GeolCarp_Vol64_No2_103

www.geologicacarpathica.sk

GEOLOGICA CARPATHICA

, APRIL 2013, 64, 2, 103—116 doi: 10.2478/geoca-2013-0007

Introduction

Shear  bands  refer  to  sub-parallel  small-scale  shear  zones
transecting an earlier anisotropy at small to intermediate an-
gles which typically develop within larger-scale shear zones.
These structures are associated with bulk simple shear or ex-
tension  parallel  to  the  earlier  anisotropy  and  had  been  pre-
sented as shear bands (White 1979; Gapais & White 1982),
C  or  C’  bands  (Berthé  et  al.  1979;  Ponce  &  Choukroune
1980;  Lister  &  Snoke  1984),  extensional  crenulation  cleav-
age  (Platt  1979,  1984;  Platt  &  Vissers  1980)  or  shear  band
cleavage  due  to  its  cleavage-like  appearance  (White  et  al.
1980;  Passchier  &  Trouw  2005).  The  main  distinction  be-
tween  compressional  crenulation  cleavage  and  extensional
shear band cleavage is based on the angle between cleavage
and  earlier  foliation  exhibiting  45—90°  for  compressional
and  less  than  45°  for  extensional  cleavage  (Passchier  &
Trouw 2005). Therefore the shear band cleavage needs to be
revealed by the complete C—S structure defined by pervasive
anisotropy S “Schistosité” and discretely spaced cleavage C
“Cisaillement”  (Berthé  et  al.  1979).  The  main  controversy
related to the field interpretation of C—S fabrics is their tem-
poral  and  kinematic  relationship,  since  within  a  shear  zone
the  C  fabrics  form  either  as  a  result  of  increasing  strain  or
due  to  the  overprint  of  an  earlier  kinematically  unrelated
anisotropy (Lister & Snoke 1984; Agard et al. 2011).

The contact zone between two major basement-cover thrust

sheets, the hanging-wall Gemeric and footwall Veporic Units,
in the Central Western Carpathians is characterized by com-

Kinematically unrelated C—S fabrics: an example of

extensional shear band cleavage from the Veporic Unit

(Western Carpathians)

ZITA BUKOVSKÁ

, PETR JEŘÁBEK

, ONDREJ LEXA

, JIŘÍ KONOPÁSEK

, MARIAN JANÁK

and JAN KOŠLER

Institute of Petrology and Structural Geology, Faculty of Science, Charles University in Prague, Albertov 6, 128 43 Prague 2,

Czech Republic; zita.bukovska@natur.cuni.cz

Department of Earth Science and Center for Geobiology, University of Bergen, Allégaten 41, N-5007 Bergen, Norway

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

(Manuscript received June 7, 2012; accepted in revised form

September 18, 2012)

Abstract: Discontinuous and kinematically unrelated C—S fabrics have been recognized along the contact between the
Gemeric and Veporic Units in the Western Carpathians. The formation of S and C fabrics within orthogneiss, quartzite and
chloritoid-kyanite schist of the Veporic Unit is associated with Cretaceous syn-burial orogen-parallel flow and subsequent
exhumational unroofing. The formation of the two fabrics characterized by distinct quartz deformation microstructure and
metamorphic assemblage is separated by an inter-tectonic growth of transversal chloritoid-, kyanite-, ± monazite-bearing
assemblage. The monazite U-Th-Pb concordia age of 97 ± 4 Ma was obtained by the laser ablation ICP—MS dating method.
The age of this inter-tectonic metamorphic stage together with existing

Ar/

Ar ages on exhumation of the Veporic Unit

indicate that despite the similar appearance to shear bands or C—S mylonites there is a time span of at least 10 Myr between
the formation of homogeneous S fabrics and superposed discrete C fabrics in the studied rocks.

Key words: Central Western Carpathians, Veporic Unit, structural geology, monazite dating, quartz deformation
microstructure, shear band cleavage, discontinuous C—S fabrics.

plicated  structure  of  Early  Cretaceous  imbrications  modified
by Late Cretaceous extension (Plašienka 1980, 1984; Lupták
et al. 2000, 2003; Jeřábek et al. 2012). The extension resulted
in  the  development  of  major  shear  zone  associated  with  un-
roofing  and  exhumation  of  the  Veporic  Unit  due  to  gravita-
tionally-driven  up-flow  of  middle  crust  in  the  core  complex
mode (Plašienka et al. 1999; Janák et al. 2001) or large-scale
polyharmonic  folding  (Jeřábek  et  al.  2008,  2012).  The  C—S
fabrics recognized within this shear zone have been previously
interpreted  as  continuous  kinematically  related  exhumation
fabrics (Hók et al. 1993; Plašienka 1993; Lupták et al. 2003).

In this study, we aim to decipher the kinematically related

versus unrelated nature of the C—S fabrics developed within
a major extensional shear zone at the boundary between the
Gemeric and Veporic Units in the Western Carpathians. The
C—S fabrics were studied in orthogneiss, quartzite and chlo-
ritoid-kyanite schist across the shear zone, which allowed us
to perform detailed structural, microstructural, metamorphic
and geochronological characterization of the two fabrics.
Furthermore based on our new data, the regional context of
the complicated structure of the eastern part of the Gemeric
and Veporic contact zone is discussed.

Geological setting

The Veporic Unit together with the Gemeric Unit to the

east—southeast and Tatric Unit to the north (Fig. 1a) repre-
sent segments of Variscan crust that had been incorporated

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Fig. 1. a – Tectonic units of the Central Western Carpathians. b – Simplified geological and structural map of the studied area including lo-
cation of the studied samples and structural cross-section A—A’; structural symbols show orientation of foliation S

(S fabric) and cleavage

(C fabric), and accompanying lineations. Map based on Geological map of the Slovak Republic 1 : 50,000 http://mapserver.geology.sk.

c– Lower hemisphere equal area projection of main structures documented in the studied area (S – foliation, L – lineation AP – fold axial
plane, FA – fold axis, and A1—A3 – Alpine deformation events). Contours are double the multiples of standard deviation above the uni-
form distribution. d – Structural cross-section across the Gemeric-Veporic contact zone with macroscopic insets. GPS coordinates of se-
lected localities: BZ13 48°42

’15.38”N, 20°18’24.12”E; BZ15 48°43’55.91”N, 20°17’03.50”E; BZ20 48°48’10.32”N, 20°13’14.10”E;

BZ22 48°48

’20.97”N, 20°14’55.78”E; BZ77 48°46’46.52”N, 20°17’09.85”E; BZ171 48°47’45.69”N, 20°16’45.87”E; BZ172

48°45

’20.16”N, 20°18’30.31”E; BZ183 48°45’48.61”N, 20°17’47.90”E; BZ188 48°45’34.55”N, 20°17’56.23”E; BZ345 48°45’17.49”N,

20°18

’30.24”E; BZ351 48°45’18.65”N, 20°18’30.47”E.

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into the structure of the Central West Carpathian wedge dur-
ing  the  Cretaceous  Eo-Alpine  convergence  (Plašienka  et  al.
1997).  The  Early  Cretaceous  thrust  sheet  stacking  of  the
structurally lower Tatric, middle Veporic and upper Gemeric
Unit  (Tomek  1993;  Plašienka  et  al.  1997)  was  followed  by
Late Cretaceous doming and exhumation of the deeper parts
of the Veporic Unit (Janák et al. 2001; Jeřábek et al. 2012).

The studied area is located in the vicinity of the north-

south  trending  contact  between  the  footwall  Veporic  Unit
and  the  hanging-wall  Gemeric  Unit  (Fig. 1b).  In  this  area,
the Gemeric Unit comprises Lower Paleozoic volcano-sedi-
mentary basement rocks of the Gelnica and Rakovec Groups
marked  by  low-  to  medium-grade  Variscan  metamorphism
(Faryad 1991) and overlying Upper Carboniferous—Permian
metasedimentary cover (Vozárová & Vozár 1988). The Ge-
meric  Unit  is  overthrust  by  the  Meliata  accretionary  wedge
complex  of  Jurassic  age  (Kozur  &  Mock  1973;  Faryad  &
Henjes-Kunst  1997)  and  the  uppermost  Silica  carbonate
nappe  system  (Fig. 1a).  Mostly  low-grade  Alpine  metamor-
phic conditions have been determined for the Gemeric Unit
(e.g. Petrasová et al. 2007). In the studied area, the Veporic
Unit  is  characterized  by  an  imbricated  structure  (Plašienka
1980, 1984) comprising from west to east and bottom to top
(Fig. 1b,c):  1  –  Variscan  basement  migmatite,  orthogneiss
and Carboniferous granitoids (Bibikova et al. 1988; Michalko
et al. 1998); 2 – Permian cover quartzite; 3 – garnet-bearing
schist;  4  –  Permian  cover  quartzite-arcose  marked  by  the
presence of chloritoid-kyanite schist (Vrána 1964; Lupták et
al.  2000)  and  5  –  Permo-Triassic  quartzite  and  marble  of
the  Foederata  cover  (Rozlosznik  1935;  Schönenberg  1946).
The  garnet-bearing  schists  were  traditionally  related  to  the
Veporic  basement  (Klinec  1966;  Vrána  1966),  however,  on
the basis of pollen analysis they have been later reinterpreted
as  Carboniferous  metasediments  of  the  Veporic  cover  be-
longing  to  the  Slatviná  Formation  (Planderová  &  Vozárová
1978; Vozárová & Vozár 1988). The degree of Alpine meta-
morphic overprint reached amphibolite facies in the Veporic
basement  (up  to  600 °C  and  11 kbar;  Vrána  1966;  Janák  et
al.  2001;  Jeřábek  et  al.  2008)  and  greenschist  facies  in  the
Foederata  cover  (up  to  380 °C  and  4.5 kbar;  Lupták  et  al.
2003).  The  metamorphic  conditions  of  chloritoid-kyanite
schists  have  been  estimated  as  530—560 °C  and  6—8 kbar
(Lupták et al. 2000). The southern part of the studied area has
been later affected by HT-LP contact metamorphism related
to the intrusion of Upper Cretaceous Rochovce I-type granite
(Kamenický 1977; Klinec et al. 1980; Vozárová 1990; Hraško
et al. 1998; Poller et al. 2001).

Structural record in the studied area

Within the hanging-wall Gemeric Unit, we identified one

penetrative metamorphic foliation overprinted by two phases
of folding. The greenschist facies metamorphic foliation S

recognized  exclusively  in  the  Lower  Paleozoic  rocks  of  the
Gemeric Unit is regarded as it was by other authors (e.g. Ho-
vorka  et  al.  1988;  Faryad  1990)  as  the  result  of  a  Variscan
tectono-metamorphic  event.  This  foliation  shows  various
orientations due to subsequent folding characterized by steep

or  south  facing  and  generally  E-W  trending  axial  planes  or
low-grade  spaced  cleavage.  On  the  scale  of  the  Gemeric
Unit,  this  latter  cleavage  forms  large-scale  positive  fan-like
structure interpreted as a result of the Early Cretaceous over-
thrusting  of  the  Gemeric  Unit  over  the  Veporic  (Snopko
1971; Lexa et al. 2003). In the proximity of the Gemer-Ve-
por boundary, both Variscan fabrics and steep Early Alpine
cleavage are affected by isoclinal folding with subhorizontal
axial planes and E-W trending axes.

In the footwall Veporic Unit, we recognized three defor-

mation-metamorphic  fabrics  which  were  subsequently  af-
fected  by  one  folding  event.  The  oldest  deformation  fabric
comprises  scarce  relics  of  high-grade  Variscan  foliation  S

in basement migmatites and schists. The first Alpine meta-
morphic foliation S

heterogeneously affects both basement

and cover and dips generally to the E or SE under shallow to
intermediate angles (Fig. 1b,c). The S

fabric bears mineral

and stretching lineation L

defined by shape preferred ori-

entation of quartz aggregates and white mica, which plunges
generally to the east (Fig. 1b,c). The S

is axial planar to the

locally preserved isoclinal folds affecting Variscan foliations
in the basement and bedding in the cover. The fold axes are
typically E-W trending and so subparallel to lineation L

. In

the basement, the S

is only heterogeneously overprinted

by discrete S

cleavage, while in the cover the S

becomes

dominant deformation fabric. This late cleavage dips to the E
or SE at steeper angles than the foliation S

and bears an

east-plunging mostly muscovite-bearing lineation (Fig. 1c).
The S

is axial planar to the locally developed isoclinal

folds F

characterized by N-S trending axes. The S

is de-

fined mainly by shape preferred orientation of chlorite and
white mica. The last deformation event is associated with
upright folding of all previous fabrics and led to the develop-
ment of small-scale crenulations as well as large-scale folds
F

with generally E-W trending axial planes (Fig. 1b,c).

This late stage folding is associated with the development of
a sinistral transpressional shear zone along the NE-SW
trending Gemer-Vepor boundary to the south from the studied
area (Lexa et al. 2003).

In the studied area, the S

and S

fabrics typically show

the low angle extensional shear band cleavage relationships
characterized by discrete cleavage S

cross-cutting the foli-

ation S

(Fig. 2) and thus in the subsequent text, the two

fabrics will be referred to as C and S fabrics, respectively.
These C—S fabrics form an angle ranging between 10 and
30° and are characterized by the normal top-to-the-east sense
of shear. The L

and L

lineations (Fig. 1c) are both per-

pendicular to the C—S intersection implying the synkinematic
character of the two fabrics (Passchier & Trouw 2005).

Analytical techniques

The C—S fabrics in the Veporic Unit were analysed in or-

thogneiss, chloritoid-kyanite schist and quartzite (Figs. 2 and
3a), which allowed us to characterize both fabrics in terms of
quartz deformation microstructure and texture, metamor-
phism and age. The analyses were performed on the thin sec-
tions parallel to the XZ plane of finite strain ellipsoid,

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namely parallel to L

and L

lineations and perpendicular

to intersection of C—S fabrics.

Quartz deformation microstructure have been quantitatively

analysed  by  means  of  the  Computer  Integrated  Polarization
microscopy (CIP) technique of Panozzo Heilbronner & Pauli
(1993)  and  the  Electron  Backscatter  Diffraction  (EBSD)
technique  using  the  HKL  system  attached  to  the  scanning
electron  microscope  TESCAN  at  the  Institute  of  Petrology
and  Structural  Geology,  Charles  University  in  Prague.  The
grain size and grain shape statistics were obtained from man-
ually digitized grain maps based on CIP-derived misorienta-
tion  images  (Heilbronner  2000)  using  the  PolyLX  Matlab

toolbox (Lexa 2003). In this paper, the average 2D grain size
is defined as 1 sigma range of the area weighted logarithmic
mean of equal area diameter. The grain shapes are character-
ized by particle (PAROR) and surface (SURFOR) orientation
distribution functions (ODF) (Panozzo 1983, 1984) shown in
the rose diagrams.

Chemical analyses of selected minerals were carried out

using a EDS detector X-Max 50 (Oxford Instruments) at-
tached to the scanning electron microscope TESCAN Vega
at the Institute of Petrology and Structural Geology, Charles
University in Prague. The analyses were obtained with accel-
erating potential 15 kV and beam current 1 nA. Matrix cor-

Fig. 2. Field photographs (a, b) and micrographs (c, d) of C—S fabrics in the Veporic Unit: a – basement schist, b – Permian quartzite,
c – chloritoid-kyanite schist, d – quartzite (crossed polarizers).

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rection procedure XPP was used based on Phi-Rh-Z method.
The  precision  control  was  held  by  repeated  analysis  mea-
surements  on  known  phases,  mainly  standards.  Standards
that were used for each analysed element (element, detection
limit  of  2  sigma  in  weight  %):  albite  (Na,  0.1);  synthetic
periclase (Mg, 0.04); synthetic Y

(Al, 0.1); sanidine

(Si, 0.16); sanidine (K, 0.04); wollastonite (Ca, 0.04); syn-
thetic rutile (Ti, 0.06); synthetic Cr

(Cr, 0.06); rhodonite

(Mn, 0.08); hematite (Fe, 0.08); pentlandite (Mn, 0.12).

Chloritoid analyses were normalized to 12 oxygens, chlo-

rite was normalized to 14 oxygens and white mica analyses
were normalized to 11 oxygens (see Table 1). The classifica-
tion of white mica followed Tischendorf et al. (2004). X

defined as X

= Mg/(Mg + Fe).

U-Th-Pb dating of monazite was performed directly from

polished thin sections by laser ablation ICP—MS analysis fol-
lowing  the  technique  described  in  Košler  et  al.  (2001).  A
Thermo-Finnigan Element 2 sector field ICP—MS coupled to a
193 nm ArF excimer laser (Resonetics RESOlution M-50 LR)
at  Bergen  University  was  used  to  measure  Pb/U  and  Pb/Th
isotopic  ratios.  The  laser  was  fired  at  5 Hz  using  energy  of
40 mJ/pulse and beam diameter of 7 micrometers, while the
sample was moved underneath the laser beam to produce lin-
ear raster pits ( < 5 µm deep) in the monazite grains. The ab-
lation  was  done  in  He  (0.65 l/min).  A  fragment  of  a  large
monazite crystal from a granulite in the Androyan Complex
in Madagascar (555 Ma: U-Pb TIMS age by R. Parrish, pers.
comm.  and  557 ± 20 Ma:  electron  microprobe  chemical  dat-
ing by Montel et al. 1996) was used to calibrate the Tl-Bi-Np
tracer  solution  that  was  analysed  simultaneously  with  the

ablated  monazite  samples.  In  addition,  two  monazite  sam-
ples  with  known  TIMS  ages  (Tarasinga  leptynite,  India,
953 ± 4 Ma – Aftalion et al. 1988; and garnetiferous gneiss from
the  Lake  Baikal  Complex,  Russia,  1862 ± 4 Ma  –  Aftalion
et al. 1991) were periodically analysed during this study for
quality  control  and  yielded  concordia  ages  of  957 ± 43 Ma
(n = 5 ) and 1868 ± 89 Ma  (n = 3 ), respectively (n = number  of
analyses; all uncertainties are 2 sigma).

Quartz deformation microstructure

All studied samples show two distinct quartz microstruc-

tures related to S and C fabrics as exemplified by two sam-
ples  in  Fig. 3a,  namely  orthogneiss  sample  BZ15  and
quartzite  sample  BZ77  (for  location  see  Fig. 1).  The  S  fab-
rics are defined by recrystallized quartz aggregates with larger
grain  size,  which  are  cross-cut  or  modified  by  localized  C
fabrics  forming  tails  of  recrystallized  grains  with  consider-
ably smaller grain size (Fig. 3a). The aggregates show grain
size within the  ± 1 sigma range of 45—184 µm (d

mean

= 91 µm)

for orthogneiss and 140—403 µm (d

mean

= 237 µm) for quartz-

ite, while the tails show grain size within the range of 20—56 µm
(d

mean

= 33 µm) for orthogneiss and 47—140 µm (d

mean

= 81 µm)

for quartzite (Fig. 3d).

The quartz grains are strongly elliptical in orthogneiss ag-

gregates while the grains in tails from both lithologies and
quartzite aggregates show weak ellipticity (Fig. 3a). The shape
preferred orientation of quartz grains characterized by particle
ODF (PAROR) is subparallel to the long axis of either the

Table 1: Representative chemical analyses of muscovite (Ms), phengite (Ph) and chlorite (Chl) from orthogneiss sample BZ20B, chloritoid
(Cld), chlorite (Chl), margarite (Mrg), paragonite (Pg) and muscovite (Ms) from chloritoid-kyanite schist samples BZ183, BZ349 and
BZ351H and garnet core and rim (GtI, GtII) from garnet-bearing schist BZ188 (for location of samples see Fig. 1).

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Quartz texture

The crystal preferred orientation (CPO) of quartz c-axes

shows  similar  patterns  for  both  orthogneiss  and  quartzite
samples.  Within  the  aggregates  defining  the  S  fabric,  the
c-axis CPOs are characterized by two-point peripheral maxi-
ma,  which  are  symmetrically  distributed  around  the  aggre-
gate long axis at the distance of approximately 50° (Figs. 3b,
4a). Additionally, the aggregate in orthogneiss sample BZ15
shows  two-point  peripheral  c-axis  submaxima  distributed
symmetrically  around  the  aggregate  long  axis  within  ~ 15°
distance. On the other hand, the aggregate in quartzite sam-
ple BZ77 shows minor c-axis submaximum in the centre of
the pole figure. The aggregate double point maxima in both
samples are interpreted as results of activity of the basal  a
slip  system  while  the  submaxima  suggest  prism  a   slip  in

the case of quartzite and prism [c] slip in the case of orthog-
neiss (e.g. Schmid & Casey 1986). By using the fabric open-
ing thermometer of Kruhl (1996, 1998) modified by Morgan
& Law (2004), the c-axis opening angle of ~ 80° (Figs. 3b, 4a)
corresponds to ~ 550 °C.

Within the tails defining the C fabric, the c-axis CPOs show

single  girdle  patterns  inclined  with  respect  to  C  planes
(Figs. 3b,  4b,c).  This  inclination  is  more  pronounced  in  or-
thogneiss sample BZ15 compared to quartzite sample BZ77 as
indicated by the angle of 46—52° and 75° between the single
girdle  trace  and  C  fabric  trace  in  the  pole  figures  (Figs. 3b,
4b,c). The highly inclined c-axis single girdle pattern is char-
acteristic for combined activity of rhomb  a  and prism  a  slip
systems (Keller & Stipp 2011) and suggests a normal sense
of  shearing  along  the  C  planes  (Lister  &  Williams  1979;
Simpson & Schmid 1983; Schmid & Casey 1986).

Fig. 4. The lattice preferred orientation data of recrystallized quartz within S aggregate (a)
and C tail (b, c) in sample BZ15 (same region as in Fig. 3, a – center, b – left, c – right)
obtained by means of electron back-scattered diffraction (EBSD). Each pole figure in lower
hemisphere equal area projection contains the number of measured grains, minimum and
maximum of the density distribution and contours corresponding to 0.5 multiples of uni-
form distribution.

Petrography and mineral

chemistry

Within the imbricated structure of the

studied  area  several  lithologies  have
been  evaluated  by  means  of  petrogra-
phy  and  mineral  chemistry.  These  are
from bottom to top: 1 – basement or-
thogneiss;  2  –  cover  quartzite  (lower
package,  see  Fig. 1c);  3  –  basement
garnet-bearing  schist;  4  –  chloritoid-
kyanite schist of probably cover affinity
and  5  –  cover  quartzite  (upper  pack-
age, Fig. 1b,c). The studied cover rocks
are distinguished as the Rimava Forma-
tion  (Plašienka  et  al.  1997).  In  ortho-
gneiss and chloritoid-kyanite schist, the
analysis revealed that both S and C fab-
rics  are  associated  with  distinct  meta-
morphic records.

In orthogneiss, the S fabric is defined

by  metamorphic  mineral  assemblage
of  biotite,  chlorite,  white  mica,  albite
and  quartz.  In  contrast,  the  discrete  C
fabric  contains  only  chlorite,  white
mica and quartz. While chlorite in both
fabrics  shows  identical  composition  to
(X

= 0.56, sample BZ20B, Table 1),

the chemical analyses of white mica re-
vealed  three  generations  that  include
muscovite I,  phengite  and  muscovite II
(sample  BZ20B  in  Figs. 5a,b  and  6a).
The  first  generation  of  white  mica
(muscovite I)  is  represented  by  large
flakes (ca. 1 mm in size) that are asso-
ciated neither with the S, nor the C fab-
ric and are probably of magmatic origin
(Fig. 4a). The Si content in muscovite I
varies  between  3.09—3.15 a.p.f.u.  (Ta-
ble 1,  Fig. 6a).  Muscovite I  flakes  are
overgrown  by  a  second  generation  of
white  mica  (phengite)  which  is  com-

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Fig. 5. BSE images showing white micas in orthogneiss sample BZ20B (a, b) and mineral assemblage in chloritoid schist samples BZ351H
(c) and BZ183 (d) and their relation to C—S fabrics. a – Large muscovite grain (Ms I) overgrown by phengite (Ph) and younger muscovite
(Ms II) within C fabric. b – Phengite within S fabric replaced by muscovite II within C fabric. c, d – Peak assemblage of kyanite, chlori-
toid, white mica, chlorite and quartz in chloritoid-kyanite schist associated with S fabric being cross-cut by C fabric defined by muscovite-
chlorite. Mineral abbreviations: Ap – apatite, Chl – chlorite, Cld – chloritoid, Ky – kyanite, Ms – muscovite, Pg – paragonite,
Ph – phengite, Qz – quartz, Rt – rutile.

mon in the S fabric (Fig. 5a,b). In accordance with the classi-
fication  of  Tischendorf  et  al.  (2004),  this  white  mica  is
phengite  and  contains  3.27—3.38 a.p.f.u.  of  Si  (Table 1,
Fig. 6a).  The  last  generation  of  white  mica  (muscovite II)
with  3.1—3.15 a.p.f.u.  of  Si  (Table 1,  Fig. 6a)  replaces  the
earlier  phengite  and  it  is  associated  with  the  C  fabrics
(Fig. 5a,b).  An  identical  compositional  sequence  of  white
mica was previously reported from the Veporic basement by
Sulák et al. (2009), however, in their study no relationship to
the deformation structures has been revealed.

The overlying lower cover package quartzite (sample

BZ171) consists of quartz, phengite, monazite, zircon and il-
menite. The chemical analysis of white mica did not reveal
major compositional differences between S and C fabrics in
individual samples. The white mica in quartzite samples lo-
cated closer to the basement orthogneiss is phengite with
3.11—3.34 a.p.f.u. of Si (Fig. 6b).

The overlying garnet-bearing schist typically consists of

quartz, biotite, muscovite, chlorite, ilmenite, ± garnet and

± t schermakite. In sample BZ188 located near the chloritoid-
kyanite schists (Fig. 1b), the garnet consists of two composi-
tional varieties (Fig. 7) with core garnet (GtI) rich in
magnesium, manganese and iron (alm

60—70

, sps

9—13

, prp

9—12

grs

5—6

, Fig. 7, Table 1) and rim garnet (GtII) enriched in cal-

cium (alm

57—62

, grs

20—22

, prp

6—7

, sps

5—6

Fig. 7, Table 1). Such

a compositional zoning has been previously described from
identical  garnet-bearing  schist  from  the  Blh  Valley  by
Korikovsky  et  al.  (1990)  and  Jeřábek  et  al.  (2008).  On  the
basis  of  PT  calculations  the  later  authors  relate  the  garnet
core and rim to the Variscan and Alpine metamorphism, re-
spectively,  implying  the  basement  origin  of  these  schists
(Vrána 1964; Korikovsky et al. 1990; Jeřábek et al. 2008).

The Rimava Formation chloritoid-kyanite schist located at

the contact between the basement schist and Permian cover
quartzite (samples BZ351H, BZ345 and BZ183) consists of
kyanite, chloritoid, white mica, chlorite, quartz ± tourmaline
and accessory apatite, ilmenite, rutile, zircon ± monazite ± all-
anite ± xenotime (Fig. 5c,d). The chloritoids show radial-

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Fig. 7. a – BSE image showing garnet from tschermakite-garnet schist with orientation of compositional profile (sample BZ188). b – Com-
positional profile across garnet grain.

growth  appearance  which  is  commonly  transversal  to  the
S  fabric  and  cross-cut  by  the  C  fabric  (Figs. 2c,  5c,d).  This
indicates an inter-tectonic growth of the kyanite, chloritoid,
white  mica,  chlorite,  monazite  and  quartz  assemblage.  The
chemical  analyses  of  white  mica  revealed  the  presence  of
muscovite, paragonite and margarite, associated with a chlo-
ritoid-  and  kyanite-bearing  assemblage  (Table 1,  Fig. 6d).
The  X

in chloritoid within different samples ranges be-

tween 0.17—0.34 and shows slight but irregular zoning.
Within individual samples the X

in chloritoid differs

mostly by 0.02—0.09. The C fabrics are characterized by
muscovite, chlorite and quartz assemblage. The chemical

Fig. 6. Compositional diagram for white mica from (a) or-
thogneiss  sample  BZ20B,  (b)  quartzite  sample  BZ171C
and (c) arkose sample BZ172B (for location of samples see
Fig. 1  and  for  representative  white  mica  analyses  see  Ta-
ble 1).  The  diagrams  show  (a)  three  white  mica  genera-
tions in orthogneiss: original magmatic muscovite (Ms I),
phengite  (Ph)  from  the  S  fabric  and  younger  muscovite
(Ms II)  from  the  C  fabric  (see  Fig. 5a,b)  and  (b,c)  single
generation  of  white  mica  represented  by  phengite  in
quartzite  (b)  and  muscovite  in  arkose  (c).  The  distinction
between  phengite  and  muscovite  is  based  on  Tischendorf
et al. (2004).

composition of chlorite and muscovite associated with S and
C fabrics, respectively, did not reveal major differences so
that the X

in chlorite is ~ 0.51 and the Si content in mus-

covitic mica ranges between 2.95—3.08 a.p.f.u.

The upper cover package quartzites and arkoses are formed

by white mica-quartz ± chlorite ±albite and accessory ilmenite,
rutile ± apatite ± zircon ± monazite  (Fig. 2d).  The  chemical
analysis of white mica did not reveal major compositional dif-
ferences between S and C fabrics in individual samples. The
rock  is  phengite  absent  comparing  to  the  cover  quartzites
(BZ171).  White  mica  is  muscovite  with  3.09—3.19 a.p.f.u.  of
Si (BZ172B in Fig. 6c; for location see Fig. 1).

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Table 2: Laser ablation ICP-MS U-Th-Pb data for the sample BZ345. Only

208

Pb/

232

Th and

206

Pb/

238

U isotopic ratios and corresponding

ages are presented. Determination of

207

Pb/

206

Pb and

207

Pb/

235

U ages was precluded by low signal intensity of

207

Pb.

Discussion

The C—S fabrics at the contact between the Gemeric and Ve-

poric Units have been previously interpreted as synkinematic
and  related  to  localization  of  deformation  within  the  large
scale detachment shear zone developed during unroofing and
exhumation of the Veporic Dome (Hók et al. 1993; Plašienka
1993; Lupták et al. 2000; Janák et al. 2001). Indeed, the out-
crop  observations  of  C—S  fabrics  in  the  Veporic  Unit  show
that  lineations  on  both  fabrics  formed  at  a  high  angle  to  the
fabrics  intersection,  implying  its  formation  in  a  continuous
kinematically related single-event. In the following discussion
we bring the petrography-petrology, deformation microstruc-
ture  and  geochronology-based  evidence  suggesting  that  the
studied S and C fabrics in the Veporic Unit were in contrast
formed  during  two  independent  and  kinematically  unrelated
tectonic events.

As already mentioned in the structural description, the

studied S fabric is related to subhorizontal Alpine metamor-
phic foliation S

identified elsewhere throughout the Ve-

poric  Unit.  In  the  basement,  this  fabric  is  associated  with
phengite,  garnet,  chloritoid,  staurolite  and  kyanite-bearing
assemblages with  estimated PT conditions ranging between
5—11 kbar and 430—620 °C (e.g. Janák et al. 2001; Jeřábek et
al. 2008). In addition, Jeřábek et al. (2008) documented that
S

foliation is associated with the growth of Ca-rich garnets

marked by prograde compositional zoning. The thermody-
namic PT calculations revealed that the core to rim composi-
tional changes in these garnets correspond to an increase in
both pressure and temperature of up to 1.5 kbar and 50 °C
(Jeřábek et al. 2008). On the basis of this evidence, they con-
cluded that the formation of subhorizontal S

fabric is asso-

ciated with burial of the Veporic Unit and not its exhumation
as previously thought (Snopko 1967, 1971; Hók 1993;
Plašienka 1993). Furthermore, it has been proposed that the
Veporic Unit experienced an Early Cretaceous pure shear
dominated E-W orogen-parallel flow in the lower crust trig-
gered by the orogenic thickening due to overthrusting of the
Gemeric Unit from the south (Jeřábek et al. 2008, 2012).

The thrusting along the Gemer-Vepor interface most likely

led  to  the  formation  of  imbricated  structure  revealed  in  the
studied  area  by  the  bottom  to  top  structural  succession  of
basement  orthogneiss,  cover  quartzite,  garnet-bearing  schist,

chloritoid-kyanite schist and cover quartzite (Plašienka 1980,
1984). The subhorizontal S (S

) fabric in these rocks is asso-

ciated with the growth of phengite and garnet-bearing assem-
blages  (Figs. 5,  6).  The  garnets  in  the  garnet-bearing  schist
sample BZ188 are characterized by two compositional vari-
eties, which show identical chemical composition and zoning
patterns as garnets that were previously reported from the Blh
Valley  to  the  southwest  of  the  studied  area  (Vozárová  &
Krištín  1985;  Korikovsky  et  al.  1990;  Jeřábek  et  al.  2008).
There,  the  garnet I  cores  and  garnet II  rims  have  been  inter-
preted as Variscan and Alpine with PT estimates of  ~ 580 °C at
~ 6 kbar and 510—540 °C at 8—9 kbar, respectively (Jeřábek et
al. 2008). Based on the presence of the two generations of gar-
net in the studied schists, we interpret these rocks as parts of
an  imbricated  Veporic  basement  that  overthrusted  Permian
cover  quartzites.  This  interpretation  contrasts  with  the  previ-
ously assumed Carboniferous deposition age and Veporic cover
affinity  (Planderová  &  Vozárová  1978;  Vozárová  &  Vozár
1988) or Gemeric affinity of these schists (Plašienka 1984).

The observed transversal growth of chloritoid and kyanite

with respect to the S fabric (Fig. 6d) documented in the chlori-
toid-kyanite schist suggests an inter-tectonic growth of this as-
semblage, thus distinctly separating the formation of S and C
fabrics (see also Jeřábek et al. 2012). The chloritoid and kya-
nite-bearing assemblage in these schists has been used to con-
strain metamorphic PT conditions of 6—8 kbar and 530—560 °C
(Lupták et al. 2000). The distinct white mica compositions
revealed from the structurally lower and upper belt of cover
quartzites (Figs. 1, 6) might indicate a difference in meta-
morphic grade that is most likely related to the hanging-wall
and footwall position of the two belts with respect to the de-
tachment shear zone cross-cutting the imbricated structure of
the Gemeric-Veporic contact zone.

The C (S

) fabrics developed within this shear zone are

defined by the lower grade chlorite- and muscovite-bearing
assemblage (Figs. 5, 6) and show systematic top-to-the-east
sense of shear observed either macroscopically (Fig. 2) or in-
ferred from the inclination of quartz c-axis single girdle
CPOs (Fig. 3b). These metamorphic and kinematic observa-
tions are consistent with the activity of the major detachment
shear zone at the Gemer-Vepor boundary associated with ex-
humation and unroofing of the Veporic basement (Plašienka et
al. 1999; Janák et al. 2001; Jeřábek et al. 2012). The Alpine

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metamorphic field gradient across this detachment is charac-
terized by rapid transition from low-grade metamorphism in
the hanging-wall Gemeric Unit and Veporic Permo-Triassic
Foederata  cover  to  higher  grade  metamorphism  within  the
footwall  Permian  quartzites  and  arkoses,  and  Veporic  base-
ment (Lupták et al. 2000, 2003). The main detachment is lo-
cated  within  the  Permian  quartzitic-arkosic  rocks  as
suggested by sharp metamorphic contrast between the mus-
covite-bearing  arkose  sample  BZ172  and  chloritoid-kyanite
schist  samples  BZ183,  BZ345  and  BZ351  (for  the  position
of the detachment see map in Fig. 1b). Towards the structur-
al  footwall  in  the  west,  the  garnet-bearing  basement  schist
(sample  BZ188,  Fig. 1)  and  underlying  phengite-bearing
Permian  quartzite  (sample  BZ171,  Fig. 1)  are  expected  to
record similar metamorphic conditions as the chloritoid-kya-
nite schists, which are in turn fairly similar to the basement
metamorphic conditions in the west.

Quartz microstructures and textures from S and C fabrics

corroborate well the above-discussed metamorphic character
of  both  fabrics.  Larger  quartz  grain  size  together  with  the
transition from basal  a  to prism [c] slip systems within the
S fabric point to medium metamorphic conditions and a wa-
ter  saturated  environment  (Okudaira  et  al.  1995),  which  is
consistent  with  550 °C  obtained  from  the  fabric  opening
thermometer (Kruhl 1996, 1998; Morgan & Law 2004). On
the other hand, the smaller quartz grain size and the activity
of rhomb  a  and prism  a  slip systems within the C fabric is
characteristic for greenschist facies metamorphic conditions
(e.g. Stipp et al. 2002). Following the interpretation of (Kilian
et  al.  2011),  the  inclination  of  the  surface  ODF  maximum
with  respect  to  orientation  of  particle  ODF  maximum  and  C
fabric (Fig. 3) is related to quartz crystal preferred orientation
being  dominated  by  rhomb  a   and  prism  a   slip  systems.
Thus  it  is  suggested  that  the  surface  ODF  maximum  together
with overall monocline symmetry of surface ODF within the re-
crystallized C tails is promoted by a high amount of rhombohe-
dral grain boundaries (Kuntcheva et al. 2006).

The dated monazite appears in close association with the

inter-tectonic  chloritoid  and  kyanite-bearing  assemblage
(Fig. 8a,b)  indicating  that  monazite  formation  post-dates  the
burial-related S fabric. For this reason, the U-Th-Pb concordia
age of 97 ± 4 Ma (Fig. 9) should be treated as the limiting age
for the development of S fabric in this region. On the contrary,
the  C  fabrics  are  associated  with  exhumation  of  the  Veporic
Unit and thus their formation age can be constrained by the
previously  published

Ar/

Ar cooling ages. The in situ

Ar/

Ar UV laser probe dating of white mica (Janák et al.

2001) from chloritoid-kyanite schist below the main detach-
ment provided a mean age of 73 ± 8 Ma ( ± 1 sigma, sample
HAN2). The same authors obtained similar ages of 72 ± 7 Ma
and 77 ± 9 Ma from two other basement metapelite samples to
the west of the studied area. On the other hand, a large number
of

Ar/

Ar cooling ages obtained by step-heating method

from micas in the Veporic basement and cover concentrate be-
tween 87—83 Ma (Maluski et al. 1993; Dallmeyer et al. 1996;
Kováčik et al. 1996; Putiš et al. 2009) indicating slightly older
age of the exhumation process. One way or the other, these
geochronological constraints indicate at least 10 million years
time gap between the formation of the S and C fabrics.

Conclusions

Independent, kinematically unrelated C—S fabrics have been

identified  in  the  Alpine  metamorphosed  rocks  of  the  Central
Western Carpathians along the boundary between major base-
ment-cover Gemeric and Veporic Units. The C—S fabrics occur
within  a  major  detachment  shear  zone,  which  cross-cuts  the
earlier imbricated structure related to overthrusting of the Ge-
meric Unit over Veporic. The evidence from deformation micro-
structures,  petrology  and  geochronology,  suggests  that  the  S
fabric formed during an Early Cretaceous subhorizontal lateral
flow  associated  with  overthrusting  of  the  Gemeric  Unit  and
burial  of  the  Veporic  Unit,  while  the  C  fabric  originated  via
Late  Cretaceous extensional shearing within the major  detach-
ment shear zone associated with exhumation of the Veporic Unit.

Acknowledgments:  This  work  was  financially  supported  by
the research Grant from the Czech Science Foundation GACR
205/09/1041, the Ministry of Education, Youth and Sports of
the  Czech  Republic  Research  Plan  No. MSM0021620855,
Charles  University  Science  Foundation  GAUK  5041/2012;
and  by  Slovak  Research  and  Development  Agency  (Project
APVV-0080-11  to  M.  Janák),  the  Slovak  Scientific  Grant
Agency VEGA (Project 2/0013/12 to M. Janák). F. Finger, R.
Vojtko and D. Plašienka are thanked for their careful reviews.

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