10_tavsanli_zone_GSL_sp_1984.pdf

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doi:10.1144/GSL.SP.1984.017.01.331984; v. 17; p. 455-466Geological Society, London, Special Publications

A. I. Okayblueschists

Distribution and characteristics of the north-west Turkish Geological Society, London, Special Publications

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D i s t r i b u t io n a n d c h a r a c t e r i s t ic s o f t h e n o r t h w e s t T u r k i s h

b l u e s c h i s t s

A . I . O k a y

SUM MA RY: Nor th-wes t Turkeyencom passes two m ajor tec ton ic un i ts , the Pont ides andthe Anatol ides, separated by the Izmir-Erzincan suture. The Anatol ides, the metamor-phosed northe rn extension of the T aurides, consist of several zones. The more southerlyAfyon Zone is an Early Palaeozoic to Maastr icht ian Tauride shelf- type sequence whichrests on gneisses of the M enderes M assif. T he A fyon Zo ne underw ent greenschist faciesmetamorphism, gradual ly increasing in grade with depth, and overthrust by HP/LTmetamorphic rocks and peridot i tes . A HP/LT metamorphic bel t several hundred ki lo-metres long const i tutes the second Anatol ide zone.There are two tectonic uni ts in theblueschist sequence. A lower m ore recrystallised blueschist unit consists of a thick basalmarb le series ov erlain by meta-cherts , metabasi tes and meta-shales. A n u pper uni t , with awider dis tr ibut ion, shows only incipient HP /LT metam orphism , and consists of shales ,radiolar ian cherts , basic volcanic rocks, pelagic limestones and greywackes. The HP /LTrocks are tectonical ly overlain by a peridot i te nappe, withou t HP/LT m etamo rphism.Steeply dipping ma jor faul ts separate blueschists from the In ner Po ntide sequence, w hichconsists of a Permian-Triassic metam orphic basement o verlain by carbona tes and U pperCretaceous f lysch. Especial ly in the Ankara region, Upper Cretaceous f lysch containsabun dant ophiol i t ic ol is tol i ths. Post-orogenic Palaeocene sedim ents are t ransgressiveover the H P/L T me tamo rphic bel t and the peridot i te nappe. The blueschist sequence mayhave been the north-facing An atol ide/T auride platform margin, subducted during theLate Cretaceous. Very fast upl if t in the col l is ion zone, aided by buo yancy of subductedcontine ntal crust , generated ol is tostromes in the P ontides and em placed peridot i te nappesover the Anato l ide /Taur ide p la t form.

T h e A l p i n e m o u n t a i n c h a i n w as c r e a t ed b y t h ec o l li s io n o f E u r a s i a a n d G o n d w a n a d u r i n g th eL a t e M e s o z o i c a n d Te r t i a r y. A b r o a d z o n eo f c o l li s io n o f th e t w o m e g a c o n t i n e n t s e x t e n d sf r o m t h e A p e n n i n e s i n I ta l y t o t h e Ta u r i d e s a n dP o n t i d e s i n Tu r k e y. T h i s z o n e i s m a r k e d b y ap i l e o f n a p p e s , o p h i o l i t e s , p e l a g i c s e d i m e n t sa n d H P / LT m e t a m o r p h i c r o ck s . R e g i o n a l l y i m -p o r t a n t H P / LT m e t a m o r p h i c p r o v in c e s o cc u r int h r e e d i f f e r e n t p a r t s o f t h e A l p i n e c h a i n :W e s t e r n A l p s , C y c l ad e s i n G r e e c e a n d n o r t h -w e s t Tu r k e y. T h e a i m o f t h i s p a p e r i s t o g i v e ag e n e r a l d e s c r i p t i o n o f t h e l e a s t k n o w n o f t h et h r e e H P / LT m e t a m o r p h i c p r ov i nc e s. L o n g -s t a n d i n g p r o b l e m s o f t h e f o r m a t i o n a n d u p l i f to f b l u e s c h i st s a n d t h e p r o c e s s e s i n c o l l i s i o nz o n e s a r e d i s c u s s e d i n a r e g i o n a l g e o l o g i c a lf r a m e w o r k . T h e d e s c r i p ti o n is b a s e d o n t h er e c e n t l i t e r a t u r e p l u s t h e a u t h o r ' s o w n f i e l d -w o r k , w h i c h t o g e t h e r p r o v i d e a g e n e r a l p i c t u r eo f m u c h o f n o r t h - w e s t Tu r k e y.

e o l o g i c a l s e t t i n g

M a j o r s u t u r e s c a n o f t e n b e r e c o g n i s e d b y t e c t o -n i c j u x t a p o s i t i o n a c r o ss n a r r o w o p h i o l i t e z o n e so f t o t a l l y d i ff e r i n g s t r a t i g r a p h i e s a n d f a u n a lp r o v i n c e s . T h e s u t u r e r e p r e s e n t i n g t h e m a j o r

o c e a n ic a re a b e t w e e n E u r a s ia a n d G o n d w a n ad u r i n g t h e M e s o z o i c , a n d p r o b a b l y e a r l ie r , c a ns a fe l y b e p l a c e d i n Tu r k e y i n th e I z m i r - A n k a r a -E r z i n c a n Z o n e ( l z m i r - E r z i n c a n s u t u re ) . D u r i n gt h e M e s o z o i c , a p a r t f r o m a m a j o r I z m i r - E r z i n -c a n o c e a n , t h e r e w e r e a l s o m i n o r o c e a n i cb a s i n s , f o r e x a m p l e s e p a r a t i n g t h e A p u l i a -Ta u r i d e m i c r o p l a t e f r o m G o n d w a n a ( B i j u -D u v a l e t a l 1 97 7 ). H o w e v e r , t h e s e w e r e n a r r o wa r e a s o f o c e a n i c c r u s t p r o b a b l y o f s h o r t d u r a -t i o n , a n d t h e r e s u l ti n g m i c r o c o n t i n e n t s c a n b ea s si g n ed t o o n e o f th e m e g a c o n t i n e n t s .

T h e I z m i r - E r z i n c a n s u t u r e d i v id e s Tu r k e yi n t o tw o m a j o r u n i ts : t o t h e n o r t h t h e P o n t i d e s ,a n d t o t h e s o u t h t h e Ta u r i d e s , a n d t h e i r m e t a -m o r p h o s e d e q u i v a l e n t s , . th e A n a t o l i d e s ( F ig s 1 ,2 K e t i n 1 9 6 6) . T h e I z m i r - A n k a r a - E r z i n c a nZ o n e o f B r i n k m a n n ( 19 6 6) i s a r e g i o n a l de -p r e s si o n , w h e r e u l t ra m a f i c a n d H P / L T m e t a -m o r p h i c r o c k s , l y in g t e c to n i c a l l y o v e r t h e A n a -t o l id e s , w e r e p r e s e r v e d f r o m e r o s i o n .

P a l a e o g e o g r a p h i c a l l y, th e a r e a s o u t h o f t h ei z m i r - E r z i n c a n s u t u r e b e l o n g s t o t h e A n a t o -l i d e - Ta u r i d e P l a t f o r m ( ~ e n g r r 1 9 79 ), w h i c h w a sl i n k e d t o G o n d w a n a . D u r i n g t h e M e s o z o i c t h ea r e a w a s a w i d e B a h a m i a n - t y p e c o n t i n e n t a lp l a t f o r m ( B e r n o u l l i L a u b s c h e r 1 97 2) : T h eE u r a s i a n r e a l m t o t h e n o r t h o f t h e I z m i r-E r z i n c a n s u t u r e w a s t e c t o n i c a l l y m o r e a c t i v e

4 5 5


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4 5 6 A I O k a y

Mediterranean . . . . .PONTIDESANATOLIDES

b[ueschist facies ~ greenschist facieshigh grade metamorphism

~ ~ TAURIDES

FIG. 1. Majo r tectonic units of western andcentral Turkey; only the Anatolide zonesare differentiated. A re a of Fig. 2 is indi-cated by dashed lines. NA F, North A nato-lian Fault; EF, EcemiwFault.

du r ing the M esozo ic , and cha rac t e r i zed by im-por t an t c l a s t i c s ed imen ta t ion and bas i c vo l can -i sm (Fourq u in 1975; Be r gou gnan Fourqu in1980) . Nor th -wes t Turkey encompasses a r easb e l o n g in g t o t h e E u r a s i a n , t h e S a k a r y a Z o n e o ft h e P o n t i d es , a n d G o n d w a n a r e a l m s , t h e A f y o nZo ne o f the A na to l ides , and wi th pe lag i c s ed i-men t s , vo l can ic and u l t r amaf i c rocks r eco rd ingan ocean ic a r ea s epa ra t ing the two con t inen t s .

Afyon Zone Anatol ides)The Aryan Zone i s a t yp i ca l she l f - t ypePa laeozo ic -Mesozo ic s eque nce o f the Taur ides(F ig . 4 ) . I t cove r s l a rge a r eas i n Cen t r a l An a to -l ia and extends as fa r eas t as the Bolkarda[~region (Fig . 1) ; to the w es t i t form s the cover ofthe gne i s se s o f t he M ende res Mass i f. TheA r y a n Z o n e c a n b e c o r re l a t e d w i th t h e B o l ka r -da~ Un i t o f r ( 1976) . Low -grade r eg iona lme tam orph i sm , a s we ll a s it s i n t e rna l s t ruc tu ra lse t t i ng , p l aces t he Aryan Zone in t he Ana to -l ides (Ketin 1966).

A t t he b ase o f t he A fyo n Zo ne is a th i cks e q u e n c e ( > 1 5 0 0 m ) o f m e t a - s a n d s t o n e s, m e t a -s i l t s t ones and me ta -qua r t z i t e s w i th r a r eme tabas i t e and r ec rys t a l l i s ed l imes tone ho r i -zons . A l tho ugh the s equ ence i s spa r se ly fos s i-

l i f e rous , Dev on ian foss il s a r e found in t he basa lpar t of the c las t ic sequence in the I lg ln region

s~T__

F - - - I N e o g e n e c o v e r~ F ] I]rcm ~ 1 7 6 ~ ~ d ~

Peridot i teliPILT metam orphic rocks iAnoto[ides ) -~

, ~ Aryan Zo ne (Anato[ides){===~ ffesozoic-Terticwy cov er ~ SakQryclZone

Pre-Liossic basem ent ,I (Pontides) o 1 s 3 o 4I . . I

P o l a t l

FIG. 2. Geotectonic ma p of north-west Tu rkey showing the tectonic units discussed in the text. ESF,Eski~ehir Fault.


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Distribution and characteristics of north west Turkish blueschists 4 5 7

nor th o f Ko nya (N iehoff 1964). The m e tac l a s -t i c s pas s up g radua l ly in to da rk g rey r ec rys t a l -l i zed l imes tones , wh ich have y i e lded Carbo-n i f e r o u s to U p p e r P e r m i a n f u s u l in i d s i n t h eA fyo n r eg ion (Er i~en 1972). Th e Tr i a s s i c s equ-ence s t a r t s w i th a basa l me ta -cong lomera te ,cons i s t ing o f me ta - sands tones , me ta - s i l t s tonesand in t e rca l a t ed a lga l l imes tones . The r e s t o ft h e M e s o z o ic i s r e p r e s e n t e d b y a t h ic k s e q u e n c eo f p l a tf o r m c a r b o n a t e s , w h i c h e x t e n d t o M a a s -t r i ch t i an (F ig . 4 ) . The ca rbona te s a re loca l lyove r l a in , by an U pp er M aas t r i ch t i an toP a l a e o c e n e ' w i l d fl y s c h ' c o m p r i s i n g P e r m i a n ,Ju ras s i c and Cre t aceous l imes tone o l i s to l i t h s(Ak den iz K ona k , 1979; Ko nak , 1982) . As t r o n g l y t e c t o n i s e d v o l c a n o - s e d i m e n t a r y c o m -p l e x w it h in c i p ie n t H P / LT m e t a m o r p h i s m a n d ape r iodo t i t e nap pe , l i e s t ec ton ica l ly ove r t heca rbo na te s and f ly sch (F ig . 3 ) .

HP/LT metamorphic belt Anatolides)R o c k s a f f e c t e d b y H P / LT m e t a m o r p h i s mo c c u p y a n e l o n g a t e W N W- E S E a r e a i n n o r t h -w e s t Tu r k e y, e x t e n d i n g f o r o v e r 3 5 0 k m f r o mt h e r e g i o n o f O r h a n e l i e a s t w a r d t o Yu n a k ( F ig s1 2 ) . Th e wid th o f t he b luesch i s t be l t i n -c reases towards the eas t : i n t he Tav~an h r eg ionb luesch i s t s a r e 50 km wide ; i n the eas t t he w id tho f the b luesch i s t be l t i s o f t he o rde r o f 100-1 3 0 k m . T h e e a s t w a r d e x t e n s i o n o f t h e b l u e -sch i s t be l t i s ab rup t ly t e rmina ted by a poor lyd e f i n e d N N W- S S E t r e n d i n g m a j o r f a u l t , w h i c hj u x t a p o s e s b l u e s c h i st s a n d t h e U p p e r M e s o z oi c -Te r t ia r y s e d i m e n t a r y se q u e n c e o f th e H a y m a n abas in (F ig . 2 ). Fa r th e r sou theas t , n o r th o fKonya (Bay iq 1968) and in the Bo lka rda~ r e -g ion (B lumen tha l 1955 ; ~a lapku lu 1980) sod ica m p h i b o l e - b e a r i n g m e t a - v o l c a n i c r o c k s a r e i n -

S ANATOL DES PONT DES N~ ,,~AF_YON. Z DN ... PERDOTTE BLUESEHST SAKARYAZONE

5 I 15 lu

FIG. 3. Simp lified structural section across north-west Turkey. Th e intern al imbrication an d faultin gin the A fyon Zo ne and in the blueschist sequence are n ot sho wn. Line of section shown in Fig. 2 asA-A ' .

A s s o c i a t e d w i t h th e t e c to n i c e m p l a c e m e n t o ft h e p e r i d o ti t e s, t h e A f y o n Z o n e w a s i n te r n a l l ys l ic e d a n d i m b r i c a t e d i n p o s t - P a l a e o c e n e t im e .Sou th o f I zmi r t he Mesozo ic l i t ho log ie s o f t heA f y o n Z o n e r e st d i r e c t l y o n t h e g n e i ss e s o f t h eM e n d e r e s M a s s i f w i t h a t h i n i n t e r v e n i n g t e ct o-n i c s li c e o f P a l a e o c e n e f ly s ch ( B a ~ a n r K o n a k1981) . However, i n some a reas the th i ck basa l

c l a st ic s e q u e n c e o f t h e A f y o n Z o n e p a s se sd o w n w a r d w i t h o u t t e c t o n i c b r e a k i n t o t h egne i s ses o f the M end eres Mass i f . It s eems l ike lytha t t he gne i s ses o f the M end eres M ass i f r ep re -s e n t o ld ( ? P a n - A f r ic a n ) m e t a m o r p h i c b a s e m e n to n w h i c h P a la e o z o i c a n d M e s o z o ic s e q u e n c e o ft h e A f y o n Z o n e w e r e d e p o s i t e d p r i o r t o t h eA l p i n e r e g i o n a l m e t a m o r p h i s m ( D i i r ret al.1978) . The low-grade g reensch i s t f ac i e s me ta -m o r p h i s m , w h i c h h a s a f fe c t ed t h e A f y o n Z o n e ,shows a p rogres s ive inc rease in g rade towardst h e d e e p e r l e v e l s o f t h e s e q u e n c e . T h e P a l a e o -

zo ic me ta -c l a st i c s hav e the cha rac t e r i s t i c min e ra la s semb lage : qua r t z + a lb i t e + phen g i t e +ch lo r i t e + b io t i t e , whereas the Mesozo ic ca r-bon a te s and the f ly sch a re l i t t le a ff ec ted by them e t a m o r p h i s m a n d t h e c a r b o n a t e s a r e c o m -m on ly fos s i l if e rous .

t e r ca l a t ed wi th r ec rys t a l l i zed l imes tones andp s a m m i t i c sc h is ts . I t i s n o t k n o w n w h e t h e r t h e yr e p r e s e n t t h e s o u t h e a s t w a r d c o n t i n u a t i o n o f t h en o r t h - w e s t Tu r k i s h b l u e s c h i s t b e l t o r w h e t h e rt h e y a r e p a r t o f t h e A f y o n Z o n e , w h i c h h a sunde rgone a h igh -p res su re g reensch i s t f ac i e sm e t a m o r p h i s m i n t h e s e r e g i o n s .

I n t h e s o u t h , r o c k s a f f e ct e d b y t h e H P / LT

m e t a m o r p h i s m r e s t w i th a t e c to n i c c o n t a ct o nt h e c a r b o n a t e s a n d f l y sc h o f t h e A f y o n Z o n e . I nt h e n o r t h , s t e e p l y - d ip p i n g f au l ts j u x t a p o s eb luesch i s t s w i th the p re -L ias s i c basem en t o f theP o n t i d e s e q u e n c e . T h e i m p o r t a n t E s k i ~ e h i rf au l t (F ig . 2 ) , marked by ex tens ive b recc ia t ionand se rpen t in i t e l enses (Okay 1980c) , i s a l soc h a r a c t e r i z e d b y s h a r p c h a n g e s i n g r a v i t y a n dmagne t i c anomal i e s . In a f ew p laces , such a ss o u t h o f B u r s a ( L i s e n b e e 1 9 7 1) , th e b a s e m e n trocks o f t he Po n t ide seque nce l i e w i th a l ow-ang le t ec ton ic con tac t ove r t he b luesch i s t s .

B luesch i s t s a r e t ec ton ica l ly ove r l a in by ap e r i d o t i te n a p p e , w h i c h i s n o w l a rg e ly p re -s e r v e d i n t h e r e g i o n a l d e p r e s s io n b e t w e e n B u r -sa and Esk i~eh i r.

M o s t o f t h e r o c k s a f fe c t e d b y t h e H P / LTm e t a m o r p h i s m i n n o r t h - w e s t Tu r k e y c o n s i s t o f


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4 5 8

Afyon Zone Anatot ides)

A I O k a y

Sakarya Zone Ponfides)

I I I i 1. . . . . . . . M o .

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HP/LT metamorphics e q u e n c e

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S S S S S S ~S S s S S S S

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Rodlolorlonc h e w li i

FIG. 4. Generalized synthetic stratigraph ic sections of the tectonic units of north-w est Turk ey. Th ethicknesses of the HP/L T metamorphic sequences are very approximate. De v., Devonia n; Carb.,Carboniferous; Per., Permian; Tr., Trias; Cr., Cretaceous; Cen., Cenomanian; Tur., Turonian;Camp., Campanian; Ma., Maastrichtian; Pal., Palaeocene; U., Upper; L., Lower.

a s t rong ly t ec ton i sed vo lcano- sed imen ta ry com-p l ex , w h i ch a p p e a r s t o b e u n m e t a m o r p h o s e d i nthe f i e ld bu t on ca re fu l examina t ion r evea l s ani n c i p i e n t H P / LT m e t a m o r p h i s m ( O k a y 1 9 8 2 ) .Comple te ly recrys ta l l ized , schis tose b lueschis t s

m ak e up 30--40 of the 'b lueschis t ' t e r ra in . Inth is r e spec t r e se mblan ce i s s t r ik ing to t he F ran -c i scan t e r r a in i n Ca l i fo rn i a , whe re mos t rocksa l s o a p p e a r t o b e u n m e t a m o r p h o s e d .

I n c i p i e n t l y m e t a m o r p h o s e d v o l c a n o -s e d i m e n t a r y c o m p l e x

These rocks occu r a s s t eep ly -d ipp ing imbr i -ca te s l ices underneath mass ive per idot i tes .They l i e t ec ton ica l ly ove r t he ca rbona te s andthe f ly sch o f t he A rya n Zo ne , o r ove r the t rue

b luesch i s t s . The rock - types i n dec reas ing o rde ro f abun dance a r e : py roc l a s t i cs , ba s i c vo lcan icrocks , r ed and g reen pe l ag i c sha l e s , r ad io l a r i anche r t s , pe l ag i c l imes tones , g r eywackes , syn -sed imen ta ry b recc i a s , manganese depos i t s ,ke ra tophyres and ne r i t i c l imes tone o l i s to l i t h s

(Kaya 1972 ; Okay 1982) . Pene t r a t i ve de fo rma-t ion i s absent in the sequence , and the rocksappea r t o be unme tamorphosed in t he f i e ld .The charac ter i s t ic fea ture of th is complex i s thec lose and r epea t ed sed imen ta ry in t e r ca l a t i on o fd i fferent roc k types : a typica l sp i l i te -sha le-cher ts equence , fo r example , can occu r 3 -4 t imesove r a 100 m w ide sec t ion (O ka y 1981, F ig . 4).Talc and serp ent in i te outcro ps of var ious s izesma rk nu mer ous t h rus ts in the vo lcano- sed imen-tary com plex . Tectonic s l ices of green-schis t - fac ies metabas i tes a re found in the vol -cano- sed imen ta ry complex in t he Tav~anh r e -g ion (O kay 1982) . Much o f the s t rong t ec ton ismaffec t ing th is sequence was probably re la ted tothe emplac em en t o f t he pe r ido t i t e nappe , andc l ea r ly p o s t- d a t es H P / L T m e t a m o r p h i s m .

Because o f t he s t rong t ec ton i sm, t he t h i ck -nes s o f t he vo lcano- sed imen ta ry complex i sd i ff icu l t to es t imate . Minimum th icknessesrange f rom 160 me t r e s i n t he Orhane l i a r ea(Lisenbee 1971) to 250 metres in the Tav~anl la r ea . D a ta on the age o f depos i t ion o f the


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Distribution and characteristics

complex i s spa r se ; pe l ag ic l imes tones f rom theMura tda~ l (B ing61 1977) and eas t o f Ged iz( A k d e n i z K o n a k 1 97 9) y i e l d C e n o m a n i a nages . Servais (1981) ass igns a tenta t ive LateJu ras s i c -Ea r ly Cre t aceous age to the r ad io -

l a r i a n c h e r t s f r o m t h e v o l c a n o - s e d i m e n t a r yc o m p l e x s o u t h o f l n 6 n i i .

A n o tab le f ea tu re o f t h i s vo lcano - sed imen -t a ry c o m p l e x is t h e p r e s e n c e o f H P / LT m i n e r a l ssuch a s l awson i t e an d a rago n i t e i n the ve ins andam ygda les in the vo lcan ic rocks ; ca l c i t e in pe l a -g i c limes ton es i s r ec rys t a l l ized to coa r se g ra inso f a ragon i t e . Assoc ia t ed wi th th i s i nc ip i en tH P / LT m e t a m o r p h i s m t h e re h a s b e e n e x te n s iv es o d i u m m e t a s o m a t i s m i n v o l v i n g t o p o ta c t ic r e-p l a c e m e n t o f a u g i t e b y s o d i c p y r o x e n e i n t h ev o l c a n i c r o c ks . T h e m e t a m o r p h i c c o n d i t o n s a r e

e s t i m a t e d a t 5 - S k b a n d 2 5 0 - 30 0 ~ ( O k a y1982).

lueschists

The rock types a re s imi l a r t o the vo lcano-s e d i m e n t a r y c o m p l e x e x c e p t t h a t t h e r e i s ath i ck basa l m arb le un i t bu t no u l t r amaf i c rocks .

W h i t e m a s s i v e a n d l o c a ll y c h e r t y m a r b l eusua l ly occurs a s a s eve ra l k i lome t re - th i ck un i tb e n e a t h i n t e r c a l a t e d m e t a b a s i t e s , m e t a - c h e r t sa n d m e t a - sh a l e s . T h e c o n t a c t b e t w e e n t h e m a r -

b l e a n d t h e m e t a - v o l c a n o - s e d i m e n t a r y se q u -e n c e i s p r i m a r y a s m a r b l e h o r i z o n s a n d b l o c k sa r e o b s e r v e d i n t h e m e t a - v o l c a n o - s e d i m e n t a r ys e q u e n c e n e a r t h e m a r b l e c o n t a c t ( ~ o ~ u l u1967 ; Yen iyo l 1979 ; Okay 1980a , c ) . In someareas , such a s in the S iv r ih i sa r r eg ion , m arb lea l so occur s a s s eve ra l hund red me t re - th i ck ho r i -z o n s w i t h in m e t a b a s i t e s a n d m e t a - c h e r ts . Afo l i a t ion is gene ra l ly we l l deve lo ped in a l l rockt y p e s i n t h e g l a u c o p h a n e - l a w s o n i t e a n d g l au c o -p h a n e - e p i d o t e z o n e s , w h e r e i t is d e f in e d b y t h ep a r a l l e l o r i e n t a t i o n o f m i c a a n d s o d i c a m p h i -

bo le g ra ins . A t l ea s t two ph ases o f i soc lina lf o l d i n g a r e p r e s e n t i n t h e g l a u c o p h a n e - l a w -son i t e zone rocks (Okay 1980c) . The th i cknesso f t he b luesch i s t un i t i s d if f icu l t t o e s t ima tebecau se o f i n t ense fo ld ing ; appa re n t t h i ck -n e s s e s o f t h e m e t a - v o l c a n o - s e d i m e n t a r y s e q u -ence a re ca . 1000-1500 m.

L a w s o n i t e , g l a u c o p h a n e - l a w s o n i t e a n dg l a u c o p h a n e -e p i d o te z o n e s h a v e b e e n m a p p e din va r ious pa r t s o f t he N or thwe s t Tu rk i shbluesc his t be l t ( (~o~ulu 1967; Ok ay 1980a, b ;Ku lak sm 1981). T yp ica l m ine ra l a s sem blages in

t h e m e t a b a s i t e s a n d m e t a - c h e r t s f r o m t h e Ta v -~anh r eg ion a re sho wn in Tab le 1 . A cha rac t e r-i s t i c f ea tu re o f t he no r th -wes t Turk i sh b lue -sch i s t s i s t he p rograde na tu re o f t he mine ra la s semblages . The rocks gene ra l ly do no t exh ib i tt h e r e t r o g ra d e t e x tu r e s a n d m i n e r a l s c o m m o n

of north west Turkish blueschists 4 5 9

in o the r t e r r a ins , so tha t p rog rade s t ages o fm e t a m o r p h i s m c a n e a s i ly b e d i s ti n g u i sh e d . T h eH P / LT m e t a m o r p h i s m i n n o r t h - w e s t Tu r k e y i scha rac t e r i zed by an in i t i a l s t a ti c me tam orph ice v e n t w i t h t h e d e v e l o p m e n t o f a l a w -

son i t e + sod ic py ro xen e + ch lo r i t e a s sem blagein the bas i c vo lcan ic rocks , wh ere sod icp y r o x e n e is p s e u d o m o r p h o u s a f te r a u g it e . A tth i s l awson i t e zone s t age the p r imary igneoustex tu re w as l a rge ly r e t a ined (~o~u lu 1967;O kay 1980b). Th i s s t a t i c r ec rys t a ll i za t ion wasf o l l o w e d b y a s e c o n d m e t a m o r p h i c e v e n ta s soc ia t ed wi th the onse t o f pene t r a t ive de -f o r m a t i o n . S o d ic a m p h i b o l e f o r m e d a t t h e e x -pense o f sod ic py roxe ne an d ch lo r i t e du r ing th iss e c o n d m e t a m o r p h i c p h a s e . A l a t e g r e e n s c h is to v e r p r i n t , w i t h d e v e l o p m e n t o f e p i d o t e a n d

ca lc i c amph ibo le , i s r epor t ed f rom the Miha l iq -ok (~o~u lu 1967) and S iv r ih i sa r (Ku laks i z1981) areas.

(~ o~ ulu a n d K r u m m e n a c h e r (1 9 67 ) d a t e db luesch i s t s f rom the Miha liqc~k r eg ion by theK / A r m e t h o d : p h e n g i t e s f r o m tw o g l a u c o p h a n esch i st s gave ages o f 65 and 82Ma. A n u ppe r ageo f b l u e sc h i s t m e t a m o r p h i s m i s g iv e n b y M i d d l eP a l a e o c e n e s e d i m e n t s u n c o n f o r m a b l y o v e r -l y in g t h e v o l c a n o - s e d i m e n t a r y c o m p l e x a n dp e r i d o t i t e i n t h e Yu n a k ( Ye n i y o l 1 9 7 9 ) a n dE m i r d a ~ ( U m m a n Ye rg 6 k 1 97 9) a r e as .

L o w e r a n d M i d d l e E o c e n e c o n g lo m e r a t es a n dl imes tone s a re a l so t r ansg res s ive ove r t he pe r io -d o t it e a n d b l u e s c h i s t i n t h e Ta v ~ a n h , Yu n a k( Ye n i y o l 1 97 9) a n d S i m a v ( A k d e n i z K o n a k1979) a reas . Thu s , t h e age o f b luesch i s t me ta -m o r p h i s m i s c o n s t r a i n e d t o l i e b e t w e e n C e n o -m a n i a n a n d M i d d l e P a l a e o c e n e . A f u r t h e r a g econs t r a in t i s g iven by a bun dan t b luesch i s t de t r i -t u s in t h e U p p e r C a m p a n i a n f ly s ch o f t h eH a y m a n a b a s i n ( B a t m a n 1 97 8).

Eclogi tes

E c l o g i t e s a r e r e p o r t e d f r o m t h e M i h a l i q o ka n d S i v r ih i s a r a r e a s. I n t h e M i h a l i g o k r e g i o nthe supposed ec log i t e s occur a s t ec ton ic inc lu -s ions in pe r ido t i t e . Ho we ver, chem ica l ana lys i sof the ec lo gi te (~o ~u lu 1967) sugges ts tha t i tm a y b e a n a n d r a d i t e - h e d e n b e rg i t e s k a r n r a t h e rthan a t rue ec log i t e . In the S iv r ih i sa r a r ea ,ga rne t -o rnphac i t e ec log i t e s w i th minor g l auco-p h a n e o c c u r a s s m a l l b lo c k s a lo n g a m a j o r f a u l tw i t h i n t h e g l a u c o p h a n e - l a w s o n i t e z o n e b l u e -schis ts (Kulaksm 1978) .

P e r i d o t it e n a p p e

Per ido t i t e fo rming the h ighes t t ec ton ic un i tove r bo th the b luesch i s t s and the low -grade


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4 6 0 A. I . Okay

TABLE 1. Progress ive mineral changes in the Tav~ anh area, north-west Tur key (double lines, major(20 ) miner al; single lines, minor mineral; dashed lines, sporadic occurrence)

MetamorphicZones

rockmineral

Sodic am phibole

Lawsonite

Sodic pyroxene

Chlorite

Albite

Quartz

Phengite

Alm. garnet

Spess. garnet

Pumpellyite

Epidote

Sphene

Magnetite

Hemat i te

Aragonite

Relict augite

Incipient Law sonite Glaucop hane-lawson iteMetamorphism i Zone Zone

Basic volcanic rocks Chert

m e t a m o r p h i c r o c k s o f th e A f y o n Z o n e i s l a rg e l yp r e s e r v e d i n t h e r e g i o n a l d e p r e s s i o n b e t w e e nO rhan e l i and Esk i~eh i r, a s a s ing le mass i f ove r

400 0km 2 in a rea . In the eas t pe r ido t i t e occur sas i so l a t ed k l ippen on the b luesch i s t s .T h e d o m i n a n t r o c k t y p e i s a s p i n e l - b e a r i n g

ha rzburg i t e /dun i t e t ec ton i t e (0o~ ,u lu 1967 ;L i senbee 1971 ; Okay 1980c) . Se rpen t in i za t ioni s no t ex tens ive excep t a t t he marg ins o f t hep e r i d o t it e a n d a l o n g fa u l ts . G a b b r o , o c c u p y i n gle s s t han 2% of the su r face a rea o f t he pe r ido -r i t e , occu r s a s sma l l bod ie s a f ew hundredmet re s wide wi th in the pe r ido t i t e s where i tc o m m o n l y s h o w s c o m p o s i t i o n a l l a y e r i n g ( U z1978 ; Tanku t 1980) . The common type i s a

pyroxe ne -o l iv ine -p lag ioc la se gabb ro , w i th thepyroxene o f t en u ra l i t i zed and the p l ag ioc la sesaussur i t ized .

The pe r ido t i t e i s cu t by d i scon t inuous mic ro -g a b b r o i c d y k e s a n d s t o c k s o f v a r i a b l e w i d t h( 0 . 2 - 5 m ) . T h e d e n s i ty o f d y k e s is v a r i a b l e

ave rag ing 2 -3 dykes pe r 500 me t re s ho r i zon-t a l ly. Dy kes a re c om mo nly ch i l l ed aga ins t t hepe r ido t i t e , do no t ex te nd in to the coun t ry rock ,

and l i ke the gab bros , a r e a ff ec t ed by low-gradeo c e a n f l o o r - t y p e m e t a m o r p h i s m . A l t h o u g h t h eigneous t ex tu re su rv ives , t he p r imary p l ag io -c l a se + aug it e a s sem blage in the mic rogab brosh a s b e e n r e p l a c e d b y a n a l b i t e + h o r n -b l e n d e + p u m p e l l y i t e a s s e m b l a g e ( L i s e n b e e1971 ; Yen iyo l 1979 ; Okay 1980c) . The mine ra la s s e m b l a g e s in t h e d y k e s a n d g a b b r o s i n d i c a tetha t t he pe r ido t i t e un i t has no t unde rgoneH P / LT m e t a m o r p h is m .

The upp e r pa r t s o f t he idea l oph io l i t es e q u e n c e a r e a p p a r e n t l y a b s e n t i n n o r t h - w e s t

Turk ey ; t h i s cou ld be du e to e ros ion , o r i t cou ldbe p r ima ry. I t i s s ign i f i can t t ha t no com ple t eo p h o l it e s e q u e n c e h a s b e e n d e s c r ib e d a l o n gthe I zmi r-Erz incan su tu re where pe r ido t i t e s a req u i te c o m m o n .

The re a re no r e l i ab le iso top ic o r o the r da t a


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D i s t r i b u t i o n a n d c h a r a c te r i st i cs o f n o r t h w e s t T u r k i s h b l u e s c h is t s 461

for the age of the per idot i te ; i t s emplacementover the vo lcano-sed imenta ry complex mus t bepos t -Cenomanian bu t p re -Midd le Pa laeocene .

Sakarya Zone Pont ides)The Sakarya Zone cor responds approx imate lyto the Mysisch-Galat ische Schol le of Br ink-

m a n n (1966), to the Inner Pon t ides o f Ber-gougnan and Fourquin (1980) and to theSak arya cont inen t of ~eng6 r Yl lmaz (1981) .In wes te rn Turkey the Zone occup ies rough lythe a rea be tween the Nor th Ana to l i an Fau l tand the Izmir-Erzincan suture (Fig . 1) . TheSakarya Zone consis ts of a pre-Liass ic meta-morph ic basem ent and a cover o f Mesozoic toTer t iary c las t ics and carbonates . The s t ra t igra-phy, which is complete ly di fferent f rom theAfyon Zone, i s wel l descr ibed in the Bi lecik(Al tmh 1975; Saner 1980) , and Ankara (Bat-man 1978; Akyi i r ek 1 981 ; Un alan 1981) re-gions , and is summarized in two general izedstratigraphic sections in Fig. 4.

The basem ent o f the Sakarya Zone consi s tso f a th ick , de fo rmed , va r i ab ly metamorphosedsequence o f g reywackes in te rbedded wi th bas icvolcanic rocks , shales and rare l imestones . Theupper pa r t s o f th i s sequence con ta in ab undan t

ol is to l i ths of Permian and Carboniferous l ime-s tone in a matr ix o f greyw acke and shale. Smal l(


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4 6 2

fo r exam ple a s g ra in - f lows wi th g l aucop hane -l awson i t e s ch i s t f r agmen t s , f i r s t occu r s i ng r e yw a c k e s o f t h e U p p e r C a m p a n i a n - M a a s -t r i ch t i an f ly sch (Ba tm an 1978) and i s com mo na long wi th se rpen t in i t e de t r i t u s i n the Pa laeo -

c e n e a n d E o c e n e c l as ti c s ( N o r m a n R a d1971).

Calc alkaline plutonism and Neogenedeposits

D u r i n g t h e E a r l y Te r t i a ry i m p o r t a n t c a lc - a lk a -l ine p lu ton i sm a ffec t ed the who le o f no r th -wes tTurke y. Seve ra l i nd iv idua l s tocks in t rudepe r ido t i t e , b luesch i s t and the low-grade me ta -m o r p h i c r o c k s o f th e A f y o n Z o n e ( F ig . 2 ). T h ed o m i n a n t p l u t o n i c r o c k - t y p e i s a h o r n b l e n d e - -b io t i t e g rano d io r i t e (B i i rk i it 1966). A ge de te r-m i n a t i o n s o n t h e s e g r a n o d i o r i t e s r a n g e f r o mE a r l y P a l a e o c e n e t o L a t e O l i g o c e n e ( A t a m a n1974; Bing61et al 1982) . Miocene cong lomer-a t e s, c o m m o n l y c o n t a i n i n g g r a n o d i o r i te f ra g -me n t s , a r e t r ansg res s ive ove r t he g ranod io r i t e s .Th e ca l c -a lka l ine p lu ton i sm o f no r th -wes t Tur-key seem s to be c lose ly r e l a t ed to the up l i f t o ft h e H P / LT m e t a m o r p h i c ro c ks , a n d m a y b e t h er e s u l t o f r a p i d n e a r - i s o t h e r m a l d e c o m p r e s s i o nof the th i ck ene d con t inen ta l c rust o f no r th -wes t

Tu r k e y.T h e P a l a e o c e n e a n d E o c e n e w a s a p e r i o d o f

up l i f t fo r muc h o f no r th -wes t Turke y, so tha tsed im en t s o f t h i s age a re r e s tr i c ted . A t t heb e g i n n i n g o f t h e M i o c e n e t h e a r e a w a s r e la t iv e -l y s t a b le w i t h n u m e r o u s l a k e s s e p a ra t e d b yh igh lan ds o f pe r ido t i t e and b luesch i s t . Te r-r e s t r i a l and l acus t r ine Neogene sed imen t s a rewide ly d i s t r ibu ted in no r th -wes t T urke y (F ig .2 ) , an d cons i s t l a rge ly o f l imes tone , t u ff, sha l ea n d l ig n i t e o f M i o c e n e a n d P l i o c e n e a g e ( B r in k -mann 1976) .

DiscussionThe s t r ik ing con t r a s t s o f s t r a t ig raphy in theA f y o n a n d S a k a r y a Z o n e s p o i n t t o t h e e x i s t -e n c e o f a m a j o r o c e a n i n n o r th - w e s t Tu r k e y i np re -Ter t i a ry t imes . Ev idence fo r t he age o fopen ing o f t h i s I zmi r-Erz incan ocean in no r th -w e s t Tu r k e y, a n d i n d e e d i n t h e 1 5 0 0 k m - l o n gs u t u r e s e p a r a t i n g t h e P o n t i d e s a n d A n a t o l i d e si s ve ry spa r se . C on t in en ta l marg in sequences ,

wh ich e s t ab l i sh f a i r ly accu ra t e ly the age o fin i t i a l r i f ti ng in a reas such a s the A n ta lya r eg ion(Marco ux 1976; Ro ber t s on W oodc ock 1981) ,h a v e n o t b e e n d e s c r i b e d a l o n g t h i s m a j o r s u -ture . I t is s t i ll not c lear wh eth er th e Izm ir-E r z i n c a n o c e a n r e p r e s e n t s o n e o f t h e b r a n c h e s

A I O k a y

o f N e o t e t h y s w h i c h o p e n e d d u r i n g t h e L i a s s i c(~eng6r Yl lm az 1981), o r wh e the r i t i s t heo r ig ina l Te thys (Pa laeo te thys ) wh ich was ine x i s t e n c e fr o m t h e M i d - P a l a e o z o i c o n w a r d , a si m p l i e d b y B i j u -D u v a le t a l (1977) . A l though

pre -L ias s i c t h rus t ing and de fo rma t ion have r e -c e n t ly b e e n d e s c r i b e d f r o m t h e Ta u r i d e s ( A k a y1981; M ono d A ka y th i s vo lum e) , t he r e s tr i c -t i on o f t he Tr i a s s i c o rogeny, a s r ep resen ted byt h e m e t a m o r p h o s e d a n d d e f o r m e d K a r a k a y aFo rm a t ion , t o the Pon t ides sugges ts t ha t impor-t a n t d i f f e re n c e s b e t w e e n t h e A n a t o l i d e /Taur ides and Pon t ides ex i s t ed in p re -L ias s i ct imes . Tr iass ic bas ic volca nics , tuft s and pelag ics e d i m e n t s i n t h e B o z k l r n a p p e s n o r t h o f th eTaur ide au toch thon (0zgf i l 1976) , a l so ind ica t et h a t t h e o p e n i n g o f t h e I z m i r - E r z i n c a n o c e a n

da te s back to p re -Tr i a s s i c t imes .The s t ruc tu ra l pos i t i on o f t he b luesch i s t sb e t w e e n t h e A f y o n Z o n e a n d t h e p e r i d o f it enap pe (F ig . 3 ) i nd ica t e s t ha t t hey be long to theA n a t o l i d e r a t h e r t h a n t o t h e P o n t i d e r e a lm . I t i ssugges t ed tha t t he b luesch i s t s equence o f no r th -w e s t Tu r k e y r e p r e s e n t s p a r t o f t h e n o r t h w a r d -f a c i n g c o n t i n e n t a l m a rg i n o f t h e A n a t o l i d e /Ta u r i d e p l a t fo r m . T h e m a i n e v i d e n c e fo r t h is ist h e s u d d e n p a s s a g e f r o m t h e t h i c k p l a t f o r mcarbona te s to the pe l ag ic sed imen t s and vo lca -n ic s in the b luesch i s t s equence , wh ich i s i n t e r-

p re t ed a s due to r ap id fou nde r in g o f a ca rbon-a t e p l a t fo rm fo l lowing r i f ti ng and e s t ab l i shm en to f a con t ine n ta l marg in . Th e ne r i t i c ca rbon a teo l i s to l i t h s i n the vo lcano- sed imen ta ry complexo f t h e E m i r d a ~ a n d Ta v ~ a n l l r e g i o n s m a y b eano the r i nd ica t ion o f b lock - fau l t i ng and found-e r i n g o f a c a r b o n a t e p l a t f o r m . R a p i d s u b -m e rg e n c e o f s h a l l o w w a t e r p l a t f o r m s b y s y n -s e d i m e n t a r y n o r m a l f a u l t i n g a n d t h e i n c e p t i o nof pe l ag ic cond i t ions o ve r l a rge a reas i s cha rac -t e r i s t i c o f t he ea r ly Mesozo ic h i s to ry o f t heTe thy s , and gene ra l ly ind ica t e s r i ft i ng p re -

ced ing ocean f loo r spead ing (Bernou l l i J enk-yns 1974; Lau bsche r Bern ou l l i 1977). Thepredominance o f bas i c py roc la s t i c rocks in theb l u e s c h i s t v o l c a n o - s e d i m e n t a r y s e q u e n c e o fnor th -wes t Turk ey cou ld ind ica t e p rox imi ty to avo lcan ic i s land . The o ldes t av a i l ab le ages f romt h e v o l c a n o - s e d i m e n t a r y c o m p l e x i n d i c a t e ap re -La te Ju ras s i c age fo r t he p l a t fo rm ca rbon-a tes of the b lueschis t uni t (Servais 1981) ; accu-ra t e e s t ab l i shm en t o f the i r age wi ll p rob ab lys o lv e t h e p r o b l e m o f t h e a g e o f o p e n in g o f th el z m i r - E r z i n c a n o c e a n .

A n y p l a t e t e c t o n i c m o d e l a t t e m p t i n g t o e x -p la in the fo rm a t ion and th e p re sen t day t ec ton icpos i t i on o f t he b luesch i s t s i n no r th -wes t Tu rkeym u s t t a k e a c c o u n t o f t h e f o l lo w i n g i m p o r t a n tf ea tu res o f t he b luesch i s t s and r e l a t ed rocks :

( 1) H P / LT m e t a m o r p h i c r o c k s a r e c o n ce n -


10/13

D i s t r i b u t i o n a n d c h a r a c t e r i s t i c s o f n o r t h - w e s t T u r k i s h b l u e s c h i s t s

Taur ide Anaf0 tide P la t fo rm P0n f ides

C e n o m o n i o n

I / / / / / / / ~o \ \ \ \ \ \ \ \ \

4 6 3

l \ + + - 1 - +

E a r l y S e n o n i o n o l i s f o s f r o m e s~ ' ~ c o l c - o t k a l i ~ v o l c a n i s m

/ / I I I I I I 1 ) [~~TT~ I t + t 4 - - + t

, ' ' , , , , , , ~ , . . : + ~ + * *

M a o s t r i c h t i a n - P o t a e o c e n e ~-o p h i o l i t e n a p p e

4 _ _ ~ b l u e c h i s f d e t r i t u s

. . . . L L L I ] | | | ~ ,~ l . . l~ /~ "~ ' . '; :~ ._ _ ~ _ _ ~ _ _ _ _ . . . .

/ / / / / / ) / / / / I I:....I. -I- -t- -t- -I- -I- -I- -t- -I-I

S

FIG. 5. Schematic sequence of N-S sections illustrating a possible model for the genesis of thenorth-west T urkis h blueschists involving con tinen t-con tinen t collision. Fo r explanations see the text.

t r a t ed in no r th -wes t Turkey, and do no t occur

r e g i o n a l l y e l s e w h e r e i n t h e I z m i r - E r z i n c a nsuture .2 ) T h e b l u e s c h i st se q u e n c e s d o n o t r e p r e s e n t

o c e a n i c c r u s t b u t m a y h a v e b e e n o r i g i n a l l yc o n t i n e n t a l m a rg i n s e q u e n c e s .

3 ) The pe r ido t i t e nap pe , w h ich t ec ton ica l lyove r l i e s t he b luesch i s t s , has no t unde rgoneH P / LT m e t a m o r p h i s m . A r e g u la r o p h io l it es e q u e n c e s e e m s t o b e l a c k i n g i n n o r th - w e s tTu r k e y.

I t is be l i ev ed tha t t he ava i l ab le geo log ica ld a t a a n d t h e i n f e r e n c e s fr o m t h e s e d a t a c a n b e s t

b e e x p l a i n e d b y in v o k i n g a n o r t h w a r d d i p p i n gin t r a -ocean ic subduc t ion zone , and an i r r egu-l a r ly sh a p e d c o n t i n e n t a l m a rg i n o f th e A n a t o -l i d e /Ta u r i d e p l a t f o r m , w i th n o r t h - w e s t Tu r k e yf o r m i n g a p r o m o n t o r y d u r i n g t h e E a r l y C r e -t aceous F ig . 5a ) . The cons um pt ion o f t he

I z m i r - E r z i n c a n o c e a n e v e n t u a l l y l e d t o t h e s u b -

d u c ti o n a n d H P / LT m e t a m o r p h i s m o f t h en o r t h - w e s t Tu r k i s h c o n t i n e n t a l m a rg i n . T h es u b d u c t i o n o f t h e b u o y a n t c o n t i n e n t a l cr u st o fno r th -wes t Turkey caused up l i f t o f t he ove r-l y i n g o c e a n i c c r us t a n d m a n t l e a t t h e s a m e t i m eFig . 5b ) . D epo s i t i on o f fly sch , ca l c -a lka l ine

vo lcan i sm and h uge o l i s to s tromes o f oph io l i t i cm a t e r i a l i n t h e S a k a r y a Z o n e i n d i c a t e t h a t t h esubduc t ion o f t he con t inen ta l c rus t and up l i f th a d a l r e a d y s t a r te d i n t h e T u r o n i a n . B l u e s c h is t sm u s t h a v e b e e n l o ca l ly ex p o s e d b y t h e U p p e rC a m p a n i a n w h e n d e t r i tu s i n t h e P o n t i d e

H a y m a n a b a s i n a p p e a r s B a t m a n 1 9 78 ). T h i s i sa l so a n i n d i c a t i o n t h a t t h e I z m i r - E r z i n c a n o c e a nw a s e l i m i n a t e d i n n o r th - w e s t Tu r k e y b y t h eM aas t r i ch t i an F ig . 5c ). Con t inu ing comp ress -i o n a n d s t r o n g u p l i f t e l e v a t e d t h e S a k a r y a Z o n ea b o v e s e a l e v e l i n th e P a l a e o c e n e ; a t t h e s a m e


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4 6 4 A . L O k a y

t ime in the south , huge ophio l i te s l ices werede t ached f rom the up l i f t ed ocean ic c rus t andm a n t l e a n d m o v e d s o u t h w a r d o v e r t h e A n a t o -l i d e / Ta u r i d e c a r b o n a t e p l a t f o r m ( B o z k l roph io l i te nappes o f ~eng6r Y l lmaz ) .

Upl i f t and ex pos ure o f b lueschis t s impl iesseve ra l t ens o f k i l ome t r e s o f ve r t ica l upw ardm o v e m e n t r e l at iv e t o t h e r o c k s o f S a k a r y aZone . Th i s up l i f t , mus t have been ach ieveda long the ma jo r f au l t s , wh ich now jux taposeb lueschi s ts , f o rm ed a t 30 -35 km d ep th , and theM e s o z o i c s e d i m e n t s o r t h e b a s e m e n t r o c k s o ft h e S a k a r y a Z o n e . A n o t h e r c o n s e q u e n c e i s t h a tmos t o f the pe r ido t i t e s i n no r th -w es t Tu rkey a rep re se rved ocean ic man t l e r a the r t han ocean iccrus t .

U p l i f t t o t h e s u r f a c e

A r e m a r k a b l e f e a t u r e o f t h e n o r t h - w e s t Tu rk i s hblueschis t s i s the i r rap id upl i f t to the sur face .The younges t depos i t i ona l ages f rom the HP/LT m e t a m o r p h i c r o c k s a r e C e n o m a n i a n . I n t h eU p p e r C a m p a n i a n a n d M a a s t r i c h t i a n b l u e -sch i s t s were supp ly ing de t r i t u s t o t he Haymanabas in . Thus , t he t e rmina t ion o f the pe l ag ics e d i m e n t d e p o s i t i o n , H P / LT m e t a m o r p h i s mand up l i f t t o t he su r f ace mus t have occu r red inl e s s t h a n 2 5 M a ( C e n o m a n i a n - M a a s t r i c h t i a n ) .T h e p r o g r a d e n a t u r e o f t h e H P / LT m i n e r ala s semb lages and the gen e ra l absence o f agreenschis t overpr in t a l so indica te very fas tuplif t .

The p re sence o f a r agon i t e , j ade i t e and law-soni te in the g laucophane- lawsoni te schis t sg ives a conse rva t ive p re s su re e s t ima te o fl O k b a r d u r i n g t h e H P / LT m e t a m o r p h i s m

(Okay 1980c) . As the b lueschis t s occur as acohe r en t t e r r a in an d no t a s exo t ic b locks , a rockco lumn 30 -35 km th i ck mus t have been e rod edd u r i n g t h e U p p e r C r e t a c e o u s t o e x p o s e t h eb luesch i s t s a t t he su r f ace . Recen t t he rma l mod-

e l l i ng ind i ca t e s min imum denuda t ion r a t e s o f1 . 4 m m / y e a r o r h i g h e r f o r t h e p r e s e r v a t i o n o fb luesch is t s w i th no g reensch i s t ove rp r in t (Dr ap -e r Bon e 1981) . Such a cons t an t denuda t ionra t e g ives a max imum to t a l exhumat ion t ime o f20 -25 M a fo r b luesch i s ts fo rm ed a t 30 -35 kmdepth , which agrees wel l wi th the geologica lev idence .

As D rap e r Bon e (1981) po in t ou t , p r e sen tday e ros ion r a t e s a r e gene ra l ly t oo low fo r t herequ i r ed un load ing . They invoke t ec ton ic andquas i - t ecton ic mec han i sm s , such a s nappes o r

o l i s tos t rome f lows, to achieve the necessaryd e n u d a t i o n r a t e s . I n n o r t h - w e s t Tu r k e y t h eun load ing o f the b luesch i st s s eem s to have beenach ieved in two d i s t i nc t ways . Dur ing the La teCre t ac eous t he e ros ion was a ided by the fo rma-t ion o f mass ive o l is to s t romes w h ich were depo-s i ted in bas ins in the nor th (Fig . 5b) . Severa lthousand me t r e - th i ck chao t i c depos i t s o foph io l i t i c ma te r i a l ove r l i e ca rbona te p l a t fo rmrocks ove r l a rge a r eas i n t he Cen t r a l Ana to l i a .D u r i n g t h e u p p e r m o s t C r e t a c e o u s a n dP a l a e o c e n e , w h e n t h e S a k a r y a Z o n e w a s a ls o

t empora r i l y up l i f t ed , t he un load ing wasa c h i e v e d b y t h e d e t a c h m e n t a n d s o u t h w a r dm o v e m e n t o f p e r id o t i te n a p p e s , t e r m i n a ti n gsed imen ta t ion in t he Afyon Zone (F ig . 5c ) .

ACKNOWLEDGEMENTSor discussions on the geologyof north-west Turkey I thank Cemal G6nciio~lu,Necdet Ozgtil, A. M. Celal ~engOr, Okan Tekeli andYiicel Yllmaz. The manuscript was improved bysuggestions from A. M. Celal ~eng6r.

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