GeolCarp_Vol53_No5_315

GEOLOGICA CARPATHICA, 53, 5, BRATISLAVA, OCTOBER 2002

315 — 325

JOINTING IN THE SILESIAN NAPPE (OUTER CARPATHIANS,

POLAND) – PALEOSTRESS RECONSTRUCTION

LEONARD MASTELLA and ANDRZEJ KONON

Institute of Geology, University of Warsaw, Al. Żwirki i Wigury 93, 02-089 Warszawa, Poland; mastella@geo.uw.edu.pl,

konon@geo.uw.edu.pl

(Manuscript received August 1, 2001; accepted in revised form June 18, 2002)

Abstract: The joint network in the Silesian Nappe is composed of a shear system (diagonal sets – S

, S

) – striking in

the present position at high angles to map-scale fold axes, a single extension set T – striking sub-perpendicular to these
axes, fold-parallel joints L and L’ striking parallel or at small angles to map-scale fold axes. For palaeostress reconstruc-
tions penetrative S

, S

and T joint sets were analysed from 197 outcrops. In the palaeostress analysis the angular

difference between the

Hmax

directions calculated from shear (S

, S

) and extension T joints is notable. The angular

difference between these

Hmax

directions suggests that it is a result of a slight tectonic bending of the investigated

Silesian Nappe arc, which took place between the nappe thrusting phase and the proceeding uplift phase of this part of
the Outer Carpathian arc.

Key words: Miocene, Oligocene, Outer Carpathian arc, Silesian Nappe, tectonic bending, shear and extensional joints,
paleostress.

Introduction

The main objective of this paper is the general description and
determination of the origin of the joint network in the Polish
part of the Silesian Nappe (Fig. 1A), as well as a tentative re-
construction of paleostresses responsible for the creation of
this network. It was also tested in Ukraine and in Romania
(Fig. 1B).

This paper continues the research on jointing initiated in the

Polish part of the Outer Carpathian arc, for example, by
Książkiewicz (1968), Tokarski (1975), Henkiel & Zuchiewicz
(1988), Aleksandrowski (1989), Mardal (1995), Zuchiewicz &
Henkiel (1995), Mastella et al. (1997), Rubinkiewicz (1998),
Zuchiewicz (1998), Mastella & Zuchiewicz (2000) and in the
Inner Carpathians by Boretti-Onyszkiewicz (1968).

Penetrative systematic fractures, cutting singular beds with-

out offset related to shear or only with a marked tendency for
offset, generally perpendicular to bedding and at spacing
roughly equal to bed thickness (Mastella 1972) are analysed in
the paper. They can be entirely referred to as joints (Jarosze-
wski 1972; Hancock 1985; Dadlez & Jaroszewski 1994;
Dunne & Hancock 1994).

Geological setting

The geological structure of the Polish part of the Silesian

Nappe is well known (Książkiewicz 1977; Ślączka 1971), and
documented by detailed maps at the scale of 1:50,000, as well
as general maps at the scale of 1:200,000 (Sokołowski 1959a;
Świdziński 1958a; Burtan et al. 1981; Golonka et al. 1979;
Ślączka & Żytko 1979). According to these analyses, the Sile-
sian Nappe comprises strongly deformed folds, imbricate
thrust zones and faulted shaly-sandstone flysch beds, ranging
in age from the Cretaceous to the Miocene (Figs. 2, 3).

Methods

The observations of joints were carried out in single large

outcrops  or  in  series  of  outcrops  typically  located  in  stream
bottoms,  rarely  within  quarries.  Measurements  were  taken
from sandstone and claystone beds of varying age, thickness
and  lithology.  Measurements  from  197  outcrops  within  the
Silesian Nappe were subject to further analysis. Some of them
were already studied earlier (Mastella et al. 1997).

The analysis is based on data from selected outcrops located

in the Silesian Nappe. Joint planes were measured outside
fault zones within the first order regional folds trending in ac-
cordance with the Carpathian arc.

The measurement resolution was ±2

. In each outcrop 50 to

120 joint surfaces were measured. According to earlier papers
(Mastella 1988; Zuchiewicz 1997; Rubinkiewicz 1998) this
number constitutes a statistically representative set for joint
analysis.

In interpretations of the joints formation, the authors rely on

the uplift model, where the main assumption is that rocks
could retain residual strain energy (Price 1959, 1966).

Following Price (1959, 1966), Książkiewicz (1968),

Jaroszewski (1972) and Aleksandrowski (1989) the majority
of the joint sets had a prefolding origin (Sheperd & Hunting-
ton 1981) and they were controlled by the action of residual
compressive tectonic stresses and tensile stresses, which tend
to develop during uplift.

This is indicated by the fact that the joints of a single set

with variable strike in fold limbs, attain the same orientation
after the rotation of fold axis and fold limbs to horizontal, and
the rotation of beds in limbs to horizontal about the bedding
strike. This origin is also testified by the formation of jointing
in poorly lithified horizontal beds (Mastella 1988) and the dis-
placement of joints by flexural slip during folding (Mastella &
Ozimkowski 1979).

316 MASTELLA and KONON

In consequence, following, for example, Murray (1967),

Książkiewicz  (1968)  or  Hancock  &  Al-Kadhi  (1982),  dia-
grams of measurements after back tilting of beds to horizontal
were also prepared (Fig. 4). The stereograms with plotted con-
tours of the normals to joint surface show a unified orientation
of  the  particular  joint  sets.  Along  with  rose  diagrams,  these
projections made a basis for recognition of the dominant azi-
muths  of  joint  sets.  In  further  calculations  (Fig.  4)  (and  see
Mastella & Zuchiewicz 2000 – Fig. 5) this allows determina-
tion of the orientation of the maximum horizontal compressive
stress axes (

Hmax

) for particular joint sets.

To determine regional trends, for selected data the trend sur-

face analysis tool was applied (e.g. Davis 1973). It helped to
isolate regional anomalies by computing trend residuals. The
residuals allowed determination of where differences from the
regional background are localized. To smooth out the data the
small differences were ommitted. The residuals were comput-
ed for the first polynomial order, representing the difference
between observed values and trend values. The “order” of a
trend surface equation refers to the highest values of the expo-
nents used in the equation. On the basis of this information, a
flat trend surface map was created.

Characteristics of the joint network

At regional scale the joint network comprises five sets of

fractures (Figs. 5, 6A), which are, however, rarely all encoun-
tered together in individual outcrops. Typically, only two or
three sets occur in a single outcrop (Fig. 7). Particular sets
show relatively stable strike in relation to the strike of regional
folds. In their present position two joint sets (S

and S

) repre-

Fig. 1. A – Tectonic sketch of the Polish part of the Outer Carpathians (after Książkiewicz 1972), B – Tectonic sketch of the Car-
pathian-Pannonian region (after Linzer 1996).

Fig. 2. Lithostratigraphic column of the Silesian Nappe in the Pol-
ish part of the Outer Carpathians (simplified after Unrug 1969;
Żytko 1973; Ślączka & Kamiński 1998). The number of studied
localities for particular lithostratigraphic beds are given in circles.

JOINTING IN THE SILESIAN NAPPE – PALEOSTRESS RECONSTRUCTION 317

sent diagonal joints (Figs. 5, 7), whereas set T is almost per-
pendicular to the regional folds orientation. The remaining sets
L and L’ are sub-parallel to fold axis (Fig. 5). Due to their use-
fulness for paleostress reconstruction (Mastella et al. 1997;
Mastella & Zuchiewicz 2000) the S

, S

and T joint sets were

mainly analysed.

The S

and S

sets of the diagonal joint system

Both sets are characterized by similar morphological fea-

tures. They are generally perpendicular to the bedding. Frac-
tures several millimetres wide are filled with calcite (Fig. 8).
Both surfaces of a single non-mineralized joint fracture resem-
ble mould and cast, or have plume structures with axes parallel
to the joint/bedding surface intersection present on them. Even
on surfaces belonging to one joint set the axes of the S-type
plumes (Engelder 1985) are variably oriented, which indicates
the random sense of the initial propagation of joints (Parker
1942). The presence of such structures is attributed to the ex-
tensional opening of these fractures (Bankwitz 1965, 1966;
Engelder 1985).

Traces of joints on the bedding surfaces are typically recti-

linear (Fig. 7). Locally, instead of a rectilinear trace, an en ech-
elon shear array can occur. These fractures correspond to low
angle (R) Riedel shears (terminology after Riedel 1929; Bar-
tlett et al. 1981) (Fig. 8B), occasionally passing into continu-
ous fractures (Fig. 8A,C). They probably represent incipient
forms preceding the formation of continuous joint fractures of
the analysed system. Riedel shears included within the en ech-
elon arrays, cut only several millimetres into the beds. If the
loosening of the joints was along the en echelon array, fringe
structures appear on their surfaces.

Despite the different orientation in particular outcrops, both

sets cross at acute angles within 45

—75

(Figs. 6, 7, 9), domi-

nantly trending at 60

—69

T set

Joints of this set are distinctly different from joints of the di-

agonal system. Typically, the joint surfaces are sub-vertical.
When, however, the fold axes are tilted, they are non-kathetal-
ly oriented. Traces of the intersection with bedding are irreg-
ular, mostly curvilinear, without en echelon fractures. Mainly
S-type plume structures occur. The plume axes are common-
ly horizontal, but in rare cases they have different orienta-
tions.

Opening of these extension fractures is larger than in the

case of other fractures. They are also less commonly filled
with calcite, which, if present, is often crumbled (Tokarski et
al. 1999). Joint surfaces are usually uneven and they lack
fringe structures.

L and L’ sets

Within the entire Silesian Nappe arc, joints sub-parallel to

the orientation of the regional folds occur in two sets. Joints of
set L are sub-parallel to map-scale fold axes, whereas joints of
set L’ strike at low angles (up to 20

) to these axes (Aleksand-

rowski 1989) (e.g. Fig. 6A).

Both sets display significant similarities with respect to joint

surfaces and bed/joint intersection traces. In both sets there are
no indications for their shear origin. Typically, the traces are
curvilinear,  fading,  discontinuous  and  superimposed  on  one
another (Fig. 7B). The fissures are several millimetres wide,
rarely filled with calcite. The surfaces of a single fracture are
usually of the mould and cast type or with plume structures.
These  are  particularly  common  on  the  surfaces  of  most  L’
joints, in contrast to their rare occurrence on L joints. The lat-
ter  case  can  be  observed  in  the  hinge  zones  of  large  folds,
where  the  joints  bear  features  of  typical  radial  fractures
(Jaroszewski 1980; Price & Cosgrove 1990).

Fig. 3. Geological cross-sections through the Silesian Nappe (simplified after Sokołowski 1959b; Świdziński 1958b); for location see Fig. 1.

318 MASTELLA and KONON

W part

Middle part

E part

Azimuths Wisła

Wisła-
Skawa

Skawa-

Raba

Mszana Raba-

Dunajec

Dunajec
Wisłoka

Wisłoka-

Osława

270÷284 285÷299 320÷334 335÷349 340÷354 355÷4

0÷9

10÷19

335÷349 350÷4

20÷34

30÷54

45÷54

60÷69

75÷84

Hmax

)

310

325

357

Hmax

(T)

320

330

357

∆*

-10

-5

-3

+10

+12

* ∆ magnitude of angular difference between the

Hmax

directions calculated from shear joints

, S

) and extension joints (T)

Regional variability of the orientation of diagonal (S

, S

)

and transverse (T) joint sets

Despite the small variability of orientation within particular

outcrops, all the described joint sets display a large regional
variability (Figs. 6, 9).

Set S

of the diagonal system in the westernmost part of the

investigated part of the Silesian Nappe is W-E trending (domi-
nant class 270—284

) (Table 1, Fig. 6A), gradually changing to

320—334

between the Skawa and Raba rivers, to an almost

meridional orientation between the Dunajec and Wisłoka riv-
ers (Fig. 7A) and NNE-SSW (dominant class 10—19

) in the

easternmost part of the area (Fig. 6C).

Similarly, azimuths of S

joints change from 335—349

the westernmost part of the investigated section of the Silesian
Nappe, N-S between the Wisła and Skawa rivers, NW-SE be-
tween the Raba and Wisłoka rivers to almost E-W (dominant
class 75—84

) in the easternmost part of the area (Table 1).

Therefore both S

and S

sets change their azimuths from the

west to the east at about 100

T joints change their azimuths in a narrower range, ca. 75

from ca. 320

in the western part of the area, ca. 0

in the central

Fig. 5. Scheme of the joints pattern in folded sandstones (diagonal
shear system: S

– dextral, S

– sinistral, T – transversal, L

and L’ – longitudinal sets) (after Książkiewicz 1968 – modi-
fied). For other explanations see text.

Table 1: Variability of joint parameters.

Fig. 4. Scheme showing the method of determining the dominating
directions  and  parameters  of  the  joint  network,  based  on  measure-
ments in a recumbent fold from the Krosno Beds in the Biecz quarry
(A). Diagrams with contours of joint planes (N – number of mea-
surements):  B – before back tilting of beds to horizontal, C – af-
ter  back  tilting  of  beds  to  horizontal,  D  –  directions  of  join  sets
(shear  system:  S

– dextral, S

– sinistral; T – transversal; L

and L’ – longitudinal sets) inferred from the dominants of Fig. 4C
(values of azimuths of the dominating directions of sets are given;
the arrows indicate offset along the diagonal system). E – Selected
parameters of the joint network: double value of the shear angle 2

Hmax

– axis of maximum compressive stress. For other explana-

tions see text.

JOINTING IN THE SILESIAN NAPPE – PALEOSTRESS RECONSTRUCTION 319

Origin of joints

Diagonal system S

, S

The presented characteristic of both sets indicates that they

were controlled by the action of residual stresses which reflect
conditions in the particular tectonic phase (Price 1959, 1966).

During the incipient stage the joints were formed as initial

shear surfaces (Jaroszewski 1972). In turn, their opening took
place  (Price  1959,  1966;  Książkiewicz  1968;  Jaroszewski
1972; Engelder 1985) in the extensional mode, when residual
stresses  acted  (Zuchiewicz  1998;  Mastella  &  Zuchiewicz
2000).  The  pattern  of  en  echelon  and  feather  fractures  indi-
cates  that  S

and S

joints represent dextral and sinistral

shears, respectively (Figs. 6C, 8B). Abutting and cutting rela-
tionships (Fig. 8A,C) indicate (Jaroszewski 1980; Mandl
1988; Engelder 1989) that they are coeval. In this case the
acute dihedral angle between these sets represents the double
value of the shear angle (2

) (e.g. Handin et al. 1963; Han-

cock 1985).

Additionally, the uniform shear character of both sets within

the investigated part of the Silesian Nappe and the stable ori-
entation of the acute bisector between these two sets indicate
that both S

and S

sets form a conjugate strike-slip system

developed in a triaxial shear stress field (

) (Fig. 10).

This is in line with earlier observations from the Silesian
Nappe (Mastella et al. 1997), as well as from the Dukla Nappe
(Mastella & Zuchiewicz 2000).

Transverse T set

The common occurrence of fracture structures pointing to

their extensional development (Bankwitz 1965, 1966), charac-
ter of fissures and their filling, lack of shear indicators reveal
the  extensional  development  of  this  set  in  the  analysed  area
(Książkiewicz  1968;  Jaroszewski  1972;  Aleksandrowski
1989; Tokarski et al. 1999; Mastella & Zuchiewicz 2000). On
the  basis  of  their  perpendicular  orientation  to  regional  fold

Fig. 6. Rose diagrams of joints in the Silesian Nappe: A – western part (Wisła region), B – middle part (Raba river), C – eastern part
(Rabski stream); the sketch displays a sandstone bed with joints. N – number of measurements; for other explanations see Fig. 4. For lo-
cation of diagrams see Fig. 1A.

part, 20—25

east of the Dunajec river and ca. 35

in the eastern-

most parts of the investigated area (Table 1). Their orientation is
perpendicular to the regional fold axes (Mastella et al. 1997).

Fig. 7. Joints in a sandstone bed – A in the Mszana Dolna region
(Mszanka stream); B – near Cieszyn. For location see Fig. 1. For
other explanations see Fig. 4.

320 MASTELLA and KONON

Fig. 8. Diagonal system of joints in a sandstone bed: A – in the Szczyrzyc region, B – in the San river region, C – in the Sękówka riv-
er region. For location see Fig. 1. Other explanations as in Fig. 4.

Fig. 9. Rose diagrams of joints from outcrops: A – in the Opór river region (Skole – Ukraine), B – in the Cacica stream region (Hu-
morolui Mt. – Romania), C – in tributary of the Bistriti river region (Bacau – Romania). For location see Fig. 1A. Other explanations
as in Fig. 4.

Fig. 10. Theorethical Mohr’s stress circles representing rock stress
conditions for S

, S

joints as well as T set development (after

Price & Cosgrove 1990 – with modifications).

axes, and on theoretical (Price 1959, 1966; Jaroszewski 1972)
and regional studies (Aleksandrowski 1989; Zuchiewicz 1998;
Mastella & Szynkaruk 1998; Mastella & Zuchiewicz 2000), T
joints are interpreted as a result of the parallel action of maxi-
mum, compressional principal stress and of the minimum, ten-
sile principal stress acting perpendicular to this orientation
(Fig. 10).

The prevailed presence of horizontal plume axes on the

planes of the T joints and the discussed geometrical relation-
ship between the T joints and joints of other sets indicate that
the T joints are younger than the S

, S

sets and probably the

L set. The regional tendency to vertical orientation of the sur-
faces of the T joints points to a late- or even post-folding for-
mation of these fractures.

L and L’ sets

Taking into account the tensional character of the L joints

and their relationship to the hinge zones of regional folds, it

JOINTING IN THE SILESIAN NAPPE – PALEOSTRESS RECONSTRUCTION 321

can be assumed that their formation is linked with early buck-
ling of beds (Książkiewicz 1968; Aleksandrowski 1989). The
origin of the L’ set is unclear.

Reconstruction of the joint stress fields

The presented description shows that particular sets and sys-

tems  of  the  regional  joint  network  are  of  different  origin.
Therefore they can be linked with different stress fields of dif-
ferent  age.  The  type  and  orientation  of  the  stress  fields  is
somehow recorded within the joints, and following, for exam-
ple, Jaroszewski (1972) and Engelder (1985), and for the Pol-
ish  part  of  the  Outer  Carpathians  also  Książkiewicz  (1968),
Zuchiewicz  (1998),  Rubinkiewicz  (1998),  Mastella  et  al.
(1997), Mastella & Zuchiewicz (2000), it may be reconstruct-
ed,  particularly  from  the  diagonal  (S

, S

) and transverse T

sets.

Diagonal system S

, S

The oldest diagonal system developed within horizontal

beds in compressional conditions with positive

axes. The orientation of these stress axes can be reconstructed
after back tilting of beds to horizontal (Bucher 1920, 1921;
Ramsay & Huber 1987).

The axis of the maximum horizontal compressive stress,

marked as

Hmax

, S

) can be estimated as the bisector of

the double shear angle 2

(e.g. Fig 6A,C, 8C, 9B) (e.g. Han-

cock & Al-Kadhi 1978, 1982). Its orientation points to a dis-
tinct regional variability along the Silesian Nappe arc (Mastel-
la et al. 1997). The generalized trend

Hmax

, S

) is 310

the westernmost part of the area, and changes through N-S ori-
entations in the central part, to 35

in the east and up to 47

the easternmost part (Table 1). Thus a fan-like

Hmax

, S

)

trajectory pattern was formed, with an obtuse angle of ca. 100

and trajectories perpendicular to the bending of the Silesian

Nappe arc (Mastella et al. 1997). Similar patterns were sug-
gested for this part of the Outer Carpathians for the Early and
Middle Miocene (Nemčok 1993, Fig. 9b—d; Fodor et al. 1999,
Fig. 5b—c) and for many compressional orogens (e.g. Laub-
scher 1972; Tapponier & Molnar 1976; Angelier et al. 1986;
Huchon et al. 1986).

Transverse T joints

The T joints formed during the final phase of thrusting of

the Outer Carpathians. This suggests that the maximum com-
pressive stress was still nearly horizontal during T joints for-
mation.

As commonly recognized (e.g. Price 1959; Jaroszewski

1972; Hancock & Al. Kadhi 1978, 1982; Zuchiewicz 1998),
the strikes of these joints determine the orientation of the max-
imum horizontal compressive stress, marked as

Hmax

(T). The

orientation of this axis in the westernmost parts of the investi-
gated area has an azimuth of ca. 320

, and eastwards changes

gradually to roughly N-S between the Skawa and Dunajec riv-
ers, to ca. N35

E in the easternmost parts of the area (Table 1)

(Mastella et al. 1997). Thus, as in the diagonal system, the

Hmax

(T) trajectories form a fan-like pattern, however at a

smaller angle, ca. 70

. This pattern was also recognized in the

Central Carpathians from the Late Miocene (Nemčok 1993 –
Fig. 9f) to the Quarternary (Fodor et al. 1999 – Fig. 6), and
has recently been identified the Polish part of the Outer Car-
pathians (Jarosiński 1998).

In the paleostress analysis, the angular difference between

the

Hmax

directions inferred from

shear joints and extension

joints was noted. Estimation of the regional differences, based
on the smooth trend surface map, for the residuals computed
for the first polynomial order points to the occurrence of slight
differences between these

Hmax

directions (Fig. 11).

In the westernmost part of the investigated fragment of the

Silesian Nappe arc, the

Hmax

, S

) is deflected ca. 10

westwards from the

Hmax

(T). The angular difference gradual-

Fig. 11. Magnitude of angular difference between

Hmax

directions inferred from

the shear joints and extension joints, after 1

order

polynomial trend surface analysis in the Polish part of the Silesian Nappe.

322 MASTELLA and KONON

ly decreases eastwards and approximately at the Cracow me-
ridian changes its orientation to ca. 12

eastwards in the east-

ernmost part of the area (Table 1, Fig. 11). The identical ten-
dency for the eastwards deflection of

Hmax

, S

) in relation

Hmax

(T) also occurs in the Polish part of the Dukla Nappe

(Mastella & Zuchiewicz 2000). Comparison with data outside
the Silesian Nappe from Ukraine and Romania suggests lack
of angular differences (Fig. 9).

Conclusions

In the analysed part of the Silesian Nappe the joint network

developed in several stages characterized by different stress
orientation.

1. The beginning of the development of the joint network

should be linked with the moment when the flysch rocks of the
Outer  Carpathians,  still  in  horizontal  position,  were  lithified
enough to cumulate stresses resulting from the convergence of
the  European  plate  with  microplates  of  Pannonia  (Royden
1988), N Pannonia – ALCAPA (Alpine-Carpathian-Pannon-
ian  block  system)  (e.g.  Csontos  et  al.  1992;  Plašienka  et  al.
1997; Fodor et al. 1999), in a tri-axial stress field

with horizontal

and

and vertical

in original position.

The general trend of the maximum horizontal compressive
stress axis was N-S in this fragment of the Outer Carpathian

arc (Tapponier 1977; Tokarski 1978; Fodor 1995; Fodor et al.
1999).

The shear joint system was initiated within horizontal beds

in this stress field. In those places where the shear strength of
the rocks was exceeded, S

and S

joints of this system ap-

peared (Fig. 12 – I stage). According to Pescatore & Ślączka
(1984) and Mastella (1988), this stage began in the Oligocene
in the Silesian Nappe.

2. Along with the proceeding increase of N-S horizontal

compression, folding began (Książkiewicz 1972), probably by
the end Early Miocene—Ottnangian?, Karpatian (Oszczypko
1997, 1998). In wide fragments of the fold hinge zones, ten-
sion L joints with strikes parallel to the fold axes and features
of radial fractures appear (Mastella & Zuchiewicz 2000). At
the same time, along with the gradual uplift of the folded beds,
S

and S

joints appeared as extension fractures, as a result of

the relaxation of residual stresses. Such development of joints
took place during the entire thrusting phase.

3. In the next phase, after the Middle Miocene, when the

thrust front began to be fixed, the strong uplift of the analysed
part of the Outer Carpathians commenced (Książkiewicz
1972; Żytko 1999; Fodor et al. 1999).

With the decrease of compression, the horizontal stress axis

perpendicular to the maximum compressive axis attained neg-
ative values, what led to the formation of extension T joints
(Fig. 12 – II stage) by extension sub-parallel to the Silesian

Fig. 12. Evolution of

Hmax

trajectories in the Silesian Nappe – based on the shear joint system S

and S

and extension joint set T.

(Sketch after Pożaryski 1979; Fodor et al. 1999; Kutek 2001 – simplified).

JOINTING IN THE SILESIAN NAPPE – PALEOSTRESS RECONSTRUCTION 323

Nappe arc. This is a common feature in many collisional oro-
genic belts and in their forelands (e.g. Hancock & Bevan
1987; Julivert & Arboleya 1984; Dietrich 1989; Doglioni
1995; Nemčok et al. 1998a; Konon 2001).

The angular difference between

Hmax

, S

) and the

Hmax

(T) orientations suggests that they reflect a slight tecton-

ic bending of the investigated Silesian Nappe arc, which took
place between the nappe thrusting phase and the phase of pro-
ceeding uplift of this part of the Outer Carpathian arc.

In the gradually bent Silesian Nappe arc, shear joints were

rotated: counterclockwise (CCW) in the left part of the defor-
mation belt, and clockwise (CW) in the right part of the defor-
mation belt (Fig. 12 – II stage). In the thus bent Silesian
Nappe arc T joints developed, as a result of extension sub-par-
allel to Outer Carpathian arc.

The tectonic bending of the Silesian Nappe in the final

phase of its deformation is confirmed by the probable presence
of a bending mechanism during the formation of this part of
the Carpathian arc indented between the Bohemian Massif and
the edge of the East-European Platform. It led to the CCW ro-
tation of the Western Carpathians and CW rotation of the East-
ern Carpathians, as can be concluded from the analysis of pa-
leomagnetic data (e.g. Krs et al. 1991; Patrascu et al. 1994 and
references therein; Márton & Fodor 1995 and data compiled
by Fodor et al. 1999). Similarly, the oroclinal bending of the
Inner Carpathians, after overthrusting of the Krížna Nappe
(Kruczyk et al. 1992), confirm that the curvature of the Outer
Carpathians originated due to tectonic deformations.

The same mechanism of the formation of the Carpathian arc

can be inferred from structural data (e.g. Birkenmajer 1979,
1985; Marko 1993; Nemčok 1993; Nemčok & Nemčok 1994;
Fodor 1995; Fodor et al. 1999; Mastella & Szynkaruk 1998;
Nemčok et al. 1998a; Mastella & Zuchiewicz 2000; Konon
2001).

Test investigations in Ukraine and Romania have shown that

the tectonic bending appeared only in the Polish part of the
Outer Carpathians.

The method based on the estimation of the angular differ-

ences in the pattern of trajectories of maximum horizontal
stresses for the S

and S

as well as the T joints allowed us to

estimate the degree of bending of the Silesian Nappe between
the development of the S

, S

joints sets and the T joints set.

The constant stress field in the Silesian Nappe during the

formation of joints points to the lack of considerable reflection
of  stress  orientation  changes  in  the  investigated  fragment  of
the Carpathian arc, induced by the relocation of the subduction
zone  towards  the  Eastern  Carpathians  due  to  the  roll-back
mechanism  (e.g.  Burchfiel  &  Royden  1982;  Nemčok  et  al.
1998a,b; Fodor et al. 1999).

The probable lateral eastward escape of part of the Eastern

Alps (Ratschbacher et al. 1989, 1991; Fodor 1995), as well as
the Carpathians (Nemčok 1993) has left more significant trac-
es in the Inner Carpathians.

Acknowledgments:  The  authors  are  indebted  to  Dušan
Plašienka  and  two  anonymous  reviewers  for  their  comments
and  thorough  reviews.  Piotr  Nieścieruk,  Jacek  Rubinkiewicz
and Ryszard Szczęsny are thanked for their help in field inves-
tigations.

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