GEOLOGICA CARPATHICA, 50, 4, BRATISLAVA, AUGUST 1999
PHASE RELATIONS AND P-T PATH OF CORDIERITE-BEARING
MIGMATITES, WESTERN TATRA MOUNTAINS,
and MARIAN JANÁK
Department of Mineralogy and Petrology, Faculty of Science, Comenius University, Mlynská dolina, 842 15 Bratislava,
Slovak Republic; email@example.com
Geological Institute, Slovak Academy of Sciences, Dúbravská cesta 9, 842 26 Bratislava, Slovak Republic; firstname.lastname@example.org
(Manuscript received December 3, 1998; accepted in revised form March 17, 1999)
Abstract: Cordierite, as a product of Variscan regional metamorphism and exhumation, has been recognized in the
migmatitic metapelites of the Western Tatra Mountains, Western Carpathians. The following cordierite-producing reac-
tions have been deduced from reaction textures and phase equilibria in the system KFMASH: a) garnet decomposition
according to the reaction garnet + sillimanite + quartz + fluid = cordierite during decompression at a temperature of
~700 ºC down to a pressure of ~5 kbar; b) dehydration-melting of biotite by the reaction biotite + sillimanite + quartz =
cordierite + K-feldspar + melt due to further pressure drop to ~4 kbar at a constant, or increasing temperature to ~750 ºC;
c) melt crystallization in the leucosomes according to the reaction melt = cordierite + quartz + K-feldspar + biotite +
fluid, during cooling. Cordierite pinitization and its replacement by fine-grained phengitic white mica and pale green
Mg-rich biotite according to the reactions cordierite + sillimanite + K-feldspar + fluid = phengitic muscovite + quartz
and cordierite + K-feldspar + fluid = biotite + sillimanite + quartz took place during subsolius retrogression at a tempera-
ture of ~ 600 ºC and pressure of ~3 kbar. The origin of cordierite was also controlled by the local, more magnesian bulk
composition of cordierite-bearing metapelites. The presence of cordierite is indicative of a high-temperature/low-pres-
sure stage during the Variscan orogenic collapse in the pre-Alpine basement of the Western Carpathians.
Key words: Variscan orogen, Western Tatra Mountains, dehydration-melting, migmatites, cordierite.
Cordierite is a typical phase of the contact or regional low-
pressure metamorphic assemblages (Spear 1993; Bucher &
Frey 1994). In the Western Carpathians crystalline complexes,
cordierite was for a long time known only as a product of low-
pressure contact metamorphism, in assemblages with an-
dalusite. It was described in the contact zones of the Modra
granodiorite in the Malé Karpaty Mountains (Korikovsky et al.
1985) and Rochovce Granite in the Veporic Superunit (Vrána
1964; Korikovsky et al. 1986; Vozárová 1990). In recent years,
the presence of cordierite in gneisses and migmatites was re-
ported from the Ve¾ká Fatra Mountains (Janák & Kohút 1996)
and the Western Tatra Mountains (Ludhová 1996; Ludhová &
Janák 1996; Janák et al. 1999a,b). Here, cordierite occurs in
metapelitic migmatites, in assemblages with sillimanite and
garnet, similar to the rocks in the Ve¾ká Fatra Mountains. The
purpose of this study is to present details on the cordierite-
forming reactions and phase equilibria in the metapelitic
FMASH system, and to discuss a possible metamorphic P-T
path followed by cordierite-bearing rocks with respect to the
tectonometamorphic evolution of the Tatra Mountains (Janák
1994; Janák et al. 1996, 1999a,b).
The Tatra Mountains represent a typical core complex lo-
cated in the northernmost sector of the Tatric Superunit in the
Western Carpathians. They represent a key area for the study
of the eastern and south-eastern continuation of the Variscan
basement within the Alpine-Carpathian orogenic belt in Cen-
tral Europe (Krist et al. 1992).
The crystalline basement of the Tatra Mountains is com-
posed of pre-Mesozoic metamorphic rocks and granitoids,
overlain by Mesozoic and Cenozoic sedimentary cover se-
quences and nappes. Metamorphic rocks are more abundant in
the western partthe Western Tatra Mountains (Fig. 1),
whereas granites are more abundant in the eastern partthe
High Tatra Mountains. Within the basement, two superim-
posed tectonic unitslower and upper, differing in lithology
and metamorphic grade, have been distinguished (Kahan
1969; Janák 1994). The lower tectonic unit is composed of
staurolite, kyanite and fibrolite sillimanite-bearing mica-
schists. Two metamorphic zones (Fig. 1), staurolite-kyanite
and kyanite-sillimanite were distinguished (Janák et al. 1988).
The upper tectonic unit is lithologically variable. Near the
base of the unit, orthogneisses and banded amphibolites with
eclogite relics prevail, belonging to the kyanite metamorphic
zone (Janák 1994; Janák et al. 1996; 1999a,b). Higher levels are
composed of migmatites and gneisses, intruded by a sheet-like
granitoid pluton. They belong to the sillimanite metamorphic
zone with no high-pressure relics (Janák et al. 1988; Janák
1994; Janák et al. 1999a,b). Cordierite-bearing migmatites occur
only rarely. They have been found near Jeová (Fig. 1), in mig-
matites of diatexite type (Ludhová 1996; Ludhová & Janák
1996; Janák et al. 1999a,b), which may be regarded as roof pen-
dants of a granite pluton (e.g. Gorek 1956; Kahan 1969).
A polyphase, Variscan and Alpine deformation (Fig. 1) un-
der distinct P-T conditions was recognized in the Western
Tatra Mountains (Kahan 1969; Fritz et al. 1992; Janák 1994).
The Variscan D
deformation is defined by a mineral linea-
tion in metamorphites and is related to the top-to-the-south-
east thrusting of the upper unit onto the lower one. Subse-
deformation due to dextral or top-to-the-east shear
has been recognized in the migmatites of the sillimanite zone
as well as in the marginal zones of the granitoid pluton. The
deformation is attributed to the Variscan orogen-parallel
extension. Alpine D
deformation in brittle conditions is
manifested by top-to-the-north-west shear. The last major D
deformation is related to updoming and normal faulting in
north-south to north-west-south-east direction during Tertia-
The oldest tectonometamorphic events in the Tatra Moun-
tains seem to be Early Paleozoic, between 380 and 420 Ma
(Rb-Sr whole rock isochron of Burchart (1968); zircon single
grain data from orthogneisses of Poller et al. (1997)). Ac-
cording to Rb-Sr isochrons, the granitoid magmatism oc-
curred at 290310 Ma (Burchart 1968) or 340350 Ma
(Gawêda 1995). New zircon single-grain data from the West-
ern Tatra granites (Todt et al. 1998) yield ages of 340360
Ma. The cooling ages of micas from the granites and migma-
tites range from 330 to 300 Ma (
Ar method, Maluski
et al. 1993; Janák 1994), reflecting the late-Variscan exhu-
mation and the absence of a higher-temperature Alpine reju-
Petrography, reaction textures and mineral chemistry
At the contact of granitoid intrusion with metamorphic
rocks, a continuous change from inhomogeneous stromatitic
and diatexitic migmatites to massive granite can be observed.
The stromatitic migmatite comprises leucosomes of quartz-
plagioclase-K-feldspar, melanosomes of biotite and/or meso-
some. The mesosome mineral assemblage consists of garnet,
K-feldspar, sillimanite, biotite, cordierite, plagioclase, quartz
and muscovite. As minor minerals, zircon, monazite, xeno-
time, ilmenite, sphene, corundum and allanite were detected.
The chemical compositions of minerals were determined
using electrone microprobe JEOL 733 at Geological Survey
of the Slovak Republic in Bratislava. A point beam with op-
erating conditions of 10 nA and 15 kV was used. The data
were reduced by the ZAF method. Mineral abbreviations in
this paper are according to Kretz (1983).
Cordierite is often difficult to recognize, both in macro- and
microscale, because of its intensive pinitization. Only islands
of pure cordierite are preserved in the cores of the pinitized
grains (Fig. 2A,B); this fresh cordierite has a nearly constant
composition of Mg/Mg+Fe ~0.60 (Table 1). Three genetically
different types of cordierite have been distinguished:
1) in direct contact with garnet relics, without sillimanite
and/or biotite between them (Fig. 2C,D);
2) in direct contact with sillimanite and/or biotite. In this
case, i) sillimanite and/or biotite have resorbed garnet and
created the rims around large garnet grains (Fig. 2E); pin-
Fig. 1. Simplified geological map of the Western Tatra Mountains with the location of cordierite-bearing samples.
PHASE RELATIONS AND P-T PATH OF CORDIERITE-BEARING MIGMATITES 285
itized cordierite is not in direct contact with garnet, or ii) sil-
limanite and/or biotite are dominant phases in the flakes of
pinitized cordierite and garnet is preserved only as small rel-
ics (Fig. 2F), or iii) sillimanite and/or biotite are the only
phases (garnet is missing) in contact with pinitized cordierite
3) in leucocratic quartz + plagioclase + K-feldspar bearing
domains (Fig. 2I). The worm-like inclusions of undeformed
quartz are characteristic for this type of cordierite (Fig. 2I).
Garnet grains are of different sizes and they are strongly re-
sorbed by sillimanite and/or biotite (Fig. 2E,J), cordierite (Fig.
2C,D) or all of them. Most of the garnet is inclusion free, in-
clusions of quartz, sillimanite and biotite (fresh or chlorotized)
were only recognized in some garnet grains. The core compo-
sition values in all samples (Table 2) are 71.875.4 % almand-
ine, 5.314.3 % spessartine, 11.116.3 % pyrope and 1.92.7 %
grossular. Rim compositions (Table 2) are 70.974.3 % al-
mandine, 9.516.2 % spessartine, 10.113.9 % pyrope and
1.92.7 % grossular. The differences between core and rim
compositions are minimal. The highest core-rim composition-
al difference was observed in the spessartine end member,
which is ~3.7 % higher in the rim than in the core of the indi-
vidual garnet grain (Table 2, Grt2). Consequently, composi-
tional differences reflected by spessartine and almandine in-
crease, and pyrope as well as Fe/Fe+Mg ratio decrease from
the core to the rim, indicate a retrogression of the garnet.
Biotite is present as two distinct types. Dark brown biotite
together with sillimanite defines the metamorphic foliation
(Fig. 2K). The biotite Fe/Fe+Mg ratio is in the range 0.48
0.61 (Table 3). No compositional differences between biotite
in the matrix and biotite inclusions in garnet were observed.
Consequently, we consider biotite inclusions in garnet as
pseudoinclusions resorbing garnet interior. It is nearly im-
possible to recognize potentially true inclusions trapped
during garnet growth. Only minor biotite chloritization has
A different type of biotite is pale green biotite, intergrown
with muscovite and forming randomly oriented porphyroblasts
around pinitized cordierite (Fig. 2A,B). This type represents a
product of cordierite resorbtion (pinitization). As a conse-
quence, it is TiO
depleted, which causes its green colour and
more Mg-rich, with Fe/Fe+Mg ratio ~0.45 (Table 3).
White micas are present in several genetically different
types (Table 4).
Randomly oriented lath-shaped porphyroblasts corre-
sponding to muscovite (Ms1) with a moderate phengite com-
Table l: Chemical composition of cordierite.
Table 2: Chemical composition of garnet.
ZT 34/95 ZT 34/95 ZT 34/95 ZT 34/95 ZT 175 ZT 175 ZT 16/97 ZT 16/97
Recalculated on the basis of 12 oxygens
FeO+ = total Fe as FeO
ZT 34/95 ZT 34/95 ZT 34/95 ZT 175 ZT 175
Recalculated on the basis of 18 oxygens
FeO+ = total Fe as FeO
Table 3: Chemical composition of biotite.
ZT 34/95 ZT 34/95 ZT 34/95 ZT 175 ZT 175 ZT 175 ZT 34/95 ZT 34/95
Bt1 Bt1 rim/
Bt2mx Bt3 ingrt
Bt4mx ne ar Crd ne ar Crd
8.76 11.06 11.36
Recalculated on the basis of 22 oxygens
Sign "/" means touching of tw o phases, mx = matrix, ingrt = inclusion in garnet
FeO + = total Fe as FeO
PHASE RELATIONS AND P-T PATH OF CORDIERITE-BEARING MIGMATITES 287
Fig. 2. Photomicrographs of: A pinitized cordierite with islands of pure cordierite; marked section is shown in detail at B cordi-
erite and typical porphyroblasts of intergrowing muscovite + pale green biotite; C , D garnet relics within the pinitized cordierite;
E pinitized cordierite touching fibrolitic sillimanite resorbing garnet; F sillimanite + biotite surrounded by cordierite with pres-
ence of garnet relics; G , H sillimanite + worm-like quartz (H) within the pinitized cordierite without garnet presence; I pin-
itized cordierite with worm-like quartz within the leucosome domains; J sillimanite and biotite resorbing garnet; K prismatic sil-
limanite + dark brown biotite defining metamorphic foliation; L myrmekite.
ponent are distributed in the matrix. They are considered as a
product of K-feldspar destabilization during retrogression.
Muscovite (Ms2) intergrown with pale green biotite (Fig.
2A,B) is chemically identical with Ms1.
Fine-grained white mica (Ms3) as a product of cordierite
pinitization (Fig. 2A,B) has a phengite composition, with
up to 1.51.
Sillimanite is present both in the form of prismatic silli-
manite (Fig. 2J,K) and fibrolite (Fig. 2E). It is closely associ-
ated with dark brown biotite.
Plagioclase composition ranges between An
corresponds to oligoclase-andesine composition (Table 5). In in-
plagioclase grains, slight anorthite enrichment (
12 %) toward the rim has been detected, especially near the
contact with garnet. Plagioclase is only locally sericitized.
K-feldspar (Table 5), together with plagioclase and quartz,
is present in leucocratic domains. Locally, myrmekite has
been developed (Fig. 2L).
Quartz in the matrix is often recrystallized and segregated
The composition of garnet, cordierite, biotite and white
micas is shown on the AFM projection in Fig. 3.
Table 4: Chemical composition of white micas.
ZT34/95 ZT34/95 ZT34/95
ZT175 ZT16/97a ZT16/97b
Recalculated on the basis of 22 oxygens
FeO+ = total Fe as FeO
Table 5: Chemical composition of feldspars.
Biotite and sillimanite from the prograde stage of meta-
morphic evolution have not been recognized. Their possible
relics would be modified by fast diffusion at high tempera-
tures (Spear 1991).
Garnet resorbtion by biotite and sillimanite indicates the re-
versal of the melting reaction (1). The grossular component of
garnet was simultaneously consumed according to the reac-
sillimanite + quartz + garnet = plagioclase (2)
which is documented by the development of plagioclase
around the garnet and enrichment of plagioclase by anorthite
close to the plagioclasegarnet contact.
Although cordierite has not been observed in sharp contact
with garnet, pinitized cordierite around garnet relics (cordier-
ite type 1, Fig. 2C,D) suggests, that cordierite grew directly
from garnet by the reaction:
garnet + sillimanite + quartz + fluid = cordierite (3)
On the other hand, cordierite, which is in direct contact
with sillimanite and/or biotite (Fig. 2EH), most probably
grew due to the reaction:
biotite + sillimanite + quartz + plagioclase = cordierite +
K-feldspar + melt
In some cases, it is evident that biotite and sillimanite
which are the reactants of reaction (4), are the products of
garnet resorbtion by reversal of reaction (1). This corresponds
to the microtextural observations as described above and it is
sample ZT34/95 ZT34/95 ZT34/95 ZT16/97a ZT175 ZT175 ZT34/95 ZT34/95
100.79 100.11 101.28
Recalculated on the basis of 8 oxygens
leuc = in leucosome
FeO+ = total Fe as FeO
Fig. 3. AFM projection showing the composition of cordierite,
garnet, dark brown Fe-rich biotite Bt1, pale green Mg-rich biotite
Bt2, muscovite Ms1 and Ms2 and fine-grained phengite Ms3 from
cordierite bearing metapelites.
The observed microtextures indicate a sequence of meta-
morphic reactions. These are plotted in qualitative petroge-
netic grid in the KFMASH system with intermediate bulk Fe/
Fe+Mg composition (Fig. 4), according to Vielzeuf & Hollo-
way (1988). Suggested sequence of reactions and the P-T
path is demonstrated by arrows crossing equilibrium lines.
The presence of K-feldspar and garnet in the leucocratic
domains suggests that the early melt producing reaction was
dehydration melting of biotite reaction:
biotite + sillimanite + plagioclase + quartz = garnet + K-feldspar
Fig. 4. A part of the qualitative petrogenetic grid in the KFMASH
system for metapelites of intermediate bulk composition (Vielzeuf
& Holloway 1988) with metamorphic reactions including cordier-
ite. Arrows represent suggested sequence of metamorphic reac-
tions and P-T path.
PHASE RELATIONS AND P-T PATH OF CORDIERITE-BEARING MIGMATITES 289
shown in Fig. 2E. It is inferred that reactions (3) and (4) pro-
ceeded in the presence of melt.
Large cordierite porphyroblasts (Fig. 2I) in leucocratic do-
mains with the worm-like quartz inclusions probably grew
during crystallization of melt, according to the reaction:
melt = cordierite + biotite + K-feldspar + quartz + fluid (5)
Subsequent pinitization of cordierite indicates retrograde
reactions below solidus, i.e.
cordierite + K-feldspar + fluid = biotite + sillimanite + quartz (6)
cordierite + K-feldspar + sillimanite + fluid = phengite + quartz (7)
These reactions lead to the formation of pale green, Ti-de-
pleted, Mg-rich biotite, sillimanite and fine-grained phengit-
ic white mica (Fig. 2A,B,H).
The limited extent of cordierite occurrence in the Western
Tatra Mountains can be explained by specific bulk composi-
tion of the cordierite-bearing rocks. This is demonstrated in
Fig. 5, where garnet, biotite and cordierite core compositions
from cordierite-bearing migmatites, and garnet and biotite
core compositions from cordierite-free metapelites are plot-
ted in the AFM projection. It is obvious that both biotite and
garnet in cordierite-bearing samples have more magnesian
compositions. This demonstrates that magnesian bulk com-
position is more favorable for cordierite growth than Fe-rich-
er bulk compositions of the cordierite-free migmatites.
The influence of bulk composition on the cordierite growth
is discussed in Fig. 6. The reversal of reaction (1), garnet +
K-feldspar + melt = biotite + sillimanite + plagioclase +
Fig. 6. AFM diagram showing phase relations in a cordierite bearing samples and b cordierite free samples. Black symbols represent
cordierite-bearing migmatites, white symbols cordierite-free migmatites. Circles inside phase triangles represent the bulk compositions.
The arrows indicate compositional changes during the progress of reversal of reaction (1) garnet + K-feldspar + melt = biotite + silliman-
ite + plagioclase + quartz. Dashed tie-lines represent the phase relations in the initial stage of the reaction progress, solid tie-lines repre-
sent phase relations during the final stage of reaction progress.
Fig. 5. AFM plot of garnet (circles), biotite Bt2 (triangles) and cordi-
erite (squares) core compositions from cordierite-bearing (black sym-
bols) and cordierite free-migmatites (white symbols). Note the Mg-
richer composition of phases in cordierite-bearing rocks.
quartz, is a net transfer continuous reaction and during its
progress, both garnet and biotite becomes Fe-richer (Spear
1993). This causes the three-phase triangle sillimanite + bi-
otite + garnet to swing to Fe-richer compositions by pivoting
on its sillimanite apex. In a case of cordierite-bearing
metapelites, a rotating tie-line sillimanite + biotite in one
moment crossed the point representing bulk composition of
these rocks (Fig. 6a). Consequently, the assemblage garnet +
sillimanite + biotite was continuously replaced by the assem-
blage cordierite + sillimanite + biotite by reaction (4) biotite
+ sillimanite + quartz + plagioclase = cordierite + K-feldspar
+ melt. Cordierite-free metapelites also have a Fe-rich bulk
Table 6: Summary of results from P-T calculations by the TWQ2 method.
composition, therefore they fall within the garnet + silliman-
ite + biotite triangle and not within the cordierite + silliman-
ite + biotite one (Fig. 6b) during the whole progress of the re-
versal of reaction (1).
Pressure and temperature conditions were calculated by
the TWEEQU method (Berman 1991) with thermodynamic
data of Berman (1988, updated in March 1997). Non-ideal
activity models of garnet, biotite, cordierite (Berman & Ara-
novich 1996) and plagioclase (Fuhrman & Lindsley 1988)
were employed in the calculations. The results of P-T calcu-
lations are listed in Table 6 and the reconstructed P-T path is
shown in Fig. 8.
Large portions of leucosome together with garnet and K-
feldspar within indicate that dehydration melting curve of bi-
otite was crossed during the prograde stage of metamorphic
evolution. Widespread garnet resorbtion by biotite and silli-
manite indicates that this reaction also proceeded in the re-
verse sense. Because of the fast diffusion at high tempera-
ture, garnet and biotite compositions have been adjusted to
the actual pressure and temperature. Consequently, it is not
possible to reconstruct the real peak temperatures by garnet-
biotite exchange thermometry (Spear 1991). Therefore, the
garnet-biotite geothermometer and garnet-plagioclase-
quartz-sillimanite (GASP) geobarometer can yield only the
post-peak P-T conditions. In the calculations, we employed
the core compositions of garnet together with those of biotite
and plagioclase in the matrix. We assume that these might be
the most similar to the compositions during the peak condi-
tions, being least affected by retrogression. Such composi-
tions yield a temperature of 702+45 ºC and pressure of
5.3+1 kbar (Table 6).
The GASP reaction sillimanite + quartz + garnet = plagio-
clase used as the geobarometer is a net transfer reaction,
while the garnet-biotite geothermometer is the Fe-Mg ex-
change reaction. Moreover, diffusion rates in plagioclase are
very slow compared to diffusion rates in biotite. That means
that the closure temperature of GASP net-transfer reaction is
higher than that of the exchange garnet-biotite reaction (Flo-
rence & Spear 1995). Consequently, at the temperature of
700 ºC, the pressure was probably lower than the calculated
pressure of ~5 kbar (Fig. 8).
The calculated temperature of 700 ºC is ~50 ºC lower than
the temperature of the biotite dehydration melting reaction
according to Le Breton & Thompson (1988). This is consis-
tent with our assumption that only post-peak temperatures
can be reconstructed by thermobarometry. It is inferred that
true metamorphic peak conditions reached a temperature of
more than 750 ºC and a pressure of more than 6 kbar.
The position of equilibrium curve for the reaction (3) gar-
net + sillimanite + quartz + fluid = cordierite in the P-T space
was calculated using thermodynamic data of Berman (1988,
updated in March 1997). Continuous reaction and equilibri-
um curves for both Fe and Mg end-members are shown in
Fig. 8. Because of the flat slope of this reaction, decompres-
sion to less than 5 kbar is inferred to produce the first cordi-
Further cordierite formation together with a new portion of
melt is suggested by the reaction (4), i.e. biotite + sillimanite
+ quartz + plagioclase = cordierite + K-feldspar + melt. The
possible directions followed by the rock in crossing it (Figs.
4, 8), especially potential heating through heat advection
from the intrusion, are discussed below.
Reaction (6) cordierite + K-feldspar + fluid = biotite + sil-
limanite + quartz is, like reaction (4), a continuous reaction
and thus equilibrium curves for Fe and Mg end-members are
shown in Fig. 8. We assume that intensive pinitization of
cordierite occurred during cooling at pressures ~3 kbar. The
calculated temperature during retrogression, obtained from
garnet and cordierite rim compositions employed in garnet-
cordierite Fe-Mg exchange geothermometer, was 612+20 ºC
at an assumed pressure of 3 kbar (Table 6).
Effect of granite intrusion
A sheet-like granite intrusion, in contact with cordierite
bearing migmatites, could have been an extra heat source, in-
creasing the temperature during decompression and leading
P-T values calculated as intersections of G rt-B t geothermomether and G ASP geobaromether
Grt coresBt cores
X SpsX Prp
T values calculated with G rt-Crd geothermomether (pressure 3000bar)
X SpsX Prp
X GrsX FeCrd
PHASE RELATIONS AND P-T PATH OF CORDIERITE-BEARING MIGMATITES 291
country rocks whose initial temperature was 775650 ºC.
Since the intrusion was most probably synkinematic with
tectonic exhumation of the upper unit, and not static (Janák
1994; Janák et al. 1999a,b), the real temperature increase
should be lower than the calculated values. Finally, we de-
duce that granodiorite-tonalite intrusion could cause only
limited (~50 ºC) increase in temperature at the contact with
the surrounding rocks, as demonstrated by the dashed arrow
in the Fig. 8. Such an extent of heating is not excluded by the
petrology of these rocks. However, more extensive heating is
not probable, because it would lead to formation of a second
generation of garnet by the reaction biotite + cordierite +
quartz + fluid = garnet + melt (Fig. 4). No petrographic ob-
servations support such a case. All garnet is resorbed in the
same extent, having similar composition, and no composi-
tional reversal in individual garnet grains indicating a new
garnet forming reaction has been observed.
Advection of heat from synkinematic intrusion may, at
least close to the contact, maintain the migmatites sufficient-
ly hot during decompression, preventing rapid cooling and
crystallization of the melt.
Cordierite in the Western Tatra Mountains migmatites
originated during a retrograde part of a clockwise P-T path,
which most probably reached the metamorphic peak at more
than 750 ºC and 6 kbar (Janák et al. 1999a,b). However, only
post-peak conditions of ~700 ºC and 5.3 kbar have been re-
corded by thermobarometry.
to the cordierite-forming reaction (4). In order to test this pos-
sibility and to estimate the thermal influence of intrusion, the
program CONTACT (Spear & Peacock 1990) has been em-
ployed (Fig. 7). The Tatra granite pluton is composed predom-
inantly of granodiorite to tonalite (Kohút & Janák 1994) thus
the temperature of 850 ºC was taken as model magmatic tem-
perature of intrusion. Field observations suggest a sheet-like
shape of the Tatra granite pluton (Gorek 1956; Kahan 1969;
Kohút & Janák 1994), not exceeding the width of 2 kmthe
width assumed in our model. The temperature of the country
rocks during the intrusion was ~700 ºC, as deduced from ther-
mobarometric results (Table 6, Fig. 8). The development of ac-
tual temperature in time as a function of distance from the con-
tact (in model with initial country rocks temperature of 700 ºC
and time interval of 50,000 years), is shown in Fig. 7a. It is ob-
vious that in an aureole more than one kilometer wide, the
maximum temperature was reached after the first 50,000
years. The contact aureole, showing the maximum reached
temperature as a function of distance from intrusion, calcu-
lated for the initial country rocks temperature ranging from
650 ºC to 850 ºC (25 ºC step), is demonstrated in Fig. 7b.
The temperature increase at the contact is 40115 ºC, for the
Fig. 7. a Time evolution of temperature as a function of dis-
tance from contact with the intrusion; model for initial country
rocks temperature 700 ºC; time step 50,000 years; b Contact
aureoles for the initial country rocks temperatures from 650 ºC to
775 ºC with step 25 ºC.
Fig. 8. Quantitative petrogenetic grid and P-T path of the cordier-
ite-bearing migmatites from the Western Tatra Mts. Wet metapelite
solidus and dehydration curves of muscovite and biotite are ac-
cording to Le Breton & Thompson (1988), Thompson (1990) and
Stevens et al. (1997), reaction (4) according to Vielzeuf & Hollo-
way 1988 (the details are discussed in the text).
We propose that cordierite has originated by several reac-
tions. First cordierite could have originated by the reaction
garnet + sillimanite + quartz + fluid = cordierite, during a
post-peak decompression to a pressure lower than 5 kbar.
Further cordierite-producing reaction biotite + sillimanite +
quartz + plagioclase = cordierite + K-feldspar + melt, could
take place during continuous decompression, possibly ac-
companied by limited (~50
ºC) increase in temperature due
to the heat advection from synkinematic granodiorite-tonalite
intrusion. Finally, cordierite could have been produced dur-
ing the cooling and crystallization of melt in the migmatite
leucosome. Subsolidus retrogression led to widespread
cordierite pinitization. The origin of cordierite was also con-
trolled by the more magnesian bulk composition of cordier-
We suggest that the origin of cordierite in the Western
Tatra Mountains is an important indicator of a high-tempera-
ture/low-pressure metamorphic stage, related to orogenic
collapse of Variscan orogen in the Western Carpathians.
There are close similarities to the Ve¾ká Fatra Mountains
(Janák & Kohút 1996) and well documented parts of the
Variscan orogen in Europe, for example Brittany (Jones &
Brown 1990; Brown & Dallmayer 1996) or the Iberian Mas-
sif (Escuder Viruete et al. 1997).
Acknowledgements: This paper is a part of Ph.D. study of
L.L. and was financially supported by the Grant of the
Comenius University UK/3865/98 Variscan exhumation of
high-grade metamorphic rocks in the crystalline complex of
the Tatra Mountains. We are grateful to Pavol Siman (Geo-
logical Survey, Bratislava) for help with the microprobe
analyses, Milan Kohút (Geological Survey, Bratislava), Pa-
vel Pitoòák (Geol. Inst. Academy of Science, Banská Bystri-
ca), Branislav Lupták (Comenius University, Bratislava) and
Jana Kotková (Geol. Inst. Academy of Science, Praha) for
their help during the field work. We thank Michael Brown,
Ján Spiiak and Vladimír Bezák for their helpful and con-
structive review of this paper.
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