GeolCarp_Vol57_No3_211

GEOLOGICA CARPATHICA, JUNE 2006, 57, 3, 211—221

www.geologicacarpathica.sk

Structural record and tectonic history of the Mýto-Tisovec

fault (Central Western Carpathians)

FRANTIŠEK MARKO and RASTISLAV VOJTKO

Department of Geology & Paleontology, Faculty of Sciences, Comenius University, Mlynská dolina G, SK-842 15 Bratislava,

Slovak Republic; marko@fns.uniba.sk

(Manuscript received December 12, 2004; accepted in revised form October 6, 2005)

Abstract: The NW-SE striking Mýto-Tisovec map-scale brittle fault distinctively affects the internal zones of the Western
Carpathians. It cuts and evidently offsets Meso-Alpine tectonic units and structures and represents a zone of important
geophysical anomalies as well. Using methods of structural analysis, the complex tectonic evolution of this long living
fault has been restored. Six successive fault-slip related regional paleostress events, controlling the activity of the Mýto-
Tisovec fault have been distinguished. The oldest recognized paleostress event, with NNE-SSW maximum principal
stress axis operated after the Late Cretaceous and before the Middle Eocene. The orientation of the Miocene maximum
principal stress axis rotated clockwise from NW-SE in the Early Miocene to a NE-SW direction in the Middle Miocene
and E-W direction in the Late Miocene—Pliocene. NNW-SSE trending compression has been estimated for the Quater-
nary stress field. Correspondingly, three periods of Miocene tensional paleostress events with NE-SW, NW-SE and N-S
orientation of minimum principal stress axis has been restored as well. The Mýto-Tisovec fault kinematically fluctuated
in the changing paleostress field. However, the most evident structural records are related to the dominant dextral strike-
slip regime. Dextral transtensional tectonic regime was responsible also for opening of a narrow and deep depositional
depression – the Brezno Basin, related to the Mýto-Tisovec fault, where the Late Eocene—Early Miocene sediments of
the Central Carpathian Paleogene Basin (CCPB) fill have been deposited and later preserved.

Key words: Tertiary, Western Carpathians, structural evolution, paleostress analysis, faults.

Introduction

This  study  is  focused  on  the  reconstruction  of  the  tecton-
ic  evolution  of  the  Mýto-Tisovec  fault  having  affected
post-nappe  geological  structure  of  Internides,  the  Central
Western  Carpathians  (sensu  Mahe   1986;  Plašienka
1999).  During  the  Neo-Alpine  period  (the  post-nappe  pe-
riod  in  the  internal  zones  of  the  Western  Carpathians)
thrusting  prograded  to  external  zones,  where  Tertiary
outer  flysch  units  were  incorporated  into  the  huge  Outer
Carpathian  accretionary  wedge,  while  fault  tectonics  oc-
curred  in  the  already  consolidated  internal  zones.  The  ki-
nematic  history  of  the  Mýto-Tisovec  fault  reflects  this
processes  of  post-Cretaceous  tectonic  evolution  of  the
Central  Western  Carpathians.  This  fault  zone  offsets  Pa-
leo-  and  Meso-Alpine  tectonic  units.  A  lot  of  fault  relat-
ed  structures  including  mesoscale  ones  were  observed
and  analysed  within  the  fault  zone.  Utilizing  geological,
geophysical  and  structural  data  from  published  papers
and  archived  reports  and  utilizing  our  recent  and  former
structural  field  observations    along  the  fault  segment  be-
tween  the  Brezno  and  Tisovec  (Marko  1993b,c;  Marko  &
Vojtko  2001;  Vojtko  2003),  the  tectonic  evolution  of  the
area  has  been  reconstructed.

The internal zone of the Southern Veporic area where

the  structural  records  of  the  Mýto-Tisovec  fault  were  stud-
ied  is  built  up  by  several  superposed  tectonic  units,  creat-
ing  a  sandwich-like  character  of  geological  architecture

(Vojtko  2000).  The  lowermost  Southern  Veporic  Unit
comprises crystalline  basement  represented  predominantly
by  granitic  rocks  and  the  Foederata  sedimentary  cover
unit  of  Permian  up  to  Late  Triassic  age  (Hók  et  al.  1993;
Plašienka  1993).  The  multiple  tectonic  reduction  of  the
crystalline  basement  resulted  in  formation  of  tectonic  slic-
es,  individualized  along  NE-SW  trending  mylonite  shear
zones  (Bezák  2003).  The  Gemeric  Unit  is  represented  by
the  Upper  Paleozoic  metasediments,  predominantly  con-
glomerates,  dark  grey  shales,  limestones  and  dolomites,
which  are  locally  cut  by  Carboniferous  diorite  dykes.  The
Gemeric  Unit  was  thrusted  over  the  Southern  Veporic  Unit
during  the  Early  Cretaceous  compressional  tectonics
(Plašienka  1993,  1999;  Plašienka  &  Soták  2001).  The  Si-
licic  Unit  (Muráň  Nappe)  is  the  highest  tectonic  unit  of
the  area  containing  mainly  Scythian  shales  and  the  Mid-
dle  to  Upper  Triassic  carbonatic  sequences.

The nappe units are covered by both post-nappe Eocene

to  Lower  Miocene  sedimentary  formations  (Subtatras
group  sensu  Gross  et  al.  1984)  of  the  Brezno  Basin  and  the
Neogene  volcano-plutonic  complexes  (Bacsó  1964).

The Mýto-Tisovec fault – a review

The Mýto-Tisovec fault was first described as the Mýto

fault  by  Zoubek  (1935),  after  the  village  of  Mýto  pod
Ďumbierom  in  its  vicinity.  The  fault  was  later  known  un-
der  various  names  as  the  Tisovec  fault  (Bezák  1991),

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STRUCTURAL RECORD AND TECTONIC HISTORY OF THE MÝTO-TISOVEC FAULT

Mts  (Kubíny  1998)  up  to  the  Tisovec  town  where  it  cross-
cuts  and  slightly  offsets  the  Muráň  fault.  South-easternly  of
the  Muráň  fault  we  have  no  evidence  for  continuation  of
the  Mýto-Tisovec  fault  because  it  is  always  difficult  to  fol-
low  the  map  trace  of  a  fault  within  the  monotonous  litholo-
gy  of  a  crystalline  basement  (Fig. 1).  In  contrast  to  the
NE-SW  brittle  faults  (so-called  “Carpathian  trend”  faults),
the  NW-SE  faults  strongly  affect  geophysical  fields  and  are
zones  of  density  and  magnetic  anomalies  (Obernauer  1980,
1983).  The  NW-SE  “cross  faults”  disrupt  the  NE-SW  faults
and  Alpine  shear  zones  of  shortening  (Zoubek  1935;
Bystrický  1959;  Siegl  1976;  Klinec  1976).  Thus  their  latest
activity  seems  to  be  younger  than  the  NE-SW  faults/shear
zones.  The  Mýto-Tisovec  fault  evidently  offsets  the  Po-
horelá  shear  zone  (sensu  Zoubek  1957).  The  dextral  strike-
slip  offset  coming  from  map  interpretation  of  the  Pohorelá
shear  zone  (Zoubek  1957;  Mahe   et  al.  1964;  Klinec  1971,
1976;  Madarás  et  al.  1984;  Pulec  1985;  Bezák  1993;
Kubíny  2002)  accepted  in  Fig. 1  is  considered  to  be
ca.  4 km.  The  latest  activity  of  the  Pohorelá  shear  zone  rep-
resenting  the  tectonic  boundary  in  between  the  Hron  and
Krá ova  ho a  Crystalline  Subunits  is  Cretaceous  (Hók  &
Hraško  1990;  Kubíny  2002;  Bezák  2003),  so  the  offset  of
the  Pohorelá  shear  zone  along  the  Mýto-Tisovec  fault
ought  to  be  the  Late  or  post-Cretaceous.

Nevertheless the Mýto-Tisovec fault was founded ear-

ly  in  the  Paleo-Alpine  period  (Mahe   1969).  The  old  ori-
gin  of  the  fault  in  the  crystalline  basement  was  declared
on  the  basis  of  its  role  as  a    tectonic  border  between  the
basic  and  more  acid  varieties  of  the  Variscan  granitoids
of  the  Veporic  Unit.  The  fault  has  been  considered  to  be
reactivated  in  the  Neo-Alpine  period  as  sinistral  strike-
slip  (Zoubek  1935;  Klinec  1976;  Bezák  1988,  1991).  As
for  the  youngest  movement  normal-slip  has  been  sug-
gested  (Klinec  et  al.  1976;  Bezák  &  Klinec  1980),  thanks
to  which  Mesozoic  and  younger  sediments  were  pre-
served  in  downthrown  hanging  wall  blocks.  The  Brezno
Basin  has  been  regarded  as  genetically  related  (not  speci-
fied)  to  the  Mýto-Tisovec  fault  dynamics  as  well  (Mahe
1972;  Pulec  1985;  Bezák  1991).

Jaroš et al. (1966) described Neogene reactivization of

“cross  faults”  including  the  Mýto-Tisovec  one  from  the
area  of  the  “Hron  synclinorium”  built  up  by  a  subsided
pile  of  Meso-Alpine  Mesozoic  nappes.  The  Badenian-Sar-
matian  activity  of  the  Mýto-Tisovec  fault  is  indicated  by
occurrences  of  andesite  volcanic  bodies  (volcanic  com-
plexes  near  Brezno,  Tisovec).  In  spite  of  the  young  activi-
ty,  NW-SE  faults  do  not  operate  as  recent  drainage  ways
for  subsurface  water,  because  almost  no  water  springs  follow
these  faults.  Most  water  springs  are  related  to  the  NE-SW
faults  (Pospíšil  et  al.  1989).

Methods

A combination of field mesostructural observations

and  map-scale  structure  analysis  has  been  applied  as  the
research  approache  to  solving  the  topic.  As  the  basic
principle,  we  have  accepted  an  axiom,  that  small-scale
structures  can  be  related  to  large  regional  structures  and
that  both  scales  reflect  the  same  dynamics  and  kinemat-
ics  (Angelier  1994).

Structural research has been focussed on investigation of

brittle structures related to the paleostress field studied
along the map trace of the Mýto-Tisovec fault. It involved:

– field structural research including measurement and col-

lection of field structural data, kinematical analysis of slick-
ensides (Petit 1987; Marko 1993a), geological mapping.

– processing of structural data including orientation

and  paleostress  analysis.  For  paleostress  analysis  direct  in-
version  method  (Angelier  1984),  and  its  software  appli-
cation  Jahans  &  Villemin  in  Charlesworth  et  al.  (1992)
has  been  used.  Several  successive  tectonic  stages  char-
acterized  by  orientation  of  principal  stress  axes,  stress
ratio  ( = (

—

) / (

—

)), tectonic regime and age of de-

formations  have  been  identified.  Homogeneous  popula-
tions  of  slickensides  for  computations  of  single  paleostress
events  were  separated  and  combined  from  all  localities
(Fig.  5a—e).  This  means  that  the  whole  studied  area  of  the
Mýto-Tisovec  fault  zone  has  been  regarded  as  a  homoge-

Table 1: Names of localities, where structural measurements were realized. Age of rock bearing structures is expressed by symbols: N – Oli-
gocene—Miocene, M – Mesozoic (Silicic Unit, Foederata Unit), V – pre-Mesozoic (Veporic Unit).

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MARKO and VOJTKO

Fig. 2. Geological map of the studied area (cf. Vojtko 1999) with location of analysed outcrops.

neous  structural  domain.  The  angle  between  the  theorethical
and  measured  orientation  of  striae  was  used  as  the  discrimina-
tion  criterium  for  separation  of  slickensides  to  homogeneous
populations.

– interpretation of the gained data and structural synthe-

sis  of  field  observations  including:  restoration  of  paleo-
stress  fields  and  nature  of  regional  (map  scale)  structures,
resulted  in  the  creation  of  a  geodynamical  evolutionary
model  of  the  area.

Structural data and field observations

The data used for structural analysis were collected from

15  outcrops  (Table 1)  situated  in  the  Mýto-Tisovec  fault
zone  in  between  Brezno  and  Tisovec  towns  (Fig. 2).  Study
was  focused  on  brittle  tectonics.  Strikes  of  slickensides
and  mineral  veins  observed  in  rocks  units  of  different  age
are  presented  in  rose  diagrams  (Fig. 2).

Several dozens of kinematically defined meso-scale

brittle  faults  were  collected  from  rocks  of  various  age
(from  Variscan  crystalline  rocks  up  to  the  Badenian  vol-
canites  –  Fig. 3a).  The  kinematics  of  observed  slicken-
sides  shows,  that  the  dominant  brittle  deformation  was
generally  of  a  strike-slip  character.

The most spectacular brittle faults are exposed at the

Tisovec  quarry  (Fig. 2,  locality  7),  located  in  the  Meso-
zoic  limestones  of  the  Muráň  Nappe  Unit.  This  quarry  is
situated  just  within  the  deformational  zone  of  the  Mýto-
Tisovec  fault,  where  faults  related  to  this  zone  are  ob-
servable.  The  dominant  strike-slip  character  of  the
NW-SE  trending  subvertical  faults  is  clear  from  the  fault
surfaces  (Fig. 3b).  Even  strike-slip  duplexes  arranged  in
flower  structure  are  visible  there  in  cross-section  view  to
the  fault  plane  (Fig. 3c),  proving  the  intensity  of  strike-
slip  deformation  at  the  Mýto-Tisovec  fault.  Records  of
strike-slip  movements  along  the  faults  parallel  with
Mýto-Tisovec  one  show  multiple  fluctuation  of  the  sense

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MARKO and VOJTKO

of  movement.  The  most  evident  record  –  criteria  for
dextral  strike-slip  (accretional  mineral  steps,  tool  pits  at
the  slickenside  surface)  are  the  result  of  the  strongest
event.  However,  there  are  some  indices,  that  the  youngest
strike-slip  movement  along  the  NW-SE  trending  faults  at
Tisovec  quarry  has  a  sinistral  sense.  Anyway,  the  domi-
nant  horizontal  striations  are  overprinted  by  younger
dip-slip  striations  according  to  which  the  northern  block
subsided.

Apart from the field structural research, reambulation

of  the  geological  map  has  been  done.  According  to  the
reinterpretation  presented  here  the  Mýto-Tisovec  fault  it-
self  is  composed  of  several  overstepping  en-echelon  seg-
ments,  connected  by  bridge  areas  (accomodation  zones)
and  by  smaller  secondary  faults.  This  left-stepping  ar-
rangement  (sensu  Biddle  &  Christie-Blick  1985)  is  typi-
cal  for  dextral  strike-slip  faults.

Stress field evolution and interpretation

Processing brittle fault-slip data led to distinguishing of

five  paleostress  events.  The  youngest,  sixth  paleostress
event  of  NNW-SSE  compression  was  suggested  only  from
evident  offsets  of  map  scale  structures  and  geomorpholog-
ical  phenomena  observed  in  the  field.  The  kinematics  of
map  scale  faults  has  been  evaluated  in  several  successive
paleostress  events  listed  below.

NNE-SSW compression (Late Cretaceous/Paleocene—
Early Eocene)

The oldest brittle records from the investigated area are

those  structures,  which  were  caused  or  reactivated  by
NNE-SSW  compression  (Fig. 5a).  The  NNE-SSW  compres-
sion  induced  a  dextral  transpressional  regime  in  the  Mýto-
Tisovec  fault  zone.  The  Mýto-Tisovec  “fault”  being  a
deeply  seated  crustal  shear  zone  operated  during  this  early
stage  in  brittle-ductile  mode.  Stretching  lineations  typical
for  the  Paleo-Alpine  period  (Bezák  1993)  parallel  with  the
Mýto-Tisovec  fault  observed  in  the  Permian-Triassic
metaquartzites  (Fig. 2,  locality 10)  are  regarded  as  the
product  of  this  early  stage  in  brittle-ductile  conditions.
The  cross-cutting  Muráň  fault  had  to  operate  as  a  sinistral
transtensional  oblique-slip  with  dominant  dip-slip  separa-
tion,  when  the  western  block  subsided  (Muráň  karst  pla-
teau  and  Tisovec  karst  block).  Thanks  to  this  event,
formations  of  the  Muráň  Nappe  have  been  preserved  west
of  the  Muráň  fault.  The  age  brackets  –  the  Latest  Creta-
ceous—Early  Eocene  of  this  period  are  well  constrained
from  the  locality  Hrabušice,  situated  out  of  the  studied
area  (Marko  1993b).  There  are  exposed  N-S  map  scale
dextral  strike-slip  faults  related  to  this  paleostress  period
which  tectonically  juxtapose  Late  Cretaceous  conglomer-
ates  with  Triassic  dolomites.  These  faults  are  sealed  by
overlying  Middle  Eocene  basal  sediments  of  the  Central
Carpathian  Paleogene  Basin.

Fig. 4.  Cross-section  of  the  Brezno  Basin  verified  by  boreholes  (slightly  modified,  after  Pulec  1985).  1  –  Badenian-Sarmathian  andesite
pyroclastics;  2  –  claystone  lithofacies  (Eocene—Priabonian);  3  –  sandstone-claystone  lithofacies  (Eocene—Priabonian); 4  –  boulder  con-
glomerates (Eocene—Priabonian); 5 – conglomerate-sandstone lithofacies (Eocene—Priabonian);  6 – Veporic crystalline basement (Paleo-
zoic); 7 – fault; 8 – borehole.

217

STRUCTURAL RECORD AND TECTONIC HISTORY OF THE MÝTO-TISOVEC FAULT

NW-SE compression (Middle Eocene—Early Miocene)

During this paleostress event (Fig. 5b), a brittle transten-

sional  regime  was  induced  in  the  Mýto-Tisovec  fault  zone
and  WNW—ESE  trending  en-echelon  segments  of  the
Mýto-Tisovec  fault  developed  with  important  dextral

strike-slip  separation.  Complementa-
ry  N-S,  NNE-SSW  sinistral  faults  op-
erated  in  the  surroundings.  This
kinematics  is  visible  from  the  recent
configuration  and  offsets  of  geologi-
cal

bodies

geological

maps

(Fig. 2).  The  greater  part  of  the  dis-
tinctive  dextral  offset  of  the  cross-
cutting  Paleo-Meso-Alpine  Pohorelá
contractional  shear  zone  was  created
during  this  period.

In the early stages of this period

the  embrionic  Brezno  Basin  could
has  been  founded  as  a  strike-slip  ba-
sin.  A  narrow  slab  rimmed  by  seg-
ments  of  the  Mýto-Tisovec  fault,
which  subsided  due  to  the  local  tran-
stension  along  the  fault  zone,  was
filled  with  the  Middle-Late  Eocene
basal  formations.  The  cross-section
of  the  basin  (Fig. 4)  suggests,  that
the  normal-dextral  NW-SE  faults  op-
erated  in  the  Middle  to  Late  Eocene
as  synsedimentary  ones.

NE-SW tension (Middle Miocene)

This is complementary paleostress

field  to  the  former  one.  The  most
distinctive  record  of  this  paleostress
event  (Fig. 5c)  is  the  structure  of  the
Brezno  Basin,  which  is  spatially  relat-
ed  to  the  Mýto-Tisovec  fault  zone.  A
narrow,  relatively  deep  pull-apart  ba-
sin  was  opened.  A  550 m  thick  fill  of
Eocene-Oligocene  sediments  (Pulec
1985)  is  preserved  there,  the  young-
est  sediments  are  of  Miocene  age.
During  the  end  of  this  or  beginning
of  the  next  period,  a  facial  change
in  lithology  shows  a  radical  change
of  conditions  during  the  sedimenta-
tion.  Poorly  sorted  and  indurated
breccias  of  debris  type,  the  Late
Badenian-Early  Sarmatian  Brezno
beds  were  observed  at  the  localities
1  and  3  (Fig. 2).  They  consist  of
very  angular  blocks  of  metamorphic
rocks.  This  breccia  overlies  Oli-
gocene  sandstones  and  is  covered
by  alternating  beds  of  sands  and
variegated  clays  (Fig. 3).  According
occurrences  of  fossil  flora  in  coal

intercalations  in  the  underlying  basal  sandstones  (Sitár
1965)  the  age  of  these  debris  sediments  is  interpreted  as
post-Oligocene.  The  upper  age  limit  of  these  sediments  is
constrained  by  occurrences  of  rare  clasts  of  Badenian
volcanites.  The  coarse  poorly  rounded  and  sorted  sedi-
ments,  transported  only  a  short  distance,  could  be  ex-

Fig. 5.  Paleostress  evolution  and  kinematic  history  of  the  Mýto-Tisovec  fault.  This  model  is
schematic,  drawn  with  respect  to  the  recent  coordinates  and  orientation  of  map-scale  structures.
Structural  diagrams  represent  lower  hemisphere.  Localities  from  where  faults  of  homogeneous
populations were separated are listed in the bottom of each diagram. The age of slickenside bear-
ing rocks is expressed by codes (see Table 1). 1 – thrust and reverse fault; 2a – normal fault,
2b  –  oblique-normal  fault;  3  –  strike-slip  fault  (relative  magnitude  of  separation  is  expressed
by length of shear sense arrows); 4 – direction of compression; 5 – direction of tension;
6 – upthrown block; 7 – downthrown block (magnitude of subsidence is expressed in meters);
8a  –  sedimentary  fill  deposited  and/or  preserved  in  depressions;  8b  –  debris  sediments  of
Brezno  beds;  9  –  Mesozoic  rocks  of  Kučelach  block  (relic  of  Silica  Nappe);  10  –  Badenian
volcanites; 11 – huge rockfalls of Mesozoic rocks. MyTi – Mýto-Tisovec fault, Mu – Muráň
fault, Po – Pohorelá shear zone, CiBa – Čierny Balog fault.    Continued on the next pages.

218

MARKO and VOJTKO

plained by an emerging proximal crystalline rocks
source with high surface relief.

Preservation of the Muráň Nappe and underlying units

in  the  Tisovec  karst  block,  which  subsided  1500 m  com-
pared  to  the  Muráň  karst  plateau  is  also  a  result  of  rapid
subsidence  within  the  NW-SE  corridor  rimmed  by  the
Mýto-Tisovec  fault  from  the  north  and  parallel  Čierny
Balog  fault  (Bezák  1991,  1993)  running  southerly.  Em-
placement  of  the  NW-SE  oriented  subvolcanic  diorite
bodies  near  Tisovec  occurred  in  this  period.

NW-SE tension (Late Miocene)

There are meso-scale as well as map-scale structural

records  of  NW-SE  tension  (Fig. 5d).  Meso-scale  NNE-SSW
striking  normal  faults  (Fig. 3d,e)  were  observed  in  the  Up-
per  Eocene—Lower  Miocene  sediments  of  the  Brezno  Ba-
sin  (Fig. 2,  locality  1, 3).  NW-SE  striking  normal  faults  are
present  as  a  minor  population  too.  The  age  relations  of

these  two  populations  of  extensional  faults  are
not  clear,  but  according  to  the  paleostress  cal-
culations  they  could  be  coeval,  being  produced
by  one  single  paleostress  event  –  NW-SE  ten-
sion  (Fig. 5d).

NW-SE tension has great importance for pres-

ervation  of  the  Muráň  Nappe  in  the  western
block  of  the  Muráň  fault,  which  continuous-
ly  subsided  also  during  this  period.  A  lot  of
NE-SW  trending,  map-scale  normal  faults  de-
veloped  during  this  tensional  event.  They  cut
the  Tisovec  karst  block,  Brezno  Basin  and  they
are  responsible  for  preservation  of  the  Kučelach
outlier  of  the  Muráň  Nappe,  which  subsided
along  NE-SW  normal  faults.  The  complicated
internal  structure  in  the  Tiso-vec  karst  is  the  re-
sult  of  alteration  of  differentially  subsided
blocks  (Vojtko  2000).  The  emplacement  of  the
youngest  NE-SW  striking  volcanic  dykes  was
controlled  by  NW-SE  tension  as  well.  As  a  com-
plementary  paleostress  event  for  this  period,  a
NE-SW  (NNE-SSW)  horizontal  compression  is
suggested,  because  a  few  strike-slip  slickensides
related  to  this  stress  field  were  measured  too.  The
NE-SW  (NNE-SSW)  compression  was  coeval,  or
slightly  predated  the  NW-SE  tension.  This  pa-
leostress  field  left  a  distinctive  structural  record
in  the  Eocene  sediments  of  the  southern  margin
of  the  Central  Carpathian  Paleogene  Basin,
where  it  produced  a  numerous  population  of
conjugate  strike-slip  slickensides  with  modest
separation  (Marko  1995).

ENE-WSW compression, NNW-SSE tension
(Late Miocene/Pliocene)

This paleostress event is recorded in a meso-

scale  slickenside  population  –  frequent  NW-SE
striking  sinistral  strike-slip  slickensides  in  Meso-
zoic  rocks  and  kinematically  variegated  slick-

ensides  in  Neogene  volcanic  rocks  (Fig. 5e).  We  suggest,
that  ENE-WSW  compression  slightly  predated  NNW-SSE
tension.  During  this  period  sinistral  transtensional  regime
operated  along  the  Mýto-Tisovec  fault.  This  event  could
generate  dextral  strike-slip  movement  with  modest  magni-
tudes  of  separation  along  the  NE-SW  striking  Muráň  fault.

The preservation of a narrow belt of the Paleogene sedi-

ments  at  the  easternmost  tip  of  the  Brezno  Basin  could  be
explained  as  pull-apart  subsidence  in  overstepping  tran-
stensional  bridge  in  between  two  en-echelon  segments  of
the  Mýto-Tisovec  fault.

Large map-scale E-W trending normal faults active dur-

ing  this  period  allowed  preservation  of  Paleogene  and
Neogene  sediments  in  morphotectonic  depressions  such  as
the  Upper  Hron  Valley  Depression  (Fig. 5e).  These  faults
also  evident  in  the  recent  pattern  of  the  geological  map
(Fig. 1)  affect  the  morphotectonic  character  of  the  area,  as
well  as  the  surface  water  drainage  network  (for  example
the  Hron  river).

Fig. 5c—d. Continued.

219

STRUCTURAL RECORD AND TECTONIC HISTORY OF THE MÝTO-TISOVEC FAULT

NNW-SSE (N-S) compression (Pliocene—Quaternary?)

The youngest stress event characterized by a ca. N-S ori-

ented  maximum  principal  stress  axis  was  described  ac-
cording  to  the  map-scale  structures  arrangement  (Fig. 5f).
We  do  not  have  reliable  mesofault-slip  records  of  this  pa-
leostress  event  in  the  youngest  (Miocene)  rocks.  However,
several  slickensides  creating  homogeneous  population  re-
lated  to  NNW-SSE  compression  were  observed  only  in
Mesozoic  rocks.

The most spectacular map-scale evidence of this latest

tectonic  event  are  dextral  offsets  (ca.  200 m  magnitude  of
separation)  of  the  Kučelach  block,  bodies  of  the  Badenian
volcanites  and  the  Muráň  fault  along  the  Mýto-Tisovec

fault.  Huge  rock  falls  observed  on  the
eastern  segment  of  the  fault  are  regard-
ed  as  evidence  of  subrecent  dextral
strike-slip  activity  of  the  Mýto-Ti-
sovec  fault.  There  are  large  blocks  of
Mesozoic  rocks  fallen  down  from  the
edge  of  the  Muráň  Nappe  block  (Vojt-
ko  1999).  We  suppose  that  these
blocks  fell  down  due  to  strong  sudden
energy  triggered  by  probably  seis-
mogenic  dextral  strike-slip  along  the
Mýto-Tisovec  fault  generated  by  ca.
N-S  trending  compression  during  the
Quaternary.

Discussion and conclusions

Six successive events of tectonic

evolution  characterized  by  stress  ten-
sors  and  related  tectonic  regimes  have
been  restored  in  the  study  area.  Thanks
to  the  age  variability  of  rocks  bearing
brittle  deformations,  it  was  possible  to
restore  the  succession  of  paleostress
events.  Nevertheless,  it  was  rather  diffi-
cult  to  establish  the  precise  age  brack-
ets  for  the  paleostress  events.  It  was  not
always  possible  to  use  the  age  of  rocks
bearing  structural  records  for  dating
paleostress  events.  Sometimes  records
of  young  paleostress  events  were  not
observed  in  young  formations  as,  for
example,  records  of  ENE-WSW  as  well
as  NNW-SSE  compression.  Explana-
tion  of  this  controversy  could  lie  in
the  heterogeneous  distribution  of  the
structural  record  or  in  incorrect  dating
of  these  paleostress  events.

The importance of the youngest N-S

compression,  E-W  tension  can  be  in-
ferred  from  the  conspicuous  popula-
tion  of  map-scale  N-S  striking  faults.
These  very  frequent  faults  in  the  West-
ern  Carpathians  offset  older  stuctures.

They  could  be  generated  during  N-S  compression  as  well
as  during  complementary  E-W  tension,  which  ought  to  be
related  to  a  rollback  effect  of  subducted  crust  under  the
eastward  propagating  Carpathians  (Doglioni  et  al.  1991).
In  this  case  the  Early  Pannonian  E-W  tension  would  has
predated  the  period  of  N-S  compression.

Restored evolution of the Neogene—Quaternary paleo-

stress  field  submitted  herein  fits  well  with  the  paleostress
evolution  of  the  ALCAPA  (Alpine-Carpathian-Pannonian)
junction  area  (Nemčok  et  al.  1989;  Csontos  et  al.  1991;
Fodor  1995;  Marko  et  al.  1995;  Marko  2002).  In  spite  of
this  similarity,  no  blok  rotations  (well  known  from  the  AL-
CAPA  junction  area)  have  been  taken  into  account  in  the
geodynamic  model  of  the  Mýto-Tisovec  fault  area  evolu-

Fig. 5e—f. Continued.

220

MARKO and VOJTKO

tion.  It  has  been  decided  due  to  the  lack  of  paleomagnetic
data  from  the  northwestern  Veporic  and  a  few  zero  paleo-
meridian  rotations  measured  in  Jurassic  rocks  (Kruczyk  et
al.  1992)  in  the  similar  terrane  –  the  area  of  the  Vysoké
Tatry  Mts.

Combining the gained paleostress data with other rele-

vant  geological  information  we  have  reconstructed  the  tec-
tonic  story  of  the  study  area.  After  the  Meso-Alpine  nappe
thrusting,  shortening  of  the  Western  Carpathian  orogene
continued.  In  this  post-nappe  period  (after  the  middle/Late
Cretaceous)  further  northward  propagation  of  Carpathians
was  accommodated  in  the  internal  zones  by  brittle  faulting,
which  divided  the  Central  Western  Carpathians  into  indi-
vidually  moving  blocks.  The  NW-SE  and  NE-SW  faults  op-
erated  as  conjugate  during  the  Neogene  period.  The
Mýto-Tisovec  NW-SE  trending  fault,  deeply  seated  in  the
crust  operated  during  most  of  its  tectonic  life  as  dextral
strike-slip,  but  it  kinematically  fluctuated  in  changing  pa-
leostress  conditions.  Map-scale  structural  evidence  (Bezák
2003)  points  to  different  intensity  of  shortening  in  blocks
divided  by  the  Mýto-Tisovec  fault.  Shortening  was  realized
by  NE-SW  shear  zones,  but  the  southern  block  was  affected
by  more  numerous  shear  zones  than  the  northern  one.  The
Mýto-Tisovec  fault,  operating  during  this  early  stage  in  a
brittle-ductile  regime,  could  play  the  role  of  a  “transform”
fault  accommodating  different  shortening  in  northern  and
southern  blocks  (Fig. 3f).

The formation of the Brezno Basin and the distribution

of  Miocene  volcanic  bodies  in  the  area  were  controlled  by
the  Mýto-Tisovec  fault  activity.  It  is  clear  from  the  paleo-
stress  history,  thickness,  facial  character  of  the  Brezno  Ba-
sin  sedimentary  fill  and  its  shape,  that  it  is  small  pull-apart
basin  open  as  a  narrow  strike-slip  basin  related  to  the  early
transtensional  dextral  strike-slip  and  later  extensional  re-
gime  within  the  Mýto-Tisovec  fault  zone.  Because  Paleo-
gene  sediments  often  overlay  crystalline  basement  within
the  area  of  the  Myto-Tisovec  fault,  huge  erosion  of  Meso-
zoic  rocks  cover  before  sedimentation  of  Paleogene  clastics
ought  to  be  expected.  This  erosion,  probably  supported  by
tectonic  exhumation  (Hók  et  al.  1993;  Plašienka  1993;
Fodor  1995)  was  realized  after  nappe  thrusting  in  the  mid-
dle/Late  Cretaceous  and  before  the  transgression  of  the
Middle  Eocene  sediments.  Erosion  removed  Mesozoic
cover  and  exhumed  crystalline  rocks  in  the  area  of  the  fu-
ture  Brezno  Basin.  This  process  suggests  updoming,  ele-
vation  of  this  area,  which  could  be  the  result  of  squeezing
blocks  separated  by  NE-SW  contractional  shear  zones  dur-
ing  continuous  Neo-Alpine  shortening.  Today’s  occur-
rences  of  Paleogene  sedimentary  cover  show,  that  the
whole  area  were  covered  by  the  Paleogene  sediments,
which  were  later  eroded.  A  thicker  remnant  of  the  basin  fill
was  preserved  only  in  a  deeper  depression  –  the  Brezno
Basin,  subsided  along  the  Mýto-Tisovec  fault.  This  sce-
nario  supposes  very  strong  erosion  after  the  Paleogene,
too.  The  distribution  of  the  Miocene  volcanic  rocks  could
be  similarly  understood.  It  seems,  that  today’s  occurrences
of  volcanites  in  the  focused  area  are  only  remnants  of  a
formerly  huge  stratovolcano  (dozens  kilometers  wide  in
diameter),  which  was  eroded.  The  center  of  this  stratovol-

cano  ought  to  be  situated  northwest  of  the  Tisovec,  within
the  zone  of  the  Mýto-Tisovec  fault,  which  operated  as  a
path  way  for  ascending  volcanic  and  subvolcanic  bodies
during  NE-SW  tension.  There  are  superficial  occurrences
of  subvolcanic  varieties  of  extrusive  rocks,  which  points
to  the  great  depth  of  erosional  level  after  the  Miocene  vol-
canism.

Acknowledgments:  The  research  was  financially  sup-
ported  by  the  Slovak  Scientific  Grant  Agency  VEGA
(No. 2/4095/4-A)  and  the  Grants  of  Comenius  University
(No. 122/2002/UK,  128/2003/UK).  The  initial  version  of
this  paper  has  been  substantially  improved  by  the  per-
ceptive  comments  of  László  Fodor  and  Peter  Kováč,
whose  help  is  gratefully  acknowledged.

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