MULTISTAGE EVOLUTION OF THE SHEAR ZONE OF THE GIEWONT UNIT (POLAND) 337
GEOLOGICA CARPATHICA, 54, 5, BRATISLAVA, OCTOBER 2003
MULTISTAGE EVOLUTION OF THE SHEAR ZONE
AT THE BASE OF THE GIEWONT UNIT, TATRA MOUNTAINS
Laboratory of Tectonics and Geological Mapping, Faculty of Geology, Warsaw University, Al. ¯wirki i Wigury 93, 02-089 Warsaw,
(Manuscript received September 27, 2002; accepted in revised form March 11, 2003)
Abstract: The paper presents a mesostructural and petrotectonic analysis of rocks from the contact zone between the
Giewont and Czerwone Wierchy Units (High-Tatric nappes). Rocks occurring in the vicinity of Siad³a Turnia and Turnia
Olejarnia earlier referred to the brecciated Campilian (Late Scythian), are in reality mylonites (mainly dolomitic
mylonites), and their unique preservation was possible due to dilatant sites linked with faults developed in the basement
of the thrusting Giewont Unit. The mylonitization process as well as the thrusting of the nappe was not a one-stage, but
a multi-stage re-activated process. Its cyclicity was determined by the build up and drop of pore fluid pressure, leading
to changes of rheological behaviour of the deformation process. Fluids released to the shear zone together with the
brecciated rock formed a suspension with low friction values, which acted as a water pillow facilitating the movement
of the nappe mass. Deformation and mylonitization processes, the temperature of which reached 300 °C in some cases,
accompanied further stages of tectonic transport.
Key words: Tatra Mts, shear zone, dolomitic mylonites, fluid pressure, hydraulic fracturing, pressure solution.
The Tatra Mountains are composed of a crystalline core, over-
lain by a Mesozoic sedimentary cover and two nappes: High-
Tatric (Tatric Superunit) and Krína (Fig. 1A). They represent
the eastern prolongation of the Austroalpine tectonic system
into the Central Western Carpathians. In the Tatra Mts, Alpine
thrusting and folding took place after the Turonian and are
linked with the Mediterranean phase (Andrusov 1965). Anal-
ysis of the geometry of the Alpine thrust folding in the Tatra
Mts is difficult to conduct due to the high activity of pressure
solution processes (Bac-Moszaszwili et al. 1981; Jaroszewski
1982), and thus with the lack of sufficient data of slip struc-
tures for statistic analyses. Therefore, earlier reconstructions
of the thrust processes were based on slickensides from crys-
talline rocks of the so-called Goryczkowa island (Burchart
1963) and from the granitoid core of the High Tatra Mts (Ju-
rewicz 2000a). Earlier papers were also devoted to tempera-
tures and pressures during the Alpine thrust folding. Accord-
ing to Lefeld (1997), the pT condition of thrusting did not
exceed 200 °C and 1 kbar at the contact of granitoid core and
sedimentary cover boundary. At this time, the maximal tem-
peratures for the crystalline rocks could reach 300350 °C ac-
cording to Janák (1994), whereas Puti (1992) indicated that
they did not exceed 300 °C at depths of 68 km. Investiga-
tions based on liquid+gas fluid inclusions on slickenside sur-
faces in the upper parts of the granitoid core of the High Tatra
Mts indicate pressures of 1.41.7 kbar and temperatures not
exceeding ca. 250 °C (Koz³owski & Jurewicz 2001). For the
uppermost Krína Nappe, Grabowski et al. (1999) suggest
low temperature values (5080 °C), which indicate a cold re-
gime of folding.
This paper presents the conditions, under which the thrust
of Giewont Unit on the Czerwone Wierchy Unit developed
within the High-Tatric Nappe, on the basis of structures oc-
curring within dolomitic mylonites of the so-called Myopho-
ria beds of Late Scythian age in the vicinity of Siad³a Turnia
and Turnia Olejarnia (Figs. 1B, 2A,B).
Geological setting of the so-called
The investigation area is located on the western slopes of
the Giewont Mt, dropping towards the Ma³a £¹ka Valley (Fig.
2A). The thrust contact of dolomitic-marly breccia, consid-
ered by Kotañski (1956, 1959a) to be of Late Scythian age, re-
ferred to the Myophoria beds (Myophoria costata Zenk)
and included in the Giewont Unit, with the Urgonian lime-
stones of the Czerwone Wierchy Unit (Organy subunit op.
cit.) can be observed in several couloirs in the vicinity of Tur-
nia Olejarnia and Siad³a Turnia. In the upper part of the sec-
tion the breccias are overlain by black shales interbedded with
black bituminous limestones and yellow-weathering dolo-
mites. Platy dolomites considered by Kotañski (1959a) as the
so-called supra-Myophoria beds occur above. Older mem-
bers of the Giewont Unit can be observed under the Upper
Scythian breccias to the southeast of Siad³a Turnia (vicinity of
Kondratowa Pass). These include Upper Scythian cellular do-
lomites, Lower Scythian sandstones and crystalline rocks of
the Goryczkowa island. Deposits overlying these dolomites
represent the Anisian and begin with a regional-scale basal
conglomerate (cliff breccia), comprising poorly rounded peb-
bles of yellow-weathering dolomites and grey-green shales.
Interbedded complexes of blue-black limestones and yellow
dolomites, with total thicknesses of 70 to 160 m represent
younger Anisian members (Kotañski 1956, 1959a). The up-
permost, up to 200-m thick, part of the sequence comprises
carbonates of Doggerian, Malmian and Neocomian age and
Albian marls. The total thickness of beds in the Giewont Unit
reaches ca. 500 m and is smaller than in other structural ele-
ments of the High-Tatric Unit.
The Giewont Unit probably represents the remains of an ini-
tially larger structure (Bac-Moszaszwili et al. 1984), with beds
displaying steep northern dips (Fig. 1C). After reversal to po-
sitions prior to the young Tertiary uplift of the Tatra Mts (Ju-
rewicz 2000b), they most commonly attain 150/45N (Fig.
1D), thus pointing to a more north-western direction of tecton-
ic transport in relation to the northern directions in other units
of the High-Tatric Nappe (Bac-Moszaszwili et al. 1984; Ju-
This paper will focus on the so-called brecciated Campil-
ian, representing the Late Scythian, in the vicinity of Siad³a
Turnia (Fig. 2B,C) and Turnia Olejarnia. When describing
similar breccias from other sections in the Giewont Unit, Ko-
tañski (1956, 1959a) noted that they comprise poorly rounded,
dark grey, yellow-weathering dolomite fragments. The bind-
ing material is composed of numerous very fine dolomite frag-
ments, in some cases with visible lamination. The breccias are
of marine origin and were developed as intraformational brec-
cias during intense storms when the wave base reached the
seabed. They are cut by epigenetic calcite veins and contain
ferruginous mineralization (pyrite, limonite). It is worth not-
ing that besides sedimentary breccias, tectonic breccias also
occur: the rock is tectonically fractured and the fractures are
filled with calcite. There is a lack of transport between the
fragments. In relation to their structure, these kinds of breccias
represent crackle breccia (Kotañski 1954).
According to Jaroszewski (1982), the contact of the Krína
Nappe with the High-Tatric Unit, which is generally the con-
tact of Middle Triassic dolomites thrust on the Malmian-Neo-
comian or Urgonian limestones, is a macrostylolite developed
in the course of pressure solution. In other places, the dolo-
mites of the Krína Nappe penetrating by means of pressure
solution mechanism into the High-Tatric limestones bear trac-
es of deformation in the course of cataclastic flow. The de-
scribed below contact of the Upper Scythian dolomites of the
Giewont Unit with the Urgonian limestones of the the Czer-
wone Wierchy Unit is an example (Jaroszewski 1982).
Paulo (1997) suggested that the pyritic facies of the ferrugi-
nous Upper Scythian deposits in the High-Tatric and Krína
Nappes represent pre-salinary sediments. Brownish and black
limonites with clusterous or clotty-colomorphic texture were
described in them. X-ray diffraction analyses (Paulo 1997) in-
dicate the presence of goethite, hydrogoethite and lepidocro-
site. Zawidzka (1967), characterizing the Late Scythian of the
Krína series from a nearby site located in the western part of
the Ma³a £¹ka Valley (Sywarowa Pass), noted the presence of
crystalline sulphur, forming 1-cm in diameter concentrations,
developed in the course of sulphate reduction (anhydrite or
gypsum) by organic matter.
Plaienka & Soták (1996) described carbonate tectonic
breccias from the Central Western Carpathians formed
through fracturing and crushing with a dominant role of perco-
lating solutions under intricate fluid regimes by multiple pres-
sure solution, chemical alternations, leaching, weathering with
concentration of Fe-hydroxides and karstification; these rocks
in German terminology are referred to as Rauhwacke or Zel-
lendolomite. According to Plaienka & Soták (1996), Rau-
hwacke typically comprise carbonates (dolomites, rarer lime-
stones) and accompanying sulphate (gypsum and anhydrite),
in some cases also salt. The radically different mechanical be-
haviour of these rocks causes that dolomites undergo brittle
disintegration, as well as sulphate ductile flow, starting al-
ready at temperatures of 100 °C (Schmid 1982). Transforma-
tion of gypsum into anhydrite and the reverse process induce
stress responsible for brecciation of the carbonate rocks. The
developed intraformational breccias are referred to as dilation
breccias. According to Plaienka & Soták (1996), such brec-
cias occur in many units of the Western Carpathians in red
shales of Permian-Scythian and Norian (Keuper) age. From
the area of the Northern Calcareous Alps, Spötl & Hasenhüttl
(1998) describe evaporate rocks from a tectonic mélange (Ha-
selgebirge), the distribution of which is restricted largely to
the topmost thrust unit (Juvavicum). According to Warren
(1999), ... in older studies, the Rauhwacke itself was consid-
ered to have facilitated décollement during Alpine tectonics,
but now it is known that the evaporite-lubricated protoliths of
the Rauhwacke acted as detachment horizons during thrusting
The rocks described below, the unique character of which is
a result of tectonic processes, are a source of information on
processes linked with the Alpine nappe thrusts. The described
sites from the vicinity of Siad³a Turnia and Turnia Olejarnia
are not exceptional in the Tatra region, where the Myophoria
beds act as a lubricant for the thrust plane; on the contrary,
according to Kotañski (1959b) this is a regional phenomenon
and the Myophoria beds commonly occur in the lowermost
part of the thrust of the upper limb of the Czerwone Wierchy
fold. When describing the contact of the High-Tatric flake
with the Krína Nappe, Zawidzka (1967) also characterized
the Upper Scythian breccias of the Krína Nappe as strongly
tectonically deformed with a texture resembling that of augen-
Meso- and microstructural characteristics
of the shear zone
The tectonic contact between the Giewont and Czerwone
Wierchy Units in the vicinity of Siad³a Turnia and Turnia Ole-
jarnia is an uneven, several tens of centimetres to 23 m thick
zone with textures parallel to its local orientation, numerous
slip, mineralization and recrystallization planes. The contact
of both units is not a plane and is not clearly delimited from
the surrounding rocks; its morphology is rather complex, and
it is further deformed by small faults. The zone lacks slicken-
sides that would enable geometric analysis of the thrust and
tectonic transport directions.
Rocks occurring at the base of the Giewont Unit are vari-
ously tectonically deformed. Typically, they are strongly fold-
ed, and the folds have features of disharmonic folds developed
in ductile deformation conditions (Figs. 2C, 3A,B). In most
cases the rocks are mylonites where the mylonites are de-
MULTISTAGE EVOLUTION OF THE SHEAR ZONE OF THE GIEWONT UNIT (POLAND) 339
Fig. 1. A Study area in relation to the main geological tectonic structures of the Tatra Mts (after Bac-Moszaszwili et al. 1979). B
Schematic geological cross-section through the Giewont Unit (after Bac-Moszaszwili et al. 1979). C, D attitude of bedding in the
Giewont Unit (after SteroNet software; pole to planes): C present day position, D after vertical rotation (40° southwards around the
90/0 axis) to the pre-Late Tertiary position.
Fig. 2. A View of the SW slope of Giewont Mt. Photograph and its geological interpretation after G¹sienica-Szostak (1973). B tectonic
contact of the Giewont and Czerwone Wierchy Units in the vicinity of Siad³a Turnia. C fold deformation at the base of Giewont Unit in
the vicinity of Siad³a Turnia (scale 10 groszy coin).
fined as foliated and lineated rocks showing evidence for
strong and ductile deformation and are understood as a strictly
structural term referring only to the fabric of the rock (White
et al. 1980; Passchier & Trouw 1998). Locally, that is in the
vicinity of Turnia Olejarnia (Figs. 3E, 5D), although macro-
scopically the rock resembles strongly folded schists, the de-
gree of mylonitization is high enough to observe the preva-
lence of the matrix in relation to the porphyroclasts; when the
matrix exceeds 90 % of the rock (Sibson 1977) and the grain
size of the recrystallized matrix is typically smaller than 10
m (Hippert & Hong 1998), they can be referred to as ul-
Despite the different degree of tectonic deformation
(Figs. 4, 4DH, 5), the structural features of the described
rocks allow to distinguish them as mylonites; in most cases
they are represented by dolomitic mylonites. They comprise
clasts of dolomite (black, red and grey-yellow) of various siz-
es, shapes and degree of rounding (Figs. 3AD, 4). The brec-
cias bear traces of various stages of textural transformation,
linked with tectonic processes in the thrust zone. Most clasts
MULTISTAGE EVOLUTION OF THE SHEAR ZONE OF THE GIEWONT UNIT (POLAND) 341
Fig. 3. Different degrees of deformation in dolomitic rocks from the shear zone near Siad³a Turnia (AC) and Turnia Olejarnia (D, E); polished
surfaces. A, B microfolds in foliated mylonite and dolomite veins parallel to foliation; C strongly folded mylonite with well-developed fo-
liation and single rounded porphyroclasts; D microfolds within ultramylonite; E ultramylonite with numerous extensional fracturing (do-
lomite veins; axial part of wider veins is filled with calcite). This is evidence that the dolomite mineralization is earlier than the calcite one.
dv dolomite vein, cv calcite vein, bp boudinaged porphyroclast, rp rotated porphyroclast; mantled porphyroclast:
type object, co complex object; dashed line contour of microfolds.
do not exceed 23 cm in diameter; they are typically elongat-
ed and stretched, with the longer axis parallel to the local
elongation of structures. Lamination is in some cases quite
distinct in the clasts, which to a certain degree is an inherit-
ance of sedimentary structures, but also of dynamic recrystal-
lization (Figs. 4E, 5G). The elongation degree, resulting from
simple shear extension taking place within the thrust zone, is
sometimes so large that the structure resembles that described
by Davis & Reynolds (1996) as stretched-pebble conglomer-
ate. The elongated clasts are frequently boudinaged or form
augen-structures in a finer-grained, foliated matrix (Fig. 3B
D). Dolomite porphyroclasts are commonly flanked by fine-
grained dolomite aggregates forming mantled porphyroclasts
-type objects, Figs. 3B,D, 4DF, 5D, terminology after
Passchier & Trouw 1998). In the Turnia Olejarnia region,
flanking aggregates around dolomite porphyroclasts consist
minerals, deforming into wings and forming
objects (Fig. 5D). In many cases round-shaped porphyroclasts
bearing features pointing to rotation, and forming complex
objects (Fig. 3B,C), can be observed macroscopically.
The mylonite matrix is composed of grain fragments with a
wide range of grain size, in which the smallest ones have di-
ameters of several to several tens of microns. The flat-parallel
textural arrangement can be observed in the matrix (Fig.
4E,F). Spaces between the laminae are typically filled by sev-
eral millimetre thick veins of dolomite (Figs. 3AD, 5F). The
mylonitized rocks also bear signs of later strong tectonic de-
formation. Folds resembling disharmonic folds developed in
flow conditions (Figs. 2C, 3AD) can be observed. The folds
are typically of small sizes, and their amplitudes generally do
not exceed 10 cm. The flow shows a local arrangement result-
ing from the geometry of the contact with the underlying Cze-
rwone Wierchy Unit. In direct vicinity of the thrust surface
the small folds are isoclinal. In some cases folds with ampli-
tudes up to several tens of centimetres can be observed. The
folding is not only distinguishable in the field but also in mi-
croscopic scale, and includes both elongated clasts and folia-
tion in mylonites, as well as veins of dolomite within the lam-
inae (Fig. 4G).
Later deformation of the mylonitized rocks includes not
only folding but also extensional fractures filled with coarse-
crystalline dolomite, rarer with calcite. Such mineralization in
some cases uses the S-C fabric (Fig. 5E) and in others frac-
tures developed in course of hydraulic fracturing (Fig. 3E).
Although the described rocks commonly contain structures,
which can be used to determine the sense of shear (e.g. Figs.
3B, 4D), these are insufficient for interpretations. Their occur-
rence only proves the multistage character of the movement
and the ductile type of deformation responsible for their cre-
ation. Similarly, due to the non-planar character of the thrust
surface linked with the presence of faults in its lowermost
part, common participation of pressure solution processes and
most probably its secondary folding deforming the geometry
of the thrust zone, the orientation of the directional textures
and structures is local in character, has a large variability and
thus cannot be used in reconstructions of the tectonic trans-
port direction. Analyses of stress fields responsible for the
nappe thrusts and of directions of tectonic transport were car-
ried out on the basis of tectonic striae orientations on the sur-
faces of Alpine-age slickensides in the granitoid core of the
Tatra Mts (Jurewicz 2000a).
At this stage of investigations it is difficult to give a definite
statement whether the rocks occurring at the tectonic contact
mylonites or ultramylonites initially represented sedi-
mentary breccia (such as those commonly occurring in the
Upper Scythian) or their present character is a result of tecton-
ic processes. Although the degree of structural transformation
is very high, it can be presumed that it was the sedimentary
breccias that were the weakest lithological member, thus be-
ing most the susceptible to deformation. The latter feature was
favoured by the presence of fractures and pores, which could
develop both during the dolomitization process, as well as
during the formation of sedimentary breccia. If the original
chemical composition and rheological properties of the rock,
which acted as a lubricant during the thrusting of the particu-
lar tectonic units, were known, the physical-chemical proper-
ties during deformation could be recognized more precisely.
Unfortunately, the large participation of pressure solution pro-
cesses caused the deterioration of such unstable minerals as
halite or gypsum, the mechanical conditions of which could
significantly influence the thrusting process. Water from frac-
tures and pores, as well as that released, for example, during
dehydration of gypsum, could influence the stress values.
Knowledge of the initial lithology would also help in deter-
mining the chemistry of the fluids and evaluation of their in-
fluence on the course and magnitude of solution processes.
For instance, in the vicinity of the Glarus thrust in the Alps of
eastern Switzerland, a 36% volume decrease of flysch sand-
stones was noted in the process of Helvetic nappes formation
(Ring et al. 2001), where the open-system behaviour was
probably driven by dissolution and bulk removal of the more
soluble components of the rock due to flow of a solvent fluid
phase on a regional scale.
The character of the clast deformation (elongated and fold-
ed Fig. 3B,C), lamination of fine material and its folding
(Fig. 3AD), and the means of recrystallization (dynamically
recrystallized grains Fig. 5G) point to ductile rheological
behaviour. Lamination in the fragmented material may be
linked with the fact that the freely soluble components (calci-
um carbonate, gypsum and halite) were removed, leaving
Fig. 4. Different degree of brecciation and mylonitization of rocks
from the shear zone in thin sections; non-polarized light. A, B
brittle fracturing in brecciated dolomites, sharp-edged grains dis-
placed by microfaults; spaces between clasts filled with crystals of
dolomite; C vein of mylonite within tectonic breccia, in which
matrix is composed of dynamically deformed quartz; D crystal-
plastic deformation with stylolites parallel to foliation in my-
lonitized dolomites (upper part) and bedding parallel stylolites in
the dolomite clast (on the right); mantled porphyroclast with wings
of crystalline dolomite (in centre); E, F well developed stretch-
ing lineation, with different degree of grain size reduction, stylolites
parallel to foliation (both) and within clasts (centre of F); upper part
of F elongated and boudinaged clast; centre of F mantled por-
phyroclast with wings of crystalline dolomite; G microfolds of
mylonitic textures; H well developed stylolites occurring sub-
parallel to foliation.
MULTISTAGE EVOLUTION OF THE SHEAR ZONE OF THE GIEWONT UNIT (POLAND) 343
MULTISTAGE EVOLUTION OF THE SHEAR ZONE OF THE GIEWONT UNIT (POLAND) 345
fragments of dolomites as the residuum. Rounded porphyro-
clasts bear traces of selective pressure solution (Figs. 4D,F,
5C) in domains where the stress was relatively high (Knipe
1989). Overgrowth of silicate, dolomite and calcite grains in
strain shadows can be observed in the case of dolomite por-
phyroclasts (Figs. 3AC, 4DE, 5CD).
The next evidence of pressure solution is the presence of
stylolites on the dolomite clast margins (Fig. 4D,F), between
laminae in the mylonites (Figs. 4E,F, 5G), as well as cutting
carbonate veins and crystals (Figs. 4H, 5B). Furthermore, pro-
cesses of intracrystalline deformation (Fig. 5A,B), grain size
reduction and preferred grain shape orientation (Fig. 5E,F)
take place (cf. De Roo & Weber 1992).
Petrology and mineralogy
Analysis of thin sections in polarized light and microprobe
determined the mineral content of the investigated rocks (both
porphyroclasts and matrix), mineral veins, relations between
dolomite and calcite, as well as the means of recrystallization
of material during deformation. The petrological characteris-
tics were based on the analysis of 24 thin sections from sam-
ples collected from beneath Siad³a Turnia and Turnia Olejar-
nia. Cathodoluminescence analyses were also conducted. The
investigated rocks, however, although containing numerous
carbonate veins with large euhedral crystals, are hardly lumi-
nescent at all. This indicates the lack of distinct zones of crys-
tal growth, which may be linked with the very fast growth of
crystals at a relatively stable solution composition, or with
their later homogenization. The latter possibility due to the
multistage development of mylonites seems to be highly
Microscopic investigations (Fig. 6) were carried out on
three thin sections from Siad³a Turnia from samples lying
within 1 m from the contact with the Urgonian limestones
(Kotañski 1956) of the Czerwone Wierchy Unit, and on a
sample taken from the direct vicinity of the thrust surface in
region of Turnia Olejarnia. The earlier optical identifications
of the minerals were confirmed by investigations in SEM con-
nected to EDS detector. Microprobe images allowed recogni-
tion of the relations between the matrix components and dis-
Fig. 5. Thin sections in crossed polarizers. A, B dolomite crystals
with well developed twins and their deformation (irregular shape of
twin boundaries); C mantled porphyroclast of dolomite (
object with tails of recrystallized dolomite); D rotated porphyro-
clast of dolomite with tails of silica (
-type object) in ultramylonites
from Turnia Olejarnia; E fragment of S-C structures in ultramylo-
nites from Turnia Olejarnia; quartz in matrix is dynamically de-
formed; extensional fractures filled with dolomite crystals; F thin
dolomite vein parallel to foliation within fine-grained dolomite mylo-
nites fragment of microfold; G in central part dolomite por-
phyroclast fragment with traces of mimetic recrystallization, parallel
to primary lamination, in lower part porphyroclast with fractures,
along which recrystallization took place; bedding-parallel stylolite
also visible; black veins-mylonitized matrix with Fe-hydroxides;
H black veins-mylonitized matrix with Fe-hydroxides (as in G).
tinguishing calcite and dolomite. Several chemical analyses of
the composition of feldspars, of which most are potassium
feldspars, were also carried out.
Because the presence of sulphur was observed in the inves-
tigated rocks (Zawidzka 1967), which, according to Paulo
(1997) can be considered pre-salinary, investigations in mi-
croimages were focused on the presence of minerals typical
for evaporatic rocks (gypsum, halite). The negative result is
not, however, an evidence of their initial absence in the sedi-
ment, as pressure solution processes could lead to their com-
The bulk of the investigated rocks are porphyroclasts of do-
lomites (up to several centimetres in diameter) and matrix
also mainly dolomitic filling the space between the frag-
ments. The dolomite porphyroclasts are typically strongly
fractured, and recrystallization can be observed along these
fractures, which were not filled by later mineralization. The
dolomite crystals are elongated and distributed semi-perpen-
dicular to the fractures, which were migration paths for fluids
favouring recrystallization in the direct vicinity of fractures.
Similar recrystallization took place along sedimentary lami-
nae, which could also become paths for fluid migration and
cause the mimetic growth of dolomite crystals in the direction
of foliation (Fig. 5G). The matrix filling spaces between the
porphyroclasts, besides dolomites, the finest fragments of
which are below 10
a) aggregates of euhedral dolomite grains with sizes of sev-
eral tens of
m (Figs. 6B, 7A) and easily visible twinnings
(Fig. 5A); in some cases rombohedrons are rimmed with cal-
cite, which may be an artefact of pressure solution;
b) subhedral crystals of calcite with sizes typically exceed-
m, in some cases overgrowing euhedral dolomite
c) crystals of K-feldspars, up to several tens of
m in diam-
eter, in some cases with inclusions of romboedric dolomite
(Fig. 6A,E) or anhedral quartz crystals (Fig. 6F);
d) sporadic euhedral crystals of plagioclase not exceeding
e) anhedral quartz crystals (occurring in aggregates), with
sizes from several to several tens of
m, and hypereuhedral
quartz crystals within a feldspar-silicate layers mass (Fig. 6D
F); some crystals reveal undulose extinction indicating crys-
f) microcrystalline concentrations of SiO
filling spaces be-
tween the quartz grains (Fig. 5E) and forming tails in
objects (Fig. 5D);
g) aggregates of feldspar-silicate layers comprising grains
up to several
m in diameter (Fig. 6);
h) euhedral pyrite and iron oxides crystals up to several tens
m (Fig. 6F);
i) single sheets of chlorites not exceeding 10
m (Fig. 6C);
j) titanium oxides (<10
k) single euhedral apatite crystals (<10
The matrix is characterized by flat-parallel textures, devel-
oped in the course of cataclastic deformation, and resulting
a) distribution of flattened mineral grains (mechanical rota-
tion), as well as their later flattening and elongation;
b) preferential grain growth of some crystals, for example,
along foliation surfaces;
c) dynamic recrystallization linked with simple shear dur-
ing thrust napping;
d) stress-induced solution transfer preferential dissolu-
tion of poorly rounded clasts. In effect, stylolites are formed
on the margins of clasts, along relict bedding within the clasts
and parallel to foliation in mylonites (Fig. 5D,E,F,H).
Additionally, the rock also contains numerous veins of do-
lomites parallel to foliation, along small folds. The means of
filling the space between laminae by large hypautomorhic
crystals is evidence of growth in extensional conditions and a
Fig. 6. BSE images. Kfs potassium feldspar, Qtz quartz, Dol dolomite, Cal calcite, Py pyrite, Chl chlorite, fs+cm feld-
spar and clay minerals.
MULTISTAGE EVOLUTION OF THE SHEAR ZONE OF THE GIEWONT UNIT (POLAND) 347
envelope (Hancock 1985). Thus a process leading to the de-
velopment of a fault, which takes place due to hydraulic frac-
turing is responsible for the formation of tectonic breccia (De
Roo & Weber 1992). It is accompanied by the release of flu-
ids from the pores, thus the rock mass filling the space be-
tween the fault walls is a multiphase mixture (Treagus & Tre-
agus 2002). It can be assumed that hydraulic fracturing
spreads out gradually into the fault walls leading to their brec-
The displacement accompanying brecciation causes stress
release and the pore system within the shear zone becomes
open. In this stage the thrust zone is a flow path for fluids. The
direction of fluid flow through a brecciated rock mass is gov-
erned by the maximum hydraulic gradient (Sibson 1996). The
shear zone was a transport passageway for the rock fragments
and matrix as well as for fluids (Branquet et al. 1999). In the
thrust zone mechanical crushing and gradual mylonitization
take place during tectonic transport. The relatively larger con-
tent of dolomite in relation to calcite within the matrix and the
porphyroclasts may be a result of the fact that dolomite is less
susceptible to dissolution (Kennedy & Logan 1997). Strain
within the shear zone involves stretching lineations, lattice
preferred orientation of grains and foliation of the matrix
(Fig. 7C; cf. Figs. 4E,F,G, 5D). According to Mandal et al.
(2001) the flattening of structures may also be a result of the
increasing viscosity contrast between the shear zone and the
These processes lead to pressure solution, dynamic recrys-
tallization and grain-size reduction. According to Etheridge &
Wilkie (1979) grain-size reduction is expected to progress un-
til recrystallized grains become stable at a size that is in equi-
librium with the flow stress.
Further processes of tectonic displacement along the shear
zone are easier because of the presence in the nappe foot flu-
idized rocks of a tectonic lubricant with low viscosity, which
is a suspension comprising salt solutions, dissolved gases,
rock fragments and matrix. Wohletz & Sheridan (1979) de-
fined fluidization as a process in which the frictional force
between the fluid and the particles counterbalances the weight
of the particles and the whole mass behaves as a fluid. Gases
can be released from the solution as a result of a temporary
drop of pressure or build up of temperature. According to
McCallum (1985), gas streaming is considered to be an ad-
vanced stage of fluidization. Movements of fluid and gases
displaced on the tectonic surface along a hydraulic gradient
(Sibson 1996) favour the tectonic transport of clasts. During
tectonic transport friction drops (the angle of internal friction
decreases to values close to zero). The composite failure enve-
lope on the Coulomb-Mohr diagram is flat and the Mohr cir-
cle attains contact with the composite failure envelope even at
low absolute values of
(Fig. 8C). Tectonic transport could
take place at even inconsiderable differential stress values
), irrespective of the high or low value of
. This phe-
nomenon is similar to the one taking place at the foot of an ad-
vancing glacier a water film in the foot of the glacier al-
lows horizontal transport for long distances (Piotrowski &
relatively small degree of later deformation (Fig. 5F), which
only locally lead to grain boundary migration and twinning
deformation (Fig. 5A,B). Besides veins of crystalline dolo-
mite, veins of calcite with large interlobate crystals, uncon-
formably cutting the fold structures, are also present. The cal-
cite crystals are commonly twinned, often with traces of
deformation. In some cases the twins attain serrated bound-
aries due to grain boundary migration.
The described rocks, although spatially not forming regular
zones with a composition typical for mylonites, can be gener-
ally classified as such, both according to microtectonic defini-
tions (e.g. Passchier & Trouw 1998), the main criterion of
which is the degree and character of deformation, and accord-
ing to petrographic definitions requiring not only the defor-
mation, but also the dynamic recrystallization of grains, or the
presence of neomorphic crystals (Yardley 1991; Lin 2001), to
which in this case feldspars, recrystallized dolomite, layer sili-
cates, quartz and other minerals of the silicate group can be in-
Stages of thrust-napping and microstructure
evolution within the shear zone
at the base of the Giewont Unit
The stress values increase in conditions of horizontal com-
pression preceding nappe development of the Tatra Mts (e.g.
Andrusov 1965; Kotañski 1961; Plaienka 1991), and thus the
thrust of the Giewont Unit on the Czerwone Wierchy Unit. In
the first stage (Fig. 7A) horizontal compression causes the for-
mation of a symmetrical fold. Ductile deformation relaxes the
Further compression induces the development of simple
shear. The fold becomes more asymmetrical, for example, due
to summing up of the intrastratal slip. When beds become too
steep in relation to the directions of tectonic transport to allow
stress release through intrastratal slip, the fault plane can be
formed by breaking the cohesion of the rocks (Fig. 7B). Ac-
cording to the model of Mitra (2002), forelimb shear thrusts
form, due to rotation and layer-parallel extension of the steep
forelimbs of folds, in the late stages of folding.
At the same time, with the increase of stress values, the pore
fluid pressure builds up as well. In a fluid-saturated rock mass
the build up of fluid pressure (P
) causes the reduction of all
normal stresses (
) to give effective stresses (Fig. 8B), where
(Hubber & Rubey 1959; Sibson 1996).
In a deformed rock mass the presence of pores may be
linked with the leaching of freely soluble components, such as
gypsum (thus the term cellular dolomites e.g. Kasiñski
1981; Passendorfer 1983) and with the breccia character of
the deposits (Kotañski 1954). Fluids infilling the pores are of
a meteoric type or originate from processes such as the dehy-
dratation of gypsum. Assuming that differential stress is
small, the Mohr circle passes to the left, to the tensile failure
Kraus 1997). In the case of nappes, although the factor re-
sponsible for transport is different than in the case of glaciers,
the mechanism favouring tectonic transport is similar; instead
of a water pillow (cf. Plaienka & Soták 1996) there is a sus-
pension composed of fluids, rock fragments and matrix. Small
values of differential stress necessary for displacement may be
responsible for the non straight-line character of the nappe
tectonic movement, which is reflected in the oblique direc-
tions of tectonic transport of the Giewont Unit (from the SSE
Fig. 1D) in relation to the Czerwone Wierchy Unit (from
the SSW see Bac-Moszaszwili et al. 1984).
At the end of this stage pressure solution processes induce
the formation of stylolites, which develop parallel to bedding
within the clasts (Fig. 5G), at clast boundaries (Fig. 5D,F) and
along textural surfaces (Fig. 5E,F). Stylolites in clasts may
partially be a result of diagenesis (Smith 2000); they, howev-
er, generally originate during the tectonic stage (Newman &
A re-increase of
takes place at a simultaneous drop of
(Fig. 7D), caused among others by the migration and disap-
pearance of fluids, and the anastomosing character of the
shear zone that consisted of compressional and dilational do-
mains, for the presence of which were probably responsible
faults developed in the foot of the thrust nappe (see: De Roo
& Weber 1992). In effect, extension leading to the opening of
space between laminae and formation of mineral veins is de-
veloped in the shear stress field (Figs. 3, 5F). The veins are
filled with freely overgrowing dolomite crystals (calcite is
usually subsequent and oblique in relation to earlier struc-
tures), which do not show traces of growth simultaneous with
folding, as is the case, with for example turbiditic sandstone
shale sequences from Australia, from where Jessell et al.
(1993) described bedding-parallel laminated veins. A similar
case is described by Kennedy & Logan (1997), who noted
bedding-parallel calcite veins from mylonites of the McCon-
nell thrust (Alberta), which are relatively undeformed. The
process takes place during pure tectonic activity, in which the
shear zone is gradually cemented and immobilized, thus caus-
ing the termination of the nappe movement. This leads to the
closure of pores (although the rock reveals lower porosity
than during the phase preceding deformation), and with the
build up of stress to the re-increase of fluid pressure.
Temporary release caused by the formation of dislocations
in the basement, removal of fluids and mineralization leads to
the lithification of the deformation zone and its immobiliza-
tion. At the beginning, deformation appearing during further
stress build up is ductile in character. Meso- and micro folds
develop (Figs. 3BD, 4G). In consequence, pore fluid pres-
sure builds up thus the deformation process becomes brittle.
In the following stage the drop of stresses takes place, the
Mohr circle is closer to the composite failure envelope and the
rock cohesion is ruptured by brittle failure (Fig. 7E). Destruc-
tion due to hydraulic fracturing occurs both in the more po-
rous rocks surrounding the mylonitic zone as well as in the
mylonites themselves (Figs. 3E, 5E). Thus new parts of the
rock adjacent to the fault walls undergo brecciation, and in a
further stage mylonitization. The process, along with pres-
sure solution, which in the rock mass at the grain scale in the
gauge is much faster than the pressure solution, for example,
along stylolites and associated precipitation in veins (Renard
et al. 2000), is responsible for considerable mass loss from the
direct vicinity of the thrust. The large role of mass loss was al-
ready noticed by Vernon (1998), Ring et al. (2001) and other
authors. In the case of the Tatra nappes the selective mass loss
may be responsible for their geometric divergence from clas-
sic duplexes (Boyer & Elliot 1982).
The newly developed shear zone becomes the migration path
for fluids moving along the hydraulic gradient. In general, this
stage is characterized by similar conditions to stage C (see Figs.
7C and 7F), that is fluids causing friction drop are released into
the thrust zone, and nappe transport takes place even at low
stress values. Extensional stresses, which are responsible for the
formation of elongation structures, develop in a plane parallel
to the thrust plane. Pressure solution processes, dynamic recrys-
tallization and grain-size reduction take place. Mylonitization
becomes more advanced and locally leads to the formation of
ultramylonites. Temporal stress decrease may cause immobili-
zation of the nappe movement and return to the previous stage
(Fig. 7E), thus another cycle will begin.
Field and microscopic observations indicate that the co-oc-
currence of brittle and ductile deformation is a consequence of
repeatable brittle and ductile conditions as a result of build up
and drop of pore fluid pressure. Teixell et al. (2000) describe
the role of the change of fluid pressure in the Larra Thrust,
taking place within competent limestones in the Pyrenees.
The large role of high fluid pressure and resulting hydraulic
fracturing and large-scale pressure solution at the base of the
Krína Nappe in the Tatra Mts (wierkule Range and Sto³y
Hill) was already stressed by Jaroszewski (1982). He pro-
posed to determine all such phenomena as hydrotectonic
(cf. Kopf 1982). Branquet et al. (1994), based on investiga-
tions of fluidized hydrothermal breccia in the Colombian
Eastern Cordillera, state that brecciation during thrusting can
be regarded as a multistage process. The combination of fluid-
ization and hydraulic fracturing suggests that the pulses may
be related to successive build up and drop of the fluid pres-
sure. Kennedy & Logan (1997) observe a similar case of brit-
tle failure cyclicity and ductile deformation determined by the
change of pore fluid pressure. Gratier et al. (1999) indicated
also that brittle and ductile deformation could interact in the
Temperature during thrusting
Temperatures stated in earlier papers for Alpine thrust pro-
cesses in the Tatra Mts vary from 300350 °C for crystalline
rocks (Janák 1994) to 5080 °C for the upper Krína Nappe
(Grabowski et al. 1999).
MULTISTAGE EVOLUTION OF THE SHEAR ZONE OF THE GIEWONT UNIT (POLAND) 349
Fig. 7. Stages of tectonic evolution of the thrust between the Giewont and Czerwone Wierchy Units, illustrated (from the left): Coulomb-
Mohr diagram (
angle of internal friction,
angle of shear, C cohesive strength, P
id pressure), scheme of microstructure development within the thrust zone, deformation ellipsoid (note how the structures from the do-
main of extensional deformation rotated to the position of shortening and produced folding of boudinages and veins) and scheme of
thrust development. See text for more explanations.
The problem of temperature may to some degree be solved
by deformation observed in carbonate rocks. Experimental
data indicate (Barber et al. 1981) that dolomite deforms by
slip at temperatures <300 °C and that twinning prevails only
at temperatures of 300600 °C. Recrystallization of dolomite
cannot occur at temperatures under 300 °C (Newman & Mitra
1994). According to Burkhard (1993), deformation of twin-
ning in calcite in the form of bending takes place in tempera-
tures over 200 °C. The irregular shape of the twin boundaries
in calcite indicates (Vernon 1981) that these boundaries mi-
grated after formation, which occurred at a temperature of
about 300 °C.
The values of temperature presented in literature for the
processes of cataclasis and mylonitization in carbonate rocks
occurring in thrust zones have levels such as 300 °C for fine-
grained mylonites of the McConnell thrust in Alberta based
on the deformation mechanism map (Kennedy & Logan
1997), 300350 °C for the Sesia Zone in Western Alps
(Küster & Stöckhert 1999), and <300 °C for the Pioneer
Landing fault zone in Tennessee based on geothermal gradi-
ents (Newman & Mitra 1994).
It can thus be assumed that the temperature within the thrust
zone in the multistage process leading to the formation of the
Giewont Unit was variable and could periodically attain 200
The so-called brecciated Campilian (Late Scythian) from
sites located beneath Siad³a Turnia and Turnia Olejarnia rep-
resents dolomitic mylonites developed at the base of the thrust
of the Giewont Unit on the Czerwone Wierchy Unit (High-
Tatric units). Its unique preservation in the form of dilatant
sites is linked with faults, which originated in the basement of
the overthrusting unit. The mylonitization process, which
could take place in temperatures reaching 200300 °C, as
well as thrusting of the nappe, was not a one-stage step-like
process, but a multistage re-activated process, in which brittle
behaviour of deformation was frequently alternated by a duc-
tile rheological condition. Its cyclicity depended on the build
up and drop of pore fluid pressure, leading to the drop of
stress to an effective value and to rupturing by faulting in the
process of hydraulic fracturing (hydrotectonic phenomena). In
consequence, the formation of an open pore-system took
place, in which the contrast of viscosity between walls of the
thrust-fault and the suspension filling the space between them,
comprising fluids, rock fragments and matrix, was noted. The
presence of an almost friction-less mass in the shear zone that
acted as a water pillow moving along the pressure gradient,
induced easier nappe transport. Stresses released by displace-
ment reappeared when the fusion of the thrust limbs and
pore closure took place. This caused the build up of fluid pres-
sure, drop of stresses and hydraulic fracturing mainly in
the surrounding rock, more porous than the tectonically
changed mylonitic zone, but also in the mylonites themselves,
what made the mylonitization process more advanced. In ef-
fect, a shear zone revived, displacement and stress release
took place, and the whole cycle began once again. This pro-
cess caused the destruction of still larger and larger parts of
the rock and was responsible along with pressure solution for
considerable mass loss along the thrust zone. As a result, the
Tatra nappes do not bear the characters of typical duplexes,
but are their remainders difficult for geometric analysis.
Acknowledgments: This research was supported by an indi-
vidual BW Grant No. 1527/2 and BST Grant No. 765/2 (In-
stitute of Geology University of Warsaw). I would like to
thank Dr. Maria Bac-Moszaszwili for giving me the idea of
this research, Prof. Z. Glazer and Dr. hab. El¿bieta Dubiñska
for helpful remarks, Dr. Piotr Dzier¿anowski for help with the
microprobe analyses and Dr. hab. Magdalena Majkowska-Ja-
worowska for aid in cathodoluminescence analyses. Dr. D.
Plaienka, Dr. R. Milovský, and an anonymous reviewer ex-
tensively commented on earlier drafts of this paper; for all
their remarks I am extremely grateful. I am grateful to Dr.
Anna ¯yliñska for linguistic advice. Thanks are due to the Di-
rection of the Tatra National Park for permission to conduct
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