www.geologicacarpathica.sk
GEOLOGICA CARPATHICA, JUNE 2009, 60, 3, 193—204 doi: 10.2478/v10096-009-0013-4
Introduction
A common textural feature in eclogites resulting from re-
equilibration at pressures below those of the eclogite facies,
is the replacement of eclogite facies omphacite by symplec-
titic intergrowths of sodic plagioclase and clinopyroxene
with lower Na and Al content than the initial clinopyroxene.
In most cases, it is diopside with jadeite content below 20 %.
The resulting mineral assemblage of garnet + clinopyroxene
+ plagioclase + quartz is the same as that found in high-pres-
sure mafic granulites without evidence of an eclogite facies
evolution. Orthopyroxene is commonly formed in pressure
conditions lower than the peak recorded pressure (O’Brien
1997; O’Brien & Rötzler 2003).
Overprinted eclogites occur in several complexes of the
Variscan basement of the Western Carpathians in Slovakia.
In these rocks a high-pressure, eclogitic stage has been in-
ferred from symplectites indicating the breakdown of prima-
ry omphacite (e.g. Hovorka & Méres 1990; Hovorka et al.
1992; Janák et al. 1996, 1997; Janák & Lupták 1997; Kori-
kovsky & Hovorka 2001; Faryad et al. 2005). Eclogites with
preserved omphacite are rare. They have been found in the
eastern part of the Low Tatra Mountains (Janák et al. 2003,
2007), which belongs to the Veporic Unit of the Western
Carpathians. Here, eclogites occur as lenses and boudins in
the kyanite-bearing gneisses. Omphacite with the highest ja-
Eclogites overprinted in the granulite facies from the
Ďumbier Crystalline Complex (Low Tatra Mountains,
Western Carpathians)
MARIAN JANÁK
1*
, TOMÁŠ MIKUŠ
2
, PAVEL PITOŇÁK
3
and JÁN SPIŠIAK
4
1
Geological Institute, Slovak Academy of Sciences, Dúbravská cesta 9, P.O. Box 106, 840 05 Bratislava 45, Slovak Republic;
*
marian.janak@savba.sk
2
Geological Institute, Slovak Academy of Sciences, Severná 5, 974 01, Banská Bystrica, Slovak Republic
3
ENVIGEO, a.s., Kynce ová 2, 974 11 Banská Bystrica, Slovak Republic
4
Faculty of Natural Sciences, Matej Bel University, Tajovského 40, 974 01 Banská Bystrica, Slovak Republic; spisiak@fpv.umb.sk
(Manuscript received June 17, 2008; accepted in revised form October 23, 2008)
Abstract: Metabasites with evidence for breakdown of former eclogites and recrystallization under granulite facies condi-
tions occur in the Ďumbier Crystalline Complex of the Low Tatra Mountains, Central Western Carpathains. Textural
relationships, phase equilibrium modelling and thermobarometry have been used to determine the P-T evolution of these
rocks. Omphacite diagnostic for the eclogites facies stage is absent but its former presence is inferred from the symplectitic
intergrowths of clinopyroxene + plagioclase. The re-equilibration in high-pressure granulite facies conditions is demon-
strated by the assemblage garnet + clinopyroxene (< 10 % Jd) + plagioclase + quartz. The phase equilibrium modelling us-
ing THERIAK-DOMINO program and conventional geothermobarometry suggest the P-T conditions of 750—760 °C and
1.1—1.5 GPa for the high-pressure granulite stage. Orthopyroxene formed in the clinopyroxene + plagioclase symplectites
and kelyphites and coronas around garnet at P-T conditions of ca. 0.7—1.0 GPa and 650—700 °C. P-T evolution of granulitized
eclogites is interpreted as the result of two metamorphic events; early Variscan eclogite facies metamorphism was fol-
lowed by granulite facies thermal overprint in the Carboniferous time. The second metamorphic event was crucial for
breakdown of eclogites, these are only seldom preserved in the pre-Alpine basement of the Western Carpathians.
Key words: Western Carpathians, Low Tatra Mountains, geothermobarometry, phase equilibrium, modelling, granulites,
eclogites.
deite content (~ 40 mol %) occurs as inclusions in the garnet
whereas omphacite with lower jadeite content is present in
the matrix. Most of the clinopyroxene has jadeite content be-
low 19 mol %, forming the symplectites with plagioclase,
amphibole and quartz.
In this paper we describe the overprinted eclogites from
the western part of the Low Tatra Mountains which belongs
to the Tatric Unit of the Western Carpathians. The investi-
gated rocks show the microtextures indicative for breakdown
of former eclogites and recrystallization under granulite fa-
cies conditions with formation of orthopyroxene. The paper
describes the mineralogical and petrological features, which
constrain the P-T evolution, supported by pseudosection
modelling and thermobarometry. Preservation of eclogites is
discussed within the context of the Variscan tectonometa-
morphic evolution of the Western Carpathians.
Geological setting
The studied eclogites come from the Ďumbier Crystalline
Complex of the Low Tatra Mountains (Fig. 1). The Ďumbier
Crystalline Complex is composed of pre-Mesozoic grani-
toids, high-grade felsic rocks (orthogneisses, granulites,
paragneisses), metabasites and metaultramafic rocks (Spi-
šiak & Pitoňák 1990; Biely et al. 1992; Krist et al. 1992;
194
JANÁK, MIKUŠ, PITOŇÁK and SPIŠIAK
Petrík et al. 2006). The metamorphic rocks are intruded by a
pluton which consists of several (Ďumbier, Prašivá and Lati-
borská ho a) types of granitoid rocks, ranging from tonalite
to granodiorite and granite. These magmatic rocks occur in
the northern part of the area whereas metamorphic rocks
form the southern belt with a transitional zone of migmatites
at their contact (Bezák & Klinec 1983). The whole complex
belongs to the upper tectonic unit (Putiš 1992; Janák 1994;
Bezák et al. 1997; Plašienka et al. 1997) within the Variscan
structure of the Western Carpathians.
Overprinted eclogites form dm—m lenses in banded am-
phibolites, also referred to as the “leptyno-amphibolite com-
plex” (LAC) sensu Hovorka et al. (1994, 1997). Because of a
lack of surface outcrops, most of such lenses were found un-
derground, in the former mine for gold and tungsten, in the
so called “Jasenie-Kyslá ore deposit” (Fig. 1). The whole
complex is penetrated by veins of aplites and leucogranites.
Metabasites are intimately associated with surrounding or-
thogneisses (augen-gneisses) and migmatites, all exhibiting
mylonitization and shearing under ductile conditions. In the
metapelitic gneisses sillimanite and very rarely kyanite partly
transformed to sillimanite occur together with garnet, K-feld-
spar, plagioclase, biotite, muscovite, rutile and quartz. All
the metamorphic rocks exhibit high-grade metamorphism
and partial melting with formation of migmatites under granu-
lite facies conditions, being partly retrogressed under am-
phibolite to greenschist facies conditions (Spišiak & Pitoňák
1990; Janák et al. 2000a,b; Mikuš et al. 2007). The crystal-
line basement is overlain by Mesozoic and Cenozoic sedi-
mentary cover sequences and nappes.
Fig. 1. Simplified geological maps of a) the Western Carpathians with occurrences of high-pressure metabasites (stars), b) the central part
of the Ďumbier Crystalline Complex in the Low Tatra Mountains (modified from Biely et al. 1992), and c) the position of the investigated
metabasites in the Jasenie-Kyslá ore deposit (according to Spišiak & Pitoňák 1990).
195
ECLOGITES OVERPRINTED IN THE GRANULITE FACIES (WESTERN CARPATHIANS)
The SHRIMP dating of zircon from banded amphibolites
suggests an Ordovician (481± 5 Ma) age for the magmatic
protolith and two Variscan metamorphic events (428—411
and 338±6 Ma; Putiš et al. 2008). The electron microprobe
dating of monazite from biotite gneisses and augen-gneisses
gave mostly Carboniferous (350—340 Ma) ages, some mona-
zite cores are older (ca. 470 and 390 Ma; Petrík et al. 2006).
The age of the tonalite-granodiorite pluton (Ďumbier type)
according to zircon dating (330 ± 10, Poller et al. 2001;
343 ± 3 Ma, Putiš et al. 2003) is Carboniferous.
Petrography
The investigated rocks come from the gallery no. 4 in the
Šifrová dolina Valley north of Jasenie (Fig. 1). They exhibit
a massive texture with reddish garnet and pale green cli-
nopyroxene variably replaced by dark green amphibole. The
sample J-257 comes from the core of a lens embedded in the
leucocratic (trondhjemite-tonalite) and mafic (amphibolite,
amphibole-biotite gneiss) layers (Fig. 2). This fabric is relat-
ed to shearing and deformation during exhumation. The gar-
net and clinopyroxene-bearing lenses apparently represent
relics of eclogites, preserved as boudins in the more retro-
gressed and deformed host rocks. The bulk rock composition
of sample J-257 was determined by standard wet chemical
analysis (Table 1).
Microstructures along with variations in mineral chemistry
suggest that the investigated metabasites have experienced a
complex metamorphic history. Four stages of recrystalliza-
tion have been identified.
a) The eclogite facies stage is inferred from clinopyroxene +
plagioclase symplectites after primary omphacite (Fig. 3a,c).
Under the eclogites facies conditions the stable mineral as-
semblage may have consisted of garnet, omphacite, rutile
and quartz with minor phengite and zoisite.
b) The granulite facies stage is demonstrated by replace-
ment of omphacite by clinopyroxene + plagioclase symplec-
tites and formation of orthopyroxene. The orthopyroxene
occurs mostly in the kelyphitic rims and coronas together
with plagioclase around garnet but also in the clinopyroxene
+ plagioclase symplectites (Fig. 3c,e); it is a later phase than
garnet and clinopyroxene.
c) The amphibolite facies stage is manifested by formation
of amphibole replacing pyroxenes and garnet; it is the most
abundant phase of the matrix (Fig. 3e,f). Minor epidote, ti-
tanite, ilmenite, biotite and muscovite also belong to the am-
phibolite facies assemblage.
d) The greenschist facies stage is the latest one, with for-
mation of actinolite, chlorite, quartz and calcite, mostly in
the fractures and veins.
Mineral chemistry
The chemical composition of the major mineral phases
was determined by CAMECA SX-100 electron microprobe
at the State Geological Institute of Dionýz Štúr in Bratislava.
The operating conditions were as follows: 15 kV accelerat-
ing voltage, 20 nA beam current, counting times 20 s on
peaks and beam diameter of 2—10 µm. Mineral standards (Si,
Ca: wollastonite, Na: albite, K: orthoclase, Fe: fayalite, Mn:
rhodonite), pure element oxides (TiO
2
, Al
2
O
3
, Cr
2
O
3
, MgO)
and metals (Ni) were used for calibration. Raw counts were
corrected using on-line PAP routine. Fe
3+
in clinopyroxenes
was calculated according to the charge balance proposed by
Ryburn et al. (1976). Fe
3+
in amphiboles was calculated as-
suming an ideal stoichiometry according to Schumacher
(1997). The mineral abbreviations in this paper are according
to Kretz (1983).
Garnet forms porphyroblasts with abundant inclusions in
the cores (Fig. 3a,b). Some inclusions (amphibole, zoisite,
rutile, phengitic white mica, quartz) may have been inherited
from the prograde metamorphic stage but re-equilibrated in
the high-pressure granulite stage as deduced from their com-
position. However, many “inclusions” (amphibole, plagio-
clase, epidote, chlorite, muscovite and quartz) are connected
with matrix by fractures (Fig. 3a,b) and these were obviously
related to fluids influx during the post-granulite retrogression.
The garnets correspond to almandine (25—54 mol %) with sig-
nificant grossular (22—27 mol %) and pyrope (19—30 mol %)
contents (Table 2). The garnet compositional profile (Fig. 4)
is relatively smooth, with an initial decrease of Prp and X
Mg
concomitant with increase in X
Fe
from the core to the rim at
nearly constant Sps and slightly increasing Grs contents. A
reverse pattern with slightly increasing Prp, X
Mg
and de-
SiO
2
TiO
2
Al
2
O
3
Fe
2
O
3
FeO
MnO MgO CaO Na
2
O K
2
O P
2
O
5
H
2
O LOI Total
48.86 1.03 14.04 1.75 7.72 0.18 10.61 8.86 1.91 1.52 0.1 0.31 3.1 99.99
Table 1: Bulk rock composition of sample J-257 (wt. % oxides).
Fig. 2. Lens (boudin) of eclogite (sample J-257) embedded in the
trondhjemite-amphibolite bands.
196
JANÁK, MIKUŠ, PITOŇÁK and SPIŠIAK
creasing X
Fe
can be observed in the medium part of garnet
but close to the edge there is a decrease in Prp, X
Mg
as well
as Grs accompanied by increase in Sps, Alm and X
Fe
. The
maximum X
Mg
occurs in the garnet cores whereas rims are
depleted (Table 2). We infer that the actual rim of garnet that
existed at the peak stage is no longer present. It has been
consumed by the reactions producing kelyphite and corona
textures. The observed zonation resulted from retrogression
and partial resorption of garnet.
Clinopyroxene occurs as glomeroblastic and vermicular
grains, symplectitically intergrown with plagioclase (Fig. 3).
This indicates breakdown of primary, more Na and Al-rich cli-
nopyroxene (omphacite) to secondary clinopyroxene and pla-
gioclase. The characteristic “fingerprint” textures have mostly
been recrystallized to coarser, granoblastic aggregates (e.g.
Joanny et al. 1991; Anderson & Moecher 2007), where amphib-
ole is also present (Fig. 3c). Symplectitic clinopyroxene is diop-
side (Table 3) with very low Al and Na contents (XJd
≤
0.1). It
Fig. 3. Back-scattered electron (BSE) images. a – Garnet porphyroblast surrounded by plagioclase kelyphite. The matrix is composed of
clinopyroxene + plagioclase symplectite and lath-shaped amphibole. b – Garnet porphyroblast with line marking the location of the analy-
sed profile shown in Fig. 4. c – Symplectites of clinopyroxene + plagioclase partly replaced by amphibole. d – Symplectite of clinopy-
roxene + plagioclase partly replaced by orthopyroxene. Note a coarser clinopyroxene-plagioclase intergrowths. e – Garnet surrounded by
orthopyroxene + plagioclase + amphibole kelyphite. f – Detail of orthopyroxene + plagioclase + kelyphite in corona around partly decom-
posed garnet. Orthopyroxene itself is partly replaced by chlorite.
197
ECLOGITES OVERPRINTED IN THE GRANULITE FACIES (WESTERN CARPATHIANS)
shows slight compositional zoning with cores richer in Al and
Na with respect to the rims (Table 3), which indicates recrystal-
lization of more jadeitic clinopyroxene. Inclusions of clinopy-
roxene in garnet are small, their size is up to 10 µm and compo-
sition is similar to that of symplectitic clinopyroxene. The
composition of the “primary” omphacite has been reconstructed
from the modal proportions in clinopyroxene + plagioclase sym-
plectites (BSE image at high magnification), converting the
phase volumes (34 % Plg+66 % Cpx) to weight % using densi-
ties of 2.7 g · cm
—3
for plagioclase and 3.4 g · cm
—3
for clinopy-
roxene. Average analysis of several symplectitic domains yields
an initial jadeite content of 23 mol % (Table 3).
Orthopyroxene occurs in the clinopyroxene + plagioclase
symplectitic domains (Fig. 3d) and in kelyphitic rims around
garnets together with plagioclase and amphibole (Fig. 3e,f).
The composition of orthopyroxene is almost uniform, with
0.26—0.28 X
Mg
and < 0.5 wt. % CaO contents (Table 4).
Amphibole occurs as several compositional and textural
types. Small euhedral crystals are enclosed in the garnet cores
(Fig. 3b). In kelyphitic rims around garnets amphibole occurs
as lath-shaped crystals, or vermicular intergrowths with ortho-
pyroxene and plagioclase near the garnet (Fig. 3f). Matrix am-
phiboles are either large, strongly pleochroic, brown-green
grains, or smaller grains that replace or form part of symplec-
tites with clinopyroxene and plagioclase (Fig. 3c). These am-
phiboles are less aluminous and less sodic and correspond to
Mg-hornblende (classification according to Leake 1997). Act-
inolite is a later phase, that formed zones around or grew
along fractures within earlier amphiboles. Representative mi-
croprobe analyses of amphiboles are presented in Table 5.
Plagioclase textures suggest that it is a secondary phase
formed due to the breakdown of garnet and clinopyroxene.
Plagioclases in the symplectites with clinopyroxene have
An
25—30
(Table 6) whereas in the kelyphitic rims around gar-
nets they have An
48—78
. Albite occurs in domains containing
chlorite and actinolite.
P-T
evolution
The pressure and temperature conditions of metamor-
phism can be constrained using conventional mineral ther-
mobarometers as well as pseudosection calculations (e.g.
Powell & Holland 2008). Conventional thermobarometry
employs the equilibrium thermodynamics of balanced reac-
tions between minerals combined with the observed mineral
end-member compositions. In contrast, pseudosections em-
ploy a method of Gibbs free energy minimization in a for-
ward modelling of mineral parageneses for a given rock
composition, with the potential to provide additional petro-
genetic information. We used both methods to constrain the
anal.
point
core rim core rim core rim core rim
SiO
2
39.04
38.62
39.49
39.10
38.76
38.65
38.54
38.64
TiO
2
0.03
0.05
0.04
0.03
0.00
0.00
0.08
0.08
Al
2
O
3
21.81
21.23
21.70
21.45
22.29
21.82
22.37
22.24
Cr
2
O
3
0.02
0.30
0.01
0.07
0.00
0.00
0.00
0.00
FeO
24.30
25.93
24.23
24.25
21.52
22.77
22.33
23.21
MnO
0.87
1.18
0.82
1.03
0.80
0.85
0.74
1.01
MgO
5.53
4.74
6.37
5.27
7.60
5.67
6.24
5.56
CaO
9.26
9.06
8.16
9.79
8.53
9.87
9.55
9.90
Total
100.84
101.11
100.81
100.98
99.50
99.63
99.93
100.65
Si
3.001
2.989
3.012
3.026
2.980
2.999
2.971
2.974
Ti
0.002
0.003
0.002
0.003
0.000
0.000
0.005
0.005
Al
1.976
1.936
1.948
1.960
2.020
1.995
2.032
2.018
Cr
0.001
0.018
0.004
0.000
0.000
0.000
0.000
0.000
Fe
3+
0.087
0.097
0.093
0.085
0.085
0.085
0.082
0.086
Fe
2+
1.474
1.581
1.469
1.468
1.299
1.392
1.358
1.408
Mn
0.057
0.077
0.067
0.053
0.052
0.056
0.048
0.066
Mg
0.633
0.547
0.605
0.727
0.871
0.656
0.717
0.638
Ca
0.762
0.751
0.808
0.670
0.703
0.820
0.789
0.817
Total
8.009
8.002
8.010
7.991
8.010
8.003
8.014
8.013
X
alm
0.504
0.535
0.498
0.249
0.444
0.476
0.466
0.481
X
sps
0.019
0.026
0.023
0.503
0.018
0.019
0.017
0.022
X
prp
0.216
0.185
0.205
0.018
0.298
0.224
0.246
0.218
X
grs
0.249
0.240
0.261
0.220
0.231
0.269
0.260
0.267
X
Mg
0.300
0.257
0.292
0.331
0.401
0.320
0.346
0.312
Table 2: Representative microprobe analyses of garnet. Formula normalization to 12 oxygens.
Fig. 4. Compositional profile across garnet shown in Fig. 3b.
Length of profile is 400 µm.
198
JANÁK, MIKUŠ, PITOŇÁK and SPIŠIAK
P-T evolution of the investigated metabasites from the Ďum-
bier Crystalline Complex.
The phase equilibrium modelling was performed with the
THERIAK-DOMINO program (De Capitani 1994). This
program performs a Gibbs free energy minimization using
the algorithm of De Capitani & Brown (1987). For thermo-
dynamic calculations, bulk rock composition of sample J-257
(Table 1) was used in the simplified system NCFMASH
(Na
2
O—CaO—FeO—MgO—Al
2
O
3
—SiO
2
—
H
2
O), with water content in excess to model
the water-saturated conditions (e.g. Carson
et al. 1999; Guiraud et al. 2001). We as-
sume that effective bulk composition (e.g.
Stüwe 1997) was essentially homogeneous
on the scale of measured sample. It was
probably not significantly affected by the
garnet fractionation process since there is
an absence of growth zoning in the mea-
sured garnets but some parts of garnet that
existed at the peak-pressure stage could
have been removed from the equilibrating
volume of rock by reactions consuming
garnet and producing kelyphite and corona
textures. We used the program DOMINO
with the internally consistent mineral data-
base (JUN92, an updated version of that of
Berman 1988) and solid solution models
for garnet (Berman 1990), omphacite, am-
phibole (Meyre et al. 1997), feldspar (Fuhr-
man & Lindsley 1988) and orthopyroxene
as available from the THERIAK-DOMINO
website: http://titan.minpet.unibas.ch/minpet/
theriak/theruser.html. The calculated equi-
Table 3: Representative microprobe analyses of clinopyroxene and recalculated composition of omphacite. Formula normalization to 6 oxy-
gens and 4 cations.
type
in Grt
in Grt
symplect.
symplect. symplect. symplect. symplect. omp
calc.
SiO
2
53.90
54.09
53.49
53.01
53.70
53.48
53.30
56.57
TiO
2
0.03
0.08
0.09
0.09
0.06
0.11
0.07
0.06
Al
2
O
3
2.47
3.14
4.19
2.00
3.23
2.51
2.02
9.16
Cr
2
O
3
0.10
0.08
0.08
0.09
0.01
0.14
0.12
0.00
FeO
5.87
6.88
6.43
8.12
6.49
8.34
6.60
4.98
MnO
0.19
0.13
0.13
0.12
0.17
0.14
0.07
0.09
MgO
14.19
14.16
13.48
14.12
13.65
13.92
14.69
10.10
CaO
22.13
21.56
21.12
22.31
21.80
22.27
22.06
16.97
Na
2
O
1.05
1.28
1.41
0.44
1.08
0.67
0.80
3.43
K
2
O
0.01
0.00
0.01
0.01
0.01
0.01
0.02
0.05
Total
99.94
101.40
100.42
100.30
100.20
101.60
99.79
101.41
Si
1.980
1.964
1.954
1.962
1.970
1.955
1.969
1.993
Ti
0.001
0.002
0.003
0.002
0.002
0.003
0.002
0.002
Al
0.107
0.134
0.180
0.087
0.140
0.108
0.088
0.381
Cr
0.003
0.002
0.002
0.003
0.000
0.004
0.003
0.000
Fe
3+
0.003
0.022
0.004
0.013
0.000
0.019
0.026
0.000
Fe
2+
0.178
0.187
0.193
0.239
0.199
0.236
0.178
0.147
Mn
0.006
0.004
0.004
0.004
0.005
0.004
0.002
0.003
Mg
0.777
0.767
0.734
0.779
0.747
0.759
0.809
0.531
Ca
0.871
0.839
0.827
0.885
0.857
0.872
0.873
0.641
Na
0.075
0.090
0.100
0.032
0.077
0.048
0.058
0.234
K
0.000
0.000
0.000
0.001
0.000
0.000
0.001
0.002
Total
4.001
4.011
4.002
4.006
3.997
4.009
4.010
3.933
X
Jd
0.07
0.06
0.09
0.01
0.07
0.02
0.03
0.23
Table 4: Representative microprobe analyses of orthopyroxene. Formula normalization to
6 oxygens and 4 cations.
SiO
2
52.50
52.69
51.98
52.38
52.78
52.56
TiO
2
0.04
0.05
0.05
0.06
0.03
0.05
Al
2
O
3
0.95
0.72
0.70
0.40
0.61
0.74
Cr
2
O
3
0.16
0.15
0.14
0.04
0.05
0.09
FeO
27.83
27.60
27.20
27.32
26.48
26.30
MnO 0.51
0.48
0.53
0.54
0.52
0.57
MgO
19.58
19.49
19.17
19.40
20.25
19.90
CaO
0.53
0.50
0.49
0.56
0.57
0.51
Na
2
O 0.01
0.04
0.03
0.06
0.00
0.02
K
2
O
0.01
0.02
0.01
0.01
0.00
0.01
Total 102.20
101.82
100.34
100.83
101.33
100.76
Si
1.961 1.972 1.975 1.980 1.977 1.979
Ti
0.001 0.001 0.002 0.002 0.001 0.001
Al
0.042 0.032 0.031 0.018 0.027 0.033
Cr
0.005 0.005 0.004 0.001 0.001 0.003
Fe
3+
0.030 0.021 0.013 0.018 0.017 0.006
Fe
2+
0.840 0.843 0.851 0.846 0.813 0.822
Mn
0.016 0.015 0.017 0.017 0.017 0.018
Mg
1.090 1.087 1.086 1.093 1.131 1.117
Ca
0.021 0.020 0.020 0.023 0.023 0.021
Na
0.001 0.003 0.002 0.004 0.000 0.001
K
0.001 0.001 0.001 0.001 0.000 0.001
Total
4.007 3.999 4.003 4.003 4.006 4.001
X
Mg
0.56
0.56
0.56
0.56
0.58
0.58
librium phase diagram is shown in Fig. 5. The isopleths of
mineral compositions were computed for a fixed bulk com-
position with the program DOMINO. The isopleths corre-
sponding to measured mineral compositions for garnet,
omphacite, orthopyroxene and plagioclase constrain the P-T
conditions of equilibrium assemblages (Fig. 6).
Pressure and temperature conditions were also calculated by
the application of several standard geothermometers and
199
ECLOGITES OVERPRINTED IN THE GRANULITE FACIES (WESTERN CARPATHIANS)
geobarometers, determined by the coexisting mineral assem-
blage. Temperatures were obtained from garnet-clinopyroxene
(Powell 1985; Krogh Ravna 2000) and garnet-orthopyroxene
(Harley 1984; Sen & Bhattacharya 1984) geothermometers. In
garnet + clinopyroxene + plagioclase + quartz assemblages,
pressures were calculated from the Mg end-member reaction
according to Newton & Perkins (1982), Moecher et al. (1988)
and Powell & Holland (1988). In Powell & Holland’s calibra-
tion, both Hodges & Spear (1982), and Ganguly & Saxena
(1984) garnet mixing models were employed. In those involv-
ing garnet + orthopyroxene + plagioclase + quartz, calibra-
tions of Newton & Perkins (1982) and Powell & Holland
(1988) with Mg end-member and Moecher et al. (1988) with
Fe end-member reaction were used.
Table 5: Representative microprobe analyses of amphibole. Formula normalization to 23 oxygens and 16 cations.
Table 6: Representative microprobe analyses of plagioclase. Formula normalization to 8 oxygens.
anal.
point kelyphite symplect. symplect. symplect. kelyphite kelyphite symplect. kelyphite
SiO
2
56.64
62.76
61.11
60.97
58.36
48.11
61.20
51.01
Al
2
O
3
28.01
24.17
24.62
24.48
26.18
32.57
24.87
31.63
FeO
0.32
0.22
0.08
0.26
0.39
0.45
0.16
0.22
CaO
10.13
5.54
5.63
5.93
8.07
15.75
6.37
14.20
Na
2
O
5.96
8.77
8.38
8.53
7.01
2.39
7.90
3.46
K
2
O
0.07
0.16
0.04
0.13
0.08
0.05
0.13
0.05
Total
101.12
101.64
99.89
100.34
100.11
99.34
100.67
100.57
Si
2.521
2.743
2.714
2.705
2.610
2.219
2.701
2.309
Al
1.469
1.245
1.289
1.280
1.380
1.770
1.294
1.687
Fe
0.012
0.008
0.003
0.010
0.015
0.017
0.006
0.008
Ca
0.483
0.260
0.268
0.282
0.386
0.778
0.301
0.689
Na
0.514
0.743
0.722
0.734
0.608
0.213
0.676
0.304
K
0.004
0.009
0.002
0.007
0.004
0.003
0.007
0.003
Total
5.003
5.007
4.998
5.018
5.002
5.000
4.986
5.000
Ab
51.34
73.44
72.76
71.72
60.87
21.45
68.67
30.52
An
48.25
25.66
27.01
27.56
38.7
78.27
30.57
69.19
Or
0.41
0.9
0.23
0.72
0.43
0.28
0.76
0.29
High-pressure granulite facies P-T conditions
As demonstrated above, the formation of clinopyroxene +
plagioclase symplectites indicates a passage from eclogite
facies to the high-pressure granulite facies (e.g. Zhao et al.
1991; O’Brien 1997; O’Brien & Rötzler 2003; Groppo et al.
2007). The P-T conditions of eclogite recrystallization and
formation of high-pressure granulite facies assemblage gar-
net + clinopyroxene + plagioclase + amphibole + quartz
have been modelled from the measured composition of gar-
net cores and clinopyroxene + plagioclase symplectites (Ta-
bles 2, 3 and 6). We used the garnet with the highest X
Mg
,
clinopyroxene with the highest jadeite, and plagioclase with
the lowest anorthite in the calculations. The 0.4 X
Mg
Grt,
type
in Grt
in Grt
kelyphite
kelyphite
symplect.
symplect.
matrix
matrix
matrix
matrix
SiO
2
46.50
49.01
49.51
46.93
48.88
47.08
52.18
49.05
53.59
52.06
TiO
2
0.98
0.79
0.82
1.52
0.75
0.66
0.57
1.05
0.32
0.53
Al
2
O
3
12.54
8.31
7.87
10.15
8.34
9.96
5.35
7.87
4.34
5.87
Cr
2
O
3
0.08
0.38
0.60
0.54
0.23
0.16
0.13
0.16
0.08
0.13
FeO
t
10.23
10.84
11.51
12.64
10.77
11.75
10.16
11.01
9.94
10.18
MnO
0.10
0.07
0.14
0.16
0.17
0.05
0.10
0.20
0.12
0.17
MgO
14.36
14.82
15.12
13.36
15.44
14.35
16.98
15.36
17.11
16.44
CaO
12.15
11.58
11.90
11.28
11.71
11.56
11.74
11.89
12.14
12.01
Na
2
O
1.73
1.27
1.18
1.75
1.33
1.62
0.77
1.25
0.41
0.72
K
2
O
0.24
0.18
0.18
0.24
0.14
0.21
0.04
0.15
0.07
0.10
Total
99.06
97.38
98.89
98.72
97.76
97.40
98.02
97.99
98.12
98.21
Si
6.561
7.007
6.984
6.698
6.935
6.748
7.316
6.967
7.531
7.305
Ti
0.104
0.085
0.087
0.164
0.080
0.071
0.060
0.112
0.034
0.056
Al
IV
1.439
0.993
1.016
1.302
1.065
1.252
0.684
1.033
0.469
0.695
Al
VI
0.647
0.408
0.292
0.405
0.330
0.430
0.200
0.285
0.250
0.276
Cr
0.009
0.043
0.067
0.061
0.026
0.018
0.014
0.018
0.009
0.014
Fe
3+
0.384
0.439
0.526
0.529
0.597
0.623
0.551
0.514
0.241
0.468
Fe
2+
0.824
0.857
0.832
0.980
0.681
0.786
0.640
0.794
0.927
0.727
Mn
0.012
0.009
0.017
0.020
0.020
0.006
0.012
0.024
0.014
0.020
Mg
3.021
3.160
3.179
2.842
3.266
3.066
3.549
3.253
3.585
3.439
Ca
1.838
1.773
1.799
1.725
1.780
1.775
1.764
1.810
1.828
1.806
Na
M4
0.162
0.227
0.198
0.275
0.220
0.225
0.209
0.190
0.112
0.194
Na
A
0.310
0.126
0.124
0.210
0.146
0.225
0.000
0.154
0.000
0.002
K
0.044
0.033
0.032
0.044
0.025
0.038
0.007
0.027
0.013
0.018
Total
16.349
16.153
16.145
16.246
16.158
16.250
15.995
16.170
16.007
16.009
200
JANÁK, MIKUŠ, PITOŇÁK and SPIŠIAK
Fig. 5. Phase diagram for the composition of the investigated sam-
ple (J-257), calculated using the program DOMINO (De Capitani
1994). The shaded areas correspond to the observed assemblages.
Quartz and H
2
O are considered to be in excess.
0.9 X
Jd
Cpx and 0.25 X
An
Plg isopleths constrain ca. 750—
760 °C and 1.1—1.4 GPa stability field (Fig. 6). The isopleths
of “reconstructed” omphacite (0.23 X
Jd
) and measured gar-
net core composition intersect at 1.5—1.6 GPa and 750 °C.
The P-T conditions calculated from the Grt-Cpx thermome-
ters and the Grt-Cpx-Pl-Qtz barometers are 700—760 °C and
1.1—1.4 GPa (Table 7, Fig. 7).
Orthopyroxene formation P-T conditions
The formation of orthopyroxene appears to be at the ex-
pense of clinopyroxene and garnet. We infer that orthopy-
roxene was in equilibrium with kelyphitic plagioclase and
the outermost rim of garnet. The P-T conditions were calcu-
lated from the composition of orthopyroxene and adjacent
garnet and plagioclase. The modelled isopleths with 0.56—
0.58 X
Mg
Opx, 0.26—0.32 X
Mg
Grt and 0.4—0.7 X
An
Plg (Fig. 6)
constrain the orthopyroxene formation at ca. 0.7—0.9 GPa and
680—700 °C. The Grt-Opx thermometers in combination
Grt-Cpx
Grt-Cpx-Pl
Assemblage
P ref
T P T
KR T
ref P
NP P
PH+HS P
PH+GS P
M Mg
Grt+Cpx+Pl+Qtz 1
751
716
700
1.15
1.1
1.29
1.25
1.5
760
733
800
1.26
1.21
1.38
1.36
Grt-Opx
Grt-Opx-Pl
P ref
T H T
SB T
ref P
NP P
PH+HS
P
M Fe
Grt+Opx+Pl+Qtz
0.7
659
717
650
0.76
0.72
0.94
1
674
735
750
0.81
0.76
1.1
P — Powell (1985), KR — Krogh Ravna (2000), PH — Powell & Holland (1988), HS — Hodges & Spear (1982), H — Harley (1984),
GS — Ganguly & Saxena (1984), SB — Sen & Bhattacharya (1984), NP — Newton & Perkins (1982), M — Moecher et al. (1985).
Table 7: Summary of P(GPa)—T(°C) estimates based on thermobarometric calculations.
with the Grt-Opx-Pl-Qtz barometers yield P-T conditions of
650—740 °C and 0.7—1.1 GPa (Table 7, Fig. 7).
Discussion
Eclogite facies rocks in the crystalline basement of the
Western Carpathians are rare. Eclogites with preserved om-
phacite from the eastern part of the Low Tatra Mts near
He pa show the maximum pressure and temperature condi-
tions of around 2.5 GPa and 700 °C. The metamorphic P-T
path reflects nearly isothermal decompression during exhu-
mation (Janák et al. 2007; Fig. 8). In contrast, eclogites from
Jasenie show a very strong overprint at ca. 1.5—1.1 GPa. As
in many eclogites overprinted in granulite facies (e.g.
O’Brien et al. 1992; O’Brien & Vrána 1995; Guo et al. 2002)
the orthopyroxene-producing stage has not allowed major
diffusive resetting of zoned garnet but has led to differential
decomposition of garnet rim (O’Brien & Vrána 1995). Actu-
al garnet composition in equilibrium with plagioclase, sym-
plectitic Cpx and later Opx is therefore very difficult to
determine. For this reason the local equilibrium and effective
bulk system for calculating the P-T conditions of post-peak
stage need to be considered. In spite of these difficulties, the
application of phase equilibrium modelling and conventional
geothermobarometry as described above, yields essentially
consistent results for the investigated metabasites from Jasenie.
The eclogitic mineral assemblages are preserved because
reactions during decompression commonly consume the
rocks’s fluid and the system becomes water-undersaturated.
Extensive retrogression may occur due to external fluids in-
filtration (Heinrich 1982; Carson et al. 1999; Guiraud et al.
2001). These circumstances may explain the breakdown of
the eclogitic assemblage in the investigated rocks. Water-sat-
urated conditions can be deduced from the presence of
phengite, zoisite and amphibole. Pargasitic amphibole can
be stable in high-pressure conditions as documented by
phase equilibrium modelling (Fig. 5) and experimental data
(e.g. Poli & Fumagalli 2003) but the majority of amphibole
forming the symplectites, kelyphites and matrix clearly post-
dates the peak pressure conditions. This can be related to ex-
ternal fluids infiltration, most probably from the dehydrating
country rocks like the metapelitic gneisses and migmatites.
Moreover, we assume that thermal overprint in high-pres-
sure granulite facies conditions played an important role in
the evolution of these rocks. There are two possibilities to
201
ECLOGITES OVERPRINTED IN THE GRANULITE FACIES (WESTERN CARPATHIANS)
Fig. 6. Isopleths for a – X
Jd
in clinopyroxene, b – X
Mg
in garnet, c – X
Mg
in orthopyroxene and d – X
An
in plagioclase calculated with
program DOMINO (De Capitani 1994). Bold lines refer to measured core compositions of garnet and symplectitic clinopyroxene and pla-
gioclase. Dashed lines refer to measured compostions of garnet rims, orthopyroxene and kelyphitic plagioclase. Dashed-dotted line refers to
reconstructed omphacite composition. The circles constrain the region of crosscutting of the isopleths. The bold circles mark the estimated
peak P-T conditions and empty circles those of orthopyroxene formation.
explain such thermal overprint. Heating due to thermal re-
laxation and slow uplift during a single metamorphic event,
or thermal overprint on partly exhumed eclogites due to
a second metamorphic event.
Although the first alternative may be supported by texture
with a relatively coarser clinopyroxene + plagioclase sym-
plectites than that common in rapidly exhumed eclogites
(Anderson & Moecher 2007), the second possibility is
favoured from field relations and geochronological data.
Overprinted eclogites with zircons of early Variscan age
(Putiš et al. 2008) are accommodated in high-temperature
and medium- to low-pressure rocks (mostly migmatites),
some of them showing the transition of kyanite to sillimanite
(Janák et al. 2000a). These are accompanied by voluminous
granitoids of Carboniferous age (Petrík et al. 1994; Putiš et
al. 2003; Petrík et al. 2006). Thermal overprint on partly ex-
humed eclogites seems to be related to metamorphism and
partial melting at upper mantle/lower crustal levels. Follow-
ing this overprint, the eclogites together with their host rocks
were emplaced from the upper mantle/lower crustal depths
by ductile extrusion and mid-crustal thrusting. In the West-
ern Tatra, overprinted eclogites (Janák et al. 1996) and their
202
JANÁK, MIKUŠ, PITOŇÁK and SPIŠIAK
Fig. 7. Calculated P-T conditions from conventional geother-
mobarometry.
Fig. 8. P-T paths for eclogites from the Variscan basement of the
Western Carpathians. A – eclogites from He pa (Janák et al. 2007),
B – eclogites from Jasenie (this study). The metamorphic facies grid
is from Okamoto & Maruyama (1999). BS – blueschist facies, EA –
epidote amphibolite facies, AM – amphibolite facies, HGR – high-
pressure granulite facies, Lw—EC – lawsonite eclogite facies, Ep—
EC – epidote eclogite facies, Amp—EC – amphibole eclogite fa-
cies, Dry—EC – dry eclogite facies. The quartz-coesite curve is
calculated from thermodynamic data of Holland & Powell (1998).
host rocks (Janák et al. 1999) are accommodated in a hang-
ingwall (upper unit) of an inverted metamorphic sequence,
above the micaschists.
There are similarities with granulitized eclogites from the
internal parts of the Variscan orogen in the Bohemian Mas-
sif (e.g. O’Brien 2008). Here the eclogites formed earlier
(420—380 Ma) than granulite-facies metamorphism (340 Ma),
which was related to late stages of exhumation of the hot oro-
genic lower crust (Schulmann et al. 2002, 2008). We suggest
that such thermal overprint during the Carboniferous time was
crucial for the breakdown of eclogites in the Western Car-
pathians.
Conclusions
(1) Reaction textures and phase equilibrium modelling
suggest that metabasites from the Ďumbier Crystalline Com-
plex of the Western Carpathians underwent high-pressure
metamorphism at eclogite facies conditions.
(2) The eclogites were re-equilibrated in high-pressure
granulite facies conditions of 750—760 °C and 1.1—1.5 GPa.
Orthopyroxene was formed in lower P-T conditions of ca.
0.7—1.0 GPa and 650—700 °C. Water-saturated conditions
and thermal overprint facilitated the breakdown of eclogites
during exhumation.
(3) Our study supports a two-stage tectonometamorphic
evolution of the Western Carpathian’s crystalline basement
during the Variscan orogeny. The new data underline the
close similarity with internal parts of the Variscan orogen in
Central Europe.
Acknowledgments: We thank P. O’Brien, S.W. Faryad and I.
Petrík for their helpful reviews. This work was supported by
the Slovak Research and Development Agency under the con-
tract APVV-51-046105, and Scientific Grant Agency VEGA,
Grant No. 2/6092/26 and 2/0031/09. Thorsten Nagel (Univer-
sity of Bonn) is thanked for his help with the THERIAK-
DOMINO program.
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