GeolCarp_Vol51_No3_159

GEOLOGICA CARPATHICA, 51, 3, BRATISLAVA, JUNE 2000

159168

COUNTERCLOCKWISE ROTATIONS OF THE NEOGENE ROCKS

IN THE EAST SLOVAK BASIN

EMÖ MÁRTON

, DIONÝZ VASS

and IGOR TÚNYI

ELGI, Columbus u. 17-23, 1145 Budapest, Hungary

Technical University, Department of Environmental Studies, T.G. Masaryka 24, 960 53 Zvolen, Slovak Republic

Geophysical Institute of the SAS, Dúbravská cesta 9, 842 28 Bratislava, Slovak Republic

(Manuscript received March 17, 1999; accepted in revised form March 15, 2000)

Abstract: Paleomagnetic investigation of sedimentary and volcanic rocks of the East Slovak Basin gave information

about the counterclockwise (CCW) rotation of the Neogene units of Eggenburgian to Middle Sarmatian age. The

Eggenburgian sediments (1 loc. 20 spec.) show about 80° CCW rotation, the zeolitized rhyolite tuffs of Lower Badenian

age (2 loc. 19 spec.) show a 40°60° CCW rotation, the rhyolites (1 loc. 3 spec.) of Upper Badenian age about 50°

CCW rotation, the sediments of Lower-Middle Sarmatian age (1 loc. 6 spec.) gave CCW rotation of about 20° and the

youngest post-Sarmatian rhyolite (1 loc. 9 spec.) did not yield any rotation. The rotation was preceded by left lateral

penetration of the Tissia units into the West- and East-Carpathian boundary zone.

Key words: Western Carpathians, East Slovak Basin, Neogene sedimentary and volcanic rocks, paleomagnetism,

counterclockwise rotation.

Introduction

Recent communications, concerning paleomagnetism (Orlický

1996) and paleomagnetism plus isotope dating (Márton &

Pécskay 1995) of the north-eastern corner of the Inner Car-

pathians suggest that the counterclockwise declination rota-

tions observed on late Badenian-Sarmatian volcanics might be

of tectonic significance.

Orlický interpreted observations from the East Slovak Basin

(ESB) in terms of fault-related small-scale block movements,

while Márton and Pécskay envisage a kind of triangle, bor-

dered by the Hornád/Hernád-line, the Szolnok-Maramures fly-

sch belt and the NE Outer Carpathians, which could have ro-

tated as a unit in late Sarmatianearly Pannonian times. This

rotation would be about 45 Ma younger than the final coun-

terclockwise rotation of the central part of the Inner Western

Carpathians (Márton & Márton 1996; Márton et al. 1996).

The aim of the present study is to seek support for the coun-

terclockwise rotation in the East Slovak Basin also from sedi-

ments or volcano-sedimentary rocks and constrain the timing.

The sampling sites and localities of the present study are

shown on a schematic geological map in Fig. 1, and on a sche-

matic geological map of the pre-Tertiary basement (Fig. 2).

Geology and tectonics

The ESB started to open as a shear basin in the early Mi-

ocene (Eggenburgian, about 22 Ma B.P.). At the beginning, a

narrow furrow opened along the Pieniny Klippen Belt. The

marine transgression reached the basin from the remnant fly-

sch basins of the Outer Carpathians. At the end of the Eggen-

burgian, prograding deltas (Èelovce, Lada) entered the basin,

marking its temporary closure. Deposits of Ottnangian age

(1917.5 Ma B.P.) are missing (Fig. 3).

The ESB started to re-open in the early Karpatian (17.5 Ma

B.P.), by extension (Kováè et al. 1994a). Later, the character

of the paleostress field progressively changed, and shear be-

came the dominant factor in the evolution of the ESB. Shear

controlled basin evolution (Fig. 3) characterizes the late Kar-

patian through late Sarmatian period (1711.5 Ma B.P.). Dur-

ing this period, the basin had the features of a typical pull-

apart basin, including the migration of subsidence centres

(from NW to SE, in recent coordinates) and rapid subsidence

(Vass et al. 1988). The thickness of the deposits during this

period is more than a thousand metres and the whole basin

fill is 80009000 m thick in the centre. Other pull-apart fea-

tures of the basin are the en echelon arrangement of faults,

flower structures on major fault zones, and dismatch between

units of the basement.

The basement of the ESB is built of very different tectonic

units (Fig. 2). These are the Veporic Superunit represented

by the Krína Nappe, Humenné Mesozoic Horst and Veporic

Superunit of the Èierna Hora Mts. partly covered by Central

Carpathian Paleogene. The Kritchevo-Iòaèovce Unit formed

by metamorphic rocks, including slightly metamorphosed

Eocene marine deposits considered by Soták et al. (1993) to

be equivalent of the Vahic/Penninic Superunit. This supe-

runit may correspond to the Nádudvar Formation, or the

Szolnok-Maramures Flysch; the Zemplinic (Zemplén) Unit,

which probably belongs to the Tisza (Tissia) Superunit

(Körössy 1963; Grecula & Együd 1977); the Gemeric Supe-

runit, Bükk Unit and Meliatic Unit (which may represent the

NE promontory of the Pelsó Megaunit which escaped from

the Central Alpine and NW Dinarides area (Kázmér &

Kovács 1985; Haas et al. 1995).

By the end of the pull-apart evolution of the ESB, a strong

andesite volcanic activity started. This volcanic activity is

considered as subduction related and during the Sarmatian

the basin was in an interarc position (Vass et al. 1988).

160 MÁRTON, VASS

and TÚNYI

The recent geophysical evidence of the former pull-apart

character of the basin is the thin continental crust in the south

(including 89 km of basin fill deposits 27 km) which be-

comes thicker (32 km) in the North-Northwest (efara et al.

1987), the high heat flow (more than 110 Wm

) and the high

geothermal gradient (53 °C/km, Král et al. 1985).

The pull-apart history of the basin ended with the Sarma-

tian. During the Pannonian the subsidence significantly

slowed down and the Pannonian deposits are only a few hun-

dred metres thick.

During or after the Pontian, basin inversion took place.

Pliocene deposits are fluvio-lacustrinal and are restricted to

the SE corner of the basin.

Sampling and laboratory measurements

We drilled the Eggenburgian sediment at one, and the

zeolitized tuff of Badenian age at three localities. All these

are in well-controlled tectonic positions. Sarmatian volca-

nosedimentary rocks and andesite were collected at three

localities.

In addition to the sediments and sediment-like deposits,

two rhyolite domes were also sampled. At one of them,

which was earlier sampled by one of the authors (I. Túnyi)

hand samples were taken and subsequently drilled in the lab-

oratory, the other was drilled in the field. A total of 92 inde-

pendently and magnetically oriented samples were taken.

Standard-size cylinders were cut from the drill-cores, mea-

sured and stepwise demagnetized by the thermal and AF

methods or by combining the AF and thermal methods, IRM

and low susceptibility versus temperature experiments were

also carried out to help the identification of the magnetic

minerals. Stepwise thermal demagnetization was carried out

in Bratislava, the other experiments in Budapest.

Results and assessment of data

The samples from the two rhyolite domes yielded excellent

paleomagnetic directions. The NRMs are in both cases sin-

gle-component (Fig. 4), the carrier of the remanence is mag-

netite (Figs. 5a and 6a) and the site mean directions are sta-

tistically very well defined (Table 1).

Fig. 1. Simplified geological map of the East Slovak Basin and sampled sites. Explanation: 15: Neogene sedimentary basin fill and neo-

volcanics. 1 Pliocene; 2 Late Miocene, a sediments, b rhyolite; 3 neovolcanics Middle and Late Miocene in age, a pre-

dominantly andesites and andesite volcano-clastics, b rhyolite; 4 Middle Miocene, a sediments, b zeolitized tuff (Hrabovec

Tuff); 5 Early Miocene (Karpatian); 6 Central Carpathian Paleogene; 7 Outer Carpathian Flysch; 8 Klippen Belt; 9 Meso-

zoic of Krína Nappe Unit; 10 Paleozoic and Mesozoic of Zemplinic Unit; 11 Peleozoic and Mesozoic of Silicic Superunit, Meliat-

ic Unit and Veporic Superunit undivided; 12 Proterozoic of Zemplinic Unit; 13 sample sites, see Fig. 2 and Table 1.

COUNTERCLOCKWISE ROTATIONS OF THE NEOGENE ROCKS IN THE EAST SLOVAK BASIN 161

Fig. 2. Recent situation of the pre-Tertiary units in the East Slovak Basin basement and in its surroundings. 1 faults or unspecified

boundaries of tectonic unit; 2 overthrust lines; 3 state boundaries; 4 sample sites, loc. Nos. (see Table 1); H.F.B. Hornád/

Hernád fault belt.

loc.

no.

locality/site

n/no

D°

l°

age

dip°

Hrádok

rhyolite

SM 111119

9/9

183

363

183

10.513.2 Ma

Lesné

rhyolite

SM 113132

3/4

312

249

312

late Badenian

2b*

Lesné

rhyolite

SM 1133

16/2

311

1080

311

late Badenian

Oreské

zeolitized tuff

SM 112030

11/11

319

early Badenian

226/35

Kuèín

zeolitized tuff

SM 113442

8/9

304

early Badenian

200/55

Niný Hrabovec

zeolitized tuff

SM 11921203

6/12

20middle Badenian

8/50

Lada

claystone

SM 114369

20/21

289

281

30Eggenburgian

269/28

Slanèík

andesite

SM 117683

6/8

338

middle Sarmatian

336/10

Svinica

tuff

SM 118491

11/8

506

062

late Sarmatian

272/9

Table 1: East Slovak Basin site and locality mean paleomagnetic directions of the present study.

n/no numbers used/collected samples; D°,I° (D

°, I

°) declination, inclination before (after) tilt correction; k and

° statistical parameters (Fisher 1953);

* statistics is based on number of speciment (n).

162 MÁRTON, VASS

and TÚNYI

Fig. 3. Schematic lithology, sedimentary cycles and paleostress diagrams of the East Slovak Basin (according to Kováè 1994a, modified).

The zeolitized rhyolite tuffs are weakly magnetic. This ex-

plaines that the demagnetization curves of the NRM are less

smooth than those of the rhyolites. Nevertheless, the compo-

nents of the NRM are well defined (Fig. 7). The IRM acqui-

sition curves suggest that the magnetic mineral is soft (Fig.

6b), and this combined with the stability (Fig. 5b) or moder-

ate increase (Fig. 7) of the susceptibility on heating, suggest

that the NRM is most likely residing in magnetite. The site

mean paleomagnetic directions are statistically fairly well

defined and depart significantly from that of the local direc-

tion of the present Earths magnetic field (Table 1).

The sediments are of different ages and of different litholo-

gies. The Eggenburgian locality, Lada, where several horizons

of the clay stone intercalations in the thick sandstone sequence

were sampled, yield a good paleomagnetic direction. The

Zijderveld diagrams reveal that the NRM is practically single-

component (Fig. 8), the main carrier of the magnetization is

magnetite (Fig 8a, Fig. 6b), though sometimes goethite may

also contribute to the NRM (Fig. 8b). At Lada, the majority of

the samples carry characteristic remanence, with direction sig-

nificantly different from that of the Earths present field at the

sampling area (Table 1). Of the sediments collected at other lo-

calities, Niná My¾a was unstable, while Svinica yielded a

mean direction which is interpreted as a recent overprint (Ta-

ble 1 and Fig. 9). At Slanèík, 6 samples of the collected 8 are

clustered away from the present field direction (Table 1 and

Fig. 10), while two are aligned with the present field (rejected

when computing the locality mean direction).

Discussion

The East Slovak Basin is situated on the ALCAPA (and Tis-

sia) overriding plate of a subduction/collision zone, close to

the inner margin of the accretionary prism. The present (as-

sumed) configuration of the flysch accretionary prism (Outer

Carpathians and the arcuate shape of the Carpathians) suggests

that the collision between the subducting North European and

the overriding Carpathian-Pannonian plates was oblique. The

oblique collision, proceeded by oblique subduction resulted in

164 MÁRTON, VASS

and TÚNYI

Fig. 5. Low-field susceptibility versus temperature curves for

Lesné (upper diagram) and Niný Hrabovec (lower diagram).

Heating curves are of darker, cooling curves are of lighter colour.

Fig. 6. IRM acquisition curves. a Lada (SM1143A) and exam-

ples for zeolitized rhyolite tuffs; b rhyolite doms; c Sarma-

tian sediment Slanèík.

compression oblique to the convergence zone, and produced

shear stress along it. It is generally accepted that in the Car-

pathians the oblique convergence led to bending and final for-

mation of the accretionary prism, i.e. to the whole arcuate

shape of the Outer Carpathians. Along and near the convergent

margin, pull-apart or shear basins were generated. Such basins

connected to the Western Carpathians are the Vienna Basin,

the narrow furrows along the inner side of the Pieniny Klippen

Belt in NW Slovakia, the Transcarpathian Basin, including its

autonomous western part, the ESB.

The ESB was regarded as a pull-apart basin opened by a

major right-lateral strike-slip fault of NW-SE direction (Roy-

den & Báldi 1988; Vass et al. 1988). The lateral displacement

or wrench faulting caused the breaking up of the area into

elongated blocks by en echelon faults and the blocks

moved relative to each other along faults, corresponding to

Riedel Shears of the strain ellipsoid. The elongated blocks,

termed Riedel Flakes (Dewey 1982) when generated by

right lateral strike slip, are expected to suffer clockwise rota-

tion. Contrary to the prediction of the model by Royden &

Báldi (1988), the paleomagnetic results from the ESB sug-

gest counterclockwise rotation.

The oldest rock where we observed CCW rotation is Egg-

enburgian. The angle is about 80°. This locality (Lada) is in

the transition zone between the Central Carpathian flysch ba-

sin and the ESB (in fact, it is lying on the Central Carpathian

Paleogene).

East of this locality, in the ESB proper, the angle of rota-

tions is smaller at the same time, the rocks studied here are

also younger. The oldest of them are the zeolitized rhyolite

tuff, which yields an overall mean direction of D = 297° I =

64°, k = 28,

= 24° (the statistics are based on the number

of sites, which is 3) when sites 3 and 4 are corrected, site 5 is

not corrected for the local tilts (in all other combinations the

tilt test is negative, tilt test by Watson & Enkin 1993).

Among the younger rocks, sampling points 2 and 8 are char-

acterized by moderate CCW declination deviation and point

1 shows no deviation from the present North (Fig. 10).

Orlický (1996) and Nairn (1967) observed similar rotations

on late Badenian-Sarmatian igneous rocks in the southern mar-

gin of the basin. Thus we can conclude that with the exception

of 1 site, i.e. the youngest one, all observations suggest that the

major part of the ESB basin (i.e. the part that started to open

after the Ottnangian, and subsided most intensively in the Sar-

matian) rotated in a CCW sense by an average angle of about

45°. The rotation observed at Lada seems to be larger and is

difficult to relate to the history of the major part of the ESB.

Perhaps it characterizes the movements of the Central Car-

pathian area more than that of the ESB.

COUNTERCLOCKWISE ROTATIONS OF THE NEOGENE ROCKS IN THE EAST SLOVAK BASIN 167

Fig. 9. Svinica. Two examples showing the viscous character of the

remanence. Upper diagram: the Z component of the NRM on AF

demagnetization up to 50 mT (AF500), stored in the laboratory in a

vertical position for 3 weeks and measured again (AF500R). Lower

diagram: the Z component of the NRM on combined AF and ther-

mal demagnetization up to 300 °C, stored in the laboratory in a ver-

tical position for two months, demagnetized in an AF field of 20 mT

(AF200) measured and demagnetized up to 50 mT (AF500). Stored

for another 3 weeks in the lab with Z in the same vertical position

and remeasured (AF500R). It is important to note that when the

specimens are stored in the laboratory field between demagnetiza-

tion runs, the original NRM directions, which were close to the

present field, are not recovered during the new demagnetization run.

Fig. 10. Site and locality mean paleomagnetic direction with con-

fidence circles. The numbers refer to Table 1 (data in heavy print).

Stereographic projection. All inclinations are positive on the plot,

i.e. site mean directions with reversed polarity (1 and 5) are shown

as equivalent normal polarity directions.

However, the rotation of the ESB may be connected to that

of the Tokaj Mts., due to the similar angle and timing of the

rotation (Márton & Pécskay 1995). Concerning the exact

timing of the rotation, the CCW rotation of the mid-late Sar-

matian Slanèík, in addition to the previously existing indica-

tions obtained on igneous rocks of Sarmatian age, points to

the late Sarmatianearly Pannonian time. We cannot be more

precise, since the only reliable paleomagnetic result in our

data set, showing affinity to stable European directions, is

Hrádok at Michalovce, (rhyolite extrusion) with K/Ar ages

ranging from 10.9 to 14.3 Ma B.P. (Merlich & Spitkovskaya

1974; Vass et al. 1978)

Nevertheless, the constraint on timing is precise enough to

suggest that the major part of the ESB together with the

Tokaj area must have been emplaced 45 Ma later than the

Central Carpathian-North Hungarian block, with the North-

South running zone as the best candidate for a boundary be-

tween them in the area of the present Slánské vrchy Mts. in

the Hornád/Hernád fault zone. The structural unroofing of

the basement of the East Slovak Basin (in the sense of Soták

et al. 1993), when the Iòaèovce-Krichevo Unit was exhumed

during the Miocene extension can be corelated with the

above mentioned CCW rotation of the basin sedimentary fill

contemporaneus with volcanics.

The origin of the CCW rotation in the area of the East Slo-

vak Basin may also be explained in another way. At least two

basement units, the Zemplinic Unit and Iòaèovce-Kritchevo

Unit, have affinities to the Tissia Superunit. The Zemplinic

Unit was correlated with the Tissia and/or Mecsek Mts.

(Körössy 1963; Grecula & Együd 1977 and others). The

Iòaèovce-Kritchevo Unit and especially its Iòaèovce part, i.e.

the unit directly proved by wells as the ESB basement, ac-

cording to Vozár et al. (1993) may belong to the Szolnok-

Maramures Flysch and/or Nádudvar Formation. The Fig. 2

shows that both units could come to present position by left

lateral strike-slip from the SW. This left lateral motion pre-

ceded the left that is CCW rotation of the ESB. The relation

between sens of the strike-slip motion and the following

block rotation is documented by Torres & Slivester and Sen-

gör, Gorur & Saroglu (in Allen & Allen 1992).

Acknowledgement: This work was partially supported by

OTKA (Hungarian National Science Foundation) research

Grant No. T015988 and VEGA (Slovak Scientific Grant

Agency) research Grants No. 5136 and 5222. The authors

are thankful to M. Kalièiak for description of localities

Niná My¾a, Slanèík and Svinica as well as for fruitful re-

comendations.

168 MÁRTON, VASS

and TÚNYI

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