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GEOLOGICA CARPATHICA, DECEMBER 2005, 56, 6, 463—472

www.geologicacarpathica.sk

40

Ar/

39

Ar dating of detrital mica from the Upper Paleozoic

sandstones in the Western Carpathians (Slovakia)

ANNA VOZÁROVÁ

1

, WOLFGANG FRANK

2,4

, JÁN KRÁ

3

 and JOZEF VOZÁR

4

1

Department of Mineralogy and Petrology, Faculty of Natural Sciences, Comenius University, Mlynská dolina, 842 15 Bratislava,

Slovak Republic;  vozarova@fns.uniba.sk

2

Department of

 

Geological Sciences, University of Vienna, Althanstrasse 14, 1090 Vienna, Austria

3

Geological Survey of Slovak Republic, Mlynská dolina 1, 817 04 Bratislava, Slovak Republic

4

Geological Institute of Slovak Academy of Sciences, Dúbravská cesta 9, P.O. BOX 106, 840 05 Bratislava 45, Slovak Republic;

geoljovo@savba.sk

(Manuscript received June 24, 2005; accepted in revised form October 6, 2005)

Abstract:  Dating of detrital white mica taken from the Carboniferous-Permian sediments of the Western Carpathians
provided powerful results for determination of source areas. Two groups of samples were studied, first from the Carbonif-
erous formations of the Northern Gemeric Unit and second from the Pennsylvanian-Permian sequence of the Hronic Unit.
Both units are extremely important for the geodynamic reconstruction of the Western Carpathian Variscan Orogen, as the
Northern Gemeric Late Paleozoic reflects the development of a Variscan collision suture and the sedimentary history of
Hronicum formations allows reconstruction of the timing of rifting processes in the hinterland. Rift-related sediments of the
Hronic Unit show a trend of increasingly older detrital mica in an upward direction. Three samples from the Nižná Boca
Formation, belonging to Kasimovian—Gzhelian (Stephanian B-C), were investigated from the Hronic Unit. The
stratigraphically lowest sample yielded an age of 309 ± 3 Ma. The samples from the middle and upper portion of the Nižná
Boca Formation delivered successively older ages of 318 ± 2 Ma and 329 ± 2 Ma respectively. The time gap between the
average cooling in the source region and the age of sedimentation in the basal part of the Nižná Boca Formation does not
exceed 5 Myr, whereas at the top of the same formation this time difference reaches about 20 Myr. The trend to older ages
in higher stratigraphic levels in this tectonic unit is further corroborated by a sample derived from the Permian Malužiná
Formation, 2

nd

 megacycle, which yielded a still older age of 342 ± 3 Ma. These cooling ages of the source area reflect

development of the Hronicum terrestrial rift and heterogeneity of the source area, with gradual rifting and cooling of the
lithosphere. Four samples from the Northern Gemeric Unit were also investigated. A multi-grain sample from the Mississip-
pian Hrádok Formation yielded a 465 ± 2.5 Ma cooling age of the source area. This proves the existence of Ordovician
crustal fragments in the Variscan collision suture. Newly-formed fine-grained muscovite gave a distinct staircase pattern
from 87 Ma at the rim to 142 Ma in the core. It reflects composite Alpine overprint of these metasediments. Multi-grain
analyses of detrital mica from the Moscovian (Westphalian) Rudňany Formation sandstone and from an orthogneiss pebble
from the associated conglomerate yielded ages of 385 ± 3 Ma and 372 ± 2.5 Ma, which reflect a uniform Variscan source.

Key words: Western Carpathians, Upper Paleozoic sandstones, 

40

Ar /

39

Ar dating, source area, detrital mica.

Introduction

The present Alpine chain is built on continental crust con-
solidated at the end of the Variscan orogenic cycle. The
pre-Mesozoic Western Carpathian basement registered all
the main orogenic periods during its long evolution since
the Precambrian, which led to stepwise converging of
Gondwana-type pieces of crust (detached from Gondwana)
and to their final continent—continent collision in the
Variscan orogenic belt from the Late Devonian to the Car-
boniferous time. Due to development of syn- and post-oro-
genic Carboniferous and Permian sedimentary basins,
relics of which are preserved in all units of the Inner West-
ern Carpathians (Fig. 1), the detrital material derived from
the newly formed orogenic belt was preserved.

The 

40

Ar /

3 9

Ar age of detrital mica grains in Upper Pale-

ozoic sandstones provides direct evidence for the ages of
source areas from which the sand detritus was derived. The
interpretation of provenance has to consider the post-sedi-

mentary evolution of the studied rocks, especially the Al-
pine low-grade metamorphic overprint in some tectonic
units. Samples rich in detrital micas were collected from
Carboniferous metasandstones and sandy metapelites from
the Northern Gemeric Unit and Pennsylvanian  and Permi-
an sandstones from the Hronic Unit (Fig. 1). Both units are
extremely important for the geodynamic reconstruction of
the Western Carpathian Variscan Orogen, as the Northern
Gemeric Late Paleozoic reflects the evolution of a Variscan
collision suture. Additionally, the basal clastics of the
Hronicum can yield information on the former basement
of this unit and throw new light on the continental rifting
process responsible for the formation of these deposits.

Geological setting

Like most other collision fold belts, the Western Car-

pathians have been traditionally divided into external and

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464

VOZÁROVÁ, FRANK, KRÁ  and VOZÁR

internal structural zones, which are divided by the Pieniny
Klippen Belt (for summary see Biely et al. 1996a,b; Plašien-
ka 1995, 2003). The main differences between these struc-
tural zones are the age of the main Alpine events and the
intensity of their deformational and metamorphic effects.
These are: (1) external zone, the Late Cretaceous / Early
Paleocene to Oligocene / Early Miocene subduction / ac-
cretion and collision events; (2) internal zone, the Late
Jurassic HP / LT subduction event and Early / middle Creta-
ceous collision, associated with nappe stacking.

The internal part of the Western Carpathian orogenic

system is divided into the pre-Gosau nappe system and
overlying post-nappe Upper Cretaceous to Neogene sedi-
mentary and volcanic formations. The pre-Gosau nappe
system originated from sedimentary basins deformed dur-
ing Kimmerian to Mediterranean phases. Each such unit
consists of a crystalline basement and a characteristic Up-
per Paleozoic / Mesozoic envelope sequence, which either
rests on its original basement (Tatricum, Northern and
Southern Veporicum, Zemplinicum, Northern and South-
ern Gemericum) or was detached and displaced as a nappe
onto a different basement (Hronicum, Meliaticum, Turnai-
cum and Silicicum). Continental Upper Paleozoic sedi-
ments, unconformably overlain by Lower Triassic quartzose
clastic deposits and Middle Triassic shallow-water carbon-
ate are characteristic for Tatricum, Veporicum, Zemplini-

cum and Hronicum. The Carpathian Keuper Formation is
typical of the Late Triassic of the Tatricum and Northern
Veporicum, contrasting with  dolomites and limestones
in the Hronicum.

The fragments of the Upper Paleozoic sedimentary basin

fillings, as well as their substrate are preserved only within
the internal Western Carpathians, as part of the principal
Alpine crustal-scale units (Tatricum, Northern and South-
ern Veporicum, Zemplinicum, Northern and Southern Ge-
mericum), and several cover nappe systems (Hronicum,
Meliaticum, Turnaicum and Silicicum). As mentioned
above, the investigation is focused on 

40

Ar /

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Ar multi-

grain dating of detrital white mica from the Carboniferous
rocks of the Northern Gemeric Unit and from the Pennsyl-
vanian and Permian rocks of the Hronic Unit (Fig. 1).

The Hronicum is a rootless Alpine unit, partly divided

into two subunits – Šturec and Choč Nappes (Andrusov
et al. 1973). Both subunits contain Late Paleozoic volca-
no-sedimentary formations, variably preserved as a conse-
quence of tectonic reduction during nappe thrusting.
Remains of these sedimentary complexes are known in
many mountain ranges in the Western Carpathians; the best
preserved segments being situated on the northern slopes of
the Nízke Tatry Mts. There are no remnants of the underly-
ing pre-Kasimovian—Gzhelian (pre-Stephanian) basement.
Tectonic slices of granitoid blastomylonites found in the

Fig. 1.  Map showing the main tectonic units of the Slovak part of the Western Carpathians, studied area and localization of samples
(modified after Biely et al. 1996).

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465

40

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Ar DATING OF DETRITAL MICA FROM THE UPPER PALEOZOIC SANDSTONES (SLOVAKIA)

basal part of the Šturec Nappe may be indicative of its com-
position (Andrusov 1936; Vozárová & Vozár 1979). The
Nižná Boca Formation, Stephanian according to macroflora
(Sitár & Vozár 1973) and microflora (Planderová 1979), is a
generally clastic regressive sequence with distinct tendency
of coarsening upward. Abundant massive and graded-bed-
ded grey or dark-grey sandstones with minor mudstone in-
tercalations, as well as layers rich in coalified plant detritus
indicate a fluvial-lacustrine delta association. Syngenetic
volcanism is represented by dacitic volcaniclastic detritus
mixed with non-volcanic material, less frequently by thin
dacite tuff layers and small lava flows. The Permian sedi-
mentary rock complexes (the Malužiná Formation) are de-
veloped gradually from the underlying Stephanian. They
comprise a thick succession of red-beds which developed in
three regional megacycles arranged above each other. An
integral part of this formation is the polyphase rift-related
andesite-basalt volcanism with a continental tholeiitic mag-
matic trend (Vozár 1977, 1997; Dostal et al. 2003). The mi-
croflora proved the Early and Late Permian age of the
Malužiná Formation (Planderová 1973; Planderová &
Vozárová 1982). This assumption is supported by 

206

Pb /

238

U

and 

207

Pb /

235

U dating of 263± 11 Ma copper sulphides from

uranium-bearing layers of the upper part of the second mega-
cycle (Legierski in Rojkovič et al. 1992).

The  Northern Gemeric  Unit comprises relics of Bashkiri-

an-Visean flysch (the Hrádok and Črme  Formations in the
Ochtiná Group; Vozárová 1996) and fragments of two
Variscan terranes (the Klátov and Rakovec Terranes;
Vozárová & Vozár 1996), which differ from each other in
tectono-metamorphic development and probably also in
protolith age. Their gradual amalgamation took place in the
Mississippian. This can be concluded from the uppermost
Visean-Serpukhovian shallow-water carbonate-clastic de-
velopment (the Lubeník Formation; Vozárová 1996) which
after stratigraphic hiatus in the Bashkirian (Namurian B—C),
is unconformably overlapped by Moscovian marine post-
orogenic sediments. This overstepping marine “molasse”
also rests on Mississippian flysch (in the eastern part of the
Northern Gemeric Zone) and therefore seals a late Variscan
thrust belt. Detrital micas were also dated from the Missis-
sippian metasandstones of the Hrádok Formation and from
metasandstones of the Pennsylvanian Rudňany Formation.

The  Hrádok Formation consists of a dark-grey and

black  clastic flysch sequence – metaparaconglomerates,
metasandstones, metapelites, interlayered with metabasalts,
metamicrodolerites and basic metavolcaniclastics. Very rare
sedimentary rocks, found only in thin layers, are lydites and
siliceous metapelites. Slabs of ultramafic rocks (oceanic
crust fragments) represented by antigoritic serpentinites
and tremolite-talc schists are integral part of this deep-
water turbidite slope / rise sequence. A monotonous com-
plex of dark-grey metapelites, overlying the relatively
coarse-grained basal part of the Hrádok Formation, yield-
ed microflora indicating the Late Tournaisian—Visean
age (Planderová 1982; Bajaník & Planderová 1985).

Moscovian (Westphalian) formations (Dobšiná Group

consisting of Rudňany, Zlatník and Hámor Formations;
Vozárová 1996) are preserved within the Northern Ge-

meric Unit as tectonically reduced fragments. Basal con-
glomerates of the Rudňany Formation unconformably
overlap the Klátov Terrane gneiss-amphibolite complex,
metasediments and metabasalts of the Rakovec Terrane
as well as the Mississippian  flysch sequence of the Črmel
Formation in the eastern part of Northern Gemeric Unit.
Coarse-grained delta-fan sediments contain detritus de-
rived from these underlying pre-Pennsylvanian  rock com-
plexes. Black shales and micaceous metasandstones are a
normal member of the fining upward Rudňany Forma-
tion. The floral finds (Němejc 1947) confirm the West-
phalian A—B age.

Sample description

Hronic Unit: Three samples (WCA-4 / 01; WCA-7 / 01;

WCA-8 / 01) were selected for age determinations from the
Nižná Boca Formation sandstones. The dominant components
are quartz grains (from 44 to 55 %), lithic fragments (from
13 to 19 %), feldspars (from 11 to 14 %) and clastic mica
(from 2 to 7 %), with variable contents of primary matrix
(from 14 to 25 %). Fragments of dacitic volcanites and their
volcaniclastics, as well as different types of phyllites and
metaquarzites were recognized among the lithic clasts (ratio
Lv / L = 0.77). Plagioclase prevails among the feldspar
clasts (plagioclase / alkaline feldspar ratio is 0.6). The ma-
trix is slightly recrystallized, with newly-formed illite,
chlorite and calcite.

Clastic mica of the Malužiná Formation sandstone

(WCA-3 / 01) was separated from the upper part of the 2

nd

megacycle. Compared with the Nižná Boca Formation
sandstones this sediment is rich in feldspar. Generally, sand-
stones from the 2

nd

 megacycle of the Malužiná Formation

contain: 49—58 % quartz grains, 10—12 % alkali feldspars,
8—9 % plagioclase, 6—7 % clastic mica, 1—3 % volcanic
clasts, 0.5—1 % other lithic clasts (mostly different type of
phyllites) and 15—22 % matrix, rich in hematite pigment.

Generally, the grade of metamorphism did not ex-

ceed  the diagenesis / anchizone boundary (according to
pumpellyite + prehnite  assemblages in diorite dykes: Vrána
& Vozár 1969; illite crystallinity indices from pelites:
Plašienka et al. 1989; Šucha 1989).

Northern Gemeric Unit:

 Two groups of detrital mica were

analysed from the Rudňany Formation. The first of these was
derived from a white orthogneiss pebble of the Rudňany For-
mation boulder conglomerates (WCA-9 / 01) and the sec-
ond from the sandstones associated with the plant-bearing
horizon in the upper part of the Rudňany Formation
(WCA-9 / 98). Components of the Rudňany conglomerates
are different gneiss types, amphibolites, metabasalts and
their volcaniclastics and metasediments (more detail see
Vozárová 1973; Vozárová & Vozár 1988).

The white gneiss pebble is represented by medium-

grained, medium-banded orthogneiss showing structural
features of foliated granitic-gneiss. The porphyroblasts
of alkali feldspars (Or

95

Ab

5

) and plagioclases (Ab

88—74

An

9—25

Or

0.3—1.7

) are associated with quartz occurring in

the bands of mosaic type crystals, muscovite (content of TiO

2

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466

VOZÁROVÁ, FRANK, KRÁ  and VOZÁR

is ranging from 0.23 to 1.22 wt. %; Na / Na + K = 0.04—0.06;
Fe / Mg= 0.46—2.45)  and strongly altered biotite (transformed
into iron-rich chlorite). Zircon and garnet (Alm

68—70

Pyr

3—8

Grs

2—20

Sps

5—22

) are the principal accessory minerals.

The mineral composition of associated sandstones reflects

the same source area as the Rudňany conglomerates, namely
a newly formed Variscan mobile zone. The sandstones are
rich in lithic fragments (51 %), with less quartz (36 %) and
feldspars grains (13 %) and detrital mica (2 %) (average of
8 analyses). The primary matrix is recrystallized consisting of
newly-formed chlorite + muscovite + quartz. The grade of Al-
pine metamorphism corresponds to the lower greenschist
facies (IC = 0.21—0.23 [

∆ °2Θ], Ir=1.0—1.08; Vozárová &

Šucha, unpublished). Coarse- to medium-grained metasand-
stones of the Mississippian Hrádok Formation are generally
relatively rich in quartz (in most samples more than 80 %).
Subordinate components are plagioclase, detrital mica and
lithic fragments. Primary coarse-grained detrital mica was
separated from sample WCA-1 / 00. The strong Alpine over-
printing is documented by fine-grained metamorphic mica,
which was separated from sample WCA-3 / 00.

Generally, the rocks of the Ochtiná Group were meta-

morphosed in LP greenschist facies (Sassi & Vozárová
1987; geothermal gradient approx. 40 °C / km, estimated
T = 350—370 °C at a low pressure). The illite crystallinity
indices correspond to these estimates (in the range of
0.17—0.23 [

∆ °2Θ]; Ir index=1; Vozárová & Šucha, unpub-

lished). These assessments are supported by the assemblage
Act + Chl + Alb+ Ep in the associated metabasic rocks. A
Variscan age of metamorphism is suggested by the presence of
pebbles derived from the lithologically and stratigraphically
corresponding rock complex (Črme  Formation) within the
Westphalian conglomerates in the eastern part of Northern
Gemericum. A distinct Alpine overprinting is assumed.

Analytical procedure

The geochronological investigations were performed in

the Ar laboratory of the Institute for Geological Sciences,
Vienna University in 2002. The analytical procedure is
the same as described in Frimmel & Frank (1996).

Interpretation of the ages

General remarks:

 The carefully separated and cleaned

samples of detrital muscovites were measured in the form
of multigrain samples of a few mg, which means that the
spectra represent an average age of several thousands of
individual grains. One can assume that during the separa-
tion procedure mainly the rims of the grains have been re-
moved and therefore the obtained age spectra mainly
reflect information from the inner portions of the detrital
grains. The disturbances in the low temperature steps do
not exceed a few percent. Apart from the reason just men-
tioned, this is well in line with the absent or negligible
thermal overprint of the samples and the well preserved
state of the detrital micas.

In addition to the now available age spectra of multi-

grain samples, histograms of single grain ages are needed
to understand the age variation among the detrital micas
in a single sample. Such investigations are planned in a
more detailed future study.  However, we feel that the
rather well defined plateau-type age patterns of the dia-
grams indicates that mixing of micas from source regions
with largely different ages or thermal histories with dis-
cordant age patterns was limited or missing. Apart from
one sample of the Hrádok Formation the results reflect a
provenance from various domains of the evolving
Variscan Orogen.

Samples from the Hronic tectonic unit:

 Three samples

from the Nižná Boca Formation, belonging to Stephanian
B-C, have been investigated from this unit. The strati-
graphically lowest sample (WCA-8 / 01) yielded an age
of 309± 3 Ma (Fig. 2, Table 1). The samples (WCA-7 / 01;
WCA-4 / 01) from the middle and upper portion of the
Nižná Boca Formation delivered successively older ages
of 318± 2 Ma and 329± 2 Ma respectively (Figs. 3, 4; Ta-
bles 2, 3).

The time gap between the average cooling in the source

region and the age of sedimentation in the basal part of
the Nižná Boca Formation does not exceed 5 Myr, where-
as on top of the same formation this time difference reach-
es about 20 Myr. If we assume that the result from these

Fig. 2. 

40

Ar/

39

Ar apparent age diagram of detrital white mica from

the basal part of the Nižná Boca Formation, sample WCA-8 / 01.

Table 1: Analytic data of detrital white mica from the basal part of
the Nižná Boca Formation, sample WCA-8 / 01.

3068                                          WCA-8/01 

Step T 

(

o

C) % 

39

Ar 

40

Ar* 

40

Ar*/

39

Ar App. 

age 

  1 

  620 

  3.4 

94.5 

  8.19 ± 1.7 

244.8 ± 4.3 

  2 

  680 

  6.3 

96.4 

  9.85 ± 0.7 

290.5 ± 2.0 

  3 

  720 

10.5 

98.0 

10.32 ± 0.2 

303.3 ± 0.6 

  4 

  770 

26.5 

99.2 

10.54 ± 0.1 

309.3 ± 0.4 

  5 

  820 

17.1 

99.3 

10.65 ± 0.3 

312.3 ± 0.9 

  6 

  860 

  6.8 

98.6 

10.52 ± 0.5 

308.8 ± 1.5 

  7 

  925 

  5.6 

97.4 

10.33 ± 0.4 

303.6 ± 1.2 

  8 

  980 

   5.7 

97.4 

10.19 ± 0.9 

300.0 ± 2.8 

  9 

1060 

13.7 

98.4 

10.66 ± 0.5 

312.6 ± 1.6 

10 

1250 

 4.4 

95.2 

10.48 ± 1.4 

307.8 ± 4.4 

J = 0.017745 ± 0.4 %  

           Total gas age:      305.3 ± 2.8 Ma 

                                                        80 % plateau age:      309.3 ± 2.7 Ma 

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467

40

Ar/

39

Ar DATING OF DETRITAL MICA FROM THE UPPER PALEOZOIC SANDSTONES (SLOVAKIA)

Fig. 3. 

40

Ar/

39

Ar apparent age diagram of detrital white mica from

the middle part of the Nižná Boca Formation, sample WCA-7/01.

Fig. 4. 

40

Ar/

39

Ar  apparent  age  diagram  of  detrital  white  mica

from the upper part of the Nižná Boca Formation, sample WCA-4/01.

Table 3: Analytic data of detrital white mica from the upper part

of the Nižná Boca Formation, sample WCA-4/01.

3048                                          WCA-4/01 

Step  T (

o

C)  %

39

Ar   %

40

Ar* 

40

Ar*/

39

Ar 

App. age 

  1 

  620 

  3.1 

96.6 

29.47 ± 0.4 

250.8 ± 0.8 

  2 

  680 

  4.1 

97.1 

34.33 ± 0.4 

289.1 ± 1.0 

  3 

  720 

  4.5 

98.0 

36.90 ± 0.7 

308.9 ± 1.9 

  4 

  770 

10.9 

99.1 

38.25 ± 0.6 

319.3 ± 1.7 

  5 

  820 

18.5 

99.4 

39.19 ± 0.1 

326.5 ± 0.4 

  6 

  860 

13.3 

99.4 

39.58 ± 0.2 

329.5 ± 0.6 

  7 

  925 

  9.7 

99.2 

39.89 ± 0.3 

331.8 ± 1.0 

  8 

  980 

  6.7 

98.4 

39.34 ± 0.3 

327.6 ± 0.9 

  9 

1060 

16.5 

98.8 

39.53 ± 0.2 

329.1 ± 0.5 

10 

1250 

12.7 

97.8 

39.98 ± 0.2 

332.5 ± 0.6 

J = 0.005062 ± 0.4 %  

           Total gas age:      323.2 ± 2.4 Ma 

                                                        77 % plateau age:      329.3 ± 2.1 Ma

 

three  samples  reflects  a  typical  feature  in  these  clastic  de-

posits  —  which  has  to  be  further  tested  —  this  indicates

the  evolution  of  the  erosional  source  region  from  more  lo-

cal  and  rapidly  uplifted  areas  to  a  wider  region  in  which

older  portions  are  incorporated.  In  the  simple  case  that

only  deeper  levels  in  the  same  basement  source  area  were

eroded  one  should  expect  gradually  younger  ages  in  higher

stratigraphic  levels.  Of  course,  the  age  distribution  in  the

source  area  may  have  been  complex  considering  also  the

age  variation  among  the  various  Variscan  magmatic  and

metamorphic  crystalline  rock  complexes  which  contributed

a  substantial  portion  of  the  rock  fragments  and  the  detrital

micas  of  the  clastic  deposits  (broad  spectrum  of  Variscan

muscovite  K/Ar  data:  Cambel  et  al.  (1990); 

40

Ar/

39

Ar  cool-

ing  ages  data  from  Tatricum  and  Veporicum:  Maluski  et  al.

(1993),  Dallmayer  et  al.  (1996),  Janák  (1994);  U-Pb  zircon

data: Poller et al. (2000), Poller & Todt (2000)).

The  trend  to  older  ages  in  higher  stratigraphic  levels  in

this  tectonic  unit  is  further  corroborated  by  sample

WCA-3/01  which  is  derived  from  the  Permian  Malužiná

Formation,  2

nd

  megacycle.  It  yielded  a  still  older  age  of

342±3 Ma  with  negligible  saddle  shaped  rejuvenation  at

medium  temperatures  (Fig. 5,  Table 4).  Such  features  are

often  observed  when  samples  have  suffered  some  over-

printing.  As  overprinting  in  sediments  can  be  excluded,

overprinting  in  the  source  region  could  be  a  possible  rea-

son  for  this  feature.

Of  course,  the  ages  obtained  cannot  be  interpreted  as  uni-

form  ages  in  the  source  regions.  As  they  are  derived  from

multigrain  samples  a  mixture  from  micas  with  somewhat

different  ages  can  be  expected.  Most  probably  the  variation

did not exceed the time span of the Variscan cycle.

However,  the  limited  data  from  Carboniferous/Permian

sediments  from  the  Hronic  tectonic  unit  are  compatible

with  the  formation  of  a  tectonic  graben  in  a  recently  up-

lifted  basement  and  later  successive  widening  of  the  ero-

sional  source  area  including  older  regions  from  the

Variscan  belt.

Muscovite  K/Ar  (these  data  published  between

1957–1988  were  reviewed  by  Cambel  et  al.  1990)  and

40

Ar/

39

Ar  data  from  Tatric  and  Veporic  basement  units

generally  give  a  broad  age  spectrum  although  Hercynian

cooling  is  completely  preserved  in  many  cases  (Maluski

et  al.  1993;  Dallmayer  et  al.  1996;  Krá¾  et  al.  1997;  Ko-

hút  et  al.  1998;  Hók  et  al.  2000).  Very  typical 

40

Ar/

39

Ar

plateau  ages  lie  between  340–320 Ma. 

40

Ar/

39

Ar  musco-

vite  data  often  show  rather  discordant  spectra,  which  are

interpreted  as  a  result  of  Alpine  rejuvenation.

Samples  from  the  Carboniferous  of  the  Northern  Ge-

meric  Unit:  Four  samples  from  this  unit  were  investigat-

ed.  The  most  interesting  result  was  found  from  sample

WCA-1/00  of  the  Mississippian  Hrádok  Formation  near

Ochtiná  village.  Here  a  well  defined  plateau  age  of

465±2.5 Ma  was  measured  (Fig. 6,  Table 5).  The  low  tem-

Table 2: Analytic data of detrital white mica from the middle part

of the Nižná Boca Formation, sample WCA-7/01.

3065                                          WCA-7/01 

Step  T (

o

C)  % 

39

Ar  % 

40

Ar* 

40

Ar*/

39

Ar 

App. age 

  1 

  620 

  2.8 

94.2 

  9.49 ± 1.5 

280.9 ± 4.2 

  2 

  680 

  5.2 

97.2 

10.56 ± 0.4 

309.9 ± 1.3 

  3 

  720 

  7.0 

98.6 

10.71 ± 0.6 

313.9 ± 1.9 

  4 

  770 

19.5 

99.2 

10.81 ± 0.2 

316.7 ± 0.6 

  5 

  820 

20.4 

99.4 

10.90 ± 0.3 

318.9 ± 0.9 

  6 

  860 

  8.7 

99.5 

10.80 ± 0.4 

316.3 ± 1.4 

  7 

  925 

  6.7 

99.0 

10.65 ± 0.3 

312.2 ± 0.9 

  8 

  980 

  6.1 

98.8 

10.63 ± 0.4 

311.7 ± 1.4 

  9 

1080 

18.4 

99.3 

10.98 ± 0.1 

321.3 ± 0.4 

10 

1250 

  5.1 

99.0 

11.01 ± 0.4 

321.9 ± 1.3 

J = 0.017745 ± 0.4 %  

           Total gas age:      316.0 ± 2.4 Ma

                                                        91 % plateau age:      317.8 ± 2.2 Ma

background image

468

VOZÁROVÁ, FRANK, KRÁ¼ and VOZÁR

Table 5: Analytic data of detrital white mica from the Hrádok For-

mation metasandstone, sample WCA-1/00.

Fig. 6. 

40

Ar/

39

Ar  apparent  age  diagram  of  detrital  white  mica

from the Hrádok Formation metasandstone, sample WCA-1/00.

Fig. 7. 

40

Ar/

39

Ar  apparent  age  diagram  of  newly-formed  fine-

grained  white  mica  from  the  Hrádok  Formation  metasandstone,

sample WCA-3/00.

Table 6: Analytic data of newly-formed white mica from the Hrá-

dok Formation metasandstone, sample WCA-3/00.

Table 4:  Analytic  data  of  detrital  white  mica  from  the  Malužiná

Formation, 2

nd

 megacycle, sample WCA-3/01.

Fig. 5. 

40

Ar/

39

Ar  apparent  age  diagram  of  detrital  white  mica

from the Malužiná Formation, 2

nd

 megacycle, sample WCA-3/01.

3064                                            G-1/00 

Step  T (

o

C)  % 

39

Ar  % 

40

Ar* 

40

Ar*/

39

Ar 

App. age 

  1 

  620 

  1.3 

92.6 

17.28 ± 1.2 

482.4 ± 4.9 

  2 

  680 

  1.9 

93.8 

17.13 ± 0.7 

478.9 ± 2.9 

  3 

  720 

  2.3 

96.0 

17.08 ± 1.0 

477.5 ± 4.2 

  4 

  770 

  7.4 

98.1 

16.73 ± 0.2 

469.0 ± 0.8 

  5 

  820 

17.7 

99.5 

16.62 ± 0.1 

466.2 ± 0.5 

  6 

  860 

18.1 

99.7 

16.57 ± 0.1 

465.0 ± 0.3 

  7 

  925 

19.8 

99.6 

16.55 ± 0.1 

464.6 ± 0.3 

  8 

  980 

  9.6 

99.5 

16.57 ± 0.1 

465.0 ± 0.6 

  9 

1060 

20.0 

99.7 

16.58 ± 0.1 

465.2 ± 0.4 

10 

1250 

  2.0 

98.6 

16.53 ± 0.6 

464.0 ± 2.3 

J = 0.017745 ± 0.4 %  

           Total gas age:      466.2 ± 2.7 Ma 

                                                        87 % plateau age:      465.2 ± 2.4 Ma

 

2990                                            G-3/00 

Step  T (

o

C)  % 

39

Ar (rel.)  % 

40

Ar* 

40

Ar*/

39

Ar 

App. age 

  680 

10.7 

93.2 

2.70 ± 0.6    87.4 ± 0.5 

  720 

10.3 

95.6 

2.79 ± 0.6    90.4 ± 0.5 

  770 

14.6 

96.3 

2.90 ± 0.5    93.8 ± 0.5 

  820 

16.7 

97.8 

3.34 ± 0.5  107.6 ± 0.5 

  860 

12.6 

96.5 

3.09 ± 0.4  101.2 ± 0.5 

  925 

  9.3 

95.1 

3.09 ± 0.4 

99.9 ± 0.4 

  980 

  5.8 

91.8 

3.13 ± 0.6  100.9 ± 0.6 

1060 

15.4 

97.2 

3.52 ± 0.3  113.3 ± 0.4 

1250 

  4.5 

89.0 

4.46 ± 1.2  142.2 ± 1.7 

J = 0.018400 ± 0.4 %  

           Total gas age:      102.2 ± 1.2 Ma 

                                                        80 % plateau age:        97.8 ± 1.2 Ma

perature  steps  of  this  diagram  exhibit  some  higher  ages,

which  is  unusual  for  undisturbed  spectra  of  detrital  mus-

covites. A 

39

Ar recoil effect (

39

Ar loss from altered miner-

al  lattice  during  irradiation)  resulting  from  strongly

weathered  rims  of  the  detrital  grains  seems  to  be  a  possi-

ble  explanation  for  this  feature.

We  think  that  this  well  defined  concordant  age  spec-

trum  reflects  the  cooling  in  the  source  region  and  not

mixing  of  widely  differing  ages.  In  the  Alps  such  Early

Paleozoic  ages  have  been  often  measured  with  Rb/Sr

whole  rock  dating  on  orthogneisses,  but  are  only  seldom

preserved  in  the  minerals.  During  sedimentation  of  the

Hrádok  Formation  such  a  crustal  element  obviously  de-

livered  the  dominating  clastic  contribution.  The  ques-

tion  arises  if  such  ages  are  typical  of  the  Hrádok

Formation  or  restricted  to  local  occurrences  therein.

Metasandstone  sample  WCA-3/00  is  also  derived  from

the  Hrádok  Formation.  Here  a  metamorphic  overprint  in

the  matrix  is  visible.  Fine-grained  phengite  from  the  ma-

trix  could  be  separated  from  this  location  and  yielded  a

distinct  staircase  pattern  from  87 Ma  at  the  rim  to

142 Ma  in  the  core  (Fig. 7,  Table 6).  Alpine  metamorphic

3067                                          WCA-3/01 

Step  T (

o

C)  % 

39

Ar 

40

Ar* 

40

Ar*/

39

Ar 

App. age 

  1 

  620 

  1.1 

95.3 

10.55 ± 1.9 

317.6 ± 6.2 

  2 

  680 

  4.4 

97.4 

11.28 ± 0.9 

337.6 ± 3.2 

  3 

  720 

  6.8 

99.3 

11.54 ± 0.5 

344.7 ± 1.7 

  4 

  770 

22.4 

99.5 

11.49 ± 0.2 

343.4 ± 0.7 

  5 

  820 

14.6 

99.5 

11.45 ± 0.2 

342.3 ± 0.8 

  6 

  860 

  6.4 

99.1 

11.30 ± 0.8 

338.4 ± 2.7 

  7 

  925 

  7.1 

98.6 

11.20 ± 0.6 

335.6 ± 1.9 

  8 

  980 

  7.9 

98.4 

11.32 ± 0.6 

338.7 ± 1.9 

  9 

1060 

21.1 

99.2 

11.48 ± 0.2 

343.2 ± 0.5 

10 

1250 

  8.3 

98.3 

11.52 ± 0.3 

344.2 ± 1.1 

J = 0.018250 ± 0.4 %  

           Total gas age:      341.6 ± 2.8 Ma 

                                                      100 % plateau age:      341.6 ± 2.8 Ma

 

background image

469

40

Ar/

39

Ar DATING OF DETRITAL MICA FROM THE UPPER PALEOZOIC SANDSTONES (SLOVAKIA)

Fig. 8. 

40

Ar/

39

Ar apparent age diagram of gneiss pebble muscovite

from the Rudòany Formation conglomerate, sample WCA-9/01.

Table 7:  Analytic  data  of  gneiss  pebble  muscovite  from  the

Rudòany Formation conglomerate, sample WCA-9/01.

Table 8:  Analytic  data  of  detrital  white  mica  from  the  Rudòany

Formation sandstone, sample WCA-9/98.

Fig. 9. 

40

Ar/

39

Ar  apparent  age  diagram  of  detrital  white  mica

from the Rudòany Formation sandstone, sample WCA-9/98.

3058                                            WCA-9/01 

Step  T (

o

C)  % 

39

Ar  % 

40

Ar* 

40

Ar*/

39

Ar 

App. age 

  1 

  620 

  1.9 

94.4 

13.10 ± 0.7 

377.0 ± 2.3 

  2 

  680 

  4.2 

97.2 

13.19 ± 0.4 

379.4 ± 1.5 

  3 

  720 

  5.5 

98.1 

13.06 ± 0.3 

376.1 ± 0.9 

  4 

  770 

19.0 

98.7 

12.92 ± 0.2 

372.4 ± 0.7 

  5 

  820 

22.9 

99.4 

12.95 ± 0.4 

373.3 ± 1.4 

  6 

  860 

  9.3 

99.5 

12.93 ± 0.2 

372.6 ± 0.6 

  7 

  925 

  7.1 

98.9 

12.90 ± 0.3 

371.8 ± 1.0 

  8 

  980 

  8.2 

99.0 

12.92 ± 0.3 

372.4 ± 1.0 

  9 

1060 

17.2 

99.3 

12.89 ± 0.1 

371.7 ± 0.4 

10 

1250 

  4.7 

98.9 

12.89 ± 0.5 

371.7 ± 1.6 

J = 0.017745 ± 0.4  %    

                Total gas age:     373.0 ± 2.7 Ma  

        88 % plateau age:     372.4 ± 2.6 Ma

3051                                              G-9/98 

Step  T (

o

C)  % 

39

Ar  % 

40

Ar* 

40

Ar*/

39

Ar 

App. age 

  1 

  620 

  1.3 

93.4 

43.86 ± 1.6 

361.7 ± 5.4 

  2 

  680 

  3.2 

97.8 

45.71 ± 0.5 

375.5 ± 1.5 

  3 

  720 

  4.5 

98.5 

45.78 ± 0.9 

376.0 ± 3.0 

  4 

  770 

13.4 

99.1 

47.01 ± 0.1 

385.1 ± 0.5 

  5 

  820 

29.2 

99.7 

46.83 ± 0.4 

383.8 ± 1.3 

  6 

  860 

  9.2 

99.1 

47.33 ± 0.8 

387.5 ± 2.9 

  7 

  925 

  8.7 

99.7 

47.09 ± 0.3 

385.7 ± 0.9 

  8 

  980 

  5.3 

99.2 

47.59 ± 0.9 

389.3 ± 2.4 

  9 

1060 

17.6 

99.6 

47.22 ± 0.5 

386.6 ± 1.6 

10 

1250 

  7.6 

98.4 

47.53 ± 0.4 

388.9 ± 1.2 

J = 0.005062 ± 0.4  %   

                Total gas age:     384.7 ± 3.4 Ma  

        90 % plateau age:     385.8 ± 3.2 Ma

evolution,  in  the  Northern  Gemeric/Veporic  contact

zone,  was  related  to  the  growth  of  the  Western  Car-

pathian  orogenic  wedge  mainly  during  the  Cretaceous

time.  It  was  a  consequence  of  crustal  thickening  and

post-burial  thermal  relaxation  of  geotherms  during  the

initial  stage  of  exhumation,  connected  with  local  intru-

sions  of  the  Cretaceous  granitoids  (Vozárová  1990;  Janák

et  al.  2001).

One  can  expect  that  small,  still  older  age  domains  exist

in  the  tiny  phengites.  Because  stepwise  heating  of  multi-

grain  samples  cannot  produce  gas  from  a  single  domain,

it  is  always  a  mixture  from  different  domains.  We  there-

fore  interpret  this  result  as  a  typical  formation  age  over  a

prolonged  time  of  crystallization  with  some  strongly  re-

juvenated  clastic  remnants.

From  the  Westphalian  Rudòany  Formation  we  investi-

gated  two  samples.  Sample  WCA-9/01  (quarry  near  Zá-

vadka  village)  is  a  muscovite  from  a  large  orthogneiss

pebble,  it  yields  an  exceptionally  well  defined  plateau

age  of  372±3 Ma,  reflecting  the  age  of  cooling  of  the  or-

thogneiss  in  the  source  area  (Fig. 8,  Table 7).

A  slightly  older  age  (Fig. 9,  Table 8)  386±3 Ma  was

measured  on  detrital  micas  from  sandstones  near  Rudòa-

ny  village  (sample  WCA-9/98).  Such  Late  Devonian

ages  are  obviously  typical  in  the  Westphalian  clastic

sediments.  They  indicate  a  time  difference  between  cool-

ing  and  sedimentation  of  approximately  50–60 Ma.

Discussion and interpretation

The  fundamental  fact  that  the  substantial  part  of  the  late

Variscan  crust  was  remobilized  and  shortened  during  the

Alpine  compression  events,  leads  to  the  greatest  difficulty

in  the  reconstruction  of    the  Variscan  Orogeny  in  the

Western  Carpathians.  The  Western  Carpathian  Upper  Pa-

leozoic  sedimentary  basins  originated  in  consequence  of

Variscan  continent/continent  collision  of  two  micro-

plates.  Relics  of  these  colliding  microplates  are  pre-

served  as  fragments  of  crystalline  basement  rocks  within

the  main  crustal-scale  units  of  the  Alpine  Western  Car-

pathians  internides  (the  Tatricum,  Northern  Veporicum,

Southern  Veporicum,  Hronicum,  Zemplinicum  and  North-

ern  Gemericum;  Fig. 1).  The  three  types  of  Variscan  crys-

talline  fragments  in  the  Alpine  Western  Carpathians  were

distinguished  as:  the  Central  Western  Carpathian  Crystal-

line Zone (CWCZ), the Northern Gemeric Zone (NGZ) and

Inner  Western  Carpathian  Zone  (IWCZ).  The  main  differ-

ences  between  these  zones  are  in  their  Variscan  geody-

namic  evolution  as  well  as  in  the  chronological  and

spatial  evolution  of  Upper  Paleozoic  basins  (Vozárová

1998).  These  crustal  fragments  correspond  to  two  collid-

ing  microplates,  one  represented  by  medium-  to  high-

graded  crystalline  complexes  and  magmatites  of  the

CWCZ  (crystalline  rock  complexes  and  derived  Upper  Pa-

leozoic  post-orogenic  sequence  preserved  in  the  Tatricum,

background image

470

VOZÁROVÁ, FRANK, KRÁ  and VOZÁR

Veporicum, Zemplinicum and Hronicum) and the second
represented by the IWCZ low-grade crystalline (Lower Pale-
ozoic complexes of the Southern Gemeric Unit with its
Permian cover). The CWCZ were separated from the IWCZ
by the NGZ (preserved in the Northern Gemeric Unit), with
the Mississippian deep water turbidites (Noetsch—Veitsch—
Ochtiná zone after Flügel 1990; North Gemeric—Veitsch
zone after Neubauer & Vozárová 1990).

The Variscan convergence led to closing and suturing

of the Rakovec oceanic domain, easternmost remnants of
the Rheic Ocean. The main collision stage occurred dur-
ing the Late Devonian—Mississippian.  This was associated
with the origin of the intrasuture deep to shallow water em-
bayment during the Mississippian. Representative are sedi-
ments of the Ochtiná Group, primarily the turbidites of the
Hrádok Formation. The relatively old 465 Ma 

40

Ar /

39

Ar

age of detrital mica (Fig. 6, Table 5), from the metasand-
stones of the Hrádok Formation, reflects the existence of
crustal fragments with the imprint of intra-Ordovician
events in the supposed collision suture zone. (The term
“Caledonian” is used for magmatic-metamorphic process-
es as a certain time interval.) Similar Caledonian age data
are preserved within the Central and Southern Alps, in ar-
eas of a lower-grade Alpine overprint. Orthogneisses and
paragneisses from different complexes were dated at about
440—470 Ma, based on Rb / Sr whole-rock analyses and U-Pb
zircon data (Grauert 1966; Köppel et al. 1980 and others).
Eclogite facies metamorphism at ca. 470 Ma is indicated by
Sm-Nd analyses on whole rock and garnet in the Gotthard
Massif (Gebauer et al. 1988; Gebauer 1990). There is a clear
proof for compressional events starting with the formation
of eclogites, probably in a subduction zone setting, at ca.
470 Ma (Gebauer et al. 1988; Gebauer 1990).

Cambrian-Ordovician magmatic and metamorphic activi-

ty is also documented by 514± 24 Ma U-Pb zircon data
(Putiš et al. 2001) and 468± 24 Ma EMPA monazite ages
(Janák et al. 2002) from the Tatricum and Northern Vepori-
cum metamorphic complexes in the Western Carpathians.

The 

40

Ar /

39

Ar age of detrital mica from the Mississippian

of the Northern Gemeric Unit is the first evidence of Ordovi-
cian crustal fragments within the supposed Variscan collision
suture in the Western Carpathians. The sedimentary filling of
this intrasutural remnant basin was the only possibility for
the preservation of such old relics, because Variscan conver-
gence completely overprinted and reworked these Ordovi-
cian crustal fragments. The climax of the Variscan collision is
dated by the 

40

Ar /

39

Ar ages of detrital mica as well as or-

thogneiss pebble muscovite from the Westphalian Rudňany
Formation, which gave cooling ages of 385.8± 3.2 Ma and
372± 3 Ma, respectively (Fig. 8, Table 7).

The dynamics of convergence were modified by the dex-

tral translation between Europe and Africa (Ziegler
1988; 1990) and the formation of the Pennsylvanian conti-
nental basins in the CWCZ. The 

40

Ar /

39

Ar ages from detrital

mica of the Pennsylvanian and Permian sediments of the
Hronicum document clearly that increasingly older pieces of
the continental crust were involved in erosion due to wrench
faulting and rifting behind the Variscan suture zone
(Figs. 2, 3, 4, 5; Tables 1, 2, 3, 4). The relatively broad time

span in 

40

Ar /

39

Ar ages of detrital micas is related to

a temporal progression of the Hronicum rift system. The tec-
tonic development of this terrestrial rift, interpreted from the
distribution of lithofacies, the composition of detrital materi-
al and the character of synsedimentary volcanism, shows that
the upper-crustal extension was spatially variable. According
to a numerical model of Buck (1991) the mode of extension
is controlled by crustal thickness and thermal conditions at
the time of rifting. In a core-complex mode the upper-crustal
extension is concentrated over a narrow region, while the
lower crust is thinned over a broad area. This occurs when the
crust, due to crustal thickening in the compressional stage, is
hot and thick. The younger 

40

Ar /

39

Ar ages of detrital mica

from the Nižná Boca Formation, could reflect this initial
stage of rifting. When the lower crust flows slowly, then the
mode of extension depends on the strength of the lithos-
phere: a)  wide-rift  mode – hot and weak lithospere; b) nar-
row-rift mode – cold and strong lithosphere (Buck 1991).

As indicated by the chemistry of synsedimentary vol-

canism, and differences between the 1

st

 and 2

nd

 eruption

phase (Vozár 1997), the Upper Paleozoic Hronic sedi-
mentary basin may be an example of a region that has
passed through all three stages. Dominant silicic volcan-
ism during sedimentation of the Nižná Boca Formation
may have accompanied core-complex mode extension
and may have resulted from decompression melting. In
contrast, dominant andesite-basalt tholeiites as synsedi-
mentary volcanics during sedimentation of  the Malužiná
Formation (Vozár 1997; Dostal et al. 2003) indicate rath-
er colder and stronger lithosphere, with mantle-derived
magma ascent along rift-related faults. The sedimentary
architecture was controlled by episodicity of footwall-
generated sediment discharge into depocenters leading
to a heterogeneity of provenance. The 

40

Ar/

39

Ar ages of

detrital micas from Hronicum sediments support this
model.

Conclusions

Dating of detrital white mica taken from the Carbonifer-

ous-Permian sediments of the Western Carpathians provid-
ed important results for the determination of source areas.
Two groups of studied samples, from the Carboniferous
formations of the Northern Gemeric Unit and from the
Pennsylvanian-Permian sequence of the Hronic Unit
yielded the following ages:

1 – Northern Gemericum: A multi-grain sample from the

Pennsylvanian Hrádok Formation yielded a 465± 2.5 Ma
cooling age of the source area. This age proves the exist-
ence of Ordovician crustal pieces in the initial stage of
Variscan collision suture. Newly-formed fine-grained mus-
covite gave a distinct staircase pattern from 87 Ma at the
rim to 142 Ma in the core. It reflects a composite Alpine
overprint of these metasediments.

Multi-grain analyses of detrital mica and orthogneiss

pebble muscovite from the Westphalian Rudňany Forma-
tion yielded 385± 3 Ma and 372± 2.5, reflecting a uniform
Variscan source.

background image

471

40

Ar /

39

Ar DATING OF DETRITAL MICA FROM THE UPPER PALEOZOIC SANDSTONES (SLOVAKIA)

2  –  Hronicum:  Rift-related  sediments  of  the  Hronic  Unit

showed  a  trend  of  increasingly  older  detrital  mica  upward.
Cooling  ages  in  the  source  area  may  reflect  the  development  of
Hronicum  terrestrial  rift  and  the  heterogeneity  of  the  source
area,  with  gradual  rifting  and  cooling  of  the  lithosphere.

Acknowledgments:  The  authors  are  grateful  to  N.
Froitzheim,  F.  Ebner  and  I.  Petrík  for  their  helpful  sug-
gestions  and  critical  review  of  the  manuscript.  This  work
was  supported  by  Grant  No.  1 / 1036 / 04  from  Slovak
Grant  Agency  VEGA  and  Project  No.  APVT-51-002804.

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