GeolCarp_Vol59_No2_89

GEOLOGICA CARPATHICA, APRIL 2008, 59, 2, 89—102

www.geologicacarpathica.sk

Introduction

During  the  latest  Carboniferous-Early  Permian  times,  the
final  phase  of  the  Variscan  orogenic  extension  produced
series  of  small  strike-slips  and  extensional  continental
basins  across  the  Central  and  Inner  Western  Carpathians
realm.  Within  these  basins  continental  successions  of  Upper
Pennssylvanian-Cisuralian  (Stephanian  to  Autunian)  age
were  deposited.

Following the end of Variscan contraction in the latest

Carboniferous  times,  subsequent  Stephanian  and/or  Early
Permian  magmatic  activity  and  basin  formation  in  both
the  internal  Variscides  (the  area  within  the  Central
Western  Carpathians)  and  the  external  Variscides  (the  area
of  the  Inner  Western  Carpathians)  took  place.  Within  the
external,  the  Inner  Western  Carpathian  Zone,  post-
Variscan  sequences  are  developed  only  in  the  Southern
Gemeric  Unit.  Here,  the  Early  Permian  autochthonous
continental  Rožňava  Formation  (lower  part  of  the
Gočaltovo  Group  defined  by  Bajaník  et  al.  1981),  is

Upper Jurassic—Lower Cretaceous tectonothermal events in

the Southern Gemeric Permian rocks deduced from electron

microprobe dating of monazite

(Western Carpathians, Slovakia)

ANNA VOZÁROVÁ

, PATRIK KONEČNÝ

, JOZEF VOZÁR

and MILOŠ ŠMELKO

Comenius University Bratislava, Faculty of Natural Sciences, Department of Mineralogy and Petrology, Mlynská dolina, pav. G,

842 15 Bratislava, Slovak Republic; vozarova@fns.uniba.sk

State Geological Institute of Dionýz Štúr, Mlynská dolina 1, 817 04 Bratislava, Slovak Republic; konecny@gssr.sk

Geological Institute, Slovak Academy of Sciences, Dúbravská cesta 9, P.O. Box 106, 840 05 Bratislava, Slovak Republik; geoljovo@savba.sk

(Manuscript received January 15, 2007; accepted in revised form December 13, 2007)

Abstract: The age and chemical composition of monazite from the Permian acid metavolcanic/volcaniclastics of the
Southern Gemeric Unit (from the 1

and 2

volcanogenic horizons of the Rožňava Formation) and the Bôrka Nappe (the

Bučina Formation) was studied by the microprobe chemical method. Monazites from the 2

volcanogenic horizon of the

Rožňava Formation as well as from the Bôrka Nappe occur mostly in the form of small irregular grains about 5—10

µm

in size always surrounded by the metamorphic white mica-phengite. Although substantial zonality in single grains was
not observed, inter-granular variation in composition is much pronounced and it is mainly attributed to the variation in
ThO

concentration in the range from 0.9 to 14.5 wt. % (5.1 wt. % in average). Monazites from the 1

volcanogenic

horizon of the Rožňava Formation are larger, ~ 30—40

µm in diameter, and most of them are showing concentric zonality

related to the age. Rounded cores mostly of Permian age are surrounded by Alpine rims. ThO

concentration is more

restricted up to 7.2 wt. %. The average is correspondingly lower  ~ 3.5 wt. %. The majority of the monazites from the
Permian  acid  metavolcanic  rocks  record  an  Alpine  tectonothermal  event  around  148 ± 8 Ma.  Alpine  age  data  divided
according  to  the  statistical  modeling  present  two  successive  sub-events  yielding  ages  of  167 ± 12  and  136 ± 10 Ma.
Jurassic event is interpreted as a strong reworking linked to the subduction/accretion processes. Obduction of the Meliata
accretionary prism, and strong subduction-related fluid flow over the Southern Gemeric domain including its Permian
envelope  unit  are  presumed.  The  successive  Early  Cretaceous  (136 ± 10 Ma)  compression  within  the  Inner  Western
Carpathians  domain  was  followed  by  polyphase  Alpine  tectonic  evolution  connected  with  the  gradual  Cretaceous
collision and indentation at about 100 Ma. The evidence for the Early Permian magmatic event at 276 ± 25 Ma in the 1

volcanogenic horizon of the Rožňava Formation recorded in the corroded monazite cores is presented for the first time.

Key words: Western Carpathians, Southern Gemeric Unit, monazite dating, Early Permian metavolcanites, Alpine
overprint.

considered as a relic of the former basin filling related to
the initial stage of post-Variscan rifting (Fig. 1a). The
compositionally

mature

siliciclastic

sediments

are

connected with the rift-related rhyolite-dacite subaerial
volcanism.

The Southern Gemeric crystalline basement complex

and  its  Permian  envelope  is  overthrusted  by  the  Late
Paleozoic—Mesozoic  Bôrka  Nappe  complexes  of  the
Meliatic  Unit  (Fig. 1b).  Within  the  our  study  area,  the
Bôrka  Nappe  Late  Paleozoic  sequence  is  represented  by
the  Bučina  Formation  sequence.  This  is  composed  of  a
huge  mass  of  rhyolite-dacite  volcaniclastics  associated
with  scarce  volcanites  (Mello  et  al.  1998).  Lithologically
is  very  similar  to  the  Southern  Gemeric  Permian  envelope
unit.  This  was  the  reason  why  the  whole  Permian  sequence
of  the  Bôrka  Nappe  was  formerly  classified  as  the
Rožňava  Formation,  in  spite  of  basic  differences  in  the
tectonic  position  and  tectonometamorphic  deformation  of
different  parts  (Bajaník  et  al.  1984).  For  this  reason,  the
main  goal  of  our  investigation  was  the  age  determination

JURASSIC—CRETACEOUS TECTONOTHERMAL EVENTS DEDUCED FROM ELECTRON MICROPROBE (SLOVAKIA)

of the acid volcanogenic horizons in the two tectonic
units and the correlation of their tectonothermal history.

On condition of negligible initial common lead in

monazite

the

total

measured

microprobe

corresponds  to  the  age  and  Th  contents  (Suzuki  &  Adachi
1991a,b,  1994;  Montel  et  al.  1996).  The  monazites  present
in  the  Southern  Gemeric  and  the  Bôrka  Nappe  acid
metavolcaniclastic  rocks  were  used  for  chemical  dating  of
the  magmatic  and  metamorphic  events.

Geological setting

The late Variscan, post-orogenic overstep sequence of

the  Southern  Gemeric  Unit  (Fig. 1a)  is  represented  only
by  the  Permian  continental  and  near-shore,  lagoonal-
sabcha  sedimentary  complexes.  They  unconformably
overlapped  their  Lower  Paleozoic  basement,  the  volcano-
sedimentary  deep-water  turbidites  of  the  Gelnica  Group
and  the  Štós  Formation  (defined  in  the  Variscides  as  the
Gelnica  Terrane,  Vozárová  &  Vozár  1996).  The  setting  of
the  Permian  envelope  sequence  is  identical  in  almost  all
localities.  It  occurs  either  in  the  tectonic  underlier  of  the
high-pressure  Bôrka  Nappe  of  the  Meliatic  Unit  or
directly  below  the  Turnaic  Unit.

The Permian volcano-sedimentary complex is generally

characterized  by  a  high  content  of  mineral  mature  detritus
mainly  in  its  basal  part.  Conspicuous  upward  fining  is
accompanied  by  a  relative  decrease  of  mineralogical
maturity  and  grain-size  of  sediments  (Vozárová  1977).  The
whole  sequence  is  subdivided  into  two  lithostratigraphic
units:  the  Rožňava  and  Štítnik  Formations  (Fig. 2).

The characteristic lithotype of the Rožňava Formation

is the oligomictic, quartzose conglomerate, with the
indistinct

stratification.

The

whole

sequence

subdivided  vertically  into  two  large  cycles,  starting  with
conglomerate  horizons  at  the  base  of  each  and  a
sandstone-shale  member  between  their  two.  Dominant
are  stream  channel  and  sheet-flood  deposits,  with
unimodal  transport  system.  On  the  basis  of  microflora
(Planderová  1980)  the  Early  Permian  age  of  the  Rožňava
Formation  is  assumed.  Both  conglomeratic  horizons  are
connected

with

rhyolite-dacite

subaerial

volcanism.

Their  chemical  composition  corresponds  to  the  calc-
alkaline  and  alkaline  magmatic  type.  This  intra-basin
acid  volcanism  took  place  within  two  relative  short  time
periods,  and  ceased  at  the  end  of  main  phase  of  crustal
extension  as  a  response  to  the  Variscan  late-orogenic
collapse.  The  magma  ranges  in  composition  from  calc-
alkaline  rhyolite  and  rhyodacite  to  alkaline  quartz-alkali
feldspars  trachyte.  The  emplacement  of  the  Rožňava
Formation  acid  volcanites  was  accompanied  by  the
eruption  of  volcanic  ashes,  laterally  extensive  block  and
ash  flows  and  their  reworked  epiclastic  deposits.  The
initial  stage  of  volcanism  (1

conglomeratic horizon) is

associated with ignimbrites. The schematic overview of
lithostratigraphic relationships is shown on Fig. 2.

The gradually prograding Štítnik Formation is a

monotonous complex of cyclically alternating sandstones,

siltstones  and  shales.  Lenses  of  carbonatic  sandstones  and
dolomitic  limestones  (calcitified  dolostone,  “dedolomite”)
with  intercalations  of  shales  occur  only  in  its  upper  part.
Thin  lenses  of  phosphatic  sandstones  and  sediments  with
extremely  high  content  of  albite  (albitolites)  are  solitary.
The  sediments  contain  relatively  high  amounts  of  rhyolite/
dacite  detritus,  presumably  redeposited  from  the  Rožňava
Formation.  The  sedimentary  environment  is  interpreted  as
alluvial-lacustrine  and  lacustrine,  with  high-alkaline  and
eutrophic  lakes  in  some  places,  prograding  into  near-shore,
lagoonal-sabcha  facies  (Vozárová  &  Vozár  1988;  Vozárová
&  Rojkovič  2000).  Late  Permian  biostratigraphic  age
determinations  are  known  only  from  the  uppermost  part  of
the  Štítnik  Formation  (Šuf  1963).

Sequences of the Southern Gemeric Permian are

deformed  and  recrystallized,  within  metamorphic  grade
reaching  P-T  conditions  from  the  anchizone  to  low-
temperature  part  of  the  greenschist  facies  (Šucha  &  Eberl
1992;  Vozárová  1996;  Vozárová  &  Rojkovič  2000).

In the Nižná Slaná Depression (to the north of Štítnik

and in the vicinity of Jelšava) numerous tectonic scales

Fig. 2. Gočaltovo Group lithostratigraphic scheme: 1 – con-
glomerate, 2 – sandstone, 3 – shale, 4 – dolomitic limestone,
5 – albitolite, 6 – phosphatic sandstone, 7 – rhyolite—dacite py-
roclastics, 8 – tuffaceous/sedimentary mixed rocks, 9 – rhyolite-
dacite.

VOZÁROVÁ, KONEČNÝ, VOZÁR and ŠMELKO

of  the  Upper  Paleozoic  and  Mesozoic  rock  complexes  of
the  Bôrka  Nappe  occur  (Fig. 1b).  The  high-pressure
Bôrka  Nappe  rock  complex  represents  a  relic  of  the
accretionary  prism  originated  as  a  result  of  the  Jurassic
subduction

the

oceanic

bottom

and

thinned

continental  margin  of  the  Meliata  Ocean  (Mello  et  al.
1998).  Their  relationship  to  the  underlying  Lower  and
Uper  Paleozoic  rock  complexes  of  the  Southern
Gemericum  is  tectonic  in  all  sections.  The  part  of  the
Bôrka  Nappe  tectonic  scales  (defined  in  the  Jasov  and
Bučina  Formations)  consists  of  siliciclastic  sediments
associated  with  the  huge  mass  of  rhyolite-dacite
volcaniclastics  and  volcanites  in  places  (Fig. 3).  The
complex  rich  in  acid  volcanic  material  was  first  denoted
by  Fusán  (1959)  as  the  Bučina  Beds  and  linked  to  the
autochthonous

Late

Paleozoic

envelope.

Further

investigations  proved  their  allochthonous  position  on
the  Paleozoic  rock  complexes  of  the  Southern  Gemeric
Unit.  Later,  the  whole  complex  was  redefined  as  the
Bučina  Formation  and  coordinated  with  the  Bôrka
Nappe  (Mello  et  al.  1997,  1998).  But  likewise,  a  distinct
lithological

similarity

(mature

clastic

detritus

and

petrological  and  geochemical  equal  volcanism)  with  the
Southern  Gemeric  Rožňava  Formation  exists  (Bajaník  et
al.  1984).

In contrast to the Rožňava Formation, the Bučina

Formation  with  only  a  minor  sedimentary  fill  contains
mostly  products  of  rhyodacitic  volcanism,  namely  lava
flows,  ash  beds  generally  of  phreatomagmatic  origin  and
ignimbrites.

Sediments,

such

redeposited

acid

volcaniclastics mixed with mineral mature quartzose
detritus

conglomeratic

and

sandy

grain

size

distribution are most frequent. Even though, no
biostratigraphic data from sediments had been obtained,
the

high

grade

petrological

and

geochemical

similarity of the both volcanic formations justifies the
correlation of the Bučina Formation with the Permian.

Analytical methods

The monazites were analysed using the electron micro-

probe  Cameca  SX-100  in  the  Department  of  Microanaly-
sis  at  State  Geological  Institute  of  Dionýz  Štúr  (Slovak
Geological  Survey)  in  Bratislava.  The  analytical  condi-
tions  suitable  for  the  monazite  dating  have  to  meet  some
compromising  measurement  conditions  to  achieve  suffi-
cient  counts,  measuring  time  and  the  degree  of  contami-
nation  of  the  analysis  place.  It  was  used  15 kV  accelerat-
ing  voltage  which  is  sufficient  for  REE,  Th,  U,  Pb  lines
excitation.  It  is  less  harmful  for  contamination  of  the
analysis  place  and  for  the  ZAF  correction  factors  that  are
lower  in  the  case  of  20 kV.  Lead  was  measured  130 s,  Th
35 s,  U  65 s,  REE  25 s  and  all  other  elements  15 s.  High
beam  current  100 nA  was  used  to  achieve  the  sufficient
counts  for  statistical  counting.  Natural  minerals  and
chemical  compounds  were  used  for  the  calibration:  Al-
Al

Si-SiO

P-apatite,

Ca-wollastonite,

REE-

(REE)PO

, Pb-PbS, U-UO

and Th-ThO

. Th, U, Pb, Y, P

were measured with LPET, REE with LLIF, As-GaAs

and

Si,  Al  with  TAP  analysing  crystal.  X-ray  Ka  lines  were
used  for  Si,  Al.  Ma  lines  were  used  for  Th,  Pb  and  Mb
line  for  U,  La  and  Lb  line  for  REE  elements.  The  existing
interferences  between  REE  elements  and  PbM

-YL

and UM

-ThM

were corrected with an empirical cor-

rection factor.

Chemical monazite analyses were recalculated to the

ages  using  the  statistical  model  developed  by  Montel  et
al.  (1996).  A  program  DAMON  developed  by  P.  Konečný
(during  2004—2006)  was  used  for  recalculation  procedure
as  well  as  age  histogram  and  isochrone  construction.  More
detailed  information  on  measurement  conditions  and  the
recalculation  method  is  given  in  Konečný  et  al.  (2004).

Sample characterization

Four samples were selected for the electron microprobe

dating  of  monazite  from  the  Permian  metavolcanic  rocks
of  the  Southern  Gemericum  and  the  Bôrka  Nappe
(Fig. 1a,b).  Samples  1/SM  and  2/SM  are  located  in  the
upper  conglomerate  horizon  of  the  Rožňava  Formation,
in  the  area  of  Šebeková  Hill,  south  of  Gočaltovo  village.
Both  are  associated  with  the  second  volcanogenic

Fig. 3. Bôrka Nappe lithostratigraphic scheme based on Mello et
al. (1997, 1998).

JURASSIC—CRETACEOUS TECTONOTHERMAL EVENTS DEDUCED FROM ELECTRON MICROPROBE (SLOVAKIA)

concentrations below 0.5 wt. % resulting in large stan-
dard deviation of calculated chemical age.

The BEI images cannot reveal the zonality in single

small  monazites.  The  chemical  composition  between
grains  has  quite  substantial  variability.  Most  of  the
chemical  changes  are  attributed  to  the  thorium.  ThO

varies  from  very  low  concentrations  of  0.9 wt. %  up  to
14.5 wt. %  (5.1 wt. %  in  average).  The  uranium  content  is
quite  low;  the  UO

concentrations are between 0.023 and

0.735 wt. % (0.278 wt. % in average).

The monazites from the sample 4/SM (1

volcanogenic

horizon  of  the  Rožňava  Formation)  are  different.  The
main  feature  is  their  concentric  zonality  (Fig. 4d,e,f).  The
resorbed  lighter  cores  are  surrounded  by  distinct  dark
zones  which  gradually  transform  into  lighter  broad  rims.
The  monazites  here  are  bigger  than  in  previous  samples
(1,  2,  3/SM)  having  an  average  size  of  about  30—40

µm.

Average concentration in ThO

is lower, ~ 3.5 wt. % and

reaches up to 7.2 wt. %. The range in UO

concentration

is comparable with other samples.

The chemical composition of the monazite from all

samples  recalculated  to  end-members  is  illustrated  in
Fig. 5.  The  major  solid  solution  part  of  the  crystal  struc-
ture  is  filled  by  monazite-(Ce).  The  cheralite  and  hutton-
ite  content  is  even  less.  The  monazite-(Ce)  content  is  rel-
atively  high,  94.2 mol %  in  average  (from  85.1  to
99.1 mol %).  Almost  pure  monazite-(Ce)  end-members
are  also  present.  The  average  huttonite  content  is  low
(1.5 mol %).  Few  monazites  can  contain  up  to  7.5 mol %.
Cheralite  content  is  higher  than  the  huttonite,  reaching
4.3 mol %  on  average  with  the  range  from  0  to
13.2 mol %.

The yttrium concentration in the majority of studied

monazites is relatively low (between 0.3—0.5 wt. % Y

)

suggesting

subordinate

xenotime-type

substitutions.

Elevated Y

concentrations above 1.0 wt. % (up to

3.3 wt. %) have been encountered in a few monazites
from sample 4/SM.

Dating results

The monazite chemical analyses and apparent ages

from  the  Permian  volcanic  rocks  of  the  Gočaltovo  Group
and  Bučina  Formation  are  listed  in  Table 1  and  Table 2.
All  48  apparent  obtained  ages  are  presented  in  the  age
histogram  (Fig. 6).  They  are  clearly  separated  into  three
main  age  populations:  Silurian,  Permian  and  Alpine.  The
oldest  Silurian  age  records  were  found  only  in  two  mona-
zite  cores  coming  from  the  1

volcanogenic horizon of

the  Rožňava  Formation  (sample  4/SM).  Permian  mona-
zites  are  frequently  present  in  the  sample  4/SM  and  only
one  record  has  been  found  in  the  2

volcanogenic hori-

zon of the Rožňava Formation (sample 2/SM). Alpine
monazites are present in all the studied samples.

Sample 1/SM: the age is based on 8 points measured in 6

monazite  grains  giving  a  weighted  average  of  149 ± 30 Ma.
The  MSWD = 0.6  suggests  a  more  concentrated  data  set
relative  to  the  normalized  Gaussian  distribution.  Sample

horizon of the Rožňava Formation. Sample 4/SM comes
from the basal part of the Rožňava Formation (1

volcanogenic  horizon).  Sample  3/SM  is  located  near  the
Bučina  height,  in  the  Bučina  Formation,  which  is  the
main  lithostratigraphic  sequence  of  the  partial  tectonic
scale  of  the  Bôrka  Nappe  (Fig. 1b).

The Southern Gemeric Permian metavolcanites and

metavolcaniclastics  have  a  mainly  felsitic  and  vitroclas-
tic  character.  The  related  metavolcaniclastics  contain  a
small  amount  of  deformed  relics  of

β-quartz, perthitic al-

kali  feldspars  and  scarce  biotite  as  well  as  abundant  frag-
ments  of  felsites  and  recrystallized  volcanic  glass.  The
volcaniclastics  from  the  first  volcanogenic  horizon  of  the
Rožňava  Formation  are  characterized  by  distinct  preser-
vation  of  ignimbrite  structure,  with  relics  of  deformed
“fiam

”. The newly formed metamorphic mineral assem-

blage  is  represented  by  the  fine-grained  aggregate  of
quartz + phengite ± chlorite ± albite.  The  chemical  compo-
sition  of  the  acid  volcanites  largely  falls  into  rhyolite-dac-
ite  peraluminous  suite.  They  typically  contain  4.5 %—
5.4 %  alkalies  highly  dominated  by  K

O and have fairly

low levels of MgO, CaO and FeO

. The Rožňava Forma-

tion volcanites are generally markedly enriched in B, Zr
and Rb and only slightly enriched in La and Y and deplet-
ed in Ba, Sr and V (Vozárová in Marsina et al. 1999).

In petrological and geochemical composition, the

Bučina  Formation  volcanites  and  volcaniclastics  as  well
as  zircon  typology  show  a  distinct  similarity  with  the
South-Gemeric  rhyolite-dacite  volcanism.  Both  represent
a  rift-related  A-type  magmatism  (Šmelko  2007)  connect-
ed  with  the  Variscan  post-orogenic  extension  and  ther-
mal  relaxation.  This  coincides  with  the  former  results  of
Broska  et  al.  (1993)  based  on  zircon  typology.

Monazite

Monazite, a REE bearing phosphate, is largely distrib-

uted in the studied rocks. Its grain size in the samples 1/
SM, 2/SM (2

volcanogenic horizon of the Rožňava

Formation)  and  3/SM  (tectonic  scale  of  the  Bôrka  Nappe)
varies  from  1  to  20 µm,  while  the  crystals  about  5—10 µm
prevail.  The  monazites  are  mostly  surrounded  by  the
metamorphic  white  mica—phengite.  In  some  places  the
columnar  monazite  is  parallel  oriented  with  the  lepido-
blastic  orientation  of  the  metamorphic  mica  (Fig. 4a).
Most  grains  are  angular,  hypidiomorphic  in  shape
(Fig. 4b,c).  It  seems  that  almost  every  small  monazite
grain  is  homogeneous  in  composition,  although  small
size  prevents  a  detailed  observation  of  the  zonality  in
BSE.  Some  zonality  is  observed  only  in  a  few  larger
grains  (Fig. 4b,c).  Dark  zones  located  in  the  otherwise
homogeneous  monazite  grains  show  unclear  relations  to
the  monazite  shape  or  core-rim  position.  In  Fig. 4b  the
dark  zone  can  probably  be  interpreted  as  some  type  of
oscillation  growth  (?).  In  Fig. 4c  the  dark  zone  occupies
the  center  of  the  small  monazite  grain  while  the  larger
grain  in  the  vicinity  is  fairly  homogeneous.  The  dark
zones  are  mostly  free  of  Th  or  can  reach  only  negligible

VOZÁROVÁ, KONEČNÝ, VOZÁR and ŠMELKO

2/SM

: the weighted average of 15 points measured in 13

monazites gives 149 ± 10 Ma (MSWD = 0.39). Only one
grain

was

less

confidently

dated

(?)

Permian

(264 ± 128 Ma),  due  to  a  large  error  resulting  from  a  low  Th
content.  Sample  3/SM:  the  chemical  age  obtained  from  10
points  measured  in  9  monazite  grains  is  164 ± 26 Ma
(MSWD = 0.43).    Sample  4/SM:  nine  monazite  grains  were
analysed;  we  obtained  22  point  data  which  split  into  three

Fig. 4.  BSE  image  of  selected  monazite  grains.  a  –  Irregular  monazite  grain  surrounded  by  the  metamorphic  white  mica—phengite
(sample  1/SM);  b,  c  –  Dark  zones  in  monazites  having  unclear  relation  to  the  mineral  shape  (sample  1/SM);  d  –  Hypidiomorphic
monazite  grain  with  the  lighter  Jurassic  core  and  the  youngest  Early  Cretaceous  rim  (sample  4/SM);  e  –  Hypidiomorphic  monazite
grain  with  the  light  Permian  core  and  darker  rim  of  Jurassic  age  (sample  4/SM);  f  –  Irregular  monazite  grain  with  Permian  core
displaying of strong resorbtion and bordered by an Early Cretaceous rim (sample 4/SM).

age groups. The oldest Silurian group (2 grains) gives ages
of 421 ± 95 and 413 ± 72 Ma. Silurian ages are always situat-
ed

the

monazite

cores.

Permian

data

group

(average = 275 ± 13 Ma,  8  grains)  is  always  preserved  in  the
light  distinctly  resorbed  monazite  cores.  Young  Alpine
group  ages  has  approximately  the  same  range  as  in  the  other
samples,  giving  the  average  age  147±25 Ma  (9  grains).  The
two  youngest  ages  ~100 Ma  were  revealed  in  the  thin  light

JURASSIC—CRETACEOUS TECTONOTHERMAL EVENTS DEDUCED FROM ELECTRON MICROPROBE (SLOVAKIA)

rim  (Fig. 4d).  Almost  all  monazites  have  corroded  Permi-
an  cores  surrounded  by  dark  zone  low  in  Th  preventing
reliable  dating  and  subsequently  rimmed  by  Alpine  mon-
azite.

Discussion

The Alpine tectonic evolution of the Western Car-

pathian  internides  is  traditionally  interpreted  as  a  result
of  Cretaceous  crustal  shortening  of  Variscan  basement
crustal  fragments  and  their  Upper  Paleozoic  basin  fillings
associated  with  décollement  of  Upper  Paleozoic-Meso-
zoic  sedimentary  sequences  (Andrusov  1936,  1968;  An-
drusov  et  al.  1973;  Plašienka  et  al.  1997).  This  fact  was
well  documented  by  the  radiometric  ages  of  newly
formed  white  mica  from  the  Gemeric  Unit  (

Ar/

cooling  ages  ranging  from  106  to  82 Ma,  Dallmeyer  et  al.
1996;  Vozárová  et  al.  2005,  from  W  part  of  the  Northern
Gemericum)  as  well  as  the  Early  Cretaceous

Ar/

cooling  ages  from  amphibole  and  paragonite  from  the  vi-
cinity  of  the  Sú ová  granite  body  (140 Ma,  Vozárová  et
al.  2000).  The  U-Th-Pb  monazite  ages  from  the  uranium
vein  mineralization  of  the  North-Gemeric  Permian  forma-
tion  (124±10 Ma,  Rojkovič  &  Konečný  2005),  as  well  as
from  the  quartz-stibnite  veins  penetrating  the  Southern
Gemeric  Early  Paleozoic  basement  (120±9 Ma,  Hurai  et
al.  2006),  confirms  fully  this  first  stage  of  the  polyphase
Cretaceous  collisional  evolution  in  the  Gemeric  Unit.

Fig. 5. Chemical composition of the monazite-(Ce) recalculated to
monazite,  brabantite  and  cheralite  end-members  (mol  %).  Jurassic
monazites  show  strong  huttonite  substitution  trend  while  Permian
monazites  define  two  trends,  one  to  the  huttonite  and  the  other  to
the  brabantite  substitution  trend.  Silurian  monazites  approach
composition close to the monazite end-member.

This  collision  event  is  well  documented  by  the  formation
of  the  Gemer  Cleavage  Fan  structure  overprinting  the
pre-Mesozoic  metamorphic  fabric  of  the  Northern  and
Southern  Gemeric  basements  together  with  their  Upper
Paleozoic-Triassic  cover  formations  as  well  as  the  Juras-
sic  fabric  of  the  Bôrka  Nappe  to  the  south  (Lexa  et  al.
2003).

The strongly deformed and imbricated Permian-Mesozo-

ic  sequence  of  the  Bôrka  Nappe  represents  the  bottom  part
of  the  Meliata  Ocean  accretionary  wedge.  It  is  formed  by  a
system  of  thrust  sheets  consisting  of  thinned  continental
margin  fragments  (Permian  clastics  and  volcanites,  Triassic
limestones  and  dolomites),  deep-water  sediments  (?Triassic
to  Jurassic  limestones  and  turbidites)  and  blueschist  facies
metabasalts  (Mello  et  al.  1998).  The  Permian  metasedi-
ments  of  the  Bôrka  Nappe,  which  were  defined  as  the  Buči-
na  and  Jasov  Formations  (Mello  et  al.  1998),  have  more
lithological  features  in  common  with  the  Permian  cover  se-
quence  of  the  Southern  Gemeric  basement  represented  by
the  Rožňava  Formation  of  the  Gočaltovo  Group.  They
conspicuosly  differ  from  the  Rožňava  Formation  by  the
substantially  higher  intensity  of  deformation  and  meta-
morphic  recrystallization.  The

Ar/

Ar ages derived

from  metamorphic  phengite  yielded  Late  Jurassic  ages  for
the  Bôrka  Nappe  metamorphism  (160—150 Ma;  Maluski  et
al.  1993;  Dallmeyer  et  al.  1996;  Faryad  &  Henjes-Kunst
1997).  This  pre-Cretaceous  tectonothermal  event  was  con-
nected  with  subduction-related  processes  of  the  Meliata
Ocean,  as  well  as  formation  of  accretionary  wedge  (Mock  et
al.  1998;  Mello  et  al.  1998)  and  its  northwestward  obduc-
tion  over  the  Southern  Gemeric  basement  (Mello  et  al.
1998;  Lexa  at  al.  2003).

The monazite Th-U-Pb age data yield three pop-

ulations  (Fig. 6).  The  Alpine  monazites  with  the  average
age  of  150 Ma  (weighted  average  = 148 ± 8 Ma,  n = 37,
MSWD = 0.7)  recording  the  peak  of  the  early  Alpine
metamorphism  (Fig. 7).  Alpine  generation  of  monazites  is
present  in  all  studied  samples  in  the  highest  quantity.  The
frequency  histogram  of  the  Alpine  ages  in  Fig. 6  shows
slight  bipolar  distribution  and  relative  large  dispersion  in
the  range  of  ages  which  may  indicate  at  least  two  Alpine
events.  To  separate  these  events,  the  Alpine  ages  were
subjected  to  the  statistical  age  data  modeling  based  on
minimizing  the  residual  sums  in  the  two  sub-sets  as
described  by  Montel  et  al.  (1996).  The  modeling  assumes
that  the  data  sorted  according  to  the  increasing  age  are
separated  into  two  sub-sets  at  some  age  boundary.
Mathematical  test  is  a  part  of  the  used  DAMON  software
(Patrik  Konečný)  used  for  the  age  calculations  and
handling.  The  Alpine  ages  were  separated  by  statistical
modeling  at  the  150 Ma  border.  The  first  subgroup  of  data
with  a  weighted  average  age  of  167 ± 12 Ma  (MSWD = 0.17,
n = 17,  probability  1.0;  Fig. 8)  reflects  the  pre-Cretaceous
tectonothermal  event  caused  by  the  subduction  of  the
Meliata  Ocean.  These  obtained  average  ages  show  a  good
coincidence  with  the  previous

Ar/

Ar dating of

metamorphic  phengite  from  the  Bôrka  Nappe  complex
(160—150 Ma;  Maluski  et  al.  1993;  Dallmeyer  et  al.  1996;
Faryad  &  Henjes-Kunst  1997).  The  second  sub-group  of  the

JURASSIC—CRETACEOUS TECTONOTHERMAL EVENTS DEDUCED FROM ELECTRON MICROPROBE (SLOVAKIA)

Table 1: Continued.

age  data  set  had  a  weighted  average  age  of  136±10 Ma
(MSWD = 0.37,  n = 20,  probability = 0.99;  Fig. 9).  This
average  value  reflects  starting  of  the  Early  Cretaceous
polyphase  structural  evolution,  which  was  evoked  by
the  successive  collision  and  indentation  in  the  Inner
Western  Carpathians.

The youngest ~ 100 Ma light coloured rims sur-

rounding the monazite grains from the 1

vol-

canogenic  horizon  of  the  Rožňava  Formation  (sample
4 / SM,  Fig. 4d)  are  genetically  related  to  the
proceeded  Cretaceous  compression  stage,  associated
within

the

Southern

Gemeric

Unit

with

the

development of the Gemer Cleavage Fan (according
to Lexa et al. 2003).

The chemical age data of the monazite from

Gočaltovo  Formation  metavolcanites  also  confirm
the  record  of  the  paleo-Alpine  tectonothermal  event
in  the  Southern  Gemeric  Unit,  which  coincided  with
the  formation  of  the  Meliata  Ocean  accretionary
wedge.  In  fact,  the  Permian  metasediments  and
metavolcanites  of  the  Southern  Gemeric  Unit  show
distinct  crystallization  schistosity  and  flattening  of
coarse  clasts,  which  are  parallel  to  the  well  preserved
sedimentary

bedding.

Thus,

the

high-pressure

metamorphosed  tectonic  scales  of  the  Bučina  and
Jasov  Formations  of  the  Bôrka  Nappe  represent  thrust
sheets  of  the  thinned  continental  margin  which  is
consistent  with  the  Southern  Gemeric  cover.  These
are  lithologically  and  mineralogically  consistent
with  the  Permian  coarse-grained  envelope  sequence
of  the  Southern  Gemeric  Unit  (Reichwalder  1973;
Bajaník  et  al.  1981,  1983,  1984).  Evidence  of  the
Late  Jurassic  monazite  ages  (150—160 Ma)  from  the
metavolcanites  of  the  Gočaltovo  Group  allow  us  to
state  that  the  thinned  continental  margin  represented
by  the  Southern  Gemeric  basement  and  its  Permian
envelope  was  intensively  reworked  during  Late
Jurassic  as  a  response  of  subduction/accretion  pro-
cesses  and  closing  of  the  Meliata  Ocean.  These
results  fully  confirmed  the  suggestions  derived  from
structural  analysis  presented  by  Lexa  et  al.  (2003).

Since the stage of deformation and metamorphic

recrystallization  of  the  Rožňava  Formation  sed-
imentary  complexes  did  not  reach  high-pressure
conditions,  it  is  difficult  to  presuppose  that  it  was
dragged  into  the  Meliata  subduction  zone.  The  Late

Fig. 7.

Histogram

and

isochrone of the monazite
ages for the whole Alpine
populations.

100

VOZÁROVÁ, KONEČNÝ, VOZÁR and ŠMELKO

provenance from the underlying Lower Paleozoic pro-
tolith is highly probable.

Conclusions

The Early Permian magmatic event at 276 ± 25 Ma has

been determined for the first time from the Rožňava
Formation

volcanites.

This

volcanic

activity

was

connected  with  the  late  Variscan  rifting  as  a  response  to
the  foreland  collapse  of  the  Western  Carpathian  Variscan
collision  belt.  Isolated  relics  of  the  Silurian  ages  (421  and
431 Ma)  found  within  the  Permian  monazite  cores  are
interpreted  as  the  inherited  relict  from  the  source  rocks,
extracted  probably  from  the  Lower  Paleozoic  protolith.

Chemical monazite dating from the Permian meta-

volcanites

and

metavolcaniclastics

the

Southern

Gemeric  Gočaltovo  Group  and  Bôrka  Nappe  records  the
Late  Jurassic  tectonothermal  overprinting.  The  sets  of
monazite  age  data  from  17  points  measured  on  16
monazite  grains  confirm  the  weighted  average  of
167± 1 2 Ma.  The  obtained  results  confirm  the  age  of  the

Fig. 8.

Histogram

and

isochrone of the Jurassic
population of monazites.

Fig. 9.

Histogram

and

isochrone of the Early
Cretaceous population of
monazite.

Fig. 10.

Histogram

and

isochrone of the Permian
population of monazite.

subduction/accretion  processes  related  to  the  tectono-
thermal  overprint  of  the  Meliata  accretionary  wedge,  in
which  fragments  of  the  Southern  Gemeric  continental
margin  (slivers  of  the  Bučina  Formation)  were  also
involved.  Existence  of  the  identical  ages  in  monazite  grains
from  the  volcanites  of  the  Southern  Gemeric  Unit
documents  the  high  intensity  of  the  subduction-related
fluid  flows,  which  penetrated  over  the  thinned  Hercynian
Southern  Gemeric  basement.  The  data  obtained  confirm  the
active  continental  margin  tectonic  setting  of  the  Southern
Gemeric  crystalline  basement  and  their  Permian  envelope
during  the  Meliata  subduction/accretion  orogeny.

The weighted average age of 136 ± 10 Ma reflects the

successive  Early  Cretaceous  compression.  Polyphase
Alpine  tectonic  evolution  connected  with  the  gradual
Cretaceous  collision  and  indentation  also  confirmed  by
the  youngest  age  data  set  of  100 ± 11 Ma.

Acknowledgments:  The  financial  support  of  Scientific
Grant  Agency  of  the  Ministry  of  Education  of  Slovak
Republic  and  the  Slovak  Academy  of  Sciences  (Project
No. 1/1036/04)  and  Slovak  Research  and  Development

101

JURASSIC—CRETACEOUS TECTONOTHERMAL EVENTS DEDUCED FROM ELECTRON MICROPROBE (SLOVAKIA)

Support  Agency  (Project  ID:  APVV-0438-06  and  APVT
51-002804)  is  gratefully  acknowledged.  The  authors
would  like  to  thank  M.A.  Kusiak,  D.  Plašienka  and  I.
Petrík  who  constructively  led  to  significant  improvement
of  the  manuscript.

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