GeolCarp_Vol50_No3_229

GEOLOGICA CARPATHICA, 50, 3, BRATISLAVA, JUNE 1999

229–239

SILURIAN–DEVONIAN

Ar/

Ar MINERAL AGES FROM THE

KAINTALECK NAPPE: EVIDENCE FOR MID-PALEOZOIC

TECTONOTHERMAL ACTIVITY IN UPPER AUSTROALPINE

BASEMENT UNITS OF THE EASTERN ALPS (AUSTRIA)

ROBERT HANDLER

, FRANZ NEUBAUER

, SIEGFRIED HERMANN

and R. DAVID DALLMEYER

Department of Geology and Paleontology, University of Salzburg, Hellbrunner Str. 34, 5020 Salzburg, Austria; robert.handler@sbg.ac.at

Department of Geology and Paleontology, University Graz, Heinrichstr. 26, 8010 Graz, Austria

Department of Geology, University Georgia, Athens, Ga 30602, U.S.A.

(Manuscript received May 11, 1998; accepted in revised form December 9, 1998)

Abstract:

Ar/

Ar mineral dating has been carried out within the amphibolite-facies metamorphic basement and

greenschist-facies metamorphic cover of various tectonic units within the Kaintaleck Nappe, Eastern Alps, Austria, to
evaluate the age of pre-Alpine metamorphism. Hornblendes display discordant

Ar/

Ar apparent age spectra, mini-

mum ages recorded in medium- to high-temperature gas release steps are ca. 430–405 Ma. White mica from micaschist
record discordant

Ar/

Ar age spectra with ages of ca. 350–379 Ma in medium- and high-temperature increments.

White mica from discordant aplite and pegmatite record

Ar/

Ar plateau ages of 375.4 ± 0.4 Ma and 364.0 ± 0.8 Ma

respectively. The new isotopic ages indicate that (1) mid-Paleozoic (e.g. 430–380 Ma) tectonometamorphic activity is
recorded within the basement of the Kaintaleck Nappe; (2) this basement cannot represent the metamorphic basement
for Ordovician to Late-Cretaceous sedimentary sequences of the Noric-Tirolic nappe complex (within uppermost
units of the Austroalpine nappe complex); (3) the tectonometamorphic evolution of this basement unit contrasts with
that of other basement units exposed in the Eastern Alps, where predominantly “late Variscan” (e.g. 330–300 Ma)
tectonometamorphic events are recorded in Silurian to Early Carboniferous passive continental margin sequences;
and therefore (4) at least two contrasting terranes comprise the Austroalpine basement.

Key words:

Eastern Alps, Austroalpine, basement, mid-Paleozoic, terranes,

Ar/

Ar, geochronology.

Regional geologic setting

Mesozoic convergence between African-/Adriatic-derived
and Eurasian continental elements resulted in subduction of
oceanic crust and terminated with continent-continent colli-
sion resulting in formation of the Alpine-Carpathian orogen
(Frisch 1979; Coward & Dietrich 1989; Dewey et al. 1989).
The overall tectonic evolution of the Eastern Alps has been
described by Frank (1987) and Tollman (1987). The Eastern
Alps of Austria are dominated by nappe complexes, which
were initiated within northern sectors of the African/Adriatic
realm south of the Jurassic Penninic oceanic realm. These
nappes have been collectively termed the Austroalpine nappe
complex. Initial Alpine metamorphism and nappe assembly
within this nappe complex occurred between ca. 120 and
70 Ma (see Frank et al. 1987 for a compilation of geochrono-
logical data), and was contemporaneous to the closure of
remnants of the Tethys oceanic realm, which was situated
south of the Penninic ocean (Thöni & Jagoutz 1993; Dall-
meyer et al. 1998). From footwall to hangingwall the Aus-
troalpine nappe complex may be described in terms of three
regional, internally imbricated, tectonic units (Fig. 1), which
include the Lower, Middle, and Upper Austroalpine nappe
complexes (Tolmann 1963, 1987).

Recent mapping and structural investigations within the

northeastern sectors of the Upper Austroalpine nappe com-
plex documented evidence for five Alpine nappes (Figs. 1, 2)

which include, from footwall to hangingwall, the Veitsch,
Silbersberg, Kaintaleck, Noric-Tirolic, and Juvavic nappes
(see Neubauer et al. 1994 for a more detailed description of
the stratigraphy). The age of nappe assembly is constrained
by Permian cover sequences which form hangingwall seg-
ments of the Veitsch, Silbersberg, and Noric-Tirolic nappe
complexes.

Ar/

Ar muscovite and whole-rock ages from

penetratively ductile deformed sequences of the Upper Aus-
troalpine nappe complex indicate that nappe assembly oc-
curred at 100–90 Ma (Dallmeyer et al. 1996, 1998) and was
contemporaneous with regional, sub- to lower greenschist-
facies metamorphism within hangingwall units (Frank et al.
1987; Kralik et al. 1987). Within the lowermost Veitsch
Nappe and the uppermost Juvavic Nappe only post-Variscan
cover sequences (Late Paleozoic and Mesozoic respectively)
are recorded. The Silbersberg and Noric-Tirolic nappes con-
sist of Paleozoic lower greenschist-facies metamorphic base-
ment sequences and Permian to Mesozoic cover sequences.
Only within the Kaintaleck Nappe, an amphibolite-facies
metamorphic basement is recorded, which is overlain by a
greenschist-facies metamorphic cover sequence, for which a
Late Devonian to Early Carboniferous ages have been sug-
gested (Handler et al. 1997). The preservation of pre-Alpine

Ar/

Ar plateau ages in detrital white mica of various clas-

tic units within the Veitsch, Silbersberg and Noric-Tirolic
nappe complexes, indicates that the pre-Alpine K-Ar isotopic
system was not significantly rejuvenated within the Upper

230 HANDLER, NEUBAUER, HERMANN and DALLMEYER

Austroalpine nappe complex during Alpine tectonothermal
activity (Handler et al. 1997).

Tectonic significance of the Kaintaleck Nappe

The basement of the Kaintaleck Nappe (e.g. Kaintaleck

Metamorphic Complex; Neubauer et al. 1994) comprises
several tectonic basement units which are imbricated be-
tween the Silbersberg and the Noric-Tirolic nappes. The
Kaintaleck Nappe can be traced over more than 100 km
along northeastern sectors of the Eastern Alps (Fig. 1).
Rocks comprising the Kaintaleck Metamorphic Complex in-
clude amphibolite-facies metamorphic micaschits, marbles
and retrogressed eclogite-facies metamorphic amphibolites
which were intruted by discordant pegmatite and aplite fol-
lowing initial metamorphism and deformation. At least one
of these basement units is unconformably overlain by a meta-
conglomerate which was deformed and metamorphosed un-
der greenschist-facies metamorphic conditions (Neubauer
1985). The foliation within the meta-conglomerate clearly
transects a pre-existing foliation within underlying amphibo-
lite. This relationship indicates that this meta-conglomerate
represents a cover sequence of the Kaintaleck Metamorphic
Complex (Neubauer et al. 1987). This meta-conglomerate
has been correlated with the Kalwang Conglomerate exposed
in a comparable tectonic position westward (Daurer &
Schönlaub 1987; Loeschke et al. 1990). Because of its posi-
tion at the base of fossil-bearing, low-grade metamorphic
early Paleozoic clastic sequences of the Noric-Tirolic nappe

complex, these authors suggested a late Ordovician age for
sedimentation, and subsequent workers (Frisch et al. 1984;
Neubauer et al. 1987) have interpreted the Kaintaleck Meta-
morphic Complex to represent possible remnants of a pre-late
Ordovician basement of the Noric-Tirolic nappe complex, al-
though several ductile shear zones have been locally described
between the conglomerate and overlying fossil-bearing clastic
and carbonatic sequences (Loeschke et al. 1990). On the basis
of

Ar/

Ar dating of detrital white mica for provenance anal-

yses and paleogeographic reconstructions, Handler et al.
(1997) suggested a Late Devonian–Early Carboniferous age
for the deposition of the Kalwang Conglomerate.

Geochronological evidence for a late Cambrian (e.g. 520–

500 Ma) record within the Kaintaleck Metamorphic Complex
includes U-Pb zircon data (Neubauer & Frisch 1993) for two
orthogneiss-boulders of the transgressive meta-conglomerate
(upper intercept ages ca. 500 Ma), and underlying garnet-
gneiss intercalated within amphibolite (lower intercept age ca.
516 Ma). However, additional U-Pb zircon data from other
units within the Kaintaleck Metamorphic Complex (Neubauer
& Frisch 1993) suggest a mid-Paleozoic (e.g. 400–360 Ma)
age for the amphibolite-facies tectonothermal event recorded
within this basement unit. A record of Caledonian tectonother-
mal activity markedly contrasts with the pre-Alpine evolution
defined for other basement units exposed in the Eastern Alps
which were predominantly affected by Cambrian-Ordovician
(e.g. 550–440 Ma) and late Variscan (e.g. 330–300 Ma) tec-
tonothermal activity (Frank et al. 1987; Gebauer 1993;
Hoinkes & Thöni 1993; Magetti & Flisch 1993; Neubauer &
Frisch 1993; Schulz et al. 1993; Spillmann & Büchi 1993).

Fig. 1.

Geological map of the eastern part of the Eastern Alps. Position of sample localities and sample numbers are indicated.

SILURIANDEVONIAN

Ar/

Ar MINERAL AGES 231

The present study was initiated in an effort to constrain the

age of the amphibolite-facies metamorphic tectonothermal
activity which affected various tectonic units comprising the
Kaintaleck Metamorphic Complex, and to clarify the region-
al tectonic significance of this crystalline unit within the
Austroalpine nappe complex.

Characteristic of the Kaintaleck

Metamorphic Complex

Gneisses, garnet-micaschists, and amphibolites reached am-

phibolite-facies peak metamorphic conditions. Locally, eclog-
ite-facies metamorphic conditions have been described by
Neubauer & Frisch (1993). These assemblages were subse-
quently retrogressed under epidote-amphibolite- and later
greenschist-facies metamorphic conditions. All rocks analyzed
in the present study display evidence for penetrative ductile
deformation under greennschist-facies metamorphic condi-
tions which altered previously formed, amphibolite-facies
mineral assemblages. The age of this retrogressive overprint is
unclear. However, regional observations and isotopic data
from adjacent, over- and underlying, units (Dallmeyer et al.
1996, 1998) argue for an Alpine age for the greenschist-facies
metamorphic overprint. The dated minerals represent part of
the “older” (amphibolite-facies) parageneses, and are pre-
served as structural relics, now forming porphyroclasts within
a fine-grained matrix of newly grown greenschist-facies retro-
grade metamorphic minerals.

Within amphibolites, hornblendes have been sheared along

crystallographically determined cleavage planes. Plagioclase
has been altered to a fine-grained assemblage of white mica
and epidote-clinozoisite. Hornblende and plagioclase are sur-
rounded by a fine-grained matrix of chlorite + epidote + clino-
zoisite + carbonate. A newly-developed penetrative foliation
is defined by the orientation of newly-grown chlorite and ma-
trix minerals epidote + (clino-)zoisite + chlorite + carbonate +
ore minerals. Within this matrix hornblendes have been orient-
ed parallel to the stretching lineation due to passive, external
grain rotation. Because hornblendes acted as rigid clasts dur-
ing greenschist-facies deformation, it is evident that these min-
erals represent part of an older, amphibolite-facies metamor-
phic event.

A similar greenschist-facies metamorphic overprint on an

older mineral assemblage is observed within garnet-mica-
schists. Penetrative ductile deformation resulted in plastic
elongation of older quartz grains which are elongated parallel
to the stretching lineation and display subgrain formation,
core-mantle textures, and syntectonically recrystallized grains.
Such features have been described as typical of intracrystalline
plastic deformation. Subgrains separated by low-angle grain
boundaries (Bell & Etheridge 1973) have been reported to be
the result of dislocation glide and climb under conditions of
power-law creep (Barber 1985; Langdon 1985). The dominant
annealing process for minerals which have been deformed un-
der such conditions has been reported to be syntectonic recrys-
tallization (White 1977; Etheridge & Wilkie 1979, 1981;
Gottstein & Mecking 1985). White (1976) describes core-

Fig. 2.

Schematic tectonostratigraphic profile of eastern sectors of the Upper Austroalpine nappe complex and simplified sketch of the

Kaintaleck Nappe indicating sample locations. Hatched areas represent pre-Alpine basement sequences. Thickness of individual nappes
is not scaled.

232 HANDLER, NEUBAUER, HERMANN and DALLMEYER

mantle textures as a typical feature for beginning recrystalliza-
tion along the margins of older deformed grains with high in-
ternal strain. According to Sibson (1977, 1980) the fabrics
mentioned above require minimum temperatures of ca. 250–
300

C to be rechead during deformation. Quartz grains form

elongated aggregates of individual grains which are separated
from each other by microcracks and highly curved grain
boundaries in some micaschists. Although the overall elongat-
ed grain shape would argue for plastic deformation processes,
experimental studies (Den Brok 1992) argue for a cataclastic
flow regime (Schmidt 1982) for the development of such mi-
crostructures.

Within a newly-grown matrix of fine-grained white mica

and chlorite, garnet and white mica of the older paragenesis
were deformed by cataclastic stretching and external grain
rotation parallel to the newly developed stretching lineation.
Cracks within garnets are filled with newly-grown chlorite.
The micas represent structural relics of an older mineral
paragenesis, their rims have partly been recrystallized. Simi-
lar passively rotated mica clasts have been termed mica-fish
by Lister & Snoke (1984).

Analytical techniques

Sample localities are shown in Figs. 1 and 2. A detailed

description of samples and sample localities is provided in
the Appendix. Sample preparation procedures are described
in Handler (1994).

Mineral concentrates were wrapped in aluminum-foil

packets, encapsulated in sealed quartz vials, and irradiated in
the US Geological Survey TRIGA reactor. Variations in the
flux of neutrons along the lenght of the irradiation assembly
were monitored with several mineral standards, including
MMhb-1 (Samson & Alexander 1987). Samples were incre-
mentally heated until fusion in a double-vacuum, resistance-
heated furnace following procedures described by Dallmeyer
& Gil Ibarguchi (1990). Temperatures were monitored with a
direct-contact thermocouple and are controlled to ± 1

C be-

tween increments and are accurate to ± 5

C. Blank-corrected

isotopic ratios were adjusted for the effects of mass discrimi-
nation and interfering isotopes produced during irradiation
using the factors reported by Dalrymple et al. (1981). Appar-
ent

Ar/

Ar ages were calculated from the corrected isoto-

pic ratios using the decay constants and isotopic abundance
ratios listed by Steiger & Jäger (1977). Intralaboratory uncer-
tainties are reported, and have been calculated by statistical
propagation of uncertainties associated with measurement of
each isotopic ratio (at two standard deviations of the mean)
through the age equation following the methods described by
Dallmeyer & Keppie (1987). A “plateau” is considered de-
fined if ages recorded by four or more contiguous gas frac-
tions (with similar apparent K/Ca rations) each representing
more than 5 % of the total

Ar evolved (and together consti-

tuting more than 50 % of the total quantity of

Ar evolved)

are mutually similar within a ± 1 % intralaboratory uncertain-
ty. Plateau ages are calculated by normalizing the appropriate
incremental data. Interlaboratory uncertainties are less than
± 1.5 % of the quoted age. Analysis of the MMhb-1 monitor

indicates that the apparent K/Ca ratio may be calculated as
0.518 (± 0.005)

(

Ar/

Ar)

corrected

Results

Five hornblende concentrates from four amphibolite sam-

ples, and six muscovite concentrates from three garnet-mica
schist samples, one discordant pegmatite and one aplite sam-
ple of the Kaintaleck Metamorphic Complex, and one or-
thogneiss boulder of the meta-conglomerate overlying the
Kaintaleck Metamorphic Complex have been dated by

Ar/

Ar dating technique. Analytical data are listed in Tables 1

and 2, and are portrayed as age spectra in Figs. 3 and 4.

Hornblende

Hornblendes have been collected within three different

units of the Kaintaleck Metamorphic Complex. However,
they display comparable, internally discordant

Ar/

Ar age

spectra (Fig. 3). In low-temperature gas portions they display
significant intrasample fluctuations in apparent K/Ca ratios,
which suggests experimental release of argon from composi-
tionally distinct, relatively non-retentive phases. In medium-
to high-temperature increments apparent ages display either
saddle-shape gas release patterns or decreasing stair-case
shapes. This may be caused by minor, optically undetectable
mineralogical contaminants in the concentrates, petrographi-
cally unresolvable exsolution lamellae, compositional zona-
tion of the amphibole grains, or incorporation of an extrane-
ous argon component.

These discordant spectra are interpreted to reflect Alpine

and/or pre-Alpine alteration and retrogression of previously
formed amphibolites. Apparent ages reported in the age
spectra are therefore interpreted as geologically not signifi-
cant due to probable incorporation of extraneous argon com-
ponents. However, the youngest ages recorded in medium-
and high-temperature gas release steps (430–405 Ma) might
be interpreted as the lowermost limits for closure of the K-Ar
isotopic system in hornblende subsequent to amphibolite-fa-
cies metamorphism.

Muscovite

The results from

Ar/

Ar step heating on white mica con-

centrates are presented in Fig. 4. Because the apparent K/Ca ra-
tios are very large and exhibit no significant or systematic varia-
tions throught the analyses, they are not included in this figure.

Ar/

Ar age spectra from three white mica concentrates

separated from garnet-micaschist samples 5, 6, and 7 are
shown in Fig. 4a–c. All

Ar/

Ar age spectra exhibit nearly

identical apparent age patterns. The low-temperature por-
tions of the age spectra yield ages ranging between 285 Ma
(sample 5) and 200 Ma (sample 6). Intermediate-temperature
increments of samples 5 and 7 (Fig. 4a,c) are dominated by
apparent ages of 350 Ma. The apparent ages of all samples
increase in high-temperature increments to ages ranging be-
tween 375 Ma (sample 7) and 379 Ma (sample 6). These
stair-case-type gas release spectra have been shown in other

SILURIANDEVONIAN

Ar/

Ar MINERAL AGES 233

Fig. 4.

Ar/

Ar apparent age spectra of white mica concentrates from the Kaintaleck Nappe (locations shown in Figs. 1 and 2). Data

plotted as in Fig. 3. Plateau ages are listed and plateau increments are delineated.

Fig. 3.

Ar/

Ar apparent age and apparent K/Ca spectra of hornblende concentrates from the Kaintaleck Metamorphic Complex (loca-

tions shown in Figs. 1 and 2). Experimental temperatures increase from left to right. Analytical uncertainties (two sigma intralaboratory)
are represented by vertical width of scale bars.

234 HANDLER, NEUBAUER, HERMANN and DALLMEYER

polymetamorphic terrains to reflect partial rejuvenation of
intracrystalline argon systems of white mica due to reheating
and/or deformation induced recrystallization (e.g. Scaillet et
al. 1990, 1992; Dallmeyer & Takasu 1992; West & Lux
1993). The internally discordant

Ar/

Ar release spectra of

garnet-micaschist samples 5, 6, and 7 are similar, and sug-
gest initial isotopic closure for argon occurred prior to
375 Ma. Partial loss of radiogenic argon appears to have oc-
curred during a greenschist-facies metamorphic overprint
after initial closure of the isotopic system.

Ar/

Ar stepwise heating of muscovite from discordant

aplitic gneiss sample 8 (Fig. 4d) yielded a well-defined plateau

age of 375.4 ± 0.4 Ma in the 635

C-fusion increments (to-

gether comprising 72 % of the

Ar released). A muscovite

concentrate from discordant pegmatite sample 9 (Fig. 4e)
yielded a well-defined plateau age of 364.0 ± 0.8 Ma in the
680–855

C increments (together comprising 80 % of the total

Ar released). The apparent

Ar/

Ar age spectra (Fig. 4d,e)

display evidence for only minor loss of radiogenic

Ar subse-

quent to initial isotopic closure. These data are therefore con-
sidered geologically meaningful, and are interpreted as repre-
senting minimum estimates for the time of cooling subsequent
to intrusion into previously deformed and metamorphosed gar-
net-micaschist and amphibolites.

Table l:

Ar/

Ar analytical data for incremental-heating experiments on hornblende samples from the Kaintaleck Nappe, Eastern Alps

(Austria).

Sample 3: J = 0.009980

675

362.09

0.38427 18.975

0.52

69.06

1.34

2273.3 ± 46.0

775

157.01

0.09693 31.995

1.29

83.39

8.98

1528.9 ± 15.3

825

44.39

0.03168

3.768

1.42

79.58

3.23

545.9 ± 25.5

845

22.27

0.02634

5.500

0.91

67.01

5.68

251.2 ± 15.0

865

26.30

0.02258

6.901

0.93

76.71

8.31

332.3 ± 18.8

890

33.93

0.02635 13.899

0.94

80.33

14.35

437.4 ± 33.1

920

50.23

0.03222 29.406

1.47

85.74

24.83

655.3 ± 28.5

940

52.92

0.21200 31.953

1.50

93.00

41.00

733.0 ± 42.9

960

47.73

0.03614 25.099

1.66

81.84

18.89

602.1 ± 15.9

980

40.90

0.01626 19.961

3.62

92.16

33.40

582.3 ± 5.6

1000

37.46

0.01297 18.630

6.30

93.75

39.06

547.6 ± 6.7

1020

35.73

0.01301 18.642

6.98

93.42

38.97

524.1 ± 6.5

1040

33.06

0.00963 17.815

7.11

95.70

50.30

499.9 ± 4.7

1060

30.56

0.00841 17.159

4.81

96.36

55.49

469.3 ± 12.8

1080

32.41

0.00992 17.247

3.39

95.22

47.30

489.1 ± 12.4

1100

33.89

0.00932 16.654

14.87

95.80

48.60

511.0 ± 3.3

1130

35.62

0.00761 16.434

28.40

97.38

58.72

541.2 ± 1.1

1170

37.02

0.01003 16.061

8.52

95.47

43.56

549.8 ± 5.5

Fusion

40.37

0.04306 14.015

5.36

71.25

8.85

458.9 ± 11.3

Total

39.36

0.01624 17.277

100.00

92.94

44.05

547.4 ± 7.1

Release

Temp.

[°C]

(

Ar/

Ar) (

Ar/

Ar)

(

Ar/

Ar)

Ar %

total

non-

atmos.

[%]

Apparent

age

[Ma]

Sample 1a (0.140-0.125 mm): J = 0.009878

500

49.71

0.01866

0.124

0.01

74.06

0.08

559.6 ± 38.2

600

65.42

0.09062

5.432

2.55

59.72

1.63

590.6 ± 11.1

700

40.32

0.02700

1.340

4.01

80.47

1.35

501.9 ± 6.3

770

23.45

0.01082

5.150

4.08

88.11 12.95

336.0 ± 4.9

795

31.55

0.01202

8.774

2.41

90.96 19.85

452.5 ± 7.0

816

34.50

0.00870

6.334

2.98

94.01 19.80

503.1 ± 4.9

830

31.16

0.00381

5.680

12.45

97.83 40.57

476.3 ± 2.0

845

29.98

0.00431

5.622

13.66

97.24 35.48

457.9 ± 6.1

855

29.69

0.00258

5.705

9.74

98.95 60.10

461.1 ± 7.1

865

29.12

0.00249

5.710

8.90

99.03 62.49

453.6 ± 5.8

880

27.90

0.00406

5.728

7.25

97.33 39.42

430.1 ± 7.8

895

27.10

0.00287

5.824

5.06

98.58 55.24

423.8 ± 5.7

910

26.89

0.00168

6.154

2.88

99.98 99.84

426.4 ± 10.2

930

27.95

0.00290

6.779

3.53

98.86 63.48

437.0 ± 5.8

975

29.13

0.00290

8.018

9.07

99.25 75.24

455.3 ± 6.3

Fusion

28.30

0.00254

5.925

11.41

99.01 63.40

442.3 ± 10.3

Total

30.52

0.00707

5.872

100.00

95.98 47.76

454.1 ± 6.4

Sample 1b (0.160-0.140 mm): J = 0.008996

600

51.68

0.06166

3.046

3.41

65.21

1.34

478.5 ± 7.6

700

59.34

0.03590

1.250

1.41

82.28

0.95

657.3 ± 10.1

770

41.11

0.02262

1.437

3.07

84.00

1.73

488.4 ± 7.1

795

29.89

0.01397

2.848

1.39

86.94

5.54

379.5 ± 8.4

815

35.10

0.01339

5.143

1.10

89.89

10.45

452.0 ± 10.2

870

37.54

0.01065

8.324

0.87

93.38

21.25

496.8 ± 10.6

890

36.89

0.00741

6.642

1.53

95.49

24.37

498.5 ± 7.8

905

35.40

0.00265

5.898

4.30

99.11

60.54

496.5 ± 4.1

920

32.94

0.00339

5.375

4.30

98.26

43.17

462.4 ± 4.0

935

33.09

0.00278

5.436

5.59

98.82

53.12

466.6 ± 3.5

950

32.44

0.00264

5.638

9.51

98.97

57.98

459.2 ± 1.9

965

30.56

0.00276

5.711

15.08

98.81

56.23

435.0 ± 2.4

980

29.39

0.00231

5.635

16.74

99.20

66.46

421.5 ± 1.8

1000

29.38

0.00292

5.699

8.96

98.60

53.07

419.1 ± 1.8

1030

31.62

0.00345

6.501

5.07

98.41

51.32

446.9 ± 3.1

1060

31.75

0.00263

6.296

8.62

99.13

65.10

451.3 ± 5.1

Fusion

30.58

0.00370

5.441

9.05

97.84

40.01

431.3 ± 2.7

Total

32.69

0.00632

5.441

100.00

96.59

50.00

448.1 ± 3.5

Sample 2: J = 0.009722

620

36.74

0.01498

1.341

18.99

88.23

2.44

494.4 ± 7.7

720

30.46

0.01871

1.517

2.48

82.23

2.21

393.5 ± 8.2

770

26.06

0.01298

2.873

4.28

86.15

6.02

356.7 ± 5.6

795

24.88

0.00623

3.811

2.60

93.80

16.63

369.7 ± 10.3

810

24.56

0.00985

4.725

3.39

89.67

13.05

350.9 ± 7.1

825

26.94

0.00593

6.611

6.13

95.44

30.32

403.9 ± 6.2

840

28.81

0.00421

7.127

10.62

97.65

46.06

437.9 ± 3.8

855

29.36

0.00362

7.519

10.54

98.40

56.51

448.4 ± 5.4

865

29.29

0.00387

7.765

8.68

98.21

54.56

446.8 ± 5.5

880

28.70

0.00672

7.765

3.98

95.24

31.44

427.0 ± 6.0

895

27.80

0.00266

7.558

2.40

99.34

77.26

430.8 ± 3.5

910

27.19

0.00267

7.731

4.49

99.36

78.74

422.5 ± 7.1

925

27.40

0.00470

7.736

6.71

97.18

44.80

417.0 ± 8.2

960

28.31

0.00345

7.951

8.08

98.63

62.62

435.1 ± 6.6

1000

27.91

0.00277

7.417

4.85

99.18

72.82

431.6 ± 3.5

Fusion

28.37

0.00584

7.594

1.76

96.04

35.35

425.7 ± 10.3

Total

29.69

0.00717

5.797

100.00

94.72

37.96

435.7 ± 5.5

Sample 4: J = 0.009565

650

64.88

0.12144

3.236

4.19

45.08

0.72

445.8 ± 6.1

750

32.26

0.00609

6.138

3.45

94.10

27.40

430.7 ± 4.2

790

35.14

0.02180

9.310

6.26

83.78

11.62

449.9 ± 5.3

805

29.79

0.00425

6.897

8.37

97.63

44.17

444.5 ± 1.5

815

28.79

0.00357

6.720

12.77

98.19

51.17

433.4 ± 1.6

825

28.51

0.00373

6.752

10.37

98.01

49.19

429.0 ± 1.5

835

28.34

0.00334

6.655

12.07

98.39

54.25

428.0 ± 1.5

845

27.97

0.00436

6.678

13.29

97.30

41.70

418.9 ± 1.3

855

27.56

0.00340

6.608

9.67

98.26

52.79

417.0 ± 1.9

870

26.86

0.00348

6.773

6.28

98.18

52.94

407.3 ± 1.8

885

26.69

0.00376

6.695

4.51

97.83

48.42

403.7 ± 2.1

900

27.14

0.00537

6.831

3.55

96.15

34.60

403.5 ± 2.3

915

27.77

0.00340

7.069

2.66

98.40

56.48

420.6 ± 2.6

Fusion

28.02

0.00442

7.545

2.56

97.49

46.48

420.5 ± 2.4

Total

29.92

0.00995

6.746

100.00

94.67

43.66

423.0 ± 1.7

measured

corrected for post-irradiation decay of

Ar (35.1 day

- life)

[

tot

- (

atmos

) × (295.5)] /

tot

calculated using correction factors of Dalrymple et al. (1981); two sigma,

intralaboratory errors

Release

Temp.

[°C]

(

Ar/

Ar) (

Ar/

Ar)

(

Ar/

Ar)

Ar %

total

non-

atmos.

[%]

Apparent

age

[Ma]

SILURIANDEVONIAN

Ar/

Ar MINERAL AGES 235

The

Ar/

Ar release spectra of a muscovite concentrate

(sample 10) separated from an orthogneiss boulder within the
Kalwang Conglomerate (locality near Bruck a.d. Mur) is dis-
played in Fig. 4f. In contrast to the white mica analyses dis-
cussed above, the K/Ca ratios of this sample are much lower
(Table 2), but again no significant variation and correlation
with the

Ar/

Ar ratios is visible. The argon release spectra

of this sample is disturbed, which might reflect either partial
isotopic resetting and/or mixing of different white mica phas-
es with distinct ages. However, intermediate- and high-tem-

perature gas release ages of up to 385 Ma reported in this
spectrum are interpreted as representing minimum ages for
cooling following metamorphism of the source area prior to
erosion and deposition of this conglomerate.

Discussion

The new geochronological results demonstrate that Alpine

greenschist-facies metamorphism and accompanied penetra-

Table 2:

Ar/

Ar analytical data for incremental-heating experiments on muscovite samples from the Kaintaleck Nappe, Eastern Alps

(Austria).

measured

corrected for post-irradiation decay of

Ar (35.1 day

- life)

[

tot

- (

atmos

) × (295.5)

]

tot

calculated using correction factors of Dalrymple et al. (1981)

;

two sigma, intralaboratory errors

Release

Temp.

[°C]

(

Ar/

Ar) (

Ar/

Ar) (

Ar/

Ar)

Ar %

total

non-

atmos.

[%]

Apparent

age

[Ma]

Sample 5: J = 0.009363

540

23.37

0.01716

0.061

1.68

78.29

0.10

285.2 ± 4.3

570

23.10

0.01062

0.006

3.72

86.39

0.02

309.0 ± 1.6

600

23.07

0.00806

0.005

4.93

89.66

0.02

319.2 ± 2.1

630

22.00

0.00260

0.005

6.70

96.49

0.05

326.9 ± 2.4

660

22.58

0.00106

0.005

10.62

98.59

0.13

341.4 ± 3.0

690

23.02

0.00042

0.005

9.82

99.43

0.29

350.2 ± 2.2

720

23.20

0.00077

0.005

12.51

98.99

0.18

351.3 ± 1.7

750

23.06

0.00030

0.007

5.04

99.59

0.61

351.3 ± 2.6

780

23.09

0.00090

0.004

7.76

98.83

0.13

349.2 ± 1.3

810

23.62

0.00240

0.005

6.71

96.97

0.05

350.4 ± 2.1

840

24.13

0.00095

0.005

5.85

98.81

0.13

363.4 ± 1.6

870

24.49

0.00134

0.008

7.03

98.36

0.17

366.8 ± 1.7

900

24.73

0.00054

0.007

8.39

99.33

0.36

373.4 ± 1.6

940

25.00

0.00066

0.007

6.05

99.20

0.31

376.5 ± 0.8

Fusion

24.86

0.00042

0.019

3.18

99.48

1.24

375.7 ± 1.1

Total

23.48

0.00200

0.007

100.00

97.43

0.22

350.0 ± 2.1

Sample 6: J = 0.009181

500

14.11

0.00446

0.053

1.31

90.56

0.32

200.3 ± 1.6

580

17.97

0.00353

0.014

3.50

94.17

0.11

260.5 ± 0.8

610

19.87

0.00068

0.008

6.85

98.97

0.32

299.3 ± 0.4

640

20.94

0.00093

0.017

3.34

98.66

0.50

313.3 ± 1.0

670

21.88

0.00074

0.003

4.84

98.97

0.11

327.1 ± 0.6

700

23.01

0.00084

0.009

7.81

98.90

0.28

342.3 ± 0.6

730

23.93

0.00089

0.005

8.86

98.88

0.15

354.6 ± 0.8

760

24.05

0.00072

0.010

8.36

99.10

0.38

356.9 ± 0.4

790

24.25

0.00058

0.025

8.30

99.27

1.15

360.2 ± 0.6

820

24.67

0.00050

0.008

10.51

99.38

0.43

366.2 ± 0.6

850

24.87

0.00029

0.005

10.88

99.51

0.33

369.3 ± 0.6

880

24.90

0.00028

0.019

8.73

99.65

1.83

370.2 ± 0.6

910

25.10

0.00057

0.016

8.93

99.31

0.77

371.7 ± 1.4

945

25.48

0.00016

0.015

5.57

99.79

2.51

378.5 ± 0.8

Fusion

25.45

0.00060

0.020

2.20

99.91

9.14

378.5 ± 1.0

Total

23.57

0.00073

0.012

100.00

98.96

0.87

350.0 ± 0.7

Sample 7: J = 0.009996

540

27.26

0.03447

0.021

0.63

62.62

0.02

284.2 ± 4.3

580

19.63

0.00340

0.003

3.67

94.86

0.02

307.9 ± 3.1

610

19.94

0.00165

0.003

5.26

97.53

0.05

320.5 ± 1.6

640

20.52

0.00107

0.004

6.74

98.44

0.10

331.8 ± 1.4

665

21.20

0.00113

0.003

9.81

98.40

0.06

341.8 ± 1.0

690

21.65

0.00092

0.003

8.64

90.72

0.09

349.4 ± 1.0

715

21.88

0.00116

0.005

13.05

98.40

0.11

351.7 ± 1.2

740

21.69

0.00115

0.003

7.80

98.40

0.07

348.9 ± 1.1

765

21.66

0.00096

0.005

7.30

98.66

0.13

349.3 ± 0.8

790

21.80

0.00113

0.005

6.96

98.44

0.11

350.5 ± 0.8

815

22.20

0.00162

0.003

6.58

97.82

0.04

354.4 ± 1.2

840

22.73

0.00084

0.004

6.60

98.89

0.12

365.6 ± 1.1

870

22.93

0.00047

0.003

6.71

99.36

0.16

370.1 ± 1.2

900

23.12

0.00086

0.004

6.70

98.88

0.13

371.3 ± 1.2

Fusion

23.20

0.00033

0.007

3.55

99.56

0.60

374.8 ± 1.5

Total

21.79

0.00134

0.004

100.00

98.19

0.11

349.5 ± 1.1

Sample 8: J = 0.010425

480

16.71

0.01154

0.508

1.83

79.80

1.20

234.9 ± 1.3

560

20.91

0.00305

0.036

5.53

95.67

0.32

341.6 ± 0.5

585

21.52

0.00063

0.035

12.70

99.12

1.53

362.3 ± 0.6

610

21.94

0.00028

0.037

8.35

99.61

3.59

370.2 ± 0.6

635

22.12

0.00023

0.041

8.30

99.68

4.84

373.3 ± 0.3

660

22.21

0.00041

0.038

8.42

99.44

2.47

373.8 ± 0.3

685

22.29

0.00062

0.041

7.56

99.16

1.81

374.1 ± 0.4

715

22.28

0.00049

0.047

5.07

99.34

2.61

374.6 ± 0.5

740

22.29

0.00074

0.036

7.49

99.01

1.33

373.5 ± 0.2

770

22.36

0.00048

0.047

8.69

99.36

2.68

375.8 ± 0.3

800

22.48

0.00079

0.041

7.63

98.95

1.40

376.3 ± 0.5

835

22.59

0.00078

0.029

9.01

98.96

1.01

378.0 ± 0.4

870

22.59

0.00085

0.039

6.19

98.88

1.24

377.7 ± 0.2

Fusion

22.67

0.00103

0.041

3.23

98.65

1.10

378.0 ± 0.4

Total

22.04

0.00092

0.047

100.00

98.66

2.05

368.8 ± 0.4

Total without 480 ° – 610 °C

71.59

375.4 ± 0.4

Sample 9: J = 0.009738

550

46.47

0.08424

0.028

0.68

46.42

0.01

344.0 ± 5.1

590

28.38

0.02164

0.004

1.61

77.44

0.01

349.8 ± 4.6

625

23.65

0.00449

0.020

1.46

94.38

0.12

354.9 ± 2.1

650

22.94

0.00248

0.004

3.54

96.78

0.04

353.1 ± 2.3

680

22.73

0.00042

0.003

5.90

99.43

0.21

358.9 ± 1.3

705

22.84

0.00027

0.003

9.96

99.63

0.28

361.0 ± 1.1

730

23.19

0.00034

0.003

17.30

99.54

0.25

365.9 ± 0.7

755

23.13

0.00017

0.003

11.43

99.76

0.51

365.7 ± 1.4

780

22.97

0.00013

0.004

9.39

99.81

0.80

363.6 ± 1.5

805

23.02

0.00039

0.003

9.77

99.48

0.22

363.1 ± 1.0

830

23.16

0.00043

0.004

6.13

99.43

0.26

365.0 ± 0.8

855

23.41

0.00125

0.003

9.88

98.40

0.06

365.2 ± 0.8

885

23.71

0.00021

0.003

5.31

99.72

0.43

373.9 ± 0.9

920

23.86

0.00032

0.003

5.10

99.58

0.26

375.5 ± 1.2

Fusion

23.87

0.00060

0.006

2.53

99.23

0.26

374.3 ± 1.5

Total

23.42

0.00145

0.004

100.00

98.58

0.31

364.5 ± 1.0

Total without 550 ° – 650 °C,

79.76

364.0 ± 0.8

885 °C - fusion

Sample 10: J = 0.009892

550

25.89

0.04608

1.718

0.26

47.91

1.01

208.9 ± 8.1

550

15.11

0.01380

0.394

0.35

73.18

0.78

187.2 ± 6.2

600

13.17

0.00408

2.366

0.67

92.26

15.79

205.1 ± 4.1

650

12.68

0.00186

1.327

1.48

96.47

19.44

206.1 ± 1.4

690

12.75

0.00136

0.575

2.23

97.17

11.52

208.6 ± 1.3

730

13.41

0.00088

0.457

4.43

98.29

14.14

221.1 ± 0.6

760

14.59

0.00049

0.226

4.26

99.10

12.66

241.1 ± 1.8

790

17.06

0.00075

0.162

4.53

98.74

5.86

277.9 ± 1.6

815

20.23

0.00050

0.302

5.92

99.36

16.55

327.1 ± 1.9

840

22.95

0.00039

0.272

8.92

99.57

19.22

367.7 ± 1.2

865

24.11

0.00026

0.340

12.42

99.77

35.27

385.1 ± 1.0

895

24.21

0.00028

0.275

18.62

99.72

26.59

386.4 ± 0.8

925

23.91

0.00016

0.206

19.67

99.85

35.19

382.5 ± 1.2

955

23.73

0.00018

0.324

8.65

99.86

48.55

379.9 ± 1.8

990

23.34

0.00027

0.287

6.71

99.73

28.81

373.8 ± 1.2

Fusion

22.94

0.00002

1.839

0.88

100.59

2363.54

371.3 ± 4.1

Total

21.94

0.00056

0.331

100.00

99.22

47.96

351.3 ± 1.9

Release

Temp.

[°C]

(

Ar/

Ar) (

Ar/

Ar) (

Ar/

Ar)

Ar %

total

non-

atmos.

[%]

Apparent

age

[Ma]

236 HANDLER, NEUBAUER, HERMANN and DALLMEYER

tive ductile deformation did not completely reset

Ar/

isotopic systems in hornblende and white mica of amphibo-
lite-facies metamorphic basement rocks. Alpine

Ar/

apparent ages are not recorded even in low-temperature por-
tions of the white mica analyses. The relatively low Alpine
overprint allows resolution of the chronology of the pre-Al-
pine tectonothermal history of the Kaintaleck Nappe. The
isotopic data demonstrate that amphibolite-facies metamor-
phic conditions were reached prior to ca. 400 Ma (Early De-
vonian according to time-scale calibration of Harland et al.
1990), as indicated by youngest ages reported in medium-
and high-temperature release steps of hornblende. Ages of
ca. 375 Ma are reported in medium- and high-temperature
gas fractions evolved during incremental Ar-heating analyses
of white micas from garnet-micaschist. Evidence for an early
Devonian tectonometamorphic event is also reflected by re-
sults from croscutting pegmatites and aplitic veins, for which

Ar/

Ar plateau ages of 364.0 ± 0.8 Ma (pegmatite sample

9) and 375.4 ± 0.4 Ma (aplitic gneiss sample 8) are recorded.
Additional evidence comes from an orthogneiss boulder
within the transgressive Kalwang Conglomerate, for which
maximum apparent

Ar/

Ar ages of ca. 385 Ma are record-

ed in medium- and high-temperature increments. These indi-
cate the age of cooling prior to erosion and deposition of the
respective source area. As suggested by U-Pb zircon data and
high-pressure relics in eclogitic garnet-amphibolite, this De-
vonian cooling could have been preceded by a higher grade
metamorphism (Neubauer & Frisch 1993).

Tectonic implications

The Devonian post-metamorphic cooling ages presented

in this study suggest that the Kaintaleck Metamorphic Com-
plex and its low-grade metamorphic cover (e.g. the Kalwang
Conglomerate) do not represent the basement for Ordovician
clastic sequences of the Noric-Tirolic nappe complex as sug-
gested by Daurer & Schönlaub (1978) and Neubauer et al.
(1987). By contrast, the Kaintaleck Nappe appears to repre-
sent an individual tectonic unit which was incorporated into
the Upper Austroalpine nappe complex during early Alpine
thrusting, as indicated by

Ar/

Ar plateau ages of ca. 98–

94 Ma reported for white mica and whole-rock samples from
penetrative deformed phyllite and mylonite in footwall and
hangingwall structural units (Dallmeyer et al. 1998). Devo-
nian cooling ages have been reported for detrital white mica
from Permian clastic sequences of the Silbersberg Nappe
(footwall of the Kaintaleck Nappe, Fig. 2) and may suggest a
pre-Alpine association of the Kaintaleck Metamorphic Com-
plex with sedimentary units of the Silbersberg Nappe (Han-
dler et al. 1997).

Devonian tectonothermal evolution contrasts with the re-

gional Paleozoic evolution of basement units within other
structural units of the Austroalpine nappe complex. These typ-
ically record the effects of upper greenschist- and amphibo-
lite-facies metamorphism at ca. 300–330 Ma (Frank et al.
1987). However, mineral cooling ages related to Devonian
metamorphism have been reported from several other base-

Fig. 5.

Geological sketch map of the Alps indicating locations of Silurian–Devonian mineral cooling ages ranging between 440 and 380

Ma. (1) Cliff 1980, (2) Paquette et al. 1989, (3) Neubauer & Frisch 1993, (4) Müller et al. 1999, (5) Schweigl 1995, (6) Hoinkes et al.
1997, (7) this study.

SILURIANDEVONIAN

Ar/

Ar MINERAL AGES 237

ment units of the Alpine orogen (Fig. 5). These include Devo-
nian white mica cooling ages from western sectors of the Mid-
dle Austroalpine nappe complex (Lichem 1993; Schweigl
1995; Hoinkes et al.1997) and eastern sectors of the Lower
Austroalpine nappe complex within the Eastern Alps (Müller
et al. 1999). The latter have been interpreted to date initial
high-pressure metamorphism. Additional U-Pb zircon data in-
dicating Devonian high-pressure metamorphism within the
Austroalpine basement have been reported by Cliff (1980) and
Neubauer & Frisch (1993). Frisch & Neubauer (1989) defined
the Wechsel, Pannonic, and Veitsch tectonostratigraphic sub-
divisions of the Austroalpine basement and suggested these
are characterized by Devonian deformation and metamor-
phism. Silurian-Devonian high-pressure metamorphism has
also been reported from the Helvetic basement units in the
External Massifs of the Central Alps (Paquette et al. 1989).
Largescale correlation of pre-Alpine basement units has been
carried out by Flügel (1990), Frisch et al. (1990), Neubauer
& von Raumer (1993), and von Raumer & Neubauer (1993).
These authors suggest linkages of Devonian metamorphic
basement units within the Alpine belt to the Ligerian Cordil-
lera (Matte 1986) of the southern Armorican Massif and the
Moldanubian Zone of the Bohemian Massif. Therefore the
Kaintaleck Metamorphic Complex may represent a fragment
of the Ligerian Cordillera which was deformed and metamor-
phosed during its Devonian accretion to stable Europe. It
partly rifted from stable Europe during Permian to Jurassic
extension and was finally accreted to Europe again during
the Alpine orogenic events.

Acknowledgments:

This research was supported, in part, by

a grant from the Tectonics Program of the U.S. National Sci-
ence Foundation (EAR-9316042) to R.D.D. and the Austrian
Research Foundation (P 7405-GEO and P 8652-GEO) to
F.N. R.H. acknowledges grants from the Austrian Research
Community and Austrian Government for a three-months
visit at R.D.D.’s K-Ar laboratory.

Appendix

Topographic names are from the 1:50,000 Austrian topographic

maps (ÖK 50). For more information on the geological situation at
each sampling site we refer to Neubauer et al. 1994 and references
therein.

Sample 1:

Location: ÖK 133 sheet Leoben; south of Oberdorf

in the Laming Valley on the mountain slope east of the Obertaler-
graben; roadcut on gravel road which connects the farmers Leber
and Wieser with the gravel road which leads from Oberdorf to the
Tulleralm; approximately 50 m south of the intersection; altitude
850 m: Medium grained amphibolite with weakly developed folia-
tion and mineral lineation; the amhibolite suffered minor alter-
ation under greenschist facies metamorphic conditions; old am-
phiboles and feldspars are surrounded by a new grown,
fine-grained matrix of carbonate, Mg-rich chlorite, epidote,
zoisite/clinozoisite, titanite and ilmenite, best developed along
discrete shear bands.

Sample 2:

Location: ÖK 133 sheet Leoben; Tanzenberg tunnel on

highway S6 east of Bruck a.d. Mur; bore hole-meter 112.3: Coarse-
grained, strongly deformed garnet-amphibolite; garnets and am-
phiboles belong to the old mineral assemblage and suffered external

rotation into the new developed foliation, garnets are almost com-
pletely cracked, amphiboles are oriented parallel to the stretching
lineation; the new grown matrix consists of mineral phases typical
for greenschist metamorphic overprinting of amphibolites such as
epidote, zoisite, clinozoisite, carbonate, quartz, titanite, ilmenite and
Fe-rich chlorite.

Sample 3:

Location: ÖK 133 sheet Leoben; Tanzenberg tunnel on

highway S6 east of Bruck a.d. Mur; ca. 500 m south-west of the
Tanzenberg: Amphibolite of the Ritting structural subunit; the sam-
ple mainly consists of large amphibole crystals, garnet and zoisite;
elongated zoisite crystals display a shape preferred parallel orienta-
tion; garnet is often surrounded by symplectite which is composed
of fine-grained quartz, albite, and fine-grained amphibole; large am-
phibole crystals are internally unzoned; secondary deformation is
low and expressed in minor kinking of some amphibole grains.

Sample 4:

Location: ÖK 104 sheet Müzzuschlag; southwest of

Neuberg a.d. Mürz, on top of the ridge east of the Arzbachhöhe;
altitude 870 m: Less foliated fine-grained amphibolite; amphib-
oles show no preferred orientation within a matrix of feldspar,
partly altered to sericite, epidote, zoisite, and titanite.

Sample 5:

Location: ÖK 133 sheet Leoben; south of Oberdorf

in the Laming Valley on the mountain slope east of the Obertaler-
graben; roadcut on gravel road which connects the farmers Leber
and Wieser with the gravel road which leads from Oberdorf to the
Tulleralm; approximately 60 m south of the intersection and 10 m
in the footwall of sample 1; altitude 850 m: Grayish-brown, medi-
um grained garnet-micaschist with well developed foliation; white
micas are oriented parallel to the foliation, quartz exhibits core-
mantle-textures with only minor recrystallization; garnet shows
brittle deformation, fractures are filled with new grown Fe-rich
chlorite.

Sample 6:

Location: ÖK 105 sheet Neunkirchen; on top of the

mountain ridge above the railway station at Schlögelmühl; altitude
570 m: Grayish-brown, medium grained garnet-micaschist with
well developed foliation and cataclastic texture; old quartz grains
shows core-mantle textures and undulatory extinction, feldspars are
decomposed to sericite and quartz, garnets show extreme elongation
due to brittle deformation, their cracks are filled with chlorite, white
micas suffered external rotation into the foliation; the new grown
matrix is build up by fine grains quartz, sericite, chlorite and il-
menite.

Sample 7:

Location: ÖK 133 sheet Leoben; south of Oberdorf

in the Laming Valley, on the mountain slope west of the Obertaler-
graben; roadcut on gravel road 620 m east of the farmer Maxl; al-
titude 960 m: Greenish-gray, fine-grained micaschist with well de-
veloped foliation; white micas up to 2 mm in diameter are oriented
parallel to the stretching lineation; components are quartz, clasts
of feldspar and white mica and minor epidote and zoisite.

Sample 8:

Location: ÖK 105 sheet Neunkirchen; roadcut on the

road from Pottschach to Vöstenhof, 100 m south of the castle Vös-
tenhof; altitude 500 m: White aplitic gneiss with well developed
ductile foliation and mineral stretching lineation; quartz is charac-
terized by the development of elongated grains with subgrain for-
mation, feldspars, almost only plagioclase, shows strong retrogres-
sive metamorphic overprint and sericitization.

Sample 9:

Location: ÖK 133 sheet Leoben; 550 m NNW of the

chapel in the village Laintal III; altitude 905 m: Coarse-grained,
unfoliated white pegmatite; dominant constituents are plagioclase
(partly decomposed to sericite), quartz, white micas, up to 4 cm in
diameter and 5 mm thickness, and minor garnet.

Sample 10:

Location: ÖK 134 sheet Passail; small exposure

within the forest above the farm Schwammberger north of the vil-
lage Frauenberg, east of Bruck a.d. Mur; altitude 910 m: Orthog-
neiss boulder within the Kalwang Conglomerate; elongated grains
of undulose quartz, albite, and minor K-feldspar form the folia-
tion; quartz shows low-angle grain boundaries and fine recrystal-

238 HANDLER, NEUBAUER, HERMANN and DALLMEYER

lized grains along margins of older grains; a few grains of inter-
nally zoned garnets occur along grain boundaries of quartz and
plagioclase or as inclusions within quartz; muscovite forms flakes
which are affected by microboudinage and minor recrystallization
to fine-grained sericite along margins of larger flakes.

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