GEOLOGICA CARPATHICA, 51, 2, BRATISLAVA, APRIL 2000
K/Ar DATING OF NEOGENE CALC-ALKALINE VOLCANIC ROCKS
FROM TRANSCARPATHIAN UKRAINE
, HILARY DOWNES
and BOGDAN MACKIV
Institute of Nuclear Research of the Hungarian Academy of Sciences, Bem tér 18/c, 4026 Debrecen, Hungary
Geological Institute of Romania, Caransebes Str. 1, RO-78344 Bucharest, Romania
Department of Geology Birkbeck College, Malet St., London WC1E 7HX, U.K.
ZGRE, Geologov 10, UR-295510 Beregovo, Ukraine
(Manuscript received June 22, 1999; accepted in revised form December 8, 1999)
Abstract: The Neogene Carpathian arc is a complex magmatic arc, extending from Slovakia into Romania. The
Transcarpathian region in SW Ukraine comprises the central part of this arc and was active in the Middle-Late Mi-
ocene. The volcanic structures of the Transcarpathian region can be divided into three major areas: aOuter Arc; b
Intermediate zone; cInner Arc. This division reflects the basic tectonic features of the Ukrainian Carpathians, but
differs from other parts of the Carpathian arc. The Outer Arc consists of a number of overlapping stratovolcanic
structures, generally composed of lava flows, domes, dykes/sills, volcanic necks and lahars of basaltic andesite,
andesite and dacite composition. In the Inner Arc, tuffs, ignimbrites and ash deposits of dacite, rhyodacite and rhyo-
lite are abundant. Lava flows of andesitic and basaltic-andesitic composition are present, together with domes of
dacite and rhyolite. The Intermediate zone is composed of lava domes and small andesitic shield volcanoes.
New K/Ar data obtained from 57 volcanic rock samples has yielded K/Ar ages of 13.49.1 Ma. This time interval
(~4.5 million years) is similar to that of the neighbouring Carpathian volcanic regions to the west (Tokaj Mts., Hun-
gary) and to the east (Cãlimani, Romania). Badenian rhyolitic tuffs buried within the Transcarpathian area repre-
sented the earlier phases of magmatism, but they have been dated only by biostratigraphic methods. Thus, there is no
evidence in this area for any along-arc migration of volcanism, unlike in the Eastern Carpathians of Romania. Forma-
tion of volcanic structures started simultaneously in both Outer Arc and Inner Arc volcanic areas (13.4 Ma). Different
peaks of volcanic activity were observed: (a) between 13.011.5 in the Inner Arc, interpreted as the major period of
generation of a complex of resurgent domes related to formation of a caldera, probably situated toward the central part
of the Transcarpathian depression, and (b) between 11.210.5 Ma in the Outer Arc, representing the main period of
volcano generation. The end of the volcanic activity (9.59.1 Ma) was scattered and less voluminous.
Key words: SW Ukraine, Transcarpathia, Neogene volcanic activity, calc-alkaline volcanic rocks, K/Ar dating,
Neogene calc-alkaline volcanic rocks from the south-western
part of the Ukraine (Transcarpathia) form part of the Car-
pathian magmatic arc, which extends from Slovakia into Ro-
mania, via Hungary and the Ukraine. The Transcarpathian
volcanic area is an integral part of a continuous ~120 km
long chain which starts in Slovakia (Vihorlat Mts.) and con-
tinues to Romania (Oaº volcanic area).
Previous investigations reviewed by Lyashkevich (1995)
recognized two Neogene magmatic formations in Transcar-
pathia: (1) Rhyodacitic; and (2) Andesitic. The former is lo-
cated close to and inside the Transcarpathian depression,
whereas the latter consists of a volcanic chain closer to the
Flysch area. Further west, in Slovakia three types of volcan-
ism were distinguished by Lexa et al. (1993) and Kalièiak &
ec (1995): 1. Rhyolite-rhyodacite areal volcanism (Eggen-
burgianBadenian); 2. Andesite areal volcanism (Middle
BadenianSarmatian); 3. Volcanic arc andesite volcanism
(SarmatianPannonian). The first two types correspond
roughly to the Rhyodacitic magmatic formation, and the
third one is equivalent to the Andesitic magmatic formation
of Lyashkevich (1995). Previous K/Ar data suggested an age
of 12.6 Ma for the Rhyodacitic formation and 12.310.6 Ma
for the Andesitic formation (Danilovich 1976 fide Lyash-
kevich 1995; Bagdasaryan & Danilovich 1968). K/Ar dating
was performed on alunite related to hydrothermal activity in
the Beregovo region of Transcarpathia (Rakovits et al. 1981)
in which two different events were distinguished:
15.21±0.84 Ma and 12.65±0.56 Ma.
In our study new K/Ar ages were measured for 57 samples,
covering most of the Transcarpathian volcanic centers. We
sampled massive, non-vesicular rocks from both outcrops
and boreholes drilled by the Transcarpathian Geological Ex-
ploration Company (Beregovo). Although we have not un-
dertaken detailed geological mapping of the eruptive succes-
sion, our new data will considerably improve the
understanding of the space-time evolution of the volcanic ac-
tivity in the Transcarpathian region of the Carpathian arc.
K/Ar age determinations were done at the Institute of Nu-
clear Research of the Hungarian Academy of Sciences in
Debrecen, Hungary. The freshness of specimens was evalu-
84 PÉCSKAY et al.
ated by microscopic investigation of thin sections and
strongly altered specimens were eliminated. Conventional
experimental methods were used in the determination of the
argon content. K/Ar dating was carried out on whole rock
samples, except for one dacitic rock (UA-3), from which bi-
otite was dated.
Argon was extracted from 0.10.3 mm sized whole rock
samples by RF fusion in Mo crucibles, in previously backed
glass and stainless steel vacuum system.
Ar spike was
added from pipette system, and the evolved gases were pu-
rified using Ti and SAES getters and liquid nitrogen traps.
The purified argon was measured in the static mode, using a
15 cm radius magnetic sector type mass-spectrometer built
in Debrecen. Recording and evaluation of argon spectrum
was controlled by a microcomputer. Details of the instru-
ments, the applied methods and results of calibration have
been described elsewhere (Balogh 1985; Odin 1982).
Approximately 0.1 g of finely ground sample was digested
in acids and finally dissolved in 0.2 M HCl. Potassium was
determined by flame photometry with a Na buffer and Li
internal standard. The inter-laboratory standards Asia1/65,
LP-6, HD-B1, GL-O and atmospheric Ar were used for
checking the measurements. Atomic constants suggested by
Steiger & Jäger (1977) were used for calculating the age. All
analytical errors represent one standard deviation (68 % ana-
lytical confidence level). For stratigraphic classification, the
time-scale of Central Paratethys (Vass & Balogh 1989) has
In the geological context, the Transcarpathian volcanic re-
gion is located approximately on the boundary between the
Pieniny Klippen Belt and the Carpathian flysch belt in the
north, and the Neogene East Slovak and Transcarpathian ba-
sin in the south (Fig. 1). The volcanism is in part related to
the development of the Transcarpathian depression from
Badenian until Pannonian times (Vass et al. 1988; Kalièiak
& Pospíil 1990). A NWSE longitudinal fault system was
significant in the evolution of the Transcarpathian depres-
sion, and the faults acted as pathways through which mag-
mas reached the surface. During the Late Miocene to
Pliocene, these fault systems were arranged in regional left
lateral transtensional corridors, along which several pull-
apart basins were formed (Csontos 1995). Conjugate NE-SW
faults were active mainly during SarmatianPannonian
times, when important extension and sedimentation took
place (Kalièiak & Pospíil 1990).
From the geotectonic point of view, the Transcarpathian
volcanics are situated on the northern margin of the Zemplín
block, the north-easternmost part of the major ALCAPA*
block in the Intracarpathian area, at its contact with the Eur-
asian plate (Csontos 1995; Haas et al. 1995). There is a sig-
nificant difference in the crustal structure between the AL-
CAPA block (~20 km thickness) and the Eurasian plate
(~40 km thickness), according to the seismic profile HSS-
III, which suggests that the suture zone is situated just below
the accretionary flysch belt in the Ukraine. Seismic and mag-
netotelluric data suggest an asthenospheric upwelling in the
central part of Transcarpathian depression, where the as-
thenosphere-lithosphere boundary is considered to be situat-
ed at a depth of ~60 km (Babuska et al. 1986).
The volcanic activity in the SW Ukraine is very complex
and strongly related to the development of sedimentary ba-
sins (mainly the Transcarpathian depression which forms a
part of the much larger Pannonian Basin) since Badenian
times. A huge volume of volcanic products (mainly volcani-
clastics) is buried within the sedimentary pile. Their thick-
ness varies between several tens of meters and several hun-
dred meters. They are buried below the outcropping volcanic
areas as a consequence of tectonic movements (Kalièiak &
From the distribution of the outcropping volcanic rocks in
the SW Ukraine, three volcanic areas can be defined. These
are oriented ~NWSE (Fig. 2), strongly suggesting that, their
orientation was controlled by major tectonic lines:
1. The Outer Arc volcanic area is composed of a row of
eight adjacent and partially overlapping composite andesitic
volcanoes (Poprieèny, Antalovski, Hotar, Obavski-Kamen,
Demianov, Martinski-Kamen & Tolstoi-Tupoi) (Fig. 2). The
Tolstoi-Tupoi volcano forms a link towards the SE with the
complex shield volcanoes and lava dome structures of the
Oaº area (Romania). In the westernmost part Poprieèny vol-
cano forms a link with another row (NWSE oriented) of ad-
jacent overlapping volcanoes belonging to the Vihorlat Mts.
All eight volcanoes are similar in size, and evenly spaced
(~15 km apart). Much of the following volcanological inter-
Fig. 1. General map of the Carpathian-Pannonian area showing the
study area (quadrangle) in Transcarpathian Ukraine and NE Hun-
gary. 1 Carpathian Units; 2 Outcropping intermediate calc-
alkaline volcanic rocks; 3 Buried acidic calc-alkaline volcanic
rocks; 4 Outcropping acidic calc-alkaline volcanic rocks; 5
Alkali-basaltic volcanic rocks.
K/Ar DATING OF NEOGENE CALC-ALKALINE VOLCANIC ROCKS 85
pretation of the Outer Arc area is based on the unpublished
data of Zobkov & Titov (1977). The volcanic activity was
dominantly effusive. The central cone facies is strongly erod-
ed and besides lava flows and lava domes, intrusive dykes or/
and necks and different volcanic breccias can be found,
sometimes affected by hydrothermal alteration. Numerous
porphyritic and aphanitic lava flows were distributed around
the source area of each volcano, with their eastern and west-
ern slopes buttressed against lavas of the neighbouring vol-
cano. The longest lava flows (~1520 km) are distributed to-
wards the south, indicating a lower initial topography in this
direction. Some lithic-rich debris flows can also be found in
distal areas. In the sedimentary basement in the north-eastern
part of Obavski-Kamen volcano several sills were also
Poprieèny volcano seems to be the most complex in the
chain, and can be characterized as a stratovolcano. Based on
lithofacial observations made mainly in Slovakia, Kalièiak
et al. (1995a) pointed out the existence of two proximal
structural levels: the lower one is characterized by the pre-
dominance of pyroclastic deposits whereas the upper one is
dominated by lava flows. The distal volcanic area, fringing
the volcano along its western edge, is characterized by flu-
vio-lacustrine deposits. The petrography is similar in both
levels, consisting of pyroxene-bearing andesites and/or ba-
saltic andesites. The Poprieèny stratovolcano has on its
northern periphery a rhyolitic dome, which is not considered
to belong to the edifice (Kalièiak et al. 1995b). A dacitic
dyke was observed in the central part of the volcano, intrud-
ed into pyroxene-bearing andesites.
2. An Intermediate zone is represented by lava domes and
small shield volcanoes (mostly andesitic) in two isolated ar-
eas (Drisinsko and Shalanski) (Fig. 2). The whole intermedi-
ate area also contains abundant buried acid volcaniclastic de-
posits of Badenian and Sarmatian age.
3. The Inner Arc, around Beregovo town, is a cluster of
dacite and rhyolite domes. According to borehole data, the
compositional spectrum of the rocks is wider, including ba-
salts, basaltic andesites and andesites, along with the pre-
dominant dacites and rhyolites. Furthermore, boreholes
drilled in Hungary, close to the Ukrainian border (e.g.
Gelénes-1) and near Beregovo (Derekaszeg-8) (Fig. 3) re-
vealed, in addition to older sedimentary and volcanic depos-
its (Lower to Upper Badenian), a thick buried pile (>600 m)
of rhyodacitic volcaniclastic deposits (mainly ignimbrites),
Sarmatian in age (Kulcsár 1968). The cluster of domes
around Beregovo could be interpreted as a resurgent dome-
complex related to caldera formation (Pantó 1966). The cen-
tre of the caldera was probably situated near the central part
of the Transcarpathian depression.
Fig. 2. Volcanological sketch map of the Transcarpathian Neogene volcanics.
86 PÉCSKAY et al.
The analyzed Transcarpathian volcanic rocks consist of
plagiophyric pyroxene basaltic andesites, andesites and dac-
ites, and relatively plagioclase phenocryst-poor to aphanitic
andesites, dacites and rhyolites. The volume of aphanitic
rocks is larger in the eastern part of the Outer Arc (Tolstoi-
Tupoi volcanic cone, Oaº) and also for the rhyolites from
the Inner Arc. Andesites are the dominant volcanic prod-
ucts of the Outer Arc, but some rare dacites and rhyolites
can be found. In contrast, in the Inner Arc, rhyolites and
dacites are dominant, but basalts, basaltic andesites and
andesites can also be found.
Eruptive history based on K/Ar data
Although numerous age determinations have been carried
out in our study (Table 1), the data are insufficient to recon-
struct the evolution of each individual volcanic edifice.
According to our data the oldest volcanic edifice is Po-
prieèny (13.4 Ma), the western volcano in the Outer Arc. A
long time interval (13.410.2 Ma) has been determined for
the Poprieèny volcano. Based on the borehole data (C11
reached the Mesozoic metamorphic basement at 590 m) and
geophysical data, this volcano is tilted southward (Kalièiak
et al. 1995b). Consequently the oldest volcanic rocks (Lower
Sarmatian) are exposed only in the northern part of the volca-
nic edifice. Much younger volcanic rocks were taken from
the southern slopes of the Poprieèny (Lower Pannonian),
(Kalièiak et al. 1995a). A similar age (13.3 Ma) was mea-
sured on a sill (UA-13) intruded into the flysch deposits
north of the Obavski-Kamen volcano but the geological
meaning of this radiometric age is questionable due to the
large analytical error (>1 Ma).
In the Outer Arc the most detailed analytical work has
been made in the Obavski-Kamen volcano (15 samples). The
samples were collected not only from outcrops, but also from
several massive rocks pierced by borehole C-30T, located on
the western slope of the volcano, from borehole 260, on the
southern slope and borehole 7T in the eastern part of the vol-
cano (Table 1). After drilling more than 1100 m of volcanic
deposits borehole C-30T reached the sedimentary basement
at 1150 m. In a continuous drilling interval (5531167 m) the
volcanic structure was shown to be typical of a stratovolca-
no, with intervals of thick massive lava flows and thin inter-
calations of volcaniclastic deposits (mainly tuffs). However,
some intrusions (dykes or sills) are also present. In the east-
ern and southern slopes of the volcano the boreholes (265,
7T) reached the oldest volcanic rocks (12.912.2 Ma). The
ages obtained in the C-30T borehole in the depth interval
8191148 m are slightly younger (11.611.3 Ma). The out-
cropping lava flows, close to the vent area, yield ages of
10.710.3 Ma. The youngest ages were determined on the
core samples taken from C-30T borehole (9.89.3 Ma) from
two intervals at different levels: 660 m and 910 m. These
younger ages are probably related to an intrusive origin. This
database makes it possible to consider the 3.6 million years in-
terval of volcanic activity of the Obavski-Kamen volcano as
being representative for the entire Outer Arc volcanic area.
The rest of the samples from the other volcanoes of the
Outer Arc (Poprieèny, Antalovski, Hotar, Demianov, Martin-
ski-Kamen, Tolstoi-Tupoi, Oaº) were collected mostly from
outcrops, or shallow drillholes. In Poprieèny, where the
whole succession was dated, the interval of volcanic activity
is very similar to Obavski-Kamen (13.410.0 Ma) (Kalièiak
et al. 1995a and this work). For the rest of the volcanic struc-
tures in the Outer Arc, where mostly the upper lava flows
were sampled, the ages correspond to the younger activity of
Obavski-Kamen (11.29.1 Ma). In this interval we have a
higher volume of erupted products between 11.2 and 10.5 Ma
(Fig. 4 and Fig. 5). We would expect a similar eruptive vol-
ume for each volcano during this interval of activity, as the
volcanoes have almost identical dimensions and show obvi-
ous lateral symmetry (Fig. 2).
In the Intermediate volcanic area andesitic rocks are domi-
nant on the surface. There are only a few outcrops in this
area and, with one exception (UA-31), all the samples were
taken from different boreholes. The age of the andesitic
rocks ranges between 12.6 and 11.6 Ma, with one exception
(UA-23, K/Ar age: 9.5 Ma). A pyroxene-bearing dacite from
Drisinsko area has a similar petrography to the Tarpa dacite
(T-96, K/Ar age:10.5 Ma) from the Inner Arc, but yielded a
different age (UA-37, K/Ar age:11.4 Ma).
On the basis of borehole data (Fig. 3), it has been estab-
lished that in the Inner Arc, significant acid volcanic activity
took place during Badenian and Sarmatian times (Maleev
Fig. 3. Borehole stratigraphy in the Transcarpathian depression
(location: Gelénes and Derekaszeg) showing the relationships be-
tween Badenian and Sarmatian tuff layers.
K/Ar DATING OF NEOGENE CALC-ALKALINE VOLCANIC ROCKS 87
1964; Kulcsár 1968; Rakovits et al. 1981). The Gelénes
borehole (NE Hungary) penetrated about 700 m of Badenian
rhyolite ignimbrites (14.7 Ma) and another 700 m of Sarma-
tian rhyodacitic ignimbrites (13.011.0 Ma) (Széky-Fux et
al. 1987). Close to Beregovo, the borehole Derekaszeg-8
shows 376 m of rhyolitic Badenian tuffs and 80 m of Sarma-
tian acid tuffs (Kulcsár 1968). The outcropping volcanic
rocks are dominantly acidic in composition (rhyolites and
dacites), and pierce the acid volcaniclastic rocks. In addition,
basaltic andesites and andesites of 13.811.5 Ma were found
in boreholes in the eastern part of the Inner Arc area.
On the basis of the radiometric dating the basaltic andesite
(408, K/Ar age: 13.8 Ma) is the oldest volcanic product anal-
ysed in the Inner Arc, and agrees well with the age of the
oldest volcanic product from the Outer Arc (13.4 Ma). How-
ever the great analytical error (1.2 Ma) suggests that this ba-
Table 1: Analytical data of the Neogene volcanic rock of Transcarpathian region, SW Ukraine and NE Hungary. Abbreviation: Apx (py-
roxene andesite), Bapx (pyroxene basaltic andesite), Dpx (pyroxene dacite), R (rhyolite), D (dacite), Dam,bi (amphibole biotite dacite).
Lahova, Bh 265/330m
Chopivko Bh 423/391m
Drisino, Bh. 327/587m
327Drisino, Bh. 327
88 PÉCSKAY et al.
saltic andesite was probably affected by secondary alteration.
On the other hand, the presence of some excess argon cannot
be excluded. Consequently, we may relate the open question
of the geological age of the oldest intermediate volcanic
rocks to the lack of suitable sample for radiometric dating in
the Inner Arc. The acid rocks in the Inner Arc (mainly rhyo-
lites) are slightly younger and show a longer interval of vol-
canic activity (12.811.5 Ma). This latter period corresponds
to the climax of volcanic activity in the Inner Arc, and possi-
bly suggests that the end of the volcanic activity was related
to a large caldera situated further south. If we consider that
the Inner Arc volcanic area was related to caldera formation
documented as starting around 13 Ma ago, then the interval
of volcanic activity during which the caldera, Outer Arc and
Inner Arc were all active was between 13.411.5 Ma.
On the basis of radiometric data, the Neogene volcanic ac-
tivity in E Slovakia, NE Hungary and NW Romania took
Fig. 4. Histogram of the new K/Ar age data in the Transcarpathian
Fig. 5. Individual K/Ar measurements (showing the analytical er-
ror bars) for different volcanic structures. Acidic rocks in black,
intermediate rocks in white.
place in the same time interval (approx. 15.59.0 Ma) (Péc-
skay et al. 1995; Széky-Fux et al. 1987). Volcanic activity
constrained by biostratigraphy started with eruption of acidic
tuffs in the Badenian. The location of the source of this vol-
canic activity is unknown. These tuffs contain andesitic lithic
fragments which must represent an older phase of eruptive
activity. In SE Slovakia, older rhyolite tuffs were also recog-
nized (Eggenburgian) (Orlický et al. 1974). In the Tokaj-
Slánske mountains, the peak of intermediate volcanism is
slightly older (12.5 Ma) than in the VihorlatGutinsky area
(Vass et al. 1978; Kalièiak & Repèok 1987; Pécskay et al.
1986). It is significant that the stratovolcanoes and the ex-
tended andesitic lava flows of the VihorlatPoprieèny
GutinskyOaºGutîi range were all formed contemporane-
ously during Sarmatian and Early Pannonian times (139
Ma) (Durièa et al. 1978; Kalièiak et al. 1995a,b; Kovács et
al. 1997; Pécskay et al. 1994).
Our present data set has extended our understanding of the
evolution of the Neogene calc-alkaline volcanoes of Tran-
scarpathia and adjacent areas. After eruption of the Badenian
K/Ar DATING OF NEOGENE CALC-ALKALINE VOLCANIC ROCKS 89
rhyolite tuffs, voluminous andesitic magmas were erupted
mostly in the Outer Arc area. Andesitic volcanic activity
started simultaneously in both the Outer Arc and Inner Arc
areas in Transcarpathia (13.8 Ma and 13.4 Ma, respectively),
but ceased around 11.5 Ma ago in the Inner Arc (except for
the Tarpa dacite dome (10.5 Ma) formed within the assumed
caldera) and around 9.0 Ma in the Outer Arc. In the Inner
Arc, eruption of acidic and intermediate volcanics alternated
during the Sarmatian. The most vigorous interval of volcanic
activity was 11.210.5 Ma in the Outer Arc and 13.011.5
Ma in the Inner Arc.
The lifetime of the volcanic activity was between 13.8 and
9.1 Ma, similar in all the range from the Vihorlat (Slovakia) to
Cãlimani (Romania), as pointed out by Pécskay et al. (1995).
Taking into account the K/Ar data obtained in the Vihorlat and
Oaº-Gutîi volcanic regions, a significant peak can be observed
in the histogram which reflects the contemporaneity of the
volcanism along the arc from the Vihorlat to the Gutîi.
Acknowledgements: We thank the Royal Society for their
financial support, the Beregovo Geological Expedition for
making our fieldwork possible and for access to borehole
material, and the Geological Institute of Romania for support
of fieldwork by its scientists. The Institute of Nuclear Re-
search of the Hungarian Academy of Sciences is thanked for
making the analytical work possible and for support for the
field work. We are grateful to Kadosa Balogh for his helpful
reviews of the manuscript. The authors thank J. Lexa,
A. Varitchev and K. Balogh for their helpful comments.
Many thanks are due to Éva Svingor for her kind assistance
during the drafting the manuscript.
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