Genesis and transformations of monazite, florencite and ... · Genesis and transformations of...

Genesis and transformations of monazite, florencite and

rhabdophane during medium grade metamorphism:

examples from the Sopron Hills, Eastern Alps

Geza Nagy a,*, Erich Draganits b, Attila Demeny a, Gyorgy Panto a, Peter Arkai a

aLaboratory for Geochemical Research, Hungarian Academy of Sciences, Budaorsi ut 45, H-1112 Budapest, HungarybInstitut fur Geologie, Universitat Wien, Althanstrasse 14, A-1090 Vienna, Austria

Abstract

Electron microprobe studies on the age, mineral chemistry and alteration on accessory LREE-phosphate minerals have been

carried out in medium-grade metamorphic rocks of the Sopron Hills belonging to the Lower Austroalpine tectonic unit.

Monazite (and xenotime) is relatively common, whereas rhabdophane and florencite are restricted to certain rock types. A first

generation of monazite was formed in mica schists during the pre-Alpine, Hercynian metamorphism at 575–700 jC and 1.8–

3.8 kbar as evidenced by P–T data from the literature, their mineral paragenetic and textural characteristics and supported by

Th–U–total Pb ages of ca. 300 Ma. In orthogneisses, monazite is rare and of igneous origin. Kyanite quartzites and

leucophyllites that were formed by Mg metasomatism contain inherited monazite from the precursor rocks. A new generation of

monazite was also formed during the Alpine metamorphism at V 550 jC, 13 kbar according to the literature data, giving ages

around 75 Ma. Pronounced negative Eu anomalies were found in the igneous monazites (Eu/Eu * < 0.35), while most of the

metamorphic monazites have moderately negative Eu anomalies (Eu/Eu*>0.4). Small differences have been observed in Y and

HREE contents, whereas the LREE sections of the rare-earth element (REE) patterns nearly coincide. Th and Ca enter the

monazite structure at the expense of REE, nearly according to the brabantitic replacement 2REE3 + XTh4 + +Ca2 + . In some

mica schists, monazite is altered to rhabdophane. Rhabdophane, distinguished from monazite by quantitative electron

microprobe analysis by low-oxide total, is found in many mica schists and orthogneisses. It forms fine-grained aggregates, often

attached to apatite or monazite. It usually has higher Y and Ca contents and a less pronounced negative Eu anomaly than that of

coexisting monazite. It may have been formed either by crystallization from REE-containing hydrous solutions or from

monazite reacting with Y–Ca-containing solutions. Florencite appears only in some leuchtenbergite-bearing leucophyllites,

kyanite quartzites and REE-rich clasts. It is often idioblastic and may be grown on apatite or monazite. It is chemically close to

its ideal composition, but Ca, Sr and Th may replace REE in minor amounts. In some grains, ThO2 may reach 10 wt.%. The

data indicate that the charge balance is maintained by different mechanisms in low- and high-thorian florencite. No Y or HREE

(above Gd) could be measured in florencite. No fractionation was observed between coexisting monazite and florencite;

however, monazite inclusions in florencite are depleted in La–Ce and enriched in HREE.

D 2002 Elsevier Science B.V. All rights reserved.

Keywords: REE minerals; Polymetamorphism; Eastern Alps; REE geochemistry; Th–U– total Pb geochronology

0009-2541/02/$ - see front matter D 2002 Elsevier Science B.V. All rights reserved.

PII: S0009 -2541 (02 )00147 -X

* Corresponding author.

E-mail address: [email protected] (G. Nagy).

www.elsevier.com/locate/chemgeo

Chemical Geology 191 (2002) 25–46

1. Introduction

At present, petrogenetic studies on the basis of

index mineral assemblages and thermobarometric

evaluation of rock-forming minerals are common,

but relatively little is known about the behaviour of

the rare-earth element (REE) minerals during the

metamorphic processes. In order to better understand

the accessory REE minerals of metamorphic rocks, we

investigated their occurrence, abundance, composition

and textural relationships in the petrologically well-

known Sopron Hills.

Anomalously high REE and Th concentrations

were discovered in the Sopron Hills by Fazekas et

al. (1975) who identified florencite and monazite in

the REE-rich samples. Florencite in concentrations up

to 40% and grain sizes >1 mm is present in certain

clasts of leuchtenbergite (local name of Mg–clino-

chlore)-containing kyanite quartzite or kyanite schist.

Monazite grains found in quartzites and mica schists

usually are smaller and rarely reach 0.1 mm. In

adjacent areas to the West, Kiesl et al. (1983) inves-

tigated the bulk REE contents of rock samples and

their heavy mineral fractions from comparable Lower

Austroalpine tectonic units in the region of Birkfeld

(Styria, Austria), and the REE minerals from lazulite

veins in the Austroalpine basement of the Fischbacher

Alps have been investigated and used for Th–U–total

Pb age determination by Bernhard et al. (1998) and

Bernhard (2001).

The REE minerals investigated in this paper are

monazite (monoclinic CePO4, P21/n), rhabdophane

(hexagonal CePO4�nH2O, n = 1, e.g. Jones et al.,

1996, or n = 0–0.5, e.g. Strunz, 1970, P6222) and

florencite (trigonal CeAl3(PO4)2(OH)6, R3m or R32).

Xenotime (tetragonal YPO4, I41/amd) and sporadic

allanite (monoclinic (Ca,Ce,Y)2(Al,Fe)3(SiO4)3OH),

P21/m) will not be treated. Monazite and rhabdophane

compositions and abundances have been published by

Nagy and Arkai (1999) and by Nagy and Draganits

(1999) for the Hungarian and Austrian part of the

hills, respectively. Bulk-rock REE contents have been

compared to monazite and xenotime compositions by

Panto et al. (1999). In the present work, we summa-

rize the chemical and textural features of monazite,

rhabdophane and florencite. Combining these data

with U–Th–total Pb ages for different monazite

generations permits us to derive information on the

formation, transformation and alteration of these

LREE minerals during metamorphism.

2. Geological setting

The metamorphic rocks of the Sopron Hills repre-

sent the easternmost outcrop of the Austroalpine

basement, belonging to the Lower Austroalpine nappe

system (Kishazi and Ivancsics, 1985; Fulop, 1990;

Draganits, 1998). The rocks display a complex poly-

metamorphic history; the existence of large-scale,

Cretaceous ductile thrusts and normal faults and

Tertiary brittle faults in association with poor outcrop

conditions further complicate the geologic situation.

In the Sopron area (Fig. 1), two different lithological

units have been distinguished. Biotite-rich mica schists

and gneisses with well-preserved pre-Alpine andalu-

site, thin quartzitic layers, coarse-grained pegmatites

with weakly developed foliation occur mainly in the

uppermost levels of the crystalline series. They have

been distinguished from markedly foliated, chlorite-

and garnet-rich, retrogressed mica schists in close

contact with medium-grained orthogneisses. Draganits

(1998) named the former lithological group Obrenn-

berg–Kaltes Brundl Series (OKB Series), whereas the

latter was called Sopron Series; in Hungarian terminol-

ogy the OKB Series is called Brennberg Mica Schists

and the Sopron Series corresponds broadly to theVoros-

hıd Mica Schists (Fulop, 1990; Kovacs et al., 1996).

The Brennberg Mica Schists (OKB Series) mainly

comprise biotite–sericite–chloritoide–garnet–schists

and biotite–sericite–sillimanite–schists with stauro-

lite relics. Biotite–andalusite– sillimanite schists,

which represent the best preserved pre-Alpine rocks

in this area, have been found in a few places (Kishazi

and Ivancsics, 1986; Draganits, 1996). Kyanite–leuch-

tenbergite–muscovite quartzites (‘‘grey quartzites’’,

Kishazi and Ivancsics, 1986) also occur in this series.

The Voroshıd Mica Schists (Sopron Series) are

characterised by monotonous diaphthoritic mica

schists with varying quartz contents and numerous

rectangular to rhomboic pseudomorphs, probably after

staurolite. These pseudomorphs contain either sericite,

or sericite with chloritoid, or chloritoid with kyanite,

depending on the bulk chemistry and the degree of

Alpine overprint; relics of staurolite within these pseu-

domorphs are scarce. The metamorphic temperature

G. Nagy et al. / Chemical Geology 191 (2002) 25–4626

slightly surpassed the garnet isograd producing small,

idioblastic–hypidioblastic garnet grains. Leucocratic,

moderately foliated, medium-grained gneisses are

associated with these mica schists. The orthogneisses

are dominated by the quartz–plagioclase–K feldspar–

muscovite–biotite(–garnet) assemblage; however, the

sericite–chlorite–quartz–albite assemblage character-

istic for the lower greenschist facies is also frequently

formed. At some localities (e.g. the Varis quarry), the

original granitoid rock has been preserved as meta-

granite, showing original magmatic textural and min-

eralogical characteristics.

This series contains muscovite– leuchtenbergite

(local name for Mg–clinochlore)–schists (tradition-

ally called ‘‘leucophyllites’’) and kyanite–leuchten-

bergite–muscovite) quartzites (‘‘white quartzites’’,

Kishazi and Ivancsics, 1986), whose formation has

been related to metasomatic processes along Alpine

shear zones (Huber, 1993; Demeny et al., 1997). The

leucophyllites show a continuous transition from the

neighbouring orthogneisses with distinct chemical

(alkali loss, H2O and Mg gain) and mineralogical

changes (muscovite and feldspar break down, phen-

gite and Mg–chlorite formation) (see Demeny et al.,

1997). Kishazi and Ivancsics (1986) explained the

formation of leucophyllites, ‘‘white quartzites’’ and

‘‘grey quartzites’’ by Mg metasomatism, with orthog-

neisses and mica schists as protoliths.

A special rock type enriched in REE minerals

(monazite and florencite) has been found in debris in

the area of the Sopron series (Fazekas et al., 1975).

These loose blocks contain florencite and/or monazite

Fig. 1. Geological map. a =Brennberg Mica Schists; b =Voroshıd Mica Schists; c = gneisses; d = leucophyllites; e = kyanite quartzites;

f = inhabited area.

G. Nagy et al. / Chemical Geology 191 (2002) 25–46 27

in rock-forming amounts (up to 40% modal abun-

dance), in addition to kyanite, leuchtenbergite, quartz,

muscovite and Cl-bearing apatite. They may have

originated from an eroded vein (Fazekas et al., 1975).

Based on the mineralogical similarities (leuchtenber-

gite, kyanite and Cl–apatite contents), the vein could

have been related to the Mg metasomatism responsible

for kyanite–quartzite and leucophyllite formation.

The OKB and Sopron Series also differ in their

metamorphic history. The Sopron Series shows evi-

dence of two amphibolite-grade metamorphic events,

while the OKB Series displays an even more complex

history, in which remnants of staurolite included in

andalusite indicate an amphibolite-grade metamorphic

event before the main andalusite, sillimanite and

biotite-forming event, followed by a final amphibo-

lite-grade metamorphic event with kyanite, staurolite,

chloritoid and garnet growth (Lelkes-Felvari et al.,

1984; Kishazi and Ivancsics, 1985). Preliminary iso-

tope age determinations on samples from the Sopron

Hills as well as on similar rocks in the Eastern Alps

point to a Hercynian age for the first event, followed

by a Permian low-P/high-T event and a final Eo–

Alpine high-P/low-T overprint (Draganits, 1996;

Berka et al., 1998; Schuster et al., 1998; Balogh and

Dunkl, 1998; Berka, 2000; Schuster et al., 2001).

Due to the rare preservation of the Hercynian

minerals, P/T estimates are difficult, but the occurrence

of staurolite and garnet points to amphibolite-grade

conditions for the Hercynian event. On the basis of

mineral stability fields and thermobarometric calcula-

tions, Torok (1999) obtained 575–620 jC and 1.8–2.5

kbar for the biotite–andalusite–sillimanite schists,

with 650–700 jC and 2.4–3.8 kbar for the highest

temperature mineral assemblage. For the Alpine high-

pressure metamorphism Draganits (1996) estimated

550 jC and 9.5 kbar, whereas combined studies on

fluid inclusion microthermometry and mineral chem-

istry in gneisses yielded 450–500 jC and 12 kbar and

520–600 jC and 13–14 kbar, respectively (Torok,

1996, 1998). Demeny et al. (1997) applied oxygen

isotope thermometry and phengite barometry for deter-

mining the formation conditions of leucophyllites and

related rocks, obtaining 560 jC and 13 kbar in good

agreement with the obtained Alpine metamorphic

conditions. Textural characteristics (mineral inclusions

and intergrowth, deformation) indicate that the mon-

azites and florencites of the leucophyllites, kyanite

quartzites and the REE-rich debris rock were formed

during the Alpine metamorphism. However, monazites

have been preserved in gneisses and mica schists as

remnants of pre-Alpine magmatism and metamorphic

events. Thus, the P–T conditions described above for

Hercynian times may be applied to the REE mineral

formation as well.

The investigated samples are listed with their main,

metamorphic index and REE minerals in Appendix A.

3. Methods

The main and metamorphic index minerals were

identified by optical microscopy and powder X-ray

diffraction. The textural relations were examined in

thin sections by optical microscopy, in thin or pol-

ished thick sections by electron microprobe analyser

(EMPA). The microprobe work was carried out on a

JXA-733 (JEOL) instrument equipped with three

wavelength dispersive spectrometers (WDS) and an

energy dispersive spectrometer (EDS).

The REE and other heavy accessory minerals have

been identified by EMPA. The whole surface of the

section was examined by backscattered electron (BSE)

images so that each grain of rutile or heavier minerals

with ca. 10-Am size or apatite with ca. 50 Am diameter

could be detected. Most of the minerals were qualita-

tively analysed by EDS, monazite and rhabdophane

were distinguished by quantitative analysis (Fig. 2a).

Quantitative mineral analyses were carried out by

WDS-s, using the method described by Nagy (1993), in

which a parabola fitted to peakless ranges of the X-ray

spectra determines the background for the lanthanide

analytical peaks. (Analytical conditions were: 20 kV

accelerating voltage; 40 nA electron current, five times

4 s counting time; the electron beam was opened to 6 or

3 Am diameter (depending on the grain size), focused

only if absolutely necessary. Lines used for analysis

were: Ka for light elements (Ca, P, Si, Al, Mg); La for

most REE, Ba and Sr; Lh for Pr; Ma for Th; Mh for U.

Pre-measured correction factors were applied to elim-

inate the effect of Ce–Sm, Pr–Eu, La–Gd, Ce–Gd and

Th–U line overlaps. The following standards were

used: glasses of Drake and Weill (1972) for REE, Du-

rango apatite for P and Ca from E. Jarosewich (Smith-

sonian Institute, Washington); oxide for Th, Y3Al5O12

for Al, SrBaNb4O10 for Sr and Ba, K-412 (NBS) glass


for Mg from C. M. Taylor (Stanford, CA); URuSi for U

from T. Gortmuller (Kammerlingh Onnes Lab, Lei-

den). Rough data were corrected by conventional ZAF

method. The points of analyses were set on BSE image

to eliminate cracks and uneven mineral surfaces.

Rhabdophane was always analysed with monazite in

the same run in order to eliminate any systematic errors.

The detection limits (in oxide wt.%) are about 0.15%

for La, Ce and Pr, about 0.1% for Nd–Yb and for U,

about 0.05% for other elements. The uncertainties

(calculated from 2r) of a representative monazite

analysis can be seen in Table 1. The Eu anomaly, i.e.

Eu/Eu* values, were calculated using the formula

given by Poitrasson et al. (1995, Table 1). The chon-

drite values of Taylor and McLennan (1985, p. 298)

were used.

Analyses for monazite Th–U–total Pb age deter-

mination were done at 20 kV, 80 nA beam current, with

100 s (10� 10 s) counting time on peak and 50 s

(5� 10 s) for background on both sides. Lead was

measured on the PbMa line for a PbSe standard and Th

and U as above. As our instrument has only two PET

crystals, the Pb content was measured twice at each

point, and the two values were evaluated independ-

ently. In order to decrease Pb background, the counter

was switched to ‘‘Differential’’ state, eliminating the

high-energy part (high order Th and U lines, etc.). In

the case of the monazite grains, the Pb background

showed a linear dependence on Th content. Consider-

ing this, the background was estimated from a straight

line fitted for each analysis of the session, instead of the

individual measurements. The detection limit for Pb at

2r confidence level is 0.012%.

Matrix effects were corrected by the ZAF method.

Instead of calculating each case separately, we calcu-

lated the correction factors for monazites with differ-

ent Th and U contents in advance, similar to Montel et

al. (1996). Under our circumstances, the correction

factors depend slightly on Th and U contents.

The age values were calculated from series of Pb–

Th–U data, as described by Suzuki et al. (1991), more

detailed in Suzuki and Adachi (1994) and discussed in

detail by Cocherie et al. (1998). The measured Pb

contents are plotted as a function of Th* (see below);

the points of equal ages should lie along a straight line,

with the slope depending on the age. After fitting a

straight line on the data points, the age can be calcu-

lated from the slope of the line, whereas the Y-axis

intercept equals the initial Pb content of the monazite.

Measurements done by Suzuki et al. indicated that at

the time of formation, monazite is free of Pb. Montel et

al. (1996) summarised the problems of Th–U–total Pb

method and described an alternative method for eval-

uation (the comparison of the two evaluation methods

is also given in Cocherie et al., 1998).

The abovementioned Th* is the measured Th plus

an equivalent Th value calculated from the U contents

from which the same amount of Pb would have

developed. The exact value of Th* depends on the

age. We applied the following approximation:

Th* ¼ Thþ 3:15 � Uwhich below 400 Ma gives small error (at 400 Ma, if

Th is missing, the error caused in age is + 3%, if the

Fig. 2. Frequency distribution of oxide totals by EMPA. (a) Monazite

and rhabdophane analyses: 1 = in majority of the investigated

samples; 2 = in the three mica schists (NM-22, -115, -128) containing

abundant monazite-like grains with low oxide totals, one of them

also monazite. (b) Florencite analyses.


Th/U ratio is below 6, the error is < 1% of the

determined age; at younger ages the errors are smaller).

For just a few hundred million years old monazite,

the radiogenic Pb contents (f 0.01–0.1 wt.%) are

usually near the detection limit and could be measured

only with high uncertainty, being the main sources of

error of the individual points (an example: one repeated

Pb analysis gave 17.15 and 16.76 cps for the peak,

14.85 and 14.54 cps for background, which yielded

0.056F 0.024 and 0.049F 0.021 wt.% Pb contents,

respectively; the errors were calculated with 2r, frommeasured standard deviations). The uncertainties in the

ages were recalculated from the confidence intervals of

the fitted lines, which have been determined as

described in Czerminski et al. (1990). Age values are

given with 95% confidence in the next section.

4. Results

The three LREE phosphate minerals studied in this

paper appear in different rock types. Monazite appears

in all of the rock types examined in highly variable

amounts. Rhabdophane can be found in mica schists

Table 1

Selected monazite (M) and rhabdophane (R) analyses

Rock Bt–And–

Sil schist

Kyanite

quartzite

Gneiss

(metagranite)

Bt–And–

Sil schist

Bt–And–

Sil schist

Chl–Ser–

Grt schist

REE-rich

clast

Sample No. NM-97 DE-6 DE-13 NM-128 NM-71 NM-6 S-2

1 2 3 4 5 6 7 8 9 10 11 12 13

M, core M, rim FDa M, old M, new M, inclb M R M ?c M R R M

Y2O3 1.57 0.66 0.14 0.25 1.20 1.73 2.18 3.47 0.18 0.20 0.13 2.97 1.76 0.03

La2O3 13.07 14.43 0.96 14.36 13.71 12.45 11.99 7.60 14.22 13.57 14.36 12.39 10.97 17.15

Ce2O3 28.33 29.83 1.40 28.89 26.35 26.66 26.63 18.03 30.79 28.50 30.35 23.07 23.05 32.96

Pr2O3 2.73 2.91 0.32 2.94 2.66 3.01 2.77 2.28 3.19 3.02 3.01 2.27 2.32 2.40

Nd2O3 11.31 12.36 0.48 11.52 9.58 11.25 11.18 8.67 12.72 11.94 12.27 9.87 8.98 8.32

Sm2O3 2.23 2.21 0.16 2.07 1.73 2.44 2.51 2.16 2.29 2.14 2.29 2.00 1.71 0.69

Eu2O3 0.32 0.53 0.12 0.46 0.43 0.10 0.12 0.42 0.44 0.40 0.42 0.59 0.31 0.22

Gd2O3 1.84 1.69 0.10 1.64 1.53 2.08 2.04 2.26 1.62 1.52 2.03 2.13 1.36 0.19

Tb2O3 0.17 0.22 0.06 0.11 0.14 0.19 0.20 0.22 0.14 0.06 0.16 0.22 0.10 0.06

Dy2O3 0.63 0.51 0.04 0.23 0.47 0.62 0.74 1.06 0.25 0.19 0.26 0.93 0.53 0.11

Er2O3 0.07 0.09 0.06 0.00 0.06 0.05 0.08 0.29 0.03 0.01 0.02 0.39 0.14 0.01

CaO 1.35 0.74 0.02 0.94 2.12 2.10 1.48 8.87 0.62 0.74 0.72 2.96 4.99 1.03

ThO2 5.24 4.44 0.20 4.80 10.63 5.54 4.94 8.20 3.26 3.87 4.46 4.48 6.06 4.97

UO2 1.65 0.41 0.12 0.79 0.54 0.87 1.04 0.58 0.48 0.39 0.42 0.23 0.40 0.03

SiO2 0.00 0.15 0.08 0.19 0.34 0.06 0.41 0.23 0.07 0.14 0.14 0.38 0.01 0.00

P2O5 30.15 29.60 0.48 29.05 29.57 30.38 30.23 28.16 30.48 29.80 31.34 28.52 29.17 29.98

Sum 100.64 100.76 1.89 98.11 100.99 99.47 98.53 92.53 100.74 96.47 102.35 93.64 91.87 98.09

Eu/Eu * 0.469 0.807 0.217 0.738 0.791 0.132 0.157 0.576 0.665 0.646 0.583 0.868 0.601 1.403

Ionic numbers based on 16 oxygens

SREEd 3.561 3.750 3.655 3.313 3.456 3.474 2.784 3.721 3.593 3.607 3.432 3.069 3.603

Ca 0.226 0.125 0.162 0.355 0.350 0.248 1.528 0.103 0.127 0.117 0.517 0.870 0.175

Th 0.186 0.159 0.176 0.378 0.196 0.176 0.300 0.115 0.141 0.154 0.166 0.224 0.180

U 0.057 0.014 0.028 0.019 0.030 0.036 0.021 0.017 0.014 0.014 0.008 0.014 0.001

Si 0.000 0.024 0.031 0.053 0.009 0.064 0.037 0.011 0.022 0.021 0.062 0.002 0.000

P 3.981 3.943 3.958 3.912 3.999 3.997 3.832 4.013 4.052 4.037 3.938 4.017 4.030

SIons 8.011 8.014 8.004 8.027 8.039 7.993 8.502 7.978 7.949 7.952 8.123 8.198 7.981

Mineral abbreviations after Kretz (1983): Bt—biotite; And—andalusite; Sil—sillimanite; Grt—garnet; Chl—chlorite; Ser—sericite.a Typical error, calculated for anal 2.b In apatite.c Monazite-like grain with low oxide total.d Including Y.


and orthogneisses. Florencite appears only in some of

the leuchtenbergite-containing leucophyllite, kyanite

quartzite and REE-rich clast samples. Selected ana-

lytical results are given in Tables 1 and 3; the whole

set of analyses is available on request.

4.1. Monazite

As monazite does not contain considerable amount

of H2O or any other light element which could not be

detected by electron microprobe, the analyses with

oxide totals above 97.5 wt.%were taken to be monazite

only. Mineral grains with appearance and composition

similar to monazite, however, with lower oxide totals

will be treated in the last paragraph of this section.

In mica schists and kyanite quartzites, monazite is

abundant at certain localities (Brennberg, Voroshıd,

etc.); however, it can also be absent in other places. It

usually appears as 10–100 Am, mainly xenoblastic

grains. Some idioblastic grains were found in or among

well-preserved biotite or andalusite, which formed du-

ring Hercynian metamorphism (Kishazi and Ivancsics,

1985) and biotite may also be included in monazite

(Fig. 3a) indicating their contemporaneous formation.

In mica schists with Alpine mineral assemblages and in

kyanite quartzites, the majority of the monazite grains

have similar sizes and compositions (Fig. 3b). We

assume that these are inherited pre-Alpine Hercynian

grains. A newmonazite generation can also be found in

some of the samples with slightly (rarely highly)

different compositions and small sizes that have been

formed during Alpine events (Fig. 3c, Table 1.)

In most of the gneisses and leucophyllites, mon-

azite is rare and appears in the form of small (f 10

Am) rounded grains often included in apatite together

with zircon (Fig. 3d).

In some of the REE-rich clast samples, the Alpine

monazite has grown to over 50 Am in the form of

idioblastic grains (Fig. 4a). In other REE-rich clasts,

10–50 Am monazite grains are found together with

florencite of similar size and may contain leuchten-

bergite inclusions. Monazite can also form small

inclusions in large florencite grains.

4.1.1. Chemical compositions

The majority of the monazites analysed are chemi-

cally similar (Table 1). In most cases, only small

differences were found in the relative abundances of

REE and Y, which can be seen in chondrite-normal-

ised REE patterns (Fig. 5a) or, slightly better, on REE

patterns normalised to one of the monazites (Fig. 5b).

The following characteristics of monazite chemistry

have been observed.

a) Differences in Eu anomalies. The majority of the

monazite grains in orthogneisses and leucophyllites

have high negative Eu anomalies with Eu/Eu * < 0.4.

The monazite inclusions in apatite are characterised

by even lower Eu/Eu* ratios ( < 0.3). On the other

hand, for monazites in mica schists and kyanite

quartzites, Eu/Eu* ratios are between 0.4 and 1 with

a few exceptions (Figs 5a and 6).

A positive Eu anomaly (Eu/Eu*>1) has been

observed in some of the Alpine monazites: in a few

grains in kyanite quartzite and in each point analysis

of a REE-rich clast (sample S-2, which was used for

Th–U–total Pb age determination).

b) Differences in Y and HREE contents. The LREE

parts of the chondrite-normalised patterns nearly coin-

cide, the HREE parts are, more or less, steeper. Y and

HREE change parallel to each other. In the case of

monazites in gneisses and leucophyllites with the

strongest negative Eu anomalies, the range of Y con-

tents may exceed 4 oxide wt.%. The monazites with

moderately negative Eu anomalies, i.e. in kyanite

quartzites, in mica schists and partly in gneisses and

leucophyllites Y2O3 < 2 wt.% with a few exceptions

(Fig. 6). Zoning in Y content was observed in two

monazite grains in mica schists, as the Y decreased, Eu/

Eu* increased slightly towards the grain boundaries.

Monazite inclusions in florencites or monazite

found among florencite grains is depleted in La and

Ce (and enriched in the heavier REE and Y) (Fig. 7).

c) Differences were also found in Th and Ca

contents. In most igneous and metamorphic monazite,

ThO2>1 wt.%. However, in the REE-rich clast sam-

ples, the ThO2 content of the medium size (>10 Am)

monazite changes between 0 and 20 wt.%. The Th and

Ca contents show the same trend (Fig. 8a), at the

expense of the REE.

Th and Ca can be incorporated by monazite simul-

taneously with Ca and/or Si in order to maintain

charge balance according to the following reactions

(Van Emden et al., 1997):

2 � REE3þ X ðTh;UÞ4þ þ Ca2þ ð1ÞREE3þ þ P5þ X ðTh;UÞ4þ þ Si þ ð2Þ


Fig. 3. Backscattered electron pictures of monazite and rhabdophane grains. The numbers correspond to analyses in Table 1. (a) Idioblastic,

inhomogeneous monazite with biotite inclusions among biotite (Bt) and andalusite (And) grains. (b) Xenoblastic pre-Alpine monazite in kyanite

quartzite. (c) Alpine monazite grains in the same kyanite quartzite. (d) Monazite (Mnz) and zircon (Zrn) inclusions in apatite (grey rounded

grains), and rhabdophane (Rha) attached to apatite in gneiss. (e) Monazite (brighter) and monazite-like grains with low oxide total (darker). (f)

Monazite (brighter core) altered to rhabdophane (darker margin) in biotite–andalusite– sillimanite schist. Note that the biotite (Bt) has been

chloritised (Chl) next to the altered grain.


Fig. 4. Backscattered electron pictures of LREE minerals. Numbers in (a) and (b) refer to analyses in Table 1 and in (c)– (f) to Table 3. (a)

Alpine monazite (white), Cl–apatite (grey) and kyanite (black) in a REE-rich clast sample (S-2). (b) Rhabdophane (white) among muscovite

grains in a schist with Alpine minerals, not containing monazite (sample NM-6). (c) Florencite (grey) grown on pre-Alpine monazite (white) in

kyanite (Ky). The space among the two marked grains is filled with leuchtenbergite (dark grey). The rock is kyanite quartzite. (d) Idioblastic

florencite grains (white) among muscovite (brighter) and leucophyllite (darker) lamellae, in leucophyllite. The circle on the upper florencite was

caused by the electron beam during analysis. (e) Zoned florencite in a REE-rich clast. The white zones contain numerous small monazite

inclusions. (f) High-thorian parts (encircled) in low-thorian florencite in the same REE-rich clast.


In monazites of the Sopron Hills, the ‘‘brabantitic’’

replacement, i.e. the joint entry of Th and Ca:

2 � REE3þ X Th4þ þ Ca2þ ð1aÞ

is the most important. Deviations from this relation

are caused in most cases by entry of U and Si (Fig.

8b). In addition, most inclusions in apatite have

excess Ca content.

4.1.2. Th–U–total Pb ages

An idioblastic monazite inside biotite has been

measured in one of the biotite–andalusite–sillimanite

schists (sample DE-10). Repeated measurements gave

two similar ages: 300F 41 Ma (Table 2) and 310F 34

Ma (Fig. 9a), which support the opinion that the

monazite was formed in the main pre-Alpine Hercy-

nian metamorphism. In a kyanite quartzite (grey

quartzite, sample DE-6) which has two different

monazite generations, the medium size (15–100

Am) primary grains gave nearly the same age:

296F 41 Ma (Fig. 9b), overlapping well within the

limits of error and supporting the theory that they

were inherited from the precursor mica schists.

In the kyanite quartzite mentioned above, the

small (V 7 Am) grains of the second-generation

monazite have lower Pb contents (Fig. 9b), often

below the detection limit. This indicates a younger

age of formation; however, the data points cluster

around a straight line only with weak correlation

(r2 = 0.54). Slightly larger, 10-Am size monazite

grains in a white quartzite (sample DE-12) that was

presumably formed from different source rock

(gneiss) by Mg metasomatism gave an age of

83F 19 Ma (Table 2, Fig. 9b). The biggest size

grains (f 50 Am) of the new generation monazite

(with wide range of Th contents) appear in one of the

REE-rich clast samples (S-2). Some grains are char-

acterised by very low Th* and Pb contents

(Pb < 0.012 wt.%, i.e. the detection limit), proving

that this monazite type contained no excess Pb and

has not suffered Pb loss; thus, the Pb vs. Th*

regression line used for age calculation can be forced

through the origin. Excluding the data below detec-

tion limit, however, forcing the fitted line through the

origin, yields 71F 8 Ma. Using the whole data set

(including those below detection limit) without forc-

ing the fitted line through the origin (as in the other

cases) yields 70F 11 Ma (Fig. 9a). This range of

error seems to be more realistic, taken the high

uncertainties of the individual analyses into consid-

eration (alternative treatment: replacing of the data

below detection limit by Pb = 0 yielded a similar age:

69F 11 Ma). We presume that the younger monazite

formed simultaneously in the kyanite quartzites and

REE-rich clasts and that the differences are caused by

analytical uncertainties. The age data obtained on the

second-generation monazite indicate their formation

during the Eo–Alpine metamorphic event.

The Th–U–total Pb ages obtained are in good

agreement with our knowledge of Hercynian and

Alpine metamorphism. Extension of the method to

other rock samples will presumably supply new or

more detailed knowledge on the development of the

Eastern Alps.

Fig. 5. REE patterns of selected monazite (A–D) and rhabdophane

(E) analyses. A= in biotite–andalusite– sillimanite schist; B = in

biotite–muscovite–garnet schist; C = independent grain; D = inclu-

sion in apatite; E = rhabdophane; C–D–E are in the same gneiss

(metagranite). (a) Normalised to chondrite. (b) Normalised to

monazite ‘‘A’’.


4.1.3. Monazite-like grains with low oxide totals

Mineral grains with oxide totals between 93.7 and

96.5 wt.% were found in abundance in three mica

schist samples (Fig. 2a), one of them also containing

monazite. They are similar to monazite both in appear-

ance, grain size (10–60 Am) and composition (Table

1). In BSE images, they seem slightly darker than

coexisting monazite (Fig. 3f), indicating the presence

of some light component. This is most probably H2O,

though other light elements can also be present in

approximately 5 wt.% amount, based on the difference

from 100%. This group of grains may be rhabdophane

with 0.5 H2O, or an unknown variety of monazite.

4.2. Rhabdophane

LREE-phosphate grains with oxide totals below

96.5 wt.% and with appearance different from the

Fig. 6. Eu anomaly vs. Y2O3 contents in monazite and rhabdophane (a) in mica schists and ‘‘grey’’ quartzites, (b) in gneisses, leucophyllites and

‘‘white’’ quartzite (originating from gneiss). Legend: monazites: A= in mica schist; B = in kyanite quartzite; C = inclusions in apatite (in gneiss

and in leucophyllite); D = in gneiss; E = in leucophyllite. F =monazite-like grains with low oxide totals (in three mica schists).

G = rhabdophanes. Note that each monazite inclusions in apatite fall below Eu/Eu * = 0.3. Five of the rhabdophane analyses, marked with

arrows, fall between Y2O3 = 4.5 and 6.0 wt.%.


monazite are widespread both in mica schists and in

orthogneisses. They form fine-grained aggregates con-

taining usually < 10-Amgrains with similar appearance

to rhabdophane described by Sawka et al. (1986) or

Banfield and Eggleton (1989). The aggregates are often

attached to apatite in gneisses (Fig. 3d), andmay appear

on altered monazite grains in mica schists (Fig. 3f) or

individually as pseudomorphs (Fig. 4b).

Quantitative analyses revealed that most of these

grains have a rather constant, nearly stoichiometric P

contents (between 3.8 and 4.1 pfu in 47 cases from 58

analyses) and high Y+REE contents (between 3 and 4

pfu in 45 cases, Fig. 10a). No elements other than REE,

Y, P, Th, U, Ca and Si could be determined by EMPA.

Fe and Mn may be present in small concentrations

( < 0.5 wt.%), as the REE-dominated part of the EMPA

spectra did not allowmore precise analysis. The spectra

would also allow small amounts of Cr and V, but their

low concentrations in the host rock (V 10 ppm) would

argue against it. The oxide totals fall between 85.7 and

96.4 wt.% (Fig. 2a). The only knownmineral with such

or similar composition is rhabdophane.

In the case of EMPA of rhabdophane, the difference

of the oxide totals from 100% is nearly equal to the H2O

Fig. 7. Chondrite-normalised REE-patterns of coexistent monazite

and florencite (a) in a REE-rich clast sample and (b) in a grey

quartzite. Legend: M1=medium size monazite; M2= small mon-

azite grain included in florencite [on (a)] or in the middle of

florencite aggregate [on (b)]; F = florencite.

Fig. 8. (a) Ca vs. Th, (b) Ca + Si vs. Th +U in monazite and

rhabdophane, expressed in ionic numbers recalculated on basis of

16 oxygens. Legend: A=monazite excluding inclusions in apatite,

B =monazite inclusions in apatite, C = rhabdophane. The dashed

lines correspond to entry in equal amounts. Four rhabdophane

analyses fall between Ca = 1.5 and 2.5, and three of them between

Ca + Si = 2.1 and 2.6, marked with arrows on the respective figures.


content (in about 1 wt.%) as demonstrated by Bowles

and Morgan (1984) determining the water contents by

differential thermal analysis. The sample that was

analysed by them has low Ca content, while our

LREE-phosphate grains have notable Ca contents (up

to 9 oxide wt.%) that exceed the equivalent Th (plus U)

content according to the brabantitic replacement reac-

tion (1) (Fig. 8a). Mineral grains with similar compo-

sition as our analysis 7 in Table 1 have been identified

by electron diffraction by Dorfman et al. (1993) and

described as calcium rhabdophane. Among the mon-

azite alteration products, Poitrasson et al. (2000) also

found a LREE-phosphate phase with similar composi-

tion (MO133) and with hexagonal structure, deter-

mined by laser Raman spectroscopy, which is the struc-

ture of rhabdophane. They observed a REE, Th and Ca

substitution, coupled with monoclinic to hexagonal

Table 2

Selected analytical results (in wt.%) used for Th–U– total Pb age

determination

Biotite–andalusite–

sillimanite schistaKyanite quartziteb

Sample: DE-10 Sample: DE-12

One f 100-Am grain Several f 10-Am grains

Th

(wt.%)

U

(wt.%)

Pb(1)

(wt.%)

Pb(2)

(wt.%)

Th

(wt.%)

U

(wt.%)

Pb(1)

(wt.%)

Pb(2)

(wt.%)

5.60 1.36 0.122 0.134 1st group

3.12 0.46 0.024 0.052 3.18 0.86 0.029 0.029

5.66 0.87 0.115 0.136 2.71 0.89 0.029 0.015

7.43 0.76 0.114 0.135 8.73 1.01 0.032 0.043

6.19 0.67 0.113 0.118 11.75 3.64 0.090 0.092

2.93 0.38 0.060 0.053 8.02 1.88 0.045 0.065

5.12 0.54 0.096 0.098 4.40 0.98 0.022 0.050

5.89 0.85 0.107 0.112 10.21 3.16 0.080 0.078

3.22 0.52 0.057 0.052

3.49 0.39 0.034 0.058 2nd group

3.61 0.48 0.051 0.058 1.45 3.19 0.109 0.098

3.30 0.40 0.061 0.056 5.07 1.16 0.071 0.076

5.16 0.45 0.081 0.100 5.75 0.48 0.072 0.079

5.46 0.56 0.097 0.099 5.01 0.36 0.083 0.090

2.79 0.44 0.058 0.060

3.15 0.33 0.059 0.050

5.32 0.47 0.071 0.071

4.66 0.47 0.055 0.078

5.34 0.80 0.088 0.097

5.36 1.38 0.128 0.132

6.75 0.89 0.104 0.095

6.82 0.78 0.085 0.118

2.92 0.38 0.041 0.048

4.18 0.53 0.080 0.080

a The first of the two data sets measured on the same grain,

which is not plotted on Fig. 9a. The equation of the fitted line:

Pb =� 0.006(F 0.026) + 0.01332(F 0.0018)�Th*, r2 = 0.82, from

which T= 300F 41 Ma.b Two groups separated by Pb contents, see Fig. 8b. The

equation of the line fitted on the first group: Pb = 0.003

(F 0.020) + 0.003688(F 0.00083)�Th*, r2 = 0.89, from which

T= 83F 19 Ma. The second group was not used for age calculation.Fig. 9. Pb vs. Th* contents of monazites with fitted lines. The Pb

analyses are duplicates in each measured point and the two analyses

are plotted with different symbols. (a) A= an idioblastic grain in

biotite–andalusite– sillimanite schist, giving 310F 34 Ma (contin-

uous line). B = idioblastic grains in a REE-rich clast. The line fitted

for all of the points yields 70F 11 Ma (dashed line). Omitting the

points falling below the detection limit of Pb (grey area); however,

forcing the fitted line through the origin would give 71F 8 Ma. C =

typical error for individual measurement. (b) A and B: grey quartzite.

A=medium size grains of first-generation monazite in grey quartzite,

the fitted (upper continuous) line gives 296F 41 Ma. B = small

second-generation monazite grains with low Pb contents. C and D:

white quartzite containing only small monazite grains. C = young

generation, from the fitted (lower continuous) line 83F 19 Ma was

obtained. D = presumably old monazite, not used for age calculation.


structure transition, which is different from the sub-

stitutions typical of monazite and is directed towards

apatite stoichiometry (see their Fig. 6). According to

the Ca vs. SREE+Th diagram, our rhabdophane data

cluster around the line given by them, except for four of

the five points with SiO2>2 wt.% (Fig. 10b).

Though we have no direct crystallographic data on

these groups’ mineral grains, based on the above-

mentioned arguments, we infer that they are likely to

be rhabdophane.

In the Sopron Hills, rhabdophane has lower LREE

and higher HREE contents than monazite in the same

(or similar) samples (Table 1), i.e. the chondrite-

normalised REE pattern of the rhabdophane is less

steep and the Y content is higher. The Eu anomaly is

always moderately negative, Eu/Eu* = 0.4 to 1, even

in orthogneiss samples (with only one exception) (Fig.

6). The oxide totals have a wide spread around 93%

(Fig. 2a), i.e. the water contents fall around the ideal

value calculated by one water in one molecule. In one

grain, 3 wt.% PbO has been found.

Based on appearance and Ca content, rhabdophane

could be distinguished from monazite by qualitative

examination. No rhabdophane was found in leuchten-

bergite-bearing rocks.

4.3. Florencite

In leucophyllite and kyanite quartzite florencite

forms microscopic ( < 50 Am), often idioblastic grains

(Fig. 4d), sometimes grown on apatite or—more

Table 3

Selected florencite analyses

Rock Kyanite quartzite Leucophyllite REE-rich clast

Anal. 1a 2b 3 4 5

Y2O3 0.01 0.03 0.00 0.04 0.01

La2O3 6.46 6.48 6.62 8.66 8.34

Ce2O3 13.04 12.80 14.33 13.25 10.91

Pr2O3 1.05 1.39 1.55 1.12 0.61

Nd2O3 4.45 5.00 5.31 2.94 1.65

Sm2O3 0.76 0.92 0.67 0.24 0.10

Eu2O3 0.32 0.13 0.13 0.02 0.03

Gd2O3 0.70 0.63 0.39 0.56 0.40

Dy2O3 0.08 0.00 0.00 0.03 0.06

Er2O3 0.00 0.00 0.00 0.01 0.00

ThO2 0.55 1.20 1.35 0.80 9.94

SrO 0.69 0.21 0.16 0.58 0.67

CaO 0.72 1.12 0.37 1.44 0.71

Al2O3 31.89 31.10 29.99 30.01 28.66

P2O5 26.97 28.61 28.39 28.93 28.27

Sum 87.69 89.62 89.26 88.63 90.36

Ionic numbers based on 11 oxygens

SREE 0.829 0.827 0.893 0.822 0.693

Th 0.011 0.023 0.026 0.015 0.194

Sr 0.034 0.010 0.008 0.028 0.033

Ca 0.066 0.100 0.034 0.129 0.065

Al 3.192 3.047 2.990 2.964 2.896

P 1.939 2.014 2.033 2.053 2.052

SIons 6.070 6.020 5.983 6.012 5.934

a Attached to monazite.b Independent grain.

Fig. 10. Plots of atomic proportions in rhabdophane, recalculated on

basis of 16 oxygens. (a) Th +U, Ca, Si and P vs. SREE+Y. (b) Ca

vs. SREE+Y+Th. The straight line is taken from Poitrasson et al.

(2000), determined from compositions of fresh and altered parts of

altered monazites, leading towards apatite stoichiometry. Deviation

from the line can be observed in case of four analyses with SiO2>2

wt.%.


often—on monazite (Fig. 4c). In REE-rich clast sam-

ples, large (>0.1 mm, often >1 mm) idioblastic or

subhedral, usually zoned florencite crystals appear

(Fig. 4e and f). The crystals often contain small

( < 10 Am) monazite, cheralite, Th–silicate, Cl–apa-

tite and muscovite inclusions, usually in certain zones.

4.3.1. Chemical composition

Besides LREE, Al and P, minor amounts of Ca (up

to 2 oxide wt.%) and Sr (up to 1 oxide wt.%) are

usually found. In addition, Th entry was detected in

many cases, up to 10 oxide wt.% in certain grains

(Fig. 4f). Neither Y and heavy REE (above Gd), nor

U, Ba and Mg could be detected (Table 3).

Ca, Sr and Th replace REE causing an inverse

relation between Ca + Sr + Th and SREE (in ionic

numbers) (Fig. 11a). The charge balance, however,

is not maintained according to an analogue of bra-

bantitic substitution, which would mean in this case

2 � REE3þ X Th4þ þ ðCa2þ þ Sr2þÞ;i:e: Th ¼ Caþ Sr

The analytical data differ strongly from this relation

(Fig. 11b), suggesting different charge balance mech-

anisms for low- and high-thorian florencite.

Where florencite was formed from or after mon-

azite (e.g. Fig. 4c), their chondrite-normalised REE

patterns are parallel until Gd (Fig. 7), i.e. no fractio-

nation could be observed between them, similar to the

observations of Bernhard (2001). On the other hand, a

strong fractionation could be observed between flor-

encite crystals and their monazite inclusions, or when

small amounts of monazite are formed among flor-

encite grains (Fig. 7). It seems that florencite prefers

LREE causing monazite inclusions depleted in LREE,

in decreasing order with increasing atomic number.

Zoning of florencite grains seems to be common,

even in small grains. It is usually caused by changes in

Fig. 11. Entry of minor elements in florencite, expressed in ionic

numbers recalculated on basis of 11 oxygens. (a) Ca + Sr + Th vs.

REE, straight line denoting ideal replacement. (b) Th vs. Ca + Sr.

Legend: Q = kyanite quartzite, L= leucophyllite, C = low thorian

florencite in REE-rich clasts, T = high thorian florencite in a REE-

rich clast.

Fig. 12. Differences of REE patterns in two florencite grains (F1 and

F2) in a REE-rich clast sample. F2-z1 and -z2: different zones in F2

grain.


Ca/REE or Ca/(REE + Sr) ratio, or by Th entry.

Differences in REE patterns of the different zones or

different grains were also observed (Fig. 12).

5. Discussion

5.1. Igneous and metamorphic monazite and Eu

anomaly

Monazite inclusions in apatite, together with zircon,

appear in several orthogneiss samples including the

least metamorphosed metagranite (from Varis quarry).

They have pronounced negative Eu anomalies (Eu/

Eu * < 0.3), pronounced Th contents (ThO2 approxi-

mately 5–9 wt.%) and medium to high Y contents

(Y2O3 = 0.8–3.7 wt.%). These inclusions may have

crystallized from the melt before apatite. An alternative

possibility for their formation would be exsolution

from apatite caused by high-grade metasomatism, as

described by Harlov and Forster (2002) and experi-

mentally proved by Harlov et al. (2001) and Harlov et

al. (2002). However, such exsolved inclusions would

lie parallel with the c axis of apatite and are poor in Th

( < 0.5 wt.%), which is not observed in our rocks.

The low Eu content, i.e. the pronounced negative

Eu anomalies of these monazite grains indicate that

europium formed Eu2 + ions prior to or during crys-

tallization of monazite and has been incorporated by

plagioclase in place of Ca (Henderson, 1984), rather

than by monazite. The relatively high range of Y and

HREE contents may have been caused by the higher

temperature during formation, similarly as described

by Franz et al. (1996) for metamorphic monazites.

We assume that independent monazite grains with

similarly high negative Eu anomalies and other chem-

ical characteristics also crystallized from the granitic

melt as well as the inclusions in apatite. Highly

negative Eu anomalies have also been found in

igneous monazites of Sierra de Guadarrama (Spain)

by Casillas et al. (1995): Eu/Eu * < 0.22 in 10 of the

published 11 analyses.

The majority of monazite grains in mica schists

formed during pre-Alpine metamorphic processes.

The analyses gave slightly higher Eu contents and

less negative Eu anomalies than igneous monazites in

orthogneisses. The moderately negative Eu anomaly

may have been inherited from the REE minerals of the

sedimentary source rocks or may have been formed

during the Hercynian (or a pre-Hercynian) metamor-

phism after disintegration of minerals having positive

Eu anomalies such as plagioclase. The slight increase

in Eu anomaly has also been observed in rhabdo-

phanes and secondary monazites, see below.

Monazite grains with moderately negative Eu

anomalies found in orthogneisses and leucophyllites

must have formed under different conditions than

inclusions in apatite which have pronounced negative

Eu anomalies; however, there is no sign that they may

have crystallized from another melt or from the same

melt in different (oxidizing) conditions. Thus, we

assume that monazite grains with moderately negative

Eu anomalies found in gneisses are also metamorphic

and not igneous in origin. No such monazite was

found in the least metamorphosed metagranite.

The compositions of nodular and igneous mona-

zites were compared by Read et al. (1987), who

found that nodular monazites, originating during dia-

genesis and low-grade metamorphism, have charac-

teristically higher Eu and lower Th contents. From the

data of their Table 3, Eu/Eu*>0.55 for nodular (i.e.

metamorphic) monazites and < 0.15 for monazites in

granitic pegmatites and granitic rocks can be calcu-

lated, though the results of individual microprobe

analyses on nodular monazites (their Table 5) give

different Eu anomalies in some cases. They suggest

that the relatively high Eu content is the result of

recrystallization.

Change of the Eu anomaly during metamorphism

has also been observed by Lanzirotti and Hanson

(1996), who described two populations of metamor-

phic monazites. The younger monazite has higher Th

and HREE contents and a less negative Eu anomaly

than the older generation. Their first generation mon-

azite has a high negative Eu anomaly, as do most of

the metamorphic monazites described by Pan (1997).

It seems that the moderately negative (or positive) Eu

anomaly is not generally characteristic of metamor-

phic monazites.

The differences in Y (and HREE) contents in the

metamorphic monazites may have been influenced

by P–T changes. However, they also reflect the

differences in availability of these elements (i.e. in

HREE contents of REE-containing fluids) during

monazite formation, as described by Bea and Mon-

tero (1999).


5.2. Monazite alteration and rhabdophane formation

Though monazite is a highly resistant mineral and

under dry conditions it can, at least partly, survive even

granulite facies metamorphism at 800 jC and 6 kbar

(Watt, 1995), it may become unstable under hydro-

thermal conditions (see, e.g. Cesbron, 1989). Jeffries

(1985) demonstrated the increase of Ca, Th, Si and Al

contents during hydrothermal alteration of monazite in

chloritized granite as well as replacement of monazite

by apatite and Ca-, Th- and Si-rich minerals. Lanzirotti

and Hanson (1996) found that early monazite which

decomposed during chloritization of biotite was

replaced by apatite. Poitrasson et al. (1996) described

two types ofmonazite alteration involving atomic subs-

titutions: first during chloritization at 284F 16 jCwith

preservation of the P–O framework of the crystal, the

second during greisenization at 200F 30 jC with par-

tial destruction of the framework. More recently, Poi-

trasson et al. (2000) described new hydrothermal

monazite alteration mechanisms, including formation

of allanite and a newly formed REE-phosphate phase

during sericitization at 290F 30 jC in acidic hydro-

thermal conditions. They identified the later as a

‘‘hexagonal apatite-like phase’’, which is presumably

rhabdophane, taking the composition (analysis MO133

in their Table 1) into consideration. Finger et al. (1998)

and Broska and Siman (1998) described monazite

alteration to apatite – allanite – epidote coronas in

amphibole facies metamorphism (at 600 jC, 6 kbar in

the first case). Replacement of monazite by allanite or

by LREE-rich apatite and cheralite was demonstrated

by Bea and Montero (1999). Bernhard (2001) found

monazite replaced by florencite in hydrothermal laz-

ulite–quartz veins and in their alteration zones.

In the Sopron Hills complex alteration of monazite

to rhabdophane has been observed in mica schists.

Altered monazite grains appeared in two slightly

chloritized biotite–andalusite– sillimanite schists,

always in contact with biotite (Fig. 3f). The altered

part has given a composition of rhabdophane. Sim-

ilarly, altered monazite was found in a chloritic

chloritoide–muscovite schist (which entirely lost the

original pre-Alpine mineral assemblage), the altera-

tion product proved to be rhabdophane by composi-

tion. In certain mica schists, rhabdophane was found

both as alteration product on monazite and independ-

ently, with similar compositions.

In most cases, however, rhabdophane appears inde-

pendently of monazite grains or even their existence in

the rock. It often appears attached to apatite, especially

in orthogneisses. This implies that rhabdophane has

been formed from REE-containing hydrous fluids.

Comparing the compositions of rhabdophane and

monazite found in the same sample, rhabdophane is

always enriched in Ca, Y, HREE and usually in Eu;

the Eu anomaly of rhabdophane is in general less

negative than that of the monazite which can be seen

best in gneisses. These differences were found both in

the case of independent monazite and rhabdophane

grains as well as in the case of fresh and altered zones

of the monazite. While the LREE and P contents of

the rhabdophane may originate from the monazite

(either by disintegration or by alteration), the excess

Y, HREE and Eu contents must originate from other

sources. The excess HREE may have originated from

other disintegrated REE-containing minerals, most

likely from xenotime or, maybe, from garnet as

described by Bea and Montero (1999). The source

of excess Eu, especially in gneiss, was presumably

plagioclase. Th can also be enriched in rhabdophane

compared to monazite; however, the opposite has also

been observed. In general, we found higher variations

in Th contents in rhabdophane (within one sample,

even within one aggregate of grains) than in monazite.

Taking into consideration the low P–T stability

field (T < 400 jC at 0.5 kbar, T < 200 jC at 1 kbar)

determined by Akers et al. (1993), rhabdophane must

have been formed at near-surface conditions, but not

in soils though, since Ce fractionation was not found

in rhabdophane in any case, in contrast to the cases

described by Sawka et al. (1986), Banfield and

Eggleton (1989) and Braun et al. (1990).

5.3. Alpine monazite and florencite

Secondary monazite and florencite related to the

Alpine metamorphism have been found in some of the

kyanite quartzites, leucophyllites and REE-rich clasts,

often in the same sample, sometimes in close prox-

imity. As all of these are leuchtenbergite-containing

rocks that have been formed by Mg metasomatism;

this process is assumed to have produced Alpine

monazite and florencite.

In kyanite quartzites, the new generationmonazite is

of small size (V 10 Am) and has slightly higher Y (f 1


oxide wt.%) and HREE contents than the medium size

pre-Alpine monazite in the same or similar samples (0–

0.65%). The spread in Th contents of new generation

monazite is also larger. The chemical differences imply

that Alpine monazite may have been formed either

from rhabdophane or in a similar way as rhabdophane

but at a higher temperature and pressure (as rhabdo-

phane is stable only under low P–T conditions, Akers

et al., 1993). Florencite may have also crystallized from

REE-containing hydrous fluids on the surfaces of

apatite or monazite grains in some cases. Preexisting

rhabdophane must have disintegrated in this process.

When Ca, Sr and Th replace REE in florencite, the

charge balance is maintained by two different mech-

anisms as deduced from low- and high-thorian com-

positions (Fig. 11b). The effective mechanism is

presumably determined by the physicochemical con-

ditions rather than by the available Th contents. This

may be the reason of formation of the Th mineral

inclusions in large florencite crystals previously docu-

mented by Fazekas et al. (1975).

6. Conclusions

The metamorphic complex of the Sopron Hills

(Western Hungary–Eastern Austria) consists mainly

of orthogneisses and polymetamorphic mica schists.

Earlier studies revealed local REE enrichments that

drew attention to the importance of REE minerals. We

have shown that accessoric monazite was formed in

several generations during Hercynian and Alpine meta-

morphic processes. Orthogneisses contain relic igneous

monazites and some grains that may have formed

during the Alpine metamorphic events, whereas mica

schists contain mainly metamorphic monazites. Igne-

ous and metamorphic monazites have distinct chemical

characteristics, with the former having a pronounced

negative Eu anomaly, whereas the latter has either

moderately negative or, in the case of some Alpine

grains, a positive Eu anomaly. The pronounced neg-

ative Eu anomaly in igneous monazites may be related

to plagioclase crystallization from the granitic magma.

Based on Th–U–total Pb age dating by EMPA,

monazite was formed in two events, f 300 and f 75

Ma. Monazite in biotite – andalusite – sillimanite

schists formed at f 300 Ma simultaneously with

biotite and andalusite, so its formation conditions fall

between 575–700 jC and 1.8–3.8 kbar (Torok, 1999).

This monazite has survived high-pressure Alpine

metamorphism with about 550 jC and 13 kbar peak

conditions (Demeny et al., 1997, Torok, 1998). For the

young generation of monazite found in kyanite–leuch-

tenbergite-bearing rocks formed in the Alpine meta-

morphic event, f 550 jC/13 kbar is the upper limit of

their formation conditions.

A LREE-phosphate phase with low oxide totals

(85–96.5 wt.%) was also observed in a number of

metamorphic rocks studied. Although crystallographic

data are not available due to the fine grain size, the

chemical characteristics suggest that the phase is

rhabdophane. It may have formed by either in situ

monazite alteration or complete REE mobilisation and

precipitation from hydrothermal fluids. It forms fine-

grained aggregates in orthogneisses and mica schists,

contains relatively high amounts of Ca and f 7 wt.%

H2O. Our investigations draw attention to the careful

examination of monazite by qualitative EMPA so that

possible rhabdophane formation is not overlooked.

Florencite has been found only in leuchtenbergite-

bearing rocks of the complex. Thus, its formation can

be attributed to the fluid movements responsible for

the Mg metasomatism suggested for these rocks.

Florencite seems to be more selective for LREE than

monazite. Ca, Sr and Th enter florencite in place of

REE. During this replacement, the charge balance can

be maintained by two different processes, one of them

allows high Th contents up to 10 oxide wt.%, while

the other one allows only low Th contents.

Acknowledgements

The authors are indebted to J. Ivancsics (Sopron)

for guidance in the field and help in geological

interpretation and to T. Gortmuller (Leiden) for

supplying the U standard. We thank J.-M. Montel,

F. Poitrasson and D. Read for their helpful advices and

constructive review of the manuscript. E.D. thanks

Bernhard Grasemann for many years of fruitful

cooperation, deep insights into geology and endless

support. The present work was supported by the

Hungarian Scientific Research Fund (OTKA) pro-

grams no. T015993 (G.N.) and no. T032198 (Gy.P.)

and by the Austrian Science Fund (FWF) through

project P-14129-Geo (E.D.). [EO]


Sample Qtz Ms Bt Pl Kfs And Ky Sil Grt Chl Cld Lbg Pg St Mnz Xen Rha Flo ?

Biotite–andalusite– sillimanite schists

DE-10 + + + + + + + + + +

DE-11 + + + + + + + + + +

NM-71 + + + + + + + + + +

NM-97 + + + + + + +? +? + +

NM-106 + + + + + + + (+) (+) + +

NM-114 + + + + + + + + + +

NM-115 + + + + +? + + +? +? + +

NM-128 + + + + + + + + + + + +

Mica schists with Alpine minerals

AP-K + + + + + + + + +

DE-8 + + + + + + + + + + +

APVh + + + + + + + +

I-2 + + + + + + + + + +

I-4 + + + + + + +

NM-6 + + + + + + +

NM-105 + + + + + + + +

NM-7 + + + + +

NM-18 + + + + + +

NM-22 + + + + + + + +

NM-59 + + + + + (+) +

Gneisses

DE-13 + + + + + + + +

I-1 + + + + + + + + + + +

I-3 + + + + (+) +

DE-2 + + + + + + + + + + +

DE-17 + + + + + + +

DE-18 + + + a + + +

DE-22 + + + (+) +

DE-23 + + + a + +

NM-82 + + + + (+) +

NM-121 + + + + + (+) +

NM-94 + + + + + +

NM-111 + + + + + + +

Leucophyllites

DE-1 + + + +

DE-4 + + + + + + +

DE-19 + + + + +

DE-20 + + + + +

DE-25 + + + + +

NM-85 + + + + + +

Kyanite quartzites

DE-6 + + + + + + + +

DE-7 + + + + + + + +

I-5 + + + + + + +

DE-12 + + + + + (+) +

NM-89 + + + + +

Appendix A

Samples from the Sopron Hills with REE accessory minerals used in this work, with main metamorphic index and REE minerals

(continued on next page)


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