING ASSEMBLAGES ETC. 623

in the montj~llite structure and vice versacan be used as a measure of the temperatureattained during the contact metamorphism.The experimental results from R. WARNEll

and W. LUTH (1972) have shown (6g. 8)that the activity of monticellite in the fame­rile solid solution at temperatures lowerthan 1100" C is practically indepen<knt ofthe existing pressure, thus within this tem­perature field no assumption of the existingpressure must be made. Fig. 9 depicts thedata points from experiments for 2000 barsplotted in a -InK (K = activity of onespecies in the structure of the other species)versus liT plot for both sides of the solvus.The extremely good linearity in the first caseis a further argument for the use of thissolid solution series as a geothermometer.1300

11"C)900 1100700

2

6

'0

2 3

2OrT'--,--r-r'--V-~T70

f'(Kb.d

Fig. 8. - P·T diagram wilk isoplelh$ of montic'e!.lile lICtivit)' in forsrcrite. (From R. WUNEl andW. Lunt, 1972).

The equations of the straight lines trans·formed in terms of temperatures in centi·grade are:

5.0r------------,-lnK.2

U

l

...

3.0

3.0

'.5

'/n"Cl'·r'".-----.,".,--,,".,,----"Ui-"--"'-.,.,.--,.T.,,-,(a)

'/n·Cl"':L;---:-;;---;';;--7f-==-;-.-c!.D.. D.. I.G U U'ID-3

(b)

Fig. 9. - (.) I"K, versus lIT plot for the er:perimenlll dau. at 2 kban; I"K, = activity of. mooticd­Iile in fonleritC.. (b) InK. versus 1fT pkM: for the er:pcrimcntal dau. at 2 kb.n; InK. = Ktivily of.fonlCritc in moolicdlile.

624

eooTI'IJ

750

700

Forsterite

T(Q

800

700

600

P. ULMER

Forsterite

MonticeHite9

TI'c1

Da ta points(, I

Data points(bl

core margm margin core ma.rgln

H'CI

ma. co ma.75;rJ-~·~~~~

Data points

lel

Monticellite TI'OForsterite

TI'Q9 850

850 800

Jm. "Forsterite

ma co ma margin core margin m.800 750 ' , , , , ,

Data points Data points Data pointsId J Ie I If)

Fig. 10. - (a) Temperature profile Ihrough a forSlerite grain. . (b) Temperature profile through aforsterite grain. _ (c) Temperature profile through a momicellite grain. - (d) Temperature profile througha momicellite grain.. (~) Temperature profile through a forsterite grain. - (j) Temperature profile throughgrain 10 (t) with fine focussed electron beam.

I I1

(2)

n'el =

TI'C) =

5587.87

2.4659 -lna ~~Q

4429.16

Results

Some profiles have been made throughforsterite and monticellite grains using anARL-electron microprobe with wave· andenergy-dispersive detection systems ate pre­sented in fig. 10 in terms of temperatures.They can be separated into two differentgroups:

MONTICELLITE-CLINTONITE BEARING ASSEMBLAGES ETC. 625

",0 50

F,,..._=;;,

S,Fig. 12. _ Solid .5OIulions in c1intonile .00 c1ino­pyroxeoc: ilCOOrding 10 c:lectron microprobe .n-Iysisin lhe: syslan SiOrMgO.AIA.Di 0:= diopsidc:, Mo 0:= monticc:llilC:, Fo 0:= forslerill:,

,6,12°) Chi 0:= chlorile. Cl 0:= dinlOnile. Sp 0:= spine!.

forsteritediopsidemonticellitespinelchlorite

Fig. 11 ..- SiOrMgO-AIA diagnffi proi«tc:d fromalciu:: .nd fluid.

10 (a), (b) and (c) represent profiles fromrocks which have been affected by retrogradeoverprinting. These profiles show a core withtemperatures between 800 and 900" C anda border zone with temperatures rangingfrom 5500 to 6500 C.

The profiles 10 (d) and (d represent rockswithout any visible overprinting of the pri­mary assemblage and show a homogeneoustemperalUre distribution pattern around850" C.

Geothermometry confirms the observa­tions from thin sections that two differentmetamorphic events have occurred, of whichthe second one has not affected all the rocks.

Fig. 10 (f) shows the same forsterite as10 (e) but analysed with a fine focussedelectron beam (I !-Lm). The homogeneous di­stribution pattern is lost in the central partof the grain. X-ray dislCibution patterns ofCa-Ka rays show that the central part of theforsterite has exolved calcium-rich lamellae.However they are too fine to determineexactly (monticellite?). Exolution is limitedto the central part of the grain and is pro­bably the result of cooling after formationat high temperatures, as it is known fordinopyroxenes (Diallag).

5. Pha8e relationship.

In the literature only two studies one fromJ. RtCE (1979) on the Boulder aureole and

one from K. BUCHER (1976) on the Bergellaureole. have been published concerningc1imonite-hearing marbles, however bothwithout any monticellite occurrence. 1here­fore petrological studies on the phase rela­tionships have been made here.

1he following relevant phases have beenchosen:

Forsterite, diopside, dintonite, monlicel­lite. spinel, chlorite and calcite plus aH~-C02 lIuid.

The best diagram for presentation IS aSi02-AI~,()3-MgO diagram projected fromcalcite and fluid (Fig. Ill. This is an idea­lized diagram, showing only the magnesiumend members. The minerals are presented aspoints neglecting tschermak exchange vectorsin the phases.

A more realistic diagram is presented infig. 12 based on electron microprobe analyses,but without chlorite. Clinopyroxene and din­tQni{e show a strong dependence on thecoexisting assemblage and vary in ,he di­rcedon of the tschermak exchange vector.

Magnesium endmembers have been usedfor the calculation of the reactions:

Mg2SiO~

CaMgSi06

CaMgSiO~

MgAbO~

M8:lAbSiaOu,(OH)",(dinochlorel

and dintonite has been set on the tielinediopside-spinel. According to electron micro­probe analyses and thin section observations

Fo,Ct)"'ft/ \ +c.co3

A \ ::dZ"R k' \-'F+-+,*

A tchu

t - --6pf io)

l0- (ot.ro)

626 P. ULMER

Fig. 13. - ,-Xcoz diagram at 500 bars for the system SiO.MgO-ALO*CaO-HO-CO" with the phasesforsterite, diopside, monticellite, clintonite, chlorite, spinel, calcite, HrO and COr.

(no forsterite or chlorite involved in theformation of clintonite) the composition is:

clintoniteCa( Mg2.ssAl. ea ) ( Alz.ueSit.ss )Oro( OH )z

In this system (6 phases, 3 components)with two degenerations, L1 reactions can becalculated, Tab. 1). When available, thermo-dynamic data from HrrcnsoN et al. (1978)have been used in the calculation of thestable T-X-2 sections. A new enthalpy valuefor chlorite was calculated from an expe-riment of T. \0Trnrvrenr (1980). Since nodata are available for clintonite, the entropyand heat capacity terms have been estimatedand the enthalpy is calculated from an expe-riment of G. Hoscnx (1976). The pres-sure was fixed at 500 bars according tostratigraphic considerations (about 2 km ofoverburder at the time of intrusion).

Fig. 13 shows the stable T-X*, section at

500 bars constructed after the method ofH.rW. Dev (1,972\ and checked in the tem-perature range from 350-800" C.

6. Diecuseion of the resulta in theT-X"ro diagram

The first high temperature contact meta-morphism can be associated with certaintywith the formation of the cumulates (temp.up to 900" C) which developed at extremelyhigh X.o, as indicated by the formation ofmonticellite before clintonite. This means thatreaction 1 occurred before reaction 2. Duringthis primary phase of metamorphism, an an-nealing texture of monticellite formed to-gether with spinel gtains. In a second phase,X"o, diminished. Large cystals of clintoniteformed by consumption of monticellite andspinel. Clintonite was mainly formed by at-taining.reaction 11 in a monticellite-bearingassemblage. Diopside must have been con-

MONTICELLITE-CLlNTONITE BEARING ASSEMBLAGES ETe. 627

7. Conclusions

The sediments, originally conSIsting ofmarly dolomites, show two different meta­morphic events with clear age differences andlocal and petrological association with thedifferent plutonic masses. The first metamor­phism took place progressively towards thecontact with the gabbroic cumulates of theCornonc di Blumone and attained tempera­tures around 900" C at the contact, at a highXco. value of the fluid involved.

The second metamorphism started fromthe tonalite intrusion near the contact andalong veins, and resulted in a retrograde over­printing. The Auid composition was on thewater-rich side and the temperarure attainedaoout 5500 C which is typical for this lOna­lite Contacr metamorphism and has been con·firmed by carbonate geothermometry madeby U. ROESLI (1982) in the same region.

As a consequence, the tonalites of the Redi Castello, as well as the mafic-ultramaficcumulates of the Cornone di Blumone havecrystallized in situ at a very shallow crustallevel. In other words, the cumulates havenot been dragged up from depth by the to­nalitc intrusion. The arguments are: themaximum depth for marly dolomites of thiskind is 2 km at the rime of intrusion (40 m.y.ago). The carbonates clearly show two dif­ferent metamorphic events related to the sur­rounding plutonites. The cumulates had to·tally cooled down when the tonalites wereintruded.

stopped before equilibrium could be attained.The equilibration of monticellite and forste­rite at grain boundaries confirms the obser­vations in the T-Xcoz diagram, as far as mon­dcellite is only stable at temperarures as lowas 550" C, if the Xco. is < 0.1. The low valueof the Xco.. is on one hand the productof H~O rich fluids coming from the tonaliticrocks which carry much more volatile com­ponents than gabbroic cumulates, and on theother hand the result of the lOtal consumptionof the carbonates during the first meta­morphic event.

Acknowledgementr. - I greatly appreciate the as­sislance of Gretchen Frueh·Green wnh the Englishtranslation and V. TROMMSOORFF for discussionsand constructive review. The support of Schweize­rischer Nationalfonds, No. 2.805-080 is gratefullyacknowledged.

,.-,.."1.1"'"

•... ll..... _. _Illb."""""""

,-U~ 17 .5CIO g.15311 -1.523 -.00'111I ,~", ""<3l -1l.132 -0.2.\161 -S ••3' -.OOOSO m ...• ,~'.

1'7.11! '.S6100 ....no -.01l16 705:3"• ... '.' ·-1&9191 31&.130 3.'''1 ...." _.0'171' ll"»o1

• ••• ••• ~,. .5.m g."U6T -S.!7I -.OOI7D 1,3&<12

• ., ... ,.. -'CI677 '9l!.lOI l.D'1"'7 -2'.33 -.0'1001 .llS701'l, -IS lU_S ,.. -l1lOO'l9 ~.91C S."1.7 ~.. -.026.9 2<2..19

• ., ••• ••• .~. '1.'\10 D.SlOlO ....3.. -.003l5 2S,n.• ., ,.. ,.. _.nO...l , .2S5'5 -t.WI -.OO'1W 31lD'1D.. ., ,.. ,.. -" •.m '.D3SU -15.63 -.003<' S5351&

" , ., .~. SO.1J9 O.Sl6(l. ,.w -.DD6'9 ~..

TABLE 1Reactions and reactions parameters for thesystem 5iO, - MgO - Al~O., . CaO . HiO ­

CO ~ with the phllses

...«1... S , (fo,«) I, _t.....l.

l... ·n··l...,.b 1"'/" 1"ll.3'~'!n' C. (...."" ,

Po = fOr5terite, Di = diopside, Mo = monticellite,Ct = dimonite, Chi = chlorite, Jp = spincl, Cc =calcite, H,.Q and CO,.

sumed before forstcrite and calcite during theformation of monticellite (reaction 1) and soreaction 2 could not take place. On the otherhand when diopside is present reaction 2has taken place and all the spinel was con­sumed or rimmed so that reaction 11 wasblocked.

The rocks further away from the COntactnever attained reaction 1 and clintoniteformed only by reaction 2 during the secondphase. The change in the fluid composirioncould be the result of the total consumptionof the carbonates so that the supply of CO~from the caroonates was diminished, or aH~O rich fluid was intruded from outside.

The second retrograde metamorphism tookplace at a low Xco, value and lower tempe­ratures (around 550" Cl, which is reasonablefor contact metamorphism initialized by anintermediate plutonic rock. The reactionswere retrograde and fluid consuming, and

'. <".$o.(~l) , '0' 'I • 2<, • _ • 2COl

l. (CM."'.'o' , ~.1 • UII • c•• 3HzO • ltt • ClIl

l. Ho••n , 2C>\ • 3« • 1e<' 1$0' 11 "HzII' 1COz

•• (.0,...., , SCM •• '1 • lle<' lS 3« • 17HzII' l1ClIl

S. ('0.«' , co, • 01 • <c, • S'" • So • ''\10 • "Ill&. ( n , SCM • 'e< " 700 ...... le•• 11HzII • >COl

'. ( , , 15cM • U« • M.o • "1 • GC, • 5"'211 • nc.

I. "'.0Il , CM • 2c, • '0 • l'" • So • ''\10 • lClIl

•• <c••"" , le... lc, • S'o • 'So • lol • 'l"z0 • lCOl

10.(111....) , 3<01 • l$o • 3e< • 3« • no • ""z0 • 3'0:!

11.(II••e>1> ,3(" l.o' 5e< 'So' 3HzII • 3'02

"".Illllrh••<>n...... , 0' ... ' 1...,

628 P. ULMER

REFERENCES

BIANClll A. e DAL PIAZ G.B. (1937) - If UIIOT~

mNidionll/~ dtl massiuio d~J/'Adamtllo. Rtlll~it>ni sul r,lt/}.m~nlo ~ sludi prtliminlrri dtlla ~ona

rompr~s. Ir. t. V.II~ Sftlb,o t 1'111111 VIIUt dtlC1I8111O. Boil. UII. GnJI. hal., Roma, vol. LXII,pp. 1-87.

BIANCHI A. COAL PIU G_B. (1937 a) • Alltlnut,tOiot.;ct>pttrot,rllftco dtlJ'Adllmt/lo m~rtd;onalt.

rttiont Irll 10 Stllbio td II C118t11O. Mem. 1s1.Gcol. Univ. Padova, vol. XX, pp. '·16 con cmlgcol.-pcu. I; 12.XlO.

BIANCIII A., H1Et:E O. (1946) . 1....tI Xilnloplliu dd·I'AdamtUo m~ridionll1t. Periodiro di Minculogia,

Romlll, anno XV, n. 1·3.BIANCHl A., C.ULEG.... I E., j06STltAlBIZEIl P.G.

(1970) . / lipi ptlrogrii/iti londa",~nlafi dtl Piu·10nt dtl/'AJllmtffo. Tonaliti . Quaf~odiorili _Graf/odiofili ~ loro vafieta ltuCOCral~. Mem. 1s1.Cool. Miner. Univ. Padova, vol. XXVII, pp. 1·146.

BMACK PI!TER (1981) . Slrucluf~S if/ Iht South·wtllCffl bofder ollh~ AJam~1I0 In/fusion (AlpiBrtsciant, 110/y). Sehwci1.. Mineral. Pctrogr. Mitt.,vol. 61. pp. }7·.'50.

Bucuu·NuRMINEN K. (1976) - OUUftnu and clN­mistf)' 01 Xanlhoph)'lIilt in Rool Ptnd.nl1 01lhe Btft.tlf Gr.nitt, Sondfio, NOfllNrn Italy.Sehweil. Minet1ll. Peltogr. Min., vol. 56, pp.413426.

BUKNHAM W.e., HOU..oWAY j.R. and DAvIs N.F.(1969) . TMmod,namic propnlits 01 wllftr to1000 btJrs. GcoI. Soc. Am., Special Paper Num­ber 132.

WU-EGA.I e Du PIAZ G.B. (1973) - Fitld r~·IlItiOluhlp bttwun IIx mlllf/ i"ntolls ",IISUS 01tIN Adamrflo inlrllsi/lt mlluil (Norllxrn 11111,).Mem. 1s1. Gt'Ol. Miner. Univ. Padova, vol. XXIX,pp. 1-39.

CoLBElTALOO DINo (1940) . PtlrOl,rll/UI dtl Mon/~Blumon~ (AJllmtlfo MNidionlllt). Mem. 1st. Gcol.Univ. Padova, vol. XIV, pp. 1_.'51.

DAY H.W. (1972) - Gtomtlrical analysis 01 pbtJutquilibfia in t~rnary sys/~ms 01 six phtJus. A~r.). Sei., vo1. 272. pp. 711-734.

HEI.GESON e.H., DELANY ].M., NES61TT H.W. andBnD DK (1978) - Summary and critiqu~ ollb~Ih~rmodyna",ic propeflies 01 rock·lormin" min~­

rals. Amcr. ]. Sei., vol. 278·A, pp. 1·229.HII!KE QpLlNA (194.'5) . f giadmenli di conlallo d~l

Monl~ COSlon~ (Adamello M~ridionaltl. Mem.[st. Gcol. Univ. Padova, vol. XV, pp. 1-44.

HOSCHEK G. (1976) . ZUf Stabililiil "on Cfinlonilim Sysl~m CaD-MgO-A/.orSiOrH.o.cO,. Fort­schr. Mineral., vol. .'54, pp. 3941.

JOESTF.N RAYMOND (1976) - High.umptrlllur~ con·lacl mnamorphism 01 carbonat~ focks in tI shal­low crusllI/ ~nlJironmtllt, CristmllS Mountains,Big Btnd &t,ion, Ttxas. Amer. Minenl08isl, \'01.

, pp. 776-781.KEl.IICK D.M. and JACOBS G.K. (1981) • A modifttd

Rtti/icb-Kwong tqualion lOT H.o, CO. andH.o..cO. mixtur~s aJ t/tl/attd prtSSllrtS IInd I~",·

ptrll/llfts. A~r. J. Sei., va!. 281, pp. 735-767.KUSHIIO I. and YOOEl. H.s. (1%4) _ Brtakdown

01 montictffi/~ and .Iu~",aniu al high prtssur~s.

Carnegie Insl. Wash. Y"k Book, vol. 6J, pp.81.83.

MAUIODA ROBEtTO (19.'54) - Geolot,ill tieU. VII1I~

dl B/umon~ (Alla Vaffe tirf C.8I11O) ntll'Atill'mti/o MNidionll1~. Mem. 1s1. Geol. Mincr. Univ.Padova, vol. XVII, pp. 148.

OUSCH M. and SEIFFElT F. (1976) . Slability andPMU ftlalions 01 IflCJtlMdrll/ c./dum briul~

miclIs (clintonilt I.roup). Jour. of PeltOlO£y, vol.17, pp. 291·314.

OLESCH M. (I975) - SynlMsis and solid solubililyin IrioctalNJral hrilflt micas in tM syst~m CaD·MgO-Al.CJ,SiO,. A~r. Mioct1llogisc, vol. 60, pp.180-199.

REUSSElI ERIC (1982) - Forlranprogrllmm~ ~ur Bt­fuhnung /JOn isobaftn T-X (fluid) kurvtn (iflttrnalf~POft). InslitUl fur KrislalJogllphie und Peno­graphic dcr ETH, Zurich.

RICE JACK M. (1979) . Pnrology 01 C/inlonitt·heafing mafbi~s in Boulder Aureole, Montana.Amcs. Minelllogisl, vol. 64, pp. 519-526.

ROlllE R.A., HEMlNGWAY 8.5. and FISHEI j.R.{l979l . Thumodynamie proptrlies 01 mintra!sand rtla/~d substancts al 298.15 K and 1 hllrprtssurt and tll higlxr I~mp. Gcol. Survey Bull.,14.'52.

ROESLI Uuuu. (1982) • Geologit und Pelro~rll'pbi~ d~s sud/icMn AJa",t/lo: VII Valft titl CIII­'1110. Diplomarbeil ETH, ZUsich.

SANElO E. (1940) - 1....tI Slrulturll dtIJlI Xllnlopbyl.lite. Period. Miner., Roma, val. Xl, pp. .'5}·n.

SKIPPEN G.B., VU.OUAT W. (I970) - XCDFOR:A Forlran IV PrOl,r.",,,, lor ell/culating tqllilibrillon T·XCO. sections. Univ. Carhon Gcol. Pap.,Ollawa, Canada, 1970-73.

SKIPPEN GB. (1971) - Exptr.mtntal dala lorrtllClions in silietous ",lIrblts. jour. of Geology,vat 79, pp.

SKIP.PEN G. and TIOMMSDORFF V. (1973) _ Invariantphllu r~llltions IImonl, minua/s on T·X (fluid)stelions. Am~r. J. Sei., vo!. 27.'5, pp. 561-.'572.

TItACY ROBUT j. (1979) - Monlietllitt marblt alCtlsc(Jd~ Mounlain. Adirof/dack Mountllins, NtwYork. Amer. Mineralogisl, vol. 63, pp. 991·999.

TROMMSDORFF V., ScHWANDER H. (1969) - Brucil·marmor~ in den Btrg~llualpen. Sehweiz. Mineral.Peuogr. Mitt., vol. 49/2, pp. 333·340.

ULMEl PETER (1982) • Gtologit und Petf08raphi~

des siidiich~n Adamdlo: V / . Vaii~ dd Ca8afo.Diplomarbeit ETR, Zurich.

WARNU R.D. and LUTH W.e. (l97J) - Two phastdata lor IIx join monlicdli/~ (CaMgSiO.}/OfSlt.rit~ (MI,SiO,); txptrimenlal ruulls tlnd numt­ricll1 tlnalysis. Amc:r. Mineralogist. vol. .'58, pp.998-1008.

WIDMUK TORBJOUN E. (1980) - The rtllCtionChlOfitr + D%mitr = Spintfl + Forstitt +e.tcitt + Carbondioxidt + VIatrr. Conlrib.Mineral. Petrol., vol. 72, pp. 17.'5·179.

ZEN E-AN (1966) - Constflletion 01 pressuu-trmpt­. rlltuTt dillgranu lor lIflllticompontntr rystrms IIlurtlx mtthod 01 Schrtintm,,1eNS: A gtomtlric .p­proacb. U.s. GcoI. Surv. Bull., vol. 122.5.