Int J Earth Sci (2000) 89 : 336±349

 Springer-Verlag 2000

ORIGINAL PAPER

U. Poller ´ M. Janµk ´ M. Koh‚t ´ W. Todt

Early Variscan magmatism in the Western Carpathians:

U±Pb zircon data from granitoids and orthogneisses

of the Tatra Mountains (Slovakia)

Received: 19 February 1999 / Accepted: 3 December 1999

Abstract This study presents the first U±Pb zircon

data on granitoid basement rocks of the Tatra Moun-

tains, part of the Western Carpathians (Slovakia). The

Western Carpathians belong to the Alpine Carpathian

belt and constitute the eastern continuation of the

Variscides. The new age data thus provide important

time constraints for the regional geology of the Carpa-

thians as well as for their linkage to the Variscides.

U±Pb single zircon analyses with vapour digestion and

cathodoluminescence controlled dating (CLC-method)

were obtained from two distinct granitoid suites of the

Western Tatra Mountains. The resulting data indicate

a Proterozoic crustal source for both rock suites. The

igneous precursors of the orthogneisses (older gran-

ites) intruded in Lower Devonian (405 Ma) and were

generated by partial melting of reworked crustal mate-

rial during subduction realated processes. In the

Upper Devonian (365 Ma), at the beginning of con-

tinent±continent collision, the older granites were

affected by high-grade metamorphism including partial

melting, which caused recrystallisation and new zircon

growth. A continental collision was also responsible

for the generation of the younger granites

(350±360 Ma). The presented data suggest multi-stage

granitoid magmatism in the Western Carpathians,

related to a complex subduction and collision scenario

during the Devonian and Carboniferous.

Key words Granitoids ´ U±Pb zircon dating ´

Variscides ´ Tatra Mountains ´ Carpathians ´

Cathodoluminescence

Introduction and geological setting

The Western Carpathians belong to the Alpine±Car-

pathian orogenic belt, which evolved as a classical

area of the Alpine orogeny during Mesozoic±Cenozoic

time (Plasienka 1995; Plasienka et al. 1997). Their pre-

Mesozoic rock complexes, however, belong to the

Variscan basement within the Alpine±Carpathian oro-

genic belt (Krist et al. 1992; Putis 1992; Neubauer and

von Raumer 1993; Hovorka et al. 1994; Bezµk et al.

1997).

Absolute age data, done by U±Pb geochronology

on zircons, are lacking for the basement rocks. The

intrusion sequence in the Tatra Mountains is not

known in detail and also the time constrains for major

metamorphic events in pre-Variscan time do not exist.

In order to get a better understanding of the pre-Var-

iscan and Variscan geology of the Western Carpathi-

ans, precise geochronological data are needed. Con-

sequently, the new single zircon data of this paper

contribute significantly to the reconstruction of the

eastern and southeastern continuation of the Variscan

belt in Central Europe, at the boundary between the

Bohemian Massif and the Alpine±Carpathian orogen.

This study deals with the Variscan basement rocks

± orthogneisses and granites ± exposed in the Western

Tatra Mountains (Fig. 1). They belong to the Tatri-

cum, a major tectonic unit in the Western Carpathians

that was only weekly affected by Alpine metamor-

phism (Krist et al. 1992). The crystalline basement of

the Tatra Mountains is composed of pre-Mesozoic

metamorphic rocks and granitoids, overlain by Meso-

zoic and Cenozoic sediments. The metamorphic rocks

are most abundant in the western part (Western Tatra

Mountains), whereas in the eastern part (High Tatra

Mountains) the granites are more common. The base-

U. Poller (

)

) ´ W. Todt

Max-Planck-Institut für Chemie, Abt. Geochemie,

Postfach 3060, D-55020 Mainz, Germany

e-mail: [e-mail]

Tel.: [phone]

Fax: [phone]
M. Janµk

Geological Institute, Slovak Academy of Science, D‚bravskµ 9,

842 26 Bratislava, Slovak Republic
M. Koh‚t

Dionyz Stur Institute of Geology,

Geological Survey of Slovakia, 817 04 Bratislava,

Slovak Republic

337

ment is divided into two tectonic units, differing in

metamorphic grade and lithology (Kahan 1969; Janµk

1994).

The lower unit, exposed only in the Western Tatra

Mountains, is composed of medium-grade micaschists.

A kyanite±staurolite zone and a kyanite±sillimanite

zone have been distinguished (Janµk et al. 1988; Janµk

1994). Pressure±temperature constrains obtained on

the kyanite±staurolite relics resulted in upper amphi-

bolite facies conditions (ca. 640 C and 7 kbar; Janµk

1994). A recent petrological investigation on garnet-

bearing micaschists of the lower unit gave evidence

for medium-pressure and medium-temperature con-

ditions (6±9 kbar, 650±750 C; Gurk 1999).

The upper unit shows high-grade metamorphism

and migmatisation due to partial melting. Its lower

part is formed by older granites (orthogneisses), kyan-

ite-bearing paragneisses and banded amphibolites with

garnet- and clinopyroxene-bearing eclogitic relics (Ja-

nµk et al. 1996), indicating high-pressure (HP;

Fig. 1 A Simplified geotectonic map of Europe after Mosar

(1998). B Simplified geological map of the Western Tatra Moun-

tains

338

10±14 kbar)/high-temperature (HT; 700±800 C) con-

ditions. Several samples of the older granites (orthog-

neisses) from this HP±HT part of the upper unit were

investigated in this study. Higher levels belonging to

the sillimanite zone contain sillimanite, K-feldspar and

cordierite-bearing migmatites indicating medium- to

low-pressure

and

high-temperature

conditions

(750±800 C; 4±6 kbar; Janµk et al. 1999). This unit

was intruded by a sheet-like granitoid pluton. Ranging

from leucogranite to biotite tonalite and hornblende

diorite (Koh‚t and Janµk 1994), the muscovite±bi-

otite±granites to granodiorites (younger granites) are

the most abundant rocks. For this study several

(younger) granite samples of this pluton were analysed

as well.

It is assumed that both, the lower and the upper

units, were originally one petrological entity and were

later separated by shearing. In fact, there is a gradual

increase in the P±T conditions from the micaschists of

the lower unit to the retrograde garnet amphibolites

and the migmatites of the upper unit.

The crystalline basement of the Tatra Mountains

has been affected by the Variscan and Alpine defor-

mations (Kahan 1969; Fritz et al. 1992). Among the

two (D1 and D2) Variscan deformation phases, D1 is

related to southeastward thrusting of the upper unit

onto the lower unit. Asymmetric tails of K-feldspars

in older granites of the upper unit show the SE sense

of thrusting (Fritz et al. 1992; Janµk 1994). Defor-

mation D2 was related to EW extension and took

place under ductile conditions. D2 largely overprinted

former deformational features and has also affected

the granitoids (Koh‚t and Janµk 1994). Reliable time

constraints on the Variscan P±T and tectonometamor-

phic evolutions in the Tatra Mountains are still lack-

ing.

Alpine influence is documented by mostly brittle

deformation (D3) at lower P±T conditions, indicating

northwest-directed shearing during Late Cretaceous

compression. Magnetic fabrics record this shear sense.

D4 is related to updoming during Tertiary extension

and uplift.

Rb±Sr whole-rock data of Burchart (1968) on the

older granites (orthogneisses) of the Tatra Mountains

have indicated an Early Palaeozoic tectonometamor-

phic event between 420 and 380 Ma. Unfortunately,

the large error of these data prevents a good res-

olution of distinct events for the investigated suites.

Additionally, the Rb±Sr isochron data are contradicto-

ry: according to Burchart (1968) the granitoids should

have crystallised during 310±290 Ma, whereas Gaweda

(1995) reported data constraining an intrusion

between 350±340 Ma. Possibly Gaweda took samples

from the Western Tatra, whereas Burchart (1968)

analysed some rocks which belonged to the High

Tatra suite, which was recently dated by Poller et al.

(1999a) to be 315 Ma in age.

Several authors have published cooling ages of

white micas from the granitoids and migmatites

obtained by the

40

Ar/

39

Ar method range between 330

and 300 Ma (Maluski et al. 1993; Janµk and Onstott

1993; Janµk 1994). Apatite fission track data record

the final uplift of the Tatra Mountains in Tertiary

time, 15±10 Ma ago (Kovµ› et al. 1994).

The aim of this paper is to present first precise

U±Pb single zircon data from older and younger gran-

ites of the Tatra Mountains, documenting magmatic

events during Devonian and Carboniferous times. The

new data enable the definition of a timescale for the

several intrusions of granitoid rocks in the Western

Tatra Mountains. The results allow distinguishing two

different generations of granites and, additionally, the

age determination constrains the polyphase metamor-

phic overprint of this region. The data are discussed

with respect to the early Variscan evolution of the

Tatra Mountains and to the general geodynamics of

the Variscan mountain chain.

Sample description

The investigated rocks are from the upper unit of the

Western Tatra Mountains (Fig. 1). Besides three

coarse-grained porphyric older granites (orthogneisses)

representing the HP±HT suite of the upper unit, three

younger granites of the later intruded pluton were

also investigated in order to obtain precise U±Pb zir-

con data on the timing of magmatic events in the

Tatra Mountains. Both groups of granites can be dis-

tinguished by the grade of metamorphic overprint as

well as by their ages (see Results), but not by their

textures, and are therefore named older and younger

granites.

The older granites (orthogneisses) crop out in the

Ziarska Valley (UP 1002), the Jamnickµ Valley (UP

1014) and near the summit of Baranec (UP 1025).

Whereas the samples UP 1002 and UP 1014 were

taken from the lower part of the upper unit, near to

the border with the lower unit, sample UP 1025 is sit-

uated at the top of the upper unit, in close association

with migmatites, retrograde garnet-bearing amphibo-

lites and younger granites. Overall, the investigated

older granites show solid-state deformation in ductile

to brittle conditions (Patterson et al. 1989; Gapais

1989).

The older granites are coarse grained, with porphy-

ric, augen-like K-feldspar or and plagioclase grains of

2±3 cm size, and exhibit a mylonitic S-C fabric (BerthØ

et al. 1979; Lister and Snoke 1984). The K-feldspar

shows microcline twinning and its asymmetrical tails

indicate dynamic recrystallisation. The composition of

plagioclase ranges from albite to andesine, and zona-

tion is not observed. Several generations of plagioclase

can be defined by textural features as well as by

microprobe analyses: plagioclase I has An 35±40, pla-

gioclase II An 18±30 and plagioclase III has albite

composition (Koh‚t and Janµk 1994). Most of the

older plagioclase grains (I+II) are elongated and par-

339

tially recrystallized. This elongation is due to rotation

during the deformation. The third generation is found

interstitially between the older crystals. Locally, myr-

mekite has developed. The micas form characteristic

ªmica-fishº porphyrocblasts. The muscovite is slightly

phengitic, and the biotite is Fe-rich and often replaced

by chlorite. Quartz shows undulose extinction, the

grains are elongated and recrystallized, and form rib-

bons. Rotations of newly grown subgrains together

with recrystallisation of the former magmatic crystals

are responsible for the described phenomena (Fitzger-

ald and Stünitz 1993; Passchier and Trouw 1996).

Subordinate garnet (almandine 70±75 mol %, spessar-

tine 15±22 mol %, pyrope < 15 mol %, grossular

< 5 mol %) is strongly retrogressed and often com-

pletely replaced by chlorite (Janµk et al. 1993). Acces-

sory apatite, zircon, monazite and opaque phases

(magnetite  ilmenite) occur.

The investigated younger granites are exposed near

the summits of Baranec (UP 1023), Rohµc (UP 1040)

and Bystrµ (UP 1036). The sampled rocks are coarse

to medium grained granodiorite to monzogranite and

are composed of quartz, plagioclase, K-feldspar,

biotite and muscovite (samples UP 1023 and UP

1040). Sample UP 1036 is free of white mica and

K-feldspar is much less abundant than plagioclase.

Euhedral and subhedral feldspars are randomly orient-

ed, often being partly replaced by sericite. The micas

are weakly deformed with local development of kink

bands. Quartz grains show undulose extinction and,

similarly to the older granites, beginning subgrain

crystallisation is observed.

Analytical techniques

For each sample approximately 20 kg fresh material

was prepared by crushing, grinding and sieving. Heavy

minerals were separated from the < 500-mm fraction

using a Wilfley table. The heavy mineral fraction was

then treated separated with heavy liquids, and a

Frantz magnetic separator refined the zircon fraction.

For all samples, cathodoluminescence (CL) mounts

were prepared for CL documentation. The CL imag-

ing was performed on a Hitachi S 450 at the Max-

Planck-Institut für Chemie, Mainz (Germany).

The isotopic measurements were done either on

single zircon grains from the zircon fraction of the

samples or on half zircon crystals recovered from the

CL mounts (CLC method; Poller et al. 1997).

The zircons were transferred and placed into a spe-

cial Teflon bomb with small holes for each individual

grain (Wendt and Todt 1991). A

205

Pb ±

233

U or a

202

Pb ±

233

U mixed spike and 28n HF were added into

each hole and the bomb was placed in an oven at

200 C for approximately 5 days. After complete dis-

solution, the samples were dried down and 6n HCl

was added, followed by 1 day in the oven at the same

temperature. After this step the zircons were com-

pletely in solution, homogenized with the spike and

ready for the measurements.

After drying, the samples were loaded on Re single

filaments with silica gel. The isotopic measurements

were done on a Finnigan MAT 261 mass spectrometer

in peak-jumping mode using a secondary electron mul-

tiplier.

The total Pb blank was 3 pg. For blank Pb correc-

tions the following ratios were used:

206

Pb/

204

Pb = 18.59;

207

Pb

204

Pb =15.73. For the common Pb

correction galena of the Tatra Mountains was meas-

ured. The resulting values for correction were:

206

Pb/

204

Pb =18.493;

207

Pb

204

Pb =15.665. All ratios were cor-

rected for fractionation using the NBS 982 standard as

reference (Todt et al. 1996) and for U using a U-nat

standard solution. The analyses were corrected with

parallel determined fractionation values scattering for

Pb between 2.9 and 3.1½ per Damu for the period of

measurements (Loveridge 1986).

Results

The U±Pb zircon data for the different granitoids (see

Table 1) clearly indicate two separate magmatic

events in the Western Tatra Mountains, a Lower

Devonian formation of the older granites or future

ªorthogneissesº, and an Upper Devonian/Lower Car-

boniferous crystallisation of the younger granites.

Older granites (orthogneisses)

Under CL the zircons from the older granites show

several components. Besides few homogeneous mag-

matically zoned zircons, crystals with inherited core

components or resorbed core areas dominate (typical

CL photographs; Fig. 2). Whereas zircon UP 1025-14

is a single-phased grain (Fig. 2A), grown during one

magmatic stage (crystallisation), grain UP 1025-39

(Fig. 2B) is a two-phase crystal with mixed age infor-

mation, showing an inherited core, surrounded by

euhedral magmatic zones. Also zircon UP 1002-1

(Fig. 2C) has an inherited core and an outer magmatic

zone, but in this case the core itself shows a very inho-

mogeneous internal structure. Since such complex

grains yield ambiguous age data, they were excluded

from the dating.

For the U±Pb zircon dating of the older granites

both described methods, the conventional single-zircon

dating and the CLC dating, were applied (see discor-

dia plots; Fig. 3A±C).

The older granite UP 1002 from Ziarska valley was

dated with five zircon grains (Fig. 3A). Whereas the

lower intercept of the discordia line is fixed by a con-

cordant data point of a homogeneous igneous zircon,

the discordia itself is defined by four other grains, con-

taining more or less large inherited cores. The upper

intercept age is 1980  37 Ma and reflects detrital

340

Fig. 2 Cathodoluminescence

images of zircons from A ± C

older granites and D ± F

younger granites of the Tatra

Mountains. See text for

detailed description

341

grains from the source of the magma, and the lower

intercept age is 406  5 Ma due to magmatic crystals.

The MSWD value for the discordia is 2.6.

The older granite UP 1025 from Baranec was dated

with six grains (Fig. 3B). All data points fit within the

error of the concordia line. Two different crystallisa-

tion stages are documented by the zircon ages: the

first one again around 405 Ma (3 zircons) and the sec-

ond one around 360 Ma. Both stages are represented

by homogeneous magmatic zircons. Therefore, the

older Baranec granite should have seen two magmatic

stages, the first one, representing the intrusion age,

and the second one, constraining a high-temperature

overprint under melting conditions, e.g. anatexis dur-

ing the rise of the magma. This fits well with the new

P±T (750±800 C, 4±6 kbar) data observed on the

neighbouring migmatites (Janµk et al. 1999).

The older granite UP 1014 from Jamnickµ valley

was dated by seven grains of prismatic and pyramidic

shape (Fig. 3C). They define a discordia line through

zero with an upper intercept of 362  13 Ma (Fig. 3C).

The upper intercept is again constrained by concor-

Table 1 U ± Pb zircon data. CLC cathodoluminescence controlled; VD vapour digestion

No. Sample

Method Measured isotopic composition

a

Isotopic ratios

b

Utot/

Pb*

206

Pb/

204

Pb

2s

207

Pb/

206

Pb

2s

208

Pb/

206

Pb

2s

206

Pb*/

238

U

2s

207

Pb*/

235

U

2s

207

Pb*/

206

Pb

2s

UP 1023, Baranec granite

1

UP 1023-1 CLC

16.13

554.63

1

2.84

0.08316

1

20 0.07939

1

65 0.05836

1

48 0.4623

1

85 0.05745

1

60

2

UP 1023-8 CLC

18.14

896.03 26.77

0.06852

1

55 0.03581

1

75 0.05306

120 0.3834

192 0.05239

177

3

UP 1023-2 VD

16.94

655.23

1

7.07

0.07514

1

16 0.06165

1

23 0.05619

1

32 0.4119

1

63 0.05318

1

49

4

UP 1023-4 VD

17.45

797.58 11.81

0.07135

1

24 0.05267

1

24 0.05451

1

48 0.4002

1

80 0.05324

1

65

5

UP 1023-5 VD

16.83

279.25

1

3.60

0.10672

1

27 0.14398

1

52 0.05619

1

46 0.4266

127 0.05505

130

UP 1036, Bystra granite

1

UP 1036-1 VD

16.55

166.71

1

0.74

0.14116

1

30 0.24942

1

71 0.05643

1

35 0.4182

1

91 0.05375

128

2

UP 1036-4 VD

18.04

983.78 10.68

0.06823

1

17 0.05149

1

16 0.05234

1

32 0.3858

1

50 0.05347

1

42

3

T2-29

CLC

16.93

404.15

1

3.98

0.08946

1

27 0.11345

1

46 0.03415

1

23 0.2554

1

44 0.05424

1

67

4

T1-12

CLC

26.14

310.55

1

1.99

0.10087

1

16 0.19101

1

48 0.05534

1

32 0.4092

1

79 0.05363

1

80

UP 1040, Rohace granite

1

UP 1040-23 CLC

13.04

238.34

1

1.86

0.13078

1

32 0.24138

1

73 0.06641

1

43 0.6560

136 0.07165

1

35

2

UP 1040-29 CLC

16.43

331.76

1

3.85

0.09584

1

27 0.17645

1

70 0.05474

1

33 0.3955

1

98 0.05240

1

97

3

UP1040-33 CLC

15.55

592.15

1

8.90

0.07946

1

41 0.10593

1

92 0.05891

1

55 0.4485

118 0.05521

1

98

4

T2-9

CLC

31.45

332.27

1

3.24

0.09956 188 0.17975

865 0.02844

356 0.2198

306 0.05605

1

98

5

UP 1040-1 VD

17.64

294.35

1

3.12

0.10413

1

26 0.15996

1

58 0.05249

1

37 0.3957

1

92 0.05467

122

6

UP 1040-2 VD

17.40 1501.68 16.72

0.06349

1

15 0.04079

1

16 0.05410

1

30 0.4018

1

44 0.05386

1

30

7

UP 1040-3 VD

17.03

248.43

1

1.89

0.11301

1

27 0.18683

1

58 0.05417

1

38 0.4070

1

92 0.05450

114

8

UP 1040-4 VD

14.94

131.22

1

1.88

0.16838

1

52 0.36670

141 0.05843

1

61 0.4780

280 0.05934

1

29

9

UP 1040-5 VD

15.83

101.76

1

0.52

0.19598

1

38 0.45885

112 0.05488

1

41 0.4013

148 0.05303

217

10 UP 1040-6 VD

17.63

490.58

1

4.14

0.08400

1

23 0.15408

1

48 0.05034

1

32 0.3791

1

64 0.05433

1

60

11 UP 1040-7 VD

15.77

250.75

1

2.50

0.11141

1

37 0.24787

1

91 0.05503

1

44 0.4098

128 0.05401

1

13

UP 1002, Ziarska orthogneiss

1

UP 1002-C VD

13.77 1468.64 11.96

0.06466

1

10 0.09090

1

23 0.06523

1

68 0.4936

1

71 0.05488

1

21

2

UP 1002-D VD

1

4.39

438.40

1

3.89

0.14065

1

34 0.12168

1

47 0.20021

240 3.0308

550 0.10979

1

86

3

UP 1002-F VD

12.27

221.99

1

1.11

0.12667

1

21 0.24885

1

51 0.07148

1

39 0.6109

101 0.06198

1

89

4

UP 1002-H VD

13.11

164.86

1

0.72

0.14760

1

26 0.26138

1

65 0.07008

1

46 0.5812

120 0.06015

123

5

UP 1002-M VD

12.52

156.56

1

0.98

0.15616

1

31 0.29635

1

91 0.07147

1

53 0.6340

153 0.06433

160

UP 1014, Jamnicka orthogneiss

1

UP 1014-B VD

17.42 3046.25 34.12

0.05833

1

12 0.15648

1

40 0.04824

1

35 0.3564

1

38 0.05358

1

20

2

UP 1014-C VD

15.29 1659.66 10.73

0.06279

1

12 0.14012

1

38 0.05615

1

52 0.4188

1

54 0.05409

1

21

3

UP 1014-D VD

16.08

287.17

1

2.31

0.10476

1

25 0.15715

1

47 0.05791

1

49 0.4330

1

99 0.05423

1

97

4

UP 1014-E VD

29.85 1172.53 21.92

0.06715

1

18 0.13770

1

45 0.02903

1

23 0.2194

1

36 0.05481

1

50

5

UP 1014-F VD

15.34

384.11

1

1.46

0.09137

1

18 0.24528

1

63 0.54024

1

39 0.3991

1

59 0.05358

1

55

6

UP 1014-G VD

15.34

738.50

1

9.38

0.07377

1

21 0.09883

1

36 0.05987

1

43 0.4475

1

76 0.05421

1

59

7

UP 1014-H VD

15.52

530.24

1

2.22

0.08113

1

14 0.18777

1

51 0.05525

1

41 0.4090

1

53 0.05397

1

41

UP 1025, Baranec orthogneiss

1

UP 1025-14 CLC

13.98

236.50

1

0.88

0.11361

1

14 0.22906

545 0.06382

1

35 0.4617

1

81 0.05247

1

77

2

UP 1025-30 CLC

14.96

547.12

1

5.32

0.07892

1

21 0.l6390

1

43 0.05893

1

77 0.4252

109 0.05282

1

57

3

UP 1025-A VD

15.63 1306.41 38.37

0.06533

1

21 0.10324

1

35 0.05705

1

35 0.4268

1

72 0.05427

1

61

4

UP 1025-B VD

13.30

602.29

1

6.89

0.078l1

1

16 0.17927

1

50 0.06452

1

40 0.4807

1

73 0.05397

1

58

5

UP 1025-D VD

16.51

700.24 12.65

0.07460

1

18 0.08931

1

33 0.05596

1

67 0.4159

103 0.05390

1

88

6

UP 1025-E VD

13.58

886.47 13.49

0.06986

1

18 0.13093

1

41 0.06484

1

40 0.4780

1

71 0.05347

1

54

Asterisk indicates radiogenic lead

2s errors refer to 2s standard deviation of the mean of two to

six blocks; given are the last 2 (3) digits

a

Corrected for fractionation

b

Corrected for blank, spike and common Pb

342

dant analyses. Some of the analysed zircon grains

show slight Pb loss, possibly due to the metamorphic

overprint of the samples.

The Devonian age around 405 Ma (UP 1002, UP

1025) is interpreted as crystallisation and emplacement

age of the precursor of the future orthogneisses,

whereas the younger 360 Ma event is explained as

later metamorphic overprint during the thrusting of

the upper onto the lower unit.

Younger granites

The zircons from the younger granites are less compli-

cated than those of the older granites. Most grains

show either a homogeneous magmatic zonation (sin-

gle-phase crystals) or a combination of inherited core

and outer magmatic rim. Resorbed core areas, such as

those observed in some zircons of the older granites,

do not occur (typical zircons; Fig. 2D±F).

Grain UP T1-29 (Fig. 2D) is representative of the

single-phase zircons, showing only magmatic zonation.

In contrast, crystal T1-23 (Fig. 2E) documents two

growth phases: a magmatically zoned, highly lumines-

cent core, and a magmatically zoned, but less lumines-

cent, rim. As the inner core is rounded, it presumably

represents an older inherited component, rather than

a magmatic phase with different chemical composi-

tion. Zircon UP 1023-8 (Fig. 2F) contains a small

rounded inherited core, which is surrounded by a

broad overgrowth. Such composite grains would pro-

vide both age information and constrain a discordia

line with inherited upper and magmatic lower inter-

cept ages. Consequently, the U±Pb dating of the gran-

itoids was performed using the conventional as well as

the CLC method.

For the younger granite UP 1023 from Baranec,

three zircons were concordant (Fig. 4A). Together

with two core-bearing crystals they define a discordia

with a poorly defined upper intercept age of 1770 

800 Ma and a lower intercept at 347  14 Ma. The

large error of the upper intercept age is due to the

small amounts of inherited material in grains UP

1023-5 and UP 1023-8 (Fig. 2F); therefore, it was not

possible to characterise the age of the protolith more

precisely.

The emplacement age of the younger granite UP

1036 from Bystrµ was dated by four grains, which

define a discordia line through zero. The upper inter-

cept at 357  16 Ma is constrained by concordant zir-

cons (Fig. 4B).

The geochronology of zircons from the younger

granite UP 1040 from Rohµc is more complicated and

for this sample two discordia lines have been drawn

(Fig. 4C). Six zircons were combined to a discordia

line going through zero, yielding an upper intercept of

369  19 Ma. A second discordia with five zircons has

a lower intercept at 363  11 Ma, fixed by concordant

zircons, and an upper intercept yielding an age around

2530  400 Ma. Both discordia lines result in overlap-

ping Upper Devonian granite emplacement ages that

are constrained by concordant data points. As for the

Baranec granite, the inherited component in the dis-

cordant zircons of the Rohµc granite was not large

enough to provide a good spread and therefore a

better characterisation of the upper intercept age.

Fig. 3A ± C

206

Pb/

238

U vs

207

Pb/

235

U plots for the older granites

of the Western Tatra Mountains

343

Discussion and conclusion

The presented age data documenting Early Variscan

magmatism in the Western Tatra Mountains are diffi-

cult to connect with plate tectonics; therefore, addi-

tional features from geochemistry have to be added

for a better understanding of the situation.

The new U±Pb zircon data document two distinct

magmatic events in Lower Devonian and in Devonian/

Lower Carboniferous time. Following Poller et al.

(1998, 1999b), the early Devonian granites represent

former S-type or hybrid H-type granitoids (ASI values

above 1.1), which are dominated by a source material

of crustal characteristics (such as old metasediments),

documented by eNd(0) values between-6 and -10, and

eSr(0) values scattering between 72 and 140. The

Pb±Pb isotopic composition also confirms the upper

crustal character of the investigated rocks (Poller et

al. 1999b).

On the basis of several discrimination diagrams

using SiO

2

, Zr, Rb, Y and Nb (see Table 2), a volcan-

ic-arc to collisional environment is inferred for the

two granite suites of the Western Tatra Mountains. In

the Rb vs (Y+Nb) diagram after Pearce et al. (1984;

Fig. 5) all investigated samples fall inside the VAG

field. This diagram uses Rb as the discriminating ele-

ment between volcanic arc and collisional regimes.

Due to metamorphic processes and other influencing

factors, such as weathering, since the emplacement of

the rocks, Rb enrichment would be much more proba-

ble than depletion. Therefore, the characterisation of

the Western Tatra granites as volcanic-arc rocks (or

active continental margin magmatites, which cannot

be distinguished using geochemical parameters) seems

to be reasonable. In addition, the REE spectra of the

Western Tatra granites show the typical pattern of arc

to collision-related granitoids (Pearce et al. 1984).

Fig. 4A ± C

206

Pb/

238

U vs

207

Pb/

235

U plots for the younger gran-

ites of the Western Tatra Mountains

Fig. 5 Rb vs (Y+Nb) plot after Pearce et al. (1984) to discrimi-

nate different tectonic settings for granitoids. VAG volcanic arc

granites; COLG collisional granites; WPG within-plate granites;

ORG ocean ridge granites

344

Thus, a Devonian subduction-related melting with

generation of principal crustal granites (with weak

juvenile influence) mainly from old metasedimentary

material is supposed for the Western Tatra (Poller et

al. 1999b). The close association with HP metamor-

phic rocks (retrograde eclogite; Janµk et al. 1996) sug-

gests that the older granites represent anatectic melts

inside the continental crust that were generated at HP

conditions ( ~ 10 kbar) during subduction. These proc-

esses should have taken place approximately 406 Ma

ago, the emplacement age of the older granites. Upper

intercept ages indicate the involvement of crustal

material of Proterozoic age.

The Carboniferous age around 365 Ma (upper

intercept age of Jamnickµ older granite, concordant

age of Baranec solder granite) is documented by

newly grown zircons with typical magmatic zonation

(Fig. 2A). Therefore, the older granites must have suf-

fered a high-temperature stage after the crystallisation,

responsible for these new concordant zircons. This is

also confirmed by the dehydration melting of musco-

vite and biotite in the neighbouring migmatites (Janµk

et al. 1999). The CL images of the zircons show the

homogeneous oscillatory zonation of these grains and

gives evidence that subsequently no resetting or Pb

loss happened (in this case the structures visible with

CL would be diffuse; Poller and Huth 1999). These

grains, showing no Pb loss at all, must have crystal-

lised again during the high-temperature overprint of

the older granites. Thus, the 365-Ma age dates the

Table 2 Major element (in

weight percent), trace and rare

element (in parts per million)

data of older and younger

granites of the Western Tatra

Mountains. n.d. not detected

Older granites

Younger granites

UP 1002

UP 1014

UP 1025

UP 1023

UP 1036

UP 1040

(wt. %)

SiO

2

1

70.44

1

63.63

1

67.80

73.76

1

70.90

1

73.10

TiO

2

11

0.26

11

0.82

11

0.55

1

0.08

11

0.40

11

0.21

Al

2

O

3

1

16.32

1

17.15

1

16.86

14.71

1

14.87

1

15.12

Fe

2

O

3

11

2.57

11

5.49

11

3.40

1

0.73

11

2.79

11

1.79

MnO

< 0.01

11

0.07

11

0.05

1

0.01

11

0.03

11

0.03

MgO

11

1.14

11

2.38

11

1.54

1

0.24

11

1.00

11

0.51

CaO

11

1.72

11

2.89

11

2.43

1

3.16

11

2.93

11

1.09

Na

2

O

11

6.04

11

3.97

11

4.46

1

0.53

11

4.97

11

4.39

K

2

O

11

1.38

11

2.61

11

2.18

1

4.95

11

1.04

11

3.09

P

2

O

5

11

0.04

11

0.10

11

0.15

1

0.11

11

0.37

11

0.07

GV

11

1.01

11

1.02

11

1.02

1

0.98

11

1.01

11

1.02

Sum

100.92

100.13

100.44

99.26

100.31

100.42

(ppm)

Ba

300

792

549

2481

307

826

Co

1

48

1

32

1

32

11

65

1

31

1

37

Cr

1

20

1

72

1

17

111

4

11

8

11

3

Cu

1

19

1

17

1

13

11

10

11

3

11

7

Ga

1

15

1

22

1

20

11

12

1

16

1

19

Nb

11

5

1

16

1

10

111

3

11

7

11

7

Ni

11

9

1

28

1

14

111

6

11

5

11

2

Pb

n.d.

n.d.

n.d.

11

40

n.d.

n.d.

Rb

1

57

1

86

1

75

11

75

1

28

1

71

Sc

11

7

1

15

1

10

111

3

11

8

11

5

Sr

300

429

515

1

312

357

310

Th

n.d.

n.d.

n.d.

111

2

n.d.

n.d.

U

n.d.

n.d.

n.d.

n.d.

n.d.

n.d.

V

1

55

112

1

79

11

11

1

30

1

23

Y

11

6

1

13

1

10

111

6

1

27

1

12

Zn

1

35

131

1

88

11

32

1

50

1

39

Zr

1

28

187

145

11

39

1

97

1

97

La

11

3.88

1

41.37

1

25.25

11

13.40

1

45.28

1

16.27

Ce

11

7.85

1

79.44

1

50.94

11

25.45

1

92.37

1

32.25

Pr

11

0.98

11

9.71

11

6.40

111

3.05

1

11.87

11

3.82

Nd

11

3.93

1

36.06

1

24.14

11

11.51

1

43.61

1

13.97

Sm

11

1.07

11

6.48

11

4.75

111

2.36

11

9.81

11

2.59

Eu

11

0.88

11

1.46

11

1.34

111

1.86

11

1.88

11

0.64

Gd

11

1.16

11

4.85

11

3.58

111

1.75

11

8.48

11

1.98

Tb

11

0.18

11

0.60

11

0.44

111

0.20

11

1.19

11

0.28

Dy

11

1.08

11

2.90

11

2.28

111

1.05

11

6.35

11

1.58

Ho

11

0.18

11

0.47

11

0.38

111

0.17

11

1.05

11

0.29

Er

11

0.47

11

1.05

11

0.93

111

0.41

11

2.31

11

0.83

Tm

11

0.06

11

0.11

11

0.12

111

0.06

11

0.27

11

0.13

Yb

11

0.33

11

0.68

11

0.69

111

0.38

11

1.29

11

0.70

Lu

11

0.05

11

0.10

11

0.11

111

0.06

11

0.17

11

0.09

345

mid-Devonian metamorphism, which should have

reached 750±800 C, 8±10 kbar (Janµk et al. 1996; Lud-

hova and Janµk 1999). Such temperatures imply that

partial re-melting of the older granites that occurred

approximately 40 Ma after their emplacement caused

the new growth of magmatic-zoned zircons.

This can be attributed to substantial crustal heating

due to the detachment or break-off of a downward

oceanic slab (e.g. Blanckenburg and Davis 1995). Also

convective removal of the lithospheric root (Platt and

England 1994) at the end of subduction is possible.

Most propable is the collision of two continental

blocks (microplates) causing crustal thickening up to

50 km. Such a thickened continental crust will produce

not only high-temperature but also high-pressure con-

ditions as detected in the upper unit assemblages of

the Tatra. Therefore, such a collisional event together

with the upwelling mantle could have triggered wide-

spread partial melting of the crust and might be

responsible for the metamorphic overprint of the older

granites during Middle to Late Devonian time. Later,

the younger granites could have intruded into higher

crustal levels during the thrusting of the upper unit

onto the lower unit, as suggested by field and struc-

tural observations (Fritz et al. 1992; Janµk 1994). The

younger granites were only weakly influenced by these

shearing processes because of their upper position in

the crust.

The evolutionary scheme of the Western Tatra

Mountains as described above has to be discussed also

in the context of the Variscan geology of Central

Europe. In palaeotectonic reconstructions of the Early

Palaeozoic (Frisch and Neubauer 1989; Flügel 1990;

Neubauer and von Raumer 1993; Stampfli 1996), the

Western Tatra Mountains are seen as a lateral prolon-

gation of the Eastern Alps and of the Eastern Carpa-

thians as a part of the Hun superterrane (Stampfli

1996). It has migrated since the Silurian, towards the

Laurasian continent. The advancing drift is enreg-

istered by Silurian±Devonian active continental mar-

gin rocks (Heinisch 1988; Neubauer and Sassi 1993;

Loeschke and Heinisch 1993; Schönlaub 1993) and has

been confirmed by palaeomagnetic data (Schätz et al.

1997; Tait et al. 1998).

Consequently, two distinct geological situations

must be envisaged, the break-up and drift of the

future Variscan basement areas on the Gondwana

side, and the accretion to collision of the continental

blocks on the Laurasia side. This critical period of the

Devonian, when certain areas (microplates) amalga-

mated with the continents, is recorded by the dating

of the Western Tatra granites.

A common Early Variscan (420±380 Ma) tectono-

metamorphic evolution has been discussed by Dall-

meyer et al. (1996) for the Eastern Alps, the Western

Carpathians and for the Apuseni mountains. Com-

pared with the former adjacent domains, the influence

of the Silurian±Devonian metamorphic event is found

in several tectonic slices composing the Austroalpine

and Penninic units of the Eastern Alps (Neubauer et

al. 1999). Early Variscan HP metamorphism around

360 Ma (von Eynatten et al. 1996) is reported by

Ar±Ar data on detrital minerals (phengite and glaco-

phane) in sediments of the Cretaceous cover. Compa-

rable Ar±Ar ages were also found for detrital micas

from Upper Austroalpine sediments (Handler et al.

1997) and record an Early Variscan metamorphism

(400±360 Ma). For the Kaintaleck Nappe (Upper Aus-

troalpine) Neubauer and Frisch (1993) discussed a tec-

tonothermal activity during the mid-Palaeozoic. A

Variscan HP evolution is discussed by Schulz (1990),

which has to be related to the general Early Variscan

convergence (Frisch and Neubauer 1989; Ring and

Richter 1994). Such data are confirmed by Sm±Nd

garnet ages from the Ötztal eclogites (Miller and

Thöni 1995).

In the Tatricum (Lower Austroalpine nappes) a

Devonian metamorphic event (Neubauer et al. 1999)

is inferred from Rb±Sr mineral isochrons (Cambel and

Kral 1989). Similar data obtained on white micas from

the Wechsel unit (Neubauer et al. 1999) are inter-

preted to represent the Devonian peak of metamor-

phism.

The described metamorphic evolution is also

reported from the Bohemian Massif, where U±Pb zir-

con ages around 390 Ma were found in the Erbendorf-

Vohenstrauss zone (Teufel et al. 1986; Teufel 1987).

The Rb±Sr whole-rock data indicate medium-pressure

conditions around 384 Ma (Teufel 1987) in the Dros-

sendorf unit.

Appreciating this general tectonic situation, it is

concluded that the older granites of the Western Tatra

Mountains received their metamorphic overprint

under collisional conditions during Late Devonian/

Early Carboniferous times, when they were involved

in shearing and upthrusting of continetal crustal blocks

(plates).

The younger granites (UP 1040, UP 1036, UP 1023)

have ages between 363  11 and 347  14 Ma. Their

geochemical characteristics with ASI values between

1.05 and 1.25 indicate a hybridic character. This means

that the investigated granites were generated by anat-

exis of crustal material from different origin.

Reworked oceanic crust from the downward slab was

involved in this magma generation as well as remolten

continental sediments, which build the main part of

the new granitoid magma. The influence of the

reworked oceanic crust is visible in the Pb±Pb isotopes

as well as in the eNd (0) values, scattering between ±5

and ±7 (Poller et al. 1998, 1999b). A contribution of

basaltic mantle material, such as MORB, is not con-

strained by the isotopic characteristics. The geotec-

tonic setting of the younger granites, as inferred from

the geochemical characterisation (Fig. 5), is again a

volcanic-arc to active continental margin regime and

therefore the same as for the older granites.

The oldest of the investigated granitoids is the

granite UP 1040 from Rohµc, with a crystallization

346

age of 363  11 Ma, which is coeval with the recrystal-

lization age of the orthogneisses. In good correspond-

ence with this age are the crystallization ages of the

granite UP 1036 (Bystrµ) with 357  16 Ma and of the

granite UP 1023 (Baranec) with 347  14 Ma. Thus,

the crystallization of the granitoids in the Western

Tatra Mountains started 363  11 Ma ago and ended

before 347  14 Ma in Lower Carboniferous time.

The crustal-dominated character of the Tatra gran-

ites is also indicated by very old detrital zircon ages

obtained for the sample UP 1040 from Rohµc (2530 

400 Ma) and for the granite UP 1023 from Baranec

(1770  800 Ma). However, due to the absence of

larger inherited cores, the crustal sources were not

better constrained. Nevertheless, a Proterozoic compo-

nent as the main source for the granitoids of the Tatra

Mountains is suggested.

Low eNd (0), high initial

87

Sr/

86

Sr ratios and crustal

residence ages around 1400 Ma suggest that this last

magmatic event in the Western Tatra Mountains was

probably related to heating from upwelling mantle

after detachment of the lithospheric root (Blanken-

burg and Davies 1995). Such a scenario may also be

Fig. 6A ± C Simplified geodynamic evolution of the Western

Tatra area during Early Variscan time

347

responsible for the involvment of the reworked

oceanic crust. Similar intrusion ages of granitoids

related to the Variscan collision were reported for

granitoids from the Malµ Fatra, the Velkµ Fatra and

the StrasocskØ Mountains (355  10 Ma; Koh‚t et al.

1997; Krµl et al. 1997). K±Ar and Rb±Sr mineral and

whole-rock analyses of granitoids from the Tatric and

Veporic units of the Carpathians resulted in ages

between 348  2 and 362  21 Ma (Cambel et al. 1980;

Bagdasaryan et al. 1986; Krµl et al. 1987).

Although the envisaged two-step model of granite

evolution during advancing collision of continental

blocks (microplates) seems to be reasonable and in

agreement with available data in the Variscides, the

question of the direction of the subduction in Silurian

and Devonian times is still unanswered.

Considering the Silurian active continental margin

at the northern border of Gondwana (Stampfli 1996),

subduction could have continued in this same sense up

to the Devonian. Consequently, the older granites of

the Western Tatra may represent late granites from

this active continental margin, probably indicating

crustal thickening due to the collison of two micro-

plates at the northern border of Gondwana. This sub-

duction sense would fit the general evolution discussed

by Franke et al. (1993) and Reischmann and Anthes

(1996).

However, the thrusting of the lower onto the upper

unit happened in mid-Devonian time. Field evidences

confirm that the upper unit was thrusted to the south-

east onto the lower unit (Janµk 1994).

It remains unknown which sense the subduction

had before the final Variscan collision, which should

have caused the slab break-off and triggered the gen-

eration of the younger Western Tatra granites. Never-

theless, this model would fit a scenario proposed by

Neubauer et al. (1999) for the Eastern Alps and with

the stacking discussion about the evolution of the

Bohemian Massif (Schulmann et al. 1998) and the

Western Variscides (Matte 1998).

The new U±Pb zircon ages distinguish clearly two

granite generations in the Wesetern Tatra Mountains.

The older granites intruded in deep crustal levels dur-

ing Late Silurian to Early Devonian times at an active

continental margin or a volcanic arc. During this peri-

od, the Tatra Mountains are supposed to be part of a

microplate at the northern margin of Gondwana

(Fig. 6A), relatively in the southeast to the Saxothur-

ingian and Moldanubian units.

During to the following closure of the ocean and

the crustal accretion, another microplate (B) from the

southeast collided with the ªTatra plateº and due to

the thickening of the crust the older granites were

transformed into the present orthogneisses (Fig. 6B).

The subsequent collision with microcontinent C, pos-

sibly Armorica, caused the generation and emplace-

ment of the younger granites in Late Devonian/Early

Carboniferous time (Fig. 6C).

During the same time, the upper unit is thrusted

onto the lower unit, which is formed by the former

accretionary wedge sediments of microcontinent C.

The intrusion of the younger granites took place dur-

ing rapid exhumation and in higher crustal levels.

Although the proposed evolutionary scheme fits

well with the geodynamic concepts for the Variscan

orogeny, integrated studies are needed for a detailed

geologically reasonable reconstruction of the Variscan

crustal evolution in the Tatra Mountains and the

Western Carpathians.

Acknowledgements We are grateful to J. Huth for help with

SEM and to G. Feyerherd and I. Bambach for the final styling

of the figures.We thank L. Feld for correction of the style. A.

Hofmann is gratefully acknowledged for providing the possibility

to work at the MPI and for critical review of the manuscript.We

also thank J. von Raumer, M. Raith, P. Blümel and an anony-

mous reviewer for critical and helpful comments which

improved previous versions of the paper. This work was sup-

ported by the Max-Planck-Gesellschaft and the DFG (PO

608/1-1).

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