Petrophysical control on the mode of shearing in.pdf

Acta Geologica Polonica, Vol. 56 (2006), No. 2, pp. 159-170

Petrophysical control on the mode of shearing in

the sedimentary rocks and granitoid core of the

Tatra Mountains during Late Cretaceous nappe-

thrusting and folding, Carpathians, Poland

EDYTA JUREWICZ

Laboratory of Tectonics and Geological Mapping, Faculty of Geology, Warsaw University, Al. ˚wirki i Wigury 93,

PL 02-089 Warsaw, Poland. E-mail: edyta.jurewicz@uw.edu.pl

ABSTRACT:

J UREWICZ , E. 2006. Petrophysical control on the mode of shearing in the sedimentary rocks and granitoid core of the

Tatra Mountains during Late Cretaceous nappe-thrusting and folding, Carpathians, Poland. Acta Geologica Polonica ,

56 (2), 159-170. Warszawa.

In the Tatra Mts., the variability of structures within the granitoid rocks and their sedimentary complexes depends on the

physical properties of the rocks, particularly on their porosity and sensibility to dissolution. In the relatively homogeneous

and low porosity granitoid rocks, the shear surfaces are planar and smooth without damage zones around the shear

planes. They did not develop open spaces during shearing, which prevented fluid migration and hydrotectonic phenom-

ena. In the sedimentary rocks, mechanical, mostly bedding anisotropy controlled the geometry and morphology of the

shear zones. High porosity and recurring changing in pore fluid pressure determined the cyclic character of the thrust-

related shearing processes. Fluids appearing within the thrust-fault fissure played the key role in tectonic transport and

selective mass-loss processes (hydrotectonic phenomena). The mass-loss process was an effect of mechanical disintegra-

tion, pressure solution and cavitation erosion. The multistage character of the thrusting processes resulted in a gradual

increase in mass loss value and in geometrical complication of the shear zones. Within the Czerwone Wierchy Nappe, the

minimum value of the mass-loss estimated from a restored cross-section is in the range of 15-50%.

Key words: Hydrotectonic phenomena, Mass loss, Pressure solution, Cavitation erosion,

Tatra Mts.

INTRODUCTION

deformation structures within the crystalline core

formed under similar conditions and in the same stress

field and do not have their equivalents in the sedimenta-

ry complexes.

The tectonic style of nappes in the transitional zone

from the basement to the cover was often studied (e.g.

E PARD & E SCHER 1996, K WON & M ITRA 2006). The

change in the geometry of structures in the cover nappes

commonly reflects the inhomogeneous character of the

deformed rocks caused e.g. by palaeofaults responsible

In the Tatra Mts., Late Cretaceous thrust-napping

processes affected not only the rocks of the nappe units

but also the crystalline core and its autochthonous sedi-

mentary cover (e.g. A NDRUSOV 1968; K OTA¡SKI 1963;

B AC -M OSZASZWILI & al. 1984). Shear stress generated

due to basement shortening in the Fatricum and north

Veporicum was responsible for the nappe-thrusting

process in the Tatra Mts. (P LA ˇ IENKA & al. 1997). The

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EDYTA JUREWICZ

for stress perturbation and formation of fault-related

folds (W ISSING & P FIFFNER 2003). The aim of this paper

is to show that the complex geometry of the nappe struc-

tures and thrust surfaces in the Tatra Mts. are insepara-

bly connected with lithological heterogeneities of the

deformed rocks, in particular with the presence of evapo-

rites (so-called Rauhwacke) as mechanically weak

detachment horizons at the basal thrusts of the nappes.

The specific pattern of the Tatra Mts. nappes, as

observed today, is a consequence of the hydrotectonic

phenomenon (J AROSZEWSKI 1982), which originated at

the base of the nappes and was associated with large-

scale mass-loss processes (J UREWICZ 2003). In earlier

interpretations (B AC -M OSZASZWILI & al . 1981), decrease

in mass in the vicinity of the thrust was connected with

pre-thrusting erosion, while the present author is of the

opinion that this process originated during thrusting due

to fluid migration associated with the hydrotectonic phe-

nomenon (J UREWICZ 2003, J UREWICZ & S ¸ABY 2004).

Mts. is composed of two older structural elements: the

metamorphic sequences of the Western Tatra Mts. and

the granitoid rocks of the High-Tatra Mts. (e.g. P UTI ˇ

1992; J ANÁK 1994). The crystalline core of the Tatra Mts.

is overlain by Mesozoic sedimentary sequences, which

correlate well with Austroalpine units (H ÄUSLER & al.

1993; P LA ˇ IENKA & al. 1997). Three groups of structural

units are composed of Mesozoic sedimentary strata

(K OTA¡SKI 1963): (1) the High-Tatric autochthonous sedi-

mentary cover; (2) two High-Tatric nappes: the Czerwone

Wierchy Nappe (divided into the Zdziary and Organy

units) and the Giewont Nappe; (3) the Sub-Tatric nappes

of Kríˇna and Choˇ. The nappe-thrusting and folding in

the Tatra Mts. are of approximately Late Cretaceous age

and were traditionally linked with the Mediterranean

orogenic phase (A NDRUSOV 1965). The Tatra massif is

overlapped by carbonate deposits of the so-called

Nummulitic Eocene and a post-orogenic Palaeogene fly-

sch sequence (e.g. B IEDA 1959; G EDL 1999). In the topo-

graphic sense the Tatra massif emerged at the surface due

to its Miocene rotational uplift around the W-E horizon-

tal axis (northerly tilting; S OKO¸OWSKI 1959; P IOTROWSKI

1978; B AC -M OSZASZWILI & al. 1984; J UREWICZ 2000a).

The youngest sediments in the area of the Tatra Mts. are

related to Pleistocene glaciations and Holocene erosion-

accumulation processes.

During Late Cretaceous–Eocene times, the

Carpathian area formed part of a larger Alpine-

Carpathian orogen formed by south-eastward subduction

GEOLOGICAL SETTING

The Tatra Mts. are the northernmost part of the

Central Western Carpathians. They are composed of a

Variscan crystalline basement and its sedimentary com-

plexes belonging to the Tatric-Fatric-Veporic nappe sys-

tem (Text-fig. 1) (A NDRUSOV 1968; M AHEL ’ 1986;

P LA ˇ IENKA & al. 1997). The crystalline core of the Tatra

Fig. 1. The main geological tectonic structures of the Tatra Mts. (after B AC -M OSZASZWILI & al . 1979)

PETROPHYSICAL CONTROL ON THE MODE OF SHEARING IN THE TATRA MOUNTAINS

161

of the Penninic Ocean (135–55 Ma) and a later collision

of the European and Adriatic continents (55-40 Ma;

N EM ˇ OK & N EM ˇ OK 1994; N EM ˇ OK & al. 1998). The age

of Alpine thrusting and folding is progressively younger

from south to north. The northward migration of nappes

from the hinterland to the foreland is well docu-

mented by the diachronous position of the pre-orogenic

flysch and the progressively younger ages of the sedi-

ments involved in the cover nappes towards the foreland

(L EFELD & al. 1985; P LA ˇ IENKA 1996, 2003). As in the

case of the crystalline core, the sedimentary cover was

also deformed during Alpine thrusting and folding but,

due to the different physical properties of the rocks, in a

different manner.

crystalline core and the sedimentary cover, the granitoids

of the High Tatra Mts. are much more useful than the

metamorphic sequences of the West Tatra Mts. Here, the

granitoid rocks are younger, and, thus less deformed.

The relatively homogeneous and isotropic structure of

the granitoids is responsible for the geometry of the

shear zone patterns.

With regard to their age, three groups of structures

can be distinguished within the granitoid core of the

High-Tatra Mts.: (a) pre-Alpine structures, (b) structures

produced by Late Cretaceous nappe-thrusting and (c)

structures brought about by the Neogene rotational

uplift of the Tatra massif (J UREWICZ 2002; J UREWICZ &

B AGI¡SKI 2005). Owing to the character and geometry of

the deformation, the nappe-thrusting related fault and

shear zones of the High-Tatra Mts. can be subdivided

into three groups: (a) steeply-dipping shear zones com-

prising mylonites or cataclasites (Text-figs 2A, B), (b)

low-angle slickensided faults (Text-fig. 2C) and (c) high-

angle slickensided faults (J UREWICZ 2000b, 2002).

G ROCHOCKA -P IOTROWSKA (1970) additionally distin-

guished the so-called “uniform slip zones” composed of

several parallel fault-planes, which can be included into

the latter (c) group of structures. The cataclastic and

mylonitic zones (a) formed, in general, during a pre-

Alpine deformation stage, and were reactivated during

the Neogene uplift as sinistral strike-slip faults or oblique

normal-slip faults (305/60) (J UREWICZ 2002; J UREWICZ &

B AGI¡SKI 2005). The high-angle slickensided faults (c)

are genetically related to the rotational uplift in the

Neogene (S OKO¸OWSKI 1959; P IOTROWSKI 1978; B AC -

M OSZASZWILI & al. 1984; J UREWICZ 2002). These kinds

of faults commonly occur within the sedimentary cover

and nappe units (Text-fig. 2D), thus their ages are

unequivocally younger than Late Cretaceous. The group

(b) comprises low-angle and smooth slickensided faults,

whose orientation points to their relationship with the

Late Cretaceous thrusting event (J UREWICZ 2000a).

Within the Tatra granitoid core, most thrust surfaces

and faults that can be linked with the Alpine folding are

characterised by shallow dips transformable into original

southern dips (i.e. preceding the Neogene tilting –

J UREWICZ 2000a). An analysis of tectonic transport

directions based on striae on such slickensides occurring

within the crystalline rocks of a tectonic cap (so-called

“Goryczkowa Island”) was made by B URCHART (1963).

The low-angle slickenside faults from the granitoid core

of the High-Tatra Mts. allowed a reconstruction of the

Late Cretaceous stress field to be made (J UREWICZ

2000a). The structural analysis of the crystalline core and

the nappe units which was proceeded by a back-tilting of

the Tatra block by c. 40°, to a position it occupied prior to

the Neogene rotation (B URCHART 1972; K RÁL ’ 1977;

TYPE AND ORIGIN OF SHEAR ZONES IN THE

TATRA MTS.

During Early to Late Cretaceous times, the thinned

continental crust of the basement of the Fatric-Tatric

Basin showed a lateral rheological heterogeneity

caused by lithospheric extension and rifting (cf.

V AUCHEZ & al. 1998). This favoured the formation of

low-angle anisotropy and consequently of major flat-

lying thrusts and detachments (see G HEBREAB 1998).

Above the roof thrust of the thrust system slightly dis-

turbed strata may have been present, whereas imbri-

cate structures and a hinterland dipping duplex could

have formed below (see B OYER & E LLIOT 1982).

Initially, assuming a simple model of folding, thrusting

and duplex formation could have been complicated by

the large lithological variability and rheological hete-

rogeneity of the deformed rocks. When the subduction

had completely consumed the basement of the more

southerly sedimentary zones, the crystalline basement

of the High-Tatric series also underwent compression

and thrust-related shearing. The fact that crystalline

rocks are also included in the nappes and that they

were detached at depths of at least several (c. 10) kilo-

meters (L EFELD & J ANKOWSKI 1987), suggests that the

detachment was preceded by compression, which

resulted in reverse faulting (e.g. B AC -M OSZASZWILI &

al. 1984). In some cases, reverse faults may have origi-

nated due to the changing of the sense of movement on

originally normal faults. This is evidenced e.g. by the

angle of 60° between the surface of the sedimentary

contact of Seisian sandstones with the crystalline rocks

and the Giewont Nappe thrust (B AC -M OSZASZWILI &

al. 1979; J UREWICZ 2005). During later stages of the

thrusting and folding the surface of this fault was

deformed (see below).

To compare the deformation structures within the

162

EDYTA JUREWICZ

P IOTROWSKI 1978; K OVÁC ˇ& al. 1994; J UREWICZ 2000a,

b), indicated the prevailing northern direction of tecto-

nic transport. The NW direction is older than the N

direction. This can be inferred both from the orientation

of slickenside of striae within the granitoid core

(J UREWICZ 2000a), as well as from the distribution of

bedding attitudes in the sedimentary complexes on

Lambert-Schmidt stereogram plots (J UREWICZ 2000 b).

Fig. 2. Deformation structures in the Tatra Mts. A – very fine-grained tectonic gouge within the shear zone in granitoid rocks, Bandzioch Cirque (160/60),

High Tatra Mts. (pre-Alpine deformation phase, reactivated during the Neogene). B – polished surface of the ductile-folded of foliation in granite

mylonites within the lower part of the shear zone within the Bandzioch Cirque (160/60), High Tatra Mts. (pre-Alpine deformation phase). C – low-angle

dipping fault plane coated with quartz and epidote (315/35), Zmarz∏a Pass, High Tatra Mts. (reverse fault forming during Late Cretaceous deformation

phase, preceding the Tatra rotational uplift). D – surface of a normal fault coated with quartz and chlorite (290/70), Seisian sandstone, NW slope of the

Ciemniak Mt., High-Tatric nappes (Neogene uplift related). E – stylolitic character of the contact between the Urgonian limestone of the High-Tatric

nappes (pale) and Anisian dolomite of the KríÏna nappes (dark); Sto∏y Hill (Late Cretaceous deformation phase). F – strongly folded dolomite mylonite

at the base of the Giewont Nappe, High-Tatric nappes (Alpine deformation phase)

PETROPHYSICAL CONTROL ON THE MODE OF SHEARING IN THE TATRA MOUNTAINS

163

The older NW striae were partly destroyed by younger,

more northely directed striae and, currently can be

observed on few slickenside planes. This may indicate

that either a gradual change of the maximum principal

(σ 1 ) stress orientation from the NW to N position took

place during thrusting, or that a counter-clockwise rota-

tion of the basement occurred under conditions of a sta-

ble stress field of constant orientation (J UREWICZ 2000b).

Other evidence for the basement counter-clockwise rota-

tion during Late Cretaceous folding and thrusting or for

the changing dirrection of thrusting was found from the

analysis of bedding attitudes. The latter analysis points to

the fact that the higher and earlier overthrust units (the

Kríˇna and High-Tatric nappes) show signs of a NW-

directed compression whereas the rocks of the later

deformed autochthonous sedimentary cover display a N

compression orientation (J UREWICZ 2000b). Structural

investigations within the crystalline massif and sedimen-

tary cover (J UREWICZ 2000a, b) made it possible to eval-

uate the angle of post-Turonian and pre-Eocene nappe-

folding counter-clockwise rotation around a vertical axis

to be c. ~45 o .

The en-bloc rotation of the basement during the

nappe-thrusting seems to have only slightly influenced

the orientation of the slickenside surfaces within the

crystalline core. Because the rocks of the crystalline core

were the last to be incorporated into the Late Cretaceous

thrusting, it can be assumed that their activation did not

require as many stages as in the case of the shear zones

within the sedimentary complexes. Likewise, they were

not subjected to deformations during the younger tec-

tonic events, in which the stress field did not favour pos-

sible reactivation of the Alpine slickenside surfaces; at

that stage they attained an almost semi-perpendicular

position to the plane of the shear stress.

The shear zones in the sedimentary complexes that

can be linked with nappe thrusting are typically devoid of

slickenside striae. Their surfaces are not planar, but of

complex morphology, and in some cases (e.g. in the floor

of the Zdziary Unit) show signs of folding. Deforma-

tional structures at the base of the nappes, ductile in

nature, are extremely variable and show signs of multiple

activation. They are thus not suitable for kinematic

analysis of the tectonic transport directions and recon-

struction of the stress field.

regard to their physical properties influencing the course

of the deformation processes. The granitoids of variable

mineral composition, including quartz, feldspars and

micas, show typically in laboratory tests a larger uniaxial

compression strength than the carbonate rocks (granite:

c. 60-230 MPa; carbonate: c. 15-130 MPa), and a dis-

tinctly lower and rather uniform porosity (granite: c. 0.4-

3.7%; carbonate: c. 0.1-30%) (P INI¡SKA 1997, 2000). The

key factor controlling the deformation processes in the

Tatra Mts. sedimentary rocks was lithological varia-

bility. The presence or absence of bedding in the car-

bonate rocks, variable susceptibility to pressure solution,

and different proportions of marl and clay intercalations

distinctly influenced the rock anisotropy. One of the

many reasons for the geometric complication of the tec-

tonic structures in the Tatra Mts. may have been thick-

ness changes due to sedimentation on rotated blocks.

Such a situation may be observed on the Mt. Kominy

Tylkowe in the High-Tatric autochthonous cover, where

K OTA¡SKI (1959) and R UBINKIEWICZ & L UDWINIAK

(2005) ascertained thickness reduction of the Lower and

Middle Triassic deposits by c. 30-50%. The High-Tatric

stratigraphic succession shows indirect evidence of

synsedimentary listric normal faulting associated with

the rotation of beds in the hanging wall from horizontal

to a steeper dip (J UREWICZ 2005). The formation of

listric faults resulted in the propagation of fault-related

synclines (see K HALIL & M C C LAY 2002) that developed

further at younger tectonic stages.

The granitoid core of the High-Tatra Mts. bears

numerous slickensides. Their surfaces are planar,

smooth and coated with quartz, epidote or chlorite.

Investigation of fluid inclusions in syn-kinematically

grown quartz slickenfibres on these faults indicated sta-

ble P-T conditions of the deformation. Quartz crystal-

lized under pressures of c. 1.45-1.7 kbar (145-170 MPa)

and temperatures of c. 212-254°C (J UREWICZ &

K OZ¸OWSKI 2003). These values allow estimation of the

depth of deformation along the Late Cretaceous faults at

c. 6-7 km. The pressure and temperature within the sedi-

mentary rocks that must have been deformed at shallow-

er depths, proved to be more variable. The temperatures

obtained from the shear zone within the High-Tatric

nappes, determined from chlorite and feldspar ther-

mometers, varied in the range 300-350 o C (J UREWICZ &

S ¸ABY 2004). The twinning in dolomite also indicates

temperatures in excess of 300 o C. In a similar situation, a

major dispersion of temperature values (213 to 471 o C)

and thus of pressure (20-540 MPa) was found by

M ILOVSKY ∂& al. (2003) from investigation of fluid inclu-

sions in the basal cataclasites of the Muráˇ Nappe, part

of the Silicicum cover nappe system (southern part of the

Central Western Carpathians). Thus the P-T conditions

COMPARATIVE ANALYSIS OF SHEAR ZONE

DEFORMATIONS IN THE TATRA MTS. GRANI-

TOID CORE AND SEDIMENTARY COMPLEXES

When compared to the sedimentary carbonate rocks,

the granitoids show both similarities and differences with

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