GeolCarp_Vol59_No6_515

GEOLOGICA CARPATHICA, DECEMBER 2008, 59, 6, 515—524

www.geologicacarpathica.sk

Introduction

Paleomagnetic  study  has  been  widely  used  in  recent  years
for successful reconstruction of geodynamic development of
geologically  complicated  regions.  Such  study  has  been  car-
ried  out  for  several  years  in  southern  parts  of  the  Western
Carpathians,  as  well  (Márton  et  al.  1991,  1995;  Kruczyk  et
al. 1998; Túnyi et al. 2004).

The present paper extends the previous study concerning Tri-

assic  rocks  from  the  southern  part  of  the  Silicic  Unit  (Silica
Nappe, Slovenský kras Mts) in the area of Rožňava (Kruczyk et
al.  1998).  There,  in  the  studied  Hallstatt  limestones,  we  were
able  to  discern  two  secondary  components  of  NRM  (Natural
Remanent  Magnetization)  of  different  polarity  that  were  ac-
quired in two different times: the reversed component originat-
ed during the Oligocene and the normal component originated
during the Middle Miocene. The inclination of the Middle Mi-
ocene  component  indicates  that  it  was  acquired  at  a  paleolati-
tude of about 35°N. Values of declinations of R (Reverse) and
N (Normal) components indicated two CCW rotational phases
of the whole region: about 50° between Oligocene and Middle
Miocene and 30—40° in the post-Middle Miocene times. These
results  agreed  with  earlier  conclusions  by  Márton  et  al.  (1995
and papers cited there) concerning the Pelso tectonic megaunit
which also comprises the Silica Nappe.

Now we present the results obtained for the Triassic lime-

stones and serpentinites as well as Upper Cretaceous sand-
stones sampled in several exposures situated further to the

Post-Cretaceous differential block rotation in the Slovenský

raj Mts (Western Carpathians, Slovakia):

inferences from paleomagnetic data

IGOR TÚNYI

, JADWIGA KRUCZYK

, MAGDALENA KĄDZIAŁKO-HOFMOKL

and JÁN MELLO

Geophysical Institute, Slovak Academy of Sciences, Dúbravská cesta 9, 845 28 Bratislava, Slovak Republic; geoftuny@savba.sk

Institute of Geophysics Polish Academy of Sciences, Ks. Janusza 64, 01 452 Warszaw, Poland; magdahof@igf.edu.pl

State Geological Institute of Dionýz Štúr, Mlynská dolina 1, 817 04 Bratislava, Slovak Republic

(Manuscript received October 31, 2007; accepted in revised form March 14, 2008)

Abstract:  Results  of  paleomagnetic  study  of  Triassic  limestones,  sandstones  and  serpentinites  of  the  Stratená  and
Bôrka Nappes (Silicic and Meliatic Units), as well as of the Upper Cretaceous sandstones (Gosau Group) from the area
of the Slovenský raj Mts and Dobšiná area are presented. Characteristic components of remanence were isolated in six
localities representing several nappe slices. The isolated characteristic remanences are carried by secondary minerals.
They are of chemical origin and normal polarity. They were probably acquired during the latest Cretaceous at paleolatitudes
of about 28°N to 22°N showing that the area was in that time of African affinity. The whole study area moved from the
South to North, nappes and nappe slices formed due to intensive compressive Paleoalpine tectonics. During the transtensive
and extensive Neoalpine periods of Alpine orogenesis they disintegrated into different blocks which moved mainly
horizontally, some of them were backthrusted, or rotated. Finally they were amalgamated into the recent megablocks.
The individual rotations calculated against the reference declination Dref = 6° for European data for  the Miocene are as
follows: Dolka 1: 21° CW (Clockwise), Dolka 2: 15° CW, Dedinky: 14° CCW (Counter-clockwise), Kopanec: 41° CCW,
Dobšiná: 55° CCW, Dobšinská  adová jaskyňa: 16° CW.

Key words: Western Carpathians, Silicic and Meliatic Tectonic Units, Triassic limestones, Cretaceous sandstones,
paleomagnetism, paleorotations.

North, in the area of Slovenský raj Mts and vicinity of Dob-
šiná  town.  They  belong  to  the  northern  part  of  Silicic  Unit
(Stratená Nappe), to the Meliatic Unit (Bôrka Nappe) and to
the postnappe Gosau Formation. According to their geologi-
cal description (see the following part) each exposure repre-
sents  a  separate  (partial)  nappe  slice.  Our  previous
interpretation (Túnyi et al. 2004), based on preliminary col-
lection of samples suggested the presence of a primary com-
ponent  of  NRM  in  the  studied  rocks.  But,  as  we  were  not
quite  satisfied  with  the  results,  we  took  new  samples  from
some of the same exposures and from several new ones. Our
new results added to the previous ones lead to the new inter-
pretation – it seems that the studied rocks carry secondary
remanence  acquired  during  or  shortly  after  the  Late  Creta-
ceous. Nappe slices were independently rotated later, in con-
nection  with younger Alpine movements.

Geological outline

The paleomagnetic study was focused on the area of the

Slovenský Raj Mts and vicinity of Dobšiná (Fig. 1). Samples
were taken from rocks which were previously attributed to the
so  called  “North  Gemeric  Mesozoic”  (Mahe   in  Mahe   et  al.
1967). Recently interpretation became more complicated – 4
Alpine tectonic units in tectonic superposition (from the base
upward):  Veporic,  Gemeric,  Meliatic  (including  the  Bôrka
Nappe)  and  Silicic  (Stratená  and  Vernár  Nappes)  are  distin-

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TÚNYI, KRUCZYK, KĄDZIAŁKO-HOFMOKL and MELLO

guished here (Fig. 2). The Upper Cretaceous (Gosau Group)
and Paleogene sediments represent the overstepping post-
nappe complexes.

Structural measurements and facies relations have led to the

conclusion  that  the  nappes  were  thrust  one  above  the  other  in
the  direction  from  the  South  to  the  North  (in  today’s  coordi-
nates),  most  probably  in  the  Early  Cretaceous.  This  was  fol-
lowed by emersion and denudation of strata (prevailingly of the
upper parts of the Silicic Unit), and later by transgression of the
Upper Cretaceous formations (Gosau Group) over mostly Trias-
sic, to lesser extent Jurassic formations of the Silicic Unit.

Geological structure was later modified by sinistral transpres-

sional  movements  along  the  Muráň  strike-slip  fault.  These
movements resulted in origination of partial tectonic units and
slices of the Stratená Nappe, mainly that of the Glac partial unit
with the Červený Štros slice and Geravy partial unit with Hýl
slices (Mello et al. 2000a,b) (Fig. 2). Partial tectonic units and
slices  were  backthrust  upon  the  Upper  Cretaceous  sediments.
Together with the Vernár partial nappe from the opposite side
of the Muráň fault they form a typical fan-like structure. The or-
igin of this structure is very well dated in the Laramian period,
because  the  above  mentioned  backthrusting    involved  the  Se-
nonian  sediments  (Fig. 3)  and  predated  deposition  of  the
Eocene transgressive basal conglomerates of the  Borové For-
mation (Mello et al. 2000a,b).

Compressional and transpressional movements ceased at

the beginning of the Cenozoic period. No more nappes or
tectonic slices were formed later in the Inner Western Car-
pathians. The Paleogene formations are only slightly folded
and disturbed with several fault systems (E—W, NE—SW and
NW—SE directions, Filo in Mello et al. 2000b).

Due to the lack of Neogene sediments in the area it is not

possible  to  document  reliably  the  Neogene  tectonic  move-
ments,  but  from  the  records  in  older  formations  and  from
studies  of  Neogene  formations  in  neighbouring  lowland  ar-
eas it is obvious, that for the Neogene Period an extensional

Fig. 1. Situation sketch of the studied area.

Fig. 2. Geological units in the area of the Slovenský raj Mts and Dobšiná vicinity (according Mello et al. 2000) and sampling localities. Post-
nappe Formations: 1 – Podtatranská Group (Paleogene), 2 – Gosau Group (Late Cretaceous). Paleoalpine Nappes: SILICIC UNIT:
Stratená Nappe: 3 – Glac partial unit with Červený Štros slice, 4 – Geravy partial unit with Hý slices, 5 – Vernár Nappe. MELIATIC
UNIT

6 – “Meliatic Unit s.s.”, 7 – Bôrka Nappe. GEMERIC UNIT: 8 – Krompachy Group (Permian), 9 – Dobšiná Group (Carbonifer-

ous), 10 – Klátov and Rakovec Group (Devonian—Early Carboniferous). VEPORIC UNIT: Sedimentary cover: 11 – Foederata and Revúca
Group (Carboniferous—Triassic). Crystaline complexes: 12 – Krá ova ho a Complex, 13 – Faults, Alpine thrust contacts, contacts of partial
units and backthrusts, 14 – Line of geologic cross-section (Fig. 3). Sampling localities: Silicic Unit (Middle and Late Triassic): 1 – Dol-
ka 1, 2 – Dolka 2, 3 – Dedinky, 4 – Kopanec, 5 – Smižanská Maša, 6 – Biele Vody, 7 – Pod Kopancom, 8 – Stratená. Meliatic Unit
(Bôrka Nappe): 9 – Dobšiná (abandonned quarry). Gosau Group: 10 – Dobšinská adová jaskyňa. Arrows – paleomagnetic directions
(see Fig. 9).

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POST-CRETACEOUS DIFFERENTIAL BLOCK ROTATION IN THE SLOVENSKÝ RAJ MTS (W CARPATHIANS)

tectonics is characteristic. It is expressed mainly by faults
with different directions.

Sampling

For paleomagnetic measurements, 48 hand samples were

taken from 10 localities (Fig. 2):

A. Silicic Unit, Stratená Nappe – limestones of Middle

and Late Triassic: Dolka (1), Dolka (2), Dedinky (3), Ko-
panec (4), Smižanská Maša (5), Biele Vody (6); sandstones
of Early Triassic: Pod Kopancom (7), Stratená (8).

B. Meliatic Unit (Bôrka Nappe) – Middle Triassic ser-

pentinites: Dobšiná (9).

C. Gosau Group – Upper Cretaceous sandstones: Dob-

šinská adová jaskyňa (10).

Methodology

Rock-magnetic experiments leading to identification of mag-

netic minerals – carriers of natural remanence were performed
in  the  Warsaw  Paleomagnetic  Laboratory.  They  comprised
thermal  demagnetization  of  saturation  isothermal  remanent
magnetization (SIRM) acquired in the field of 5 T, during heat-
ing in air to 700 °C in non-magnetic space in the air (apparatus
of  TUS-Poland).  The  thermal  demagnetizing  curves  bring
blocking  temperatures  Tb,s  characteristic  for  ferromagnetic
minerals present in the studied specimen. Another thermomag-
netic  method, called Lowrie method (Lowrie 1990) consists on
magnetizing a specimen in three mutually perpendicular direc-

tions  in  high  field  (1.4 T),  intermediate  field  (0.4 T)  and  low
field  (0.1 T).  Thermal  demagnetization  of  these  three  compo-
nents  discerns  between  minerals  of  different  coercivities  and
blocking  temperatures.  For  several  specimens  mineralogical
analysis  in  reflected  light  was  also  performed,  unfortunately
amount of magnetic minerals – carriers of natural remanence
was  very  low  in  all  specimens  except  the  serpentinites  where
magnetite was observed (analysis was done by Siemiątkowski
from the Polish Geological Institute, Wrocław).

Standard paleomagnetic study was performed mainly in the

Slovak  Paleomagnetic  Laboratory  where  Natural  Remanent
Magnetization  (NRM) was cleaned thermally by consecutive
heating using non-magnetic furnace and measured with a JR-5
magnetometer  from  AGICO  comp.  Only  a  few  specimens
were demagnetized in the Warsaw Laboratory with alternating
field AF (cryogenic SQUID magnetometer with AF demagne-
tizer from 2G Enterprises, USA). All results of demagnetiza-
tion were analysed in the Warsaw Laboratory with the special
program package of Lewandowski et al. (1997). The final pa-
leomagnetic results were obtained only for six localities. They
are included in Table 1 and shown in Fig. 9a,b. The mean data
of isolated characteristic components are presented in situ and
after corrections in Fig. 9a,b.

Results

Silicic Unit

(1) Dolka (settlement) 1, Stratená Nappe, Geravy partial

unit, Dachstein organodetritic limestone (Late Triassic) – 5

Fig. 3. Geological cross-section through the SE part of the Slovenský raj Mts and Dobšiná vicinity (according Mello et al. 2000, partly modi-
fied). Postnappe Formations: 1 – Gosau Group (Late Cretaceous). Paleoalpine Nappes: SILICIC UNIT: Vernár Nappe: 2 – Dachstein
Dolomite (Late Carnian—Norian?), 3 – Lunz Member (Late Julian—?Tuvalian), 4 – Wetterstein Dolomite (Fassanian—Early Julian). Stratená
Nappe (Glac and Geravy partial Units): 5 – Dachstein Limestone (Late Carnian—Norian), 6 – Hallstatt Limestone (Norian), 7 – Reingra-
ben and Mürztal Member (Julian), 8 – Waxeneck Limestone (Carnian), 9 – Wetterstein Dolomite (Langobard—earliest Carnian), 10 – Wet-
terstein and Steinalm Limestone (Late Anisian—Cordevolian), 11 – Gutenstein Formation (Early Anisian), 12 – Werfen Formation
(Scythian). MELIATIC UNIT: “Meliaticum s.s.”: 13 – claystones, radiolarites (Late Jurassic), 14 – mèlange of shales, radiolarites, pale-
obasalts and serpentinites (Late Jurassic or younger). Bôrka Nappe: 15 – phyllites with metabasalt tuffs (Triassic—Jurassic?), 16 – serpen-
tinites (Triassic?). GEMERIC UNIT: 17 – Krompachy Group (Permian), 18 – Dobšiná Group (Carboniferous), 19 – Rakovec (a) and
Klátov (b) Group (Devonian—Early Carboniferous), 20 – Gelnica Group (Ordovician—Devonian). VEPORIC UNIT: 21 – Sedimentary cover
(Carboniferous—Triassic), 22 – Krá ova ho a Crystaline Complex.

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TÚNYI, KRUCZYK, KĄDZIAŁKO-HOFMOKL and MELLO

Fig. 4. Saturation isothermal remanent magnetization versus temperature (SIRM-T) curves characteristic for the studied localities.

hand samples. Thermomagnetic analysis (Fig. 4a) indicates
some amount of maghemite and hematite as carriers of mag-
netic remanence. Magnetic susceptibility attains small nega-
tive values (from —8 to —5

×10

—6

uSI) indicating domination

of  diamagnetic  minerals,  nevertheless  specimens  possessed
natural  remanence  of  40—550 µA/m,  measurable  with  both
SQUID  and  JR-5  equipment.  From  the  5  hand  samples  16
specimens became demagnetized thermally to 650 °C and 5
with  alternating  field  to  120 mT  (Fig. 6a,b).  Thermal  treat-
ment was effective up to 300—400 °C, at higher temperatures
the  intensity  of  NRM  increased  and  its  directions  became
chaotic.  Alternating  field  demagnetization  was  effective  up
to about 50—80 mT, in higher fields specimens acquired spu-
rious remanences. Analysis of demagnetization curves shows
the presence of one or two components: one isolated at lower

temperatures (up to 150—250 °C) and, sometimes, the second
one isolated at higher temperatures. Fig. 7a presents the direc-
tions  of  all  the  isolated  components  of  NRM.  The  cluster
formed in the first quadrant and composed of the lower tem-
perature  component  of  NRM  is  treated  as  the  component  of
characteristic remanent magnetization (ChRM, Fig. 8a). It was
obtained for 9 specimens (from the 5 hand samples) only from
thermal  demagnetization  results,  results  obtained  from  AF
cleaning lie far outside the cluster. The paleomagnetic results
are included in Table 1, as described above.

(2) Dolka (settlement) 2, Stratená Nappe, Glac partial

unit, Hallstatt limestone (Late Triassic) – 10 hand samples.
Magnetic susceptibility is negative and ranges from —8 to
—10

×10

—6

uSI, but despite the dominance of diamagnetic

minerals these rocks possess natural remanence with intensi-

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POST-CRETACEOUS DIFFERENTIAL BLOCK ROTATION IN THE SLOVENSKÝ RAJ MTS (W CARPATHIANS)

Locality
N/n

φ/λ [º]

Bedding

Az/dip [º]

Dm/Im

in situ [º]

αº

Plat

m [º]

Dabc/Iabc

[º]

Plat

abc [º]

Rotation [º]

∆D=Dref-Dm

Dolka 1
5/9

48.83/20.32 300/35

27/51

10/30

353/38 21

21CW

Dolka 2
5/11

48.85/20.33 290/10

21/47

9/25

10/46

15CW

Dedinky
6/12

48.83/20.34 300/25

352/47

12/15

338/29 15 14CCW

Kopanec
7/19

48.90/20.32

*0/50

**350/40

328/37

10/13

335/8

41CCW

Dobšiná
3/15

48.78/20.33 ***0/15

311/39

12/41

318/28 15 55CCW

Dobš. ľadová
jaskyňa 2/4

48.82/20.28 270/70

22/40

8/131

325/29 16

16CW

Geographical position of the region: Lat: 48.90N, Long: 20.30E. Reference direction for the study area for Miocene calculated according to the Stable
European data of (Besse & Courtillot 2002): Dref = 6º, Iref = 62º. * — bedding coordinates for samples nr 11–14; ** — bedding coordinates for samples
nr 53–58; *** — coordinates of the bedding of overlying sediments; N — number of hand samples; n — number of directions taken for calculations;
φ/λ — geographical coordinates of locality; Az — azimuth; Dm/Im — declination and inclination of characteristic magnetization for sample positions in
situ; αº

/k — parameters of Fisher statistics; Plat m — paleolatitude for samples position in situ; Dabc/Iabc — declination and inclination of characteristics

magnetization for samples position after bedding correction; Plat abc — paleolatitude for samples position after bedding correction.

Table 1: Final paleomagnetic results.

ty ranging from 2 to 400 µA/m (in one sample intensity ac-
quired  ca.  1100 µA/m).  It  was  easily  measurable  in  both
Laboratories. Thermomagnetic results indicate dominance of
hematite.  Its  presence  is  visible  on  the  SIRM-T  curve
(Fig. 4b)  and  on  the  Lowrie  thermal  curve  obtained  for  the
highest coercivity component acquired in 1.4 T (Fig. 5a). 17
specimens  were  demagnetized  thermally  and  4  with  AF.
NRM  usually  consisted  of  one,  rarely  of  two  components
(Fig. 6c,d).  Thermal  demagnetization  curves  revealed  two
components  of  remanence  –  one  isolated  at  low  tempera-
tures (up to 150 °C) and another one at higher temperatures.
In  the  AF  treated  specimens,  in  the  field  of  20—30 mT,  we
isolated the characteristic component of remanence with di-
rections close to the directions of the low temperature com-
ponent isolated thermally. In specimens cut from the single
strongly magnetic sample, the component with the same di-
rection was isolated along the whole curve of demagnetiza-
tion  (20—500 °C).  Taking  all  this  into  account  we  treat  the
described component as the characteristic one, the directions
of  all  isolated  components  are  shown  in  Fig. 7b  and  the  di-
rections of ChRM – in Fig. 8b. The final paleomagnetic re-
sults are included in Table 1 and in Fig. 9a,b.

(3) Dedinky (village), Stratená Nappe, Geravy partial

unit, Steinalm-limestone (Middle Triassic), 7 hand samples,
15 specimens demagnetized thermally and 3 – with AF.
Susceptibility ranges from —5 to 23

×10

—6

uSI showing the

dominating  presence  of  dia-  and/or  paramagnetic  minerals.
Various  amounts  of  ferromagnetic  minerals  are  responsible
for  the  natural  remanence  which  remains  in  a  broad  range:
2—800 µA/m.  Thermomagnetic  analysis  performed  by  heat-
ing  of  the  SIRM  (Fig. 4c)  and  by  the  Lowrie  method
(Fig. 5b)  indicate  the  dominant  presence  of  hematite.  Be-
cause  hematite  is  clearly  discernible  on  high-coercivity  and
intermediate-coercivity heating curves (Fig. 5b) we suppose
that it appears in two different grain sizes, perhaps connected
with different metamorphic events. The same plot shows the
presence of magnetite and some phase with a blocking tem-
perature  of  about  250 °C  (goethite?).  Alternating  field  de-
magnetization  reveals  presence  of  single  component  NRM

demagnetized  along  the  whole  spectrum  of  fields  (Fig. 6f).
Thermal cleaning usually revealed the presence of two com-
ponents  out  of  which  one  had  a  direction  corresponding  to
the direction isolated with AF (Fig. 6c). This component was
isolated in various ranges of unblocking temperatures – low
(up  to  150 °C),  intermediate  (up  to  250 °C)  and  high  range
(up to 500—650 °C). The directions of all the isolated compo-
nents are shown in Fig. 7c and the distribution of character-
istic directions – in Fig. 8c. The final paleomagnetic results
are presented in Table 1 and Fig. 9.

(4) Kopanec (saddle), Stratená Nappe, Červený Štros slice,

Reingraben  Member  (dark  sandy  shales,  Late  Triassic)  –  9
hand  samples.  Thermomagnetic  analysis  indicates  the  pres-
ence  of  hematite,  magnetite  and  goethite  (Fig. 4d,  Fig. 5c,d).
Magnetic susceptibility ranges from —10 to —6

×10

—6

uSI prov-

ing the dominance of diamagnetic minerals, but the intensity
of NRM is measurable and ranges from 6 to 300 µA/m. The
results of these rocks did not correspond to AF demagnetiza-
tion – after cleaning with 120 mT 70—90 % of initial NRM
was  left  (Fig. 6g),  due  to  a  high  amount  of  high-coercivity
minerals.  Thermal  cleaning  revealed  the  presence  of  either
one  or  two  components  of  NRM  isolated  at  lower  (up  to
150—300 °C) and higher temperatures (400—650 °C). The di-
rections of all of them are shown in Fig. 7d. Out of this dis-
tribution  we  isolated  the  characteristic  component  of  NRM
in  unblocking  temperatures  of  400—600 °C,  their  directions
are  presented  in  Fig. 8d.  The  final  results  are  given  in  Ta-
ble 1 and Fig. 9.

Four of the sampled localities from this unit: (5)

Smižanská Maša (6 hand samples), (6) Biele Vody (4 hand
samples), (7) Pod Kopancom (2 hand samples) and (8)
Stratená (2 hand samples) did not provide reliable paleomag-
netic results and will not be further discussed here.

Meliatic Unit (Bôrka Nappe)

(9) Dobšiná (abandoned quarry), serpentinites (probably

Middle Triassic in age), 3 hand samples. Thermomagnetic
study shows the presence of magnetite (Fig. 4e) and some

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TÚNYI, KRUCZYK, KĄDZIAŁKO-HOFMOKL and MELLO

Fig. 5. Results of the Lowrie method obtained for Dolka 2, Dedinky and Kopanec.

hematite, small grains of magnetite were also identified mi-
croscopically in reflected light. Magnetic susceptibility rang-
es from 2800 to 27,000

×10

—6

uSI and intensity of NRM

attains 15,000—20,000 µA/m. Thermal cleaning of five spec-
imens cut from 3 hand samples usually revealed two compo-
nents  of  NRM,  one  isolated  at  lower  temperatures
(50—300 °C)  and  another  one  isolated  at  high  temperatures
(350—650 °C) – Fig. 6j. The higher temperature component
is treated as the characteristic one. Fig. 7d shows the distri-
bution  of  the  directions  of  all  the  isolated  components,  and
Fig. 8d – distribution of directions of ChRM. The final re-
sults are included in Table 1 and Fig. 9.

Gosau Group (post-nappe formation)

(10) Dobšinská adová jaskyňa (railroad cut), sand-

stones  (Upper  Cretaceous).  Here  only  2  hand  samples  were
taken  in  the  field,  nevertheless  we  performed  the  standard
rock-magnetic  and  paleomagnetic  experiments  on  them.
Thermomagnetic  analysis  reveals  the  presence  of  goethite
and magnetite and/or maghemite (Fig. 4f). Magnetic suscep-
tibility  ranges  between  600  and  1100

×10

—4

uSI and the in-

tensity  of  NRM  –  between  about  200  and  570 µA/m.  4
specimens were demagnetized thermally, revealing the pres-
ence of either one or two components of NRM (Fig. 5j). In
specimens  where  two  components  were  isolated,  the  direc-
tions  of    the  one,  isolated  at  lower  temperatures  (350 °C),
corresponded to the direction of the single component isolat-

ed over the whole temperature range (till 600 °C) in speci-
mens from the other demagnetized sample. Components
with these directions were treated as characteristic ones and
their directions are shown in Fig. 8f, while the directions of
all isolated components are given in Fig. 7f. The final results
are included in Table 1 and Fig. 9.

Discussion

As we have shown in the previous part, the NRM from

five localities (Nos. 1—4, 9) comprising sediments is carried
by  a  small  amount  of  ferromagnetic  minerals  identified  as
magnetite/maghemite and hematite, and, more rarely – go-
ethite.  The main mineral in serpentinites is magnetite which
appears there in a great amount of small grains. According to
the  knowledge  of  the  serpentinization  processes  (see
O’Hanley  1996)  it  is  a  secondary  mineral  that  is  usually
formed  in  several  stages  of  serpentinization.  The  studied
sliver  of  serpentinite  probably  originated  somewhere  to  the
south as a fragment of an ophiolite suite and became obduct-
ed upon the Gemeric Unit as a part of Bôrka Nappe (Meliatic
tectonic unit, see Mello et al. 1998) in the Late Jurassic—Ear-
ly  Cretaceous.  Magnetic  minerals  identified  in  all  other  lo-
calities  –  maghemite,  hematite,  goethite  also  seem  to  be
secondary.

According to investigations of the Slovak karst Mts in

Kruczyk et al. (1998), the temperature in this area did not ex-

523

POST-CRETACEOUS DIFFERENTIAL BLOCK ROTATION IN THE SLOVENSKÝ RAJ MTS (W CARPATHIANS)

Fig. 9. Mean ChRM’s in situ (a) and after correction for bedding (b).

ceed 250 °C after its emplacement and it was justified that
characteristic remanence, which most probably is of chemi-
cal origin, was often isolated in the low temperature ranges.

The situation in the Stratená Nappe is different. Studies of

the CAI (Conodont Colour Alteration Indices, Gawlick et al.
2002), have revealed that in contrast to the Silica Nappe in the
region  of  the  Slovak  karst,  the  sedimentary  sequences  of  the
Stratená Nappe show a high thermal alteration (CAI 5.5—6.0).
It  coincides  with  our  results  obtained  for  Dedinky  village
where  secondary  ChRM  was  isolated  in  low,  intermediate
and high temperature ranges. In all localities the ChRM is of
normal polarity.

The geological description brings some constraints con-

cerning the age of the characteristic component – it had to
be acquired during or after the Late Cretaceous – the age of
the sandstones from the Dobšinská adová jaskyňa locality.
The post-Late Cretaceous age of this component is also im-
plied by similarities of its directions obtained for limestones
from localities Dolka 1 and Dolka 2 – exposures situated on
different sides of the backthrust plane (Laramian in age) sep-
arating the Glac and Geravy partial nappes of the Silicic
Unit. All this suggests that the characteristic chemical rema-
nence isolated here is of post-Laramian age.

Figure 9a,b presents distributions of mean directions ob-

tained for each exposure with their appropriate ovals of confi-
dences in situ (a) and after correction for tectonics (b). The in
situ pattern seems to be more logical and easier interpreted
than the pre-tectonic one. From Fig. 9 and Table 1 it is readily
seen that the in situ inclinations are not much different, as well
as the paleolatitudes, whereas after correction their scatter in-

creases. The rocks have obtained their ChRM during shifting
to the North when the layers were partially tilted.

Table 1 and Fig. 9a show that the in situ directions of lo-

calities  Dolka  1,  Dolka 2  and  Dobšinská  adová  jaskyňa  lie
very close together – statistically they represent one direction
of: Dm = 23°, Im = 46° and paleolatitude 27°N. A similar pale-
olatitude  (28°N)  is  shown  by  rocks  from  Dedinky,  although
their declination is different (352°). Kopanec and Dobšiná re-
veal slightly lower inclinations and paleolatitudes and declina-
tions  different  from  each  other  and  from  the  remaining
localities. We therefore surmise that the rocks from Kopanec
saddle and Dobšiná quarry acquired their remanences at lower
latitudes than those from the previous four localities.

The paleolatitudes of 31°N, 28°N and 21—23°N obtained

here  are  lower  than  the  paleolatitude  of  35°N  obtained  for
Triassic limestones from the region of the Slovak karst Mts
in  the  southern  part  of  the  Silica  Nappe  (Kruczyk  et  al.
1998). In the cited paper we stated that these rocks acquired
their secondary remanence during the Miocene and were lat-
er shifted to the North and rotated against the Stable Europe-
an Plate. Comparing paleolatitudes obtained from the Silica
Nappe  in  the  area  of  the  Slovak  karst  Mts  and  from  area
studied  here  we  suppose  that  the  latter  rocks  acquired  their
secondary remanence earlier than the former ones, when the
region of Silica was in more southern latitudes. Such low in-
clinations  implies  an  African  affinity  of  the  studied  region
when it acquired the isolated chemoremanent CRM. Accord-
ing to Westphal et al. (1986) the inclination calculated after
African data for the Late Cretaceous is about 48°N and our
results  indicate  that  the  studied  rocks  were  remagnetized  at
that time or only shortly afterwards. Later, the whole studied
area, especially the Silicic Unit was shifted from the South to
North  and  became  faulted,  folded  and  divided  into  smaller
tectonic  units  (nappe  slices).  The  observed  differences  in
declinations (Fig. 9a, Table 1) may reflect Tertiary rotations
of individual tectonic slices which took place over the whole
Carpathian  range  during  the  younger  periods  of  the  Alpine
orogeny.  This  tectonic  activity  ended  during  the  Miocene.
Kruczyk et al. (1998) stated that final rotation of the Slovak
karst area took place after the Middle Miocene. We assume
that  similar  events  took  place  during  the  same  time  in  the
area of the Slovenský raj Mts and Dobšiná vicinity and com-
pare  the  presented  data  with  the  reference  ones  calculated
from  data  for  the  Stable  European  Plate  for  the  Miocene
(Besse & Cortillot 2002) Dref = 6°N, Iref = 62° as we did for
rocks  from  the  Slovenský  karts  Mts.  The  amounts  of  rota-
tions are included in Table 1 – they are different for differ-
ent  localities  because  they  represent  different  nappe  slices
rotated  independently:  15—21° CW  slices  containing  Dol-
ka 1,  Dolka 2,  and  Dobšinská  adová  jaskyňa,  14° CCW
slice of Dedinky, 41° CCW slice of Kopanec and 55° CCW
slice  of  Dobšiná.  The  obtained  values  are  the  final  results,
we are not able to discern whether rotations took place dur-
ing one or more episodes or when they happened. The rota-
tions  calculated  against  the  Miocene  data  encompass  all
rotational episodes that could take place since the individual
slices  acquired  their  ChRM.  We  suppose  that  the  different
mean  directions  of  ChRM  found  in  Kopanec  and  Dobšiná
are  due  to  near-by  faults.  It  is  also  probable  that  the  small

524

TÚNYI, KRUCZYK, KĄDZIAŁKO-HOFMOKL and MELLO

sliver  of  the  Meliatic  Unit  represented  by  serpentinite  from
the locality Dobšiná moved differently than the nappe slices
of the Stratená Nappe. The results can be compared with pa-
leomagnetic  studies  of  Mesozoic  carbonates  in  the
Strážovské  Vrchy  Mts  in  the  Central  Western  Carpathians
(Grabowski  et  al.  in  print)  where  secondary  magnetization
probably  dating  from  the  Late  Cretaceous  was  also  identi-
fied. In comparison with results from the Southern and East-
ern  Slovakia  as  well  as  from  the  Spišsko  Gemerské
Rudohorie  Mts  (Inner  Western  Carpathians)  we  can  con-
clude  that  the  Miocene  paleodirections  obtained  from  the
sedimentary and alternated rocks of those areas have similar
trends (Márton et al. 1996, 2000; Kruczyk et al. 2002).

Conclusions

Characteristic components of remanence were isolated in

six localities representing different nappe slices. Characteris-
tic remanences are carried by secondary minerals and are
overprints by remanence of chemical origin and normal po-
larity. They were acquired in the Upper (or uppermost) Cre-
taceous at paleolatitude of about 28°N to 22°N showing that
the area was at that time of African affinity.

The whole study area moved from South to North, and the

nappe slices were formed due to intensive tectonics and ro-
tated during the younger periods of Alpine orogenesis in co-
incidence with tectonic movements of the Slovak Western
Carpathians.

Acknowledgments: The study was performed in the frame-
work of international cooperation program between the Insti-
tute of Geophysics of the Slovak Academy of Sciences and
the Institute of Geophysics of the Polish Academy of Scienc-
es as well as with support of VEGA Grant No. 7008.

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