GeolCarp_Vol57_No1_47

GEOLOGICA CARPATHICA, FEBRUARY 2006, 57, 1, 47—56

www.geologicacarpathica.sk

The Savcôlô Thrust Fault (Kôrþehir, Central Anatolia):

a backthrust fault, a suture zone or a secondary fracture in

an extensional regime?

M. TEKIN YÜRÜR and YURDAL GENÇ

Hacettepe University, Department of Geological Engineering, 06532 Beytepe, Ankara, Turkey; tyurur@hacettepe.edu.tr

(Manuscript received November 30, 2004; accepted in revised form June 16, 2005)

Abstract: Large exposures of granitic and metamorphic rocks characterize the geology of Central Anatolia, in Turkey.
These basement rocks crop out mainly between the Tuz Gölü and Ecemi fault zones, two major fractures of strike-slip fault
character. During the Neogene, detachment faulting along the Tuz Gölü Fault (TGF) zone caused the deposition of several
thousand meters of sediments in the large intracontinental Tuz Gölü Basin. In the western parts of Central Anatolia and near
Kôr ehir town, another fracture zone runs almost parallel to the SE-trending TGF zone, separated from the TGF by a narrow
(

~ 30 km) and rectangular granitic belt. Along this fracture known as the Savcôlô Thrust Fault (STF), metamorphic and

plutonic rocks overthrust middle Eocene detrital rocks of the sedimentary cover along a relatively narrow (

~ 100 m)

crushing zone. In some previous works, this structure is presented as a backthrust of the Anatolian block, or a suture zone
along which two continental Central Anatolian blocks were amalgamated. Recent detailed mineral exploration studies reveal
that the area at the north of the STF comprises several low-angle normal faults along the surfaces of which the Eocene and
the underlying metamorphic rocks moved southwards until they were juxtaposed to southern granitic rocks along steeply
or moderately dipping contacts. The fault surfaces are several km long, slips of a few kilometers are clear and ductile
deformation is observed in the Eocene clastic rocks. Immediately to the north of the STF, Eocene rocks are asymmetrically
folded with a southern vergence, a displacement sense not compatible with the northerly movement observed at the STF
zone and suggesting a causal relationship between thrusting and normal faulting. A possible explanation of this extension
may be the southwards tilting of the foreland due to the northwards overthrusting and the following gravitational move-
ments. The folding style in the foreland and the very narrow width of the thrust zone, however, preclude such a crustal
loading to induce extension in the foreland. In the Savcili area where the thrust fault is observed, we do not see any evidence
to account for crustal shortening, as it should be observed in the vicinity of a major compressional structure as previously
advanced. How this thrust formed in an extensional regime and how this post-middle Eocene crustal extension is associated
with the southern Neogene Tuz Gölü Fault zone remain to be explored.

Key words: Turkey, Central Anatolia, Kôr ehir metamorphites, Savcôlô Thrust Fault, Tuz Gölü Fault, normal faulting.

Introduction

The structural features of the Anatolian block are the re-
sults of geodynamic processes that opened and closed the
Tethys Ocean in the Eastern Mediterranean. Ketin (1966)
reviewed the previous proposals of the orogenic divisions
of this part of the Tethysides. engör & Yôlmaz (1981) and

engör and co-workers ( engör et al. 1985) explained var-

ious points of the Anatolian geology. After several de-
cades of geological research that resulted in a large
number of papers (regional scale: (Ketin 1966; Brinkmann
1976; Görür et al. 1998); local scale: (Ketin 1955; Ataman
1972; Erkan 1976; Erkan & Ataman 1981; Oktay 1981;
Seymen 1981, 1982, 1984, 2000; Göncüoûlu et al. 1991;
Aydôn & Önen 1999; Whitney & Dilek 1998; Boztuû
2000; Dirik 2001; Whitney et al. 2001; Gautier et al.
2002; Güleç et al. 2002; Piper et al. 2002; Ku çu et al.
2002; Genç 2003)), the internal parts of the Anatolian
block known as Central Anatolia (Fig. 1) still remain the
structurally most poorly understood sector of Anatolian
block. Large outcrops of metamorphic and granitic rocks
characterize the geology of Central Anatolia, in particular

near Kôr ehir city (Fig. 2). The non-metamorphic cover be-
gins with the Upper Cretaceous rocks near Kôr ehir (Ketin
1955), overlain by Tertiary sediments comprising middle
Eocene sedimentary clastic rocks and carbonates, and
Neogene detrital rocks (Oktay 1981; Seymen 1982). To
the west of Kôr ehir and near Savcôlô town, the metamor-
phites tectonically overlie the Eocene rocks along a frac-
ture zone (Oktay 1981), namely the Savcôlô Thrust Fault
(STF). According to Seymen (1982, 2000), the STF is one
of the major fractures of Central Anatolia and extends for
about 150 km in a SE—NW direction. Noting that the com-
pression in Anatolia is absorbed by south-verging thrust
faults, engör & Yôlmaz (1981) interpreted the STF as a
back-thrust fault of the Anatolian interior. For Görür et al.
(1998), two crustal blocks of Central Anatolia were su-
tured along this structure.

Recent detailed mapping and field observations under-

taken for mineral exploration studies (Genç 2004; Genç &
Yürür 2004) near this structure indicate, however, a struc-
tural setting of extensional character that is highly incom-
patible with the compressional tectonic interpretations
advanced by previous workers for the area considered. In

THE SAVCILI THRUST FAULT (KIRýEHIR, CENTRAL ANATOLIA)

domain to check if both regimes could be parts of the same
tectonic phase. We think that deciphering this structural
contrast is of great importance to better understand the geo-
logical past of this part of the Anatolian Tethysides for
which the previous tectonic models are not satisfactorily
supported by field observations.

Geological setting

The Fig. 2 illustrates the geology of the area on a re-

gional scale. Near Kôr ehir, low- to high-grade metamor-
phites comprise gneissic rocks, migmatites and various
metamorphic rocks (such as mica-schists, calc-schists, mar-
bles, quartzites, etc). The depositional age of these meta-
morphites is Paleozoic (Genç 2003) whereas controversial
ages are proposed for their metamorphism. According to
Pollak (1958) and Brinkmann (1971, 1976), metamorphic
rocks are the products of a polyphased deformational his-
tory. Some workers, however, do not find any trace of pre-
Alpine movements in Central Anatolia (Ketin 1966; Erkan
1976; Seymen 1984; Whitney et al. 2001). New petrogen-
ic and radiometric data obtained from metamorphic and
plutonic rocks of Central Anatolia indicate a single-phase,
Late Cretaceous regional metamorphism related to crustal
thickening, and a later high-temperature overprint associ-

ated with magmatism, uplift and exhumation (Erkan &
Ataman 1981; Seymen 1982; Whitney & Dilek 1998;
Whitney et al. 2001). Granitic rock exposures are distrib-
uted over a large area in Central Anatolia but the largest
outcrop is located to the NE of the Tuz Gölü Fault (see
Fig. 2). In the area investigated, granites intrude the meta-
morphites as shown by the baking of these latter in con-
tact with the plutonic rocks. In the study area, the earliest
units of the sedimentary cover are nummulitic middle
Eocene clastic rocks with pebbles derived from the meta-
morphic and granitic rocks, overlain by Eocene lime-
stones. Generally poorly cemented detrital rocks of
Neogene age cover the oldest units. Metamorphic folia-
tions generally trend NW—SE, and the Eocene beds usual-
ly have gentle dips towards the south. Foliation and
bedding surfaces locally become almost vertical near the
Savcôlô Thrust Fault where the Eocene rocks are folded
and also in places where tilting occurred due to detach-
ment faulting. The Neogene strata remain subhorizontal
almost in the whole area.

Morphology

As seen in the digital elevation model (DEM) (Fig. 3),

the study area is located in a region characterized general-

Fig. 3. A – Digital elevation model (DEM) of the region showing the topography of Central Anatolia, prepared using 1:250,000 topo-
graphic maps. Artificial lighting from West with a 45

° zenith angle. The rectangle denotes the location of Fig. 4. Vertical exaggeration

is 2. EF – Ecemi Fault, KA – Kayseri, KI – Kôr ehir, NE – Nev ehir. B – Block diagram of the DEM with the same lighting and
vertical exaggeration parameters.

YÜRÜR and GENÇ

ly by a low, gentle rolling topography, with well-pro-
nounced, subparallel alignments of moderate heights
trending more or less parallel to the direction of the two
major fracture zones, the Tuz Gölü and Ecemi Faults.
Near Kayseri, the well-marked relief is due to the Quater-
nary Erciyes stratovolcano that developed along the Ece-
mi Fault. Although covered in several places by Neogene
deposits, these alignments of older rocks, in particular the
metamorphic and plutonic rocks of Central Anatolia, ap-
pear to create a large curvilinear structure with a south-
ward convexity.

In our study region, this low-relief landscape comprises

several large Quaternary depositional areas (such Tuz Gölü
Basin, Seyfe Basin). These areas represent basins bounded
by strike-slip faults ( engör 1980; engör et al. 1985).

Fig. 4 is a high-resolution DEM of the region around the

study area, prepared on the basis of 1:25,000 scale topo-
graphic maps. The DEM is displayed with a vertical exag-
geration of 2 and artificial lighting from the west, the best
direction to emphasize the structural morphology due to
shadowing. The DEM shows a generally mild topography
disturbed by the NW-SE alignment of numerous hills, like
the Aliöflez Mount. To the NE of this alignment, a terrain
much subdued in grey tones corresponds to relatively low
relief topography. This topographic texture is again ex-

Fig. 4. Digital elevation model (DEM) of the region in the vicinity of the Savcôlô Thrust Fault, shown by white line (STF), and the
Savcôlô Detachment Fault (SDF) drawn by black line. (DEM is prepared based on the digitization of 1:25,000 scale topographic maps.)
Vertical exaggeration is 2 and the artificial illumination is from West with a 45

° zenith angle. Rectangles and numbers in them represent

the locations of Figs. 5, 6, 9 and 10.

pressed far from the hilly terrain and towards the Hirfanlô
dam lake to the SW. We will see in the next sections that
this hilly alignment delineates the starting line of slices
that moved more or less southwards along detachment
faults whilst another southern lineament, sub-parallel to
this line, corresponds to the trace of the Savcôlô Thrust
Fault. Almost no topographic signature could be associat-
ed to the fault trace in the DEM.

The Savcôlô Thrust zone

The Savcôlô Thrust Fault (STF) is observed typically

near Sôddôkdede (Fig. 4) along a contact between the
northern Eocene detrital rocks and the southern metamor-
phic and magmatic rocks (Fig. 5). Along the faulted con-
tact that dips about 45°, the Eocene strata are reversed and
folded. A few hundreds of meters northerly, the Eocene de-
trital rocks are exposed in a south-vergent asymmetric
fold, a folding geometry in contradiction to the northerly
thrusting movement. The thrust zone does not affect a
zone larger than a few hundreds of meters north of which
the Eocene beddings have gentle dips. To the south of the
STF, a large area is composed of granitic rocks most of
which remain under the Hirfanlô dam lake. Further south,

YÜRÜR and GENÇ

plutonic rocks crop out again along the granitic belt that
extends up to the Tuz Gölü Fault zone (Fig. 2).

The thrust fault can also be observed on the southern

flanks of the SE-trending hills (Figs. 3, 4). One of these
topographic highs is the Aliöflez Mount, comprising at
the lowest parts wollastonite-bearing calc-silicatic
gneisses overlain by Eocene rocks that crop out in the
highest parts (Fig. 6). The surface of the southern flank of
this mount is an extensional fault that will be described
in the next section. The flank ends at a small stream
where the sedimentary and metamorphic rocks are juxta-
posed to granitic rocks along a subvertical contact. Dips
of the beddings/foliations of the sedimentary/metamor-
phic rocks gradually increase when approaching the con-
tact that appears to be an almost vertical reverse fault
along which the southern plutonic rocks overthrusted the
northern cover units. The granitic rocks of the contact
are highly fractured and have an arenitic appearance.
Near the contact and within the granites, subhorizontal
tensional fractures filled with few centimeters thick cal-
cite suggest subvertical stretching of the material associ-
ated with subhorizontal shortening.

Evidence of extensional tectonics

In the vicinity of the Savcôlô Thrust Fault (STF), exten-

sional tectonics are shown by the presence of low-angle
normal faults cropping out between the SE—NW trending
alignment of hills, such the Aliöflez Mount, at the north,
and the thrust zone, at the south. There, metamorphic rock
slices capped by Eocene rocks moved downslope and
southwards along normal faults from the highest points of
these hills, for about 2 km to end up on the thrust zone
along and south of which granitic rocks crop out (for geo-
logical map and cross-section, see Fig. 6). The Fig. 7 illus-
trates a general view of the study area in which normal and
thrust faulting are shown. In many places, varied mesoscop-
ic structures (Fig. 8) attest to the low-angle normal faulting.
Amongst them, there are faulted contacts between Eocene
limestones and Eocene clastic rocks (Fig. 8a and b), fault
surfaces traced with shear fractures bisected by groove
marks, slickenlines and elongated pebbles of the Eocene
basal conglomerates due to shearing, found in both the
Eocene and metamorphic rocks (locally calc-silicate gneiss-

es) (Fig. 8a,b,c,d,e,f and g). In the topographically highest
parts, at the ùnlidaû Mount for instance, the movements be-
tween gliding slices are accommodated by several N-trend-
ing strike-slip faults (Fig. 8d). There, the southern faces of
the Eocene rocks are extensively fractured (marked as
“stretched rocks” in Fig. 8d), possibly as a result of splitting
due to extensional forces that existed between the hanging-
wall rocks that slid and those that remained in place. On the
gently dipping detachment fault surfaces, slickenlines are
clear within Eocene rocks (Fig. 8e). At Lele Hill, normal
faulting is obvious at the summit of the hill within meta-
morphic rocks (Fig. 8i). Downwards and in metamorphic
rocks, the fault surfaces display an almost flat geometry
when viewed from afar, and in detail, the surfaces are fre-
quently cut by crescent-shaped extensional fractures with
downslope concavity, most of them dipping with high an-
gles in the same sense as the surface dips (Fig. 8h). Along
these structures, metamorphic rocks are offset for several
centimeters downslope so as to generate a step-like mor-
phology on the surface. Again in metamorphic rocks, the
transport direction is suggested by groove marks, but also
by quartzite fragments embedded in the foot-wall block sur-
face (Fig. 8g). Some elongate-shaped of these accreted ob-
jects have their long axes aligned parallel to the groove
marks but they are not associated with a channel-shaped tail
often observed along fault surfaces, an observation that is
used to better determine the shear sense. Near the STF where
the hanging-wall blocks can be observed, mylonitization
affects the Eocene strata at the bottom parts of these blocks
(see the sheared and elongated pebbles of the middle
Eocene basal conglomerates in Fig. 8b and f). Further field
observations are necessary to establish a detailed rock
stratigraphy (undeformed, mylonitic, brecciated mylonitic
zones etc.) associated with detachment faulting.

The geometry of the cross-section and kinematic mark-

ers observed suggest a general downslope tectonic trans-
port in an approximately N-S direction and towards the
south (Fig. 9).The transport is accommodated by normal
faults with steeply to moderately dipping surfaces while
the dip of the fault becomes almost horizontal in some
parts of the flank between the northern heights and the
southern STF (see Fig. 6). This geometry of this kilometric
low-angle normal fault, where the dip angle of the fault
surface decreases away from its topographically high sec-
tor, is similar to detachment faults already recognized

Fig. 7. Mosaic of photographs taken to show the Savcôlô Detachment Fault and Savcôlô Thrust Fault, in a N-S section at the western vi-
cinity of the Aliöflez Mount.

YÜRÜR and GENÇ

Fig. 9. Lower hemisphere Schmidt projection of structural data col-
lected on and near the Savcôlô Detachment Fault surfaces. Normal
and strike-slip faults and associated lineations together with kine-
matic indicators like groove marks, extensional fractures and veins,
and southward concave crescent structures suggest a NNE—SSW ex-
tension, accommodated by the displacements of hanging-wall units
from NNE towards SSW.

Fig. 10. Geological cross-section around the Karaabalô village (see Fig. 4 for its location). Vertical exaggeration is 2.

from previous studies (e.g. Harris et al. 2002). We therefore
call this structure the Savcôlô Detachment Fault.

These gravitational movements have generated a gently

rolling landscape characterized by the repetition of whit-
ish Eocene outcrops in particular near the hill alignment.
A good example can be observed near Karaabalô village
where several low-angle normal faults have generated this
morphological feature along several kilometers (Fig. 10).
Another aspect of these tectonics is the tilting of the
Eocene strata to almost vertical (Fig. 11) in the vicinity of
Ebri im village. This is likely the result of block rotations
about horizontal axes due to movements along normal
fault surfaces.

Significance and cause of thrusting

As seen in digital elevation models, the Savcôlô Thrust

Fault (STF) is associated with almost no topographic sig-
nature, and in the field, its width of not more than a hun-
dred of meters does not suggest the presence of an
important crustal structure, as it would be when consider-
ing the geotectonic role previously ascribed to this struc-
ture (e.g. Görür et al. 1998). Morphologically, the STF is
much less pronounced compared to the elements of the
surrounding extensional structures.

The field data do not allow us to propose a chronology

for the thrust and detachment faulting events in the study
area, and these events may well have occurred in different
periods. Nevertheless, the folding vergence of the foreland
units suggests that the crustal portions that moved by de-
tachment faulting were stopped against the granitic mass-
es to the south. A structural scenario in which the Eocene
rocks and their metamorphic basement rocks have moved
along detachment faults and were blocked by a southern

THE SAVCILI THRUST FAULT (KIRýEHIR, CENTRAL ANATOLIA)

Fig. 11. Geological cross-section around the Ebri im village (see Fig. 4 for its location).

granitic relief during a post-middle Eocene period is con-
ceivable since the middle Eocene clastic sedimentary
rocks comprise granitic pebbles indicating that during
Eocene deposition clastic rocks were supplied by material
from a subaerial source of granitic rocks. In the Eocene
conglomerates, the nature of the clastic material becomes
dominantly granitic when approaching the southern gra-
nitic exposures. Consequently, it may be proposed that a
regional crustal extension was accommodated by detach-
ment faults in the post-middle Eocene time, and that the
northern slices could not move further south than the gra-
nitic heights. At this point, the question is if the granitic
rocks were not affected by these extensional displace-
ments. Alternatively, thrusting may have a structural link
with the Neogene activity of the Tuz Gölü Fault (TGF), in
the SW of the study area. It may be induced due to the mi-
gration of the detachment faulting activity from the study
area towards the TGF, a phenomenon that is known from
earlier works (e.g. Lister & Davis 1989).

Crustal extension in the study area may have initiated

during the Neogene time as in the Neogene activity of the
TGF (Dhont et al. 1998; Çemen et al. 1999). On a larger
scale, this extension seems to be coeval with the Aegean
extension at the west of Turkey (Dhont et al. 1998; Koçy-
iûit et al. 1999; Bozkurt 2000; Seyitoûlu et al. 2002), a
geotectonic event generally attached to subductional pro-
cesses between the African and Eurasian plates in the East-
ern Mediterranean (e.g. Seyitoûlu & Scott 1996).

Conclusions

Field observations undertaken around the Kôr ehir city, in

Central Anatolia, suggest that the Savcôlô Thrust Fault
(STF) zone developed in an area that experienced exten-
sional tectonics accommodated by low-angle normal faults,
in the post-middle Eocene period. The vicinity and paral-
lelism of the compressional and extensional structures as

well as the geometry of the foreland folding suggest a struc-
tural causality between the gravitationally moving blocks
and the thrusting event. We interpret the STF as a secondary
structure developed on the northern flank of a granitic belt
due to the collision of this belt front with the southerly glid-
ing metamorphic and sedimentary slices. Further research
has to be concentrated to understand how this thrust formed
in the extensional regime and how this regime is associated
with the southern nearby detachment faulting event along
the Tuz Gölü Fault zone.

Acknowledgments: We are thankful to Halil Türkmen, ge-
ologist at MTA, for his help and assistance during the
field work. We also wish to express our thanks to Dušan
Plašienka and Erdin Bozkurt whose subtle suggestions
were useful to improve the paper.

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