GeolCarp_Vol58_No5_465

GEOLOGICA CARPATHICA, OCTOBER 2007, 58, 5, 465—475

www.geologicacarpathica.sk

Introduction

The Bakony Mts occupies the central and southern part of
the Transdanubian Range (TR), an elevated tectono-
morphological ridge outstanding from the surrounding
low hills and plains formed by Upper Miocene to Quater-
nary sediments (Fig. 1). The TR reveals unique informa-
tion on the structural evolution of the western part of the
Pannonian Basin and represents the connection between
the Eastern Alps and Western Carpathians.

The TR is interpreted as the uppermost Cretaceous thrust

sheet within the Alpine nappe pile (Fig. 1) based on seismic
reflection profiles (Tari 1994, 1995), magnetotelluric
soundings (Ádám et al. 1984; Horváth et al. 1987) and
geochronological-tectonic studies of the outcropping
footwall (Fodor et al. 2003). During the rifting of the
Pannonian Basin System, the former thrust planes were
reactivated as detachment faults, and the Transdanubian
Range is situated in the hanging wall of a Miocene
detachment fault system running down from the Kőszeg-
Rechnitz Windows (Tari 1996). Related to this
detachment faulting, the hanging wall was moderately
dissected by normal faults. However, normal faulting was
followed by 2 major structural events recognized by
earlier studies (Mészáros 1983; Kiss et al. 2001); (1) late
Middle Miocene dextral faults with strike-slip type stress

Miocene dextral transpression along the Csesznek Zone of

the northern Bakony Mountains

(Transdanubian Range, western Hungary)

ADA KISS

and LÁSZLÓ I. FODOR

Eötvös University, Institute of Geography and Earth Sciences, Department of Applied and Environmental Geology,

Pázmány Péter sétány 1/C, H-117 Budapest, Hungary; ada@iris.elte.hu

Geological Institute of Hungary, Stefánia 14, H-1143 Budapest, Hungary; fodor@mafi.hu

(Manuscript received June 5, 2006; accepted in revised form March 15, 2007)

Abstract: The authors performed geological mapping and microtectonic measurements around the Csesznek Zone in the
northern Bakony Mts, Transdanubian Range, Hungary. As a result of structural observations a new structural-geological
map was created for this area. Four tectonic phases were separated by the analysis of stress field. The oldest tectonic event
detected in the research area was defined by a WNW—ESE compression and we attribute a Middle Eocene to the earliest
Miocene (50—18 Ma) timing to this phase. On the basis of structural measurements and regional considerations we can
tentatively separate two deformational events in the late Early to Middle Miocene (18—11 Ma) time span. The older “syn-
rift phase” (18—14.5 Ma) is characterized by NE—SW tension and the younger phase is marked by NNW—SSE compression
and perpendicular tension. This strike-slip-type stress field with transpressional character formed or reactivated the main
dextral faults and associated overturned en echelon folds and thrusts in the Csesznek Zone. The latest, Late Miocene to
Pliocene(?) extensional deformational phase (11—3? Ma) segmented the range with normal faults. The newly recognized
transpressional character of the Csesznek Zone indicates that a short syn-rift event of the western Pannonian Basin was
followed by widespread transpression, as it was also described in other parts of the Transdanubian Range. This transpression
can be connected to basin inversion in the easternmost Alps, and important contractional deformation in the eastern
Southern Alps, and northernmost Dinarides. The intensity of this transpression was declining to the NE, where the extensional
deformation prevailed and was influenced by the subduction still going on along the Eastern Carpathian thrust front.

Key words: Miocene, Pannonian Basin, Transdanubian Range, strike-slip tectonics, transpression, stress field.

field (with NNW—SSE compression); (2) and another rela-
tively important Late Miocene tensional phase.

In our paper we present new paleostress data and

structural observations from the northernmost edge of the
Northern Bakony Mts from a deformation zone, which we
will name as the Csesznek Zone (Fig. 1). Although the
zone seems to be part of the systematic WNW striking
dextral faults of the Transdanubian Range, it was not
described up to the present. We demonstrate dextral
faulting in a transpressional setting, which resulted in
unusually strong folding of Paleogene rocks. Together
with other faults, the Csesznek Zone marks a late Middle
Miocene transpressional deformation, which was
widespread in the western Pannonian Basin and also in the
Eastern Alps and northernmost Dinarides.

Geological setting

The Castle Hill of Csesznek represents a WNW—ESE di-

rected, elongated ridge bordered by significant faults
(Figs. 2, 5A). This narrow structure is built up by the Upper
Triassic Dachstein Limestone Formation and Eocene
bioclastic-nummulitic limestone (Szőc Formation). The
platform-type Dachstein Limestone Formation is the most
frequent Mesozoic sedimentary rock in this part of the

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MIOCENE DEXTRAL TRANSPRESSION ALONG THE CSESZNEK ZONE (WESTERN HUNGARY)

calculation, faulting events with similar paleostress axes
were grouped into distinct tectonic phases.

We completed the microtectonic measurements with

structural mapping of the area. In particular, we modified
the fault pattern of earlier maps (Gyalog & Császár 1982).
Outcrop-scale observations, the determined stress axes,
apparent map displacements and cross-sections were used
to determine the fault kinematics, which were not
completed on earlier maps of the area of study (Gyalog &
Császár 1982; Knauer et al. 1983).

Structural analysis

Phase 1

The first stress field is defined by a WNW—ESE

compression, which can locally deviate up to E—W
orientation (Fig. 3). Calculated

is horizontal,

is verti-

cal or horizontal. NW-striking sinistral and W to WSW-
striking dextral microfaults and reverse faults belong to
this phase (see stereograms on Fig. 3).

We detected 7 microfaults belonging to this phase at the

site Bakonyszentkirály (Fig. 3), where Triassic and
Eocene limestones host reverse faults. Conjugate strike-
slip faults are typical structures at the sites “Útibánya”,
“Dudar” (Márton & Fodor 2003), and “Fenyőfő” (Kiss &
Fodor 2003) (Figs. 2 and 3). Near the Telegdi Roth Line,
Sasvári et al. (2003, 2007) also observed sinistral slip
along NW-trending faults.

The youngest deformed sediments belong to the Upper

Oligocene Csatka Formation, thus the phase might have
been active during most of the Early Miocene. A precise
upper time constraint cannot be deduced from the research
area, but projection from northern Hungary suggests pre-
Ottnangian (pre-18 Ma) timing (Fodor et al. 1999; Márton
& Fodor 2003). On the other hand, Eocene age of the
stress field and related structures were proved in several
parts of the Transdanubian Range. Syn-sedimentary
structures were demonstrated in the Buda and Gerecse
Hills (Fodor et al. 1992; Magyari 1994; Sztanó & Fodor
1997, respectively). In the Vértes Hills syn-sedimentary
dykes and faults were perforated by Eocene molluscs and
sponges (Kercsmár 1996, 2005) or were mineralized with
syn-diagenetic iron coating (Mindszenty & Fodor 2002).
The kinematics of these faults are similar to those
observed near Csesznek, so we suggest Middle Eocene to
earliest Miocene timing for phase 1.

Geological cross-sections (Fig. 4) can give a hint for an

early deformation along the main fault zone. The
thickness of the Eocene formations (between the top of the
Triassic and the bottom of the Upper Oligocene) changes
considerably on the two sides of the Csesznek Zone (e.g.
between boreholes Cse-96, -15 and -130, -133 on Fig. 4).
Further NE from the fault zone the Eocene thickness is
constant, but a clear facies change occurs with a transition
from a shallow marine to a shallow bathyal depositional
environment from SSW to NNE (from the Szőc Limestone
to Padrag Marl Formations). The explanation for this

difference can be the following: 1) syn-sedimentary
Eocene motion of an early Csesznek Zone inducing
pronounced subsidence and facies change in the northern
block, 2) latest Eocene to earliest Oligocene faulting of the
formerly isopach Eocene rock body and subsequent Early
Oligocene erosion of the southern block prior to Late Oli-
gocene sedimentation, or 3) post-Oligocene large-scale dex-
tral displacement, which juxtaposed two blocks with
completely different Eocene sequences. Facies and thick-
ness differences seem to prevail in a larger area (along the
northern rim of the Bakony Mts) thus we suggest that the
Eocene deformation and the two other solutions together
can result in the present-day structural setting.

Phase 2

The next deformation is marked by NE—SW tension.

Conjugate normal and oblique-normal faults represent the
typical outcrop-scale structures (Fig. 3). These faults were
observed at the “Útkanyar” and “Útelágazás” sites in
Triassic and Eocene limestones, respectively (Fig. 3). It is
possible that a dextral-normal fault of this phase bounds
the southern block composed of Triassic and Eocene rocks
(Fig. 2). Other similar structures in the surroundings can be
attributed to this phase, like the important Mór Graben
(Fig. 1, Budai et al. 2005).

The minimal stress axis of this phase is not very different

from that of the next phase 3. The separation is based on the
difference in style of deformation, and on regional
considerations, coming from the entire Pannonian Basin.
This latter suggests that NE—SW tension was characteristic
of the rifting phase of the Pannonian Basin (Fodor et al.
1999), starting in the late Early Miocene (Ottnangian) and
persisting up to early Middle Miocene (middle Badenian,
from ~ 18 to ~ 14.5 Ma) (Fodor et al. 1999).

Phase 3

The third tensor group (Fig. 3) is defined by NW—SE to

NNW—SSE compression and perpendicular tension.
Calculated

is sub-horizontal,

is often sub-horizontal

(strike-slip stress field) or vertical (compressional stress
field).

Many slickensides show dextral and sinistral strike-

slip kinematics, but gently dipping reverse or oblique-
reverse faults also occur (Fig. 3). On a small-scale we can
observe such reverse faults on the Castle Hill, e.g. gently
dipping reverse microfaults at “Bozót” and “Kőmosó”
outcrops (Fig. 3). These reverse faults were combined
with strike-slip microfaults, so the fault pattern suggests
transpressional deformation.

Map-scale structures of this phase are significant dextral

faults (Fig. 3), which constitute the Csesznek Zone. The
presented cross-sections seem to suggest that the origin of
some of the faults may belong to phase 1, but the dominant
kinematics, and the map-scale fault pattern of the Csesznek
Zone were achieved during the transpressional deformation.

The contact of the dextral Csesznek Zone and the sur-

rounding Oligocene Csatka Formation is tectonic. At

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MIOCENE DEXTRAL TRANSPRESSION ALONG THE CSESZNEK ZONE (WESTERN HUNGARY)

“Utas” outcrop we observed the strike-slip contact of the
Oligocene, Triassic and Eocene blocks (Fig. 3). The main
fault branch separates the Eocene and Oligocene
formations with pinched Triassic rock slivers (Fig. 4).

We constructed two geological cross-sections based on

well data around the Csesznek Zone (Figs. 2, 4). In the
geological section (Fig. 4) the formation boundaries are
clearly tectonic between the folded-overturned Eocene to
Triassic units and the thick Oligocene formation. The most
significant borehole (Cse-82) is found just SE of the folded
Parkoló outcrop, near the southern boundary of the zone
(Fig. 4). This well contains the repetition of Oligocene and
Eocene layers (Knauer, pers. comm., 2003) indicating post—
Oligocene compressional or transpressional strike-slip
tectonics.

The uplifted Csesznek Zone might be expected to be

dominated by folds and reverse faults, which initially
developed at a high angle to the zone (Sanderson &
Marchini 1984). These faults have a combination of reverse
and strike-slip displacement. In fact, outcrop-scale faults
often have oblique-reverse slip (Fig. 3, “Parkoló”, “Bozót”,
“Kemping”, “Útelágazás” sites). On the cross-sections, on
either side of the blocks faults dip inward, producing
wedge-shaped uplift (Fig. 4). In general these bounding
faults will be steep, oblique-slip faults, but they may flatten
upwards (Sanderson & Marchini 1984). They typically dip
under uplifted blocks producing a positive flower structure.

The transpressional character is confirmed by over-

turned folds, which occur in the nummulitic Szőc Lime-
stone west and east of the castle (Fig. 3); the eastern fold
appeared on the earlier map (Gyalog & Császár 1982). To

the east of the castle, near the road, the exposed fold has a
sub-horizontal limb and a ~ 15 m high overturned limb
with a sharp hinge zone (Fig. 5B). Slickenside lineations
are typical on bedding planes of the steep to overturned
limb. One Nautilus sp. from the Eocene limestone, situated
at layer-parallel position, was also deformed by layer-
parallel slip and bears striae on its sides (Fig. 5B). These ob-
servations point to flexural slip folding. The fold axis is
trending E—W (Fig. 5B, stereogram), sub-parallel to the
zone boundary. Eastward the fold may step to another fold,
located on the Nyerges Hill (Fig. 3), which also trends E—W.
The northern border of the continuation of the Castle Hill
(the Nyerges Hill) can be an en echelon thrust belonging to
the dextral-reverse fault system.

The other overturned fold is located at the western edge

of the castle ridge, above the Kőmosó valley (Figs. 3,
5D). Bedding within the Eocene rocks near the creek dip
30—40º to the north and higher up bend to a sub-vertical
to slightly overturned position (Figs. 4, 5C,D). The sub-
vertical position of the strata can be verified by the
presence of bedding-parallel nummulite tests and
undulating bedding planes (Fig. 5C). The direction of the
fold axis is WSW—ENE, being en echelon to the main
dextral fault. Summarizing the observations we can say that
the transpressional phase activated the long dextral faults
bordering the castle ridge, and formed the WNW—ESE
directed Csesznek Zone itself and the connecting en
echelon structures.

This structural phase affected Eocene formation within

the Csesznek Zone (outcrop “Utas”, “Parkoló”, “Kőmosó”).
The imbricated Oligocene formation is affected by this

Fig. 4. Geological cross-sections throughout the Csesznek Zone. Note slightly changing geometry of the transpressional fault zone.

471

MIOCENE DEXTRAL TRANSPRESSION ALONG THE CSESZNEK ZONE (WESTERN HUNGARY)

deformation, which confirms the post-Oligocene timing of
deformation (Cse-82 borehole, Figs. 2, 4).

Folding was also detected in the outcrop of Dudar by

Taeger (1936), confirmed by our observation (location on
Fig. 1, stereogram on Fig. 3). The youngest deformed rock
in the surroundings of Csesznek was the Upper Oligocene
Csatka Formation at Fenyőfő, ~ 10 km to the west from the
Csesznek Zone (Kiss et al. 2001), where the geometry of
conjugate strike-slip faults is very similar to that observed
in the Csesznek Zone. More precise time constraint cannot
be given from the northern Bakony Mts. On the other hand,
similar structures of the central Bakony Mts (Telegdi Roth
Line) indicate a mid-Miocene, more strictly Sarmatian age
of deformation (Kókay 1976, 1996; Mészáros 1983).

Phase 4

The last stress field is well represented throughout the

area. The phase is characterized by (W)NW—(E)SE tension.
Meso-scale structures of this extension are conjugate
normal faults and in some cases strike-slip faults.

Map-scale structures of this phase are N—S trending dex-

tral-normal oblique faults, which cut through earlier dex-
tral strike-slip faults of the Csesznek Zone itself (Fig. 3).
Such a normal fault occurs west of the castle, and dis-
places sub-vertical to overturned Eocene and Triassic

rocks (Fig. 5C,D). Within sub-vertical Eocene nummulitic
limestone we observed a meter-wide tensional gap filled
with clastic sediment (redeposited Oligocene?).

The extensional Aranyos and Kökényes Grabens are

other map-scale structures, which are located west and south
of the research area, respectively (Fig. 2, Kiss & Fodor
2003). The brittle structures of this phase can be identified
at Bakonyszentlászló in lower Pannonian clay, so the age of
this stress field can be late Pannonian or younger, Pliocene
or even Quaternary. The age and the directions of the stress
axes are similar to the latest Sarmatian—Pannonian tectonic
phase described from the Porva Basin (Kiss 1999). The
phase may correlate with a significant extensional event
(post-rift event) in the latest Tertiary.

Discussion

Description of phases and connection with vertical-axis
rotations

The oldest tectonic event (phase 1) represents a strike-slip

type deformation, which might have changed temporally or
spatially from transtension to transpression or even pure
compression (Fig. 6). The deformation pattern and the stress
field are similar to a number of observations derived from

Fig. 6. Correlation of stress field, rotations and major tectonic events in the Bakony Mts the simplified pattern of significant tectonic
elements are drawn in black colour; less significant elements are grey.

472

KISS and FODOR

the central and northern Transdanubian Range (discussed
in an earlier chapter). Along the Telegdi Roth Line Sasvári
et al. (2003, 2007) measured pre-Ottnangian strike-slip
faults. Their phases “2” and “3” could correspond to our
“phase 1”. In the Csesznek area, we have few data to sepa-
rate two distinct phases.

The stress field might have induced an early phase of

slip of Eocene age along the nascent Csesznek Zone. The
modest faulting could induce differential subsidence
between the southern and northern fault blocks and
indirectly control the facies distribution in the Eocene
basin. We may assume normal or oblique-normal
kinematics along the incipient Csesznek Zone, which
was sub-parallel to the WNW—ESE trending maximal
horizontal stress axis (

). On the other hand, the

bulk of the strike-slip faults could be connected to the “es-
cape/extrusion tectonics” of the Transdanubian Range and
the whole Alcapa (Alpine-Carpathian-Pannonian) block
(Csontos et al. 1991; Fodor et al. 1999; Sasvári et al. 2003).

The first brittle phase of faulting was followed by a coun-

terclockwise rotation of approximately 30º. Although the
time constraints are not very good in the Csesznek area, we
suggest that the change from phase 1 to phase 2 could cor-
respond to the first rotation event of Márton & Márton
(1996) and Márton & Fodor (1995, 2003), having occurred
between 18 and 17 Ma (Fig. 6).

The next deformation events (phases 2 and 3) took

place in the late Early to Middle Miocene (Ottnangian to
Sarmatian, 18—11 Ma), which traditionally corresponds to
the rifting event of the Pannonian Basin. On the basis of
the structural geometry and style of deformation we can
tentatively separate two tectonic phases within this
deformation. The older (phase 2) is characterized by
NE—SW tension and represents the early syn-rift phase of
the Pannonian Basin. The fault pattern was mainly marked
by normal faults, but strike-slip faults with normal
component of slip could also appear. This phase was not
clearly recognized in the work of Kiss et al. (2001) but
demonstrated in more recent publications (Kiss & Fodor
2003; Márton & Fodor 2003; Sasvári et al. 2003,
“phase 4” of Sasvári et al. 2007).

The most significant deformation phase 3 is marked by

NNW—SSE compression and perpendicular tension. This
strike-slip type stress field with transpressional character
formed the main dextral faults and associated overturned
en echelon folds and thrusts. Detailed discussion of this
deformation within and around the Transdanubian Range
will be given in the next chapter. This deformation can be
detected in other areas of the Transdanubian Range, as far
north as the Vértes Hills (Kiss et al. 2001; Márton & Fodor
2003). It is interesting to note that Sasvári et al. (2003,
2007) did not really identify this stress field, their
phases “4” and “5” are slightly different from our calcula-
tions. This difference can be attributed to varying outcrop
conditions and/or different grouping of strike-slip faults.

Comparing the maximal horizontal stress axis of

phases 2 and 3 a slight change of 15—20º in a clockwise
direction can be detected (Fig. 6). This change in orienta-
tion can be correlated with the second rotation event of

the Pannonian Basin, indicated by Márton & Márton
(1996) and Márton & Fodor (1995). Following the compi-
lation of Márton & Fodor (2003) the second rotation was
about 15º in the Bakony Mts and occurred in the middle
Badenian, around 16—14.5 Ma. A similar (apparent) clock-
wise change in stress direction can be deduced from the
dextral faults of the TR; Mészáros (1983) and Tari (1991)
indicated a relative chronology between older WNW and
younger NW-striking dextral faults. All these data are in
agreement with our data, namely the amount of rotation
and its time span correspond well with the angular differ-
ence and the timing of phases 2 and 3.

The latest, Late Miocene extensional deformational

stage (phase 4) segmented the Csesznek Ridge with nor-
mal faults. This phase corresponded to a noticeable “post-
rift” deformation registered in the northern Bakony by
Kiss et al. (2001) and along the Telegdi Roth Line by
Sasvári et al. (2007, their phases “5 and/or 6”). Márton &
Fodor (2003) indicated a young 25º CCW rotation in the
Late Miocene or Pliocene. This rotation might have con-
tributed to the change in stress field from phase 3 to 4
(Fig. 6). However, our data are not enough to decide about
the structural role and timing of this rotation.

Analogue transpressional structures in the Transdanub-
ian Range

Though a few structural elements were already drawn on

maps (Knauer et al. 1983), the recognition of the
transpressional deformation along the Csesznek Zone is a
novelty. The characteristic feature of the zone is that the
amount of contraction seems to be larger than along
similar zones; the deformation resulted in overturned
beds, development of folds and reverse faults.

The Csesznek Zone can be compared to similarly ori-

ented dextral faults, which regularly cross-cut the central
and southern Bakony Mts, some of them with a
transpressional character. The Csesznek Zone itself may
continue in the Gaja fault of the eastern Bakony Mts.
However, the exact identity has not been established yet
(Fig. 7). Closest to Csesznek, the NW—SE striking faults of
the Porva Basin could have a normal-dextral displacement
rather than a transpressional character (Kiss et al. 2001);
this kinematic change can easily be explained by the
difference in strike (Fig. 7).

Along the WNW-striking Telegdi Roth Fault (Figs. 1,

7), Mesozoic rocks were thrust over Middle Miocene
strata (Balla & Dudko 1989; Csontos et al. 1991; Kókay
1996). Deformation generally affected Middle Miocene
formations, but Upper Miocene rocks are not deformed.
Kókay (1976) and Mészáros (1983) suggested that the
main activity of the Telegdi Roth Fault was late Middle
Miocene (Sarmatian) in the best-studied Várpalota Basin
(Figs. 1, 7) although minor activity is probable through
Ottnangian—Karpatian and Badenian sedimentation.

The Herend fault of the central Bakony Mts (Fig. 7)

shows dextral kinematics, based on displaced markers and
fault-slip data (Kókay 1966; Tari 1991; Fodor et al. 1999).
It is related to early Badenian and Sarmatian basin subsid-

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MIOCENE DEXTRAL TRANSPRESSION ALONG THE CSESZNEK ZONE (WESTERN HUNGARY)

Fig. 7. Simplified structural framework of the Alpine-Carpathian region (modified after Fodor et al. 1999) showing the spatial extent of
late Middle Miocene transpression. Frame indicates location of Fig. 7B with detailed sketch of transpressional structures of the Bakony Mts.

ence (in the west and in the east, respectively). The fault
interacts with and partly reactivates Cretaceous thrusts in
its eastern termination (Tari 1991).

In the southern Bakony Mts the Padrag fault (Fig. 7) has

~ 1.5—2 km separation, measured by the displaced Eocene
sequence (Mészáros 1983). The fault also dismembers the
Litér thrust by the same amount (Dudko in Budai et al.
1999). The displacement was accommodated by thrusting
in the Balaton Highland (Mészáros 1983; Tari 1991;
Budai et al. 1999; Fodor et al. 2005) showing the connec-
tion of contractional and strike-slip deformation. Reverse
faulting or the combination of reverse and strike-slip fault-
ing can be postulated south of Lake Balaton, where Balla
et al. (1987) and Csontos et al. (2005) documented con-
tractional structural elements on seismic reflection pro-
files (Fig. 7).

NE of the Bakony Mts, in the Vértes Hills this phase is

represented only by outcrop-scale faults. Márton & Fodor
(2003) described syn-rift normal faults, which are cut by
reverse faults presumably belonging to this post-rift
transpressional phase. This observation may imply that
the intensity of the transpressional deformation decreases
north—eastward, and no sign was documented northward,
in the Gerecse and Buda Hills. In these areas only normal
and oblique-normal faults of the syn-rift and/or post-rift
phases appear, without interruption by strike-slip faulting
(Fodor et al. 1999).

Alpine analogous structures

Traces of the Middle Miocene transpressional event

occur west of the Bakony Mts, in the Eastern Alps. The
south-western basin-margin of the pull-apart Fohnsdorf
Basin (Fig. 7) is connected to the transpressional dextral
Pols-Lavanttal fault system (Sachsenhofer et al. 2000). N-
S compression resulted in the deformation of basin fill,
uplift of the E—W trending basement ridge. The age of
the deformation post-dates the middle Badenian, but

cannot be determined more precisely (Sachsenhofer et al.
2000).

The formation of the pull-apart Trofaiach Basin (Fig. 7)

in the Eastern Alps is related to the E—W trending
Trofaiach strike-slip fault connected to the wrench corri-
dor formation during the Miocene lateral extrusion of the
Eastern Alps (Gruber et al. 2004). Later uplift of the base-
ment rocks and tilting of the oldest basin fill are related to
post-middle Badenian compression (Gruber et al. 2004).

Further to the south, important dextral slip can be

documented along the Periadriatic fault system (PF). The
NW—SE striking dextral tear faults and NW- to NNW-di-
rected thrust planes of the Klagenfurt Basin (Fig. 7) af-
fected the Middle Miocene (Sarmatian) sediments
(Laubscher 1983). The basin subsidence was supposedly
initiated by the distributed dextral strike-slip and thrust
displacement along the northern Karawanken front
(Nemes et al. 1997). The final NNW-directed thrust of the
Karawanken Mts onto their forelands is characterized by a
positive flower structure, which is kinematically linked to
dextral transpressive shearing along the Periadriatic fault
(Polinski & Eisbacher 1992). Pre-Pliocene dextral
transpression is also present along the Slovenian segment
of the PF, and can be separated from younger neotectonic
deformation (Fodor et al. 1998). Further to the east,
Tomljenović & Csontos (2001) demonstrated Sarmatian
transpression in western Croatia (WCr, Fig. 7).

The eastern Southern Alps originated as a result of

polyphase compressional deformation of late Tertiary age.
The ENE—WSW striking Valsugana structural system (Va
on Fig. 7) is Serravallian to Tortonian in age (Doglioni
1987; Castellarin & Cantelli 2000). The intense activity
of this compressional event is documented both by
stratigraphic and structural data which indicate some 4 km
uplift in the hanging wall of the Valsugana thrust between
12 and 8 Ma. The deformation can be in part younger.

This short summary indicates that an important shorten-

ing phase occurred in the eastern Southern Alps—north-

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KISS and FODOR

western Dinarides and in the easternmost Alps. Time con-
straints vary from place to place, but generally can be
bracketed in the late Middle Miocene to earliest Late Mi-
ocene, between 14 and 10 or 8 Ma, although younger re-
activation also occurred in some areas. Thrusting was
often associated with dextral strike-slip faults. The
transpressional deformation of the Bakony Mts and the
Csesznek Zone can be connected to this widespread event.
The intensity of this transpressional deformation seems to
decrease north-eastward within the Transdanubian Range.

The recognition of this transpressional-strike-slip phase

in the TR may have implications for the whole
geodynamical framework of the Pannonian Basin. The late
Early Miocene to Middle Miocene widespread rifting
event of the Pannonian Basin is generally marked by
normal faults, although locally strike-slip faults are also
present, particularly in the TR. We demonstrated that this
tensional (locally transtensional) event was followed by a
transpressional deformation in the southern and central TR.
This late Middle Miocene event seems to be coeval with
renewed rifting in the eastern Pannonian Basin. Thick
sedimentary, volcano-sedimentary layers were deposited,
among others, in the Zagyva Graben and East Slovak Basin
(Kováč et al. 1995). In this latter basin faulting was com-
bined with differential rotation (Márton et al. 2000), which
also enhanced faulting. The accelerated subsidence can be
connected to the subduction below the Eastern
Carpathians, which was still active in this time span
(Ma enco 1997). While the East Carpathian subduction
front was relatively short, the connected back-arc extension
was restricted to the neighbouring eastern Pannonian Basin
(Fig. 7). This also means that the short subduction front
could not bring enough suction force to the western
Pannonian and Eastern Alpine areas, which could not “es-
cape” from the renewed push derived from the north-mov-
ing Adriatic plate (Fig. 7). Thus the syn-rift extension ended
here by the late Middle Miocene and was replaced by com-
pressional or transpressional deformation. This type of de-
formation prevailed up to recent times in the Southern Alps
and in the Eastern Alps, but changed again to extension in
the western Pannonian Basin (including the TR), where
considerable normal faulting reoccurred again in the early
Late Miocene.

Conclusions

Microtectonic data, field observations and well data dem-

onstrate significant transpressional deformation along the
Csesznek Zone, Bakony Mts, western Hungary. For the ob-
served NNW—SSE compression we favour late Middle Mi-
ocene timing ( ~ 13—11 Ma). The Csesznek Zone is similar
to other dextral transpressional faults of the Transdanubian
Range (e.g. Telegdi Roth Line), although it might have ac-
commodated larger contraction. Comparison to other Al-
pine transpressional elements suggests that this deformation
was widespread in the easternmost Alps, Southern Alps,
north-western Dinarides and also in the western Pannonian
Basin, while the subduction and connecting tension were

still active further to the east. The difference in deformation
style can be explained by two boundary conditions: the re-
newed northward push of the Adriatic microplate, and the
shorter subduction front in the Eastern Carpathians. The
first effect induced important ~ N—S shortening in the
Southern and Eastern Alps and western Pannonian Basin,
while the second could not provide enough driving force to
eastward lateral shift and extension of the whole Pannonian
Basin. In consequence, syn-rift extension ended earlier, in
the late Middle Miocene in the western Pannonian Basin.

Acknowledgments: L. Fodor benefited from the Bolyai
János scholarship of the Hungarian Academy of Sciences.
The research was supported of the Hungarian Scientific
Research Found OTKA No. 42799.

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