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665
Geologische Rundschau
75/3
[ 665-683 [ Stuttgart 1986
Hercynian-thrust related shear zones and deformation of the Varied Group on
the contact of granulites/Southern Moldanubian, Bohemian Massif/
By PETR RAJLICH, JAROSLAV SYNEK, MICHAL SARBACH and KAREL SCHULMANN, Praha*)
With 18 figures and 1 table
Zusammenfassung
Drei Deformationsphasen der variszischen tektonischen
Entwicklung sind in der Bunten Gruppe des siidlichen
Moldanubikums des B6hmischen Massivs enthalten. Die
Deformation ist mit der yon NW nach SE orientierten
Uberschiebung von grogen Krusteneinheiten mit Granuli-
ten verbunden. Die Entstehung yon jiingeren N-S und
NW-SE verlaufenden Scherzonen kann auf die Uberschie-
bungsbewegung bezogen werden. Die Strukturentwick-
lung beginnt mit F1 isoklinalen Falten, die wahrscheinlich
den nichtmetamorphisierten Sedimenten aufgepr~igt wur-
den. W~ihrend der Abschlugphase der Formung wurden sie
stark gepl~ittet und es entstand die B1 Boudinage. Die
Aplitg~inge, Migmatitisation der Paragneisse und Meta-
morphose der Gesteine sind gleichzeitig. Die D2 Deforma-
tionsphase wurde dutch einfache Scherung der Einheit her-
vorgerufen und es entstanden Falten verschiedenen tekto-
nischen Stils in der Umgebung starrer Einschliisse und die
Blattverschiebung an der Grenze yon Granulit und Bunter
Gruppe. Die F1 und F2 Falten liegen parallel zur Streck-
ungslineation und Uberschiebungsrichtung ab. Die j/ingste
Deformation ist charakterisiert durch eine spektakul~ire
Boudinage und Falmng der senkrecht stehenden FI~ichen.
Abstract
The three deformation phases inferred from the detailed
structural analysis of the Cesk~ Krumlov Varied Group re-
cord the Hercynian development of the Southern Moldan-
ubian of the Bohemian Massif. The deformation is related
to the NW-SE thrusting of the large crustal units including
granulites. The formation of the NS and NW-SE trending
shear zones is connected with the thrust movement. The
structural development begins with F1 isoclinal fold forma-
tion, that could originate in unmetamorphosed sediments.
In the final stage, they were strongly flattened and B1 bou-
dinage developed in the rocks. Aplite dykes and migmatiti-
zation of paragneisses occurred at the same time the rocks
*) Author's address: P. RAJLICH, J. SYNEK, M. SARBACH
and K. SCHULMANN, Institute of Geology and Geotech-
nics, Czechoslovac Academy of Sciences, V Holegovi~k~ch
41, 182 09 Praha 8, Czechoslovakia.
were metamorphosed. The D 2 deformational phase was
produced by the simple shear deformation of the unit and
folds of various styles around rigid inclusions and the stri-
ke-slip shear zone near the boundary of the granulite and
the Varied Group were formed. The F 1 and F2 folds are pa-
rallel with the stretching and mineral iineation indicating a
NS to NW-SE direction of the thrusting. The youngest de-
formation is characterized by spectacular boudinage and by
folding of the vertically oriented planes.
R~sum6
L'&ude structurale d&aill& de la Strie Vari& du Mol-
danubien m&idionai dans le Massif de Boh~me a permis de
distinguer trois phases de dtformation dans le d&eloppe-
ment tectonique varisque. Cette dtformation est li& au
charriage, du Nord-Ouest vers le Sud-Est, de grandes uni-
tts crustales comportant des granulites. La gentse de zones
de cisaiIlement plus jeunes, d'orientation N-S et NW-SE
peut &re li& au m&me processus de charriage. Le d&elop-
pement structural commence avec des plis isoclinaux F1 en-
gendr& vraisemblablement dans les stdiments non m&a-
morphis&. Au stade final de leur formation, ils ont &6 tr~s
aplatis et un boudinage B1 est apparu. L'intrusion de filons
d'aplite et ia migmatitisation des paragneisses sont contem-
poraines du m&amorphisme. La deuxi~me dtformation D 2
a &6 le fair d'un cisaillement simple; ~ ce moment se sont
form& des plis de style tectonique tr~s vari&, localis& fr&
quemment autour d'inclusions rigides. De cette &ape date
8galement le d&rochement ductile entre les granulites et la
S&ie Vari&. Les plis F~ et F2 sont paralI~les 5. la lintation
d'&irement (lin4ation rain&ale) qui indique la direction
N-S 5. NW-SE du charriage. La dtformation la plus jeune
comporte un boudinage spectaculaire et le plissement des
plans d'attitude verticale.
KpaTKOe co~lep~aHtle
B IIecTpbIX OTYIO~eHrt~tX tO)KHOFO (Mo~aaHy6croro)
6oreMcroro MaccriBa OTMeqeHbI TpH qba3bi ~/eqbopMa-
LII4H BO BpeMfl BapHccKoFo TeKTOHHqecKoFo pa3BHTHSt.
~e~opMaIIn~ CBIt3aHa C HaZlBI4rOM 60~btUOH e~HHHHM
Kop•r, cojlepmaulefi rpaHynI4TbI, opHeHTHpOBaHHt,Ie C
NW Ha SE. HoaB:ieHrie IIO31IHel;ImHX 3OH CM~tTFISt npoc-
666 P.
RAJLICH et
al.
THpammHxc~i Ha N-S ~ NW-SE, MO)KHO CB~3aTb c
jIB~X~eHHeM Ha~IBHra. Pa3BHTHe cTpyKTyp gaqHHaeTc~ C
H3OKJIHHaYlbHOfI CKJIa/IKH F b KoTopa~ MorJIa HeCTIt He-
MeTaMOpqbII3IlpOBaHHbIe ce~IHMeHTt,I. BO BpeM~l 3aBep-
I.tIeHH~ npo~3omJIo ee ynnonleHHe H no~B~I~C~ 6y/I~I-
Ha~ B 1. IIoItBYleHHe ]Ia!~IKOB tI )KHn anYlIITa, MHFMaTH3a-
llHa naparHeficoB
~ MeTaMOp(~H3M IIOpO/I
npoTeKanH
O~IHOBpeMeHHO. dPa3a/IeqbopManH~ D2 oKa3aJIaCb BbI3-
BaHHOkI HpOCTMM cKaJIBIBaHHeM 3THX cTpyKTypHMX
eJIHHI411 14 rlpHBeJla K HO~IBJIeHHIO CKJIajIoK pa3JH4qHoro
TeKTOHHqeCKOFO CTI/IJ]I:I~ oKpy)KeHHblX BKpanJIeHHIIMH H
CjIBHYaMtl Ha rpaHHHe rpaHy~laXOB H
IleCTpblX
OT.JIo~e-
HH!TI. CK.IIaJIKH F 1 !4 F 2 paCHOYIO)KHJIHCB
napan.lle.rlbHO I{
HpOCTHpaHHIO II nHHeI:IHOCTH MHHepaYIOB 14 o6pa3oBaJIIl
Ha~IBIIF, IIpOCTHpaIOUlIII~IC~I B HanpaBJleHHI4 N-S/Io NW-
SE. llo3~iHefnlla~l /leqbopMallH~ xapaKTepilayeTcla
CHJIbHbIM 6y~IHHaXteM H CMgITHeM B CKJIfljIKH HJIOCKOC-
TeI:I, CTOI;III~HX OTBeCHO.
Introduction
The Hercynian orogeny fashioned, granulite-
bearing terrains in Europe mostly exhibit an alloch-
tonous position (PIN, VILZEUF 1983, W~t3ER & BEHR
1983, BUt<G & MATTE 1978). Investigation of structu-
res contained in them provide also evidence for the
mode of emplacement of the granulite bodies. From
this point of view, structural analysis of the CeskT~
Krumlov Varied Group and of the adjacent granulite
bodies was carried out on the basis of comparison of
the styles of small structures contained in both units.
Feldspar porphyroblasts, boudins and folds were
used for quantification of strain in the rocks. The va-
ried lithology of the CeskT~ Krumlov Varied Group
records several stages of deformation and description
of the structure of the Varied Group and outline of
the most important shear zones will be given in this
paper. Structural analysis of granulites will be des-
cribed elsewhere (RAJHCH, SVNEK in prep.).
Regional
geological setting and the
survey of
previous research
The Varied Groups of the Moldanubian are arran-
ged in three strips called the Su~ice-Votice, Cesk~
Krumlov and South Moravian. They represent the
youngest metamorphosed sedimentary rocks in the
Moldanubian and they are often associated with gra-
nulites. The Cesk~ Krumlov Varied Group (fig. 1)
forms a narrow belt between the town of Horni
Plan~ (48~ lat, 14~ long) running across the
region of CeskT~ Krumlov, Rudolfov horst under the
T~ebofi sedimentary basin into the vicinity of Karda-
~ova I~eeice (49~ lat, 14~ long). It is compo-
sed mainly of plagioclase-biotite paragneisses (BaL-
ze~, 1936). The different layers of sedimentary origin
are represented by quartzitic paragneisses, quartzi-
tes, erlans to erlan marbles, crystalline limestones,
tremolitic limestones, graphitic gneisses and graphi-
tic quartzites. Amphibolites, garnetiferous amphi-
bolites and amphibolic gneisses are volcanogenic in
origin. They form intrusions - mostly dykes espe-
cially in the carbonaceous sequences (HEGzNBAWr
1936) and probably can also be synsedimentary with
the country rocks (in paragneisses). In contrast to
other heterogeneous rocks from the Varied Group,
amphibolites are also found in the underlying Mono-
tonous Group (BA>zER 1936, JEN~K & VAJNEt<
1968). The smaller intrusive bodies of aplites, dyke
granites and lamprophyres constitute the youngest
,,membres<~ of the Group (BaLZER 1936, HEC~NBART
1936, MAUTNeR 1936), fig. 3. Its real thickness is not
known. A 1576 m structural borehole (fig. 2a) passed
through the rocks of the Varied Group and reached
the bottom of this formation. The ,,real thickness<<
disclosed by this borehole is estimated at 1300 m (fig.
2a).
The greater thickness of the marbles from the NE
part (fig. 2b) of the Varied Group is explained by
HEGENBARTH 1936 as being due to tectonic thickening
through thrusting.
All the boundaries of the Varied Group represent
important Hercynian shear zones. To the NW, the
Varied Group is surrounded by North-South tren-
ding strip of foliated granites, on the west by youn-
ger granitic bodies and on the SE it is thrusted over
the paragneisses of the Monotonous Group of the
Moldanubian. On the NE side its continuation is in-
terrupted by the granulite body of the Blansk~ Les
Mts.
Paleontological evidence published in the last few
years strongly supports the late Palaezoic age of the
Varied Group suggested 1926 by Su~ss (ANDRUSOV,
CORNA 1976, KONZALOVA 1980, PACLTOVA 1984), in
Fig. 1. Principal shear zones and geological units of the area. The heavy numbers: 1 - BlanskT~ Les. Mts. granulites, 2 - Pra-
chatice granulite, 3 - K~i~tanov granulite, 4 - Varied Group thrust, 5 - Monotonous Group thrust, 6 - Kaplice micaschistes.
Symbols in the map: 1 - durbachites, 2 - granites, 3 - inclusions of ultramafic rocks (outcropping), 4 - hidden ultramafic
rocks following aeromagnetic survey, 5 - orientation of the stretching lineation in the strike slip zones and inside the larger
thrusted units, 7 - the Lfisenice (Bor~ov) - V&~n~ shear zone lower limit, 8 - the lower limit of the Main South Bohemian
thrust (boudary between Monotonous Group paragneisses and Kaplice mica-schists), 9a and d- low dip thrust sense, b and
e - strike slip sense.
Hercynian-thrust related shear zones and deformation 667
t
\.q
///
/
/
",/4
/ /
/ (~)
i, ~&~ ,
Q~
/
~y VARIED
GROUP
THRUST
\\ \
' xX"
~
incluslons of uLtramaflc ~i~hldden uHramaflc rocks
rocks [outcropping)
~
KQp[ice "mlcaShlS~S"
~q :;;%2; :12;:oo
the L~senlcelBor{ov]
~;~-V6t~nf shear zone
I
~Monotonous group
l~l
PotypInase stre~chmg
[ineahon zones
[~
7~MQtn
South
Bohemlen thrust
•:•
..... p .... t .... ~ st ..... L .......
NETOLICE
;;~-~.. ~,/
J
CESKY
\
\
\
\
2km
lilil
r~.~>~ u /'~ I ~.J "
o \ 8ralEslava f A
WIEN .o "~ 0 s [
I i i I BUDAPESTO
668 P.
RAJLICH et
al.
contrast to works by other authors suggesting Upper
Precambrian age of the rocks and the autochthonous
position of the granulites (ZouBEK 1976, KODYM
1976, CHALOUPSKs 1977 and others).
During the polyphase deformation, the rocks were
metamorphosed into the garnet-amphibolite facies.
The temperature of metamorphism according to the
isotopic graphite-carbonate geothermometer varied
in the range from 480 ~ to 609 ~ C (ClZEK et al. 1984).
The grade of metamorphism was more elevated on
the NE side closer to the BlanskT~ Les Mts. granuli-
tes. Geochemical research carried out on the graphite
deposits by JII~ELE & Kt~IBEK (1984) reveals sedimen-
tation in the isolated saline basin. The quartz content
of the marbles after ZOUBEK (1953) is a consequence
of their regressive sedimentary character. JEN~ &
VAJNER (1968) explain the reef character of the lime-
stones and biogenic origin of graphite accumulations
in terms of the neritic facies of the sedimentation.
FIALA et al. (1983) point out the association of meta-
volcanics with quartzites, K - metapelites and carbo-
nates, formed they suggest, from the shelf sedimen-
tary facies of volcanic islands.
JE~,~EK & VAJNE~ (1968) describe the nonhomoge-
neous deformation of the Varied Group and relative
abundance of small scale structures in it, in compari-
son with the underlying Monotonous Group. They
assume their mutual tectonic separation (see also
BALZE• 1936), not susceptible to observation in all
the parts because the contact is often penetrated by
younger granitic intrusions. ZELENKA (1927) inter-
preted the structural discordance of the Varied and
Monotonous Group as a overthrust plane of the Va-
ried Group nappe. According to HOCHSTETTER
(1854), KODYM (1972),
VAN
BRE~MEN et al. (1982) and
RAJLICn & SYN~K (in prep.) granulites have an al-
lochthonous position inside the surrounding units
and underwent the partially retrogressive metamor-
phism at the same time as the latter (JAKE~ 1969).
Principal shear zones in the region
The following shear zones were found in the broa-
der region investigated. The main shear zone is the
NE-SW trending Main South Bohemian Thrust
which is a ductile shear zone, along which successi-
vely higher metamorphic rock series were thrusted
from the NW to the SE. The lowest unit lying mostly
to the SE is represented by the Kaplice micaschists
that follow the Monotonous Group paragneisses,
A ~
o ~ _~
lw
NW ~,~
mz c]>
as3
T
~~176 (
T /
z ,
T ~
~~176176 7
"~ SE
as,
/'/
,t
Fig. 2a. Geological section through the area, for position see Fig. 1, Explanations same as in figure 1.
Hercynian-thrust related shear zones and deformation
669
o
t ] i J i
i
i
[
I
g
~n
o
~ T
i I i J J [ i i i i
JJ .... ],,,
I i
g
9
EIJ
CERNA
MUCKOV
m
BENDING
3F SECTION
~ERTICE
NEZIPOTO~i
3OREHOLE
4OVOSEDLY
30BRKOVICE
F
c
5 VY~N~
m -
4 Fig. 2b. Longitudinal geological cross section through the
area.
Varied Group paragneisses with subordinate marble
lenses and Varied Group with the granulites of the
Blansk~ Les Mts., K?i~anov and Prachatice granu-
lite bodies. The branches of the thrust can be traced
in accordance with the variable lithology of the
thrust slices. The Varied Group itself is separated
from its base by an important shear zone, called the
Lisenice - V~t~nf shear zone (thrust).
The granulite-containing unit represents the
highest thrust sheet and it was segmented by later
and/or contemporary shear zones into several of the
above-mentioned blocks of granulite bodies (fig. 1).
The most important shear zones dividing the granu-
lite bodies are: Lhenice NS trending shear zone and
(~esk~ Krumlov shear zone, which propagates furt-
her to the NW behind the Lhenice shear zone and se-
parate the Prachatice and K~i~anov granulite mas-
sifs. The Blansk;~ Les Mts. granulite is sheared in the
East by the smaller NS trending shear zone. The
Cesk~ Krumlov Varied Group is bounded by the ab-
ove-mentioned shear zones and they were decisive
for the tectonics style of small structures contained in
it. The importance of the shear zones for the struc-
ture of the area was stresses by V~ANA (1979). In con-
trast to us, he timed the major overthrust as D3 later
deformation. Similarly, VAN BR~EMEN et al. (1982)
noticed that the granulites from Southern Bohemia,
such as those at L~ov and Blansk37 Les Mts., occur in
the vicinity of the NE-SW trending broad shear zo-
nes (up to 60 km long) and they connected the uplift
of granulites with NW-SE oriented thrust.
The Lfisenice - V~t~ni ductile
shear zone
(thrust)
This shear zone represents the branch of the Main
South Bohemian Thrust, along which the granulites
together with the Varied Group were thrusted from
the NW to the SE. Its strike is NE-SW and in the
field it displays rather uniform dipping foliations
(40-60 ~ to the NW (fig. 4). The folds are scarce and
their axes are dispersed in the diagram along the great
circle of the plane of the shear zone. This would sug-
gest that they originated in the inhomogeneous shear
inside the shear zone similar to the sheath folds
(COBBOLD & QUINQUIS 1980). Several stage of faul-
ting (reverse and normal faulting) can be recognized
using the criterion of small scale structures (BRUNEL
1983), boudins, S and C planes (CHouK~OUNE, GAPA-
IS, MATTE 1983), transected aplite dykes etc. (fig. 5).
670 P.
RAJLICH et
al.
ml ma ~
ize 1
I
ic b,otltlc-rnusc~lhc Orthognels~s, gr(:nuMes, granuLdEc crysto[hne calc-slhcote
........ pQi QgnelsSes ~ po~ ag~:ls~eds .... ~ ................... ~1 ........ ~ ............ [~ .......... [~ .....
grQphffes,graPhlt m
~] orthogne,sses ........... ~ ........ ~ ............. F~ ................
C) B
\
I
A
A' line of cross sechon
i, / hneohon
lohatlon
fold median llne
mineraL IlneQtlon
axes
of recumbent i~o
ckmal folds
ax s o u r[ n ~LmL ~r
fO~s f p g t I
81 bOudmage
i \\ ~\ ~ B 2 bOUQlnage
ax~S
of
bOUdln$
~ Jndlv~ded
LAZEC
%
Fig. 3. Geological map of the area. 1 - biotitic paragneisses, 2 - migmatitized biotitic paragneisses, 3 - biotitic-muscovitic
orthogneisses, partially migmatites, 4 - granulites, granulitic gneisses, 5 - amphibolites, 6 - crystalline limestones, 7 - calc-
silicate rocks, - 8 - leucocratic orthogneisses, 9 - graphites, graphitic gneisses, 10 - serpentinites, 11 - two-mica granites, 12
- line of cross section, 13 - lineation, 14 - foliation, 15 - fold median line, 16 - mineral iineation, 17- axes of recumbent iso-
clinal folds, 18 - axes of upright similar folds, 19 - B1 boudinage, 20 - B 2 boudinage, 21 - axes of boudins undivided.
Amphibolite dykes formed mostly buckle folds
with an axis direction parallel to the X-stretching li-
neation. The stretching lineations (BRuxEL 1983) are
poorly preserved and, when present as stretched
feldspar porphyroblasts, they indicate the reverse
fault movement inside the shear zone. This sense of
movement in the first stage is indicated mostly by the
almond structures (fig. 5) interpreted according to
the classification of Bt<uNeL (1983). We have rarely
found amphibolite boudins stretched in the X direc-
tion. Many of the oldest structures were later oblite-
rated by migmatizatiou, recrystallization, etc. The
NW-SE elongation of ultramafic rocks inside the
Blansk~ Les Mts. granulites is probably the conse-
quence of stretching during the thrust.
Fig. 4. Pi-diagram of structural elements in the Lfi.senice -
(Bor~ov) - V~'nl shear zone, 1 - poles of foliation, 2 -
stretching lineation and striation, 3 - folds. I~
N
/
A AA 9
', ~ I ",
+ +
Q?=. +
9 + 1
A. ~ @ _k§ _
+
9 + ++% /
++ /
\ /
§ /
Q 3A
Hercynian-thrust
related shear
zones and deformation 671
w
,,, 7/
/111 / li!i ~
i/1
r
/// /
A /
W
50 cm
E
Fig. 5. Structural elements giving the sense of shear in the L~isenice- Bor~ov- V~t~ni shear zone. A- transected aplite dykes,
B - asymmetrical folding on the lower side of the boudin, C- development of the structure of almonds, D - bending of folia-
tions.
The younger movement on the shear zone points
to normal faulting or to reverse fault movements;
normal faulting seems to be the most important. In
this stage the rocks were traversed by anastomosing
brittle- ductile shear zones several cm to several met-
res wide, with striation. They sometimes also con-
tain up to 1 m thick bands of mylonites with crushed
minerals and incipient formation of stretching linea-
tion. This stage of the shear zone formation was tra-
ced into the environs of Jindfich.uv Hradec (L~seni-
ce) where it occurs in the oldest plutonic rocks of the
Hercynian Central Moldanubian pluton (KLEegA &
RAJLICH 1984). This permits tracing of the shear zone
for a distance of 80 km and documents its prolonged
Hercynian activity.
The (~esk~ Krumlov Shear Zone
This shear zone marks the transition of the struc-
tures from the Varied Group into the Blansk~ Les
Mts. granulite body. The shear zone caused dishar-
monical folding and thickening of marble lenses of
the Varied Group which was scraped from the un-
derlying paragneisses (fig. 2b). It deflects also the
lineations and fold axes from the NS trend which is
present in the central part of the Varied Group (fig. 6)
into NW-SE direction. It is also marked by the deve-
lopment of the strong stretching lineation of the
feldspar porphyroblasts contained in amphibolites
(HEGENBART 1936, fig. 16). During the progressive
shear, the 1st stage boudins of quartzite and amphi-
bolite were stretched. The strong parallelism of all
the linear structural elements also arises from the
contour diagrams (fig. 7).
The deflected lineation from the NS to NW-SE di-
rection inside the ~esk)7 Krumlov Shear zone was
used for the computation of the y shear strain and of
the relative displacement of the border blocks using
the method of BAK et al. (1975). The direction of con-
tact is 286.5 ~ the angle between the lineation and the
contact (ul = 27.28 ~ and the angle of deflection (u2)
is 37.38 ~ In the nomogram published by BA~ et al.
(1975) these values yield ay shear strain equal to 1.5.
This gives a sinistral displacement of the order of 8.25
km for a width of the zone of 5.5 km.
The integration of the surface of the ~ shear strain
in the fig. 18 calculated using the X/Z ratio of strain
ellipsoids from within the shear zone yields a value of
7.7 km.
Interesting relationship exist between the CeskT~
Krumlov shear zone and the L~isenice - V~tfnl shear
zone. The dip of the stretching lineations is the same
in both (figs. 4 and 7). This can be explained by the
uniform sense of movement of all the elements but by
differing velocities of blocks within the thrusted unit
(between the BlanskT~ Les Mts. granulites and the
neighbouring Varied Group). The granulite reacted
672 P. RAJLICH et al.
\ _/,,'2J ( :" f---<~i~
Fig. 6. Analysis of orientation of structural elements in the (~esk~ Krumlov Varied Group, A- homogeneous domains of li-
near elements in the area, 1 - iineations and fold axes, 2 - axes of boudins, 3 - mean vectors, 4 - elipse of the 95 % confidence
interval. B - flow lines of foiiations, 1 - L~isenice- (B or~ov) -V~t~nl shear zone, 2 - Cesk~ Krumlov shear zone, 3 - Lhenice
shear zone, C - strike and dip of foliations approximated through the 3 ra degree polynominal surface. D - strike of foliation
approximated through the 5 th degree of the poiynominal surface, E - dip of foliations approximated through the 5 th degree
of the polynominaI surface.
as a more rigid body in this context. The greater duc-
tility in the Varied Group could be engendered by
the fluids and temperature rise connected with the
ascension of the granulite body documented by the
increasing metamorphism of the Varied Group to the
NE and by the helical structures connected with the
intense shearing phenomena (fig. 14a) observed in
the garnetiferous amphibolites in the (~esk~ Krum-
lov shear zone (HEGENBART 1936). The main left-
hand sense of strike-slip shearing changed in time as
is documented by the drag fold development, fig. 8.
The deformation of the Varied Group
D~ deformational stage
Three main stages of fold formation were observed
in this zone. The earliest folds tentatively classified as
F1 folds are tight, isoclinal, strongly flattened with
the fold axial plane parallel to the surrounding folia-
tion. They correspond mostly to the 3D through 5F
classes of HUDLrSTON (1973). They fold the clear-
dark cm-wide banding of limestones (primary or ac-
centuated by metamorphism), compositional laye-
ring of amphibolites, amphibolitic paragneisses,
calc-silicate felses inside the marbles, etc.
The F1 folds in the area can also be angular, sharply
kinked with plane limbs. The folded rock volume
here is mostly bounded on both sides by undisturbed
foliation planes (fig. 10a). They probably correspond
to shear zones or kink folds rather than to the folds
produced by folding of multilayers induced by com-
pressive stress in the models of COBBOLD et al. 1971.
This would also be indicated by the probable low an-
gle between the folded zone and the normal to the
layering. We suppose that they can be compared to a
strongly flattened analogue of kink folds from the
thinly layered metamorphosed Palaezoic limestones
of the Barrandium in Central Bohemia (fig. 10b).
The flattening or transpression (SAND~t~SON &
MARCI-tlNi 1983) in the later stage of fold formation is
reflected by the boudin formation prior to the later
F 2 fold formation (fig. 11D). These earliest boudins
are considerably stretched in the direction of the
Hercynian-thrust related shear zones and deformation 673
stretching mineral lineation and, in the Cesk~ Krum-
lov shear zone, they have the character of strongly
prolate three-axial ellipsoids (fig. 12A). The rounded
shape of the boudins is characteristic. RAMB~RG
(1955) has explained the variation in the shape from
angular or barrel-shaped to lenticular in terms of the
degree of plastic deformation experienced by the
more competent layer prior to rupture. The rounded
ends of boudins are also correlated with the degree of
ductility of the boudinaged layer (RaMsaY 1967) and
their shape is a strong argument for the lesser ducti-
lity contrast between the boudinaged layer and the
surrounding matrix. The B1 boudinage is a product
of the ls~ stage of vertical flattening in the area, pro-
bably connected with aplite injection. The lesser
ductility contrast between the boudinaged layer and
the surrounding matrix is probably influenced by a
fluid phase present in the rocks similar to the first
stages of deformation of rocks from the Varied
Group of the Su~ice - Votice area (RAJLICH & SYN~K
1984).
D2 deformational stage
The later F2 folds mostly originated in the outer
envelope of the boudins or amphibolite dykes
through the inhomogeneous flow of marbles around
them (fig. 12 and fig. 11 A,D). Their morphology
and symmetry depends on the morphology of bou-
dins and inclusions and they mostly have the charac-
teristics asymmetry of folds radiating out from a
19~13~10~5~3~1POINTS 12~10~6~3~1 P
5 ~5~ 3=-.1 P
25~20~10~5>1 P
H
190~90~50~20 ~6~1P
50~30~20~5~1 P
209
50~30~20~5~1 P
4~3~2~1 p
=
24~15~7~3~1P
Fig. 7. Orientation diagrams of structural elements in the Varied Group. A- dip lines of foliations for the whole area, B - li-
neations for the whole area, C - fold axes for the whole area, D - dip lines of foliations in the eastern part of the domain I
from the fig. 6, E- lineations in the eastern part of the domain I, F1,2 - fold axes for the eastern part of the domain I, G - axes
of boudins in the whole area, H - dip lines of foliations in the western part of the domain I, I- iineations in the westen part of
the domain I, J - orientation of tremolite crystals in the marbles (domain II, fig. 6).
674 P. RAJLICH et al.
..... /-157-TL]U..77. .... - ................ ~ -,~__ ~
loom ~ cm
i+
.................. :_"_.;:'.::: .-.T..17. Q .. >
%/
Fig. 8. Small scale structures from the (~esk~ Krumiov shear zone, a- detail of the faulted edge of the B2 boudin, b - oblique
deformation of the B2 boudin with >,en &helon<, boudinage in the thinner underlying layer due to simple shear, c- B2 bou-
dins with similar Fa interboudin folds, d - Fa buckle fold with subhorizontai fold axial plane produced by vertical flattening
in the amphibolite dyke in the limestone with partial dismembering due to the incipient boudinage, the AL 1 mineral linea-
tion is parallel to the fold axis, e - intensively folded thin calc-silicate layer intersecting the Bl-boudin and adjacent limesto-
nes, f- refolded earliest isoclinal F1 fold with ALl mineral lineation parallel to the fold axis, g- partially desintegrated, mo-
dified fold train produced by simple shear in the aplite dyke in the paragneisses, h- drag fold originated in the simple shear in
the aplite dyke in the paragneisses.
single center. The tightest folds are rather closer to
the nucleus or to the boudins, and the width of the
rotated strata segment increases with decreasing am-
plitude of the folds (fig. 9b). The morphology and
progressive shape changes correspond to the shear
folds studied by BERTH~ & BRUN (1980) from the
South Armorican shear zone. The nucleation and de-
velopment of F2 folds may be engendered by the ear-
liest B1 boudins (fig. 11A) or by earlier F1 folds. So-
metimes they form an envelope around the stretched
B1 boudine (fig. 12A) and here their formation could
be induced by the rotation of the rigid inclusion (fig.
13 in GHOSH 1975). All these observations suggest
that they originated by progressive inhomogeneous
simple shear. Some F2 fold complexes forming
slightly extended fans inside the marble strata may be
compared with the sheath folds of COB~OLD &
QUINQUIS
(1980). In the eastern part of the area the
folds with vertically reoriented foid planes were par-
tially unfolded during later deformation (fig. 14e).
The F2 folds can also occur as buckle folds folding
the calc-siIicate veins inside the larger lithons separa-
ted by the shear zones (fig. 12B and fig. 13). The de-
velopment of these folds is connected with the mu-
tual shear movement of 2 to 10 m thick lithons inside
the rock. Typical structures originated on the shear
boundary (fig. 13), indicating the amplitude and the
mutual direction of movement along the shear. The
morphology of these lithons and their boundaries
(fig. 13) correspond well to the structures described
in glaciers by HAMBReY (1977) indicating strong stret-
ching of the lithon boundaries and fold and boudin
development inside the lithons according to the
schema given by RAMSAY (1980). In the later case, the
F2 fold formation is due to lithon rotation and shea-
ring in the XY plane of the strain ellipsoid, similary
to the cases described by GuRau (1980) in the rock
mass inhomogeneously flowing in the X direction of
Hercynian-thrust related shear zones and deformation 675
r I
' I
f I
I
"~" ?
9 (
I
1 I ',
: 9 L
I
I
I
r. I
I
/:l
/ 9 I
I
***1 5'
llll
o9 I
i II [I
Fig. 9a. Visual morphological analysis of F1 folds in the dia-
gram of HUDLESTON (1973).
l .......... i
I
.......... i I
I...
I
I
i!
r
i .......... : I
)"'.. i f("'...
._ 9 i/i 9
.. , ..
I ~ [ ;
I i i 9
I.- - -
>'---- '~'--'
f,.
I [1!
.......................................... , ...... l ...! ..~
[
I "'
I "',..,
9 I!
ll:li
Fig. 9b. Visual morphological analysis of 394 F2 folds in the
diagram of HUDLESTON (1973). The arrows indicate a pro-
gressive change in the shape of the folds from the outer to
the inner envelope. The different lines deliminate the fields
of frequency of fold shapes.
the strain ellipsoid (fig. 12B). This could be one of
the mechanisms of formation of folds with axes pa-
rallel to the stretching lineation.
The F2 folds are noncylindrical and coaxial with F1
folds, forming type I interference patterns after RAM-
SaY (1967). Their morphology is complex and stron-
I
....
" m: ~: ..... '
......
, .......... :[.~ .........
I {
ifr i/i
"..
.........
"!. ',
I h i i !
J
fl"" i
I
I
t" I
I - ~"
'i I ~
i!
i i
if
I
I
"'""..,,...
J
/
i i i
I
I
Fig. 9c. Visual morpholol ical classification of the F3 folds
in the diagram of HUDLESTON (1973).
gly variable in the classification of RAMSAY (1967) or
HUDL~STON (1973) (fig. 9b). Generally, the most
complicated shapes of asymmetrical folds are found
successively in the direction from the center to the
border of the extension fan (fig. 9b).
The deformed calc-silicate veins in marbles that
sometimes cut across amphibolite boudins and the
surrounding rock, eventually filling in the opened
foliation planes during the origin of the F2 folds, are a
product of explusion of a fluid phase during this sta-
ge. The mineral lineation of amphibolites and plagio-
clases has the same azimuth and inclination as the F2
folds. It can also be assumed that the metamorphism
occured to the highest degree in this stage.
D3 deformation
The youngest stage of deformation is marked by
strong boudin formation in the rocks to which the in-
terboudin fold formation is related. The vertical
a plite dykes which intruded just before the deforma-
uon or in its final stage are folded into buckle folds
with a subhorizontal fold plane. In the thicker dykes,
mullion structures were formed at the points of con-
tact with the surrounding marbles. Inside the marble
strata, the youngest deformation produced spectacu-
lar examples of B2 boudins (fig. 14 f., fig. 15). Boudi-
naged layers often display initial rotation and ,,en
echelon,, boudinage in the sense of RAMSAY (1967),
where the asymmetric movement of the surrounding
matrix is caused by oblique pure or by simple shear.
676 P.R.AJLICH
et
al.
. . " , m . ///.~11 /" /~
................ .... ., .;ds/y
Fig 10a Typioal morphology of the earliest Fi folds inside /~~ ~
9 " " / "< ",/- ", "51YY/1
the limestone layer. /~/~ ~/~-J/'~ ~')5~/~
In some places, the segregation of lithons, with the ~///f//~/~/~\~
9 . / //// ////~ ~ /
competent inclusion or the rotation of material lines ~ ~//~/~ ~/(.~
along them, produced asymmetric overturned folds ///~'///~.5~//~ U2~ ~-}l ~'k
9 ~.////j~/~ 7//,/,,;A,\\
Upright similar cylindrical folds of unified morpho- /~S//~-(~ ~
logy originated in the subhorizontal layers (classes "//,/ 7/ ~'///
C-El) of HUDL~STON (1973), (fig. 9c). The vertical
strata with the B1 boudins were refolded to form the
zig-zag patterns of S~N~UPX~ (1983). Locally the
B2
boudins in the buckle folds display characteristic
slightly trapezoidal structures (type b in fig. 19 of
S~N~UPX~ 1983), as evidence of the moderate ducti-
lity contrast between the boudins and enclosing duc-
tile matrix (fig. 14d).
The B 2
boudin shape is more rectangular or bar-
rel-shaped compared to the B~ boudins. In this stage,
the rounded extension necks are also lacking. Thus
9 NW
\
~J
7
Fig. 10b. Example of kink folds in the shear zone in Upper
Paiaezoic limestone of Barrandium area in the Central Bo-
hemia.
there is a marked increase in the difference of the
competency between the boudinaged layers (quart-
zites and amphibolites) and the limestone matrix.
This was interpreted in terms of the absence of a fluid
phase in the stage of the development of the
B 2
bou-
dins. They were controlled both by extension and
80
cm
+ I
Fig. 11. Fold structures in the marbles of the Varied Group, A- complex pattern of superpositlon of F2 shear folds on earlier
F1 isoclinal folds and on the aplite B1 boudins (a). The thickening of the calc-silicate layers in the fold hinges is also visible. B
- the earliest F~ fold modified by
D2
and Da deformation, C - combination of a larger shear fold inside the lithon with small
shear folds on the lithon boundary. D - strongly modified F1 fold with earliest B1 quartzites boudins (q).
Hercynian-thrust related shear zones and deformation 677
G , B
A /r /
~*-z ~ ////./// o
Fig. 12. Various styles of folds with axes parallel to the X axis of the strain ellipsoid, A- folds originated through the inho-
mogeneous flow and probably also through the rotation of amphibolite inclusions, B - shear folds produced by the rotation
of lithons in the XY plane of the strain ellipsoid, a - aplite dyke.
shear fracturing, as postulate a by GAY & JAzGEt~
(1975). In the final process, a slight barelling also oc-
cured (fig. 15), with collapse of the boudin edges
along the normal faults.
The direction of the Ba boudin axes (fig. 7) is simi-
lar for the whole area and indicates uniform exten-
sion in the NW-SE direction. We assume that it cor-
responds to the continuation of the thrusting with
the vertical flattening.
Strain
analysis in the Varied
Group
The feldspar porphyroblasts containing amphibo-
lites from the CeskT~ Krumlov shear zone were cut
following the XZ and YZ planes of the strain ellip-
soid (DuNNET 1969). At the Lazec locality the strain
of feldspar porphyroblasts was measured at the
joints parallel to the main planes of the strain ellip-
soid (HossAc~ 1968). The strain Rs ratio was compu-
Fig. 13. Complex shear and fold structures in the calc-silicate and aplite dykes in the marbles originated in the processus illu-
strated in the Fig. 12.
678 P. RAJLICH et al.
Locality R• Ry~ R• a:b:c K
Dol~rkovice I 25.36 2.30 11.02 11:1:0.43 2.9
Dobrkovice II 18.3 2.44 7.51 7.5:1:0.41 2.3
Nad Vy~n)Tm 2.14 1.75 1.22 1.2:1:0.57 0.4
Dobrkovice tra~ I 2.19 2.02 1.08 1.1:1:0.5 0.1
Dobrkovice tra~ II 2.02 1.22 1.65 1.6:1:0.82 2.5
Lazec I 1.94 1.12 1.73 1.7:1:0.89 0.2
Lazec II 2.76 2.06 1.33 1.3:1:0.48 0.4
Boudins 1.8
1.15
1.45
1.5
Slavkov boudins 1.88 1.5 1.26 1.27:1:0.67 0.2
extension
D 7 %A %B %C
2.54 4.80 55.4 ~0.7 -74.2
2.2 4.04 416 -39.3 -71.8
0.6 0.78 37.8 12.7 -35.6
0.7 / 33.4 23.5 -39.1
0.5 0.72 49.5 - 9.7 -25.96
0.6 0.68 50.0 -13 -22.9
1.4 1.05 54.5 15.6 44
1.97 0.48 34.0 5.2 -29
Table I. Strain elipsoid parameters in the (2eskT~ Krumlov
ted using the method of SHIMAMOTO & IKEDA (1976),
the harmonic mean (LISLE 1977) and the R/g5 plot
(DuNNET-SIDDANS 1971). From the Rs ratios of singu-
lar planes, the strain ellipsoid of constant volume, the
K-parameter (FLINN 1962), the D-parameter (RAM-
SaY & HU~ER 1983) and the percentage stretching
along the individual ellipsoid axes was computed.
They shear strain was also computed for the X > Y>-
Z elipsoids (RAMSAY 1967, RAMSAY & GRAHAM 1970).
The strain curve was used for estimation of the duc-
tile component of the displacement on the CeskT~
Krumlov shear zone.
Two types of strain ellipsoids are revealed by the
analysis. The first group represents strongly prolate
ellipsoids with K > 2. These forms originated inside
the (2eskT? Krumlov shear zone (fig. 18) in the pro-
gressive simple shearing. The second group (locali-
ties Vy~n7~, Lazec II, Dobrkovice tral:) contains ob-
late ellipsoids with a K parameter of less than 0.4.
This ellipsoid originated during the vertical flatte-
ning of rocks before the formation of the Cesk7?
Krumlov shear zone.
The method of FEROUSON & LLOYD (1984) yielded
different values for the extension of boudin in the
X/Z plane of the strain ellipsoid (Tab. I). The youn-
ger boudinage obliquely segmented the older bou-
dins.
A large degree of extension along the axial traces of
the F 1 folds is a consequence of plastic extension
along the direction normal to the maximum shorte-
ning of the rocks. The ~/k 1/k. 2 ratio computed by
the method of GRAY & DURNEY (1979) varies between
1.6 and 0% fig. 17.
Structural style of the SW area and in the area
close to the Lhenice shear zone.
The NS Lhenice shear zone dividing the Blansk7~
Les Mrs. and Prachatice granulite bodies is characte-
Shear zone
rized in the area on the western side of the Varied
Group by the NS trending lineations and flat dipping
foliations (fig. 6). The general lack of variegated in-
tercalations lead to a general lack of fold structures.
The latter are found only in the most southwestern
part of the Varied Group. The fold axes and the mi-
neral lineations are still parallel in this region. The
biggest fold found in the outcrop in the whole Varied
Group (fig. 14c) is also located here. Its axis trends
NW-SE and it is parallel to the long axis of the ear-
liest boudins and to the mineral lineation.
Discussion
The flat dips of foliations and the NW-SE stret-
ching lineation in the whole area as well as the struc-
tural elements in the V&fnl- Lfisenice shear zone in-
dicate a thrust direction for the Varied Group from
the NW to the SE. This also corresponds to the ol-
dest ,,movement~, structures in the Blansk~7 Les Mrs.
granulites (fig. 3) indicated by the stretching of ul-
tramafic inclusions which represent after our opinion
the oldest stretching lineation.
The parallelism of all structural linear elements re-
presents the direction of the transport of the thrusted
units and was recorded for several thrust zones
(BuR~ & MATTE 1978, Bt<UNEL 1983, MATTE 1983) etc.
It was not clear whether the uniform orientation of
the F1 fold axes and the stretching lineation is due to
their simultaneous formation as was demonstrated
experimentally by WAT~INSON (1975) and by field
examples (NICOLAS & BOUDIEt< 1975, ESCHER & WAT-
TERSON 1974) or to reorientation of earlier folds simi-
lar to the field example described by BELL (1978).
Considering the important amplitude of thrust that
would be necessary to bring the granulites up from
the lower crust and stretch the ultramafic inclusions
Hercynian-thrust related shear zones and deformation 679
Fig. 14a. - shear folds in the migmatitized garnetiferous amphibolites from the contact with the Blansk~ Les Mrs. granulites.
b- sheath folds (eye) in the marbles in the (~ eskT~ Krumlov shear zone. c- large fold with axis parallel to the mineral lineation
in the amphibolitic paragneisses on the western side of the (~eskT~ Krumlov Varied Group. d - partially unfolded F1 folds in
the amphibolite dyke, e - folded layer of the B1 boundinaged amphibolite dyke, f- B 2 boudins with faulted edges and with
oblique rotation of smaller boudins. The stretching of the feldspar porphyroblasts along the X axis of the strain elipsoid in
the large boudin is also visible.
it would appear that the older folds could be reorien-
ted in the D2 deformation stage.
The three stages of deformation inferred from our
study, i.e. folding and flattening- ductile shearing-
brittle/ductile extension, indicate the development
of the thrust and heat penetration through it. The
flattening of the first stage would indicate the condi-
tions of pure shear in the central part of the thrusted
unit. The penetration of shearing into the thrust oc-
curred through segmentation of the latter into several
680 P. RAJLICH et al.
Rxy
,Dla
113
oDlb
~
~ .~176
"k- 1
o p2,uV:O, a,
[I 4 Ryz
Fig. 16. Flinn's k-graph of strain elipsoide obtained for
feldspar pophyroblasts in the amphibolites; for the loca-
tion, see fig. 18, D - Dobrkovice locality, L - Lazec locali-
ty, V - Vy~n~ locality.
units disected by the transverse NW-SE shear zones
and through the superposition of the deformation in
the regime of the progressive simple shear. The latest
stage occurred during the increase of the ductility
contrast inside the rocks is a result of the ascent of the
Central Moldanubian pluton. As stated by VAN
BREeM~N et al. (1982), processes ranging from ductile
to brittle shear brought the granulites up from the
base of the crust into the zones of retrograde to am-
phibolite and even to green-schist facies metamor-
phism. The best age estimate is considered by the au-
thors to be 341 _+ 4 Ma zircon for the early stage of
shearing and 345 + 5 Ma for the granulite facies me-
tamorphism.
The main stage of metamorphism in the rocks of
the Varied Group very probably occurred between
the D1 and D2/F2 deformational stages. This is evi-
dent from the formation of calcsilicate layers in the
4
Fig. 15. Example of the complex boudinage in the amphi-
bolite dyke in the marbles inside the (~eskT~ Krumlov shear
zone,
Hercynian-thmst related shear zones and deformation 681
~1.1-
-OB
07
\\,?,
-0.4
\
x
-03
-0.2
Fig. 17. Field of x/'k ~/~. _, ratio in the F1 folds from the Va-
ried Group.
marbles and from the oriented growth of feldspars,
tremolite etc. The beginning of this phase was ac-
companied by the intrusions of aplites. It is also
highly probable that, at this time, the granulite body
was progressively uplifted and metamorphosed toge-
ther with the surrounding rocks to the amphibolite
facies degree which was progressive for the rocks of
the Varied Group. The oldest folds recorded can
point to rather brittle behaviour of the rocks at the
beginning of the shearing and such a low ductility
would indicate the upper crustal conditions of the
deformation.
Summary and Conclusions
The various shear zones and polyphase deforma-
tion are connected with the rise of the South Bohe-
mian granulites. The most important shear zones are
that in the NE-SW direction parallel to the Main
South Bohemian Thrust, along which the lithologi-
cally differing thrust sheets were thrusted from NW
to the SE. The granulites are contained in the upper-
most thrust slice which was segmented in a later stage
by the NS and NW-SE ductile shear zones.
The CeskT~ Krumlov Varied Group lying in the
immediate contact with the granulite was affected by
polyphase deformation connected with the thru-
sting. Three main stages of deformation and fold
formation were revealed. The oldest F1 are isoclinal
2 lkm
•
D2 shear zone
/t ~ Fold axes
/7 Minepal Iineation
,7 Boudin axes
51 /// :
2~ '~-
/
/
~32.30
47' .~ I/o e ir "
o
- ~ 151~ ~////////A
---4 / -'- "'b, >
ii ~ o o
iillll
9 , '~-~
25 18~ ,25 .~_ ~,,, .'qB'_ Ol
~,
"~' ~,~'~2~ 5~ 1~=.~L--~7,3o ,, 22 ,
,
~o 37D~
~,
~ I,o
~< ",~,,o
7oFr /f
'% ~<' ' +~
22\
35 20 19 .,~.~,** -
A'
Fig. 18. The lineation and strain ellipsoid map of the Varied Group with the F shear strain profile across the NE part of the
Varied Group.
682 P. RAJLICH et al.
and strongly flattened and rounded B1 boudins ap-
peared in the last stage.
F 2
folds mostly originated in
the progressive simple shear and they were formed in
the marbles around the nuclei represented by aplite
and amphibolite boudins. The youngest stage is
marked by an increase in the viscosity contrast and
boudins with angular shape were formed. The apli-
tes, pegmatites and granite dykes began to intrude af-
ter the F1 fold formation. There is strong parallelism
between the stretching and mineral lineation and the
azimuth and plunge of the fold axes, especially in the
F 2
fold formation stage. The deformation is conside-
red to be a ductile response of rocks to the thrusting
of the Varied Group together with the BlanskT~ Les
Mts. granulites. The different velocities of the Varied
Group and granulites are reflected in the NW-SE
shear zone formation between the two units at a later
stage of the thrusting.
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