Goncuoglu, M.C., Dirik, K. & Kozlu, H., 1997. Pre-Alpine and Alpine terranes in Turkey: Explanatory Notes to the Terrane map of Turkey. Ed: D. Papanikolaou & F.P. Sassi. IGCP Project No: 276 Final Volume: Terrane Maps and Terrane Descriptions. Annales. géol. Pays Helléniques, 37, 515-536.
PRE-ALPINE AND ALPINE
TERRANES IN TURKEY:
Explanatory notes to the
Terrane Map of Turkey
M.Cemal
GÖNCÜOGLU*, Kadir DIRIK* and Hüseyin KOZLU**
* ODTÜ,
Jeoloji Müh.Böl, Ankara.
** TPAO,
Arama Grubu, Ankara.
ABSTRACT: The Turkish orogenic collage can be divided into a number of
tectono-stratigraphic units or terranes trending in E-W direction. These units,
corresponding with various tectonic settings, such as active and passive
continental margins, arc and suture complexes, were generated as a result of
the closure of three main oceanic areas: Pan-African, Hercynian and/or
Palaeotethyan and Neotethyan. The terranes related to the Pan-African and
Hercynian and/or Palaeotethyan cycles are represented by disrupted/ metamorphosed
tectono-stratigraphic units within the alpine terranes.
In this paper, we will discuss the lithologies, tectonic settings and
assemblage of these terranes, correlate them with the adjacent areas and try to
re-organize the pre-alpine tectonic classification of Turkey.
INTRODUCTION
Turkey has been located
at the boundary between the two mega-continents: Gondwana to the south and
Laurussia to the north. It is generally accepted that during its geological
history, numerous continental fragments belonging to one of these
mega-continents were rifted off from the main body and amalgamated to the next,
so that the Anatolian realm is made of several oceanic and continental
“terranes” with different geological features. The last main orogenic event,
the alpine orogeny, related to the closure of various Neotethyan branches
directly controls the present distribution of these terranes.
In this paper we aim to
describe the Pan-African and Hercynian and/or Palaeotethyan terranes which are
represented by disrupted and metamorphosed tectonic inliers within the alpine
terranes, as well as their alpidic evolution. The classification of these
terranes will be mainly according to the alpine entities, based on published
and unpublished state-of-art data.
DESCRIPTION AND CORRELATION OF THE TURKISH TERRANES
The description of the
Turkish terranes will be mainly based on their the classification for the
alpine period, the most prominent orogenic event which controls not only the
final geographical distribution of the pre-Alpine tectonic units but also
changed their initial features. From south to north the alpine terranes are:
the Arabian Plate, the northern edge of the Gondwanean Arabian-Libyan Platform;
the SE Anatolian Ophiolite Belt, remnants of the southern branch of Neotethys;
the Tauride-Anatolide Composite Terrane, an alpine continental block; North
Anatolian Ophiolite Belt, the allochthonous oceanic assemblages of the
Neotethyan Izmir-Ankara-Erzincan Ocean; Sakarya Composite Terrane, another
alpine continental block; Intrapontide Ophiolite Belt, remnants of a small
branch of the Izmir-Ankara-Erzincan Ocean and Istranca/Istanbul Terranes,
representing the southern and active margin of the Laurussia (Figs 1, 2 and 3).
The Arabian Plate
The Arabian plate in
southeast Anatolia comprises two main alpine tectonic zones : Southeast
Anatolian Autochthone and Bitlis Zone, representing the sliced and
metamorphosed northern edge of the former.
A-
Southeast Anatolian Zone (SAZ):
This unit is the
northern promontory of the Arabian Platform, which mainly consists of a
pan-African basement and its Paleozoic-Tertiary cover.
Terrane boundaries:
SAZ is separated from the northerly located Bitlis Unit by an active thrust
zone, known as “SE Anatolian Fold and Thrust Belt”, which can be traced
south-eastward for hundreds of kms (Zagros Fold and Thrust Belt). The thrusting
in has started in Miocene.
Pre- alpine history: The pre-Cambrian metamorphic basement of SAZ
is not observed in Anatolia. A local unconformity has been reported between the
submarine lavas and pyroclastics of intermediate composition, alternating with
red epiclastics and shales of presumably Precambrian age and the Paleozoic
cover. The volcanic rocks are interpreted as products of Late Pan-African
arc-related volcanism (Şengör, 1991).
Cambrian is represented
by fluvial-deltaic type clastics at the bottom, grading into shelf type
carbonates and shallow marine clastics, which are followed by Ordovician
coastal to shallow marine clastics. During Early Silurian a regional
depositional break occurred in the region. The Late Silurian-Late Devonian
deposition began unconformably with continental clastics and restricted marine
sediments, was followed by tidal-dominated clastics and terminated with
regressive (fluvial) sediments in the central part of SE Anatolia. In the
eastern areas, however, the Ordovician clastics are overlain by coastal to
shallow marine sediments of Upper Devonian-Lower Carboniferous age (Perinçek et
al, 1991). A regional depositional break of Late Carboniferous-Early Permian
age indicates to an important uplifting event, which is very probably related
to the closure of a northerly-located Late Paleozoic oceanic basin.
Late Permian shelf-type
carbonate deposits which are transitional to Triassic shallow marine sediments,
on the other hand, indicates to the stabilization of the platform conditions in
the northern margin of Gondwanaland during Late Paleozoic.
Alpine history: The alpine
cycle in SAZ has started with the Middle Triassic rifting (Altıner, 1989) and
opening of the “Southern Branch of Neotethys (Şengör and Yılmaz, 1981)” between
Arabian and the Tauride Platforms. The deposition on SAZ up to the Early
Cretaceous is characterized by platform carbonates. During Late Cretaceous a
flip to foreland deposition and arrival of northerly-derived ophiolitic nappes
is recorded. Bi-modal volcanism (Erler, 1984), related to the opening and
southward propagation of foreland basins and deformation of foreland sediments
are further features.
Overstep sequences in
SAZ are represented by Upper Maastrichtian-Lower Miocene shallow marine
sediments. During late Lower Miocene the second set of allochthons were
emplaced onto the SAZ.
B- Bitlis Zone (BZ):
BZ consists of a large
number of northward dipping slices of metamorphic and sedimentary rocks. It
represents the northernmost edge of the Arabian Platform, which has been
deformed and metamorphosed during the closure of the Southern Branch of
Neotethys.
Terrane boundaries: BZ
is composed of post-Eocene imbricated tectonic slivers. The primary contact to
the northern terrane, SE Anatolian Ophiolite Belt, is a thrust surface. Towards
west BZ is bounded by the East Anatolian Fault, a major left-lateral
strike-slip fault.
Pre- alpine history:
The basement rocks of the BZ comprise various para-gneisses, migmatites,
amphibolites, micaschists and ortho-gneisses. Bands and lenses of kyanite
eclogites are found as minor intercalations within the gneisses (Okay et al,
1985). Petrographic data indicate to a plurifacial HT/HP event in the basement
(Göncüoğlu and Turhan, 1984). The pre-Lower Paleozoic age of the metamorphism
in the basement is clearly documented by the presence of HT/HP metamorphic clasts
in the basal micro-conglomerates of the Lower Paleozoic cover. Rb/Sr isochrone
ages about 450my from the basement (Helvaci and Griffin, 1984) confirm the
geological data. A pan-African age has been assigned to the metamorphic
basement complex.
The basement is
unconformably overlain by a Low Grade metamorphic sequence of Lower Paleozoic
age, where Givetian-Frasnian fauna could be documented in the recrystallized
limestones. This lower part of the sequence is followed by olistostromal felsic
metavolcanic/volcanoclastic rocks with blocks of recrystallized limestones and
intruded by granitoids of Carboniferous age (Göncüoğlu, 1984). Permian-Lower
Triassic platformal carbonates unconformably covers these rocks. The regional
Permian unconformity and the presence of Carboniferous granitoids strongly
suggests to a Hercynian event in BZ.
Alpine history: In BZ, the initiation of the alpine cycle is characterized by the Middle
Triassic metavolcanics and -volcanoclastics, which are related to the rifting
and opening of the “Southern Branch of Neotethys. These volcanic rocks are
conformably overlain by a condensed series, mainly consisting of metapelites
interlayered with basic metavolcanics, metacherts and metatuffs of Upper
Triassic-Lower Cretaceous age. This sequence is interpreted as the northern
slope deposits of the Arabian passive margin. Ophiolites and ophiolitic
olistostromes of Upper Cretaceous age are observed as thrust sheets on the
metamorphics. The metaclastics of the alpine cover sequence contain paragenessis
that indicate to an alpine LOW GRADE metamorphic event. This alpine overprint
is documented by geological and radiometric data (Yılmaz, 1975; Yazgan, 1984).
Overstep sequences in
BZ are represented by Middle Eocene shallow marine sediments. During the ?Lower
Miocene the BZ is imbricated and emplaced on the foreland deposits of the SAZ.
Equivalents of Bitlis
Terrane occur as metamorphic inliers within the Sanandaj-Sirjan Zone of the
Zagros Belt.
Southeast Anatolian Ophiolite Belt
The Southeast Anatolian
Ophiolite Belt is composed of different imbricated structural units
representing oceanic and island-arc assemblages of the Southern Branch of
Neotethys.
Terrane boundaries: Southeast
Anatolian Ophiolite Belt is separated from the northern Tauride-Anatolide
Terrane by pre-Maastrichtian north-verging thrusts, which were reactivated
during Late Tertiary. I-type calcalkaline plutonic bodies (Baskil Magmatic Arc,
Yazgan and Chessex, 1991) of Late Cretaceous age, created by the northward
subduction of the Southern Branch of Neotethys at the southern active margin of
the Tauride-Anatolide Platform (Malatya-Keban Metamorphics) represent the
lowermost tectonic sliver of this terrane.
Alpine history: In the
tectonic slivers with almost complete ophiolitic sequences (Guleman
Ophiolites), the relative abundance of peridotites versus lherzolites,
abundance of podiform cromites and plagiogranites and a deplated mantle
composition are the striking features indicating to a supra-subduction setting.
Further meta-ophiolitic slivers intruded by dioritic-granodioritic bodies of
Upper Cretaceous age (Kömürhan Metaophiolites; Yazgan and Chessex, 1991) and
its volcanic cover (Yüksekova Complex; Perinçek and Kozlu, 1984) are
interpreted as ensimatic arc complexes (Yılmaz, 1993). Slices of HP/LT
metamorphosed basalts are reported from the eastern part of the belt (Göncüoğlu
and Turhan, 1984). The paleontological data from the pelagic sediments of the
epi-ophiolitic rocks suggest that the age of the ophiolitic unit is
Jurassic-Upper Cretaceous.
Ophiolitic lithologies
of the Southeast Anatolian Ophiolite Belt very probably represents a variety of
supra-subduction zone type tectonic settings and can be correlated with the
Oman Ophiolites in the east.
Tauride-Anatolide Composite Terrane
Tauride-Anatolide
Composite Terrane represents the continental platform between the Neotethyan
Izmir-Ankara-Erzincan Ocean to the north and the Southern Branch of
Neotethys to the south. It comprises
three groups of structural units. From north to south these are
Kütahya-Bolkardağ Belt, representing the northern margin of the platform,
Menderes Terrane, representing the metamorphic central part and Tauride Belt, a
package of mainly non-metamorphic nappes.
A- Taurides:
Taurides or the Tauride
Belt is represented by a pre-Cambrian basement and its non-metamorphic
Paleozoic-Mesozoic cover made of platformal sediments. The Late Cretaceous
closure of the northern and southern branches of Neotethys gave way to a
double-verging napped structure, which consists of a number of
tectono-stratigraphic units with distinctive stratigraphic and structural
features characterizing different depositional environments of the platform.
Based on Özgül’s (1976) palinspatic restoration, these units are arranged from
north to south as: Bozkır Unit, Bolkar Dagı Unit, Aladag Unit, Geyikdagı Unit,
Antalya Unit and Alanya Unit.
Terrane boundaries:
The initial thrusting of ophiolitic nappes and marginal sequences onto the
Tauride platform has started duringEarly Eocene. In Mid-Miocene the entire
nappe-pile has been re-thrust on the Late Tertiary cover.
Pre- alpine history:
Limited outcrops of mildly metamorphosed Precambrian rocks are reported from
different parts of the Taurides. The relatively well-studied areas are located
in Karacahisar Dome, Sandıklı Area, Anamur-Silifke Region in Central Taurides
and Feke Area in Eastern Taurides. Karacahisar Unit is represented by strongly
deformed monotonous pelitic and psammitic rocks, which are interpreted as
distal turbidites (Kröner and Sengör, 1990). Locally, sills and dikes of
diabase and volcanoclastic intercalations are reported from the upper parts of
the unit. Early Middle Cambrian sedimentary rocks overlie the Karacahisar Unit
with a gentle unconformity. On the
basis of "partial illite recrystalization" Kröner and Sengör (1990)
suggest that the metamorphism was at very low grade. Detritial single zircon
ages and paleontological data suggests
that the age of the metamorphic/deformational event is pan-African (Kröner and
Sengör, 1990). In Sandıklı area highly sheared and mylonitized porphyroids,
unconformably covered by Early Middle Cambrian clastics and limestones yielded
xenocryst single zircon ages about 550 my which also suggests the presence of a
late pan-African igneous activity.
An almost complete
Paleozoic sequence with platform-type deposition can be well correlated with
the Southeast Anatolian Paleozoic sequences, thus indicating that Taurides and
the Southeast Anatolian Zone formed together the northern part of a huge
platform contiguous to the Gondwanaland. The absence of late Paleozoic
sediments, an important regional unconformity during Early Upper Permian and
the presence of Carboniferous pyroclastics in the northern tectonostratigraphic
units on the other hand suggests a Late Paleozoic event to the north of the
Tauride Platform. The Permian sequence represented by epicontinental carbonates
is followed in the south and north of the platform by rift related Lower-Middle
Triassic sediments and volcanics which indicate to the opening of Neotethyan
basins and thus the beginning of the alpine cycle.
Alpine history: Middle
Triassic-Lower Cretaceous time interval in the central part of the platform was
dominated by neritic carbonates, while in the northernmost margin, facing the
Izmir-Ankara-Erzincan Ocean pelagic conditions continued. During the Senonian
the oceanic basins to the south and north of the platform started to close.
Ophiolitic as well as marginal sequences were thrusted from north onto the more
external parts of the platform, the resulting crustal thickening generated a
metamorphic zone (Menderes and Kütahya-Bolkardag units) to the north of it. The
arrival of these external nappes onto the Taurides is Early Eocene.
The oldest lithologies
of the overstep sequences in the Central Taurides is Lutetian in age (Özgül,
1976). The final re-thrusting of basement nappes in Western Taurides, however,
is Middle Miocene.
The
tectono-stratigraphical units of the Tauride Belt can be well correlated with
the non-metamorphic platformal nappes (Pre-Apulian, Plattenkalk, Ionian,
Tripoliza and probably Almyropotamos Units) of the external Hellenides. A more
detailed correlation of these units is out of the scope of this outline.
The most crucial unit
of the Taurides for the correlation with the Hellenides is the Bozkır unit,
consisting of Triassic-Cretaceous pelagic sediments interlayered with basic
volcanics and slices of ophiolites, which are interpreted as oceanic
crust-starved slope-margin sequences. This unit is observed as a nappe-pile on
the platformal carbonates of the Taurides. The lithology and the structural
position of these nappes is very similar to Pindos Units, which are assumed to
be the remnants of a medial oceanic basin, between Pelagonian and the external
Hellenide Platform. Bozkır Unit, however, is interpreted as allochtonous
assemblages of the Izmir-Ankara Ocean, which have been tectonically transported
ca 300km toward south, passing on the internal platform units such as
Kütahya-Bolkardag and Menderes. So that in contrast to the western areas, and
relying only on the structural position of these oceanic units we do not
suggest an oceanic basin between Menderes/Pelagonian and Taurides/external
Hellenides.
B- Anatolides:
Anatolides represent
the metamorphic northern margin of the Tauride-Anatolide Platform, separated
from the Sakarya Composite Terrane by the Neotethyan Izmir-Ankara Suture.
Anatolides consist of two huge crystalline complexes: the Menderes Massif to
the west and the Central Anatolian Crystalline Complex to the east.
Kütahya-Bolkardag Belt represents the northern and less metamorphic peripheral
belt of the Menderes Massif and also corresponds to the allochtonous units such
as Bozkır and Bolkar Dag Unit of Özgül (1976), which are observed as nappes on
the northern flank of the Taurides.
a- Menderes Terrane
(MT): This metamorphic core-complex forms the western nuclei of the Anatolides.
Its petrographic features have been relatively well studied by various authors
(e.g. Dora et al, 1991). The Menderes Terrane comprises of a pre-Alpine
"gneissic core" and an alpine "schist and marble envelope"
where also evidences of a Late Paleozoic event is hidden.
Terrane boundaries:
The northern boundary of MT is rather a tectonic zone, where less metamorphosed
slices of Kütahya-Bolkardag unit are thrusted onto the former.
Pre- alpine history:
The core of the Menderes Terrane consists, in ascending order of migmatites,
para- and orthogneisses (leptites), amphibolites, granulites and eclogites. It
is generally accepted that the "core" of MT has experienced at least
by two progressive metamorphic events. Şengör et al. (1984b) suggest a
sedimentational age of 680my for the protoliths of the
"core"-gneisses. The first metamorphic event in the migmatized
gneisses, evidenced by a Rb/Sr whole rock isochrone age of 500my is regarded by
the same authors as the age of the pan-African high-grade metamorphism. Dora et
al (1991) confirm this data by additional Rb/Sr data. This event has probably
led to the formation of the anatectic granitoids, which yield a Rb/Sr whole rock isochron age of 470my
(Şengör et al, 1984b). Recent work (Candan,1994) suggests the presence of
relict granulitic and eclogitic metamorphisms of pan-African age in the core
series, thus suggesting a complex pan-African history.
The core is
unconformably covered by the schist unit, which starts with metaconglomerates
and consists mainly of kyanite+staurolite+garnet schists and garnet+mica
schists with minor intercalations of metaquartzites and garnet amphibolites.
Calc-schist and phyllite interlayers increase towards the top of the unit .
Based on sparse paleontological data Konak et al (1987) suggest a Paleozoic age
for this sequence. A post-pan-African/pre-alpine metamorphic event accompanied
by granite intrusions during Late Paleozoic in northern Menderes is suggested
by Şengör et al (1984b).
Alpine history: The schist
unit is conformably overlain by platform type marbles, calc-schists and
dolomitic marbles of Mesozoic age. A conformable sequence represented by thin
bedded red marbles of Paleogene age forms the uppermost part of the Unit (Dora
et al, 1991). The age of the alpine main metamorphic event (Paleocene-Late
Eocene) is documented by paleontological and geochronological data (Sengor et
al, 1984, Dora et al, 1991).
Recent work suggests
that during the Neotectonic period Menderes Unit has been effected by
extensional tectonic and represents a “core-complex” (Bozkurt et al, 1993).
Papanikolaou and
Demirtaşlı (1987) assume that correlatable units in the Hellenides are “buried
below the nappes of the blueschists and the internal Hellenides, including the
allochtonous Pelagonian basement rocks”.
b-Kütahya-Bolkadağ Belt
(KBB): This unit represents the northernmost edge of the north-facing passive
margin of the Tauride-Anatolide Platform and thus the northern periphery of the
Menderes Unit. KBB constituents two alpine subunits: a northern and
discontinuous HP/LT metamorphic belt (Tavşanlı Zone of Okay, 1985)
characterizing the subducted slope of the passive margin and KBB proper.
Terrane boundaries:
KBB is overthrusted by ophiolites of the North Anatolian Suture Belt.
Pre- alpine history:
The lower part of KBB consists of olistostromal meta-clastics (mainly
greywackes) alternating with felsic-intermediate meta-volcanics and
volcanoclastics, black slates and lydites. Olistolites of Devonian-Lower Carboniferous
neritic limestones, meta-porphyroides and microgranites are very common.
Biostratigraphic data suggests a Late Carboniferous depositional age for this
part of the sequence. Özcan et al.(1988) and Göncüoğlu (1989) attributed these
lithologies to a Hercynian back-arc deposition. The metaclastics of this
basement exhibit mineral paragenesis, which correspond to a pre-alpine Low
Grade Metamorphism. The alpine event is represented by a retrograde overprint in
the basement rocks.
This lower sequence is
paraconformably covered by micro-conglomerates and recrystallized limestones of
Early Upper Permian. Alpine history: Rift related continental
red clastics of Scytian age representing the opening of the alpine Izmir-Ankara-Erzincan
ocean and thus, the separation of the Tauride-Anatolide Platform from the
Sakarya Terrane, unconformably cover the metamorphic basement. The Middle
Triassic-Lower Cretaceous deposition is characterized by continuos
platform-type carbonates, which is followed by Upper Cretaceous pelagic
micrites and radiolarian cherts. Upper Maastrichtian is represented by a
sedimentary melange/olistostrome with huge ophiolite, blueschist and neritic
limestone blocks. Oceanic lithologies of the Izmir-Ankara Ocean are observed as
pieces of a discontinuous nappe on this melange. Upper Paleocene sediments in
KBB represent the post-tectonic cover(Göncüoğlu et al, 1992a). We suggest that
KBB was imbricated during Late Cretaceous and emplaced first onto Menderes and
subsequently as huge nappes onto the Taurides during Middle Eocene.
The stratigraphy of the Tavşanlı Zone, which lies with a low-angle
tectonic contact on the Upper Cretaceous sedimentary melange of the KBB is
similar to the latter. The well-developed HP/LT metamorphism of alpine age
(Kulaksız and Phillips, 1985) in this zone is attributed to the subduction of
the passive margin sediments prior to the collision of the Tauride-Anatolide
platform with the Sakarya Terrane (Okay, 1985).
The basement of KBB can
be correlated with the Flambouron Unit, representing the basement of the
Almopia Unit in the Internal Hellenide Platform. The stratigraphy of Almopias,
in turn is similar to the Mesozoic platform deposits of KBB.
The HP/LT Tavşanlı Zone
on the other hand can be well correlated with the Ambelakia Unit in Northern
Cyclades.
c-Central Anatolian
Crystalline Complex (CACC): This unit forms the eastern continuation of the
Anatolides. It is separated from the main trunk of the Anatolides by the
Tertiary Tuzgolu Basin.
Terrane boundaries:
CACC is bounded to the north by ophiolitic slivers of the North Anatolian
Suture Belt. Its southern boundary is covered by Tertiary sediments of Tuzgölü,
Ulukışla and Sivas Basins.
Pre- alpine history:
The lowermost unit of CACC is composed of sillimanite- cordierite bearing
gneisses, pyroxene gneisses, micaschists, amphibolites, bands and lenses of
marbles/calc-silicate marbles and migmatites. The earliest event in CACC is
represented by zircon Pb/Pb model ages and Rb/Sr whole rock isochron ages
(450my) from the gneisses of the basement (Göncüoğlu, 1982), thus suggesting a
pan-African generation.
Alpine history: A thick
quartzitic band, probably representing a pre-metamorphic transgression, is
followed by an alternation of marbles, sillimanite gneisses, amphibolites,
calc-silicate amphibolites and quartzites. The upper unit of CACC consists of a
thick sequence of marbles passing upwards into cherty marbles and finally into
cherts and amphibole schists. Correlating these carbonates with those in
Kütahya-Bolkardağ Belt, Göncüoğlu et al. (1992b) suggests a Triassic-Lower
Cretaceous age for this upper unit of the metamorphic sequence. This carbonate
sequence is transitional to an ophiolite bearing meta-olistostrome and has been
overthrusted by ophiolites. The metamorphics as well as the ophiolites are
intruded by syn/post metamorphic collision-type granitoides (Göncüoglu and
Türeli, 1994). The alpine metamorphism is supported by Rb/Sr and K/Ar mineral
ages, which range between 74 and 78my (Göncüoğlu, 1982, 1986). Non-metamorphic
Upper Maestrichtian-Paleocene clastics unconformably overlie the CACC.
It is suggested that the pre-metamorphic stratigraphy of CACC is very
well correlatable with the further Anatolide units and that CACC had been part
of the Tauride-Anatolide Platform during the alpine period. The southward
emplacement of the ophiolitic nappes and related crustal thickening during the
closure of the Izmir-Ankara-Erzincan branch of Neotethys has been the cause of
the highgrade metamorphism in CACC units. The main difference from the MT is
that the ophiolite emplacement,chrustal thickening and thus the metamorphism is
earlier than the former but coeval with the KBB. We use this data to join CACC
to the Kütahya-Bolkardag Belt.
North Anatolian Ophiolite Belt
The North Anatolian Ophiolite Belt (NAOB) represents allochthonus
assemblages of the Neotethyan Izmir-Ankara-Erzincan Ocean, which were emplaced
southward onto the Tauride-Anatolide Platform during Late Cretaceous.
Terrane boundaries: In NW Anatolia units of Sakarya Composite Terrane tectonically overlie
the ophiolites. In Central and East Anatolia, the ophiolites are thrusted along
steep basement-thrusts onto Tertiary basins.
NAOB consists of huge
bodies of almost complete ophiolitic sequences and tectonic melanges of the
accretionary complex. The ophiolites display characteristic features of
supra-subduction zone-type ophiolites (Göncüoglu and Türeli, 1993). An
incipient blueschist metamorphism is reported from the mafic volcanics (Okay,
1983). Pelagic limestones and radiolarites in the melange yield ages that range
from Upper Triassic to Late Lower Cretaceous, suggesting the creation of the
oceanic crust lasted until Late Cretaceous. This data is further confirmed by
radiometric ages (79-85my) from the gabbros. Subophiolitic metamorphic soles of
Albian-Campanian age (Önen and Hall, 1993) indicate that it initially been
consumed in an intra-oceanic subduction zone. The main subduction, however, is
beneath the Sakarya Composite Terrane giving way to the formation of the Late
Mesozoic-Tertiary Pontide Magmatic Arc.
Ophiolites of the NAOB
can be correlated with the Northern Cycladic ophiolites.
Sakarya Composite Terrane
Sakarya Composite
Terrane is an alpine unit, which is bounded by the Izmir-Ankara Suture to the
south and the Intrapontide Suture to the north. It is a 100-200km wide
east-west trending belt covering almost the entire northern Anatolia. The
pre-Jurassic basement of this composite terrane constitutes numerous tectonic
assemblages, about which quite contrasting interpretations are offered.
The pre-Jurassic
tectonic assemblages can be attributed to the following groups: Central Sakarya
Terrane, Uludağ-Kazdag Terrane, Elekdağ-Çangaldağ Terrane, Küre Terrane and
Yusufeli Terrane.
A- Uludağ -Kazdag
Terrane: Both, Kazdag and Uludağ units occur as tectonic windows in NW
Anatolia.
Kazdag Unit is located in the eastern part of
the Biga Peninsula. The gneiss, amphibolite and marble that make up the core of
the Kazdağ Mountain are studied by Bingöl et al. (1975). It includes a
metaophiolite sequence with metadunite, metaharzburgite and metagabbro (Tozlu
Metaophiolite). This metaophiolite sequence overlies a thick marble horizon and
shows the same deformation and metamorphism along with the rest of the Kazdağ
Group. The Kazdağ Group is tectonically overlain by the units of the Central
Sakarya Terrane. In the west and north it is overthrusted by the alpine ophiolitic
melange (Okay et al., 1991) of the Intrapontide Ocean. Papanikolaou and
Demirtaşlı (1987) correlate the Kazdağ Group with the Rhodope Massif, however
we prefer to correlate it with the Serbo-Macedonian Terrane, where migmatitic
gneisses and marbles of Kerdilion Unit, similar to those in Kazdağ, occur as
tectonic slivers. The metaophiolites, consequently, may have a similar tectonic
setting to those in Therma-Volvi-Gomati Complexes described by Dixon and
Dimitriadis (1984).
Uludağ Unit consists of
highgrade gneisses and amphibolites covered by marbles and cherty marbles
(Ketin, 1983). The depositional and metamorphic age is unknown. It is overthrusted by the Karakaya Complex.
Considering its thick carbonate cover, Uludag Unit can be speculatively correlated
with the Anatolide Units. The correlation with Rila-Rhodope Unit (Papanikolaou
and Demirtaşlı, 1987) in Macedonia is even more speculative and could not be
justified only by the presence of similar lithologies, described by Birk
(1970).
B-Central Sakarya
Terrane (CST): The Central Sakarya Terrane is subdivided into two variably
deformed, metamorphosed and imbricated assemblages called the Central Sakarya
“Basement” and the “Karakaya Complex”, respectively. Both of them are
unconformably overlain with a major unconformity by Liassic clastics. Views on
the structural setting, ages of deposition and metamorphism are still
controversial.
Terrane boundaries:
The southern boundary of CST is an alpine thrust. Further pre-Jurassic Terranes
are either sliced with or have been thrusted onto CST.
Pre- alpine history:
Rock units of the “Basement” are exposed as E-W trending discontinuous
tectonostratigraphic units representing a Late Paleozoic (Hercynian) orogen
(Göncüoğlu, 1989). The structurally lower part (Sogut Unit) comprises
amphibolites, ortho and paragneisses, felsic to mafic metavolcanics with rare
marble interlayers and discontinious blocks of metaophiolites. The relatively
upper unit (Inegöl Unit) however consists of metabasics, metatuffs, metaclastics
with thin pelagic metacarbonate and metaradiolarite interlayers along with
blocks of metaophiolites. Calcalkaline granitoides intruded both the Sogut and
Inegöl Units. K/Ar data on the granitoids intruding the basement (290 my,
Cogulu et al, 1965) indicates that the deposition and metamorphism of the unit
should be pre Early Permian. The depositional age is suggested as post
Devonian, however, is mainly based on regional correlation and is therefore
highly speculative. The pre-Alpine metamorphism of the Sögüt Unit corresponds
to medium-high grade (Yılmaz, 1990). The Inegöl Unit is characterized by LOW
GRADE metamorphism. Göncüoglu (1989) interpreted these basement units as
fore-arc and arc assemblages of a southward subducting late-Paleozoic ocean (Southern
Hercynian Ocean).
The Karakaya Complex,
unconformably overlying the Hercynian basement includes a thick greywacke
section with Devonian, Carboniferous and Permian limestone olistoliths,
intercalated with abundant basic lava, volcanoclastics and pelagics of Triassic
age (Bingol et al, 1975). The
metamorphism is generally in HP greenschist facies conditions, the deformation
is semi-brittle, giving a broken formation character to the unit (Kaya, 1988).
The depositional age of the Karakaya Complex is Triassic so far documented by
available paleontological data.
The deformation and accompanying
metamorphism of the Karakaya Complex is post Upper Triassic - pre Liassic.
Karakaya Complex is
interpreted by Okay et al. (1991) as Permo-Triassic intra-oceanic fore-arc
deposits, sliced with Late Paleozoic-Triassic accetionary complexes of the
Paleotethyan active margin, which was located to the south of Central Sakarya
Terrane. Şengör and Yılmaz (1981), however, suggest that Karakaya Complex has
formed as a marginal basin within the Hercynian Sakarya Microplate which was
located to the south of the southward subducting Paleotethys.
Alpine history: The
deformed units of CST are unconformably covered by continental-shallow marine
sediments of Lower Jurassic age (e.g. Altıner et al, 1991). These clastics are
discordantly succeeded by Middle to Upper Jurassic platform-type neritic
carbonates, Lower Cretaceous pelagic limestones and Upper Cretaceous
turbidites, representing the carbonate platform between the Intrapontide and
Izmir-Ankara Oceans. During Late Cretaceous ophiolites of the former were
emplaced on this platform.
The basement of CST can
be correlated with the Kerdilion and Vertiskos Units of the Serbo-Macedonian
Unit, whereas Karakaya Complex is quite similar to the units of Circum-Rhodope
Belt except that the deposition in the latter continued during Early Jurassic
(Svoula Flysch of Kockel, 1977).
C-Yusufeli Terrane: This
tectonostratigraphic unit consists of Yusufeli and Tuzluca Complexes. Yılmaz
and Şengör (1985) interpret the ultramafic-mafic assemblages and associated
sediments of Yusufeli Complex together with its epi-ophiolitic cover as the
easternmost representatives of the Küre Unit and thus as Paleotethyan
ophiolites. The late Jurassic sediments overlie the oceanic assemblage of the
Yusufeli Terrane with sharp angular unconformity (Şengör et al., 198O).
Terrane boundaries:
The boundaries of Yusufeli Complex are covered by alpine sequences.
Pre- alpine history:
Konak et al. (1991) described at least four NE-SW trending tectonic slivers
(Harsdere, Demirkent, Narlık, and Kişla Zones) with major differences in
lithology and metamorphic conditions in the Yusufeli Complex.
Harsdere Zone consists
essentially of gneisses, micaschists and migmatitic gneisses. Demirkent Zone
comprises serpantinized ultramafics, meta-gabbros, meta-diabases, amphibolites
and amphibole gneisses. Blastomylonitic granitoids and syenites intruded this
metamorphic complex, which is interpreted as an ensimatic island-arc. Narlık
Zone consists of tholeiitic volcanics
interlayered with slates, tuffs and cherts, grading upwards into black,
turbiditic sandstones and siltstones with graphite bearing slate interlayers.
Kişla Zone is represented by low-grade assemblages such as quartz -muscovite
schists and muscovite-chlorite schists.
The rock-units of the
Yusufeli Complex are correlatable with the Artvin-Bolnisi block of the South
Transcaucasian Terrane of Adamia et al (this volume). The most important
limitation, however, is that the latter is ascribed to a Variscan event,
supported by numerous radiometric data from the igneous complexes.
Tuzluca Complex at the
Iranean border is a relatively less known structural element, which consists of
a Pre-Cambrian? crystalline basement, covered by non-metamorphic Paleozoic
(Devonian-Permian) sequences. Similar lithologies are observed as allochtonous
blocks within the alpine East Anatolian Accretionary Complex and Pulur Massif.
Tuzluca Complex corresponds to the Nahcevan Block in northwestern Iran.
Alpine history: The orogenic complex of Yusufeli is
unconformably covered by Lower Jurassic terrestrial and shallow-marine
sediments that grade upwards into the arc-related volcanics and volcanoclastics
of Upper Mesozoic-Tertiary age. This alpine cover is the common overstep
sequence in the whole northern edge of the Sakarya Composite Terrane. It is
generally accepted that this magmatic event should be related to the northward
subduction of the Izmir-Ankara-Erzincan Ocean. This alpine cover can be
followed in the Adjara-Trialeti and Talesh Zones of the South Transcaucasian
Terrane (Adamia et al., this volume).
D-Elekdag-Cangaldag
Terrane: Elekdag-Çangaldag Terrane is characterized by imbricated thrust sheets
of volcanic-arc type metabasic and metafelsic rocks, metamorphic
subduction/accretion complexes and an ophiolitic basement (Çangal Dag Ophiolite
and Elekdag Ophiolite) which is made up sliced basic lavas, sheeted dykes,
mafic- and ultramafic cumulates and serpantinised peridotites (Eren, 1979;
Yılmaz, 1983; Şengör et al., 1984a; Ustaömer and Robertson, 1992). Non-metamorphic Malm clastics
unconformably seal the imbricated contacts of these tectono-stratigraphic units.
Terrane boundaries:
The Unit is overthrusted by Istanbul Terrane and tectonically overlying the
equivalents of Karakaya Complex.
Pre- alpine history:
Çangal Dag Ophiolite consists mainly of metagabbro, metadiabase,
metaspilite and occasional serpantinite bodies. Towards south Eren (1979)
reports an HP/LT assemblage. In the Çangal Dag area the ophiolites and the
overlying metavolcanics are intruded by Mid-Jurassic granitoids (Yılmaz and
Boztug, 1986) and unconformably overlain by Late Jurassic sediments indicating
a pre-Mid Jurassic age for the Çangaldag Terrane.
The immobile trace
element geochemistry of the basic volcanics within the Çangaldag Terrane
indicates a volcanic -arc type tectonic setting and thus the unit is
interpreted as remnants of a Paleotethyan ensimatic arc, that had developed on
a supra-subduction type oceanic crust (Ustaömer and Robertson, 1992).
A rather complete and
intact ophiolite is preserved in the Elekdag area at the south of Çangal Dag.
Elekdag Unit is in the form of a nappe with bands and lenses of eclogites and
overlies an ophiolitic melange along a sharp tectonic contact. The Cr/Cr+Al
ratio of the Cr-spinels of the ultramafics is >0.8 and hence suggests a
supra-subduction setting (Ustaömer and Robertson, 1992). The basal melange
complex were metamorphosed to glaucophane-bearing greenschist facies. An Upper
Carboniferous-Liassic age is suggested for the Elekdag Unit.
Elekdag-Çangaldag forms
a mosaic of various imbricated tectonostratigraphic units. Based on geochemical
data Ustaömer and Robertson (1992) suggest that the basements of the Küre and
Çangaldag Terranes are of the same origin. This correlation, however, is mainly
based on very general assumptions, affected by a large amount of uncertainty
and is completely speculative.
Alpine history: The alpine
evolution of this terrane is similar to further terranes of Sakarya Composite
Terrane, except the presence of
extensive volcanic and volcanoclastic rocks of Upper Mesozoic and
Tertiary age.
E-Küre Terrane: The
Küre Terrane is an imbricated unit, comprising slices of Early Mesozoic
clastics within a dismembered ophiolitic assemblage (Küre Ophiolite, Güner,
1980; Aydın et al., 1987; Ustaömer and Robertson, 1992). Şengör et al.(1984)
argued that the Küre Terrane represents the remnants of Paleotethys.
Terrane boundaries:
The Küre Terrane is tectonically overlain by the Istanbul Terrane. To the
south, Küre Terrane is in tectonic contact with two further subterranes of the
Sakarya Composite Terrane.
Pre- alpine history: Küre unit contains disrupted ophiolites, basic
volcanics with Cyprus-type massive sulfate deposits, deep-sea radiolarites,
turbidite sequences and flyschoidal sequences including olistostromes. Okay
(1986) suggests a Mid Triassic-Early Jurassic depositional age for the
flyschoidal sequences, which he correlates with the Karakaya Complex. Immobile
major- and trace element data on volcanic rocks indicate MORB and VAB-type
characteristics and strongly suggest that the Küre Terrane was generated in a
supra-subduction-type tectonic setting (Ustaömer and Robertson, 1992).
Pre- alpine history: The Küre Terrane is
unconformably overlain by undeformed conglomerates and sandstones of Middle
Jurassic age, passing upwards to Late Jurassic-Early Cretaceous limestones
representing the alpine platform of the Sakarya Composite Terrane. A post-Early
Cretaceous southward thrusting is reported from the Central Blacksea area
(Derman, 1993, personal communication).
Küre Terrane has been
compared with the Lipacka Flysch and the Diabase-phyllitoid Complex of the
Strandja Unit in Bulgaria (Şengör et al., 1984).
Intrapontide Ophiolite Belt
The Intrapontide
Ophiolite Belt is composed of imbricated structural units representing oceanic
assemblages generated in a northern branch of Neotethys, which is believed to
be located between the Sakarya Composite Terrane and Istranca and Istanbul
continental slivers.
Terrane boundaries: The
oceanic assemblages of the Intrapontide Ophiolite Belt are thrusted southward
onto Upper Cretaceous flyschoidal sequences of the Sakarya Composite Terrane.
To the north the ophiolites are overthrusted by the Istanbul Terrane (Goncuoglu
and Erendil, 1990)
Alpine history: Large bodies
of ultramafic and volcano-sedimentary rocks, basic lavas, radiolarian cherts
and allochtonous blocks of Jurassic-Lower Cretaceous neritic-pelagic limestones
are the main constituents of the unit Okay et al. (1991). The overstep sequence
starts with Lutetian shallow-marine
sediments.
The Intrapontide
Ophiolite Belt can be correlated with the ophiolites observed on the Lesbos
Island or with the Eastern Rhodopian Ophiolites of Papanikolaou (1989).
Istranca Terrane
Istranca Terrane is
characterized by a complex of poorly known metamorphic assemblages
unconformably overlain by Early Upper Cretaceous clastics. It represents the
eastern part of Sakar Zone in Bulgaria.
Terrane boundaries:
The terrane boundaries of the Istranca terrane is covered by the Tertiary
deposits of the Thracian Basin.
Pre- alpine history:
The metamorphic rock units in this area are described as the Istiranca Group,
which is made up of two metamorphic subunits, separated by an erosional
surface. The lower subunit consists of amphibolites and amphibole-schists with
minor intercalations of meta-pelites. The protholites of the lower subunit is
interpreted as clastics by Aydin (1974). This lower sequence is intruded by
244my old (Hercynian) granitoides with blastomylonitic textures.
The upper
subunit,unconformably overlying the amphibolites starts with
meta-conglomerates, which contain deformed clasts of the basement rocks
(Caglayan et al, 1992). Quartzo-feldspatic schists, meta-greywackes and
phyllites of ?Triassic age are the main rock-types, calc-schists and marbles
are observed as subordinate bands and lenses.
Alpine history: A thick
sequence of recrystallized fossiliferous limestones of Jurassic age
unconformably cover the metamorphics. The lower and upper subunits are intruded
by post metamorphic calcalkaline granitoids of Lower Cretaceous age. Senonian
volcanoclastites represent the non-metamorphic cover units in this area.
The pre-Triassic
basement of the Istranca Terrane in Turkey may be well correlated with the
pre-Cambrian and Hercynian basement units of the Sakar and Dervent subunits of
the Bulgarian Strandzides (Gochev and Yanev, this volume). The threefold
subdivision of the Triassic Nappes (Sub-Balkanide, Veleka and Topolovgrad
Subunits of Chatalov, 1988), related to the closure of the Paleotethys and thus
to the Cimmerides, however, has not yet been established in the Turkish part of
the terrane.
Istanbul Terrane
Istanbul Terrane
consists of a pre-Cambrian basement, unconformably covered by a well-developed
sequence, extending without any major break from Cambrian to the Upper Carboniferous. This anchi-metamorphic
Paleozoic section, representing a passive continental margin is unconformably
overlain with Lower Triassic continental clastics, which pass upwards to an
alpine-type Triassic sequence and finally unconformably covered by Upper
Cretaceous - Paleocene carbonates.
Terrane boundaries:
Istanbul Terrane is separated from the Sakarya Composite Terrane in the south
by the Intrapontide Ophiolite Belt. Okay et al. (1994) suggest that a
pre-Eocene stike-slip fault constitutes the boundary with the Istranca Terrane.
Pre- alpine history:
Limited outcrops of meta-gabbros, ortho-amphibolites and amphibole-gneisses are
reported from basement of the unit (Arpad et al, 1978). Thin horizons of
biotite gneisses and biotite - amphibole schists of para origin are observed as
thin interlayers. Blasto-mylonitic alkali-feldspar granites and
quartz-monzonites are common intrusive
constituents of the Basement Complex.
In the central part of
the Istanbul Terrane Cambro-Ordovician variegated shales and sandstones with
Trilobites and primitive Brachiopods rest with an angular unconformity on the
Basement Complex (Aydın et al, 1987). Ordovician is characterized by red
terrigenous clastics overlain by white, clean quartzites, which are followed by
Lower Silurian shales and siltstones. Devonian is represented by crinoidal and
nodular limestones with shale, silty shale and siltstone interlayers, passing
conformably into Lower Carboniferous radiolarian cherts. Most of the
Carboniferous in the south and southwest parts of the unit is represented by a
thick sequence of greywacke and shale with some lidites and cherty limestones.
In the northeast part (Zonguldak area), however, the well-known non-marine,
coal bearing units of Carboniferous are exposed. Continental clastics of
Scytian age lie unconformably over the deformed Paleozoic Sequence in western
and central parts. The easternmost outcrops of the Paleozoic sequence, are
transitional to Permo-Triassic molasse -type deposits and intruded by
granitoides of Middle Jurassic age (Yilmaz and Boztug, 1986). Şengör et al.
(1984a) has related the Carboniferous deformation of the Istanbul Terrane in
western areas to the closure of
Hercynian ocean.
Alpine history: The
pre-Alpine assemblages of Istanbul Terrane are unconformably covered by the
alpine cover sequences, which start with a well-developed alpine-type Triassic
and continue with Jurassic carbonates and Cretaceous shallow-marine clastics
and volcanoclastics.
Istanbul Terrane can be
correlated with the southern zone of the Meosian Platform and/or the Balkan
Terrane in Bulgaria.
CONCLUSIONS
Pan-African terranes in
Turkey are characterized by continental crust material intruded by collisional
to arc-type magmatics (pre-Cambrian units of Menderes and Central Anatolian
Massifs, Taurides and Southeast Anatolia) as well as ophiolitic lithologies
(basement of Istanbul Terrane).
Hercynian and/or
Palaeotethyan terranes lie mainly within the accreated terranes of northern
Turkey. In this zone Late Paleozoic platformal (Istanbul Terrane), arc-related
or oceanic (Sakarya Composite Terrane) units are imbricated with Early Mesozoic
ophiolites and island-arc volcanics (Küre, Cangal Dag-Elekdag and Yusufeli
Terranes) or rift-related sequences (Karakaya Complex).
Correlations of the
Turkish terranes with those in the adjacent areas show in general a striking
lateral continuity of the main tectonic units. The major differences,
especially with those on the western areas is mainly based on disagreements on
the geodynamic concepts or models, which may be smoothed out by the “Alpine-Himalayan Terrane Map” and the new
data accumulated within IGCP No: 276.
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Figure 1: Sketch map showing the distribution
of the alpine terranes in Turkey: 1-Cenozoic Cover, 2-Istranca Terrane,
3-Istanbul Terrane, 4-Intrapontide Ophiolite Belt, 5-Sakarya Composite Terrane;
Arabian Plate: (6-7), 6-Southeast Anatolian Zone, 7-Bitlis Zone, 8-Southeast
Anatolian Ophiolite Belt; Tauride-Anatolide Composite Terrane (9-11),
9-Taurides, 10-Menderes Terrane, 11-Kütahya-Bolkardağ Belt, 12-North Anatolian
Ophiolite Belt.
Figure 2: Accretionary diagram of Turkey with
generalized stratigraphic logs of different Alpine and Pre-alpine terranes