Dating Subduction Events in East Anatolia, Turkey

17 Pages·2012·2.15 MB·English

Turkish Journal of Earth Sciences (Turkish J. Earth Sci.R),. VOoBl.E 2R1H, 2Ä0N12S,L pIp E. T1– A1L7.. Copyright ©TÜBİTAK
doi:10.3906/yer-1006-26 First published online 02 February 2011
Dating Subduction Events in East Anatolia, Turkey

ROLAND OBERHÄNSLI1, ROMAIN BOUSQUET1, OSMAN CANDAN2 & ARAL I. OKAY3

1
Institute of Earth- & Environmental Sciences, Potsdam University, Karl-Liebknecht-Strasse 24, 14476
Potsdam, Germany (E-mail: [email protected])
2
Dokuz Eylül University, Engineering Faculty, Department of Geological Engineering, Buca,
TR−35160 İzmir, Turkey
3
İstanbul Technical University, Eurasia Institute of Earth Sciences, Maslak, TR−34469 İstanbul, Turkey
Received 29 June 2011; revised typescript received 08 January 2011; accepted 23 January 2011
Abstract: Metamorphic studies in the cover sequences of the Bitlis complex allow the thermal evolution of the massif
to be constrained using metamorphic index minerals. Regionally distributed metamorphic index minerals such as
glaucophane, carpholite, relics of carpholite in chloritoid-bearing schists and pseudomorphs aft er aragonite in marbles
record a LT–HP evolution. Th is demonstrates that the Bitlis complex was subducted and stacked to form a nappe complex
during the closure of the Neo-Tethys. During late Cretaceous to Cenozoic evolution the Bitlis complex experienced peak
metamorphism of 1.0–1.1 GPa at 350–400°C. During the retrograde evolution temperatures remained below 460°C.
39Ar/40Ar dating of white mica in diff erent parageneses from the Bitlis complex reveals a 74–79 Ma (Campanian) date
of peak metamorphism and rapid exhumation to an almost isothermal greenschist stage at 67–70 Ma (Maastrichtian).
Th e HP Eocene fl ysch escaped the greenschist facies stage and were exhumed under very cold conditions. Th ese single
stage evolutions contrast with the multistage evolution reported further north from the Amassia-Stepanavan Suture
in Armenia. Petrological investigations and isotopic dating show that the collision of Arabia with Eurasia resulted in
an assemblage of diff erent blocks derived from the northern as well as from the southern plate and a set of subduction
zones producing HP rocks with diverse exhumation histories.
Key Words: Bitlis complex, HP metamorphism, Ar dating, geodynamic evolution of SE Anatolia, subduction history
Doğu Anadolu’da (Türkiye) Yitim Olaylarının Yaşlandırılması

Özet: Bitlis Kompleksi’nin örtü serilerinde gerçekleştirilen indeks minerallere dayalı metamorfi zma çalışması Masif’in
termal evriminin ortaya konmasını mümkün kılmıştır. İyi korunmuş glaukofan ve karfolitin yanı sıra kloritoid
içeren şistlerdeki karfolit kalıntıları ve mermerlerde aragonitten dönüşme kalsitin varlığı DS–YB koşullarındaki bir
metamorfi zmayı tanımlamaktadır. Bu bulgular, Bitlis Kompleksi’nin Neo-Tetis’in kapanması sırasında yitim zonunda
derin gömülmeye uğrayarak nap yığını yapısı kazandığını göstermektedir. Petrolojik verilere dayanarak, Geç Kretase–
Senozoyik zaman aralığında Bitlis Kompleksi’nde söz konusu metamorfi zmanın zirve koşulları 350–400°C sıcaklık
ve 1.0–1.1 GPa basınç olarak belirlenmiştir. Geri dönüşüm sürecinde ise sıcaklık 460°C nin altında kalmıştır. Farklı
parajenezlerdeki beyaz mikaların 39Ar/40Ar yöntemiyle yaşlandırılmasına dayalı olarak, Bitlis Kompleksi’ndeki
metamorfi zmanın zirve koşullarının yaşı 74–79 My (Kampaniyen) olarak belirlenmiştir. Yaklaşık eş sıcaklık koşullarında
hızlı yüzeylemeyi tanımlayan yeşilşist üzerlemesinin yaşı ise 67–70 My (Maastihtiyen) dır. YB Eosen fi lişi yeşilşist fasiyesi
üzerlemesinden kaçmış ve çok soğuk koşullarda yüzeylemiştir. Bu tek aşamalı evrimler, daha kuzeyde, Ermenistan’da
Amassia-Stepanavan kenetinde belirlenen çok evreli gelişimle uyuşmamaktadır. Petrolojik araştırmalar ve izotopik yaş
verileri, Arabistan levhası ile Avrasya’nın çarpışmasının kuzey ve güneyden türeyen farklı blokların bir araya gelmesine
neden olduğunu ve bu süreç içerisinde farklı yüzeyleme tarihçelerine sahip YB metamorfi zması kayaları türeten bir dizi
yitim zonunun geliştiğini göstermektedir.
Anahtar Sözcükler: Bitlis Kompleksi, YB Metamorfi zması, Ar yaşlandırması, GD Anadolu’nun jeodinamik evrimi,
yitim tarihçesi
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DATING SUBDUCTION EVENTS IN EAST ANATOLIA, TURKEY
Introduction the Bitlis complex were given by Horstink (1971),
Boray (1975), Hall (1976), Yılmaz (1978), Çağlayan
Th is paper reports petrological and isotopic
et al. (1984), and Sungurlu (1974).
data gathered in the context of the Middle East
Basin Evolution program MEBE sponsored by a Şengör & Yılmaz (1981) and Keskin (2003)
multinational energy consortium. Th e aim is to add proposed various geodynamic interpretations.
knowledge about the structural and thermal evolution New geophysical data on the East Anatolian
of the eastern Bitlis complex and the geodynamic plateau are interpreted as revealing an upwelling of
evolution related to the collision of Arabia with asthenospheric mantle north of the Bitlis complex
Eurasia. Göncüoğlu and co-workers previously (Zor et al. 2003; Gök et al. 2007).
mapped part of the Bitlis metamorphic complex,
between Bitlis and Muş (Göncüoğlu & Turhan 1984,
Th e Eastern Bitlis Complex
1992, 1997). A study of the lithostratigraphy and the
Alpine metamorphic evolution of the Eastern Bitlis At the eastern limits of the Bitlis complex a cross
complex revealed a high-pressure low temperature section from Van to Hakkari cuts Cretaceous and
evolution (Oberhänsli et al. 2010). In this paper Tertiary sequences. Oligo–Miocene sediments near
we report isotopic ages and the geodynamic Van exhibit neotectonic structures typical for the
consequences of high-pressure from metasediments whole region. Tertiary and recent deformation led
and mafi c metamorphic rocks from the Palaeozoic to to faulting and block tilting. Th ese Oligo–Miocene
Mesozoic sedimentary cover of the Bitlis complex. sediments overlie the eastern extensions of the Bitlis
complex and are tectonically overlain by Cretaceous
ophiolitic coloured mélange, with a serpentinitic
Geological Setting of South-Eastern Turkey
and shaly matrix containing large limestone blocks
In southeast Anatolia the Bitlis complex forms an (Yüksekova formation). To the south near the Hakkari
arcuate metamorphic belt, about 30 km wide and - Yüksekova junction, the Yüksekova formation
500 km long, rimming the Arabian Platform (Figure tectonically overlies the Eocene Hakkari complex,
1a). Along the northern front of the Arabian plate a which in turn overrides the Eocene Urse formation.
set of collisional autochthonous and allochthonous All these imbricated tectonic complexes are also
structures and units include from S to N: the Great exposed along the major thrust fault bounding the
Zap anticlinorium, the Eocene olistostromes of the Arabian platform (Figure 1a).
Hakkari complex overlain by Cretaceous mélanges of Th e lithostratigraphic sequence of the Bitlis
the Yüksekova complex, the metamorphic rocks of the complex is given in a generalised columnar section
Bitlis complex and the Quaternary volcanics north of based on Turhan and Göncüoğlu (1984) and contains
Lake Van. Th e Bitlis metamorphic complex comprises (Figure 1b) from bottom to top:
Precambrian to Cretaceous rocks and is covered by
1. Pre- to Infra-Cambrian augen gneiss with
Tertiary sediments and Quaternary volcanics in the
biotite, muscovite, amphibole; amphibolites
north, while to the south it overlies the Eocene to
and garnet-amphibolites with eclogite relics
Miocene Hakkari and Maden complexes (Baykan,
(Okay et al. 1985) and schists containing
Ziyaret and Urse formations, S of Bitlis), as well as
biotite, muscovite, garnet and amphibole,
the sediments of the northern margin of the Arabian
which are the oldest portions of the Bitlis
autochthon (e.g., Yılmaz 1993). East of the Bitlis
complex.
complex the Cretaceous Yüksekova complex overlies
the Tertiary units. An early description by Tolun 2. Devonian metaconglomerates, metaquartzites
(1953) interpreted the metamorphic rocks of the and greenschists with limestone interlayers,
Bitlis complex as forming the basement of the region. reef limestones and albite-chlorite-actinolite-
Göncüoğlu and Turhan (1984), and Kellogg (1960) chloritoid schists of probable volcanogenic
interpreted the Bitlis metamorphics as equivalents of origin unconformably overlying the
the Arabian autochthonous succession and assigned Infra-Cambrian. Th ey grade upward into
a Devonian–Upper Cretaceous depositional age to volcanoclastic sequences consisting of felsic
the metasediments. Further detailed descriptions of metavolcanics and metatuff s.
2
R. OBERHÄNSLI ET AL.
3. Both formations are intruded by a mélange is exposed with a serpentinitic matrix
metagranite. Th is metagranite is not aff ected containing blocks of gabbro, basalt, chert, limestones
by the Pre-Cambrian regional metamorphism with rudists of Arabian facies affi nity (Özer 2005), and
(Göncüoğlu 1984). Its Late Cretaceous age radiolarites. Th is area was reported as an ophiolite
(Helvacı & Griffi n 1984) is poorly constrained. with a metamorphic sole (Yılmaz 1978). Th is
unmetamorphosed mélange clearly dips southwards
4. A Lower Permian limestone formation,
consisting of recrystallized limestones below the Bitlis complex. Listwaenites (Çolakoğlu
interbedded with chloritoid schists and graphite 2009) and strongly deformed and brecciated rocks
schists unconformably overlies all three units: of both complexes, ophiolitic mélange and overlying
Pre-Cambrian crystalline basement, Devonian Bitlis metamorphics, dominate the contact. Between
metaclastics and metavolcanics as well as the Permian Bitlis marbles and the ophiolite complex
the metagranite. Th is sequence grades into a conspicuous Triassic sequence (Tütü formation)
calc-schists and thin-bedded recrystallized contains relics of carpholite fi bres. Th is clearly
limestones. indicates low-grade high-pressure metamorphism
5. On top of these thinly bedded metacarbonates and not a HT metamorphic sole. East of Gevaş
an Upper Permian sequence of coarsely bedded radiolarites of the mélange complex are in steep
recrystallized limestones with interlayers of contact with mylonitic marbles. Th ese marble-
calc-schists, metasandstones and chlorite mylonites are part of a metamorphic marble-schist
schists was deposited. sequence that typically occurs at the base of the
Triassic series. Metapelitic layers contain white
6. Triassic rocks complete the section of the
mica and chloritoid. Mafi c layers are composed of
Bitlis complex. Th ey consists of recrystallized
intercalated greenschists and blueschists containing
limestones and calc-schists grading upward
into metashales, metatuff s, metadiabases and albite, chlorite, glaucophane and epidote (Çolakoğlu
metabasalts and fi nally metaconglomerates, 2009; Oberhänsli et al. 2010). Th e schist-marble
metamudstones and shales, indicating a sequence has conformable contacts with Megalodon-
drastic change in depositional conditions. bearing Triassic massive grey marbles.
Th e Permo–Triassic formations contain
In the Çatak valley (easternmost Bitlis complex,
metaquartz porphyries. Th ey are interpreted
Figure 1a) the Palaeozoic marbles show strong
as resulting from the opening of the Tethys
cataclastic disruption and earlier ductile folding.
Ocean.
Intercalated with these Palaeozoic marbles, a
sequence of black to silvery schists with mafi c layers
Basement rocks in the central Bitlis complex occurs. In these schists (Figure 2a) Fe-Mg-carpholite
contain kyanite-eclogites within garnet-mica schists relics record subduction-related metamorphic
and gneisses (Okay et al. 1985). P-T estimates conditions. Fe,Mg-carpholite has mostly reacted to
indicate temperatures between 600 and 650°C at 1.0 form chloritoid (Figure 2b, c) and quartz, but rarely
to 2.0 GPa. Based on lithostratigraphic observations kyanite. Associated mafi c rocks contain glaucophane.
a Panafrican age was assumed for these eclogites Strongly folded Palaeozoic to Permo–Triassic marbles
(Göncüoğlu & Turhan 1997). For eclogite remnants form the southern frontal part of the Bitlis complex.
in the basement of the eastern Bitlis complex a Along the Çatak River, these marbles contain fresh
pressure of 1.9–2.4 GPa and temperature of 480– Fe-Mg-carpholite but no chloritoid (Figure 2d).
540°C was deduced (Oberhänsli et al. 2010), P-T
conditions somewhat cooler than those estimated by
Okay et al. (1985) for the Gablor mountains south of Metamorphism
Muş. As yet, no age determinations for the basement
Th e bulk of the eastern Bitlis complex, especially its
eclogites exist.
basement, is made up of garnet-biotite mica-schists
Th e NE contact of the Bitlis complex near Gevaş and biotite mica-schists with HP mineral paragenesis
(Figure 1a) is of special interest. Th ere, an ophiolitic only locally preserved. Mafi c rocks correspondingly
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DATING SUBDUCTION EVENTS IN EAST ANATOLIA, TURKEY
& r
e
u ft
424344°°° ELITHOLOGYEXPLANATIONGAVAN GÖLÜTECTONIC CONTACTVVVVVVVVVVVVVVVVVVVVVVCVANTATVANmetabasalt, metatuff, metaagglo-?VVVVVVVIS▲VVVVVVVmerate,recrystalised limestone VVS▲VVAwith shale interlayersV?IVBİTLİSR▲recrystalised limestone and T4VcalcschistV▲GevaşVM??Güzelsurecrystalized limestones with▲RV?calcschist, metasandstoneE▲V??PKozlukand chlorite schist interlayersV▲▲3.UVF▲ROVNLATTcalcschist and thin beddedNVBaykanH▲ARrecrystalised limestoneV▲IUM▲SVrecristalised limestone with2RTBaşkaleIRAN▲Echloritoid schist andV▲PVgraphite schist interbeds38°.L▲▲V?SİİRTÇatakLOCAL DISCONFORMITYVVVV+▲Vmetaquartzporphyrite, felsicVVV1▲++VVV▲VPervarimetatuffV▲V++V▲▲NarlıVVVV+albite-chlorite schist, albite-▲++-actinolite schist, chloritoide-+▲N-stilpnomelane schist++A▲+recrystalisedreefÊlimestoneI+N++Ogreenschist with recristalised ▲V++limestone lensesE▲30°40°50°D▲metaquartzite++metaconglomerate▲++C+▲HAKKARİDISCONFORMITY?▲a▲▲▲s▲++▲▲p▲40°biotite schist, muscovite schist,▲i▲▲▲YÜKSEKOVAaF▲+++▲R▲biotite-garnet schist,▲O▲nNTALTamphibole schistTHNSRU++SA▲kSeecSouthArmeniaaIaR+++laBB+▲M+++metagranite▲▲▲A+++CŞemdinlietarZaGpBitlisaAntAiclamphibolite, garnet-i+35°++neRAamphibolite with lenses and F▲+++EAÇukurcaNbands of eclogite▲Eurasia▲I++Zagros-Anatolide-Tauride & +E▲biotite-garnet gneiss,Central Iran CrystallineRAIRAKmuscovite-biotite gneiss,PAophiolitesAMamphibole-biotite gneiss,enadeintareraugen gneissSeİzmirAnkara Erzincan Suture a 50°30°40° B44°4342°°ARABIAN PLATFORMTLİS MASSIFOPHIOLITES AND MELANGESBAŞKALE COMPLEX marblesEocene Hakkari ComplexQuaternary volcanic rocksmarblesMiocene sediments Eocene Maden ComplexschistsOligo-Miocene to Quaternary sedimentsEocene sedimentsschists Eocene Urse FormationCretaceous sedimentsmain anticline of the Arabian platformschists and gneisses Mesozoic Yüksekova ComplexTriassic and Jurassic sediments blue-amphibole-bearing rocksPalaeozoic clastics and carbonatessample locations carpholite-bearing rocks31Van 75, 75 A, 76Van 29, 35, 36 et al. formation (after Oberhänsli2010).42chloritoid-bearing rocksVan 77Van 26, 27 e 1. (A) Geological map of the Eastern Bitlis complex (modifi ed aft er MTA 1: 5000000 maps Cizre and Van). (B) Lithologic column adapted from GöncüoğlTurhan (1984) Mineral distribution shows blue amphibole and carpholite in the sedimentary cover of the Bitlis complex and in the Eocene Urse formation (aOberhänsli et al. 2010).
▲ 45° 40° A Bİ ur
g
38° 37° Fi
4
R. OBERHÄNSLI ET AL.
a b
ccarph
ccarph
chl
cchhll
cchd
c d
carphh
cchd
pyr
wm
Figure 2. Rock samples showing HP minerals from the cover units of the Bitlis complex. (a) Carpholite-white mica
fi bres associated with quartz and chlorite, minute chloritoid along the quartz fi bres (north of Çatak);
(b) metapelite with chlorite and white mica; small quartz exudates contain relicts of carpholite (north
of Çatak); (c) silvery chloritoid schist with white mica (Çatak); (d) carpholite and pyrophyllite layer in
marble from the southern thrust-front of the Bitlis complex (south of Çatak, north of Narlı); wm– white
mica; pyr– pyrophyllite; carph– Fe-Mg-carpholite; chl– chlorite; chd– chloritoid.
show mainly calcic amphiboles and sodic amphiboles form chloritoid and only remained stable in quartz
are scarce. veins and nodules. Th e stable mineral assemblage is
chloritoid-white mica-quartz-chlorite, sometimes
In the metasedimentary cover of the Bitlis
associated with paragonite. A few samples contain
complex silvery metapelitic schists, intercalated with
kyanite and chloritoid; others chloritoid and epidote.
calcareous marbles, contain the assemblage chlorite-
In rare cases garnet, together with chloritoid, chlorite
white mica-quartz. A greenschist metamorphic
and white mica, is found. Th is indicates a low-
overprint is obvious at fi rst glance. However, along
pressure overprint aft er HP metamorphism. Mafi c
the frontal (S) and basal parts of the sedimentary
rocks associated with these metapelites contain sodic-
cover the assemblage Fe-Mg-carpholite-chlorite-
calcic amphibole and rare glaucophane and testify to
white mica-quartz occurs. Th is is interpreted to blueschist metamorphic conditions. Th e distribution
represent the high-pressure peak event. In rare cases of Fe-Mg-carpholite and glaucophane documents
pyrophyllite-chlorite-Fe-Mg-carpholite assemblages the extent of high-pressure low-temperature
testify prograde relicts. In internal parts of the metamorphism all over the metasedimentary part of
complex most of the Fe-Mg-carpholite reacted to the Eastern Bitlis complex.
5
DATING SUBDUCTION EVENTS IN EAST ANATOLIA, TURKEY
Representative compositions of metamorphic similar rock-types and PT conditions (Crete: Th eye et
minerals of the Bitlis complex are compiled in Table al. 1992; Oman: Vidal & Th eye 1996, Alps: Bousquet
1. Electron microprobe analyses using natural and et al. 2002). Multiequilibrium calculations (Vidal
synthetic mineral standards at standard conditions et al. 1999; Vidal & Parra 2000; Parra et al. 2002;
(15 kV, 20 nA) were performed on Cameca SX 100 at Rimmelé et al. 2005) using end members of chlorite
GFZ Potsdam, at CAMPARIS Paris VI and on JEOL (clinochlore, daphnite, sudoite, amesite) and white
5800 at Potsdam University. mica (celadonite, pyrophyllite, muscovite) produced
Glaucophane in metabasites and Fe-Mg- P-T conditions indicating pressure at 0.8 –1.0 GPa
carpholite in metapelites can be used to estimate the and temperature at 320°C for the prograde relicts
P-T conditions (e.g., Oberhänsli et al. 1995, 2001). (pyr-car), pressure at 1.0–1.1 GPa and temperature
Fe-Mg-carpholite has homogeneous compositions at 350–400°C for peak conditions (car-chl-wm)
(X = 0.65–0.70 in marbles; X = 0.33–0.50 in and temperature at 370–460°C at lower pressure at
Mg Mg
metapelites). Chloritoid always has signifi cantly 0.3–0.6 GPa for the retrograde evolution (chd-chl-
lower X (0.05–0.35). Values of 8 are found for Fe- wm-ky) (Oberhänsli et al. 2010) (Figure 3). Th e Bitlis
Mg
Mg partitioning coeffi cients of carpholite/chloritoid. complex reveals a cold thermal evolution with a
Th is corresponds to values reported elsewhere for quasi-isothermal decompression.
Table 1. Representative electron microprobe analyses of HP-LT minerals from a metasediment sample of the Bitlis complex.
Van 36 chl wm chd gt car
SiO 24.24 25.55 46.98 46.98 24.65 24.76 36.72 37.49 39.35 39.32
2
TiO 0.04 0.07 0.11 0.11 0.02 0.04 0.15 0.00 0.00 0.00
2
AlO 23.47 21.70 35.84 35.84 41.54 41.61 21.16 21.37 32.29 32.36
2 3
FeO 26.46 26.52 1.73 1.73 23.99 25.27 33.78 35.73 7.29 7.70
MnO 0.17 0.08 0.00 0.00 0.00 0.01 3.08 0.00 0.14 0.10
MgO 13.58 14.73 0.65 0.65 2.84 3.07 0.73 2.07 8.78 8.80
CaO 0.00 0.00 0.00 0.00 0.00 0.00 6.08 4.91 0.00 0.00
NaO 0.01 0.04 1.36 1.36 0.02 0.01 0.01 0.01 0.00 0.00
2
KO 0.01 0.00 9.26 9.26 0.00 0.02 0.02 0.00 0.00 0.00
2
F 0.02 0.17 0.00 0.00 0.00 0.00 0.00 0.00 2.45 1.80
Sum 87.99 88.85 95.93 95.93 93.06 94.77 101.74 101.58 90.30 90.07

cat p.f.u. 14 14 11 11 6 6 12 12 8 8
Si 2.56 2.67 3.09 3.09 2.02 1.99 2.95 2.98 2.03 2.02
Ti 0.00 0.01 0.01 0.01 0.00 0.00 0.01 0.00 0.00 0.00
Al 2.92 2.68 2.78 2.78 4.01 3.93 2.00 2.00 1.99 1.98
Fe 2.34 2.32 0.10 0.10 0.00 0.07 2.27 2.37 0.32 0.33
Mn 0.01 0.01 0.00 0.00 1.64 1.70 0.21 0.00 0.01 0.00
Mg 2.14 2.30 0.06 0.06 0.00 0.00 0.09 0.25 0.68 0.68
Ca 0.00 0.00 0.00 0.00 0.35 0.37 0.52 0.42 0.00 0.00
Na 0.00 0.01 0.17 0.17 0.00 0.00 0.00 0.00 0.00 0.00
K 0.00 0.00 0.78 0.78 0.00 0.00 0.00 0.00 0.00 0.00
F 0.02 0.11 0.00 0.00 0.00 0.00 0.00 0.00 0.41 0.29
6
R. OBERHÄNSLI ET AL.
120 10 120 10
100 69.572 ± 0.184 Ma 100 69.086 ± 0.198 Ma
a)80 a)80
M K M K
e (60 5a/ e (60 5a/
Ag40 C Ag40 C
Total gas age: VAN 26 Total gas age: VAN 27
20 67.523± 0.151 Ma 20 67.977± 0.308 Ma
0 0 0 0
0 20 40 60 80 100 0 20 40 60 80 100
39Ar released (cumulative %) 39Ar released (cumulative %)
120 10 120 10
100 68.566 ± 0.882 Ma 100 67.296 ± 0.5182 Ma
Ma)80 K Ma)80 K
e (60 5a/ e (60 5a/
Ag40 C Ag40 C
Total gas age: VAN 29 Total gas age: VAN 36
20 68.201 ± 1.280 Ma 20 67.977 ± 0.747 Ma
0 0 0 0
0 20 40 60 80 100 0 20 40 60 80 100
39Ar released (cumulative %) 39Ar released (cumulative %)
120 10 120 10
74.423 ± 2.983 Ma
100 74.473 ± 1.479 Ma 100
Ma)80 Ma)80
e (60 5 e (60 5
g g
A A
40 40
Total gas age: Total gas age:
VAN 75
VAN 75A
20 73.298 ± 1.978 Ma 20 72.687 ± 3.404 Ma
0 0 0 00
0 20 40 60 80 100 0 20 40 60 80 100
39Ar released (cumulative %) 39Ar released (cumulative %)
120 10 120 10
100 75.878 ± 0.280 Ma 100 78.812 ± 0.231 Ma
Age (Ma)6800 5Ca/KAge (Ma)6800 5Ca/K
40 Total gas age: 40 Total gas age:
VAN 76 VAN 77
20 75.287 ± 0.348 Ma 20 78.361 ± 0.193 Ma
0 0 0 0
0 20 40 60 80 100 0 20 40 60 80 100
39Ar released (cumulative %) 39Ar released (cumulative %)
Figure 3. Ar plateau ages of white mica: mica of the assemblage carpholite-chlorite-white mica (samples: VAN 75, 75A,
76, 77) records the HP peak age, while mica of the assemblage chloritoid-chlorite-white mica-kyanite (VAN
26, 27, 29, 36) records the age of retrogression to greenschist facies.
Age of Metamorphism retrogression at temperatures below 460°C, still below
the closing temperature of white mica (550–600°C,
Several white micas from carpholite-bearing
metasediments (Figure 1a) were dated by laser Villa 1998; Di Vincenzo et al. 2003) and therefore
40Ar/39Ar method. Th ese micas formed during peak it is assumed that the ages can be related to the P-T
metamorphism at temperatures below 400°C and conditions of the assemblage in which mica formed.
might have recrystallized during exhumation and White micas at peak and retrograde conditions have
7
DATING SUBDUCTION EVENTS IN EAST ANATOLIA, TURKEY
Age (±1s) Ma 55.97±1.86 67.89±0.42 69.94±0.36 69.57±0.43 69.81±0.40 70.73±0.57 70.81±0.86 Age (±1s) Ma 54.42±3.03 64.53±1.02 67.19±0.62 68.59±0.53 68.20±0.42 68.40±0.88 69.12±0.71 Age (±1s) Ma 80.20±167.73 65.81±6.64 64.65±4.32 66.18±2.36 67.82±1.99 69.39±2.09 69.13±2.39
1
4039Ar*/ArK 18.96±0.63 23.08±0.11 23.78±0.08 23.66±0.12 23.74±0.10 24.06±0.17 24.09±0.28 4039Ar*/ArK 18.37±1.04 21.85±0.34 22.76±0.19 23.25±0.16 23.11±0.11 23.18±0.29 23.43±0.23 4039Ar*/ArK 62.90±61.52 22.25±2.28 21.85±1.49 22.37±0.81 22.94±0.68 23.48±0.71 23.39±0.82
39Ar K 2.31 23.21 23.71 16.03 17.08 9.86 5.37 39Ar K 1.06 3.16 7.05 12.82 16.54 18.11 10.21 39Ar K 0.09 2.13 3.67 6.31 20.84 16.66 9.40
40Ar* 49.63 93.82 98.94 98.53 99.01 98.83 100.89 40Ar* 43.06 91.05 95.19 97.37 97.28 97.91 98.75 40Ar* 4.63 26.81 69.40 84.54 93.24 95.46 94.08
plex. K/Ca 1.44 14.46 14.77 9.98 10.63 1.81 0.34 K/Ca 0.07 2.38 0.81 9.62 2.46 2.16 7.66 K/Ca 0.01 0.29 0.06 0.12 0.84 0.67 1.50
m
o
c
rom the Bitlis 3639Ar/Ar 65.27±1.50 5.16±0.08 0.88±0.04 1.22±0.13 0.82±0.12 1.11±0.22 0.03±0.31 ±0.4 Ma 3639Ar/Ar 85.16±1.43 7.37±0.44 4.21±0.20 2.16±0.10 2.29±0.07 1.80±0.93 1.03±0.11 ±0.7 Ma 3639Ar/Ar 4208.87±523 206.03±4.64 36.64±1.27 15.93±0.84 5.93±0.54 4.16±0.37 5.15±1.08 ±2.2 Ma
nts f 69.8 69.2 68.8
me e: e: e:
HP metasedi 3739Ar/Ar 0.41±2.97 0.04±0.26 0.04±0.28 0.06±0.63 0.06±0.48 0.32±0.96 1.70±1.79 Ma; Isocron ag 3739Ar/Ar 8.18±6.25 0.25±2.34 0.73±1.03 0.06±0.50 0.24±0.30 0.27±0.30 0.08±0.64 Ma; Isocron ag 3739Ar/Ar 46.58±333.60 2.04±14.14 9.86±9.27 4.87±4.80 0.70±1.83 0.88±1.94 0.39±3.83 Ma; Isocron ag
m 2 3 3
s fro 5±0. 0±0. 2±1.
4039White micaAr/Ar dating result hite mica J = 0.001662 4039Ar/Arutput (W) 38.19±0.35 24.60±0.11 24.04±0.07 24.01±0.07 23.98±0.07 24.33±0.10 23.83±0.12 e: 69.6±0.2 Ma; total gas age: 67. hite mica J = 0.001667 4039Ar/Arutput (W) 42.33±0.72 23.99±0.07 23.90±0.13 23.88±0.14 23.75±0.10 23.67±0.08 23.72±0.21 e: 69.1±0.2 Ma; total gas age: 68. hite mica J = 0.00167 4039Ar/Arutput (W) 1297.76±159 82.82±1.12 31.19±0.87 26.34±0.47 24.59±0.64 24.57±0.67 24.85±0.58 e: 68.6±0.9 Ma; total gas age: 68.
Table 2. Van 26, w Laser o 0.014 0.018 0.020 0.022 0.024 0.026 t.f. Plateau ag Van 27, w Laser o 0.014 0.016 0.018 0.020 0.022 0.024 t.f. Plateau ag Van 29, w Laser o 0.012 0.014 0.016 0.018 0.020 0.022 t.f. Plateau ag
8
R. OBERHÄNSLI ET AL.
Age (±1s) Ma 96.53±124.27 82.44±13.93 74.06±5.85 64.91±1.66 67.02±0.86 67.88±1.11 68.78±1.14 Age (±1s) Ma 1.59±1120.66 50.32±23.39 63.21±6.93 72.55±5.22 74.15±2.38 75.79±2.63 76.65±3.57 77.44±21.93 78.34±29.44 Age (±1s) Ma 52.79±30.33 62.94±9.50 72.24±6.50 74.68±4.65 74.91±6.08 77.01±12.52 75.54±10.45 76.63±31.81 82.81±48.00
2
4039Ar*/ArK32.91±43.51 28.00±4.84 25.09±2.02 21.94±0.56 22.66±0.28 22.96±0.37 23.27±0.38 4039Ar*/ArK6.82±356.18 16.02±7.55 20.20±2.25 23.25±1.70 23.77±0.77 24.31±0.86 24.59±1.16 24.85±7.19 25.14±9.66 4039Ar*/ArK16.82±9.81 20.11±3.09 23.15±2.12 23.95±1.52 24.02±1.99 24.71±4.10 24.23±3.42 24.58±10.42 26.61±15.78
39Ar K0.13 1.27 2.94 13.56 33.54 19.65 13.03 39Ar K0.06 2.77 9.33 12.39 27.35 24.76 18.19 2.95 2.20 39Ar K3.68 11.73 17.12 23.80 18.31 8.89 10.66 3.50 2.32
40Ar* 5.90 33.44 62.28 93.94 97.08 98.04 96.75 40Ar* 4.89 66.43 93.00 95.13 96.79 97.22 95.53 92.36 60.40 40Ar* 23.50 54.61 81.94 92.23 93.92 94.16 94.35 88.63 44.79
K/Ca 0.02 0.16 0.36 1.65 4.08 0.83 0.68 K/Ca 0.21 10.16 34.16 45.33 99.98 90.49 66.45 10.76 8.02 K/Ca 7.83 24.95 36.40 51.07 38.88 18.86 22.60 7.42 4.92
3639Ar/Ar 1732.57±142 189.58±9.25 52.08±2.79 4.94±0.60 2.37±0.29 1.86±0.41 3.03±0.72 ±0.7 Ma 3639Ar/Ar 448.76±28.29 27.43±0.72 5.15±0.11 4.03±0.10 2.67±0.04 2.35±0.05 3.90±0.09 6.98±0.48 55.82±1.24 7.7 Ma 3639Ar/Ar 185.37±1.59 56.58±0.56 17.27±0.18 6.83±0.13 5.26±0.10 5.20±0.20 4.92±0.14 10.71±0.53 111.03±1.97 ±7.7 Ma
0 ± 8
8. 8 3.
3739Ar/Ar 35.36±283.69 3.72±29.39 1.64±13.49 0.36±2.79 0.14±1.07 0.71±1.74 0.87±1.94 Ma; Isocron age: 6 3739Ar/Ar 2.74±2740.20 0.06±57.91 0.02±17.22 0.01±12.98 0.01±5.88 0.01±6.50 0.01±8.85 0.05±54.66 0.07±73.35 a; Isocron age: 73. 3739Ar/Ar 0.08±75.13 0.02±23.58 0.02±16.16 0.01±11.52 0.02±15.13 0.03±31.19 0.03±26.03 0.08±79.27 0.12±119.66 Ma; Isocron age: 7
7 M 4
0. 2 3.
Table 2. (Contunied). Van 36, white mica J = 0.001670 4039Ar/ArLaser output (W) 0.012539.17±41.90 0.01483.43±1.99 0.01640.23±0.60 0.01823.34±0.40 0.02023.34±0.23 0.02223.40±0.27 t.f.24.03±0.19 Plateau age: 67.3±0.5 Ma; total gas age: 67.7± Van 75, white mica J = 0.00177 4039Laser output (W) Ar/Ar 0.012139.06±6.27 0.01424.12±0.22 0.01621.72±0.03 0.01824.44±0.05 0.02024.56±0.05 0.02225.00±0.04 0.02425.74±0.03 0.02626.90±0.16 t.f.41.63±0.24 Plateau age: 74.5±1.5 Ma; total gas age: 73.3± Van 75A, white mica J = 0.00177 4039Laser output (W) Ar/Ar 0.01471.59±0.37 0.01636.83±0.10 0.01828.25±0.08 0.02025.96±0.16 0.02225.57±0.08 0.02426.24±0.09 0.02625.68±0.05 0.02827.74±0.22 t.f.59.40±0.33 Plateau age: 74.4±2.8 Ma; total gas age: 72.7±
9
DATING SUBDUCTION EVENTS IN EAST ANATOLIA, TURKEY
a a
M 1 7 4 5 4 2 9 M 9 0 2 2 5 5 2
s) 5.2 2.3 1.0 0.4 0.7 0.7 0.4 s) 2.0 1.1 0.6 0.6 0.4 0.4 0.5
1 ± ± ± ± ± ± ± 1 ± ± ± ± ± ± ±
± 7 6 6 8 6 4 4 ± 6 0 0 7 1 1 5
Age ( 62.2 70.6 74.0 75.0 75.1 77.1 76.5 Age ( 65.2 73.9 78.2 78.5 77.9 79.0 80.3

K 7 1 4 2 3 3 3 K 1 6 9 9 2 1 4
39*/Ar 5±1.7 2±0.8 8±0.3 3±0.1 6±0.2 4±0.2 3±0.1 39*/Ar 1±0.7 7±0.3 5±0.1 8±0.1 5±0.1 3±0.1 9±0.1
r 8 7 8 2 2 9 7 r 9 8 3 4 2 6 0
40A 20. 23. 24. 25. 25. 25. 25. 40A 21. 24. 26. 26. 26. 26. 27.
39Ar K 1.11 2.09 5.09 13.07 24.91 11.85 11.37 39Ar K 1.36 3.41 6.99 14.82 30.46 24.48 14.45
* 7 0 0 0 0 3 0 * 3 2 4 8 9 6 8
r 6 4 8 6 2 2 4 r 9 2 2 3 6 7 7
A 2. 8. 1. 4. 7. 8. 8. A 7. 5. 6. 8. 8. 8. 8.
40 1 7 9 9 9 9 9 40 2 8 9 9 9 9 9
K/Ca 0.13 0.26 0.41 0.97 19.15 9.11 3.04 K/Ca 0.25 0.59 6.79 14.40 16.46 3.49 7.80
3639Ar/Ar 486.18±6.516432247 23.08±1.146385174 8.15±0.476631696 5.14±0.159107786 2.47±0.127502305 1.61±0.1487715 1.50±0.199932551 Ma 3639Ar/Ar 191.98±2.29 15.03±0.54 3.52±0.29 1.49±0.14 1.19±0.07 1.20±0.10 1.16±0.12 Ma
7 6
0. 0.
± ±
0 8
39Ar/Ar 55±2.82 29±2.36 44±0.72 61±0.41 03±0.21 06±0.42 19±0.63 n age: 76. 39Ar/Ar 38±1.31 00±0.70 09±0.86 04±0.43 04±0.30 17±0.29 08±0.57 n age: 78.
37 4. 2. 1. 0. 0. 0. 0. o 37 2. 1. 0. 0. 0. 0. 0. o
r r
c c
o o
s s
I I
a; a;
684 4039Ar/Ar 163.84±1.741141542 30.19±0.745949265 27.07±0.31064942 26.66±0.097728773 25.99±0.229732194 26.41±0.21531416 26.15±0.08451482 al gas age: 75.3±0.3 M 681 4039Ar/Ar 78.28±0.44 29.16±0.34 27.38±0.12 26.91±0.17 26.60±0.11 26.96±0.10 27.43±0.12 al gas age: 78.4±0.2 M
ed). a J = 0.001 W) 0.3 Ma; tot a J = 0.001 W) 0.2 Ma; tot
Contuni hite mic output ( e: 75.9± hite mic output ( e: 78.8±
Table 2. ( Van 76, w Laser 0.014 0.016 0.018 0.02 0.022 0.024 t.f. Plateau ag Van 77, w Laser 0.014 0.016 0.018 0.020 0.022 0.024 t.f. Plateau ag
10