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JOURNAL OF PETROLOGY VOLUME S7 N U M B E R 3 RVGES 521-552 1996

F. BEADEPARTMENT OF MINERALOGY AND PETROLOGY, CAMPUS FUENTENUEVA, UNIVERSITY OF GRANADA, 1800! GRANADA, SPAIN

Residence of R E E , Y5 Th and U inGranites and Grustal Protoliths;Implications for the Chemistry ofCrustal MeltsA systematic study w ith laser ablationICP-MS, scanningelectron microscopy an d electron microprobe revealed that ~ 70 -95 wt % of REE (except Eu), Y,Th an d U in granite rocksand crustal protoliths reside within RE ETThU-rich acces-sories whose nature, composition and associations change w iththe rock aluminosity. The accessory assemblage ofperaluminousgranites, migmatites a nd high-grade rocks is composed ofmon-azite, xenotime (in low-Ca varieties), apatite, zircon, Th-orthosilicate, uraninite and betafite-pyrochlore. Metaluminousgranites have allanite, sphene, apatite, zircon, monazite and Th-orthosilicate. Peralkaline granites have aeschinite, fergusonite,samarsk ite, b astnaesite, Jhiocerite, allanite, sphene, zircon,monazite, xenotime and Th-orthosilicate. Granulite-grade gar-nets are enriched in Nd an d Sm by no less than one order ofmagnitude with respect to amphibolite-grade garnets. Granulite-grade feldspars are also enriched in LREE with respect toamphibolite-grade feldspars. Accessories cause non-Henrianbehaviour of REE, Y, Th and U during melt-solid partitioning.Because elevated fractions ofmonazite, xenotime and zircon incommon migmatites are included within major minerals, theirbehaviour during anatexis is controlled by that of their host.Settling curves calculated for a convecting magma show thataccessories are too small to settle appreciably, being separated

from the melt as inclusions within larger minerals. Biotite hasthe greatest tendency to include accessories, thereby indirectlycontrolling the geochemistry of REE, Y, Thand U. We concludethat REE,Y, Th an d U are unsuitable for petrogenetical mod-elling of granitoids through equ ilibrium-based trace-element

fractionation equations.

KEY WORDS: accessory minerals; gtochemical modelling; granitoids;REE,Y,Th,U

INTRODUCTIONThe geochemistry of rare earth elements (REE),yttrium, thorium and uranium forms the basis formany important methods of igneous petrogenesis. Inparticular, REE areprobably the most extensivelyused elements for petrogenetic modelling, as eachmajor mineral participating in the genesis of a rockis supposed to leave its own recognizable signatureon the REE pattern of that rock (e.g. Haskin, 1979,1990; McKay, 1989). REE-based modelling was firstapplied to mantle-related systems, where it hasfound undeniable success. It was then adopted forcrustal systems, despite the fact that crustal rocksalways contain REE-, Y-, Th-, U-rich accessoryminerals (hereafter called REEYThU-richminerals), which usually account for an elevatedfraction of REE, Y, Th and U contents inbulk rock(e.g. Gromet & Silver, 1983; Sawka, 1988; Bea et al.,1994a, 1994A) and may therefore disturb or evencompletely mask the effects produced by majorminerals during melting andcrystallization (Miller& M ittlefehdlt, 1982; Yurimoto et al.,1990).Since the recognition that REEYThU-rich acces-sories may play an important role incontrolling thegeochemistry of crustal melts (e.g. Watson & Har-rison, 1984; Watson, 1988; Watt & Harley, 1993), aconsiderable amount of work has been done in anattempt to understand their effects. However, thiseffort has been almost exclusively focused on threeminerals: zircon, monazite and apatite. Nevertheless,the variety of REEYThU-rich accessories in graniterocks is neither limited to these three minerals norare they always the main REE, Y, Th and U

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JOURNAL OF PETROLOGY V O L U M E 37 N U M B E R 3 J U N E 1996

carriers. Perusal of available descriptions of graniterocks as well as our routine scanning electronmicroscope (SEM) studies on Uralian and Iberiangranitoids revealed a plethora of REEYThU-richminerals whose nature, grain-size, textural position,and hence their presumable influence on the beha-viour of REE, Y, Th and U during melting andcrystallization, change notably from one rock type toanother.This paper presents the results of a systematicstudyby scanning electron microscope (SEM),electron microprobe and laser ablationinductivelycoupled plasma mass spectrometry (LA-IGP-MS)on the residence of RE E, Y, Th and U in a variety ofsamples of granitoids, migmatites and granulitesfrom Iberia, Ivrea-Verbano, the Urals, Kola andTransbaikalia. The research wascarried out withthree objectives: (1) to study the REE, Y, Th and Ucomposition of major minerals in different geologicalenvironments; (2) to learn the nature, abundance,composition, grain-size distribution, textural rela-tionships andassociations of REEYThU-rich acces-sories; (3) to determine the relative contributions ofmajor and accessory minerals toREE, Y, Th and Ubudgets in granitoids and common crustal protoliths.Based on these results, we address the behaviour ofREE, Y, Th and U in granite melts, the role ofaccessories during crustal melting, melt segregationand crystallization, the effects of pressure on theREE composition of restitic minerals and hence ofmelts, the influence of accessories on the contrastinggeochemistry of REE, Y, Th and U in differentgranite types, and the mobility of these elementsduring post-magmatic stages. We then examine thequestion of whether REE-based petrogenetic mod-elling of granite rocksunderstood as a method forinferring the behaviour of major minerals duringmelt and crystallizationmakes sense or not.

SAMPLES AND METHODSSamplesAbout 150 samples from 38 different geological unitswere selected for this work (Table 1). Slides for thinsections (optical, SEM, microprobe and LA-ICP-MS analyses) were cut from each sample. Crushingof 510 kg of rock to a grain-size of

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BE A RESIDENCE OF REE, Y, Th AND U IN GRANITES

Table 1: Studied geological unitsG eological unit Region M a in features

Diffaetititttd two-mica granites an d leucogranitePedrobernardo Central Iberia ASI ~ 1-27. Accessory dumortierite

AS I ~ 1 -25. Co rdierite-bearing facies. Accessory a ndaliorte an d dum ortierite. Related to U ore depositsAS I ~ 1-24. Accessory cordierrte and tourmalineAS I ~ 1-24 . Sillimanrte-bearing faciesAS I ~ 1 -2 1 . Cordierrte- and garnet-bearing fadesAS I ~ 1-27. Accessory andalusite and cordieriteAS I ~ 1-1-1 -2 4. High B contents. Abundant tourm aline and cordieriteAS I ~ 1 - 1 . Accessory garnet in aplitesAS I ~ 1 05 -1 -13 . Accessory garnet

AS I ~ 1-18. Garnet-rich leucogranite, with accessory muscovtte and b iotiteAS I ~ 1-26. Cordierrte leucogranite with accessory garnetAS I ~ 1 -24. Cordierite leucogranite with accessory biotite

t a T i t e sAS I ~ 1 2 4 . Biotite-cordierrte granodiorites and adamellitesAS I ~ 1 -18. Biotite adamellites, with accessory cordieriteAS I ~ 1-14 . Tw o-m ica adam ell ites and biotite granodioritesAS I ~ 1-14 . Biotite granodiorites with muscovite-bearing faciesAS I ~ 1 O a Biotite adamellites

inddloritesAS I ~ 1 02. Abundant magmatlc epidote and ti tanite. K-poor faciesAS I ~ 1 0 3 . N a > KAS I ~ 1 05 . Na ~ KAS I ~ 1 0 3 . N a < KAS I ~ 1 0 4 . K-rich faciesAS I ~ 1 0 1 . Amph ibole leucodiorites with no biotiteOphlolrt ic complex with plagiogranitei

Very high REE, Zr, Y, Nb , T h contents. MineralizedfaciesRiebeckite-aeglrlne granitesRiebeckite-aegirlne granitesRlebeckite-aeglrine granitesFerrohastingsite-riebecklte granites

Cofdierits-si l limanrte-biotite migmatites with occasional accessory garnetCordlerite-gamet-si l l imanite-biotiteGajnet-ei l l imanlte-bkitrteGarne t-blot i te-siinmaniteGarne t-blot i te-si ll imanite-cordierite

Gamet-si l l imanite-KfspOpjc-garnet-kyanite-sl lBmantteGarnet-si l l imanite-KfspGamet-kyanKe-Kfsp

AlbuquerqueTrujilloJa lamaCabeza de ArayaBoqueronesRonda leucogranitesMurzlnkaUvi ldy- l lmen

Central IberiaCentral IberiaCentral IberiaCentral IberiaCentral IberiaSW IberiaCentral UralsCentral Urals

Autochthonous anatact ic leucogranitBSAlmohallaTarayuelaPena NegraPenlummous aoamellhHoyos-GredosAlbercheDzyabykChellabinskElanchinkSubalumtnous granlteiVerkisestShartashShabryElanchlckStepnlnsk

Central IberiaCentral IberiaCentral Iberia

tes, granodiorites aCentral IberiaCentral IberiaCentral UralsCentral UralsCentral Urals

, granodhritas, tonCentral UralsCentral UralsCentral UralsCentral UralsCentral UralsTagil-Chernolstochinsk Central Urals

KhabamyPeraScaSne granitesGaliAeiroBarcarrotaKelvyKharitonovoMagni togorskMigmatitesPena NegraLosVil laresMurmansk b lockMurzinkaOsinovskGranuUtesStronaMurmansk b lockRondaCaboOrtega l

South Urals

N IberiaSW IberiaKolaTransbaikaliaCentral Urals

Central IberiaSE IberiaKolaCentral UralsCentral Urals

Ivrea-VerbanoKolaSE IberiaNW Iberia

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3-8 bars gas pressure. Wavelength was 308 nm,repetition rate 5 Hz, pulse length 30 ns and pulseenergy 100 mj. Data were acquired for 50 s, startingacquisition 10 s after ablation was initiated. Thediameter of the laser beam and gas pressure werefixed so as to produce craters with a diameter of~ 8 0 fim in diameter and 40-60 /im in depth,depending on the ablated mineral. Under these con-ditions, crystals smaller than 100 fim cannot bereliably analysed. Isobaric interferences were auto-matically corrected by the T otal Quant III softwareimplemented in the ELAN-6000, which also allowsthe response factors for all the elements to beadjusted by calibrating the system with an externalstandard with just a fewelements covering themassrange. Calibration was done using the NBS-612glass, which contains ~40 p.p.m. of most trace ele-ments, as external standard. Concentration valueswere later refined using silicon as internal standard,previously determined by electron microprobe on thesame minerals. In these conditions, detection limitsfor REE, Y, Th and U were better than 10p.p.b.Coefficients of variation (CV) obtained by mea-suring five replicates on a single grain of astro-phyllite, which appeared to be unzoned and free ofinclusions, were 4-2 rel. % for 45-6 p.p.m. La, 18-9 rel. % for 0-57 p.p.m. Y, 64 rel. % for 863p.p.m. U, 17-5 rel. % for 028 p.p.m. Th, 4-4rel. % for 471 p.p.m. Eu, and 11-3 rel. % for 0-62p.p.m. Yb. For elements with concentration higherthan 100 p.p.m., CV are normally in the range of 1-3 rel. %.

Electron microprobe mineral analysisMajor-element, REE, Y, Th and U analyses ofminerals were obtained by wavelength dispersiveanalyses with an ARL electron microprobe operatedwith PROBE software using as standards the foursynthetic glasses described by Drake & Weill(1972)RE E 1 Chgo/2, REE2 Chgo/3, REE3 Chgo/4 and REE4 Chgo/5and the following minerals:Albite Amelia Chgo/18, Mn-Hortonolite Chgo/35,Monazite SPI/32 and Zirconia SPI/47. Acceleratingvoltage was 20 kV and beam current was 20 nA.Interelemental interferences were suppressed bypeak-overlap corrections (Roeder, 1985). Detectionlimits were better than 0-10-0-05% depending onthe element and mineral analysed. Coefficients ofvariation were close to + 4 rel. % for 1 wt % con-centration and 10 rel. % for 0-25 wt% con-centration.

R E E , Th AND UC O M P O S I T I O N OF M A J O RM I N E R A L SMicasREE, Y, Th and U concentrations in micas are verylow (Table 2), close to or lower than detection limits(-001 p.p .m.) in most cases. Early LA-ICP-MSwork on muscovites gave somewhat higher levels(Bea et al., 1994a), but it isnow recognized that theywere probably produced bymicroinclusions of mon-azite and xenotime within the ablated spot. Micasfrom U-rich granites may have several p.p.m. U,especially in hydrothermalized facies, which suggeststhat uranium is absorbed asuranyl ions, probably inthe interlayer position.

Amphiboles and pyroxenesOrthopyroxenes also have negligible contents ofREE, Y, U and Th (Table 3). Amphiboles andclinopyroxenes have appreciable REE and Y, butlow Th and U contents (Table 3). Chondrite-nor-malized REE patterns of Ca-amphibole (Fig. 1)increase progressively from La to Pr and thendecrease smoothly from Nd to Lu with no Euanomaly or a small negative one, more intense inamphiboles coexisting with primary epidote (e.g.analysis 1 in Table 3). Partition coefficients forcoexisting Ca-amphibole-Ca-clinopyroxene pairs areZ>tv&cp* ~1 and DJSf /T" -2-4. REEpatterns ofCa-clinopyroxene are analogous to those of Ca-amphiboles, but at lower concentrations (Fig. 1),and have very small negative or positive Euanomalies [see also Mazzuchelli et al. (1992)].

Na-amphiboles are richer in La-Sm and Tm-Luthan Ca-amphiboles (Table 3). Chondrite-normalizedREE patterns decrease uniformly from La toDy andthen increase from Er toLu, with Er^/Lujy 0-30-6(Fig. 1). Partition coefficients for Na-amphibole-Na-clinopyroxene pairs are Z ) u p / N a ~ c p x -2-5,2>LREE1P/N*~CI>X ~6-10, Z)g3?'Na-cPx -4-6 andDTHU,P/N '1~CPX ~1~3. REE patterns of Na-clino-pyroxene are parallel tothose of Na-amphiboles fromLa toHo, but theenrichment from Er to Lu is morepronounced (Fig. 1).K-feldspar and plagioclaseFeldspars have moderate tolow LREE contents, andlow to very low HREE, Y, Th and U contents(Table 4). Partition coefficients for coexistingplagioclaseK-feldspar pairs aref l ^ -1-5, D&"*** - 0 - 3 - 3 andChondrite-normalized REE patterns of

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Table 2: Selected LA-ICP-MS analyses of primary micas (results are inp.p.m.)

YUT hLaCePrN dSmEuGdTbDyH oErTmYbLuE u / E u 'L < * / Y b

B lo t i te

10 - 0 50^320 - 0 40-110-110 - 0 00 0 00 0 00 0 00 0 00 0 00 0 00 - 0 00 0 00 - 0 00 - 0 00 - 0 0

20 2 50 0 00 0 01-170 - 1 70-110 2 50 0 00 - 0 40 0 00 - 0 00 0 00 - 0 0O-OO0 0 10 - 0 00 0 0

30 0 10 0 00- 100 - 0 30 0 00 0 00 0 00 0 00 0 00 0 00 0 00 0 00 - 0 00 0 00 0 00 0 00 0 0

40 - 0 83-410 - 0 00 0 30 0 00 0 00 0 00 0 00 0 00 - 0 00 0 00 0 00 0 00 0 00 0 00 0 00 - 0 0

50- 090- 17O-OO0 - 2 20-310 - 0 2o n0 - 0 4o n0 - 0 60- 010-O50 ^ ) 10 - 0 20 0 10- 010 - 0 06 - 8 7

14-8

60 - 0 90 - 0 10-210- 500- 500 - 0 8o n0 0 40 0 40 0 30 0 00 0 40- 010 - 0 20 0 00 0 20 - 0 03-53

1 6 - 8

M u s c o v i t e

10 - 1 90 - 7 70-110-340 -760 0 90 -000 0 00-100 0 30 0 70-100 0 3o n0 0 20-240 0 00-96

20 0 10 0 70 0 00 0 00 0 00 0 40 0 80 0 00 0 00 0 00 0 00 0 00 -000 0 00 0 00 -000 -00

30-160-160 -030 -060-150 0 30 0 80 0 30-120 0 40 0 00 0 00 0 00 0 00 0 00 0 00 0 0

10-6

40-010 - 0 00 -040 -040 -050 0 10 -040 0 10 0 00 -020 0 00 0 40-010 0 20 0 00 -020 -000 -001-35

50 -060-530 -090 0 60 0 70 -030 -000 -000 - 0 00 -05OO O0-00OO O0-000 -000 -000 -00

60 0 10-210 0 00 0 00 0 20 -000 -000 -000 0 60 0 00 0 00 0 00 0 00 0 00 0 00 0 00 0 0

Bioti tes: 1, migmatite (Pena N egra); 2, subaluminous granodiori te (Vierkisest); 3, peraluminous adamellrte (H oyos ); 4, U-rich two-m i caleucogranite (Albuquerque ); 5, subaluminous tonalite (Sh abry) ;6, peralkaline granite (Magn itogorsk ). M uscov ites: 1, U-rich two-m i caleucogranite (A lbuquerq ue); 2, two- mic a granite (Pedrobemardo); 3, peraluminous adamell ite (H oyos ); 4, migmatite (Pefia Negra); 5,migmatite (Ronda); 6, Be-rich pegmatite (M urzinka).

K-feldspar (Fig. 1) show a variable but alwaysstrong LREE-HREE fractionation, usually withintense positive Eu anomaly. REE patterns of plagi-oclase (Fig. 1) are similar but slightly more enrichedin LREE. The intensity of the Eu anomaly in bothfeldspars is highly variable. Maximum positiveanomalies (Eu/Eu* ~ 25-40) occur in feldspars frommigmatites (see analyses 4 in Table 4), whereas thesmallest Eu anomalies, even negative ones, appear infeldspars coexisting with magmatic epidote (analyses5 in Table 4) and in feldspars from extremely differ-entiated leucocratic segregates from peraluminousgranites (Bea et al., 1994a). K-feldspars and plagio-clases from granulite facies metapelites areremarkab ly enriched in LRE E, with La r ^ 50 andLajv/Smjy ~ 1 0 [e.g. analyses 3 in Tab le 4; see alsoion-probe data of Reid (1990) and Watt & Harley(1993)].GarnetAmong major minerals, garnet is the richest in Yand HREE (Table 5). The composition of garnet in

crustal protoliths shows a marked dependence onwhether they come from amphibolite or granulitefacies.Garnets from amphibolite facies are rich in HREEand Y, but have near-zero LREE, Th and U con-tents [Table 5; see also data of Harris et al. (1992)].Chondrite-normalized REE patterns (Fig. 2) aresteeply positive from La to DyEr, with Smj//Gdjy 0 6 ) , a more pro-nounced Eu negative anomaly (Eu/Eu* ~ 0-010-2),and a flatter HREE chondrite-normalized patternthan amphibolite-grade garnets [Fig. 2; Table 5;compare also ion-probe data of Reid (1990) andWatt & Harley (1993) with those of Harris et al.

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Table 3: Selected LA-ICP-MS analyses ofamphiboUs, clinopyroxenes and orthopyroxenes (results arep . p . m . )

YUT hLaCoPrNdSmEuGdT bDyHoErTmY bLuEu/EiTLa/v/Yb/v

Amp hi bole

117-9

1-760-258 - 7 0

3 9 - 48 - 0 0

3 9 - 911-5

1-449-481-537 2 31-433-700-512-900-450 - 4 22 0 2

219-3

0 0 70 0 16 - 8 5

35-37-46

35-111-3

3-438-471-347 0 71-374-110-613-530-541 0 71-31

38 - 6 90-100 - 0 02-81

1 2 01-939-132 6 10 - 8 82-460-291-250-300 - 8 30-120 7 80-151 0 82-43

44-530-140 0 01-246-721-226 8 42 0 10-681-590-231 0 50-220-420 0 50-250 0 41 -163-35

59-300 0 20 0 03-82

17-42-66

12-52-740 - 8 62-430-482-320-511-380-201-240 2 01 0 22 0 8

610-2

0-510-53

29-483-911-840-5

9 2 72-777 - 9 91-125-131-123 0 60 5 85 0 01 0 40 - 9 83-97

Cpx

14-100-180 - 0 01 193-160-492-240-740-240 6 50-100-620-120-330-050-300-051 0 62 6 8

22-710 - 0 90-O40-200 9 60-201-290-470-210-560 0 90-530-110-270-040-230-031 250-59

30-370-160 - 0 00-240-930-180 - 8 40-330-100-340 0 50-320-050-110-010 0 80 0 10-912 0 2

42-650-130-103-347-431 0 24-641-180-411-160 1 80 8 50-200-670-242 8 90-651-080 - 7 8

O px

10-340 - 0 30 0 00 0 30 0 20 0 00 0 00 0 00 0 00 0 00 - 0 00 - 0 00 0 00 0 00 0 00 0 00 0 0

20-280 0 50 0 00 0 20 0 80 0 10 0 20 0 00 0 00-010 0 00 0 00 0 00 0 00 - 0 00 - 0 00 - 0 0

Am phiboles : 1, granodiorite (Vierkises t); 2, tonalite (Vierkisest); 3, leucodiorite (Chemois tochins k); 4, tonalite (Shabry); 5, tonalite(Shabry); 6, riebeckrte, peralkaline sienite (Kharitonovo). Clinopyroxenes: 1, leucodiorite (C hemois tochins k); 2,diorite (Chemois-to c h in s k ) ; 3,gabbro- norite (Khabarny); 4, aegirine, peralkaline granite (Kharitonovo) . O rthopyroxenes: 1 , granulite (M urmans k); 2,chamockite (Kola).

(1992)] . In some granuli t ic garnets from Ivrea-Verbano s t ronal i t es we also detected significant Laa n d Ce contents (see Fig. 2) with Lajv/Smjv ~0-40-8. This feature is discussed below.Garnets from granites usual ly have an ' am p h i b o -litic' composition. Some crystals occasionally have a'granuli t ic ' core, probably rel ict in origin, sur-ro u n d ed by an ' amphiboli t ic ' r im which seems to beequi l ibra ted wi th themel t at low pressure [analyses4c and 4r in T a b l e 5, for example; see also data ofSevigny (1993)] .

CordieriteThe contents of R E E , Y, Th and U in cordieri terange from low or very low to zero (Table 5).Chondri te-normal ized REE pat terns (F ig . 2) show amoderate decrease from La to Sm , a small negativeEu anomaly and variable Gd-Lu profi les with ei thera negat ive orpositive slope.

EpidoteMagmat ic ep idote has h igh LREE and U contents ,and moderate U, H R E E a n d Y contents (Table 6).Primary epidote grains are usual ly rimmed by a filmof secondary LR EE carbonates (Fig. 3) such asbastnaesite or parisi te, produced by react ion withlate- or post-magmatic fluids. This causes the R E Econcentrations of epidote crystals from the same thinsection to vary by a factor of 50. Chondri te-nor-malized REE pat terns (Fig. 4) display a steepdecrease from La to Sm, a m o d era t e to strongpositive Eu anomaly , and a moderate decrease fromGd to Lu. Remarkably , thepar t i t ion ing of Eu intoepidote is much more intense than into feldspars( D | P i d o t e 'K 6 p ~ 20-30- )|P idotc/P |aK iocl ~820)

TourmalineTourmal ine has lowR E E , Y, Th and U contents(Table 6) . Chondr i te-normal ized REE pat terns are

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La Pr Sm Gd Dy F.r VbCe Nd Eu Tb Ho Tm Lu La Pr Sm Gd Dy Er YbCe Nd Eu Tb Ho Tm Lu10

La PrCe Nd

Sm Gd Dy Er YbEu Tb Ho Tm I.u

La Pr(Y Nd

Sm Gd Dy Er YbEu Tb "Ho Tm f

Fig . 1. Chondrite-normalized REE patterns of amphiboles, dinopyroxenes, K-feldspar andplagioclase. Shaded areas represent fieldsoccupied byanalysed specimens; the number of analyses represented isshown in parentheses. ForK-feldspar and plagioclase, lines 1, 2and 3 are representative examples of feldspars from a granulite (note the LREE enrichment) , fe ldspars coexisting with primary epidote(note the small positive Eu anomaly) and feldspar from highly fractionated peraluminous rocks (note the low REE contents and negativeEu anomaly), respectively.

so variable (Fig. 2) that atpresent it is not possibleto make any reasonable generalizations.A12O 5 p o l y m o r p h sThe concentration of REE, Y, Yh and U inall ana-lysed grains of andalusite, sillimanite and kyanitewas always lower than the sensitivity of the LA-ICP-MS system.REEYThU-RICH ACCESSORYMINERALSWe identified about 26 species of REEYThU-richminerals in common granite rocks andcrustal pro-toliths. Twenty speciesmonazite, cheralite,xenotime, huttonite, thorite, allanite, cerianite, ura-

ninite, betafite, pyrochlore, brannerite, uranosferite,bastnaesite, parisite, loparite, samarskite, aeschinite,fergusonite, zirkelite and fluoceritehave at leastone REE, or Y, or Th, or U as an essential struc-tural component. Six species have at least one ofthese elements as an occasional abundant impurity:up to a few percent in zircon, up to a few thousandp.p.m. in apatite and sphene, and up to a fewhundred p.p.m. in baddeleyite, rutile and fluorite.In the sections below we describe those aspects ofthe occurrence, composition and textural relation-ships of REEYThU-rich minerals which arerelevant to understanding the geochemistry of theseelements in granite rocks. These descriptions onlyreflect the characteristics of REE-, Th- andU-richaccessories such as they appear in common rocks,

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Table 4: SelectedLA-ICP-MS analyses ofK-feldsparandplagioclase (results are inp.p.m.)

YUThLaCsPrNdSmEuGdTbDyH oErTmYbLuEu/EiTL W Y b w

K-feldspar10-130 0 80-180-190-440 -060-270 -070 0 10 0 80 0 10 0 80 0 10 0 30 0 00 0 20 0 00-416-41

21-26

10-20 0 11-782-810 2 80 8 20-100 -660-140 0 30-130 0 30 0 70 0 20 0 70 0 2

17-117-1

30-440-370-10

10-52 0 8

2-406-570-591-680-330 -030-150 -020 - 0 50 0 10 0 30 0 0

11-623 6

40-160 3 20-011-391-630-120 2 90 -080 8 90 -080-010-060 0 10 0 2OO O0 0 2OO O

3 4 046-9

50-400-230 0 91-862 2 30-280-970 2 30-090-210 -030-190 -030 -080-010 -050-011-25

25-1

60-390-370 -080 -781 -7 10-210-470 -080-280 -070-010 -050-010 -030 -000 -020 -00

13-226-3

Plagiodat10 0 30 0 2o n0 -641-400-170 -600 0 70 0 10 -070 0 10 0 70-010 -040 0 00 0 20 0 10-44

21-6

se20 0 80 0 70 0 32-203-570-400-810-150-230-130 0 20 0 90 0 20 0 40 0 10 0 30 0 05 0 0

49-4

30-310-23o n

34-27 0 - 8

8 425-4

1-771-250-590 -060-120 0 20 0 40 0 00 0 20 0 03-74

11-54

40-430-430-107 3 35 6 00-491-380-181-440-150 -020-100 -020 -060-010 -060-01

2 6 88 2 4

50 6 50-100 -034-559-331-193-991-130-290 -980-161-010-160-260 -030-120 -020 -84

25-5

60-560-420 -091-472 6 20-200-520-121-300-120 -020-140 -030 -070-010 -060-01

33-116-5

1, Aplhe (Pedrobernardo); 2, phenocryst in porphyritic U-rich granite (Albuquerque); 3, granuli te (S tron a);4, migmatite (Pefla Negra);5, epidote-bearing granite (Vierkisest); 6, tonalite (Shabry).

no t in pegmatites, metasomatites, or highly alkalinetypes.Minerals 'with REE, Y, U or Th as essentialstructural componentsMonazite (LREEPOJ andcheralite [ThCa(P0 4)2JMonazite is the most widespread LREE-richaccessory mineral ingranitoids, where it appears asisolated minute crystals with a diameter usuallysmaller than 5060 /im, which have a great tendencyto be included within biotite (Fig. 5), garnet (Fig. 6)and apatite (Fig. 7). Monazite is more abundant insilicic peraluminous types, but maybe found in alltypes ofgranitoids, regardless of their silica contentand degree of alumina saturation. However, whencrystallization conditions were extraordinarilyfavourable for the formation of allanite, such as ingranites with magmatic epidote, monazite may bevery scarce or absent.

The composition of monazite (Table 7) varieswidely owing to substitutions among the rare earths,the effects of solid solution with cheralite[ThCa(PO 4)2] and huttonite (ThSiO4) molecules,and partial replacement of Th by U (e.g. Vlasov,

1966, p. 285; Forster, 1993; Wark &Miller, 1993;Forster & Tischendorf, 1994; Forster & Rhede,1995). Monazite is a selective mineral for LREE.Chondrite-normalized REEpatterns arealmost flatfrom La to Pr and then decrease smoothly from Pr toYb and Lu, with a strong negative Eu anomaly (Fig.8) . Nd-rich monazites are not uncomm on, especiallyin granulites (analysis 3 in Table 7). Primary mon-azite has high concentrations of thorium (T hO j ~527 wt% in unmineralized granites) and moderateconcentrations of uranium (UO2 ~0-2-3 wt%),except in U-rich granites where the situation isreversed (e.g. analysis 2, Table 7). Most thorium isincorporated into the monazite lattice through thecheralitic substitution Th ++ + C a 2 + ^ 2 L R E E 3 + ; itseems, in fact, that there is a complete solubilitybetween LREEPO + and ThCa(PO 4)2. The per-centage of cheralitic component is usually in therange of 6-18%, butmay rise to50-70% inallanite-rich granites. Single grains of monazite are oftenzoned, with roughly concentric patterns from acheralite-rich nucleus to monazite-rich rims pre-dominating. The solubility of ThSiC>4 is morelimited, usually < 5 % , even in monazites coexistingwith Th-orthosilicate, although it may occasionally

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Table 5: Selected LA-ICP-MS analyses of garnets an d cordieritesfrom metapelitic rocks and granites(results are inp.p.m.)

YUThLaCePrN dSmEuGdTbDyH oErTmYbLuEu/EiTSrrvv/Gd/v

Garnet

116 7

O i l0 0 90 -030-1404 )51-956-260 0 18-171-74

14-73-45

11-41-508 9 31 0 90 0 01 0 1

294-3

0-210 100-160-170 0 71 0 15-370 118 8 92 0 3

15-64 -30

15-22-63

17-82-430 0 50 - 8 0

35 8 6

0 0 30 0 10 -973 0 30-513-135-570-137 -691-41

10-22-237-131 268 361-450 0 60-96

426-9

0-120 0 91-754-620-613-295-750 118-222-15

20-26-41

21-13-58

21-53-120 0 50 -92

5 c24 8

0 0 80 -000-010 -040 0 10 0 80 0 60-155-454-20

60 -121-975-412-576 -710-2

0 -800-01

5 r13 5

0 -000 0 00 0 40 0 30-010-140 -090-114-693-81

44-3, 10-8

2 2 02-40

11-41-040-520 0 1

6 c45-1

0 0 30 0 40-430-530 0 70-492-810-217-392 0 7

13-12-967-351-147-101-120-140 0 3

6 r18 7

0-180 0 70 0 30 0 00 0 20-170-320 0 73-702-34

3 3 914-668 -713-6

10 015-3

0-200-50

Cordierits

10 0 70 0 50 0 50 0 80-210 0 30-120 0 30 0 10 0 50 0 10 0 50-010 0 30 0 10 0 40 0 10 -790-11

20-550-360-310 -771-720 2 00 8 90-140 -050-170 -040-300 0 90-270 0 60-400 -080 -99

30-370-160-190-471-090-150 -630-150 0 50-210 0 40-210 -04o n0-010 -070-010 8 6

40 -050-010 -070-110-120 0 00 0 00 0 00 0 00 -000 -000 -000 -000 -000 - 0 00 0 00 0 0

In the case of garnet c and r mean core and rim, respectively. Garnet 1 - 4 , garnet granuli tes (stronalites, kinzigite formation, Ivrea zone);5, garnet amphibolrte (N W Iberia); 6, granite (Pefia Negra). Cordierrte: 1, migmatite (Pefia Negra); 2, retrograde crystal after garnet (PefiaNegro); 3, leucogranite (Pefia Negra); 4, leucogranite (Ronda).

reach 30-40% in some (but not all) monazite grainsfrom a given thin section.We could not find any meaningful correlationbetween granite typology and the chemistry of mon-azite. Certainly, monazites from metaluminousgranites tend to be rich in cheralitic component andthose from Th-rich granites may be rich in huttoniticcomponent, but the compositions of grains from thesame thin section usually vary so much [see alsoWark & Miller (1993)] that it seems almost impos-sible to sketch general tendencies.Secondary monazites appear always hydrated(rabdofan?) and characteristically have very low Thand U contents (analysis 12, Table 7). Most but notall secondary monazites we analysed also have highY contents.AUaniteAllanite is, after monazite, the most importantLREE carrier in granitoids. Primary allanite may befound in all granite types except in the most per-aluminous [aluminium saturation index (ASI) > 1-2]

phosphorus-rich varieties, and is especially abundantin granites with magmatic epidote. Contrary to acommon belief among petrographers, primaryallanite and monazite may coexist in equilibrium(Fig. 9). Secondary allanite is very common, even inthe most peraluminous granites (Fig. 7).Primary allanite usually appears as idiomorphic orsubidiomorphic grains, often metamictic, with adiameter ranging from several tens of microns up toa few millimetres. They occur either alone orincluded within larger crystals, generally epidote oramphibole (Fig. 10).The chemical composition of allanite is verycomplex and may vary across a wide range [seeVlasov (1966, pp. 302-306)]. In granites, however,the compositional range of allanite is more restricted[Table 8; see also Petrik et al. (1995)]. The EREEconcentration ranges between 14 and 18 w t% with aclear predominance of LREE and a strong negativeEu anomaly (Fig. 8). Primary allanites alwayscontain some Th (ThO 2 ~05-3 wt%) , Zr (ZrO 2~0-2 wt%) and P (P 2O 5 ~0-0-2 wt%). The con-centration of these elements is positively correlated

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JOURNAL OF PETROLOGY VOLUME 37 NUMBER 3 JUNE 1996

10

-210 La Pr Sm (id Dy F.r YbCe Nd F.u Tb Ho Tm Lu La Pr Sm (Jd Dy Er YbCe Nd Eu Tb Ho Tm Lu

l a Pr Sm C.d Dy Er YbCe Nd Eu Tb Ho Tm Lu

La Pr Sm Gd Dy Er YbCe Nd F.u Tb Ho Tm LuFig . 2. Chondrite-normalized R EE pa tterni of granulite-grade and amphibolite-grade garnets, cordiente and tourmaline. Shaded areasrepresent fields occupied by analysed specimens; the number of analyses represented is shown in parentheses. For granulite-gradegarne ts, continuous lines represent abnorm ally La-C e-rich specimens from IvreaVerbano stronalites. For cordierites, 1 represents aretrograde crystal after garnet, 2 is an idiomorphic crystal from a granite and 3 comes from a migmatite.

with that of silica (Chesner & Ettlinger, 1989). Uand Y contents are usually low and do not show anysignificant correlation with other elements.

Xenotime [ ( YJ1REE ) POJ and intermediatexenotimezircon phasesXenotime is isostructural with zircon, coffinite andthorite (Vlasov, 1966, p. 230) and appears to formsolid solution series with these minerals, above allwith zircon. For convenience and arbitrarily, wehave named all members of the xenotime-zirconsolid solution series that have ZrO 2 < 12 wt %xenotime, all those with P 2O 5

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Table 6: Selected LAICP-MS analyses of tourmalines and epidotes (results are inp.p.m.)

YUT hLaCePrN dSmEuG dT bD yH oErT mYbLuEu/E iTLa/v/Yb w

Tourmaline1

0-110-240-200-150 0 70-020-090-040-010-130 0 10 0 70 0 10 0 40 0 10 0 40-010-422 5 3

20 0 61 0 40 0 00-250-630 0 60-200 - 0 00 - 0 00 0 00 0 00 0 00 0 00 0 00 0 00 0 00 0 0

30 0 7 .0-120 0 70-410-390-120-750-230 0 10-320 0 50-260 0 70-180 0 30-210 0 70-111-32

44-300 0 01-560-953-210-682-940-940 0 81-620-251-520-320-910-160-850-140-200-75

51 0 20 0 00-001-242-090-240-860-130 0 00-260 0 40-320-070-230-O40-260 0 60 0 03-22

60 0 10-070-003-87

1 3 01 654-800 8 20 0 40-490-050-220-020-050-010 0 30 0 00-19

8 7 0

Epidote1

3-777-530 3 7

53-561-3

5-2613-5

2-232-701-560-200-910-200-510 0 60-410 0 64 - 4 3

88-1

26-030 0 00-71

97-1129-

10-121-4

2-715-401 -610-231-370-260-690-100-580 0 98-17

11 3

39-560-880-042 9 99 0 71-546-191-640-691 -1 30-180-980-200-460-060-360 0 51 655-61

47-194-290-60

20-748-6

6-9020-0

3-742 7 53-250-462-530-511-310 2 21-370-202-41

10-2

53-557-290-70

1 3 02 4 - 3

2-9412-5

1-960-881-930-241-540-300-720-100-540-091-38

16-2

61-811-830-62

1 5 02 3 - 2

2-467-140-911 0 60 6 70-090-630-140-370 0 60-280-044-16

36-1Tourmaline: 1 and 4 leu cog ranges (Ronda) ; 2, U-rich granite (Albu querque); 3 and 5, migmatites (Pefta Negra); 6, granite (T rujil lo).Epidote: 1-3, granodiorites (Vierkisest); 4, granite (Vierkisest); 5 and 6 , granodiorites (Shartash).

and then another increase from Gd to Yb and Lu,not as abrupt as before. In some rare cases, LREErise to 3 wt% and produce REE patterns whichappear as if some monazitic component could also bedissolved in xenotime (Fig. 8). Additional supportfor this idea comes from the fact that Th increasestogether with LREE.Intermediate xenotime-zircon phases have lowerREE contents than pure xenotime, and the pre-dominance of HREE over LREE is also less pro-nounced (Fig. 8). In addition, they are richer inAI2O3, FeO and CaO, which increase with thezircon component.Thorium orthosilicate ( ThSiO^ minerals: huttonitean d thoriteVery low but still significant amounts of thoriumorthosilicate mineralsthe monoclinic huttonite andthe tetragonal thoriteare scattered through alltypes of granitoids. They appear as minute grainsincluded in major (Fig. 12) and accessory minerals,above all zircon (Fig. 13) [see also Rubin et al.(1989)]. Because the huttonite and thorite can bedifferentiated with SEM only by the morphology of

the sections, we could not establish the relative pro-portion of these two minerals, although the fact thatThSiC>4 minerals in metaluminous granites are oftenmetamictic, whereas in peraluminous granites theyappear remarkably unaltered, could perhapsindicate that they consist of thorite and huttonite,respectively (Bayer, 1969).ThSiC>4 minerals from granites always containseveral weight percent of REE (Table 10), with astrong predominance of HREE over LREE and deepnegative Eu anomalies (Fig. 8). Some P-rich vari-eties having high concentrations of LREE areprobably intermediate monazite-huttonite phases(analysis 3, Table 10). Uranium is usually in therange of 1-10 wt%, although grains with subequalcontents of Th and U (uranothorite?) are frequent.Uraninite (UO2)Uraninite is a common accessory in peraluminousleucogranites, where it appears as very small grains(diameter usually 2 and mayalso have up to 5 wt % of Y 2O 3 and 1 wt % of RE E,

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JO U RN A L OF PETROLOGY VOLUME 37 NUMBER 3 JUNE 1996

Fig . 3. Back-scattered electron (BSE) SEM image of a primary epidote crystal rimmed by REE-carbonate (parijite?). (Note how REE-carbonate fills radiating cracks.) Metaluminous granodiorite, Verkueat batholitb.

with a clear predominance of HREE (Table 10; Fig.15),Complex uranium mineralsRocks containing uraninite and xenotime usuallycontain other primary U minerals as well. The mostcommon species are minerals from the pyrochlorebetafite [(U,Ca)(Nb,Ta,Ti)3Og.nH2O] group. A U-Bi mineral, probably uranosferite [BiUO3(OH)2]and brannerite (UTijOe) are also occasionallyfound. All these minerals contain variable amountsof Th and REE, and are generally HREE selective(Table 10; Fig. 15).Aeschinite, samarskite,fergusonite, lopariteComplex minerals of Nb, Ti, Y, U and REE arecommon in peralkaline granitoids, usually formingcomplex aggregates of phases with a highly variablecomposition (Montero, 1995) (Table 10; Fig. 15).The most abundant species are aeschinite (low Uan d Y, high LREE), fergusonite (moderate U, Y andLREE, high HREE) and samarskite (high U, Y andH REE, low LREE). Loparite is one of the richestminerals in LaGe (see analysis 11, Table 10)although it appears to be limited to highly per-alkaline rocks.Bastnaesite andparisitePrimary bastnaesite is found only in REE-rich per-

alkaline granitoids. Secondary REE carbonates,probably parisite and/or bastnaesite, are fairlycommon in metaluminous granites, where theyappear as a product of the decomposition of allaniteand epidote (Figs 3 and 10). These minerals areextremely selective for LREE and contain negligibleamounts of Th and U.Cerianite (CtO$The oxide of tetravalent Ce is found in some hydro-thermalized granites filling cracks and veins. As cer-ianite is usually related to monazites with a deepnegative Ce anomaly (Fig. 8; analysis 1 in Table 7),it would seem to be produced through the oxidationand subsequent leaching of Ce4+ from monazitecaused by hydrothermal fluids. The concentration ofY, Th, U and REE other than Ce in cerianite isbelow microprobe sensitivity.

Zirkelite is a rare mineral which appears in low-silica granitoids together with thorite and badde-leyitc, usually asvery small inclusions in zircon (Fig.13). Its rarity and small grain-size have not per-mitted us to obtain reliable analyses, although semi-quantitative EDAX analyses with SEM indicateUO2 ~3-7 wt%, and the predominance of HREEover LREE, with Dy 2O 3 ~0-5 wt%, Er2O 3 ~ 07w t% and Y b2O 3 ~0-9 wt%.

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BEA RESIDENCE OF REE, Y, Th AND U INGRANITES

10

La Pr Sm Gd Dy Er YbC e Nd Eu Tb Ho Tm Lu La Pr Sm Gd Dy Er YbCe Nd Eu Tb Ho Tm Lu

10"

10

o? 10201

10

(17) Apatiteperaluminous

-

La PrCe Nd Sm Gd Dy Er YbEu Tb Ho Tm LuLa Pr Sm Gd Dy Er YbCe Nd Eu Th Ho Tm Lu

Fig. 4. Chondrite-normaliied REE pattern! ofepidote, zircon, apatite and sphenc. Shaded areas represent fields occupied by analyiedspecimens; the number of analyses represented is shown in parentheses. For sphene, 1 and 3 represent extreme cases of sphenes frommetaluminous granitoids (note thedecreased intensity of the Euanomaly as EREE decreases; 2 represents thecharacteristic pattern ofsphenes from peralkaline granites.

Fkocerite[(La,Ce)3F]Fluocerite is an occasional mineral in peralkalinegranitoids (Imaoka & Nakashima, 1994; Montero,1995), where it normally appears as a late mineralgrowing in interstitial positions. It contains about18-20 wt% La, 33-35 wt% Ce, 1-5-2 wt% Pr, 6-6-5 wt% Nd, 0-4-0-5 wt% Sm, 0-4-0-6 wt% Gdand

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Fig. 5. BSE-SEM image of a biotite crystal from a peraluminous granite. [Note the great abundance and small grain-size of zircon (Zr)and monazite (Mo and unlabelled) inclusions.] Pedrobernardo granite.

Fig. 6. BSE-SEM image of monazite inclusions in a garnet from a peraluminouj leucogranite. (Note how monazite U selectively includedin garnet.) Murzinka granite.

than 0-75 wt%, and LA-ICP-MS data show thatvalues between 100 and 200 p.p.m. are common(Table 11). UO2 may occasionally reach 10 wt%,but normal concentrations are between 10 and 100p.p.m. U (Table 7). The concentration of Y variesfrom a few p.p.m. to 6 wt%, and increases withincreasing phosphorus contents (Tourrette et al.,

1991). IHREE are in the range of 0-2 wt% andalso increase with phosphorus, which suggests thatsolid solution with xenotime is the main mechanismof Y and REE incorporation into the zircon lattice.Chondrite-normalized REE patterns (Fig. 4) showLajv/Smjv in the range 15 a moderate negative Euanomaly and a progressive increase in HREE, with

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Fig. 7. BSE-SEM image of secondary allanite that developed along a fracture in biotite. The pseudohexagonal large crystal u apatite.White small grains included in apatite and biotite are monazite. Hoyos granodiorite.

Gdjy-/Ybjv- 510 and occasionally Ybjy/Lujv > 1. Scis a common trace element with a concentration inzircons from granites rarely higher than some tens ofp.p.m. (Heaman et al., 1990), although we havefound one case (Albuquerque granite, Iberia) withzircons having up to 10 wt% Sc2O 3 (analysis 11,Table 11).Apatite [C a5(P O 4) 3( 0HCl) ]Apatite is a well-known abundant accessory mineralin granite rocks, especially in peraluminous grano-diorites and monzogranites, where it may reach 1%modal abundance. Apatite appears in grains ofvariable size and morphology, from small (~305/an), needle-like crystals, more characteristic of I-and A-type granites, to large (~ 500-50 /im),roughly equidimensional crystals typical of stronglyperaluminous S-type granites. Apatite crystalsusually contain small inclusions of monazite (Fig. 7).The concentration of REE, Y, Th and U inapatite is highly variable (Roeder et al., 1987) andshows marked differences according to the rock'saluminosity (Table 12; Fig. 4). Apatites from per-aluminous rocks are the richest in Y, U, Th andHREE, and have flat chondrite-normalized REEpatterns (Laj^/Lu^- ~ 1) with a strong negative Euanomaly (Eu/Eu* ~ 0 - l ) . Apatites from metalu-minous granites have less REE, Y, Th and U, andtheir REE patterns show a positive slope from La toSm, a small negative Eu anomaly (Eu/Eu* ~0-7),

and are almost flat from Gd to Lu, with~ 01 -0- 4 (Fig. 4). Apatites from peralkaline rockshave the lowest Y, REE, Th and U contents, but arethe richest in LREE, have no Eu anomaly, and showREE patterns with a steep negative slope from La toLu (La^/Lujv ~ 50-100).Sphene [CaTifSiOJ (O,OH?)]Primary sphene is a widespread accessory in meta-luminous and peralkaline granites, where it usuallyappears as idiomorphic or subidiomorphic crystalswith a grain-size in the range of 0-055 mm. Primarysphenes always contain a few thousand p.p.m. REEand Y, and a few hundred p.p.m. Th (Table 13).The concentration of U, however, is highly v ariable,from near zero to ~500 p.p.m. Chondrite-normal-ized REE patterns of sphene (Fig. 4) from metal-uminous granites increase from La to Pr-Nd, have asmall negative Eu anomaly (less intense the less REEthe crystal has), decrease from Gd to DyHo, andare almost flat from Er to Lu. Sphenes from per-alkaline rocks, in contrast, have REE patterns with anegative slope from La to Sm, no Eu anomaly, andare almost flat from Gd to Lu.Badddeyite,fiuontt andrutileThese minerals have been reported to containsomewhat elevated concentrations of REE, Y, Thand/or U (Vlasov, 1966; Heaman & Parrish, 1991).

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Table 7: Selected microprobe analyses ofmonazite crystals (results expressed in percent)

S iO 2Z rO 2A I 2 O ,FeOM gOCaONa 2OP 2O BY 2 O 3T h O 2U O 2La 2O 3C ^ O sPr2OjNdzOaS r r ^ O ,Eu 2O 3GdjO,D y 2 0 3E r2O ,YbjO,Lu 2O 3Tota l

1

0 0 00 0 10 0 00 0 00 0 02-790 0 0

3 4 0 52 8 8

10-580-18

13-622-425 5 0

18-342-160-140-590-270 0 60 0 30 0 0

9 3 - 6 1 *

2

0 - 0 00-150 - 9 90 3 00 - 0 02-150 - 0 2

28-962 8 64 7 8

13 787-83

21 012-849-762 6 30-220 - 6 60-420 - 0 20 0 1O-OO

9 9 - 3 9

34 - 7 4OO O0 - 0 00 O 10 - 0 00 4 10 - 0 0

2 1 - 0 70 9 6

27-310 8 16-43

1 8 - 8 82 8 1

13-591 1 50 1 80-490-460-180-150 0 3

9 9 6 6

4

2 5 00-170 - 0 00 - 0 00 - 0 01-280 0 0

23-512-93

1 8 - 6 41-469-18

23-343-728-512-210-241-400 6 40-070-090-01

9 9 - 9 0

5

0-400-160 0 00 - 0 00 0 01 020 - 0 0

3 0 - 0 43-628-541-588-29

25-793-74

11-203-700-140 - 8 90-590 0 80 0 30 - 0 0

9 9 - 8 1

6

0 - 0 00-050-O50-630 0 01-580-00

3 0 - 6 21-619-221-18

10-2726-47

3 0 711-48

2-550 0 80-830-370-150-110 0 2

100-34

7

0 0 00-300 0 00-210 0 02-860 0 5

28 222-369-986-478-15

24-033-57

10-462-270 0 50-390-150 0 80 0 70 0 1

9 9 - 6 8

8

0 0 80 0 00 0 00 0 00 0 02-110 - 0 0

2 4 8 03-25

1 0 0 11-358-77

25-263-65

14-993-580 0 71-670-910-160 0 30 0 0

100-69

9

0 0 00-260-000 0 50-002-110-00

28-700-04

11-750-909-31

27-203-97

12-632 0 70-151-120-380-140-120 0 1

100-91

10

0 0 00-280-000-000-001-480-00

28422-228-940-79

11-3728-16

4-2010-17

2-590-240-680-130 0 70-070 0 1

99-71

11

0-000-100-150-790 0 01-180 0 0

28-510-335-421-146-49

29363-22

16-803 0 40-191-820-310-150-120-02

99-14

12

0-920-340-620-150 0 01-750-11

25-657-670-000 486 36

20922-739-581-870-012-112-420-770-720-20

85-38'

* Contains appreciable H 2O .1, Cerianite-bearing granite (llmen); 2, U-rich peraluminous leucogranite (Albuquerque); 3, metapelit ic granulite (Strona); 4, garnetleucogranrte (M urzinka) ; 5, B-rich leucogranite (Ronda); 6,two-mica granite (Pedrobernardo ); 7 an d 8, allanite-bearing granite(M agnit ogors k); 9, allanite-bearing granodiorite (Siroslan); 10, xenotime-bearing peraluminous leucogranite (Ronda) ; 11 , xenotime-bearing migmatite (Pefta Negra); 12 , secondary monazite (Galineiro).

However, in all the samples we studied these ele-ments are below microprobe sensitivity. On theother hand, the small grain-size has not allowed usto perform reliable LA-ICP-MS analyses. Somelaser shots at crystals slightly smaller than the laserbeamand therefore with some contribution fromthe surrounding crystalsindicate that these threeminerals are LREE selective and the concentrationsof REE and Yare lower than a few tens of p.p.m.Analysis of a baddeleyite concentrate from Kovdor(Kola) also shows a minor enrichment in HREE,producing a U-shaped REE pattern, very similar tothat described by Reischmann et al. (1995) in bad-deleyite concentrates from South Africa. The U andTh concentrations are probably a few p.p.m., exceptin rutile, where U is probably in the range of 20100p.p.m.

FRACTIONAL CONTRIBUTIONOF EACH MINERAL TOWHOLE-ROCK REE, Y, ThAND U CONCENTRATIONSThe nature and, in some cases, the composition ofREEYThU-rich accessories changes systematicallywith the rock bulk-chemistry, above all with alu-minosity. Therefore, to obtain a general picture ofthe fractional contribution of major and accessoryminerals to the bulk-rock REE budget for the wholegranite spectrum, we performed a mass-balancestudy of 12 plutons from Iberia and the Urals withan average ASI ranging from 1-27 to0-78. The fol-lowing features stand out.

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La Pr Sm Gd Dy Er YbCe Nd Eu Tb Ho Tm Lu La Pr Sm Gd Dy Er YbCe Nd Eu Tb Ho Tm Lu

10

10 '

1010

Xenotime andIXZ phases

10

La Pr Sm Gd Dy Er YbCe Nd Eu Tb Ho Tm Lu

10

10

Huttonite andThoriteLa Pr Sm Gd Dy Er YbO Nd Ku Tb Ho Tm Lu

Fig. 8. Chondrite-normalized REE patterns of monazite, allanite, xenotime, intermediate xenotime-zircon phases (IXZP) and Th-orthosilicate minerals. Shaded areas represent fields occupied by analysed specimens; the number of analyses represented is shown inparentheses. Monazite; 1, Nd-rich variety, 2, Cc-depleted monazite associated with secondary cerianite (see text). Xenotime: 1, inter-med iate xeno tim e-m onaz ite phase. Th-orthosilicates: 1 and 2, LR EE- and P-rich varieties, probably monazitehuttonite solid solutionphases.

Distribution of LREE (Fig. 17)In peraluminous granites, ~90~95 wt% of bulk-rock LREE contents reside within accessories (80-85wt% in monazite, the rest in apatite) and therema ining 5-10 wt % in feldspars. In metaluminousgranites, the fraction of LREE residing withinaccessories decreases to ~ 70 wt % (50-60 wt % inallanite, the rest in sphene, apatite, monazite andREE-carbonates). Amphibole accounts for 1525w t% LR EE, whereas the remaining 5-10 w t% is infeldspars and, when present, epidote. In peralkalinegranites, the fraction of LREE residing withinaccessories increases again up to 8090 wt % .Allanite is still a substantial LREE reservoir,although bastnaesite, fluocerite and aeschinite mayalso be very important.

Distribution of Eu (Fig. 17)In peraluminous granites, plagioclase and K-feldsparcontain similar fractions of total Eu, and togetherthey account for ~ 90 wt % Eu. A patite plus mon-azite accounts for ~57 wt % Eu and micas couldhave ~12 wt% Eu. In metaluminous granites,plagioclase is the most important Eu reservoir andtogether with K-feldspar accounts for ~ 70-80 w t %of total Eu. Amphibole may account for 515wt % and the rest is in allanite, sphene, apatite andmonazite. When present, primary epidote may alsoaccount for a significant fraction of total Eu. In per-alkaline granites, ~ 75 wt % Eu is in feldspars,another 10 wt % in alkali amphiboles, and the rest isdistributed in allanite, epidote, sphene, monazite,bastnaesite, niobotantalates, etc.

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JO U RN A L OF PETROLOGY VOLUME 37 NUMBER 3 JUNE 1996

Fig. 9. BSE-SEM image of an idiomorphic-zoned allanite including a cheralitic monazite crystal, apparently in equilibrium (ee text).Metaluminous plagiogranitc, Ackennanoviky complex, Khabarny.

Fig. 10. Metamictic allanite crystals included in amphibole. [Note secondary REE-carbonates filling cracks (BSE-SEM image).]

Distribution of HREE and Y (Fig. 17)In peraluminous granites, no less than 95 wt% oftotal HREE reside within accessories. In low-Cavarieties, the fraction of total REE that resideswithin xenotime is ~30-50 wt%, in apatite ~ 1525w t % , in zircon ~ 15-20 wt%, in monazite 510

w t % , and in Th-orthosilicate ~5-10 wt%. Thedisappearance of xenotime in high-Ca peraluminousgranites reinforces the roles of zircon (~ 3540 wt %of total HREE), monazite (~20 wt%) and apatite(20-25 wt%). In metaluminous granites, amphibolemay contain as much as 30-35 wt % of total HREE,whereas zircon accounts for ~3050 wt%, allanite

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Table 8: Selected analyses ofallamte crystals (results expressed in percent)

Si O 2Z rO 2AfeOjFeOMgOCaON B 2 OP J O BY 2 0 ,Th O 2UO 2

CajOjPr 2 O,

SmjOjEi^OjG d j O ,Tb^OaDy 2O 3H o ^ ,E r 20 ,T I T ^ O JYbjOj

Total

1

32-960-06

14-8618-22

1-2010-39

0-120-080-340-7200 04-479-501-282-680-430000-25n.d.0-19rvd.007nx\.00500 097-86

2

37-280-08

12-1417-53

0029-310080020220-640005-069-821-322-740-430000-36n.d.0-23n.d.0-07n.d.00 60-0197-42

3

34-15002

16-1617-500-759-860-140040-370-560004-758-9711 82-450-4300000 9n.d.003n.d.00 1n.d.00 100097-47

4

30-14000

140217070-249090-220030-190660008-94

14-131 650-48008000007n.d.007n.d.003n.d.0020 0097-11

5

36-430-28

15-6710-87

10 310-95

0-190-040-521 310004-84

10-011 -213-160-470000-37n.d.0-10n.d.004n.d.00300097-52

6

38-210-76

160410-83100

10-150-230-160-241-670004879-761-252-170360000-17n.d.006n.d.00 1n.d.00 100 097-95

7

42-661-64

13-5690 90-679-870-560-120-3651-790-224-8785 30-901-300-270-000-14n.d.0-11n.d.0-05n.d.00300096-75

8

42-351-45

13-368-910849-340-500-140-22920 50-0113-978-791-281-880-26900010-1590-0210-1010-0200-O4800060-0310-00495-76

9

33-43007

11 0116 230-108-370-190000-1471054-385-72

12-271-404070-2300-0010-13000160-085001400360-0040020000398-97

10

32-100-13

10-7417-07

00 18-780-2200 10-2361-310-1014-630

14-731-714820-30000030-17400230-1300020005300060030000397-34

11

31-880

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Fig. 11. BSE-SEM image of a xenotime- ircon intergrowth. The idiomorphic nudeui ha an external part composed of zircon and acore compriiing IXZP. The external part ii moitly composed of xenotime, with alternating thin layers of IXZP. Ronda leucogranitei.

Distribution of U (Fig. 18)The fraction of U contained in major minerals isalways

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BEA RESIDENCE OF REE, Y, Th AND U IN G RANITES

Table 9: Selected microprobe analyses of xenotime and intermediate xenotime-zircon (IX%) crystals(results expressed in percent)

S iO 2Z rO 2H fO 2AI1O3FoOM gOCaON a j OP2O6Y 2 0 ,1TiO 2U 0 2Lfl jO,C e j O ,PrjOjNdjO,SmiOjE u 2 0 3GdjO,D y i O ,ErjO,YbjOjLu 2O 3Total

1

1-110 0 00 0 30-000 2 60 0 00-100 0 0

31-844 6 9 1

0 8 51-900-020-140 0 50-420-630 0 61-864-534-414-300 6 5

100-07

2

0-310-110-12O^X)0-130-000-140-05

33-0150-07

0-180-000-030-150

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Fig. 12. BSE-SEM image of a radiation-damage structure around a metamictic Th-orthosilicate grain, probably thorite, included inamphibole. The small pseudo-hexagonal grain in the lower right part is an apatite half-including two zircon gTaini. Sirostan tonalites.

Fig. 13. BSE-SEM image of a xcnomorphic zircon grain wilh microincluiioni of Th-orthojilicatc, badddcyitc and zirkclilc Burguilloidel Ccrro diorile

lation densities in the magma near the ceiling andthe floor, respectively; i5c and 5 are the densities ofcrystal and melt, respectively; g is the gravity accel-e ra t ion; K is the magma thermal diffusivity; r\ is them ag m a viscosity; v is the kinem atic viscosity; T\ T2represents the temperature difference between floor

and ceiling; ax is the thermal expansion coefficient;an d dc is the crystal diameter.Figure 19 shows settling curves as a function of thediam eter of settling minera ls, calculated fromequation (1) for crystallizing granite melts with adensity of 2-5 g/cm 3 , viscosity from 105 to 108 poises,

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Table 10 : Selected microprobe analyses ofother REETTh U-rich accessories (results expressed inpercent)

SiOjZrOjNbjOsT a *O 8FoO"-TlOjCaONajOP20BY 2O 3T hO 2U O jUjO,C O Z O JP r2 O 3NdjOjSmjOjE u 2 O 3Gc f e O,D y j O ,ErjOjY b j O ,Lu 2O 3Tota l

1

1 3 - 2 80 - 1 00 -4 10 0 51 -930 0 01 -4 80 0 23 0 50 - 8 4

7 6 - 4 41 -4 60 0 20 - 0 60 0 20 - 1 00 0 90 0 00 - 1 50 - 2 10 - 1 60 - 1 10 0 1

99-97

2

1 7 - 6 60 0 00 -3 10 0 37 -5 30 0 30 - 5 60 - 1 40 -5 53 - 1 4

5 5 - 5 67 -3 70 - 0 00 -0 10 0 10 0 70 -1 10 0 10 - 1 00 - 4 91 0 04 - 6 30-61

9 9 - 8 2

3

1 2 - 6 00 1 20 -0 5O-OO1-240 0 04 -5 10 0 5

1 0 - 0 73 - 5 7

3 8 - 7 81-113 - 9 9

1 2 - 7 01-654 - 8 20 -900 0 10 -930 - 9 60 - 4 50 - 4 00 0 7

98-98

4

0 2 80 0 10 -660 -2 10 -970 0 00 0 00 0 30 -2 10 - 1 8

1 7 -5 17 8 - 9 3

0 0 00 0 10 - 0 00 0 30 - 0 80 0 00 1 10 - 1 60 -1 30 0 90 0 0

99-60

5

0 - 5 80 0 10 - 4 80 -1 72 - 3 50 0 60 0 10 0 40 -630 - 4 9

1 1 - 2 28 3 - 3 6

0 0 10 0 30 0 10 0 40 0 80 0 10 - 1 40 - 1 90 - 1 70 - 1 40 0 4

1 0 0 - 2 6

6

2 - 1 40 -2 5

5 4 -2 13 -1 72-619-1 83 -990 - 0 00 - 1 33- 52 - 1 47 - 2 80 - 0 60 -1 40 0 20 0 60 0 30 0 00 0 60 - 1 60-210 - 3 40 - 0 6

8 9 - 7 4

7

0 - 1 00-31

2 9 - 2 27-614 - 3 9

1 7 0 74-290-210-080-625 69

22-800-120-240 0 30-120-030-000-030-040 0 40 0 70 0 1

9302

8

0-390-714-900-313-90

17-415-630-190-012-352-592-41

12-3322-43

3-0811-90

2-620-252-412-531-250-550 0 5

100-20

9

0-140-81

24-590-827-133-596-481-990-018 3 43-145-762-196 481-336-443 0 70-394-167-194-462 0 80-19

99-78

1 0

0-610-89

25-601 0 78-545-791-390 0 50-04

12-972-98

13-330-500-900-413 0 82-460-304-297-745 0 82-570-23

100-82

11

0 0 00-00

12-280-190-02

30-512-377-140-000-100-580-06

1 7 0 824-39

1-582-570-100-010 0 40-000-000-000-00

9902

Th-orthosi l icates : 1, peralumlnous granodiorrte (Hoyos ); 2, peralkal ine granite (Ga lif ieiro); 3, pho sphotf iof i te, peralkaline granite (G ali-fieiro). Uraninite: 4, cordierrte-bearing granodiorrte (Gredos); 5, U-rich leucogranite (Albuquerque). Pyrochlore: 6, peralkaline granite(Keivy). Betafrte: 7, peraluminous granodiorrte (Hoyos). Aeschynite: 8, peralkaline granite (Kharitonovo). Fergusonrte: 9, peralkalinegranite (Galifteiro). Samarskite: 10, peralkaline granite (Galifteiro). Loparite: 11 , peralkaline syenite (Kola).

mineral densities from 4 to 6 g/cm and T\ T^ of50C. As the dependence of T\ Ti is rather weak(Bartlett, 1969), the above parameter set willrepresent the situation in most crystallizing g ranites.Figure 19 also shows a curve representing therelative mass fraction of REEYThU-rich accessoriesas a function of grain-size calculated by averagingmodal counting on granites mentioned in Fig. 17. Itis evident that even grains of 150 /imwith a densityas high as 6 g/cm 3 cannot settle appreciably within amelt with a viscosity as low as 10 poises. Un-modified uraninite crystals may have a density of10-3 g/cm3, but their diameter is usually so smallthat gravity settling is also impossible. We thereforeconclude that the fate of early crystallizedREEYThU-rich accessories is to remain in sus-

pension within the melt until a crystallizing majormineral includes them.The reasons why accessories are selectivelyincluded within a few major minerals are not wellunderstood yet, but must surely be diverse. In rockscrystallized from a melt, heterogeneous nucleationeither of the major mineral on an early-crystallizedaccessory or vice versacoupled with crystallizationrelated to local saturation adjacent to a growingphenocryst (Bacon, 1989) seem to be the mostprobable mechanisms. In metasedimentary rocks,detritic inheritance and the neoformation of acces-sories in some preferential places during sedi-mentation and diagenesis, complicated later byrecrystallization during metamorphism, are the keyfactors. It is clear in both cases, however, that

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Fig. 14. Zircon growing on a uraninite crystal (BSE-SEM image). Muranlca granite, the Urali.

La Pr Sm Gd Dv Er VbCe Nd EII Tb Ho Tm l,u La Pr Sm Gd U.v Er YbCe Nd Eu Tb Ho Tm LuFig. 15. Chondrite-normalized REE pattern! of REEYThU-rich niobotantalates, uraninite and pyrochlore-betafite minerali.

selective inclusion of REE YThU -rich accessories in agiven major mineral confers on it an indirect but stillsignificant control over the geochemistry of REE, Y,Th and U, which is almost impossible to quantitat-ively model with present knowledge.Contrasting geochemistry of REE, Y,Th and U insubaluminous vs peraluminous granitesThe geochemical behaviour of REE, Y, Th and U indifferentiated granites changes with aluminiumsaturation. In general, the higher the aluminiumsaturation index [ASI = mol. Al2O3/(CaO +N a2O + K 2O)], the stronger the depletion in REE

(except Eu), Y, Th and U in leucocratic differ-entiates (Bea, 1993). A good example, which mayhave important consequences for the understandingof heat production in the crust, is the contrastingvertical distribution of REE, Y, Th and U (and K)in vertically zoned plutons: in I-type granitoids theconcentrations of REE, Y, Th and U increase fromthe least to the most differentiated facies, accumu-lating upwards (Sawka & Chappell, 1988), whereasin S-type granitoids, in contrast, the concentrationsof REE, Y, Th and U decrease from the least to themost differentiated facies, accumulating downwards(Bea et al., 1994a). These differences are due tovariations in the nature of the major and accessory

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Fig. 16. BSE-SEM image of a complex monazite (white)-zircon (grey) intergrowth.

minerals as a consequence of changes in the alu-minium saturation, the key factor being the pro-gressive replacement of allanite and sphene bymonazite and xenotime with increasing ASI anddecreasing CaO, which seems to occur in the fol-lowing way.Peraluminous granites have higher phosphoruscontents than metaluminous granites with the samesilica content, owing to the enhancement of apatitesolubility at high ASI values (London, 1992; Bea etal., 1992; Pichavant et al., 1992; Wolf & London,1994). As the solubility of monazite and xenotimeremains very low regardless of aluminosity (Rapp &Watson, 1986; Wolf & London, 1995), phosphorus-rich peraluminous melts become saturated in mon-azite and xenotime at low REE concentrations.Precipitated REE-phosphates are then effectivelyremoved from the melt as inclusions in biotite, alsoan early crystallized mineral, thus producing astrong depletion of REE, Y, Th and U in residualmelts. Inmetaluminous melts, however, the scarcityof phosphate anions makes the saturation in REE-phosphates occur at higher REE concentrations thanin peraluminous melts, and allanite and sphenebecome the dominant REEYThU-carriers. As theseminerals are by far less effective than monazite andxenotime at removing these elements from themelt,and they do not usually precipitate massively at thebeginning of crystallization, bulk crystal-meltdistribution coefficients should remain at

E^.TTI".^ < 1 during most of the crystallization

history, thus producing somewhat enriched differ-entiates.Post-magmatic mobility of REE, T,Th and UREE, Y, Th and U are highly mobile during post-magmatic stages. SEM images revealed that (1)primary epidote is usually rimmed by a film ofLREE carbonates which also fill cracks radiatingfrom theepidote grain (Fig. 3), (2) primary allaniteis also the source of secondary migrating LREE car-bonates (Fig. 10), and (3) secondary allanite formseasily from monazite along fractures in micas (Fig.7). The mobility of REE, Y, Th and U is related tothe fact that many accessories are metamictic andare surrounded by radiation damage structures (seeFig. 12) capable of channelling the migration ofREE, Y, Th and U. It is important to emphasizethat characteristic accessories from peraluminousgranites (monazite, xenotime, huttonite) are inher-ently more stable than accessories from meta-luminous and peralkaline rocks (allanite, thorite).Effects of the pressure on the compositionof major minerals in crustal protolithsThe REEYThU composition of major minerals inamphibolite-grade metasediments and orthogneissesis very similar to that of peraluminous granites.Granulite-grade garnets, however, are noticeablyenriched in Nd and Sm and have a larger Eunegative anomaly (Fig. 2). Granulite-grade feldspars

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JOURNAL OF PETROLOGY V O L U M E 37 N UM BER 3 J U NE 1996

Table 11: Selected analyses of zircon crystals

SiO,Z rO 2H fO 2A l j O ,FoOM g OCa ON a 2OP 2 O5

YT hULaC aPrN dSmEuG dT bDyH oErT mY bLu

133-3564-77

1-970-020-5O0 0 30-000-000-01

7 7 01 5 9

12-22-607-751-135-111-430-321-940-485-422-239 962-84

2 7 - 89-18

2

3 4 - 1 362-69

2-170 0 00-090 0 00 0 10 0 70-06

19 910 5

5 4 - 55-57

13-2-84

1 3 32-480-533-740-819 0 43-76

20-14 0 5

30-93-73

33 5 0 461-97

1-140 0 00-830 0 50-160 0 70 0 0

1 3 92 5 9

28-11-656-370-503-342-451-158-904-41

47-31 9 08 2 520-4

1 8827-1

4

33-2361-05

2-290 0 00 0 10 0 00

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Table 12: Selected LA-ICP-MS analyses of apatite crystals

YUThLaCePrNdSmEuGdTbDyH oErTmYbLuEu/Eu*L W Y b *

Peraluminous11 806

41-19 -86

48 01452

30 81633

5314 6 9

54110 057 511 030 243 628 5

33-90 0 31-14

22467

55114-9

6 301 709

29 11537

58 92 3 7

7 6 913 27 4213 536 251-929 8

39-4o n1-43

31486

39 40-61

32 91156

19 88 6 532 4

12-535 9

59-232 2

5 9 -814820-6116

13-90-111-91

49 8 4

0-510 -93

29 71181

21 27 6 926 4

14-627 4

45-321 6

4 0 -294-513-687 -510-5

0-172 2 9

51736

8 2881-4

44 41632

29 41412

50 610-2

7 071266 1610 928 841-726 9

41-70 -051-11

61598

12940-7

46 31659

29 51269

45 68 8 5

6 5210 556 910 327 241-921 8

2 7 20 0 51-43

Metaluminout16 32

11-10 -70

26-210 3

24-616 610 2

28-417 8

36-323 5

51-915320-3122

17-10 -640-14

29 51

35-92-45

25-996-631 -1

21 412 4

36-524 3

5 0 528 9

63-519 629-115 2

2 4 50-640-11

31024

88 -73-17

6 0 - 417 7

43-630 0135

44-8221

44-832 0

74-819 729-817 8

28-40 -790-23

Peratkaline1257

4- 312-7

27214710

46 61220

18 958-8

18 522-6

10 018-343-34-7124-1

2-490 -96

76 -2

2317

15-346-1

27554 6 9 2

6 361643

26 477 -5

26 233-1

1352 3 650-55 6 322-7

2 -790 -90

81-9

328 4

1 8 11 8 0

28296 9 3 0

6 561 701

23 584 -4

20 72 6 0

10 718-64 6 -85-7734-1

3-371-17

65-9From peraluminous granites: 1, cordierite-bearing granodiorite (Hoyos ); 2, migmatite (Pena Negra); 3, two- mic a granite (Pedro-bemardo); 4, leucogranite (Truj i l lo); 5, U-rich leucogranite (Albuquerque); 6, garnet-bearing granite (M urzinka). From metaluminousgranites: 1 and 2, granodiori te (Vierkisest); 3, tonali te (Sirostan). From peralkal inegranites: 1-3, granite (Keiv y).

Table 13 : Selected LA-ICP-M S analyses of primary sphene crystals (results are in p.p. m.)

YUThLaCePrNdSmEuGdTbDYHoErTmYbLuEu/EiTLWYb/v

11150

0 0 016 6

11093 5 96

7 9 03240

7 8 820 46 0 6

89 -545 8

8 8 - 525 1

39-5265-

36-80 -902-82

21612

10-517 1

17526 1 0 2125652791367

24 01107

1346 9 813035 2

51-433 6

41-40 -603 5 2

32127

6 9 816 3

23949 2 7 31 77874531 994

30 01390

20 21 003

17 645 2

63 -439 0

4 7 -80-554-14

41100

19-216 1

11894315

8 193484

8 3021 26 54

8 9 8451

82-822 7

34-2323 0

32-20 -883-49

521 739 1142

315381571656683 92475

39 81844

25 91241

20 553 5

71-341 0

46-40-575-19

67 3215721 3

10873337

6 0 8 -2519

51 014039 1

55-129 0

58-116 0

2 3 816 2

21-70 9 64-53

710 022 621 9

14884 786

8 453525

7 0 718 553 4

7 8 - 041 7

8 2 024 0

36-623 4

31 20 -924-29

824 5

32-348

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JOURNAL OF PETROLOGY V O L U M E 3 7 N U M B E R 3 JUNE 1996

ASI: 1.15 -1.00 >1.00X _ . Low-Ca High-CaTyP e- S S S S S I 1 1 I M M A A A

Legend| 1 K-fe ldspar

plagioclasebiot i te+cordier i te+garneta m p h ib o le

R E E - c a r b o n a t e sniobo- tanta la tes

| | others

Fig. 17. Fractional contribution of each mineral to the whole-rock LREE, Eu and HREE budgets in iclected granite plutoru. Contin-uous line teparatei the contribution of major from accesiory minerals. Dashed line separates the contribution of accessory phosphatesfrom silicates. Dotted line separates accessory silicates from niobotantalates and carbonates. (See discussion in text.)

the exchange of Ca (from garnet) by LREE (frommonazite). In a current study on the amphibolite-granulite transition in the Ivrea-Verbano zone (Beaet al., in preparation), we detected that an elevatedproportion of monazite grains included within gran-ulite-grade garnets are partially or totally pseudo-morphed to a mixture of apatite and cheralite-richmonazite, whereas the garnet around the inclusion is

enriched in LREE. Those garnet analyses withabnormally high LaCe contents reported in Table 5and Fig. 2 were probably caused by the ablation ofsuch zones.If pressure-related differences in the REE com-position of major minerals are confirmed with moresystematic studies, their role as a potential source fordifferences in the REE chemistry of melts equili-

5 4 8

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ASI:Type:

10080

H1.00Low-Ca High-CaS S S S SI I I I M M A A A

LegendI E ] K-feldspari^ ^ p lag ioclascSSS amphibole

| | monazi te( ; : : : | xenol imc|;:j:j:j:;:;| a p a t i t e

:< i

rt: | sphene

hul toni te+thori teuranin i te

P%^ n iobo- tantalalesI ] others

oat 03211 . * o o> 1I I

Fig. 18. Fractional contribution of each mineral to the whole-rock Th and U budgets in selected granite plutonj. Continuous line sepa-rates the contribution of major from accessory minerals. Dashed line separates the contribution of accessory phosphates from silicates.Dotted line separates accessory silicates from niobotantalates and carbonates. (See discussion in text.)

10.0

8.06. 04 .02. 00 .0

/y

f\ II = iI 1 n.

k\\\lIllTlHIIm i um B f f i B l i f t A V V lo '

1.00.80.6 Z0.4 "2.0.20 .0

10 " 10' l()2 I03 I04 10"Crvstal diameter (microns)

Fig. 19. Settling curves as a function of the diameter of settlingminerals calculated with the Bartlett (1969) equation for densityintervalj between 4 and 6 g/cm3. The right vertical axis representsthe ratio between the mineral particle population densities inthemagma near the ceiling (Np^) and the floor (Npi). The curve inthe left part of the diagram represents the mass fraction of acces-sories as a function of their diameter. (Note how even 150-/jmgrains with a density as high as 6 g/cm 3 cannot settle appreciablywithin a melt with aviscosity as low as 10s poises.)

brated at amphiboli te- and granuli te-grade condi-tions, respectively, should therefore beconsidered asa subject for further investigation.Can REE be used in geochemical modellingof granite rocks?The objective of trace-element-based petrogeneticmodelling of igneous rocks is to infer the behaviourof minerals during melting and crystallization bycomparing actual trace-element distr ibution patternswith theoretical models generally calculated fromfractionation equations based on the laws of che-mical equilibrium (Allegre & Minster , 1978;Hanson, 1989) . To be useful inpetrogenetical mod-elling, a given trace element must be essentiallycontained within major minerals, obey RaoultHenry's law, and not move appreciably during post-magmatic stages. It is evident that in the case ofgTanite rocks, REE (except Eu), Y, Th and U do notsatisfy any of these conditions and simply cannot

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therefore be used for modelling the genesis of grani-toids in that manner.

CONCLUSIONSThe LREE, HREE, Y and Th fractions that residewithin major minerals are as low as 510 wt% inperaluminous andperalkaline granites, butmay riseto 2030 wt % in amphibole-rich metaluminousgranites. Eu is always essentially contained withinfeldspars, although primary epidote may alsocontain a significant proportion. The fraction of Uthat resides within major minerals is always

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