Relationships between the Sakarya Zone and the Ankara–Erzincan suture

30 Pages·2017·3.92 MB·English

Geol.Mag.155(2),2018, pp.506–535.(cid:2)c CambridgeUniversityPress2017 506
doi:10.1017/S0016756817000516
Relationships between the Sakarya Zone and the Ankara–Erzincan
suture (central-northern Turkey): geological and petrographic data
from the Ankara–Çankiri, Çorum and Amasya areas
∗
ENRICO PANDELI ‡†, FRANCO MARCO ELTER§, FATMA TOKSOY-KÖKSAL¶,
∗ ∗
GIANFRANCO PRINCIPI , ANDREA ORLANDO‡, GIGLIOLA VALLERI ,
∗ ∗
RICCARDO GIUSTI & LETIZIA ORTI
∗
DepartmentofEarthSciences,UniversityofFlorence,Florence,Italy
‡CNR-InstituteofGeosciencesandEarthResources,U.O.S.ofFlorence,Florence,Italy
§DISTAV,UniversityofGenoa,Genoa,Italy
¶DepartmentofGeologicalEngineering,MiddleEastTechnicalUniversity,Ankara,Turkey
(Received27September2016;accepted23May2017;firstpublishedonline29August2017)
Abstract –The study was performed in central-northern Anatolia (from Ankara to Amasya) to in-
vestigatetherelationshipsoftheSakaryaZoneunitsandtheIzmir–Ankara–Erzincansuture(IAES)
melange. It reveals that all the Sakarya Zone units are metamorphic and three main tectonostrati-
graphicunitshavebeendistinguishedforthefirsttime:theBAA(metasiliciclasticrockscappedby
metacarbonates and varicoloured phyllite), the BKC (poly-metamorphic garnet-bearing micaschist
andmetabasitewithawell-preservedrelictHP–LTamphiboleinalow-amphibolitictogreenschist-
facies framework) and the AMC (meta-arkose passing vertically to carbonate–phyllitic alternations
and,then,toathicksuccessionofprevailingacidictointermediate–basicmetavolcanitesandvolcanic-
rich metasediments). The BAA and AMC, whose metamorphic frameworks are of Cimmerian age,
underlie the Mesozoic carbonate cover sequences (e.g. t j –k ) that often show tectonic detach-
2-3, 3 1
mentsandslicing.ThepilingupoftheBAAabovetheHP–LTBKCcanbecorrelatedtothetectonic
superpositionoftwosimilarunits(i.e.theCimmerianÇangaldag˘ ComplexandtheAlpineMiddle–
UpperCretaceousDomuzdag˘ Complex,respectively)definedbypreviousauthorsinothersectorsof
theCentralPontidesfront.TheophioliticmelangegenerallyunderliestheSakaryaZone,butlocally
(e.g.SEofAmasya)tectonicallyrestsabovethelatter,probablyowingtoback-thrustingthatoccurred
duringtheTertiarysyn-collisionalshorteningsandthelaterstrike-sliptectonics.Wehypothesizethat,
also in these areas, the Sakarya Zone–IAES consists of a complex tectonic stack of different units,
belongingtodifferentpalaeogeographicdomainsandorogenicevents(CimmerianversusAlpineoro-
genies), but originated within a single long-lived (since Late Triassic to Paleocene/Eocene times),
progradingsubduction–accretionsysteminfrontoftheLaurasiancontinent.
Keywords: central-northern Turkey, Sakarya Zone, ophiolitic melange, stratigraphy, petrography-
mineralchemistry,structuralgeology
1. Introduction Parlak,Yilmaz&Boztug˘,2006).Moreover,witnesses
of high-pressure – low-temperature (HP–LT) meta-
TheAnatoliaPeninsulaisoneofthebestplacesinthe
morphismarelocallypreserved,especiallyinsomeof
worldtostudytheevolutionofoceanicTethyanbasins
the units belonging to the palaeocontinental margins
andthefollowingbirthoforogenicchains(Robertson
(see Section 5 below) (Okay, 2008; Aygül et al. 2016
et al. 2004; Okay, 2008; Göncüog˘lu, 2010; Okay &
and references therein), which are correlated to the
Whitney, 2010; Aygül et al. 2016). The disappear-
blueschist-facies Cycladic Island units of the Aegean
ance of oceanic basins is testified to by suture zones,
Sea(Oberhänslietal.1998;Régnieretal.2003;Ring
amongwhichtheIzmir–Ankara–Erzincansuturezone
etal.2007).Inthiscontext,theauthorsstudiedthere-
(IAESZ)orNorthAnatolianOphioliteBelt(NAOB)is
lationshipsbetweenthecontinentalunitsinthefrontal
wellknown(Fig.1)(S¸engör&Yilmaz,1981;S¸engör,
part of the composite terrane of the Sakarya Zone
1984;Göncüog˘lu,2010).Thesuturesaremostlymade
(SouthernPontideDomain)andtheophioliticmelange
up of ophiolitic units and melanges that locally show
inthecentralsectoroftheIAESZintheareasbetween
evidenceofregionalmetamorphismuptothemedium
AnkaraandAmasya,performinglithostratigraphicand
grade that occurred during the intra-oceanic shorten-
structural observations at the meso-scale along differ-
ing (e.g. the Cretaceous greenschist- to amphibolite-
enttransects(locationsinFig.2a,b,c,d),andanalys-
faciesrocksofthe‘metamorphicsoles’cutbygabbro
ing at least 150 samples for petrographic, microstruc-
and diabase dykes: Çelik, Delaloyle & Feraud, 2006;
turalandmineralchemistrycharacterizations.Thefirst
resultsofthestudy(basedon55selectedsamples)are
†Authorforcorrespondence:enrico.pandeli@unifi.it shown in this paper, which reveals a more complex
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Figure1. TectonicsketchofTurkeyandsurroundingregionsshowingthemajorsutures(Intra-PontideSuture,Izmir–Ankara–Erzincan Suture(IAES),InnerTaurideSuture,AssyrianSuture)and
continentalblocks(IstanbulZone,SakaryaZone,CentralAnatoliaCrystallineComplex(CACC)orKirs¸ehirblock,Anatolide–Taurideblock,ArabianPlatform)withthelocationofthestudyareas
(seeA,B1,B2andCsquaredareas);theTethyanaccretionarycomplexes(includingophioliticmelanges)andthemaincrystallinemassifsarealsodistinguished(modifiedfromOkayetal.2006).
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508 E. PANDELI AND OTHERS
Figure2. (a)GeologicalsketchmapoftheAkyurt–KalecikandAvciova–S¸abanözüareas(AinFig.1).
https://doi.org/10.1017/S0016756817000516 Published online by Cambridge University Press
TheSakaryaZoneandtheAnkara–ErzincanSuture 509
stratigraphic and structural framework with respect to
the previous geological knowledge about this part of
theSakaryaZonefront.
2. GeologicalframeworkofTurkey
Turkeyisakeyareaforreconstructingacoherentgeo-
dynamic model for the Eastern Mediterranean area.
In particular, the geological framework of the Eastern
Mediterranean is the result of a series of geodynamic
events that followed the closure of the Palaeozoic –
earliest Triassic Palaeotethys during the Late Triassic
– earliest Jurassic/Early Cretaceous Cimmerian Oro-
geny (Göncüog˘lu et al. 2004; Catlos, Huber & Shin,
2013; Okay & Nikishin, 2015; Aygül et al. 2016),
developing intra-oceanic arc, inter-arc and back-arc
areas(e.g.Rojay,1995;Genç&Tüysüz,2010).These
eventsalsoproducedthe?Permian–Triassicriftingand
oceanspreadingoftheNeotethysintheequatorialpart
ofPangaea(S¸engör,1984),whoseclosureoccurredin
the Late Triassic to Early Cretaceous/Paleocene time
interval (Okay & Göncüog˘lu, 2004; Catlos, Huber
& Shin, 2013). The spreading of the Neotethys has
been related to a single oceanic area (S¸engör, 1984;
Stampfli,Marcoux&Baud,1991),butthepresenceof
intervening marginal basins has also been speculated
(e.g. Catlos, Huber & Shin, 2013). So, the resulting
NeotethysOceanwassubdividedintovariousbranches
whichseparatedaseriesofcontinentalblocksorcom-
posite terranes (i.e. Pontides, Anatolides–Taurides,
Arabian Platform) between Gondwana and Laurasia.
Inthisframework,theAnatolianPeninsula(i.e.Anato-
lian Plate) is geologically segmented into two main
zones, from N to S, the Pontides (Strandja, ˙Istanbul
and Sakarya terranes or complexes) and Anatolides
(Menderes Massif, Central Anatolian Crystalline
Complex = CACC or Kırs¸ehir Massif) – Taurides
(Tavs¸anlı and Afyon zones, Kütahya-Bolkardag˘ Belt)
(Fig.1) (Okay, 2008; Göncüog˘lu, 2010; Aygül et al.
2016). These are separated by the main evident ophi-
olitic suture, i.e. the IAESZ, due to the northward
subduction of the northern Neotethys branch; in con-
trast, the Assyrian suture or Southern Tauride suture
zone (TSZ) divides the Taurides from the Arabian
Platform, due to the northward subduction of the
southern Neotethys branch and southward obduction
of ophiolitic units onto the Arabian Platform itself
(S¸engör & Yilmaz, 1981; S¸engör, 1984; Göncüog˘lu,
Dirik & Kozlu, 1997; Okay, Harris & Kelley, 1998;
Okay et al. 2001; Robertson et al. 2004; Okay, 2008;
Göncüog˘lu, 2010; Robertson et al. 2014; Aygül et al.
2016). The Inner Tauride suture, between the CACC
and the Tauride block, and the Intra-Pontide suture,
between the Strandja + ˙Istanbul terranes and the
Sakarya Zone, have also been defined (see Figure1,
e.g.S¸engör&Yilmaz,1981;Okay,2008;Göncüog˘lu,
Figure2. (Continued)(b)GeologicalsketchmapoftheAlaca– 2010; Göncüog˘lu et al. 2014; Marroni et al. 2014).
Aydincikarea(B1inFig.1). According to some authors (Okay & Tüysüz, 1999;
Göncüog˘lu et al. 2004; Göncüog˘lu, 2010), this lat-
ter suture is generally related to the Late Triassic
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Figure2. (Continued)(c)GeologicalsketchmapoftheareasSandSEofÇorum(B2inFig.1).
D
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TheSakaryaZoneandtheAnkara–ErzincanSuture 511
Figure2. (Continued)(d)GeologicalsketchmapoftheAmasyaarea(CinFig.1)withlocationsofthestudiedtransectsandofthe
selectedsamples(modifiedfromMTA,2002).
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512 E. PANDELI AND OTHERS
Figure2. (Continued)(e)Legendtogeologicalsketchmapsandcross-sections.
accretion of the Sakarya terrane pro parte (Variscan 2016 and references therein). These latter are not
Massifs microplate and Cimmerian Karakaya Com- onlymadeupofserpentinizedperidotitecomponents,
plex) and of the Palaeotethys oceanic area (e.g. but also include clasts up to megaolistoliths of the
Çangaldag˘ Complex, Nilüfer unit) to the Eurasian volcano-sedimentary cover sequences (e.g. basalts,
margin. This event is testified to by the Late Tri- cherts and limestones) and of minor continental
assic metamorphism in the blueschist-eclogite and carbonate rocks. Part of the Neotethys oceanic and
greenschist facies (i.e. 205–203Ma in the Karakaya continental units suffered HP–LT metamorphism dur-
Complex; 215–204Ma in the Nilüfer unit; Okay, ing the closure of the ocean during Cretaceous (e.g.
Monod&Monié,2002). the Sakarya Zone in Okay et al. 2006; Aygül et al.
The oceanic sutures are characterized by the pres- 2015, 2016) to Eocene times (western and central
enceoftypicalorunusualmid-oceanridge(MORB-), Anatolides, e.g. the Menderes Massif in Oberhänsli
ocean island basalt (OIB-) and island arc tholeiite et al. 1997; Rimmelé et al. 2003; Oberhänsli, Candan
(IAT)-type (supra-subduction zone) ophiolitic suc- &Wilke,2010;Pourteau,Candan&Oberhänsli,2010;
cessions, including serpentinized mantle and gabbros Okay,2011;Pourteauetal.2015).Accordingtosome
covered by volcano-sedimentary covers, and of pe- authors (Okay et al. 2006 and references therein),
culiar thick ophiolitic melanges (Göncüog˘lu, 2010; the Late Cretaceous–Tertiary? subduction–accretion
Bortolotti et al. 2013; Bortolotti, Chiari & Pandeli, processes onto the Sakarya margin also included the
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TheSakaryaZoneandtheAnkara–ErzincanSuture 513
Figure2. (Continued)(f)Geologicalcross-sections(locationsshowninpartsa–d).
welding of microcontinents (e.g. the Kargi micro- Miocene age). Moreover, left-lateral, strike-slip tec-
continent). During the Tertiary collisional events, the tonics characterized by transpressional faulting (e.g.
Turkey nappe stack, which is generally characterized thestillactivewell-knownNorthAnatolianFault)was
by southern vergences, reached the present geolo- also originated by the south and southwest escaping
gical setting and some back-thrusting also locally movement of the Turkish and Aegean plates with
occurred (Okay, 2008; Göncüog˘lu, 2010; Robertson respect to the northward-directed movement of the
et al. 2014). At the same time, strong magmatic Arabic plate indenter and/or by the pull effect of the
activities took place producing intrusive bodies and Hellenic subduction (S¸engör et al. 2005; Okay, 2008
volcanic products, generally of calc-alkaline affinity andreferencestherein;Göncüog˘lu,2010).
(Göncüog˘lu,2010andreferencestherein).Finally,ex-
tensional tectonics occurred in Neogene time through
3. TheSakaryaZonefrontbetweentheAnkara
low- and high-angle normal faulting producing the
andAmasyaareas
‘core complex’-like exhumation of the deep crystal-
lineunits(e.g.MenderesMassif)andthedevelopment Thisstudywasperformedinselectedareasofcentral-
of sedimentary basins (e.g. the continental basins of northern Anatolia, to the NE of Ankara (area A in
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514 E. PANDELI AND OTHERS
Figure3. Simplifiedtectonic-stratigraphiccolumns:Akyurt–Kalecik–Bozca(transects‘a’and‘b’,‘of1’and‘of2’);Avciova–Kosrelic
(transect‘c’);Aydincik–Fuadiye(transects‘d’and‘e’),Büyüksogütözü–Kogazcale(transect‘f’),SofÇorum(transect‘g’alongthe
Çorum–Alacaroad,transect‘h’alongtheKüre–Cemilbeyroad);SEofÇorum(transect‘i’atBoyacıvillage,transect‘j’atKertme–
Çayanvillages);Amasya(transects‘k’,‘l’and‘m’).
Fig.1; Akyurt – transect ‘a’, Bozca village – transect 4. Results
‘b’,Kalecik–transect‘of1’and‘of2’inFig.2a),SW
4.a. Lithostratigraphyandpetrographicdata
ofÇankırı(areaAinFig.1;Avcıova–Kösrelikvillages
– transect ‘c’ in Fig.2a), SSE and S of Alaca (area Thelithologicalandthemainpetrographicfeaturesof
B1inFig.1;Aydincik–Fuadiyevillages–transects‘d’ the studied transects in the AOM and in the Sakarya
and‘e’,Büyüksogütözü–Kogazcalevillages–transect Zone units are described below. Simplified tectono-
‘f’ in Fig.2b), S and SE of Çorum (area B2 in Fig.1; stratigraphic schemes of the studied successions from
roadÇorum–Alaca–transect‘g’,Küre–Cemilbeyvil- differentareasaregiveninFigure3.
lages – transect ‘h’, Boyacı village – transect ‘i’,
Kertme–Çayan villages – transect ‘j’ in Fig.2c), and
4.a.1. AOM(‘k2s’,‘k2µ’,‘ωδ’,‘of’and‘k2’inMTA,2002)
the northwestern part of the Tokat Massif (area C in
Fig.1; Mahmatlar village – transect ‘k’, Kayrak vil- This unit, particularly well exposed in the Kizilirmak
lage–transect‘l’,Amasyafortressroad–transect‘m’ RiverValley(Fig.4),consistsofdifferentelementsof
in Fig.2d). In these areas, the external Sakarya Zone the Mesozoic oceanic units. In the composite tran-
units crop out and overthrust the IAESZ made up of sect ‘of’ (‘of1’ and ‘of2’ in Fig.2a) to the south of
the Ankara Ophiolitic Melange (AOM). More to the Kalecik, the AOM is an overall grey to green tec-
south of the studied localities, the latter tectonically tonicmelangeshowinga‘block-in-matrix’-typefabric
overliestheCACCoftheKırs¸ehirMassifunits(S¸engör (‘k2s’inMTA,2002)anditismadeupofheterometric
& Yilmaz, 1981; Göncüog˘lu, Dirik & Kozlu, 1997; breccia with serpentinite and serpentinized peridotite
Göncüog˘lu,2010)(seeFigs1,2a). clasts, up to boulders in size (Fig.5a) embedded in a
In particular, we analysed the oceanic AOM and medium- to fine-grained, sheared, serpentinite matrix
the lower part of the continental successions of the (foliated ‘scaly’ texture in Fig.5b). In general, mat-
Sakarya Zone. According to the 1:500000 scale rixprevailsovertheclasts.Nevertheless,theophiolitic
geological map of Turkey of the Turkish Geological melange is polymictic in a few outcrops, including
Research Department of Mineral Research and Ex- also clasts of basalt, chert and rare gabbro. Metric- to
ploration General Directorate (MTA, 2002), these hectometric-sized ophiolitic olistoliths (often brecci-
latter consist of two main units including Palaeozoic– ated,i.e.‘block-block’type)arealsocommon(‘of’in
Triassic successions that lie below the Mesozoic MTA,2002)(Fig.5c).Locally,theyarealsorepresen-
carbonate platform cover sequences. In particular, tedbyportionsofthepristinestratigraphicsuccession
the Sakarya Zone units are mapped in MTA (2002) consisting of: (a) serpentinite, cross-cut by microgab-
as the sedimentary Permian–Triassic ‘pt’, composed bro dykes (Fig.5d) and by veins of chalcedony or by
of clastic and carbonate rocks, and the metamorphic Fe-rich, concretionary or fibrous calcite; (b) stratified
Upper Palaeozoic–Triassic ‘s¸’, composed of schist, pelagic Calpionella-like limestones (Fig.5e), some-
phyllite,marbleandmetabasicrocks. times with basal cherts and basalts; (c) pillow lavas
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TheSakaryaZoneandtheAnkara–ErzincanSuture 515
Figure4. (Colouronline)TheKizilirmakValleysouthofKalecik.
(rarely characterized by a pink-reddish, radiolarian- marly limestone, more or less calcareous marls and
bearing micrite matrix, Fig.5f) with locally man- marly shales. Microscopic analyses of the calcareous
ganesiferouschertsatthetop.Moreover,levelsofsed- rocks show the presence of a pelagic fossil associ-
imentary breccia with ophiolitic and reddish to pink ation (small Globigerinidae, Ticinella sp., Rotalipora
carbonate clasts (Fig.5g) or, rarely, with only ophi- sp., Rotalipora appenninica, R. cushmani and Prae-
oliticcomponents(Fig.5h)werelocallyidentified,es- globotruncana sp. and small Globotruncanidae) that
peciallywithinthechertysuccessions. pointstoanearlyLateCretaceous(Cenomanian)sed-
The AOM of the transect ‘of2’ (see Fig.2a) tec- imentation age. Similar rocks, associated with vari-
tonically overlies a stratified conglomerate, sandstone coloured shales, cherts and ophiolitic breccias, are
and shale flysch unit that is mapped as the Paleocene also present in the AOM of the tectonic window
‘pm’ in MTA (2002) and as the Upper Cretaceous in the Kösrelik village area in transect ‘c’ (area A,
‘kk’ Karadag˘ Formation + ‘ks’ Samanlik Formation Fig.2a).
and Paleocene Dizlltas¸lar Formation in MTA (2010). (5) Another huge flysch-type body, hectometric
TheseCretaceous–Paleocenesedimentsaremappedin to kilometric in size, crops out along the road
Figure2a as ‘cp’. To the east these units thrust over from Çorum to Alaca (see asterisks in transect ‘g’
the‘e’Eoceneclasticandcarbonatesuccession(MTA, in Fig.2c). This sedimentary succession was previ-
2002)thatunconformablyoverliestheCACC.The‘cp’ ously attributed to the Sakarya units (‘pt’ in MTA,
clastic unit is also tectonically below the AOM in the 2002; ‘t2t3-10s’ in MTA, 2010), but our study re-
tectonicinliercrossedbytransect‘c’westofKösrelik veals that it is an intercalation (megaolistolith or
village (e.g. Fig.2a; see also MTA, 2010). Other fea- tectonic slice) within the AOM. This flysch is not
turesoftheAOMarelistedbelow: so different to that exposed in transect ‘d’ con-
(1)Megaolistolithsortectonicslicesofserpentinite, sisting of centimetre/decimetre-thick alternations of
basaltandminorgabbrocanbelocallyfound,particu- grey limestone, marly limestone, biocalcarenites and
larlyatthetopofthemelange(Fig.5i)(e.g.thegabbro laminated quartzose greywackes with grey to grey-
and serpentinite slices at the top of transect ‘of1’; see brownish shales and marly shales (Fig.5k). A Creta-
alsoMTA,2010). ceous (Cenomanian) age has also been attributed to
(2) Shear zones, characterized by different types of thissedimentarysuccession,basedonthefossilassoci-
cataclasiteandmylonites,areoftenrecognizableatdif- ation of small Globigerinidae, Radiolaria and Pithon-
ferent levels in the melange (Fig.5j). They are more ellaovalis.
common in the upper part of the AOM and within or (6)Olistolithsofoftenmassivecarbonaterocksuc-
at the top of megaolistoliths and tectonic wedges (see cessions, consisting of grey, grey-brown to dark grey
alsostructuraldata). limestone of uncertain stratigraphic and palaeogeo-
(3) Blue amphibole was observed in foliated brec- graphic location (olistoliths from a Mesozoic carbon-
cias with elements of serpentinite and basalt at the ate platform?) are locally present in the AOM, e.g. in
contactwiththeoverlyingMesozoiccarbonatesalong thesurroundingsofBüyükhırkavillagealongtransect
transect‘h’southofÇorum(inareaB2,Fig.2c). ‘f’,SSWofAlaca(areaB1,Fig.2b).
(4) At the southern end of transect ‘d’ (Fuadiye
village in Fig.2b), the AOM includes a pluri-
decametrical/hectometrical body of a calcareous- 4.a.2. TheSakaryaZone
marlyflyschunderathickolistolithofpillowlavasand
The Sakarya Zone is made up of prevalent low-grade
cherts.Thisflyschsuccessionismadeupofalternating
metamorphic and rarely highly diagenetic units (i.e.
gradedcalcareoussandstones,impurebiocalcarenites,
the Palaeozoic–Triassic ‘pt’ and ‘s¸’ in MTA, 2002).
https://doi.org/10.1017/S0016756817000516 Published online by Cambridge University Press