Zemplin (ZEM)
compiled: S.W. Faryad (2002)
completed:
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Definition
Age
of Protolith, Geochemistry
Lithology,
Mineralogy, Metamorphic Grade
Thermobarometry
Geochronology
Structural
Evolution
Summary
Bibliography
Links
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Definition
The Zemplin Unit or Zemplinicum is a tectonic unit, which comprises basement rocks with late Paleozoic and Mesozoic cover sequences. The basement rocks are interpreted as eastern continuation of the Cierna Hora and Branisko Mts. (Rudinec, 1965, Faryad and Vozarova, 1997), however, some authors (Grecula et al., 1981) correlated them with the Eastern Carpathian basement.
Geographic
Position
The Zemplin unit occurs in the southern part of Eastern Slovakia at border with Hungary. The basement rocks form approx 5 km x 3 km window, but their extant under late Paleozoic and Mesozoic sequences is confirmed by many boreholes.
Maps
Geological map of the East
Slovakian lowland and Zemplin Hills: 1:50000 (Banacky et al. 1992),
1:500,000 (Lexa, et al., 2000).
Boreholes
Some important boreholes penetrating basement rocks under the
Permian and upper Carboniferous sediments are:
TR-59, TR-61, ZO-8 (Slovak territory) (Grecula et al., 1981, Kubolsky et al., 1990, Faryad, 1995).
BB-1 (Slovak territory) Vozarova (1992)
Fr-5, Rbcs (Hungarian territory) (Panto, 1965, Kisházi a Ivancsics 1988)
Boundaries
and Structural Position
The Zemplin Unit is a NW-SE trending horst in the Central Western Carpathians (Slávik, 1976; Baňacký et al. 1989). The basement rocks are mostly covered by late Paleozoic sequences, which partly form thrusts. Continuation of basement rocks to west and their connection with other basement units in the Western Carpathians is probable.
Subunits
According to the structural position of metamorphic lithologies
(from up to down):
- Unmetamorphosed Tertiary rocks, mainly volcanics
- greenschist facies Permian and Upper Carboniferous sedimentary sequences
- amphibolite facies basement rocks
Correlation
The Zemplin Unit is by lithology, metamorphic conditions of basement
rocks correlated to the Tatric/Veporic Units of the Western Carpathians
(Rudinec, 1965; Mahel, 1986, Faryad, 1995). Some authors (Grecula et al.,
1981), however correlate it with that in eastern Carpathians.
Age
of Protolith, Geochemistry
Rb-Sr whole rock data of 962 ± 39 and 984 ± 108 Ma from metasediments of the Zemplin unit have been interpreted in favor of a Precambrian age of the basement rocks (Pantó et al., 1967). Muscovites from the same samples gave ages of 394 ± 52 and 450 ± 130 Ma (Rb/Sr) and 260 ± 10 Ma (K/Ar).
U-P dating from Monazite (Finger and Faryad, 1999) and K-Ar data from amphibolite (Frayad and Balogh, 2002) indicated Variscan age of 338 Ma for amphibolite facies metamorphism and 308 Ma cooling age for pegmatite.
Lithology,
Mineralogy, Metamorphic Grade
The basement rocks from the Zemplin Unit are represented by
metapelites, biotite gneisses (orthogneisses), amphibolites and
migmatites. The metapelites consist of muscovite,
plagioclase, rarely staurolite, sillimanite and kyanite. Metapelites with
graphite and biotite gneisses with plagioclase (An28), garnet (Py12,
Alm63, Grs23, Sps2) or amphibole are exposed
on the surface. Some garnet-free gneisses with plagioclase and K-feldspar,
having composition of metadacite were penetrated by borehole TR-59. Fresh
biotite has composition with XMg = 0.51, Alt = 3.5 and T= 0.2 a.f.u.
Amphibolites are exposed on the surface and found also in boreholes. They consist of plagioclase (An17-28.) amphibole ± garnet with accessory tourmaline, apatite, zircon, titanite, rutile, and ilmenite. Amphibole is tschermakite (Si = 6.38-6.60, XMg = 0.55-0.59 and XNa = Na/(Na+Ca) = 0.2) and it is partly replaced by actinolite, epidote and chlorite. Garnet reveals a weak retrograde zoning with decrease of XMg and Ca towards rims (Py17-19, Alm57-60, Grs21-22, Sps1-2). Plagioclase is mostly replaced by fine-grained white mica and epidote-group minerals.
Migmatites are found in pebbles of the late Paleozoic conglomerates and observed in the lower part of the borehole BB-1 (Vozarova, 1991). As the most common assemblages they include biotite, K-feldspar, plagioclase, quartz and rarely sillimanite and amphibole
Pebbles of granitoid rocks are found in the late Paleozoic
conglomerates of boreholes (Grecula 1989; Faryad 1995), as well as in outcrops
(Vozárová and Vozár 1988). Pegmatite penetrating gneiss is exposed on surface
in the Slovak Territory (Faryed and Balogh, 2002).
Thermobarometry
The Zemplin Unit is a polymetamorphic complex with Pre-Alpine amphibolite
facies and Alpine greenschist facies conditions. The amphibolite facies
conditions (665-700 oC/ 7.7-8.0 kbar, Faryad, 1995) were estimated
using exchange thermobarometry of garnet-biotite and themodunamic dataset of
Berman (1991). Mineral zoning indicated a retrograde P-T path to relatively low
pressures and temperatures (4 kbar, 550 oC).
Alpine metamorphism resulted appearance of muscovite,
chlorite, epidote and albite in basement rocks. Late Paleozoic rocks contains
metamorphic chlorite, white mica quartz and antracite/metantracite that
indicate very low-grade P-T consitions (Vozárová and Vozár, 1988).
Geochronology
Most K/Ar data from muscovite and amphibole gave mixed ages between Pre-Alpine and Alpine metamorphism (Faryad and Balogh, 2002). Some critical ages are:
|
|
rock type |
locality |
Mean |
Range (n) |
Source |
|
Rb/Sr wholr rock |
micaschist |
basement |
962 ± 39 984 ± 108 |
(1) |
1 |
|
Rb/Sr muscovite |
micaschist |
basement |
394 ± 52 450 ± 130 |
(1) |
1 |
|
U/Pb monazite |
micaschist |
basement |
338 ± 22 |
(1) |
3 |
|
K/Ar amphibole |
amphibolite |
basement |
338.0 ±13.0 |
(1) |
4 |
|
K/Ar muscovite |
pegmatite |
basement |
307.9 ± 12 |
(1) |
4 |
|
K/Ar plagioclase |
mylonite
amphibolite |
basement |
105.8
± 4.2 |
(1) |
4 |
|
K/Ar clay min.+WM |
amphibolite |
basement |
126.6 ± 5.2 |
(1) |
4 |
1- Pantó (1965), 2-Pantó et al. (1967), 3- Finger and Faryad (1999), 4-Faryad and Balogh (2002)
The Zemplin unit represents a NW verging nappe-slices system, formed by basement and late Paleozoic rocks. Both basement and late Paleozoic cover sequences are cut by a series of N-S directed faults.
Summary
The Pre-Alpine basement of the Zemplin Unit consists of amphibolite facies metapelite, locally intercalating amphibolites, and of orthogneisses. Granitoids are found as pebbles in the late Paleozoic conglomerates and pegmatite is exposed at surface. The pre-Alpine metamorphism was Variscan in ages, however Pre-Variscan age given by Rb/Sr dating is not excluded. Alpine metamorphism was probably Cretaceous in age and reached greenschist facies conditions.
Bibliography
Baňacký, V., Vass D.,
Eleško M., Kaličiak M., Lexa J., Straka P., Vozár J., Vozárová A. (1988):
Geological map from the southern part of West Slovakia low-land and Zemplin
Mountains, scale 1:50 000, GÚDŠ, Bratislava.
Faryad, S.W. (1995):
Geothermometry of metamorphic rocks from the Zemplinicum (Western Carapathians,
Slovakia). Geologica Carpathica, 46, 2, 113-123.
Faryad,
S.W. and Balogh, K. 2002. Variscan pegmatite and K-Ar and Ar/Ar dating from
basement rocks of the Zemplin Unit, Western Carpathians. Acta Geologica
Hungarica, 45, 193-205
Faryad,
S.W., Vozárová, A. (1997): Geology and metamorphism of the Zemplinicum basement
unit (Western Carpathians). In: P.Grecula, D.Hovorka and M.Putiš (eds.):
Geological evolution of the Western Carpathians. Mineralia Slovaca-Monograph, Bratislava, 351-358.
Finger, F., Faryad, S.W.
(1999): A Variscan monazite age from the Zemplin basement (eastern Western
Carpathians). - Acta Geologica Hungarica, 42, 301-307.
Grecula, P., Kaličiak,
M., Tözsér, J., Varga I. (1981):
Geology of the borderland between the West and East Carpathians in the work of
Jan Slávik. In: P. Grecula (Ed.): New data, correlations and problems. Seminary
"Geological days of Jan Slavik. Special Issue of Slovak Geological Survey.
17-32 (in Slovak).
Kisházi, P., Ivancsics, J., (1988): Contribution to the petrology of crystalline schists in the Zemplin structure. Bulletin of the Hungarian Geol. Soc., 2, 109-124.
Lelkes-Felvári, Gy., Árkai,
P., Sassi, F.P. (1996): Main features of the regional metamorphic events in Hungary:
A review. Geologica Carpathica, 47, 257-270.
Lexa, J.,
Bzák, V., Elečko, M., Mello, J., Polák, M., Potfaj, M. and Vozár, J.,
2000. Geological map of the Western Carpathians and adjacent areas: Scale 1:500
000. Geol. Survey of Slovak Republic, Bratislava.
Magyar, J. (1969): Geology
and petrography of the crystalline window of the Zemplinicum and the
surrounding formations. Manuscript, Comenius University, Bratislava, 1-78.
Maheľ, M. (1986):
Geological structure of the Czechoslovak Carpathians. Paleoalpine
units. Veda, Bratislava, 1-496.
Pantó, G. (1965): A Tokaji-hegység harmadkor elötti képzödményei. Magy.
Áll. Földt. Int´zet. Évi. Jelent., 227-241.
Pantó, G., Balogh, K.,
Kovács, S., Sámsoni, Z. (1967): Rb/Sr check of Assyntian and Caledonian igneous
activity and metamorphism in NE-Hungary. Acta Geol. Hung., 11,
279-281.
Rudinec, R.,Slávik, J.
(1971): Geological structure of the Eastern Slovakia Pre-Neogene basement. Geol. Práce, Spr., 53, 145-157.
Slávik J. (1976): Zemplinicum, a new tectonic unit of the
Central West Carpathians. Geol. Práce, Spr., 65, 7-19.
Vozárová A. (1991): Petrology of Crystalline rocks of
Zemplinicum (West Carpathians) (in Slovak). Západné Karpaty, Sér. Mineral. petrogr.,
geochem., metalogen. 14, 7-59.
Vozárová A and Vozár, J. (1988): Late Paleozoic in
the Western Carpathians. D. Štúr Inst. Geol., Bratislava, 314 pp.