- Email: [email protected]
Cenozoic stress field and jointing in the outer West Carpathians, Poland
J.CeoQnamics Vol.26,No. I,pp. Sl--68, 1998 (;I 1998 Elsevier Science Ltd
Pergamon PII: SO264-3707(97)00043-4
All rights reserved. Printed in Great Britain 026~3707198 $19.00+0.00
CENOZOIC STRESS FIELD AND JOINTING IN THE OUTER WEST CARPATHIANS, POLAND WITOLD
ZUCHIEWICZ”
Institute of Geological Sciences, Jagiellonian University, Oleandry 2A, PL-30063 Krak6w. Poland (Recriwd
30 January 1997; revised 9 July 1997; accepted 9 July 1997)
Abstract-The Polish segment of the outer Carpathians fold-and-thrust belt is composed of a number of North-verging nappes. Preliminary studies of joint patterns within different lithostratigraphic units of these nappes, as well as within discordantly overlying younger strata, enable one to constrain the Late Cretaceous through Quaternary stress fields of that region. In the medial segment of the area studied, joints have been analysed in several nappes, most of the data coming from the Magura Nappe. In the latter one, joint pattern suggests diversified orientation of the reconstructed maximum stress axes, depending on the age of strata. The maximum stress axis inferred from the position of the acute bisector between conjugate Coulomb-shear or hybrid-shear fractures is oriented N-S within the Turonian-Campanian, NNE-SSW in the Maastrichtian, ENE-WSW in the Palaeocene, and NNW-SSE within the Eocene through Miocene strata. The maximum stress axes reconstructed for post-Cretaceous strata of other nappes in the eastern part of the area studied are oriented NNE-SSW to NE-SW, being nearly perpendicular to the fold axes. On the other hand, the Pliocene molasses of the Inner Carpathians display joint patterns indicative of the NE-SW oriented maximum stress axis, which coincides with that in the eastern segment of the Polish outer Carpathians, both in the Paleogene strata and in the unconformably overlying Middle Miocene molasses. 0 1998 Elsevier Science Ltd. All rights reserved
INTRODUCTION The Polish segment of the outer Carpathians (Fig. 1) represents a typical fold-and-thrust belt that is composed of a stack of nappes piled one upon another throughout the middle and late Miocene times. The stratigraphic inventory of these nappes includes Cretaceous through Lower Miocene flysch strata of variable thicknesses (Ksiazkiewicz, 1977). The thrusting proceeded gradually with time towards the North and the East, as a result of
*Author
to whom all correspondence
should be addressed: 57
Fax: 0048-12-6332270;
E-mail: [email protected].
5x
W. Zuchiewict
I
I
I
8
r vwv
Fig.
1.Ages
of the last cpsode
KARPATIAN (16.5 - 17.5 Ma) AND OLDER MIOCENE BADENIAN
(13
16.5 Ma)
SARMATIAN - PANNONIAN (12 - 13 Ma) (6 12 Ma)
of thrusting
In the outer (‘arpathlans \lud>
(based on Royden.
198X) and location
of the
arex
oblique convergence between the North European and Pannonian plates (cf. Royden. 1988; Oszczypko and Slaczka, 1989 and discussion therein). The studies of joint patterns within different lithostratigraphic flysch members of the Polish outer Carpathians make it possible to constrain the Cenozoic stress field of that region (Fig. 2). Cross-fold joints are ubiquitous in flysch series of the outer Carpathians (Ksiazkiewicz. 1968; Tokarski, 197.5; Mastella, 1988: Aleksandrowski, 1989; Mardal. 1995; Zuchiewicz and Henkiel, 1995). They are composed of I- 2 sets of transverse joints (T,, T,) and a single set of joints that are perpendicular to the fold axes (T). The more frequently occurring T, and T, joints display planar. smooth. unmineralised surfaces. At some locations, set T, becomes statistically dominant. The acute bisector between sets T, and T, varies from 20 to 80 . averaging at 60 70 These sets represent conjugate Coulomb-shear and. sometimes. hybrid-shear fractures. whose bisectrix is perpendicular to the fold axes and parallel to the T joints. The latter display rough, curved surfaces that are frequently lined with calcite veins. up to IOcm thick. These properties indicate an extensional origin of the T joints. According to Ksiazkiewicz (1968). cross-fold shear fractures first originated during folding of the nysch basins. and were later transformed-during postorogenic uplift--into extensional joints. A younger generation is to be represented by longitudinal, orogen-parallel extensional joints (Ksiazkiewicz. 1968; Aleksandrowski, 1989) which are not dealt with in this paper. Another problem is the origin of joints within poorly consolidated Pliocene and Quaternary molasses. These are probably seismic joints formed due to Quaternary reactivation of shallow. sub-surface faults in the basement (Krysiak, 1987; Rauch and Tokarski. 1995). The aim of this paper is to reconstruct the Cenozoic stress field in the Polish segment of the outer Carpathians based on an analysis of the jointing both in folded nysch strata and
Cenozoic stress field and jointing in the outer West Carpathians,
Poland
59
60
W. Zuchiewicz
in unconformably overlying younger sediments. as well as to compare day pattern revealed by k-situ stress measurements.
MATERIAL
it with the present-
AND METHODS
Joints and shear fractures have been analysed at more than 100 stations within the Magma, Dukla, Silesian and sub-Silesian Nappes (Fig. 2) most of the data coming from the Magura Nappe, the innermost and largest nappe of the Polish outer Carpathians. Selected exposures of Miocene and Plio-Quaternary molasses have also been studied. Each time, 100 measurements have been made and, for stations situated in fold limbs, rotation of the beds into a horizontal position has been performed (Fig. 3). Then, kathetal crossfold joints have been identified and analysed with respect to the fold axes. The axes of maximum compression are considered to bisect acute angles between conjugate Coulombshear or hybrid-shear fractures (Price and Cosgrove. 1990: Hancock, 1991).
KESU LTS
The reconstructed axes of maximum compression are oriented in the medial sector of the Magura Nappe, N-US in the TuronianCampanian. NNE -SSW within the Maastrichtian. ENE-WSW in the Palaeocene. and NNW SSE in the Eocene through Oligocene flysch strata (Figs 4 and 5). Similar axes reconstructed for post-Cretaceous strata of the other nappes in the eastern sector of the area studied are oriented NE SW to NNE SSW (Figs 6 and 7). i.e. nearly perpendicular to the structural grain of this area Miocene molasses of the Carpathian Foredeep near Krakow (Figs 2 and 4) revjeal another pattern of jointing. There occur four sets of extensional joints perpendicular to ul and one set of gypsum veins (Rauch and Tokarski, 1995) that were formed during 4 episodes of deformation: N--S oriented Langhian extension. and 3 subsequent compressional events (N-S, NE-SW, and NW-SE). the last one being active since Pliocene times. The Pliocene coarse-elastic, freshwater molasses in the Podhale area. Inner Carpathians of 0, (cf. site 2 in Fig. 2) are cut by fractures that indicate the NE-SW orientation (Zuchiewicz, 1994). This orientation is similar to that inferred for the eastern segment of the Polish outer Carpathians (Figs 6 and 7) and that detected by breakout analyses (NNESSW) for flysch strata in the western part of the Magura Nappe (cf. Jarosinski, 1996). The Lower Quaternary. Villafranchian-type gravelstones at Witow, east of Krakow (Figs 2 and 8), are dissected by several sets of joints and small-scale faults of throws up to 1 m that probably originated due to earthquakes induced by deglaciation of the Elsterian-2 icesheet (Krysiak, 1987: Zuchiewicz. 1995). Joint sets are usually oriented W--E and NNW-SSE, whereas faults trend NE-SW and NNW -SSE. The only one, hitherto described as a Late Quaternary (Eemian?) normal fault, oriented NW SE in the Polish Outer Carpathians close to Nowy Sacz (Tokarski, 1978). does not allow us to reconstruct stress field axes. Recently performed analyses of breakouts in the Western Carpathian Foredeep (Fig. 2)
~_ ._~.~~ Fig. 3. Examples central Magura
of stereograms of jointing wthln
Upper (‘rrtLlceous-Paleogenc
___~__
___-,
fysch strata of the western and
Nappe, shown at present (A) and restored into hori;lontal position (B) attitude
of bedding.
Cenozoic stress field and jointing in the outer West Carpathians,
EDDING
SENONIAN-PALAE N
PALAEOCENE
UPPER EOCENE
Poland
61
W, Zuchiewicr
62
B n q
Pieniny Klippen Belt
1nner Carpathians
Outer Carpathians
Miocene molasses both autochthonous and allochthonous onesI
principal and subordinate thrusts -oh .I
m
Carpathian foreland E
minor thrusts and imbricated slices
orientation of the maximum stress axes inferred from
studies of joints
indicate a NNW-SSE orientation of the present maximum horizontal stress, that in the eastern part being N-S in the substratum of Miocene molasses (Jarosinski, 1994). Discussion The stress tield responsible for joint opening in the medial segment of the Polish Outer Carpathians was probably associated with the Miocene folding and thrusting. In the light
Cenozoic stress field and jointing in the outer West Carpathians, TURONIAN-MAASTRICHTIAN
Poland
63
MAASTRICHTIAN
EOCENE-OLIGOCENE PALAEOCENE
54
a Fig. 5. Orientation members
of the maximum stress axes inferred of the central part of Magura Nappe,
from joint sets within different lithostratigraphic medial sector of the Polish outer Carpathians.
flysch
of previously performed studies of joints within flysch strata, it is difficult to reconstruct unequivocally the patterns of deformation and stress field changes. The inferred position of tectonic compression (Fig. 9) could be interpreted in three ways: 1. As an effect of right-lateral rotation by approximately 150”, whose sense was closely related to the Late Alpine folding and thrusting, migrating diachronously along the Carpathian arc from the West to the East, 2. As a byproduct of alternating episodes of compression and extension of variable orientation, and 3. As a result of nonrotational change of stress axes cr, +cr3. To test these three hypotheses, it is necessary to carry out further detailed structural studies throughout all tectonic units of the Polish Carpathians. Nevertheless, one should take notice of the fact that the orientation of the dominant joint sets in the Upper Cretaceous and Paleogene-Neogene strata are different. Whereas jointing in the Senonian flysch strata is highly scattered, the Paleogene series display a fairly consistent, radial pattern of the reconstructed stress axes that are perpendicularly aligned to the overall strike of thrusts and principal folds. It appears that the previously discussed idea of at least two different episodes of folding of the Upper Cretaceous strata, during the Laramian and Miocene events (cf. Oszczypko et al., 1991) should be taken into account. The recent orientation of the maximum horizontal compression within flysch strata in the western part of Magura Nappe is NNE-SSW, changing to N-S close to the Carpathian frontal thrust (Jarosinski, 1996). Focal solutions of recent (1992, 1993) earthquakes in
W. Zuchiewicz
64
r/l
Carpathian
a
Outer Carpathians
Foredeep
j-J-J Pieniny Klippen Belt H
m
-p -
Inner Carpathians
I 0’
Miocene m I on eroded #$%~~%iis”“~ rincipal and subordinate thrusts minor thrusts of imbricated slices *es of maximum corn res@qn Inferred from the stud1 2 s of joints
Fig. 6. Orientation of the maxlmtun stress axes m the eastern sector of the Polish Carpathians. Outer Carpathian nappes: MA = Magura. DU = Dukla. SI = Siiesian, SSI = sub-Silesian. SK = Skole, ST = Stebnik.
Cenozoic
65
DUKLA NAPPE EOCENE-OLIGOCENE
OLIGOCENE
SILESIAN NAPPE OLIGOCENE-LOWER MIOCENE
OLIGOCENE
tJ If 38
33
Fig. 7. Orientation
of the maximum stress axes inferred from joint sets within different members in the eastern sector of the Polish outer Carpathians.
WlTdW - N
Rysch
WIT6W - W 350
Fig. 8. Joints
lithostratigraphic
IO
and small-scale faults within Lower Quaternary coarse-elastic sediments at Withw, Foredeep east of Krakow. Dominant orientations shown in black.
Carpathian
66
W. Zuchiewicr
Krynica area. southern part ofthe Magura Nappc. point to horizontal compression oriented NNW BE to N S (Wiejacz. 1994). These data confirm the common opinion about a N S to NNW SSE oriented Pliocene Quaternary compressive stress field in the Carpathian arc (c:f: Csontos cl/ trl.. 1991: Mueller ct trl.. 1993: ZuchiewicL. 1995: Peresson and Decker, 1996). The Miocene molasses of the C‘arpathian Foredccp and unconformably o\,erlying Lowe] Quaternary coarse-c&tic l’anglomerates witnessed several episodes of deformation. the youngest of which was asociated with ;I local position of 0, NW- SE to NNW -SSE ((:/I Rauch and Tokarski, 1995): a feature indicative of reactivation of faults in the basement of the Carpathian Foredeep.
(‘ONC’LIJSIONS
A relatively good coincidence between ~hc predominantly Early Miocene, the fan-like pattern of the maximum tectonic stress axes reconstructed for folded Paleogene Hysch and the orientation of c, inferred for younger, strata in the Polish Outer Carpathians, unconformably overlying sediments suggests that the contemporary stress field of that region has not changed significantly since Miocene times. This is probably due to the persistence of ;t generally N-S oriented collision between the Adria and European plates and related eastward escape of the Alpine lithosphcrc within the time-span discussed. No traces of a Late Miocene E W directed compressional episode. postulated by Peresson and Decker (1996). have been found so far. A word of caution should be added however. because there are no Upper Mioccnc sediments preserved in that segment of the Outer Carpathians.
Cenozoic stress field and jointing in the outer West Carpathians,
Poland
67
The youngest, Plio-Quaternary orientation of the maximum horizontal stress (N-S to NNW-SSE) coincides with that determined by well-bore breakouts (Jarosinski, 1994. 1996) and fits roughly into the pattern shown by the world stress map in that part of Europe (~6 Zoback, 1992). Ackno~ledgemenrs-Financial support for this research Poland (KBN) through grant 9T12B02009 is gratefully
from the National acknowledged.
Committee
for Scientific
Research
of
REFERENCES
Aleksandrowski, P. (1989) Structure of the Mt. Babia G&a region, Magura Nappe, Western Outer Carpathians: an interference of West and East Carpathian fold trends. Ann. Sot. Geol. Polon. 55, 375423 (in Polish, with English summary). Csontos, L., Tari, G., Bergerat, F. and Fodor, L. (1991) Evolution of the stress fields in the Carpatho-Pannonian area during the Neogene. Tectonophysics 199, 7339 1. Hancock, P. L. (1991) Determining contemporary stress directions from neotectonic joint systems. In Tectonic Stress in the Lithosphere (Whitmarsh, R. B., Bott, M. H. P., Fairhead, J. D. and Kusznir, N. J. eds) Phil. Trans. Royal Sot. London A 337, 29-40. Jarosinski, M. (1994) Measurement of directions of recent lithosphere stress in Poland based on breakout analysis. Przeglad Geolqgiczny 12, 9961003 (in Polish with English summary). Jarosinski, M. (1996) Contemporary stress partitioning in the Polish Western Carpathians. In PANCARDI Workshop 1996 “Dynamics of the Pannoniancarpathian-Dinaride System” (Decker, K. ed.) Mitt. Ges. Geol. Berghaustud. asterr 41, 112-l 13. Krysiak, Z. (1987) Tectonic features in Witow gravels. In Tertiary and Lower Quaternary graoels of the Sandomierz Basin (Rutkowski, J. ed.), Symp., Krakow, AGH, 39-41 (in Polish). Ksiazkiewicz, M. (1968) Observations on jointing in the Flysch Carpathians. Ann. Sot. Geol. Polon. 38, 3355384 (in Polish with English summary). Ksiazkiewicz, M. (1977) The tectonics of the Carpathians. In Geology qf‘ Poland, Vol. 4, Tectonics (Pozaryski, W. ed.), pp. 476618. Publ. House Wydawnictwa Geologiczne, Warszawa. Mardal, T. (1995) Joints in the outer flysch Carpathians, Southern Poland. In Mechanics of Jointed and Faulted Rock (Rossmanith, H.-P. ed.), pp. 2799283. Balkema, Rotterdam. Mastella, L. (1988) Structure and evolution of Mszana Dolna tectonic window, Outer Carpathians. Ann. Sot. Geol. Polon. 58, 533173 (in Polish with English summary). Mueller, B., Zoback, M. L., Fuchs, K., Mastin, L., Gregersen, S., Pavoni, N., Stephanson, 0. and Ljunggren, C. (1992) Regional patterns of tectonic stress in Europe. J. Geophps. Res. 97(B8), 11783-I 1803. Oszczypko, N., Cieszkowski, M. and Zuchiewicz, W. (1991) Variable orientation of folds within Upper Cretaceous-Palaeogene rocks near Szczawa, Bystrica Subunit. Magura Nappe, West Carpathians. Bull. Pol. Acad. Sci., Earth Sci. 39, 888107. Oszczypko, N. and Slaczka, A. (1989) The evolution of the Miocene basin in the Polish Outer Carpathians and their foreland. Geologica Carpathica 40, 23336. Peresson, H. and Decker, K. (1996) From extension to compression: Late Miocene stress inversion in the AlpineeCarpathianPannonian transition area. Mitt. Ges. Geol. Bergbaustud. osterr. 41, 75586. Price, N. J. and Cosgrove, J. W. (1990) Anal_ysis of Geological Structures. Cambridge Univ. Press, 502 pp. Rauch, M. and Tokarski, A. K. (1995) An approach to structural history of Miocene strata in the Carpathian foreland (Poland). Bull. INQUA Neotectonics Comm. 18, 17--20.
6X
W. Zuchiewicz
Royden. L. H. (1988) Late Cenozoic tectonics of the Pannonian Basin system. In The Pannonian Basin. A Study in Basin Evolution (Royden, L. H. and Horvath, F. eds), AAPG Memoir 45, 27-48. Tokarski, A. K. (1975) Structural analysis of the Magura Unit between Kroscienko and Zabrzez (Polish Flysch Carpathians). Ann. Sec. Gd. Polon. 45, 327-~359. Tokarski, A. K. (1978) On Quaternary fault and jointing in Nowy Sac;! Basin, Outer Western Carpathians. Polrud. ,4ntz. Sot. Grol. Polott. 48, 509-516 (in Polish with English summary). Wiejacz. P. ( 1994) An attempt to determine tectonic stress patterns in Poland. Actct Gcop/~~:s. Polon. 42, 169%176. Zoback. M. L. (ed.) (lY92) World Stress Map-maximum horizontal stress orientations. 1:40,000,000. USGS (presented at the 29th IGC in Kyoto). Zuchiewicz, W. (1994) Late Cainozoic jointing and small-scale faulting in the Polish Outer Carpathians: hints for stress field reorientation. Bull. INQUA Neofectonics Comm. 17, 34 38. Zuchiewicz, W. ( 1995) Selected aspects of neotectonics of the Polish Carpathians. F&t Qua~ernatk 66, 145~~204. Zuchiewicz. W. and Henkiel, A. (1995) Orientation of Late Cainozoic stress field axes in the light of joint pattern analysis in SE part of the Polish Carpathians. Ann&s UMCS. Luhlin, Sec. B 48, 31 1 348 (in Polish with English summary).
Pergamon PII: SO264-3707(97)00043-4
All rights reserved. Printed in Great Britain 026~3707198 $19.00+0.00
CENOZOIC STRESS FIELD AND JOINTING IN THE OUTER WEST CARPATHIANS, POLAND WITOLD
ZUCHIEWICZ”
Institute of Geological Sciences, Jagiellonian University, Oleandry 2A, PL-30063 Krak6w. Poland (Recriwd
30 January 1997; revised 9 July 1997; accepted 9 July 1997)
Abstract-The Polish segment of the outer Carpathians fold-and-thrust belt is composed of a number of North-verging nappes. Preliminary studies of joint patterns within different lithostratigraphic units of these nappes, as well as within discordantly overlying younger strata, enable one to constrain the Late Cretaceous through Quaternary stress fields of that region. In the medial segment of the area studied, joints have been analysed in several nappes, most of the data coming from the Magura Nappe. In the latter one, joint pattern suggests diversified orientation of the reconstructed maximum stress axes, depending on the age of strata. The maximum stress axis inferred from the position of the acute bisector between conjugate Coulomb-shear or hybrid-shear fractures is oriented N-S within the Turonian-Campanian, NNE-SSW in the Maastrichtian, ENE-WSW in the Palaeocene, and NNW-SSE within the Eocene through Miocene strata. The maximum stress axes reconstructed for post-Cretaceous strata of other nappes in the eastern part of the area studied are oriented NNE-SSW to NE-SW, being nearly perpendicular to the fold axes. On the other hand, the Pliocene molasses of the Inner Carpathians display joint patterns indicative of the NE-SW oriented maximum stress axis, which coincides with that in the eastern segment of the Polish outer Carpathians, both in the Paleogene strata and in the unconformably overlying Middle Miocene molasses. 0 1998 Elsevier Science Ltd. All rights reserved
INTRODUCTION The Polish segment of the outer Carpathians (Fig. 1) represents a typical fold-and-thrust belt that is composed of a stack of nappes piled one upon another throughout the middle and late Miocene times. The stratigraphic inventory of these nappes includes Cretaceous through Lower Miocene flysch strata of variable thicknesses (Ksiazkiewicz, 1977). The thrusting proceeded gradually with time towards the North and the East, as a result of
*Author
to whom all correspondence
should be addressed: 57
Fax: 0048-12-6332270;
E-mail: [email protected].
5x
W. Zuchiewict
I
I
I
8
r vwv
Fig.
1.Ages
of the last cpsode
KARPATIAN (16.5 - 17.5 Ma) AND OLDER MIOCENE BADENIAN
(13
16.5 Ma)
SARMATIAN - PANNONIAN (12 - 13 Ma) (6 12 Ma)
of thrusting
In the outer (‘arpathlans \lud>
(based on Royden.
198X) and location
of the
arex
oblique convergence between the North European and Pannonian plates (cf. Royden. 1988; Oszczypko and Slaczka, 1989 and discussion therein). The studies of joint patterns within different lithostratigraphic flysch members of the Polish outer Carpathians make it possible to constrain the Cenozoic stress field of that region (Fig. 2). Cross-fold joints are ubiquitous in flysch series of the outer Carpathians (Ksiazkiewicz. 1968; Tokarski, 197.5; Mastella, 1988: Aleksandrowski, 1989; Mardal. 1995; Zuchiewicz and Henkiel, 1995). They are composed of I- 2 sets of transverse joints (T,, T,) and a single set of joints that are perpendicular to the fold axes (T). The more frequently occurring T, and T, joints display planar. smooth. unmineralised surfaces. At some locations, set T, becomes statistically dominant. The acute bisector between sets T, and T, varies from 20 to 80 . averaging at 60 70 These sets represent conjugate Coulomb-shear and. sometimes. hybrid-shear fractures. whose bisectrix is perpendicular to the fold axes and parallel to the T joints. The latter display rough, curved surfaces that are frequently lined with calcite veins. up to IOcm thick. These properties indicate an extensional origin of the T joints. According to Ksiazkiewicz (1968). cross-fold shear fractures first originated during folding of the nysch basins. and were later transformed-during postorogenic uplift--into extensional joints. A younger generation is to be represented by longitudinal, orogen-parallel extensional joints (Ksiazkiewicz. 1968; Aleksandrowski, 1989) which are not dealt with in this paper. Another problem is the origin of joints within poorly consolidated Pliocene and Quaternary molasses. These are probably seismic joints formed due to Quaternary reactivation of shallow. sub-surface faults in the basement (Krysiak, 1987; Rauch and Tokarski. 1995). The aim of this paper is to reconstruct the Cenozoic stress field in the Polish segment of the outer Carpathians based on an analysis of the jointing both in folded nysch strata and
Cenozoic stress field and jointing in the outer West Carpathians,
Poland
59
60
W. Zuchiewicz
in unconformably overlying younger sediments. as well as to compare day pattern revealed by k-situ stress measurements.
MATERIAL
it with the present-
AND METHODS
Joints and shear fractures have been analysed at more than 100 stations within the Magma, Dukla, Silesian and sub-Silesian Nappes (Fig. 2) most of the data coming from the Magura Nappe, the innermost and largest nappe of the Polish outer Carpathians. Selected exposures of Miocene and Plio-Quaternary molasses have also been studied. Each time, 100 measurements have been made and, for stations situated in fold limbs, rotation of the beds into a horizontal position has been performed (Fig. 3). Then, kathetal crossfold joints have been identified and analysed with respect to the fold axes. The axes of maximum compression are considered to bisect acute angles between conjugate Coulombshear or hybrid-shear fractures (Price and Cosgrove. 1990: Hancock, 1991).
KESU LTS
The reconstructed axes of maximum compression are oriented in the medial sector of the Magura Nappe, N-US in the TuronianCampanian. NNE -SSW within the Maastrichtian. ENE-WSW in the Palaeocene. and NNW SSE in the Eocene through Oligocene flysch strata (Figs 4 and 5). Similar axes reconstructed for post-Cretaceous strata of the other nappes in the eastern sector of the area studied are oriented NE SW to NNE SSW (Figs 6 and 7). i.e. nearly perpendicular to the structural grain of this area Miocene molasses of the Carpathian Foredeep near Krakow (Figs 2 and 4) revjeal another pattern of jointing. There occur four sets of extensional joints perpendicular to ul and one set of gypsum veins (Rauch and Tokarski, 1995) that were formed during 4 episodes of deformation: N--S oriented Langhian extension. and 3 subsequent compressional events (N-S, NE-SW, and NW-SE). the last one being active since Pliocene times. The Pliocene coarse-elastic, freshwater molasses in the Podhale area. Inner Carpathians of 0, (cf. site 2 in Fig. 2) are cut by fractures that indicate the NE-SW orientation (Zuchiewicz, 1994). This orientation is similar to that inferred for the eastern segment of the Polish outer Carpathians (Figs 6 and 7) and that detected by breakout analyses (NNESSW) for flysch strata in the western part of the Magura Nappe (cf. Jarosinski, 1996). The Lower Quaternary. Villafranchian-type gravelstones at Witow, east of Krakow (Figs 2 and 8), are dissected by several sets of joints and small-scale faults of throws up to 1 m that probably originated due to earthquakes induced by deglaciation of the Elsterian-2 icesheet (Krysiak, 1987: Zuchiewicz. 1995). Joint sets are usually oriented W--E and NNW-SSE, whereas faults trend NE-SW and NNW -SSE. The only one, hitherto described as a Late Quaternary (Eemian?) normal fault, oriented NW SE in the Polish Outer Carpathians close to Nowy Sacz (Tokarski, 1978). does not allow us to reconstruct stress field axes. Recently performed analyses of breakouts in the Western Carpathian Foredeep (Fig. 2)
~_ ._~.~~ Fig. 3. Examples central Magura
of stereograms of jointing wthln
Upper (‘rrtLlceous-Paleogenc
___~__
___-,
fysch strata of the western and
Nappe, shown at present (A) and restored into hori;lontal position (B) attitude
of bedding.
Cenozoic stress field and jointing in the outer West Carpathians,
EDDING
SENONIAN-PALAE N
PALAEOCENE
UPPER EOCENE
Poland
61
W, Zuchiewicr
62
B n q
Pieniny Klippen Belt
1nner Carpathians
Outer Carpathians
Miocene molasses both autochthonous and allochthonous onesI
principal and subordinate thrusts -oh .I
m
Carpathian foreland E
minor thrusts and imbricated slices
orientation of the maximum stress axes inferred from
studies of joints
indicate a NNW-SSE orientation of the present maximum horizontal stress, that in the eastern part being N-S in the substratum of Miocene molasses (Jarosinski, 1994). Discussion The stress tield responsible for joint opening in the medial segment of the Polish Outer Carpathians was probably associated with the Miocene folding and thrusting. In the light
Cenozoic stress field and jointing in the outer West Carpathians, TURONIAN-MAASTRICHTIAN
Poland
63
MAASTRICHTIAN
EOCENE-OLIGOCENE PALAEOCENE
54
a Fig. 5. Orientation members
of the maximum stress axes inferred of the central part of Magura Nappe,
from joint sets within different lithostratigraphic medial sector of the Polish outer Carpathians.
flysch
of previously performed studies of joints within flysch strata, it is difficult to reconstruct unequivocally the patterns of deformation and stress field changes. The inferred position of tectonic compression (Fig. 9) could be interpreted in three ways: 1. As an effect of right-lateral rotation by approximately 150”, whose sense was closely related to the Late Alpine folding and thrusting, migrating diachronously along the Carpathian arc from the West to the East, 2. As a byproduct of alternating episodes of compression and extension of variable orientation, and 3. As a result of nonrotational change of stress axes cr, +cr3. To test these three hypotheses, it is necessary to carry out further detailed structural studies throughout all tectonic units of the Polish Carpathians. Nevertheless, one should take notice of the fact that the orientation of the dominant joint sets in the Upper Cretaceous and Paleogene-Neogene strata are different. Whereas jointing in the Senonian flysch strata is highly scattered, the Paleogene series display a fairly consistent, radial pattern of the reconstructed stress axes that are perpendicularly aligned to the overall strike of thrusts and principal folds. It appears that the previously discussed idea of at least two different episodes of folding of the Upper Cretaceous strata, during the Laramian and Miocene events (cf. Oszczypko et al., 1991) should be taken into account. The recent orientation of the maximum horizontal compression within flysch strata in the western part of Magura Nappe is NNE-SSW, changing to N-S close to the Carpathian frontal thrust (Jarosinski, 1996). Focal solutions of recent (1992, 1993) earthquakes in
W. Zuchiewicz
64
r/l
Carpathian
a
Outer Carpathians
Foredeep
j-J-J Pieniny Klippen Belt H
m
-p -
Inner Carpathians
I 0’
Miocene m I on eroded #$%~~%iis”“~ rincipal and subordinate thrusts minor thrusts of imbricated slices *es of maximum corn res@qn Inferred from the stud1 2 s of joints
Fig. 6. Orientation of the maxlmtun stress axes m the eastern sector of the Polish Carpathians. Outer Carpathian nappes: MA = Magura. DU = Dukla. SI = Siiesian, SSI = sub-Silesian. SK = Skole, ST = Stebnik.
Cenozoic
65
DUKLA NAPPE EOCENE-OLIGOCENE
OLIGOCENE
SILESIAN NAPPE OLIGOCENE-LOWER MIOCENE
OLIGOCENE
tJ If 38
33
Fig. 7. Orientation
of the maximum stress axes inferred from joint sets within different members in the eastern sector of the Polish outer Carpathians.
WlTdW - N
Rysch
WIT6W - W 350
Fig. 8. Joints
lithostratigraphic
IO
and small-scale faults within Lower Quaternary coarse-elastic sediments at Withw, Foredeep east of Krakow. Dominant orientations shown in black.
Carpathian
66
W. Zuchiewicr
Krynica area. southern part ofthe Magura Nappc. point to horizontal compression oriented NNW BE to N S (Wiejacz. 1994). These data confirm the common opinion about a N S to NNW SSE oriented Pliocene Quaternary compressive stress field in the Carpathian arc (c:f: Csontos cl/ trl.. 1991: Mueller ct trl.. 1993: ZuchiewicL. 1995: Peresson and Decker, 1996). The Miocene molasses of the C‘arpathian Foredccp and unconformably o\,erlying Lowe] Quaternary coarse-c&tic l’anglomerates witnessed several episodes of deformation. the youngest of which was asociated with ;I local position of 0, NW- SE to NNW -SSE ((:/I Rauch and Tokarski, 1995): a feature indicative of reactivation of faults in the basement of the Carpathian Foredeep.
(‘ONC’LIJSIONS
A relatively good coincidence between ~hc predominantly Early Miocene, the fan-like pattern of the maximum tectonic stress axes reconstructed for folded Paleogene Hysch and the orientation of c, inferred for younger, strata in the Polish Outer Carpathians, unconformably overlying sediments suggests that the contemporary stress field of that region has not changed significantly since Miocene times. This is probably due to the persistence of ;t generally N-S oriented collision between the Adria and European plates and related eastward escape of the Alpine lithosphcrc within the time-span discussed. No traces of a Late Miocene E W directed compressional episode. postulated by Peresson and Decker (1996). have been found so far. A word of caution should be added however. because there are no Upper Mioccnc sediments preserved in that segment of the Outer Carpathians.
Cenozoic stress field and jointing in the outer West Carpathians,
Poland
67
The youngest, Plio-Quaternary orientation of the maximum horizontal stress (N-S to NNW-SSE) coincides with that determined by well-bore breakouts (Jarosinski, 1994. 1996) and fits roughly into the pattern shown by the world stress map in that part of Europe (~6 Zoback, 1992). Ackno~ledgemenrs-Financial support for this research Poland (KBN) through grant 9T12B02009 is gratefully
from the National acknowledged.
Committee
for Scientific
Research
of
REFERENCES
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6X
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Royden. L. H. (1988) Late Cenozoic tectonics of the Pannonian Basin system. In The Pannonian Basin. A Study in Basin Evolution (Royden, L. H. and Horvath, F. eds), AAPG Memoir 45, 27-48. Tokarski, A. K. (1975) Structural analysis of the Magura Unit between Kroscienko and Zabrzez (Polish Flysch Carpathians). Ann. Sec. Gd. Polon. 45, 327-~359. Tokarski, A. K. (1978) On Quaternary fault and jointing in Nowy Sac;! Basin, Outer Western Carpathians. Polrud. ,4ntz. Sot. Grol. Polott. 48, 509-516 (in Polish with English summary). Wiejacz. P. ( 1994) An attempt to determine tectonic stress patterns in Poland. Actct Gcop/~~:s. Polon. 42, 169%176. Zoback. M. L. (ed.) (lY92) World Stress Map-maximum horizontal stress orientations. 1:40,000,000. USGS (presented at the 29th IGC in Kyoto). Zuchiewicz, W. (1994) Late Cainozoic jointing and small-scale faulting in the Polish Outer Carpathians: hints for stress field reorientation. Bull. INQUA Neofectonics Comm. 17, 34 38. Zuchiewicz, W. ( 1995) Selected aspects of neotectonics of the Polish Carpathians. F&t Qua~ernatk 66, 145~~204. Zuchiewicz. W. and Henkiel, A. (1995) Orientation of Late Cainozoic stress field axes in the light of joint pattern analysis in SE part of the Polish Carpathians. Ann&s UMCS. Luhlin, Sec. B 48, 31 1 348 (in Polish with English summary).