PALEOGENE IGNEOUS ROCKS IN THE ZALA BASIN 43
GEOLOGICA CARPATHICA, 55, 1, BRATISLAVA, FEBRUARY 2004
PALEOGENE IGNEOUS ROCKS IN THE ZALA BASIN
(WESTERN HUNGARY): LINK TO THE PALEOGENE MAGMATIC
ACTIVITY ALONG THE PERIADRIATIC LINEAMENT
, ZOLTÁN PÉCSKAY
, CSABA SZABÓ
and TIBOR NÉMETH
Eötvös University, Department of Petrology and Geochemistry, Lithosphere Fluid Laboratory, Pázmány Péter sétány 1/c, H-1117
Budapest, Hungary; email@example.com; firstname.lastname@example.org
Institute of Nuclear Research of the Hungarian Academy of Sciences (ATOMKI), Bem tér 18/c, H-4001 Debrecen, Hungary;
Hungarian Oil Company (MOL), Batthyány út 45, H-1039 Budapest, Hungary; email@example.com
Laboratory for Geochemical Research, Hungarian Academy of Sciences, Budaörsi út 45, H-1112 Budapest, Hungary; firstname.lastname@example.org
(Manuscript received February 4, 2003; accepted in revised form June 23, 2003)
Abstract: Paleogene intrusive (tonalite, diorite) and volcanic (andesite, dacite) rocks have been identified in drilling
cores from the Zala Basin, SW-Hungary. The age of these rocks has been considered to be Eocene on the basis of the
observation that volcanic rocks are intimately interlayered with sedimentary rocks deposited during Nannoplankton
Zone 15/1618. However, new K/Ar data measured on mineral concentrates (amphibole, biotite, plagioclase) from
intrusive and volcanic rocks yielded ages from 28.6±1.8 Ma to 33.9±1.4 Ma and from 26.0±1.2 Ma to 34.9±1.4 Ma,
respectively. The Early Oligocene K/Ar age of the andesite and dacite studied contradicts the previous biostratigraphic
interpretations. Furthermore, detailed petrographic study of the volcanic rocks and XRD analyses of the Eocene marl
deposits are not consistent with simultaneous volcanic activity and sediment deposition. Alternatively, we propose that
the volcanic rocks were emplaced as dykes into the Eocene marl during the Early Oligocene. However, an Eocene age of
some explosive (mostly tuffaceous) rocks is not debated. The Early Oligocene K/Ar data of the intrusive bodies coincide
with the age of other Paleogene tonalitic massives along the Periadriatic Lineament. The geochemical and radiometric
age data clearly demonstrate the Alpine connection of the either intrusive or volcanic rocks studied. During the Paleo-
gene the intrusive and volcanic rocks dislocated and as a result of the escape of the ALCAPA (Alpine-Carpathian-
Pannonian) block from the Alpine realm they reached their present-day juxtaposed setting in the Early Miocene.
Key words: Paleogene, Periadriatic Lineament, Zala Basin, geochemistry, radiometric age, calc-alkaline.
Paleogene calc-alkaline volcanic series as well as small, intru-
sive bodies have been penetrated by oil-exploring boreholes
in the Zala Basin (Fig. 1; Székyné 1957; Kõrössy 1988). On
the basis of biostratigraphic data in the northern part of the
studied area (Fig. 2), the age of the volcanic rocks has been as-
sumed to be Eocene by observing sedimentary interlayering
between the volcanic rocks and the Eocene marl (Lutetian-
Early Priabonaian Padrag Marl) deposits. Analogously, the
age of the intrusive rocks found only in the southern part of
the studied area has been also considered as Eocene, although
the Eocene marl deposits are lacking above the intrusive bod-
ies, which are covered by Miocene (Badenian) sediments (Fig.
2; Kõrössy 1988).
As the entire Paleogene succession in the studied area is
covered by Badenian sediments (Fig. 2, Kõrössy 1988), it
must have undergone intensive erosion between the Paleo-
gene (up to about 30 Ma) and the onset of the Badenian sedi-
mentation. The eroded igneous fragments covered the older
formations in the Transdanubian Central Range (Fig. 1). A de-
tailed study of Oligocene-Miocene molasse sediments (Csatka
Formation, Fig. 1) in the Transdanubian Central Range indi-
cates that the source region of the igneous clasts must have in-
volved igneous rocks akin to those in the Zala Basin, too
(Benedek et al. 2001).
Fission-track (FT) and K/Ar dating of intrusive clasts (to-
nalite) from the Oligocene-Miocene molasse indicates Early
Oligocene age (K/Ar 3034 Ma) of the source region. More-
over, the FT and K/Ar ages of the volcanic (andesite, dacite)
pebbles in the Oligocene-Miocene molasse suggest that these
clasts were derived from Oligocene (K/Ar 3135 Ma) and
subordinately from Eocene (~40 Ma) volcanic edifices, which
also argues for the presence of Oligocene volcanic activity in
the Zala Basin (Benedek et al. 2001).
In this paper we present new K/Ar data of mineral concen-
trates (amphibole, biotite, plagioclase) from intrusive and vol-
canic (not explosive) rocks from the Zala Basin and correlate
the study area with Alpine analogous regions.
The publication of drilling core names was allowed by the
Hungarian Oil Company (MOL) only in coded form.
The Zala Basin (ZB), a part of the ALCAPA (Alpine-Car-
pathian-Pannonian) megaunit, is located north of the Balaton
line, in Western Hungary. The Balaton line is interpreted as
the eastern continuation of the Periadriatic Lineament
(Kázmér & Kovács 1985; Fodor et al. 1998; Haas et al. 2000).
It is believed that the ALCAPA megaunit was displaced hori-
zontally eastward in the Miocene (Majoros 1980; Tari et al.
44 BENEDEK et al.
1993; Fodor et al. 1998; Frisch et al. 1998) as a consequence
of continental convergence between the Adriatic microplate
and stable Europe. However, small movements might have
been already initiated during the Eocene (Kázmér & Kovács
1985). The Early Oligocene (30 Ma) position of the ALCAPA
megaunit might have been still somewhere between the East-
ern and Southern Alps (Kázmér & Kovács 1985; see Fig. 2b
in Frisch et al. 1998).
In Hungary three Paleogene igneous magmatic centre can
be outlined from SW to NE along the Balaton line and its NE
continuation: 1) Zala Basin, 2) the Velence Mts, 3) Recsk
(Fig. 1; Benedek 2002).
The study area of this paper, the Zala Basin can be divided
into three structural units from south to north (Fig. 1, Fig. 2):
1) the Pusztamagyaród-Nagybakónak Zone; 2) the Ortaháza-
Kilimán Horst; and 3) the Bak-Nova Half-Graben. The base-
ment is made up mainly of Triassic formations in the south
and east, and Jurassic, Cretaceous ones in the north, which is
followed by Eocene sequences in the north and covered by
Miocene sediments (Fig. 2; Bérczi-Makk 1980; Kõrössy
1988; Haas 1993).
The igneous suites in the studied area can be divided into
two groups: 1) intrusive rocks occurring in the southern part
of the study area (intrusive zone), which continues to the NE
through Balatonfenyves (Fig. 1) and 2) zone of volcanic rocks
(the volcanic zone) characterizing the northern part. The
northern boundary of the intrusive body is outlined by a char-
acteristic dextral strike-slip fault. No evidence for contact
metamorphism of the intrusive bodies with the neighbouring
Fig. 1. Sketch-map showing the occurrences of Paleogene magmatic rocks in the Pannonian Basin. Abbreviations: PAL Periadriatic
Lineament, CsF Csatka Formation, K Karavanke tonalite, P Pohorje tonalite. Black arrow shows paleotransport direction of the
Oligocene-Miocene alluvial system (Korpás 1981). Inset shows position of some boreholes studied and the line (dotted line) of the cross-
section displayed in Fig. 2. The approximate boundaries (dashed line) of subunits distinguished in the Zala Basin are also shown.
Fig. 2. Schematic block diagram of the Zala Basin. The narrow
black field above Eocene in the Bak-Nova Half-Graben, Triassic in
the Ortaháza-Kilimán Horst and in the Pusztamagyaród-Nagy-
bakónak Zone represents thin Badenian deposits. The line of the
cross-section is shown in the inset of Fig. 1.
Mesozoic carbonates has been observed in the south. In the
upper part of the Eocene marl sequence in the Bak-Nova Half-
Graben pyroclastic, mainly tuffaceous interlayers occur
PALEOGENE IGNEOUS ROCKS IN THE ZALA BASIN 45
(Kõrössy 1988). The marl sequence was deposited between
the NP15/16 Zone boundary and NP18 (Fig. 3, about 4243
and 38 Ma, respectively) and the oldest tuffaceous layers are
known from the NP16 Zone (about 4243 Ma, Nagymarosy,
pers. com.). The petrography of the volcanic rocks and igne-
ous clasts hosted by explosive series is basically the same.
Skarn at the contact of andesite with Triassic limestone was
observed in a few drilling cores. The thickness of the entire
Eocene succession can reach almost 1000 m. The oldest cover
of the Eocene succession is Badenian sandstone and lime-
Intrusive rocks (tonalite, diorite)
Hypidiomorphic intrusive rocks contain predominant euhe-
dral plagioclase (Fig. 4). Rare potassium feldspar can sur-
round plagioclase. In general, abundant amphiboles and bi-
otites containing plagioclase inclusions are commonly
euhedral or subhedral in shape and perfectly fresh. These hy-
drous minerals appear along lineation and interstitially among
feldspars. Rare anhedral or subhedral quartz crystals fill in the
available space among the phases crystallized formerly.
Rutile, apatite, zircon and oxide minerals are common acces-
sory minerals. Garnet is a rare accessory.
Volcanic rocks (andesite, dacite)
Plagioclase is the dominant phenocryst (Fig. 4). It is a com-
mon inclusion in the subsequent mineral phases. Euhedral,
subhedral amphibole phenocrysts are fresh or surrounded by
oxide mineral rim. Euhedral biotite, sometimes containing
sagenitic rutile, is corroded and absent in the majority of sam-
ples. Quartz phenocrysts are anhedral due to resorption. Rare
clinopyroxene is euhedral and chloritized. Garnet is a rare
phenocryst containing small, elongated rutile inclusions. The
glassy groundmass is mostly altered to clay minerals (Fig. 4).
Mineral separation was carried out using standard tech-
niques (i.e. heavy liquids, magnetic separator). The samples
were handpicked and cleaned in alcohol with an ultrasonic
cleaner. Conventional analytical methods were used in the de-
termination of argon. Argon was extracted from 0.125
0.250 mm sized whole rock and mineral concentrates by radio
frequency fusion in Mo crucibles in previously baked stainless
steel vacuum systems.
Ar spike was added from a conven-
tional pipette system (calibrated against international refer-
ence samples) and the evolved gases were purified using Ti-
and SAES getters and liquid nitrogen traps. The purified argon
was measured in the static mode using a 15 cm radius sector
mass spectrometer. Approximately 0.1 mg of finely ground
sample was dissolved in acids. The residue was taken into so-
lution and K determined by flame photometry with a Na buff-
er and Li internal standard. K and Ar determinations were
checked regularly by interlaboratory standards (HD-B1, LP-6,
GL-0, Asia 1/65). All ages (Table 1, Fig. 3) have been calcu-
lated by using the constants recommended by Steiger & Jäger
(1977). Analytical errors are given in one standard deviation.
Details of the instruments, the applied methods and result of
the calibration have been described elsewhere (Balogh 1985).
The electron microprobe analysis of the main rock forming
minerals was carried out at the Department of Earth Sciences,
University of Florence, by JEOL Superprobe JXA-8600
WDS. The accelerating voltage was 15 kV, with 10 nA sam-
ple current. We used Bence & Albes (1968) correction calcu-
lation (Table 2). Natural standards were employed.
A Philips PW-1730 diffractometer was used to analyse the
clay fractions of the Eocene marl deposits interfingering with
volcanic rocks in the Bak-Nova Half-Graben. Graphite mono-
chromator using Cu-K
radiation at 45 kV and 35 mA with 1°
divergence slit and 1° receiving slit was applied. The scanning
rate was 0.05° 2
per minute from 3° to 70°. Clay minerals
were identified on ethylene-glycol solvated and heated
(350 °C and 550 °C) samples from the clay fraction (less than
m) using the method of Thorez (1976).
The very low K content of biotite concentrates (sample C-3
tonalite, C-1 tonalite Table 1) indicate that they are con-
taminated with low-K phases, for instance amphibole and pla-
gioclase. Electron microprobe analyses of biotite (Table 2)
suggests that K
O wt. % should vary between 7.929.40. On
the basis of microscopic investigations of mineral concen-
trates, the presence of plagioclase inclusions in biotite and in-
tergrowing of amphibole with biotite can cause the observed
low K content in biotite concentrates. The same problem of
preparation can be responsible for the relatively high K con-
Fig. 3. Simplified Paleogene chronostratigraphy of the Bakony Mts
(Zala) modified after Tari et al. (1993). Thick lines represent the K/Ar
age interval with errors obtained from the intrusive and volcanic rocks
studied. Abbreviations: S series, SS standard stages, CPS
Central Paratethys stages, NFZ nanno fossil zones, EZ volcanic
zone, IZ intrusive zone, x in the Padrag Marl tuff horizons.
46 BENEDEK et al.
tent of some plagioclase concentrates (C-1 tonalite, B-1
andesite, A-2 andesite, Table 1), as, apart from the alteration
of the groundmass in samples A-1 andesite, A-2 andesite and
A-3 dacite (Fig. 1), there is no evidence for secondary alter-
ation of the samples dated. In samples A-2 and A-3, the pla-
gioclase ages (27.1±1.4 and 31.6±1.3, respectively) are
younger than the amphibole ones (32.5±1.4 and 34.9±1.4, re-
spectively, Table 1) and do not fall within the range of analyt-
ical error. This phenomenon is due to the preparation tech-
nique, since after using heavy liquids the magnetic separator
was not able to separate plagioclase completely from altered
groundmass, wich resulted in younger K/Ar age.
Mineral concentrates (amphibole, biotite, plagioclase) from
the intrusives yielded K/Ar ages ranging from 28.6±1.8 to
33.9±1.4 Ma, while concentrates of amphibole and plagio-
clase from volcanic rocks give K/Ar ages between 26.0±1.2
and 34.9±1.4 Ma (Table 1). It is noteworthy that Balogh et al.
(1983) reported Oligocene K/Ar age (30.7±1.0 Ma) of a small
tonalite body NE to the Zala Basin, near to the Balaton line
(Balatonfenyves, Fig. 1).
The K/Ar ages of the tonalite samples (C-3 and C-1, Ta-
ble 1) overlap with those of the igneous plutons (Bergell,
Adamello, Riesenferner, Karawanke, etc.) aligned along the
Periadriatic Lineament (about 30 Ma, e.g. von Blanckenburg
& Davies 1995). Thus, the studied intrusive bodies can repre-
sent fragments deriving from the Periadriatic tonalite belt in
accordance with the palinspastic restoration of Kázmér &
Kovács (1985). The present-day position of the intrusive zone
studied was a result of large-scale lateral displacement during
the Miocene (Majoros 1980; Ratschbacher et al. 1991; Tari et
al. 1993; Fodor et al. 1998; Frisch et al. 1998). Therefore, the
intrusive bodies studied may have been located far west in the
Alpine realm at about 30 Ma.
The interpretation of the age data from the volcanic zone is
more complex. Our data (considering analytical error) indicate
Late Eocene-Oligocene (latest Priabonaian-Chattian) volcanic
activity, which contradicts the former concept of a Middle to
Late Eocene age of the volcanism (Fig. 3; Kõrössy 1988). Nev-
Fig. 4. Photomicrographs of representative igneous rocks studied. A Zoned plagioclase surrounded by amphiboles in hypidiomorphic to-
nalite. N+, sample C-3. B Strongly zoned plagioclase in hypidiomorphic tonalite. N+, sample C-1. C Zoned plagioclase and amphibole
phenocrysts in porphyritic andesite. The groundmass contains plagioclase, rare amphibole and glass. N+, sample B-1. 4 Amphibole and
plagioclase phenocrysts in dacite. The amphibole phenocrysts are rimmed by oxide minerals. The groundmass is altered to clay minerals.
N+, sample A-3.
PALEOGENE IGNEOUS ROCKS IN THE ZALA BASIN 47
Hypidiomorphic tonalite consisting of plagioclase
(5060), amphibole (2025), biotite (1015), quartz
(1015). Apatite, zircon and opaque minerals are
Hypidiomorphic tonalite consisting of plagioclase
(5565), amphibole (510), biotite (1015), quartz
(1520). Apatite, zircon and opaque minerals are
Porphyritic dacite with phenocrysts of plagioclase
(2535), amphibole (2025), accessory apatite,
zircon. The glassy groundmass (4050) is altered
into clay minerals.
Porphyritic andesite with phenocrysts of plagioclase
(3040), amphibole (1525), biotite (05), quartz
(05), accessory apatite, zircon. The groundmass is
altered into clay minerals.
Porphyritic andesite with phenocrysts of plagioclase
(4555), amphibole (1520), biotite (05), quartz
(05) in microcrystalline groundmass composed of
plagioclase and opaque minerals.
Porphyritic andesite with phenocrysts of plagioclase
(3040), clinopyroxene (1020), accessory garnet,
and zircon. The groundmass is
Porphyritic andesite with phenocrysts of plagioclase
(5060), amphibole (510), accessory apatite,
zircon. The groundmass is altered into clay minerals.
Table 1: K/Ar data and main petrographic features of igneous rocks from the Zala Basin, Hungary. For the sake of completeness, we pre-
sented also some unpublished K/Ar data of the Hungarian Oil Company (MOL). These data are bolded.
ertheless, some explosive (mostly tuffaceous) layers do inter-
finger with paleontologically well-dated deposits of the Eocene
marl (Kõrössy 1988, Nagymarosy, pers. com.). Further study of
explosive layers is outside the scope of this paper.
Modification of K/Ar systems due to postmagmatic processes
The formation age of the volcanic rocks could have been
modified by: (1) metamorphism, (2) hydrothermal alteration,
(3) superficial or subsurface weathering, (4) thermal effect
(due to volcanism).
Index minerals of any metamorphic overprint have not been
observed in the samples studied (Fig. 4). The pre-Late Car-
boniferous rocks of the Transdanubian Central Range under-
went low grade, regional pre-Westfalian metamorphism (Ár-
kai & Lelkes-Felvári 1987), but they were overprinted by
subsequent Alpine metamorphism (Lelkes-Felvári et al.
Table 2: Representative composition of mineral fractions dated. Abbreviations: c core, r rim, b.d.l. below detection limit.
48 BENEDEK et al.
In order to determine the maximum temperature reached af-
ter the deposition of the Eocene marl, XRD analyses on clay
mineral fractions separated from the marl were carried out
(Kõrössy 1988). The shift of 1.4 nm peak to 1.7 nm in ethyl-
ene glycol treated samples indicated the presence of smectite
(stability max. 70 °C, Glasmann et al. 1989) in the marl. This
suggested that post-magmatic (or post-Eocene) thermal modi-
fication of the volcanic rocks due to metamorphism or the
neighbouring Miocene volcanic activity (Kõrössy 1988) is not
a viable scenario to account for the discrepancy between radi-
ometric and stratigraphic data.
The Velence Mts and Recsk (other Paleogene igneous
complexes in Hungary, Fig. 1) demonstrate many features of
hydrothermal alteration (Molnár 1996), however detailed
petrographic study on the volcanic rocks suggested that hy-
drothermal alteration did not modify the samples dated
(Fig. 4). Petrographic observations and electron microprobe
analyses of dated mineral phases also exclude superficial
or subsurface alteration of the samples studied. Only alter-
ation of the groundmass was observed in samples A-1, A-2,
The age of the volcanic rocks
Concluding the preceeding sections, secondary modifica-
tion of the K/Ar system of the volcanic rocks studied cannot
be responsible for the discrepancy between radiometric and
paleontological age data. Study on abundant planktonic fora-
miniferal assemblages suggests deposition of the Eocene marl
in a water depth of about 8001200 m (Báldi-Beke & Báldi
1990). As a consequence, if volcanic activity producing vol-
canic material and marl deposition (Fig. 2) were contempora-
neous, the volcanic activity should have shown submarine
features. However, the discrete petrographic consequences of
submarine volcanic activity (pillow lava, peperite, amygdale,
blistered structure and typical chilled, variolitic texture of the
groundmass) have not been observed in the volcanic rocks
studied. In addition, this process should have been accompa-
nied by intensive chloritization, carbonitization and clay min-
eralization. None of these diagnostic features were observed
in the studied samples (Fig. 4), therefore the data do not sup-
port coeval submarine magmatism with the deposition of the
We assume that K/Ar ages measured on amphibole concen-
trates of volcanic rocks (Table 1) represent true formation
ages and were not modified significantly by subsequent geo-
logical-geochemical processes. We suggest that the volcanic
rocks studied are dykes crosscutting the Eocene marl succes-
sion. This concept is based on the following evidence: 1) the
penetrated thickness of the studied volcanic rocks is usually
not more than 5 m and 2) seismic sections and stratigraphic
considerations do not suggest post-Paleogene tectonism in the
explored sections (at least in the appropriate depth interval of
the boreholes studied), which excludes tectonic contact of
volcanic rocks studied and the Eocene marl. This interpreta-
tion resembles the situation in the Velence Mts (Fig. 1), where
Józsa (1983) described abundant andesitic dyke magmatism
of the same age (radiometric ages concentrate between 29
35 Ma) penetrating Variscan granitoid.
The younger K/Ar age of the plagioclase concentrates of
samples A-3 and A-2 (Table 1) is due to the presence of al-
tered groundmass in the separated material, which refers to
immediate alteration of the groundmass just after magmatic
Paleogene position of the studied igneous rocks
The schematic block diagram of the Zala Basin (Fig. 2)
demonstrates the tectonic connection of the intrusive zone and
the volcanic zone. Further evidence for non-uniform behav-
iour of the studied area in the Paleogene can be gained by
comparing the southern intrusive and the northern volcanic
rocks in the nature of their emplacement. According to
geobarometric calculations, the intrusive rocks studied crys-
tallized at depth of 715 km (Benedek & Szabó 2000). As the
intrusive rocks are covered by Miocene sediments at present
(Fig. 2; Kõrössy 1988), they must have undergone intensive
erosion prior to the Miocene. Consequently, if the entire area
studied had behaved uniformly during the Paleogene, the
Eocene marl sequences should have been eroded completly.
However, this is not the case in the north (Fig. 2).
Fodor et al. (1998) suggested that superficial occurrences of
Paleozoic granite in the Velence Mts and subsurface lenses
south of Lake Balaton in Hungary can be correlated with the
Eisenkappel granite (see Fig. 1 in Fodor et al. 1998). Accord-
ingly, the Hungarian granite occurrences can be interpreted as
the eastern continuation of strike-slip duplexes described in
the Central Karavanke Zone due to Miocene dextral displace-
ment along the Periadriatic Lineament system (Fodor et al.
1998). Following this concept, we suggest that the intrusive
zone studied can be the eastern equivalent of the Periadriatic
tonalite belt (von Blanckenburg & Davies 1995) and their
separation took place contemporaneously with that of the Pa-
leozoic granites (Fodor et al. 1998). Accordingly, the intru-
sive zone studied can represent a strike-slip duplex. The close
genetic relationship of the Karavanke tonalite (Fig. 1, ~30
Ma, Scharbert 1975) and the intrusive zone studied has been
successfully demonstrated by using chondrite and MORB
normalized trace element distribution diagram (Fig. 5A,B). In
contrast, the Pohorje tonalite (Fig. 1, 15.517 Ma) is enriched
in LILE (large ion lithophile elements) and La, Ce relative to
those of the intrusive rocks studied and the Karavanke intru-
sives (Fig. 5A,B). The close correspondence of the age data
and the geochemistry of the Karavanke intrusive rocks and the
studied ones support a genetic relationship between these plu-
The tectonic interpretation of the studied area means that
the Paleogene position of the volcanic zone (Fig. 1, Fig. 2)
was west of the 30 Ma position of the intrusive zone and vol-
canic rocks were juxtaposed as a result of the escape of the
ALCAPA block from the Alpine realm in the Miocene. Frisch
et al. (1998) placed the northern part of the studied area south-
east of the hidden Tauern Window and west of the present-day
setting of the Karavanke tonalite in their palinspastic recon-
struction at 30 Ma. This implies that the Karavanke tonalite is
the only possible counterpart for the intrusive zone studied
along the Periadriatic intrusive belt. Tari (1994) estimated a
dextral slip of 350550 km along the Periadriatic Lineament.
PALEOGENE IGNEOUS ROCKS IN THE ZALA BASIN 49
The suggested non-uniform behaviour of the studied area in
the Paleogene can explain why the Eocene marl in the N was
not eroded completely: different subunits of the studied area
(Fig. 2) could have undergone different Paleogene evolu-
The origin of igneous clasts found in the Csatka Formation
Benedek et al. (2001) described clasts of tonalite (30
34 Ma), andesite and dacite (3135 Ma) in the Oligocene-Mi-
ocene molasse deposits (Csatka Formation, Western Hungary,
Fig. 1). By comparing the trace element composition of the
intrusive and volcanic rocks studied and that of igneous clasts
found in the molasse, a perfect compositional (Fig. 5C,D) and
age fit can be observed. This suggests that the drainage area of
the former alluvial system must have included the Oligocene
magmatic suites now located in the Zala Basin. Sedimentary
features (direction of gravel imbrication) of the alluvial depos-
its (Korpás 1981) also support this interpretation.
Paleogene igneous rocks buried by sedimentary formations
in the Zala Basin were identified as Eocene on the basis of
biostratigraphical criteria. In this paper we present new K/Ar
data, which contradict this interpretation. The major conclu-
sions of this paper include:
1) K/Ar ages of amphibole, biotite and plagioclase concen-
trates from intrusive (28.6±1.833.9±1.4 Ma) and volcanic
(26±1.234.9±1.4 Ma) rocks studied constrain to classify
these formations to the latest PriabonianChattian. However
Eocene onset of Paleogene magmatism is apparent on the
basis of biostratigraphical data.
2) Post-magmatic processes could not modify K/Ar geo-
3) Volcanic rocks, as dykes, crosscut sediments of the
4) The intrusive zone encountered along the Balaton line is a
fragment of the magmatic belt along the Periadriatic Lineament.
Fig. 5. Chondrite-normalized REE (A) and MORB-normalized trace element (B) pattern of the intrusive zone studied (hatched field),
Karawanke (thick solid line), and Pohorje Mts (grey field). Trace element data of Karawanke and Pohorje Mts were taken from Altherr et al.
(1995) and Pamiæ & Palinka (2000). MORB-normalized trace element pattern of the intrusive (C) and volcanic (D) rocks studied (solid
line) and pebbles from the Oligocene-Miocene molasse (grey field). Data of igneous pebbles from the molasse were taken from Benedek et
al. (2001). Composition of the igneous rocks studied is taken from Benedek et al. (unpublished data). Normalizing constants of MORB are
from Sun & McDonough (1989) and that of chondrite from Nakamura (1974).
50 BENEDEK et al.
5) The Zala Basin did not function uniformly during the Pa-
leogene. The intrusive zone was situated east relative to the
volcanic zone 30 Ma, very close to the Karavanke tonalite.
The intrusive zone most likely represents a strike-slip duplex
that was formed by dextral displacement along the Periadriat-
ic Lineament system in the Miocene. Thus volcanic and intru-
sive suites in the studied area were juxtaposed as a result of
the escape of the ALCAPA block.
6) Igneous rocks in the present-day Zala Basin survived an
important erosion event between ca. 30 Ma and the Badenian
and a great amount of the eroded material accumulated in the
lower part of the Oligocene-Miocene molasse deposits.
Acknowledgements: Csaba Bokor, László Kósa and András
Németh (Hungarian Oil Company, MOL Rt.) are gratefully
acknowledged for useful comments and for permission to
publish this work. We are also grateful to László Fodor, An-
drás Nagymarosy, István Dunkl, Miklós Kázmér, Zsolt Nagy
for helpful comments. We thank Orlando Vaselli (University
of Florence) for the electron microprobe analysis. The authors
wish express their thanks to János Haas, Jaroslav Lexa and Ja-
kob Pamiæ for their helpful and critical reviews. This work
could not have been accomplished without the help of Angéla
Baross-Szõnyi, Magdolna Pálfi-Dudás and the Lithosphere
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