33 - Nw Turkey Granodiorites - CMP 1994

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Con tr ib Mine ral Pet rol (1994) 117:241 252 9 Spr inger-Ver lag 1994

N ige l B . W . H a r r i s 9 S im on K e l l e y - A r a l I . O k a y

Post-collis ion m agm at ism and tectonics in northwe st Anato l ia

R ece ived : 13 Ju ly 199 3 /A ccep t ed : 11 M a rch 1994

A b s t r a c t A s u i te o f b i o t i t e - h o r n b l e n d e g r a n o d i o r i t e i n -

t r u s i o n s h a s b e e n e m p l a c e d i n t o b l u e sc h i st - fa c i es m e t a -

s e d i m e n t s i n n o r t h w e s t A n a t o l i a , f o l l o w i n g c o l l i s i o nb e t w e e n t w o c o n t i n e n t a l m a r g i n s , n o w r e p r e s e n t e d b yt h e T a v s a n l i a n d S a k a r y a z o n e s. T h e 4 ~ a g e s o f

p h e n g i t e s a n d g l a u c o p h a n e s f r o m t h e b l u e sc h i st s , m e t a -

m o r p h o s e d u n d e r u n u s u a l l y h i g h P - l o w T c o n d i t i o n s

(P = 20 __ 2 kbar , T = 430 __ 30 ~ C) , sugg es t tha t me ta -

m o r p h i s m a p p a r e n t l y o c c u r r e d o v e r a p e r i o d s p a n n i n g

a t l e a st 2 0 M a f r o m 1 08 t o 8 8 M a . P o s t - t e c t o n i c

g r a n o d i o r i t e s w e r e e m p l a c e d d u r i n g t h e E o c e n e (5 3 to

4 8 M a ) r e s u l t i n g i n a c o r d i e r i te a n d a n d a l u s i t e - b e a r i n g

the r m a l a u r e o le , i nd i c a t ive o f p r e s su r e s o f ~ 3 kba r .

T r a c e - e l e m e n t s y s t e m a t i c s o f t h e g r a n o d i o r i t e s a r e c o n -

s i s t e n t w i t h a d e r i v a t i o n e i t h e r f r o m m a n t l e - d e r i v e d

m a g m a s b y f r a c t i o n a l c r y s t a l li s a t io n i n s h a ll o w m a g m ac h a m b e r s , o r f r o m a n a t e x i s o f c r u s t a l l i th o l o g i es o f

i n t e r m e d i a t e c o m p o s i t i o n a t p r e s s u r es < 1 0 k b a r . T h e

p r e s e r v a t i o n o f h i g h P - l o w T a s s e m b l a g e s in t h e b l u e -

s c h is t s t o g e t h e r w i t h t h e r a n g e o f ag e s d e t e r m i n e d f o r

b l u e s ch i s t- f ac i e s m e t a m o r p h i s m a r e i n d i c a ti v e o f r a p i d

e x h u m a t i o n o f d e l a m i n a t e d f ra g m e n t s f ro m a s u b d u c -

t e d c o n t i n e n t a l m a r g i n . H o w e v e r d e c o m p r e s s i o n

m e l t i ng o f t he c r u s t i s un l ike ly t o ha ve be e n a s ign i fi -

c a n t c a u s e o f m a g m a t i s m , b o t h b e c a u se e x h u m a t i o n o f

the b lue sc h i s t s f r om de e p c r u s t a l l e ve l s p r e da t e d

m a g m a t i s m b y a t l e as t 25 M a , a n d b e c a u s e o f t h e s m a l l

m e l t f r a c t i o n ( < 0 . 1 ) t h a t m a y b e g e n e r a t e d i n c r u s t a ll i th o l o g i es b y t h is p r o c e s s . M e l t i n g i n t h e m a n t l e w e d g ei s r e q u i r e d e i t h e r t o g e n e r a t e a p r i m a r y m e l t f o r t h e

d e r i v a ti o n o f m a g m a s o f i n t e r m e d i a te c o m p o s i t i o n o r

N.B.W. Harr is ( ~ ) . S . Kel leyDep ar tmen t of Ear th Sciences, Open Univers i ty ,M i l t on K eynes M K 7 6A A , U K

A.I . Ok ayITLI, M ad en Fakfiltesi, Jeoloji B61iim/i, Ayaza ~a,Is tanbul , Turkey

Editorial responsibili ty: I . Parsons

t o p r o v i d e a n a d v e c t i v e h e a t s o u r c e f o r c r u s ta l m e l t in g .

T h e c a u s e o f m e lt f o r m a t i o n i n t h e u p p e r m a n t l e m a y

b e r e l a te d t o t h e t e r m i n a t i o n o f s u b d u c t i o n f o l lo w i n gc o l l i s i o n d u r i n g t h e M i d - E o c e n e .

I n t r o d u c t i o n

F r a c t i o n a l m e l t i n g w i t h i n t h e E a r t h ' s c r u s t o r m a n t l e i s

a c o n s e q u e n c e o f t h e s o l i d u s o f t h e m i n e r a l a s s e m b l a g e

b e i n g e x c e e d e d t h r o u g h a n i n c r e a s e in t e m p e r a t u r e ,

a de c r e a se i n p r e s su r e o r a c h a ng e in t he a c t iv i t ie s o f

vo la t i l e spec i es . The s e va r i a b l e s c a n o f t e n be r e l a t e d to

t h e p r e v a i li n g t e c t o n i c e n v i r o n m e n t a s i n v o l c a n i c a r c s

o r r i f t z o n e s. T h e c a u s e s o f m a g m a t i s m f o l lo w i n g c o n t i -n e n t - c o n t i n e n t c o l l i s i o n a r e h o w e v e r p o o r l y u n d e r -

s t o o d , b o t h b e c a u s e t h e m a j o r a n d t r a c e e le m e n t s fr o m

s u c h m e l t s a r e g e n e r a l l y i n d i s t in g u i s h a b l e f r o m t h o s e

f o r m e d du r ing a c t ive subd uc t io n ( P e a r c e e t a l. 1984)

a n d b e c a u s e a w i d e v a r i e t y o f m e c h a n i s m s a r e p o t e n -

t i a l l y a va i l a b l e f o r m a gm a ge ne s i s .

D u r i n g t h e f i rs t fe w m i l li o n y e a r s a f t e r s u b d u c t i o n

h a s c e a s e d , m a g m a s m a y c o n t i n u e t o b e g e n e r a t e d i n

t h e m a n t l e w e d g e . F o r e x a m p l e , c a l c - a l k a l i n e l a v a s

w e r e g e n e r a t e d f o r a t l e a s t 1 0 M a a f t er t h e e n d o f

s u b d u c t i o n i n t h e B a s i n - a n d - R a n g e P r o v i n c e ( E a t o n

1982). M e l t i n g o f pe l i ti c l i tho log ie s o c c u r s i n t he m id -

c r us t a f e w t e ns o f m i l l i ons o f ye a r s a f t e r c o l l is i on ,r e s u l t i n g f r o m c o n d u c t i v e h e a t i n g w i t h i n t h i c k e n e d

c r u s t c o m b i n e d w i t h d i s s i p a t i v e h e a t i n g o n a c t i v e

th r us t z one s ( E ng la n d e t a l. 1992 ) . A d ve c t ive he a t ing

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

c o l l i s ion c r u s t a l m e l t i ng ( D e Y o r e o e t a l . 1989 ) a nd the

r e la t i v e c o n t r i b u t i o n s o f c o n d u c t i v e a n d a d v e c t i v e

h e a t i n g i n c o n v e r g e n t o r o g e n s h a s b e e n a s s e s s e d b ySandiford e t a l . (1992) . Upl i f t , e i the r in response to

i s o s t a t i c f o r c e s o n t h i c k e n e d c r u s t o r t o w e d g e d y -

na m ic s i n t he f oo tw a l l o f a c t i ve t h r u s t s , m a y r e su l t in

d e c o m p r e s s i o n m e l ti n g u n d e r v a p o u r - a b s e n t c o n d i-

t io n s ( L e B re t o n a n d T h o m p s o n 1 9 8 8 ; H a r r i s a n d



242

M a s s e y 1 9 9 4 ) t h u s p r o v i d i n g a p u r e l y t e c t o n i c c a u s e o f

p o s t - c o l li s i o n m a g m a t i s m . F i n a l ly , c o n v e c t i v e th i n n i n g o f

t h i c k e n e d l i t h o s p h e r e w i l l r e s u l t i n r a p i d u p l i f t ( H o u s e -

m a n e t a l. 1 9 8 1 ), c a u s i n g m e l t i n g o f th e u p p e r m a n t l e a n d

g e n e r a t i o n o f a l k a li b a s a lt s , a s h a v e b e e n e r u p t e d a c r o s s

t h e T i b e t P l a t e a u a b o u t ~ 4 0 M a a f te r t h e in i t ia l c o n t i -

n e n t - c o n t i n e n t c o l l i s i o n ( T u r n e r e t a l . 1 9 9 3 ) .

T h i s p a p e r d o c u m e n t s t h e r e s u l ts o f a s t u d y o f p o s t -

c o l l i s i o n E o c e n e g r a n o d i o r i t e s f r o m n o r t h w e s t A n a t o l i a

t h a t i n t r u d e a n d o v e r p r i n t b l u e s c h i s t - f a c i e s l i t h o l o g i e s .

T h e i m p o r t a n c e o f t h i s u n u s u a l a s s o c i a t i o n i s t h a t i t

r e p re s e n ts a n e x a m p l e o f g r a n it ic m a g m a t i s m f o r m e d

w i t h i n a c o l l is i o n z o n e w h e r e h i g h P - l o w T a s s e m b l a g e s

a r e p r e s e r v e d , p r o v i d i n g c o n s t r a i n t s o n t h e t h e r m a l a n d

t e c to n i c e v o l u ti o n o f t h e c r u s t b o t h d u r i n g e x h u m a t i o n o f

h i g h - p re s s u re a s s em b l a g es , a n d d u r i n g m a g m a e m p l a c e -

m e n t . H e n c e i t p r o v i d e s a n i d e al g e o l o g ic a l e n v i r o n m e n t

f o r a n i n v e s t i g a t i o n i n t o t h e r e l a t i o n s h i p b e t w e e n m a g -

m a t i s m a n d e x h u m a t i o n d u r i n g p o s t - c o ll i si o n t ec t on i cs .

T e c t o n ic s e t t in g o f n o r t h w e s t A n a t o l i a

The blueschist-facies assemblages of northwest Anatolia are exposedwithin the Tavsanli Zone that formed the northern passive continen-tal margin of the Tauride-Apulia plate during the Jurassic and Early

Cretaceous, facing the Neo-Tethyan ocean (Okay 1984). This se-quence was subducted by a north-dipping subduction zone beneaththe Sakarya Zone, representing the Pontide continental margin(Okay 1984). The timing of collision between the two zones is poorlyconstrained. It is certain ly earlier than Middle Eocene and probablyafter Turonian (89-50 Ma), and was predated by obduction of theophiolite fragments now exposed along the collision zone (Fig. 1).The intervening Izmir-Ankara suture is presently marked by an

active strike-slip fault that offsets Miocene conglomerates. Blue-schist-facies metamorphism is a consequence of subduc tion of sedi-menta ry lithologies, including phyllites, carbonates and intercalatedcherts (Okay 1989), and has been dated as Upper Cretaceous(65-82 Ma) by K-At dating of phengites ((~o~ulu and Krum-menacher 1967), although glaucophane K-At ages as old as 125 Maare cited in Okay (1986). Blueschist-facies metamorphism is believedto be broadly coeval with the timing of ophiolite obduction (Okay1989) although there are no isotopic constraints on the obductionage. Uplift of the blueschists was probably a result of normal fault ingalong the blueschist/ophiolite interface.

North of the suture, Miocene leucogranites of crustal origin wereemplaced into metasediments between 24 and 26 Ma ago, as ex-posed in the Uluda~ Massif (Bing61 et al. 1982). South of the suture,four post-tectonic biotite-hornblende granodiorites are emplaced

into blueschist-facies assemblages and overlying ophiolit ic frag-ments (Fig. 1), but of these only the Topuk a nd Orhaneli bodies arewell exposed. Published K-Ar ages for the Topuk intrusion rangefrom 43-64 Ma (Bing61 et al. 1982) compared with biotite-wholerock Rb-Sr ages of 49-52 Ma (Ataman 1972). For the Orhaneligranodiori te, biotite-whole rock Rb-Sr ages vary from 63 Ma(Vachette et al. 1968) to 49 52 Ma (Ataman 1972), somewhat olderthan the ages obtained from the easterly, poorly exposed,Gfirgenyayla granodiorite (44-46 Ma; Ataman 1973).

Field relations of the intrusives

The Orhanel i intrusion forms a sub-circular body, 15 km in dia-meter, emplaced 30 km south of the suture. The p luton is a ho-

mogeneous, medium-grained granodiorite, which has intrudeda blueschist-facies regional metamorphic sequence of quartz-micaschist, graphitic mica schist, metaquartzite, and minor metabasiteoverlain by marble. The metabasites are characterised by sodieamphibole + lawsonite and sodic amphibole + jadeite + paragon-

ite + quartz parageneses (Okay and Kelly 1994). Blueschist-faciesassemblages have re-equilibrated within a one-kilometre wide aure-

ole surrounding the granodiorite in response to thermal metamor-

phism. Along its western margin the granodiorite is unconformablyoverlain by Miocene dacite flows and acid tufts. A thin (2 m) basalconglomerate indicates a significant period of exposure during theMiocene, prior to eruption of the volcanics.

The fabric of the granodiorite is generally isotropic with a localfoliation along its south-eastern margin, defined by planar align-ments of plagioclase, amphibole and biotite. The emplacement of thenear-circular pluton with a marginal foliation is probably the conse-quence of syn-emplacement ballooning around the margin of a dia-piric intrusion. Forceful intrusion has resulted in asymmetric folds

around its margin, together with the development of a marginalsyncline along its northern contact. Contacts are locally concordant,with screens and xenoliths of country rock alt ernat ing with intrusivefacies over a distance of 500 m. The contact aureole along theeastern contact of the granodiorite with marble and mica schist is

marked by the development of diopside-rich skarns in the talc-silicates and the growth of biotite at the expense of phengite in themetapelites. At one locality, porphyroblasts of andalusite and cor-dierite have been recognised. Andalusi te, together with sillimanite,has also been reported in the aureole of the Topuk granodior ite tothe north (Lisenbee 1972).

The equigranular granodiorite is made up of plagioclase(50-60%, by volume), quartz (20-25%), biotite (10-15%),alkali feldspar (~ 10%), and hornblende ( ~ 5%). Plagioclaseis euhedral andesine, often with oscillatory zoning between An33and Anso. Alkali feldspar is untwinned with some perthitic exsolu-tion, and is clearly a late phase to crystallise since it is both allot-riomorphic and contains inclusions of plagioelase and horn-blende. Ilmenite and sphene are common accessories. Geochemicalsampling has been restricted to fresh exposures since many outcropsare weathered with secondary chlorite, muscovite and epidote

growth.The granodiori te is generally homogeneous at its present level of

exposure apart from the nor thern margin where a leucocratic apliticgranite is exposed, characterised by perthite, and quartz, with minorplagioclase and hornblende and accessory sphene. There is a grada-tiona l transition from the granodiori te and the aplitic carapace overa distance of ~ 5 m.

Within the granodiorite small ( < 300 mm) spherical quartzdioritic enclaves, finer grained than the host granodiorite, con-tain megacrysts of amphibole and plagioclase in an amphibole,biotite, plagioclase and quartz matrix. These have become strong-ly ellipsoidal a round the margins of the granodiorite where apenetrative fabric is preserved. The origin of the enclaves isequivocal, but their fine grain si ze coupled with their ductileresponse to deformation along the margins of the int rusion sug-

gests that they represent chilled globules of dioritic magma,that were locally deformed whilst still in a plastic state. Themegacrysts are similar in composition and habit to phases withinthe granodiorite and presumably grew during the early crystallisa-tion history of the granodiorite. Such enclaves may be the resultsof a period of dioritic magmatism that immediately pre-datesthe granodiorite intrusion, coeval with hornblende-augite dioritedykes, that are cut by the Topuk granodior ite to the north (Lisenbee1972).

The Topuk granodiorite is an elliptical pluton, 12 • 15 km, to-cally sheared by a post-emplacement east-west fabric paralle l to itslong axis and to the suture. Its core is intruded by mi-crogranodiorite, which probably represents a dyke parallel to thecontact of the roof zone (Lisenbee 1972). In other respects, itsmineralogy and mineral fabric are indistinguishable from those ofthe Orhaneli intrusion.



24 3

T e r t i a r y

~ J u r a s s i c - C r e t a c e o u s lsediments ~ Sakarya

Zone[ ~ i i ] Triassic basementr~:-~:::::::l

~ Peridotite I~ Blueschist ( Tavsanf i Zone

assemblages

~ Dacite (Miocene)

~ Granite (Miocene)

~ Granodiorite Eocene)

Fi g . 1 G e o l og i c a l m a p o f t he O r ha ne l i r e g i on o f w e s t er n T u r ke y . (O O r ha ne l i , T T opu k , Gy G 6ynf i kbe l e n , G9 G f i r ge nya y l a g r a nod i o r i te s , U1

U l uda ~ g r a n i te )

A na l y t i c a l t e c hn ique s

M i ne r a l a na l y s e s w e r e unde r t a ke n on a n SX -50 C a m e c a e l e c tr onm i c r op r o be i n t he D e p a r t m e n t o f E a r t h Sc i enc es , U n i ve r s i ty o f

Cam br idge . The acce le ra t ing vol t age was 20 kV, beam cu r rent 10 nAand beam s i ze 10gm.

W h o l e r oc k c he m i c a l a na ly s e s w e r e m a de on a n A R L 8420 +dua l gon i om e t e r w a ve l e ng t h d i s pe rs i ve X R F s pe c t r om e t e r at t heD e pa r t m e n t o f E a r t h Sc ie nce s, O pe n U n i ve r s it y . M a j o r e l e m e n t swere de te rmined f rom fused gla s s d i sc s and t r ace e l ement s (Rb, Sr ,

Ba , Nb, Z r , Y) f rom p re s sed pow der pe l l e t s . Ra re e a r th e l emen t s andT a , H f , T h , U w e r e a na l y s ed by i n s t r um e n t a l ne u t r on a c t i va t iona na l y s is a t t he O pe n U n i ve r s i t y a nd c om pu t e d u s i ng t he m e t hod o fPot ts e t a l . (1981) .

F o r A r i s o t o p e a n al y se s , p o l i sh e d sl ic es ( 1 0 m m x l 0 m mx 1 mm ) were u l t r a son ica l ly c l eaned in me than ol , w rappe d in fo i l

a nd i r r a d i a t e d by 1018 ne u t r ons c m - z a t t he F o r d R e a c t o r , M i c h i -ga n , m o n i t o r e d by ho r nb l e nde s t a nda r d m m h b l ( A ge = 520 . 4 M a ,Sa m s on a nd A l e xa nde r 1987 ). A r go n w a s e x t r a c te d f r om s m a l l a r e a sby 10 - 100m s l a s e r pu l s e s ge ne r a t e d by a c om pu t e r c on t r o l l e d

e x t e r na l s hu t t e r a nd a Spe c t r on SL 902 C W N d - Y A G l a s e r p r odu -c i ng up t o 17 W T E M oo . G a s e s r e le a s e d w e re a na l y s e d by a M A P215-50 noble -gas mass spec t rome te r . Da ta were cor rec ted for d i s -

c r i m i na t i on a nd b l a nks by t he p r oc e du r e ou t l ine d i n H a w k e s w or t h

e t a l . ( 199 2) , us ing cor rec t ion f ac tor s (39A r /37Ar )c~= 0 .00078;(36Ar/37Ar)ea = 0 .00 021 ; (~~ = 0 .0 31 based upo n

ana lys i s of ca l c ium and pota s s ium sa l t s .

M i n e r a l c h e m is t ry a n d t h e r m o b a r o m e t r y

R e g i o n a l b l u e s c h i s t m e t a m o r p h i s m

M i n e r a l a s s e m b l a g e s f r o m b l u e s c h i s t m e t a c l a s t i c s e x -

p o s e d i n t h e K o c a s u r e g io n , 1 0 k i l o m e t r e s w e s t o f t h e

O r h a n e l i g r a n o d i o r i t e , h a v e b e e n t h e s u b j e c t o f a d e -

t a i l e d t h e r m o b a r o m e t r i c s t u d y ( O k a y a n d K e l l e y 1 99 4) .



244

/ ( 1 ) X l in H b l( / ) ~- -

"~ 3

{3)(3 ) / ( 2 )

I I I600 700 800

T ( ~

F i g . 2 P r e s s u r e - t e m p e r a t u r e c o n s t r a i n t s f r o m p h a s e e q u i l i b r i a d e-

r i v e d f r o m t h e r m a l a u r e o l e o f O r h a n e l i g r a n o d i o r i t e . ( 1) A1 i n h o r n -b l e nd e ( S ch m i dt 1 9 9 2) ; (2 ) P h l + A n d + Q = C d + K f + V ; (3 )

M s + Q = A n d + K f + V ; ( 4) a v e r a g e t e m p e r a t u r e a s s u m i n ga H 2o = 0 .5 . A l l t h e r m o d y n a m i c d a t a ( e x ce p t f or 1 ) f r o m H o l l a n d a n dPowell (1985, 1990). S h a d e d a r e a ind ica tes p re fe r red P - T field for

aureo l e assu m i ng aH2o = 0 .5 . ( H b l h o r n b l e n d e , K y k y a n i t e , A n d

a n d a l u s i t e , Q q u a r t z , P h l p h l o g o p i t e , C d cord ie r i te , K f a lka l i fe ld -

spar , M s m u s c o v i t e , V v a p o u r ) . F o r e q u i l i b r i a (2 ) a n d ( 3 ) , d a s h e d

l ine s ind ic a te aH20 = 0 .5, s o l id l ine s aH 2o = 1

T h e j a d e i t e + p a r a g o n i t e + q u a r t z a s s e m b l a g e c o n -

s t ra i n s t h e p r e s s u r e t o b e t w e e n 1 2 a n d 2 5 k b a r , a n d

t h e s i l ic a c o n t e n t o f th e p h e n g i t e s g iv e s a m i n i m u m

p r e s s u r e o f 1 4 k b a r s a t 4 3 0 ~ C ( M a s s o n e a n d S c h r e y e r

1987) . P r e s su r e s a r e f u r the r c ons t r a ine d by the e qu i l i b -

r i a i n v o l v i n g c h l o r it o i d , g l a u c o p h a n e , p a r a g o n i t e , c h l o -

r i t e a n d qua r t z t o 20 _+ 2 kba r a t 430 ~ C , de r ive d f r o m

t he p r og r a m m e T H E R M O C A L C a n d t he en l ar ge d

s e lf -c o n si s te n t t h e r m o d y n a m i c d a t a s e t o f H o l l a n d a n d

P o w e l l ( 19 90 ). T h e a b s e n c e o f g a r n e t i n b o t h m e t a b a s i c

a n d m e t a p e li t ic c o m p o s i t io n s i n d ic a te s m a x i m u m t e m -

p e r a t u r e s o f a b o u t 4 5 0 ~ C , w h i l e t h e c h l o r i t o i d - g l a u -

c o p h a n e e q u il ib r ia i n d i c a te m i n i m u m t e m p e r a t u r e s o f

4 2 0 ~ a t 2 0 k b a r . T h e o v e r a l l e st i m a t e f o r t h e P-Tc ond i t i ons o f m e ta m or p h i s m i s 430 ___ 30 ~ a nd

2 0 4- 2 k b a r f o r t h e K o c a s u r e g i o n ( O k a y a n d K e l l e y

1994) . The b lue sc h i s t s e que nc e in t h i s r e g ion c a n be

t r a c e d l a t e r a ll y t o t h e w e s t e r n m a r g i n o f t h e

g r a n o d i o r i t e i n d i c a t i n g s i m i l a r P-T c o n d i t i o n s f o r t h eb l u e s c h i s t s s u r r o u n d i n g t h e g r a n o d i o r i t e .

D e p t h o f i n t r u s io n o f g ra n o d i o r i t e

C o n d i t i o n s o f e m p l a c e m e n t fo r t h e g r a n o d i o r i t e c a n b e

d e t e r m i n e d b y h o r n b l e n d e - p l a g i o c l a s e t h e r m o m e t r y

( B l u n d y a n d H o l l a n d 1 99 0) w h i c h y ie l d s t e m p e r a t u r e s

o f 7 2 0 - 7 7 0 (+_ 7 5 ~ w i t h l o w e r t e m p e r a t u r e s re -c o r d e d b y t h e r i m s o f z o n e d p l a g i o cl a s e c ry s t a ls . T h ep e a k t e m p e r a t u r e p r o v i d es a m i n i m u m c o n s t r a i n t o n

t h e l i q u i d u s t e m p e r a t u r e a n d i s c o n s i s t e n t w i t h e x p e r i-

m e n t a l l y d e t e r m i n e d c r y s t a l l i s a t i o n t e m p e r a t u r e s f o r

i n t e r m e d i a t e m a g m a s ( P i w i n s k ii 1 9 7 3 ) . E m p l a c e m e n t

m a y h a v e b e e n a t s o m e w h a t l o w e r t e m p e r a t u r e s i fa c r y t a l - m a g m a m i x w a s i n t ru d e d .

A n a p p r o x i m a t e p r e s s u re o f e m p l a c e m e n t is p r o -

v ide d by the A 1 c on te n t o f a m ph ibo le . P r e s su r e s o f

3 .4 _+ 2 .0 kb a r a r e de r ive d f r om the f o r m u la t ion o f H a m -

m a r s t r o m a n d Z e n ( 19 86 ) a n d a m o r e r e c e n t a n d p r e c is eba ro m et er (Sc hm idt 1992) yields 3.5 __+ 0.6 kba r (Fig. 2).

A sse m bla ge s f r om pe l i te s w i th in t he t he r m a l a u r e o le

inc lude a nda lu s i t e - c o r d i e r i t e - a lka l i f e ld spa r -p l a g ioc l a se -

qua r t z - b io t i t e . The p r e se nc e o f a nda lu s i t e i n t he a b se nc e

o f m u sc ov i t e i nd i c a te s t ha t c o nd i t i ons h a ve e xc e e de d

t h o s e r e q u i r e d f o r m u s c o v i t e b r e a k d o w n i n t h e a n -

da lu s i t e s t a b il i t y fi e ld w h ic h p r ov ide s a m a x im um p r e s -

sure co ns t ra in t of 3.5 kb ar ( for aH2o = 1) wh ich inc reases

to 4 k ba r ( for aH2o ---- 0 .5) . Th e bes t -con s t ra in ed equi l ib-

r ium in t he a u r e o le a s se m bla ge i s g ive n by

A n d a l u s i t e + P h l o g o p i t e + Q u a r t z =

C o r d i e r i t e + A l k a l i F e l d s p a r + H 2 0 .

T h i s p r o v i d e s a b a r o m e t e r t h a t i s s t r o n g l y d e p e n d a n t

on w a te r a c t i v i t y . I f a H 2o = 1 . 0, a m a x i m um p r e s su r e o f

2 .4 +_ 0 .8 kb ar i s o bta ine d f rom ac t iv i t ie s c a lcu la ted

f r o m m i n e r a l c o m p o s i t i o n s i n T a b l e 1 , b a s e d o n t h e

e n l a r g e d s e l f- c o n s is t e n t t h e r m o d y n a m i c d a t a s e t o f

H o l l a nd a nd P ow e l l ( 1990 ) . Th i s r i s e s t o a p r e s su r e o f

3.2 -t- 0.8 kb ar for aH2o = 0.5 (Fig . 2).

T h e r e is n o i n d e p e n d e n t e v i d e n c e f o r w a t e r a c t i v i ty

d u r i n g i n t r u s i o n o f th e g r a n o d i o r i t e , b u t t h e s t at i st i ca l

a na ly s i s o f m u l t i p l e e qu i l i b r i a p r o v ide d by c oe x i s t i ng

pha se s a s g ive n by P ow e l l a nd H o l l a nd ( 1985 ) sugge s t s

tha t a h igh w a te r a c t i v i t y r e qu i r e s a l ow p r e s su r e o f

e m p l a c e m e n t . I f a l h o = 1 t h e n t h e a v a i la b l e t h e r m o -

m e t e r s f r o m t h e c o e x is t i n g e n d m e m b e r s q u a r t z , M g -

c o r d i e r i t e , F e - c o r d i e r i t e , ph logop i t e , a nn i t e , e a s ton i t e ,

a lka l i f e ld spa r a nd a nda lu s i t e on ly p r ov ide a s t a t i s t i c a l

f i t w i th in 95% c on f ide n c e l im i t s f o r p r e s su r e < 1 kba r .

T h e c a l c u l a t e d t e m p e r a t u r e a t t h i s p r e s s u r e i s

537 __ 30 ~ C . At low er w ate r ac t iv i t ie s , th is con s t ra in t i s

r e l a xe d ; f o r an~ o = 0 .5 , t he da t a f i t up to p r e s su r e s o f3 .5 kb ar g iv ing tem pe ra tu res of 655 ___ 35 ~ C . H enc e

b a r o m e t r y f r o m p h a s e e q u i l i b ri a i n t h e a u r e o l e a n d

f r o m A 1 c o n c e n t r a t i o n s i n a m p h i b o l e f r o m t h e i g n e o u s

a s s e m b l a g e c a n b e r e c o n c i l e d a t p r e s s u r e s o f

3 . 0 -3 . 5 kba r p r ov ide d a H ~o < 1. Te m pe r a tu r e s r e c o r de db y g e o t h e r m o m e t e r s w i t h i n t h e a u r e o l e a r e o n l y o f lo c a l

s ign i f i c a nc e s inc e l a t e r a l t e m pe r a tu r e g r a d i e n t s a w a y

f r om the m a r g in o f t he i n t r u s ion w i ll be s t ee p . Th ep r e se nc e o f s il l im a n i te w i th in so m e a u r e o le a s se m bla ge s

f r o m t h e T o p u k i n t r u s i o n ( L i s en b e e 1 9 7 2 ) i n d ic a t esh ighe r t e m pe r a tu r e s w e r e r e a c he d loc a l ly i n t he a u r e o le .

W e c o n c l u d e t h a t t h e O r h a n e l i i n t r u s i o n w a s e m -

p l a c e d a t p r e s s u r e s o f 3 4 - 1 k b a r ( ~ 1 0 k m ) a n d t h a t

w a te r a c t i v i ti e s , a t l e a s t l oc a l ly w i th in t he a u r e o le , w e r el e s s t h a n u n i t y . T e m p e r a t u r e s i n t h e a n a l y s e d a s s e m -

b l a g e f r o m t h e a u r e o l e d i d n o t e x c e e d 6 90 ~ C , a l t h o u g hm a g m a t i c t e m p e r a t u r e s w e r e i n e x ce s s o f 7 70 ~



Table 1 Representative mineral analyses from Orhaneli intrusion

and country rock (P1 plagioclase, Hbl hornblende, B t biotite, Cd

cordierite, e core, r rim)

Sample Orhaneli granodiorite Thermal aureole

P1 (c) P1 (r) Hbl Bt Cd Bt

3861 3861 3861 38 61 3867a 3867a

Wt%

SiO 2 57 .8 1 59.33 45.74 36.08 47.39 34.36

TiO 2 0.01 0.00 0.92 3.51 0.02 2.85

A120 3 25.87 25.05 7.8 3 1 4. 4 9 32.53 19.9 5

Fe 20 3 0.19 0.10 4.20 1.66 -

FeO - - 11.4 4 17.84 10 . 18 22.56

Mn O 0.00 0.00 0.70 0.73 0.53 0.11

Mg O 0.00 0.00 12.30 12.22 6.11 6.28

Ca O 7.34 6.55 12 .0 6 0.00 0.05 0.00

Na 20 7.12 8.04 1.17 0.07 0.14 0.00

K2 0 0.33 0.18 0.74 9.57 0.01 9.45

Total 98.67 99.25 97.10 94.51 98.62 95.56

O 8 8 23 11 18 11

Si 2.62 2.67 6.81 2.78 4.95 2.65

Ti 0.00 0.00 0.10 0.20 0.00 0.17

A1 1.38 1.33 1.38 1.31 4.00 1.81

Fe 3+ 0.07 0.03 0.47 0.13 -

Fe z + 1.43 1.15 0.89 1.45

Mn 0.00 0.00 0.09 0.05 0.05 0.01

Mg 0.00 0.32 2.73 1.40 0.95 0.72

Ca 0.36 0.70 1.93 0.00 0.01 0.00

Na 0.63 0.01 0.34 0.01 0.03 0.00

K 0.02 8.04 0.14 0.94 0.00 0.93

G e o c h e m is t ry o f t h e O r h a n e l i a n d T o p u k in t r u s io n s

M a j o r - e l e m e n t g e o c h e m i s t ry o f th e O r h a n e l i g r a n o -d i o r i t e ind i c a t e s a un i fo r m me t a l um i nou s , c a l c -al ka l inec om pos i t i on wi t h s il ic a c on t e n t s o f 63 -65 % (Ta b l e 2) .

T h e T o p u k g r a n o d i o r i t e i n c lu d e s s o m e w h a t h i g h e r sil-i c a c on t e n t s (65 -69% ) bu t i n o t he r r e spe c t s i s ge o -

c he mi c a l l y s i mi l a r t o bo t h t he Orh a ne l i g ra nod i o r i t ea n d t o t h e G f i r g e n y a l a a n d G 6 y n f i k b e l e n g r a n o d i o r it e si n t r u d e d s o u t h o f th e I z m i r - A n k a r a s u t u r e ( E r c a n a n dTf i rke c a n 1984). The a p l i ti c s a mpl e s f rom t he Orh a ne l i

c a ra pa c e a re c ha ra c t e r i s e d by t he m a j o r e l e m e n t c he m-

i s try o f a pe ra l u mi n ous rhyo l i t e (S iO2 = 70 72% ) ,l o w er C a, F e a n d M g a n d h i g he r N a a n d K c o m p a r e d

t o t he g ra no d i o r i t e . The se t r e nds a re c ons i s t e n t wi t h

fo rm a t i on o f t he a p l it i c rhyo l it e by f r a c t i ona t i on o fa mph i bo l e a nd pos s i b l y p l a g i oc l a se f rom t heg r a n o d i o r i t i c m a g m a .

T h e t r a c e - e l e m e n t g e o c h e m i c a l t r e n d s f r o m b o t h

g r a n o d i o r i t e s s h o w e n r i c h m e n t i n L I L ( la r g e- io n -l i thophi le ) e lements (F ig . 3a ) wi th deple t ion of HFS(h i gh -f i e ld - s tr e ng th ) e l e me n t s suc h a s Z r , H f a n d HR EE

(heavy-ra re -ea r th e lements) re la t ive to an Ocean RidgeGr ani te (P earce e t a l. 1984) s imi la r to b oth volcanic -a rca nd pos t -c o l li s ion i n tru s i ons . The To pu k g ra nod i o r i t e iss l igh t ly e n r i c he d in Y a nd H RE E bu t de p l e t e d i n Ba, S r

and Th, re la t ive to the Orhane l i samples . No di f fe renceswe re foun d i n t r a c e -e le me n t ge oc he mi s t ry be t we e n t he

245

f i ne -g ra i ne d a nd t he m e d i um -gra i ne d fac ie s wi t h i n t he

Topuk i n t ru s i on , i nd i c a t i ng a c ommon sou rc e .

The a p l i t i c f ac ie s f rom t he Orh a ne l i p l u t on de m on-

s t r a te s va r i a b l e t r a c e -e l e me n t c ha ra c t e r is t i c s c om pa re dt o t h e g r a n o d i o r i t e . T h e L I L E ( R b , B a a n d T h ) a r es t rong l y e n r i c he d whe re a s Y i s de p l e t e d . Inc ompa t i b l et r a c e -e l e me n t r a t io s , suc h a s Nb / T a , a re u nusua l l y

h i gh ( > 30) fo r m a gm a t i c roc ks , r e f le c t ing t he r e l a t ives t a b il i ty o f HF S E- vo l a t i l e c ompl e xe s r a t he r t ha n c rys-

t a l / l iqu i d e qu i l i b r i um.T h e a b s e nc e o f a d e te c t ab l e e u r o p i u m a n o m a l y i n

t h e c h o n d r i t e - n o r m a l i s e d R E E p l o t f o r t h e O r h a n e l igranodior i te (F ig . 4a ) sugges ts tha t p lagioc lase f rac -

t i ona t i on ha s n o t p l a ye d a s i gn i fi c a n t ro l e it s fo rma t i on .

I n c o n t r a s t , t h e n e ga t iv e E u a n o m a l y o b s e r v e d i n s o m e

sa mpl e s f rom t he Topuk i n t ru s i on (F i g . 4a ) i nd i c a t e s

t he e qu i l i b ra t i on o f the me l t wi t h f e l d spa r . The H RE Ea n d Y d e p l e t i o n m a y b e c o n t r o l l e d b y g a r n e t i n t h e

sou rc e , f r a c t i ona t i on o f a mph i bo l e o r a c c e s so ry pha se

b e h a v i o u r w h i c h m a y b e c o m e i n c r e a s i n g l y i m p o r t a n ti n more e vo l ve d me l t s . F o r t he g ra nod i o r i t e s , t he l a c ko f c o r r e l a ti o n b e t w e e n H R E E ( o r Y) a n d Z r a b u n d -

a nc e s sugge s t s t ha t z i r c on f ra c t i ona t i on ha s no t c on -t r i bu t e d s i gn i f i ca n t l y t o RE E e v o l u t i on i n t he ma g ma .

F o r t he a p l i ti c fa ci es , Y a nd HR EE -de p l e t i on (F i g .3a ) p roba b l y r e su l t e d f rom f ra c t i ona t i on o f a mph i bo l e ,

c o n s i s te n t w i t h t h e s h if t fr o m m e t a l u m i n o u s t o

p e r a l u m i n o u s c o m p o s i t i o n s . H o w e v e r , p e t r o g e n e t i cmo de l l i ng fo r a p l it i c roc ks i s poo r l y c on s t ra i ne d d ue t o

the uncer ta in t ies in c rys ta l / l iquid d is t r ibut ion coeff i -c i e n t s du r i ng vo l a t i l e - r i c h f r a c t i ona t i on . The h i gh l y

va r i a b l e LI LE a bun da n c e s r e f l ec t the s t a b i li t y o f ac c e s-

so ry pha se s u nde r c ond i t i ons o f va r i ab l e f l u i d f l uxduring the f ina l s tages of c rys ta l l iza t ion .

A v a i la b le d a t a c a n n o t c o n f i r m w h e t h e r t h e q u a r t z -d i o r i t e e nc l a ve s we re c osa ngu i ne ous wi t h t heg ra nod i o r i t e be c a use subso l i dus f e l d spa r g rowt h ha s

c l e ar l y oc c u r re d w i t h i n t he e nc l a ves , thus mo d i fy i ng t hei n i ti a l igne ous c om pos i t i on , at l e a s t fo r LI L e l e me n t s . I tc ou l d be a rgue d t ha t t he de p l e t i on i n Ba a nd Y se e n i n

t he hos t g ra no d i o r i t e r e l a ti ve t o t he e nc l a ve s i nd i c a te s

t h a t a c o m b i n a t i o n o f a m p h i b o l e a n d b i o ti t e fr a c ti o n a -t i o n h a s c o n t r o l l e d m a g m a e v o l u t io n .

A r . A r c h r o n o l o g y

La se r - spo t a na l yse s we re pe r fo rme d on b i o t i t e , ho rn -b l e n d e a n d g l a u c o p h a n e f r o m th e O r h a n e l i a n d T o p u k

gra nod i o r i t e s , a ho rn fe l s f rom t he ma rg i n o f t heOrha ne l i i n t ru s i on , t wo b l ue sc h i s t s a nd a ga rne t a m-ph i bo l i t e a t t he ba se o f t he o ph i o l i t e s e que nc e . Ana l yse s

f rom be t we e n 5 a nd 10 l a se r spo t s we re p l o t t e d ona 36Ar / g~ ve r sus 39Ar /4~ d i a g r a m fo r e a c h s a mp l et o de t e rm i ne bo t h t he a ge a nd 36Ar /4~ i n t e rc e p t

value (Fig. 5, Table 3).

Te n l a se r - spo t a na l yse s o f b i o t i t e f rom t he Or ha ne l ig ra nod i o r i t e (4419a ) y i e l de d a good i soc h ron wi t h a n



2 4 6

T a b l e 2 C h e m i c a l a n a ly s e s f r o m O r h a n e l i a n d T o p u k i n t r u s i o n s (LOI o s s o n i g n i t i o n )

S a m p l e O r h a n e l i g r a n o d i o r i te T o p u k g r a n o d i o r i te E n c l av e s A p l i te

3 9 9 2 4 2 1 9 3 9 0 5 3 8 6 1 4 4 2 5 A 4 4 2 7 A 4 4 2 9 A 4 4 1 3 A 4 4 1 9 B 3 9 0 0 3 8 9 7

W t%S iO2 63 .65 64 .75 65 .16 65 .44 65 .86 69 .26 65 .51 55 .26 54 .11 69 .53 72 .25

T iO 2 0 .44 0 .45 0 .39 0 .40 0 .40 0 .31 " 0 .41 0 .69 0 .74 0 .17 0 .22

A lzO 3 17.27 16.66 16.67 16.88 16.65 16.08 16.82 16.34 18.48 15.65 14.91F e 20 3" 4 .37 4 .40 3 .76 3 .64 4 .39 3 .37 4 .48 7 .65 8 .05 1 .69 0 .81

M n O 0 .10 0 .09 0 .09 0 .08 0.11 0 .11 0 .14 0 .32 0 .24 0 .01 0 .01

M g O 1.77 1.91 1.48 1.46 1.76 1.06 1.26 5.78 4.49 0.17 0.08

C a O 5 .27 4 .93 4 .96 4 .77 5 .28 4.41 5 .27 7 .83 7 .25 0 .51 0 .15

N a 2 0 3 .92 3 .55 3 .99 3 .86 3 .29 3 .65 3 .62 2 .86 3.83 5 .96 4 .81

K 2 0 2.05 2.27 1.72 2.16 1.92 1.99 1.91 2.03 1.92 4.95 6.08

P 2 05 0 .23 0 .13 0 .12 0 .19 0 .14 0 .11 0 .14 0 .26 0 .14 0 .04 0 .06

L O I 0 .50 0 .68 0 .71 0 .57 0 .91 0 .49 0 .63 1 .22 0 .99 0 .37 0 .47

T o ta l 99 .57 99 .82 99 .05 99 .45 100 .71 100 .84 100 .19 100 .23 100 .25 99 .05 99 .84

P p m

R b 7 3 7 1 6 2 7 6 6 4 7 0 7 2 7 8 7 7 1 6 7 1 3 6

B a 8 4 8 6 7 2 5 3 5 6 7 2 3 4 3 4 6 7 4 0 2 6 3 4 4 8 3 1 2 9 9 1 2 6 6

S r 7 1 4 3 8 0 4 7 7 5 5 0 2 9 1 2 9 2 3 2 9 3 6 6 3 3 5 9 2 6 5 4 7

N b 10 8 9 10 7 8 9 11 14 18 21Z r 175 99 107 129 113 122 141 64 102 256 103

Y 19 17 17 17 23 21 25 44 45 11

T a 0 .54 0 .53 0 .65 0 .66 1 .00 0 .59 0 .56 0 .35 0 .64 0 .58 0 .62

H f 4.34 2.94 3.35 3.97 3.39 3.53 3.98 2.45 3.28 8.98 3.16

T h 12 .10 8 .04 9 .19 9 .42 6 .15 9 .56 8 .94 4 .46 9 .09 76 .10 12 .40

U 2.21 2.92 2.93 1.39 4.29 1.87 2.11 1.30 2.36 15.70 3.98

L a 42 .60 16 .20 23 .60 25 .60 19 .40 25 .40 27 .60 15 .10 26 .40 47 .40 34 .00

Ce 81 .70 32 .60 44 .20 51 .00 46 .60 49 .50 54 .50 39 .50 46 .30 83 .30 80 .50

N d 33 .80 16 .10 18 .20 24 .40 30 .00 21 .30 23 .80 33 .70 20 .80 30 .70 33 .10

S m 5 .13 2 .96 3 .43 4 .10 6 .80 3 .69 4 .31 7 .87 3 .81 4 .25 4 .32

Eu 1.38 0.88 0.88 1.12 1.58 0.97 1.07 1.91 0.96 1.22 0.99

T b 0 .59 0 .44 0 .49 0 .52 1 .19 0 .56 0 .67 1 .22 0 .57 0 .47 0 .40

Yb 1.89 1.80 1.88 1.87 4.65 2.32 2.69 4.52 2.65 0.82 0.66

L u 0 .28 0 .29 0 .31 0 .32 0 .77 0 .38 0 .46 0 .76 0 .47 0 .12 0 .09

a A l l F e c a l c u l a t e d a s F e 2 0 3

a ge o f 52 .6 _+ 0 .4 M a a nd a n M S W D of 1 .6 ( Fig . 5a ).

T h e n o n - r a d i o g e n i c c o m p o n e n t f a l l s w i t h i n e r r o r s o f

the a tm osp he r i c r a t i o ( 4~ = 302 _+ 8 ). F ive a na -

l y se s o f f i n e - g r a in e d b i o t i te ( w i t h m i n o r a m p h i b o l e

in t e r g r ow th ) f r om a ho r n f e l s ( 4410 ) , s a m p le d tw o

m e t r e s f r o m t h e g r a n o d i o r i t e c o n t a c t , y i el d a n i s o c h r o n

a ge o f 52 .4 _+ 1 .4 M a w i th a n M S W D of 0 .5 ( F ig . 5b )a nd a n in t e r c e p t o f 301 _ 10. S inc e a ge s f r om bo th

g r a n o d i o r i t e a n d i t s f i n e - g r a i n e d h o r n f e l s a r e w i t h i ne r r o r , t h e y i n d i c a t e r a p i d c o o l i n g a f t e r i n t r u s i o n a t

a h igh leve l in the c rus t , 52 .6 _+ 0 .4 M a ago.

L a s e r - s p o t a g e s o f s ix b io t i t e a n d t w o h o r n b l e n d e

g r a i n s f r o m t h e T o p u k g r a n o d i o r i t e ( 44 2 7 a) y i e ld e d a ni soc h r on o f 47 .8 _+ 0 .4 M a w i th a n M S W D of 1 .4 (F ig .

5 c) a n d a n i n t e r c e p t i n d i c a t i n g s m a l l a m o u n t s o f ex c e ssa r g o n ( 4 ~ = 314 _+ 5) poss ib ly re f lec t ing a rgon

i n t r o d u c e d d u r i n g t h e d e f o r m a t i o n o f th i s p l u t o n w h i c hh a s u n d e r g o n e s i g n i f i c a n t d u c t i l e / b r i t t l e d e f o r m a t i o n .T h e h o r n b l e n d e a n a l y s e s d o n o t y i e l d a s i g n i f i c a n t l yd i f fe r e n t a g e w h e n s e p a r a t e d f r o m t h e b i o t it e , t h o u g ht h e l o w e r p o t a s s i u m c o n t e n t m a k e s t h e a g e s l e s s p r e -

c is e. T h e a g e o f t h e T o p u k g r a n o d i o r i t e i s t h e r e f o r e

y o u n g e r t h a n t h a t o f t h e O r h a n e l i i n t ru s i o n, t h o u g h t h e

a ge s d i f f e r by l es s t ha n 4 M a .

T w o b l u e s c h i s t s a m p l e s w e r e a n a l y s e d f r o m t h e

s a m e l o c a l i t y ; a g l a u c o p h a n e - l a w s o n i t e m e t a c h e r t

( 4414a ), a n d g l a uc o pha n e - a lb i t e - c l i noz o i s i t e m e ta -

ba s i t e (4414b). P he n g i t e w a s n o t d e t e c t e d in e i t he r

sa m ple . S e ve n l a se r - spo t a na ly se s o f l a rge ( 1 - 2 m m

i n l e n g t h ) g l a u c o p h a n e s i n s a m p l e 4 4 1 4 a y i e l d e d a ni s o c h r o n a g e o f 1 08 .1 + 3 .7 M a a n d a n M S W D o f 1.2

( F ig . 5d ). H ow e ve r , t h i s s a m p le ha s a s ign i f i c a n t exc e s s

a r g o n c o m p o n e n t r e f l ec t e d i n t h e i n t e rc e p t v a l u e o f

486 _+ 11 a n d a l l a na ly se s r e l e a se d g r e a t e r t h a n 50%n o n - r a d i o g e n i c a r g on . T h e l o w M S W D o f t h e is o c h r o n

r e fl e ct s t h e h o m o g e n e i t y o f t h e e x ce s s a r g o n c o m p o n -e n t i n t h e g l a u c o p h a n e s , i m p l y i n g t h a t t h e a g e is r e al .

T h e a g e fa ll s w i t h i n t h e r a n g e o f K - A r a g e s

( 1 2 5 -6 5 M a ) f r o m t h e b l u e s c h is t s o f t h e T a v s a n l i Z o n e( O ka y 1986) a s doe s a l a se r 4~ a na ly s i s o f phe n -g i t e f r om a b lue sc h i s t 15 km f u r the r w e s t t ha t y i e lde d

a n a ge o f 88 _+ 1 M a ( O k a y a nd K e l l e y 1994 ) . S a m p le



A1 0 C

e ~

o

0 . 1

9

/ I

I\ \ /i

i

\ \

R i b B l a l~ h T a N I b C l e H I f Z I r S ~ ' Y b

B1 0 0

n -O

cz~

1 0

0 .1

R i b E ~a T h " Fa N I b ( ~ e H f Z [ r S m Y Y b

Fig. 3A,B Trace-element variation diagram, norm alised against

O R G (Pearce et al. 1984). A Orhane l i granod ior i te ( I 3 9 9 2 ,

[] 3905), Topuk granod ior i te (A 4425a, /~ 4429a) , Orhane l i ap l i te( 0 3 9 00 ). B ( 0 Q u a r t z diorite from Adamello Massif ,

S i O 2 = 6 5 . 2 % , D u p u y e t al. 1982, 9 Granodiorite from I d a h o ,

S iOz = 71 . 3%, C la r k e 1990, 9 Daci te from B a s i n - a n d R a n g e ,

S i O 2 = 6 3 . 1 % , D a v i s e t al . 1993) . Shaded area indicates range from

O r h a n e l i a n d T o p u k granod ior i te s

4 4 1 4 b d i d n o t h e l p c o n s t r a in t h e c h r o n o l o g y o f b lu e -

s c h i s t m e t a m o r p h i s m , t h o u g h i t e x h i b i t e d a s i m i l a r

e x c e s s a r g o n c o m p o n e n t t o 4 4 1 4 a ( F i g . 5 d ) . T h e g r e a t e r

s p r e a d i n 36Ar/4~ r a t i o s fr o m 4 4 1 4 b p r o b a b l y r e fl ec t s

l a t e r a l t e r a t i o n a n d c a r b o n a t e f i l l e d m i c r o f r a c t u r e s

o b s e r v e d i n t h e s e c t i o n .

24 7

10 0

"t -"C 3

o

EC O

1C

[ I I I I I I I 1 I I I I

L a C e N d S m E u T b Y b L u

(

I 0 0 ~

o

G O

1[

I I I I I I I I I L I I f

LaCe Nd SmEu Tb Yb ku

F ig . 4A, B Chondr i te -normal ised rare -earth e lement d i a g r a m . A O r -

h a n e l i granod ior i te d iagon a l sh ad in g ( I 3992, [] 39(1,5), T op uk

granod ior i te st ipple (A 4 4 2 5 a , A 4 4 2 9 a ) B ( I Q u a r t z diorite

f ro m A d a m e l l o M as si f, S I O 2 = 6 5 . 2 % , D u p u y e t al. 1982,

9 Granod ior i te from I daho , S iO2 = 71 . 3%, C la r ke 1990 , 9 Daci te

from New Mexico , Bas in -and Range P rov ince , S i O a = 6 3 . 1 % ,

D a v i s e t al . 1993) . Shaded area indicates range from Orhaneli a n d

T o p u k granod ior i te s

A l t h o u g h n o l a b o r a t o r y d e r i v e d a r g o n d i f f u s io nd a t a e x i s t s f o r g l a u c o p h a n e , w h e r e i t h a s b e e n m e a s -

u r e d g l a u c o p h a n e h a s g e n e r a l l y y i e l d e d c o n c o r d a n t o r

y o u n g e r a g e s t h a n c o e x i s ti n g w h i te m i c a s ( M c D o w e l l e t

a l . 1 9 8 4 a n d r e f e r e n c e s t h e r e i n ) . T h e r e a s o n f o r t h e

a p p a r e n t v a r i a t i o n o f c l o s u r e t em p e r a t u r e s p r o b a b l y

l ie s in t h e i n c l u s i o n o f s m a l l q u a n t i t i e s o f f in e - g r a i n e d

i m p u r i t i e s s u c h a s w h i t e m i c a , w h i c h h a v e a m a r k e d

e ff e ct u p o n a g e s o f th i s lo w p o t a s s i u m m i n e r a l ( S i s s o n

a n d O n s t o t t 1 9 8 6 ) . T h e r e v e r s e d s i t u a t i o n i n t h e

T a v s a n l i Z o n e m a y r e fl ec t t ru e v a r i a t io n o f t h e a g e s o f

p e a k m e t a m o r p h i s m i n th e b l u e sc h i st s. M o r e o v e r p r is -

t in e b l u e s c h i s t- f a c ie s a s s e m b l a g e s w e r e s e l e c t ed s o t h a t



<

Table 3 Ar-isotope results andisochron ages (G d granodiorite,H fl hornfels, Gt garnet, B t bio-tite, Gl glaucophane, H bl horn-blende)

Sample Lithology Mineral 4~ 4~ MSWD n Age (Ma)

4419a Gd (Orhaneli) Bt 5.409 • 0.148 301 _ 10 1.6 10 52.4 _+ 1.44410 Hfl (Orhaneli) Bt 5.433 _+ 0.039 302 • 8 0.5 5 52.6 _+ 0.44427a Gd (Topuk) Bt + Hbl 4.927 __ 0.038 314 • 5 1.4 8 47.8 _+ 0.44414a Blueschist G1 11.328 _+ 0.396 486 • 11 1.2 7 108. 1+ 3.74433 Blueschist G1 2.538 _+ 0.028 9

4415b Gt-amphibolite Hbl 10.584 _+ 0.401 292 + 15 0.9 9 101.1 _+ 3.8

0,003

0.002

0

0.001

A0.003

cO

0.003

0.002

0.001

0.052

0.001

0 0

0 0.05 0.1 0.15 0.2

,<

0.003

0.002

0.001

39Ar/4OAr

C

0 0.05 0.1 0.15 0.2

39Ar/4OAr

0.02 0,04 0.06 0.08

0

0 0.1

248

39Ar/4OAr

t h e r e i s n o p e t r o g r a p h i c e v i d e n c e t o s u p p o r t r e s e t t i n g

o f a g e s d u r i n g a g r e e n sc h i s t o v e r p r in t . F u r t h e r w o r k i s

u n d e r w a y t o r e s o l v e t h e s i g n if i ca n c e o f th e r a n g e i n

a g e s f o r b l u e s c h i s t m e t a m o r p h i s m .

T h e g a r n e t a m p h i b o l i t e ( 4 4 1 5 b) w a s s a m p l e d f r o m

a t h r u s t - b o u n d p o d b e n e a t h t h e o p h i o l i t e s e q u e n c e .

N i n e l a s e r - s p o t a n a l y s e s o f a m p h i b o l e y i e l d e d a n i s o c h -r o n a g e o f 1 0 1. 1 _+ 3 .8 M a w i t h a n M S W D o f 0 .9 . T h e

i n t e r c e p t v a l u e l ie s w i th i n e r r o r s o f a t m o s p h e r i c a r g o n( 4 ~ = 2 9 2 _+ 1 5 ) . T h i s p r o v i d e s a n a g e f o r e a r l y

0.003

0.002

0.001

0 0.05 0.1 0.15

3 9 A r / 4 0 A r

0 0.02 0.04 0.06 0.08

3gAr/4OAr

B

0.2

D

0.1

Fig. 5A-E 4~ correlation diagrams for the Orhanel i region:A Biotite from the Orhaneli granodiorite (4419a); B Biotite andhornblende from the Orhanel i aureole (4410); C Hornblende fromthe Topuk granodiorite (4427a); D Glaucophane from blueschist-facies assemblages ([~ 4414a, 9 4414b); E Hornblende from garnet

amphiboli te (4415b)

c o o l in g f r o m a m p h i b o l i t e - g ra d e m e t a m o r p h i s m o f t h e

m e t a m o r p h i c s o le o f t h e o b d u c t e d o p h io l it e .

P e t r o g e n e s is o f t h e g r a n o d io r i t e s

T h e O r h a n e l i a n d T o p u k i n t r u s i o n s a r e p a r t o f a s u it e

o f E o c e n e d i o r it e s a n d g r a n o d i o r i t e s f r o m n o r t h -

w e s t A n a t o l i a t h a t p o s t - d a t e c o l l is i o n. T h e a b s e n c e o f



c o m p o s i t i o n s m o r e p r i m i t i v e t h a n q u a r t z d i o r i t e s u g -

g e s ts e i t h e r t h a t b a s i c m a g m a s h a v e d i f f e r e n ti a t e d a n d

f a il e d to r e a c h t h e l ev e l o f e m p l a c e m e n t o f t h e m o r e

e v o lv e d m a g m a s , o r t h a t m a g m a s o f i n t e r m e d i a te c o m -

p o s i t i o n h a v e b e e n g e n e r a t e d b y c r u s t a l m e l ti n g . I n i ti a l

S r - i so tope r a t i o s l e s t ( T ) = + 30 to + 58 ; V a c he t t e e ta l. 1968 ; A ta m a n 1972] do n o t he lp r e so lve t he se a l t e r-

na t ive s s inc e suc h i so top ic r a t i o s a r e c ons i s t e n t e i t he rw i t h a s o u r c e i n t h e l i t h o s p h e r i c m a n t l e , e n r i c h e d b y

s u b d u c t i o n , o r w i t h a n a t e x i s o f a c r u s t a l p r o t o l i t h o f

i n t e r m e d i a t e c o m p o s i t i o n .

F r a c t i o n a l c r y s t a ll i s a t io n o f b as i c m e l t s

The ge oc he m ic a l c ha r a c t e r i s ti c s o f t he O r ha ne l i a nd

T o p u k g r a n o d i o r i t e s a r e c o n s i s t e n t w i t h f r a c t i o n a t i o n

f r om a ba s i c m e l t , a s c a n be s e e n by c om pa r ing the i r

t r a c e -e l e m e n t g e o c h e m i s t r y w i t h B a s i n - a n d - R a n g e d a -

c i te s t ha t r e su l t f r om f r a c t iona l c r y s t a l l i s a ti on o f ba sa l t i c

m e l t s ( D a v i s e t a l. 1993 ) o r w i th pos t - c o l l i s ion A lp ine

in t r u s ive s , suc h a s t he qua r t z d io r i t e - tona l i t e - g r a no -

d io r i t e su i te , f rom A da m e l lo ( D u puy e t a l. 1982 ) t ha t a r e

de r ive d l a r ge ly by f r a c t iona l c r y s t a l li s a t i on o f a h yd r o us

ba sa l t a t p r e s su r e s o f 8 - 10 kba r s ( B lundy a nd S pa r ks

1992) . I n t e r m e d ia t e m a gm a s f r om a l l t h r e e p r ov inc e s a r e

c h a r a c t e ri s e d b y e n r i c h m e n t o f L I L / H F S e l e m e n t ra t io s ,

a l a c k o f de p le t i on in Y a nd H R EE ( Figs . 3b , 4b ) a nd

87Sr /S 6Sr > 0 .7065 . B a a bu nda nc e s , w h ic h a r e m a r ke d ly

h ighe r i n t he B a s in - a nd - R a nge da c i t e s t ha n in e i t he r t he

A d a m e l l o o r t h e n o r t h w e s t A n a t o l i a n i n t r us i ve s , p ro b -

a b ly r e su l t f r om the r e l a t i ve s t a b il i t y o f pha se s w i th

a l a r ge p a r t i t i on c oe f f ic i e n t f o r B a , suc h a s ph logop i t e , i nt h e s o u r c e r e g i o n s o f t h e p a r e n t a l m a g m a s .

S t u d i e s o f s u b d u c t i o n - r e l a t e d f e l s i c m a g m a t i s m

( S iO 2 = 5 6 t o 7 3 w t % ) h a v e c o n f i r m e d th a t m e l t s f r o m

a g a r n e t - b e a r i n g s o u r c e a r e s t r o n g l y d e p l e t e d i n H R E E

( Y < 1 5 p p m , Y b < 1 .4 ; D r u m m o n d a n d D e f a n t 1 9 90 ).

T h e O r h a n e l i a n d T o p u k g r a n o d i o r i t e s a r e i n s u f f i c i -

e n t l y d e p l e t e d i n Y ( 1 7 - 2 5 p p m ) a n d Y b ( 1 . 8 -4 . 6 p p m )

t o h a v e e q u i l i b r a t e d w i t h a g a r n e t - b e a r i n g r e s t i t e .

M o r e o v e r i f t h e g r a n o d i o r i t e s r e s u lt f r o m f r a c t i o n a l

c r y t a l l i s a t i o n f r o m a l e s s e v o l v e d m a g m a r e p r e s e n t e d

b y t h e d i o r i t i c e n c l a v e s , Y a b u d a n c e s i n t h e u n f r a c -

t i o n a t e d m a g m a m u s t h a v e e x c e e d e d 4 0 p p m ( T a bl e 2).

T h i s s u g g e s t s t h a t t h e m e l t f r o m w h i c h t h eg r a n o d i o r i t e s a r e d e r i v e d f o r m e d i n t h e a b s e n c e o f

g a r n e t i n t h e r e st it e , a n d h e n c e r e s u l t e d f r o m m e l t i n g o f

t h e m a n t l e w e d g e r a t h e r t h a n o f t h e s u b d u c t e d s l ab .

I t i s c l e a r t ha t p l a g ioc l a se c r y s t a l l i s a t i on be c a m e

i m p o r t a n t d u r i n g t h e f o r m a t i o n o f t h e m o r e s i l ic e o u s

m a g m a s i n t h e T o p u k i n t r u s i o n w h i c h a r e c h a r a c t e r -

i s e d by s ign i f i c a n t ne ga t ive Eu a nom a l i e s ( F ig . 4a ). Th i si n d i c a t e s i n t r a - c r u s t a l f r a c t i o n a t i o n o c c u r r e d , w i t h i n

the s t a b i l i t y f ie ld o f p l a g ioc l a se . The a bse nc e o f a pp r e c i -

a b l e E u a n o m a l i e s i n t h e O r h a n e l i g r a n o d i o r i t e d o e sno t p r e c lude a n o r ig in f r om f r a c t iona l c r y s t a ll i s a ti on o f

m or e p r im i t ive m e l t s . G e oc he m ic a l t r e nds f r om pos t -

249

subdu c t ion c a l c - alka l ine la va s f r om the B a s in - a nd - R a ng e

P r ov inc e d e m o ns t r a t e t ha t f r a c t iona t ion i s dom J[ na te d b y

ol iv ine and pyroxene in the ea r ly s tages (S iO2 < 63%)

a nd p l a g ioc l a se f r a c t iona t ion o n ly be c om e s s ign i f ic a n t in

t h e g e n e r a t io n o f m o r e e v o l v ed m a g m a s ( D a v is a n d H a w -

ke sw or th 1993 ). Eu a nom a l i e s a r e a l so im pe de d by h igh

fo2 dur ing f rac t iona l c rys ta l l isa t ion .

P a r t i a l m e l t i n g o f th e c r u s t

I n c o n t r a s t t o t h e A d a m e l l o s u i t e , c o s a n g u i n e o u s g a b -

b r o s , l a m p r o p h y r i c d y k e s o r b a s i c e n c l a v e s i h a v e n o t

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

g r a n o d i o r i t e s . T h i s m a k e s a n o r i g i n b y f r a c t io n a l c r y s -

t a l li s a t io n o f m a n t l e - d e r i v e d m e l t s m o r e e q u i v o c al .

M a g m a s o f i n t e r m e d i a t e c o m p o s i t i o n c a n b e d e r i v e d

f r o m a n a t e x i s o f t h e l o w e r c r u s t b y v a p o u r - a b s e n t

d e h y d r a t i o n r e a c t io n s o f b i o t i te a n d / o r a m p h i b o l e a t

t e m p e r a t u r e s b e t w e e n 8 25 ~ C a n d 1 10 0 ~ C ( R u t t e r a n d

W y l l i e 1 9 8 8 ). T h e b i o t i te d e h y d r a t i o n r e a c t i o n i n a s-

s e m b l a g e s o f i n t e rm e d i a t e c o m p o s i t i o n s is g i v e n b y

Biotite + Qua rtz + Plagioclase= Pyroxene+ Garnet + Melt (1)

y i e l d in g a m e l t o f g r a n o d i o r i t i c c o m p o s i t i o n , a n d a t

h i g h e r t e m p e r a t u r e s t h e i n c o n g r u e n t m e l t i n g o f h o r n -

b l e n d e y i e ld s a t o n a l it i c m e l t t h r o u g h t h e r e a c t i o n

Hornblen de + Plagioctase + Qu artz

= Pyrox ene _+ Garne t + Melt (2)

T h e p r e s e n c e o f g a r n e t i n t h e r e s ti te , w h i c h c o n t r o l s t h e

b e h a v i o u r o f H R E E a n d Y i n t h e m e l t , i s f a v o u r e d b yh i g h e r p r e ss u r e s a n d a l s o b y a h i g h F e / M g r a t i o i n th e

sou r c e .

G r a n o d i o r i t e f ro m t h e I d a h o b a t h o l i t h p r o v id e s a n

e x a m p l e o f a m e l t , w i t h s i m i l a r m a j o r - e l e m e n t c o m p o s i -

t i o n t o t h e A n a t o l i a n i n t ru s i v e s, t h a t h a s b e e n d e r i v e d

f r om pa r t i a l m e l t i ng o f t he l ow e r c r u s t i n t he s t a b i l i t y

f ie l d o f g a r n e t ( C l a r k e 1 99 0) . A l t h o u g h s h a r i n g m a n y o f

t h e g e o c h e m i ca l tr e n d s o f th e O r h a n e l i a n d T o p u k

gr a nod io r i t e s , i t i s c l e a r ly m or e de p le t e d in Y a nd

H R E E ( F i g s . 3 b , 4 b ) . T h u s a l t h o u g h t h e m o d a l c o m -

pos i t i on o f a c r u s t a l sou r c e c a n no t p r e c i s e ly be i de n t i -f ie d , t h e a b s e n c e o f H R E E d e p l e t i o n i n d i c a te s t h a t

ga r ne t w a s no t a s ign i f i c a n t r e s t i t e pha se . Th i s ha sim p l i c a t io ns f o r t he de p ths o f c r u s t a l m e l t i ng .

E x p e r i m e n t a l s t u d ie s o f v a p o u r - a b s e n t m e l t i n g o f

b i o t i t e a n d h o r n b l e n d e i n d i c a t e t h a t f o r a t o n a l i t i c

sou r c e , ga r ne t w i ll be s t a b l e a t p r e s su r e s o f 10 kb a r

( R u t t e r a nd W y l l i e 1988 ) w h e r e a s f o r a sou r c e o f g r e y -

w a c k e c o m p o s i t i o n g a r n e t m a y b e s t a b l e o n t h e s o li d u s

a t p r e s su r e s a s l ow a s 8 kb a r ( V ie l z e u f a nd M on te l1992 ) . A m or e ba s i c , a m ph ibo l i t i c sou r c e w i l l y i e ld

a t o n a l i t i c m e l t t h r o u g h r e a c t i o n (2 ) w i t h g a r n e t s t a b l ea t p r e s su r e s > 8 kb a r ( R ush m e r 1991 ).

T h e t e m p e r a t u r e o f th e s o u r c e i s cl e a r ly h o t t e r t h a n

m i n i m u m e m p l a c e m e n t t e m p e r a t u r e s f o r t h e m a g m a



250

( 770 ~ C ) a nd m a y be in f e r r e d f r o m the c r i t i c al m e l t

f r a c t ion ( W ic kh a m 1987) . F o r F > 0 .3 , su f f ic i e n t t o

a l lo w m e l t e x t r a c t io n t h r o u g h b u o y a n c y , a n d a s s u m i n g

a tona l i t i c sou r c e , t he n a t e m pe r a tu r e o f a t l e a s t 950 ~ C

i s r e q u i r e d a t p r e s s u r e s a r o u n d 1 0 k b a r ( R u t t e r a n d

Wyll ie 1988) .

T h e r m a l i m p l i c a t i o n s

T h e O r h a n e l i a n d T o p u k g r a n o d i o r it e s h a v e th e r e fo r e

f o r m e d e i t h e r f r o m d i f f e r e n t ia t i o n o f b a s i c m a g m a s i n

c r u s t a l m a g m a c h a m b e r s , p r o b a b l y a t d e p t h s o f

8 - 1 0 k b a r , o r f r o m t h e m e l t i n g o f a c r u s t a l s o u r c e a t

p r e s su r e s l e ss t ha n 10 kba r . S inc e w e c a n n o t c o nc lu s -

ive ly d i s t i ngu i sh t he s e pe t r oge ne se s on the ba s i s o f

g e o c h e m i s t r y , i t is g e r m a n e t o c o n s i d e r w h e t h e r c r u s t a l

m e l t i n g c o u l d h a v e o c c u r e d b y p u r e l y t e c t o n i c p r o -

c e s se s , i n t he a bse nc e o f m a n t l e m e l t i ng .

Te m pe r a tu r e s i n e xc e ss o f 950 ~ C a t de p th s o f a bou t

50 km c ou ld no t ha ve r e su l t e d so l e ly f r om the r m a l r e l ax -

a t ion a f t e r t e c ton ic t h i c ke n ing , e ve n i f up l i ft w a s de l a ye d

by t e ns o f m i ll i ons o f ye a r s a f t e r c o ll i s ion ( Eng la nd a nd

T h o m p s o n 1 9 8 4) . M o r e o v e r t h e p r e s e r v a t i o n o f b l u e-

sc h i s t - f a c i e s a s se m bla ge s m a ke i t un l ike ly t ha t c onduc -

t i ve he a t ing p l a ye d a s ign i f i c a n t r o l e i n m e l t i ng a c r u s t a l

s o u r c e re g i o n o f t h e g r a n o d i o r i t e m a g m a .

D e c o m p r e s s i o n o f r o c k s f r o m d e p t h s o f a r o u n d

1 0 k b a r , u n d e r v a p o u r - a b s e n t c o n d i t i o n s , w i l l c e r -

t a i n l y i n c r e a s e t h e a v a i l a b l e m e l t f r a c t i o n , p r o v i d e d

r o c k s a r e c l o s e t h e i r s o l i d u s t e m p e r a t u r e s p r i o r t o

up l i f t . S inc e t he m e l t f r a c t ion a va i l a b l e de pe nds on

t h e p r e s su r e , t e m p e r a t u r e a n d w a t e r c o n t e n t o f t h es o u r c e i t i s p o s s i b l e t o e s t i m a t e t h e m a x i m u m m e l t

f r a c t i o n t h a t c a n b e o b t a i n e d d u r i n g d e c o m p r e s s i o n .

F o r e x a m p l e t h e m e l t f r a c t i o n s o b t a i n e d f o r a s o u r c e

o f i n t e r m e d i a te c o m p o s i t i o n a n d v a r ia b l e H 2 0

c o n t e n t s a r e k n o w n f o r p r e s s u r e s o f 5 a n d 1 0 k b a r

( C le m e ns a nd V ie l z e u f 1987 , F ig. 5 ) . I f w e a s su m e tha t

t h e s o u r c e r o c k h a s a w a t e r c o n t e n t o f 0. 8 % , u p l i ft

f r o m 1 0 k b a r (a t 9 5 0 ~ t o 5 k b a r w il l r e s u l t i n

a n inc r e a se d m e l t f r a c t ion o f 0 .07 . Th i s i s a m a x im um

va lue , s i nc e i t a s sum e s f i r s t l y t ha t m e l t k ine t i c s w i l l

b e s u f fi c ie n t ly r a p i d t o m a i n t a i n t h e r m o d y n a m i c e q u i -

l i b r i u m d u r i n g e x h u m a t i o n a n d s e c o n d l y t h a t u p l if t is

su f f ic i e n tly r a p id f o r t he p r o to l i t h t o f o l low i t s a d i a ba t i cp a t h d u r i n g e x h u m a t i o n ( a s l o w e r r a t e o f e x h u m a t i o n

w i ll r e su lt i n lo s s o f he a t t h r oug h c o ndu c t ion a n d a r e -

duc e d m e l t f r a c t ion ) . W e do no t know p r e c i s e ly e i t he r

t h e t e m p e r a t u r e o r t h e d e p t h o f th e s o u r c e , b u t g i v e n

tha t m e l t i ng w a s i n i t i a t e d a t p r e s su r e s l es s t ha n 10 kb a r

a n d t h e m a g m a w a s e m p l a c e d a t ,-~ 3 k b a r w e c a n s a yt h a t t h e i n c r e a s e i n m e l t f r a c t i o n o b t a i n e d b y d e c o m -

p r e s s ion m e l t i ng o f t he c r u s t d id no t e xc e e d 0 . 1 . S uc h

a low m e l t f r a c t ion c ou ld no t ha ve l e f t i ts sou r c e t h r o ugh

b u o y a n c y ( W i c k h a m 1 98 7).T h e a v a i l a b l e A r c h r o n o l o g y a l s o d o e s n o t s u p p o r t

de c o m p r e s s io n m e l t i ng s inc e t he r e is a l a p se o f a t l e a s t

25 M a ( f r om 88 to 53 M a ) be tw e e n b lue sc h i s t -f a c i e s

m e t a m o r p h i s m a n d i n t r u s i o n o f t h e g ra n o d i o r it e .

E x h u m a t i o n o f t h e b l u es c h i st s e i t h e r o c c u r e d a l m o s t

i m m e d i a t e l y a f t e r b l u e s c h i s t - f a c i e s m e t a m o r p h i s m , o r

w a s a l r e a d y u n d e r w a y a t t h e t im e p e a k t e m p e r a t u r e s

w e r e r e c o r d e d . O t h e r w i s e , c o n d u c t i v e h e a t i n g i n

a t h i c k e n e d c r u s t w o u l d h a v e r e s u l t e d i n g r e e n s c h i s t

o v e r p r i n t i n g o f t h e h i g h P - l o w T a s s e m b l ag e s . T h e r e -f o r e m e l t f o r m a t i o n m u s t h a v e o c c u r r e d c o n s i d e r a b l y

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

c o n c l u d e t h a t m e l t i n g o f a c r u s t a l s o u r c e w a s c a u s e d b y

h e a t i n g r a t h e r t h a n b y d e c o m p r e s s io n .

T h u s t h e r m a l c o n s t r a i n t s r e q u i r e t h a t i f t h e p l u t o n s

a r e d e r i v e d f r o m a c r u s t a l s o u r c e , a d v e c t i v e h e a t i n g

f r o m m a n t l e - d e r i v e d m e l ts is r e q u i r e d . I n o t h e r w o r d s

m a n t l e m e l t i ng i s e s se n t i a l f o r t he pe t r oge ne s i s o f t he

g r a n o d i o r i t e s , e it h e r t o p r o v i d e a p a r e n t a l m a g m a , a s i n

t h e c a s e o f t h e A d a m e l l o i n t r u s iv e s , o r t o p r o v i d e a n

a d v e c t i v e h e a t s o u r c e f o r c r u s t a l m e l t in g . E v i d e n c e f o r

m o r e m a f i c m a t e r i a l a s s o c i a t e d w i t h i n t e r m e d i a t e m a g -

m a t i sm i s r e s t r i c t e d to sm a l l qua r t z - d io r i t e e nc l a ve s i n

the g r a nod io r i t e . The i r f i ne r g r a in s i z e a r gue s a ga in s t

a n a u to l i t h o r ig in , a nd i s c ons i s t e n t w i th a n o r ig in f r om

a c oe va l m e l t .

R e g io n a l t e c t o n i c s a n d p o s t . c o ll is io n m a g m a t is m

T h e a v a i l a b l e s o u r c e s f o r p o s t - c o l l i s i o n m a g m a t i s m

v a r y a c c o r d i n g t o b o t h t h e g e o m e t r y o f t h e c o l li s io n

z o n e a n d t h e t i m e e l a p s e d b e t w e e n c o l li s io n a n d m a g -

m a t i s m . A d v e c t i v e h e a t i n g f r o m m a n t l e - d e r i v e d m e lt s ,

a s obse r ve d in t he A da m e l lo M a ss if , oc c u r s ove r a t im e -s c a le o f < 1 M a ( H u p p e r t a n d S p a r k s 1 98 8) w h e r e a s

c o n d u c t i v e h e at i n g , a s o b s e r v e d in t h e H i m a l a y a n o r o -

ge n , r e qu i r e s a t im e - sc a l e > 10 M a ( E ng la nd a nd

T h o m p s o n 1 9 8 4) . T h e s p a t ia l a n d c h r o n o l o g i c a l r el a -

t i o n s h i p s b e t w e e n s u b d u c t i o n , c o l li s io n , a n d m e l t i n g i n

n o r t h w e s t A n a t o l i a a r e t h e r e f o r e s ig n i fi c an t .

F i n a l c o l l i s i o n b e t w e e n t h e T a v s a n l i a n d S a k a r y a

z o n e s m u s t p o s t - d a t e o p h i o l i t e o b d u c t i o n i n t h e r eg i o n .

T h i s i s c o n s t r a i n e d b y t h e A r - i s o t o p e a g e f r o m t h e

ga r n e t a m ph ib o l i t e o f 101 .1 _+ 3 .8 M a ( F ig . 5e) w h ic h

p r ov ide s t he be s t a va i l a b l e e s t im a te f o r t he a ge o f

o b d u c t i o n o f t h e o p h i o l i te o n t o t h e c o n t i n e n t a l m a r g i n ,

t h o u g h s t r i c t l y i t r e p r e s e n t s a m a x i m u m c o n s t r a i n tbe c a u se t he l a t e t h r u s t s , w h ic h p l a c e t he oph io l i t e i n i t s

p r e s e n t p o s i t io n , a r e b r i t tl e . T h e e m p l a c e m e n t a g e s o f

t h e n o r t h w e s t A n a t o l i a n i n t ru s i v e s ( ~ 5 0 M a ) a r e s o m e5 0 M a y o u n g e r t h a n o p h i o l i t e o b d u c t i o n , b u t s i m i l ar to

d e p o s i t i o n a g e s o f M i d - E o c e n e n e r i t i c l i m e s t o n e s t h a t

u n c o n f o r m a b l y o v e rl ie t h e u l t r a m a f i c r o c k s a b o v e t h e

b l u e s c h i s t s , t h u s s u g g e s t i n g t h a t m a g m a t i s m o c c u r r e d

w i th in a f e w m i l l i on ye a r s o f c o ll i s ion .

S ince the g r a nod io r i t e s w e r e e m p la c e d a t a de p th o f10 km in to b lueschis t li thologies tha t h ad equi l ibra ted

a t d e p t h s o f ~ 7 0 k m , a b o u t 6 0 k m o f u p l if t o c c u r r e db e t w e e n b l u e s c h i s t m e t a m o r p h i s m a n d g r a n o d i o r i t e



e m p la c e m e n t . I f w e t a ke the f o r m e r a t 88 M a , a s de t e r -

m i n e d b y O k a y a n d K e l l e y ( 1 9 9 4 ) a n d t h e l a t t e r a t

53 M a ( Ta b le 3 ) , t h i s sugge s t s a m in im um e xhum a t ion

r a t e o f n e a r l y 2 m m a -1 b e f o r e e m p l a c e m e n t o f t h e

g r a nod io r i t e s . C ond uc t ive - h e a t ing m ode l s o f a s im p le

t h r u s t s y s t e m s ug g e s t t h a t r o c k s e x h u m e d f ro m d e p t h s o f

7 0 k m a n d t e m p e r a t u r e s o f 43 0 ~ C w o u l d u n d e r g o s ig ni f-

i c a n t he a t ing du r ing up l i f t due to r a d ioa c t ive he a t p r o -d u c t i o n ( E n g la n d a n d T h o m p s o n 1 98 4 ). H i g h e x h u m -

a t i o n r a t e s w o u l d r e s u l t in r e l a t iv e l y l o w m a x i m u m

t e m p e r a t u r e s , b u t b e c a u s e o f t h e r m a l i n e r ti a t h e s e w o u l d

be r e a c he d a t l ow p r e s su re s . The p r e se r v a t ion o f h igh

P - low T a s se m bla ge s a nd a bse nc e o f a r e g iona l g r e en -

s c h is t o v e r p r i n t i n t h e w e s t e r n p a r t o f t h e T a v s a n l i Z o n e

b lue sc h i s t s sugge s t t ha t e xhum a t ion d id no t r e su l t s im -

p ly f r om i so s t a t ic up l i f t o f t e c ton ic a l ly t h i c ke ne d c r u s t .

B l u e s ch i s t- f ac i e s a s s e m b l a g e s m a y b e e x h u m e d u n -

d e r c o n s t a n t t e m p e r a t u r e c o n d i t i o n s p r o v i d e d t h a t

s u b d u c t i o n c o n t i n u e s d u r i n g t h e i r e x h u m a t i o n . F o r

e x a m p l e , h i g h P - l o w T a s s e m b l a g e s m a y b e p r e s e r v e d

w i t h i n a n i m b r i c a t e d a c c r e t i o n a r y p r i s m a s a c o n s e -

q u e n c e o f u n d e r t h r u s t i n g b y c o l d m a t e r i a l d u r i n g u p l i ft

( P l a t t 1 9 9 3 ) . H o w e v e r i n t h e T a v s a n l i b l u e s c h is t s,

l i t ho log ie s a r e i nd i c a t ive o f a pa s s ive c on t in e n ta l m a r -

g i n ra t h e r t h a n a n a c c r e t i o n a r y p r is m ( O k a y 1 98 4).

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

t i n e n t a l l i t h o s p h e r e s u g g e s t s t h a t l o w m a x i m u m t e m -

p e r a t u r e s d u r i n g e x h u m a t i o n m a y b e o b t a i n e d f r o m

de la m ina t ion o f b lue sc h i s t - f a c i e s l i t ho log ie s o f t he

d o w n g o i n g s la b , f o l l o w e d b y b u o y a n c y - d r i v e n a s c e n t

( W i jb r a ns e t a l. 1993 ) . Th e p r e s e r va t io n o f b lue sc h i s t -

f a c i e s a s s e m b l a g e s r e q u i r e s t h a t e x h u m a t i o n t a k e s

p l a c e w i t h i n ~ 1 0 k i l o m e t r e s o f a n a c t i v e s u b d u c t i o nz o n e , a n d t h e m i n i m u m e x h u m a t i o n r a t e r e q u i r e d i s

1 .5 m m a - 1 s i m i l a r t o t h a t d e d u c e d f r o m t h e p r e s e n t

s tud y o f t he Ta v sa n l i b lue sc h i s t s . I n t h i s m ode l , g r e e n -

s c h is t o v e r p r i n t i n g w i l l o n l y b e a s s o c i a t e d w i t h y o u n g e r

i so top ic a ge s a nd r e l a t i ve ly s low up l i f t r a t e s .

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

p l a n a t i o n f o r t h e p o s s ib l e r a n g e o f b l u e s c h is t m e t a -m o r p h i c a g e s ( ~ 2 0 M a ) . Y o u n g e r a g e s , w h i c h c o v e r

a s i m i l a r r a n g e ( 4 2 - 2 9 M a ) a n d h a v e b e e n a s c r i b e d t o

d i f fe r e n ti a l u p l if t a n d c o o l i n g d u r i n g a c t iv e s u b d u c t i o n ,

h a v e b e e n o b t a i n e d f r o m s i n g l e -g r a i n a r g o n l a s e r p r o b e

a na ly se s o f phe ng i t e s f r om b lue sc h i s t - fa c i e s a s se m -

blages of S i fnos (Greec e) (W ijbran s e t a l . 1990, 1993) .T h e s e s t u d i e s p r e d i c t t h a t y o u n g e r b l u e s c h is t -f a c ie s

a ge s w i ll be l oc a t e d c lo se to t he p o in t o f e x t e ns iona l

d e t a c h m e n t , w h i c h i n t h e c a s e o f t h e T a v s a n l i Z o n e , is

t h e r e a c t i v a t e d t h r u s t b e t w e e n b l u e s c h is t s a n d o p h i o l i t e

f r a g m e n t s . A t p r e s e n t t h i s m o d e l c a n n o t b e t e s t e d i n

n o r t h w e s t A n a t o l i a s i n c e t h e r e a r e o n l y t w o a g e s av a i l-

a b l e f o r b l u e s c h i s t - f a c i e s m e t a m o r p h i s m f r o m t h eT a v s a n l i Z o n e , b o t h f r o m s a m p l e s l y i n g w i t h i n 2 k m o ft h e e x t e n s i o n a l d e t a c h m e n t .

T h e p r e c is e g e o m e t r y o f E o c e n e c o n v e r g e n c e b e -

t w e e n t h e T a v s a n l i a n d S a k a r y a z o n e s i s e q u i v o c a l.

A r e v er s al f r o m n o r t h w a r d s t o s o u t h w a r d s s u b d u c t i o n

251

o f o c e a n i c l it h o s p h e r e a l o n g t h e I z m i r - A n k a r a s u t u r e ,

a s sugge s t e d b y S e n g6r e t a l . ( 1984) , w ou ld e xp la in m e l t

g e n e r a t i o n i n t h e h a n g i n g w a l l o f t h e r e v e r s e d s u b d u c -

t i o n z o n e . A l t e r n a t i v e l y , a s e c o n d n o r t h w a r d - d i p p i n g

s u b d u c t i o n z o n e m a y h a v e b e e n i n i ti a te d s o u t h o f t h e

T a v s a n li Z o n e . M a g m a t i s m o c c u r r e d d u r in g t h e p e r i o d

im m e d ia t e ly f o l low ing c o l l is i on in a t e c ton ic s e t t i ng

s im i l a r to t ha t o f t he A da m e l lo M a ss i f . I n t e r e s t i n g lyb o t h p r o v i n c e s a r e c h a r a c t e r i s e d b y a n a p p a r e n t a b -

s e nc e o f s y n - s u b d u c t i o n m a g m a t i s m . N u m e r i c a l m o d -

els for P-T-t p a t h s a t s u b d u c t i o n z o n e s i n d i c a t e t h a t

s u b d u c t i o n r e s u l t s i n c o o l i n g t h e m a n t l e w e d g e , u n -

l e s s i n d u c e d c o n v e c t i o n o c c u r s a t s h a l l o w d e p t h s

( < 100 km ) , in w h ic h c a se m e l t i ng c a n o c c u r f r om th e

i n c o n g r u e n t m e l t i n g o f h o r n b l e n d e ( P e a c o c k 1 9 9 1) . I n

t h e a b s e n c e o f su c h c o n v e c t i o n , c es s a t i o n o f s u b d u c t i o n

c a n c a u s e h e a t i n g i n t h e h a n g i n g w a l l o f t h e h y d r a t e d

m a n t l e w e d g e w h i c h c o u l d t r i g g e r m e l t i n g . T h e m a g -

m a s f o r m e d b e n e a t h t h e T a v s a n l i Z o n e w e r e e i t h e r

m o d i f i e d b y f r a c t io n a l c r y s t a l li s a t i o n a n d p o s s i b le a s-

s i m i l a t i o n d u r i n g a s c e n t t h r o u g h t h i c k e n e d c r u s t , o r

t r i gge r e d c r u s t a l m e l t i n g a t p r e s su r e s l es s t ha n 10 kba r .

T h e O r h a n e l i a n d T o p u k g r a n o d i o r i t es a r e th e r e f o re

de r ive d f r om s im i l a r sou r c e r e g ions a s m a gm a s o f i n t e r -

m e d i a t e c o m p o s i t i o n f o r m e d a t a c ti v e c o n t i n e n t al m a r -

g in s. Th i s s tudy sugge s ts t ha t du r ing the e a r ly s t a ge s o f

pos t - c o l li s i on t e c ton ic s , t he s i te s o f m e l t z o ne s a r e d e t e r -

m i n e d b y t h e t h e r m a l s t r u c tu r e o f th e m a n t l e w e d g e a n d

c o n s e q u e n t a d v e c ti v e h e a ti n g o f th e c r u st , r a t h e r t h a n b y

t h e r m a l c o n d u c t i o n i n t e c to n i c a l ly t h i c k e n e d c r u s t.

Acknowledgements Financial support for this study was provided

by NATO Collaborative Research Gran t 900412 and by TUBITAKgrant TBAG 994/YBAG 0020-Glotek (AIO). Dr Graham Chinnerat the Department of Earth Sciences, University of Cambridge

is thanked for facilitating the use of the microprobe, Simon Turnerfor helpful comments and assistance with Ar analyses and MalcolmHole for a constructive review.

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33 - Nw Turkey Granodiorites - CMP 1994