mineral chemistry of ultramafic and mafic cumulates as an indicator

8/2/2019 Mineral Chemistry of Ultramafic and Mafic Cumulates as an Indicator

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Geol Rundsc h (1996) 85:64%661 9 Springer-Verlag 1996

O . P a r l a k 9 M . D e l a l o y e 9 E . B i n g 6 1

Minera l chemist ry o f u l t ramaf ic and maf ic cumulates as an ind icatorof the arc- re la ted or ig in o f the Mers in ophio l i te (southern Turkey)

Rece ived: 12 Decem ber 1995 / Acc epted: 15 June 1996

A b s t r a c t T h e M e r s i n o p h i o l it e , r e p r e s e n t e d b y a p -p r o x i m a t e l y 6 - k m - t h i ck o cean i c l i t h o s p h e r i c s ec t i o n o nt h e s o u t h e r n f l an k o f t h e T a u r u s c a l ca r eo u s ax is ,f o r m e d i n th e M e s o z o i c N e o - T e t h y a n o c e a n s o m e t im ed u r i n g L a t e C r e t aceo u s i n s o u t h e r n T u r k ey . T h e u l t r a -m af i c an d m af i c cu m u l a t e s h av i n g o v e r 3 k m t h i ck n es sc o n s is t o f d u n i t e + c h r o m i t e , w e h r l it e , c l i n o p y ro x e n i t ea t t h e b o t t o m a n d p a s s i n t o g a b b r o i c c u m u l a t e s i nw h i ch l eu co g ab b r o , o l i v i n e - g ab b r o an d an o r t h o s i t e a r eseen . Crys ta l l i za t ion o rder i s o l iv ine (Fo91_80)+ ch r o m -i a n s p i n e l ( C r # 6 0 - 8 0 ) , c l i n o p y r o x e n e ( M g # 9 5 - 7 7 ) ,plagioclase (An95.6-91.6) a n d o r t h o p y r o x e n e ( M g # 68-7 7) . M i n e r a l ch em i s t r y o f u l t ram af i c an d m af i c cu m u -l a t e s s u g g es t t h a t h i g h l y m ag n es i an o l i v i n e s , c l i n o p y -r o x en es an d a b s en ce o f p l ag i o c l a s e in t h e b a s a l u l t r a -m a f i c c u m u l a t e s a r e i n g o o d a g r e e m e n t w i t h p r o d u c t so f h i g h - p r e s s u re c r y s t a l f r ac t i o n a t i o n o f p r i m a r y b a s a l -t i c m e l t s b en ea t h an i s l an d - a r c en v i r o n m en t . M a j o r ,t r a ce e l e m e n t g e o c h e m i s t r y o f t h e c u m u l a t i v e r o c k sa l s o i n d i ca t e t h a t M er s i n o p h i o l i t e w as f o r m ed i n an a r cen v i r o n m en t . C o ex i s t i n g C a - r i ch p l ag i o c l a s e an d F o -r i ch o l i v i n e i n t h e g ab b r o i c cu m u l a t e s s h o w a r c cu m u -l a t e g a b b r o ch a r ac t e ri s ti c s . F i e l d r e l a t i o n s a s w e l l a s th eg e o c h e m i c a l d a t a s u p p o r t t h a t M e r s i n o p h i o l it e f o r m e di n a s u p r a - s u b d u c t i o n zo n e t e c t o n i c s e t t in g i n t h e s o u t h -e r n b r a n c h o f t h e N e o - T e t h y s i n s o u t h e r n T u r k e y .K e y w o r d s C u m u l a t e 9 M i n e r a l ch em i s t r y 9H i g h - p r e s s u r e f r ac t i o n a t i o n 9 S u p r a s u b d u c t i o n

Osman Parlak ([] )i . Michel DelaloyeDepartment of Mineralogy, University of Geneva,1211 Gen eva 4, Sw itzerlandFax: +41 22 3205732e-mail: [email protected] Bfng61Department of Geology, ~ukurova University,TR-01330 Adana, TurkeyPresent address:1Department of Geology, Cukurova University,TR-01330 Adana, Turkey

Introduct ionT h e e a s t e r n M e d i t e r r a n e a n o p h i o l i t e s i n s o u t h e r nT u r k e y c r o p o u t a l o n g t w o b e l t s , n a m e l y , P e r i - A r a b i cb e l t co m p r i s i n g H a t ay , B ae r B as s i t , T r o o d o s , C i l o ,G u l e m a n , Z a g r o s a n d O m a n ( R i c o u 1 9 7 1 ) , a n d t h eT au r i d e b e l t a l o n g w h i ch d i s co n t i n u o u s o cean i c l i t h o s -p h e r e f r a g m e n t s ( e . g . L y c i a n n a p p e s , A l l H o c a c o m -p l e x , B e y s e h i r - H o y r a n n a p p e s , P o z a n t i - K a r s a n t i , M e t -s i n ) i n a s s o c i a t i o n g en e r a l l y w i t h m e t am o r p h i c s o l e an do p h i o l i ti c m e l an g e a r e s een o n b o t h s i d e s o f th e ca l ca r -eo u s ax is ( F ig . l a ; J u t ea u 1 98 0; D i l ek an d M o o r e s1 99 0) . It h a s b ee n co n c l u d ed b y m an y au t h o r s t h a t m o s to f t h e o p h i o l i t e s i n T u r k ey f o r m ed i n s u p r a - s u b d u c t i o n -zone (SSZ) se t t ing (Pearce e t a l . 1984 ; Yahmz e t a l .1994 ; Rober t son 1994 ; Par lak e t a l . 1995b) .G e o ch e m i s t r y o f o cean i c b a sa l t s , m i n e r a l ch e m i s t r yan d o r d e r o f c r y st a l li z a t io n i n u l t r am af i c an d m af i c cu -m u l a t e s i n a r c - r e l a t ed / S S Z o p h i o l i t e b o d i e s [ T r o o d o s( H d b e r t an d L au r en t 1 9 9 0) , B ay o f I s l an d o p h i o l i t e ( E1 -t h o n e t a l . 1 9 8 2 ; K o m o r e t a l . 1 9 8 5 ) , B o r d e r R an g e u l -t r am af i c an d m af i c co m p l ex ( B u r n s 1 9 8 5 ; D eB ar i an dC o l e m a n 1 9 89 ), K l a m a t h m o u n t a i n s ( C o l e m a n 1 9 86 ),C a l i f o r n ia C o as t R an g e s o p h i o l i te s ( S h e r v a i s 1 9 9 0 ) ] a r ei n co n s i s t en t w i t h t r ad i t i o n a l l o w - p r e s s u r e ( 1 a t m ) p h as er e la t i on s h i p s o f M O R B s .T h i s p ap e r d ea l s m a i n l y w i t h t h e w h o l e - r o ck an d m i -n e r a l ch em i s t r y o f u l t r am af i c an d m af i c cu m u l a t e s an dd r aw s a t t en t i o n t o h i g h - p r e s s u r e c r y s t a l f r ac t i o n a t i o nf e a t u r e s o f t h e M e r s i n o p h i o l it e m a g m a c h a m b e r b e -n ea t h an i s l an d a r c / S S Z i n s o u t h e r n T u r k ey w i t h i n t h ef r a m e o f t h e T e t h y a n e v o l u t io n i n t h e e a s t e r n M e d i t e r -r an ean .

Geological f rame of the Mersin op hiol iteT h e M er s i n o p h i o l i t e co m p l ex , o n e o f t h e d i s co n ti n -u o u s o c e a n i c l i t h o s p h e r e f r a g m e n t s f o r m e d s o m e t i m ed u r i n g L a t e C r e t a c e o u s i n t h e e a s t e r n M e d i t e r r a n e a n


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Fig. 1 A Ophiolitic massifs in southern Tu rkey (Mo dified fromDilek and Mo ores 1990); B simplifiedgeologicalmap of the Mer-sin op hiolite; C Deta iled stratigraphic colu mn of the Mersinophio lite rocksre g i on , i s l oc a t e d i n t he sou t he rn pa r t o f t he Ta urusC a l c a re ous a xi s in so u t he rn Tu rke y (Fi g. l a ; Ju t e a u1 9 8 0; S e n g o r a n d Y i l m a z 1 9 8 1 ; D i l e k a n d M o o r e s1990). Th i s c om pl e x ha v i ng a pp ro x i ma t e l y 6 km t h i ck -ness cons is t s of ( in ascending s t ruc tura l order) : ophiol -i t i c me l a nge , suboph i o l i t i c me t a morph i c s , ma n t l e t e c -t on i t e s , u l tr a ma f i c a nd ma f i c c umu l a t e s , a lka l i ne (La t eJu ra s s i c -Ea r l y C re t a c e ous ) - t ho l e i i t i c (La t e C re t a -

ceous?) basa l t ic volcanics in assoc ia t ion wi th deep ma-r i ne s e d i me n t s a nd i s t e c t on i c a l l y bounde d by t heE c e m i s f a u l t t o t h e e a s t , t h e B o l k a r d a g m e t a m o r p h i cb a s e m e n t t o t h e n o r t h a n d c o v e r e d M i o c e n e c a r b o n a t esto the south and wes t (F ig . 1) .W e l l -p re se rve d u l tr a ma f i c a nd m a f i c c um ul a t e roc ksa re on l y s e e n wi t h i n t he rough l y N-S o r i e n t e d S o rgunva l l e y i n t he we s t e rn pa r t o f t he ma ss i f (F i g . l b ) . Theme a su re d de t a i l e d s t r a t i g ra ph i c s e c t i on o f t he c umu-la tes , wh ich was o ver 3000 m th ickness , s ta r t s a t th ebo t t o m w i t h u lt r a ba s ic c um ul a t e s (800 m) a nd pa s s u pi n t o ga bbro i c roc ks (2500 m) . B a sa l u l t r a ma f i c c umu-l a t e s ma i n l y c ha ra c t e r i z e d by a dc umul a t e t e x t u re s t a r t


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649w i th dun i t e s i n w h ic h s t r a t i f o r m c h r om i t e s a r e s e e n ind i f f e r e n t l e vel s . D u n i t e s a r e g r a d ua l ly f o l low e d by w e l l -l a ye r e d w e hr l i t e s w h ic h in t u r n a r e a l so g r a dua l ly ove r -l a in b y c l i n o p y r o x e n i t e s .T h e m a f i c c u m u l a t e s w i t h m e -s o c u m u l a t e , o r t h o c u m u l a t e t e x t u r e s t a r t a t t h e b o t t o mw i t h o l i v i n e g a b b r o a n d c o n t i n u e i n t o g a b b r o , l e u c o -g a b b r o a n d a n o r t h o s i te . I n t h e u p p e r p a r t o f t h e g ab -b r o i c c u m u l a t e s , p o o r l y d e v e l o p e d l a t e - s t a g e m a g m a -c h a m b e r d i f f e r e n t i a t io n p r o d u c t s c u t a l so c o u n t r y r o c ka s p l a g iog r a n i t i c i nc lu s ions . I gne ous l a m ina t ion , m ono-m i n e r a l i c si ze g r a d i n g a n d r h y t h m i c l a y e r i n g h a v e b e e no b s e r v e d a s g r a v i t y - c o n t ro l l e d a c c u m u l a t i o n s t r u c t u r e sin t he u l t r a m a f i c a nd m a f i c c um ula t e s ( P a r l a k e t a l.1995a ) . N um e r ous m ic r o - ga bb r o i c - d i a ba s i c d ike s i n -t r u d e b o t h t y p e s o f c u m u l a t i v e r o ck s . T h e c u m u l a t e h a st e c ton ic c on ta c t w i th t he t e c ton i t e s a t i t s ba se a nd w i thba sa l t ic r oc ks a t t he t op . T he y show va r i a b l e a t t i t ude o ft h e l a y e r i n g s u c h a s E -W / 6 0 S , N 6 5 E / 5 0 N W a n d N 7 0 W /3 3 N E .

Pet rographic summaryT h e c u m u l a t e s o f t h e M e r s i n o p h i o l i t e c a n b e s u b d iv -i d e d i n t o t w o g r o u p s , n a m e l y , u l t ra m a f i c a n d m a f i c c u -m u l a t e s . F o r t h e c l as s if i ca t io n a n d n o m e n c l a t u r e o f t h er oc ks , S t r e c ke i se n ( 1976 ) de f in i t i ons ha ve be e n f o l -l o w e d . U l t r a m a f i c c u m u l a t e s a r e r e p r e s e n t e d b y d u n i t e ,w e h r l i t e a n d c l i n o p y r o x e n it e . R o c k u n i ts o f t h e u l t r a -m a f i c c u m u l a t e s p r e s e r v e d t h e i r p r i m a r y t e x t u r e s a n dt h e y s h o w a d c u m u l a t e a n d m e s o c u m u l a t e t e x t u r e s .P o r e / t r a p p e d l i q u i d c o m p o n e n t ( a s a p o s t - c u m u l u sp h a s e ) b e t w e e n c u m u l u s m i n e r a l s i n t h e r o c k u n i t s o ft h e u l t r a m a f i c c u m u l a t e s a r e v e r y l i m i t e d . T h e d u n i t e sc ons i s t o f c um ulus e u he d r a l o l i v ine 90 - 95 vo l . % ( Fo90_85) w i th g r a in s i ze o f 1 . 5 -3 m m a nd 1 - 5 vo l . % c h r o m ia nsp ine l ( C r # 60 - 80% ) w i th t he g r a in s iz e be tw e e n 0 . 7 -1 m m . T h e w e h r l i te s a r e r e p r e s e n t e d b y 2 5 - 3 5 v o l .%o l i v in e a n d e u h e d r a l - s u b h e d r a l ( 5 5 -7 5 v o l .% ) c l in o p y -r o x e n e w i t h t h e g r a i n s iz e o f 0 .5 - 5 m m . T h e c o m p o s i -t i o n o f t h e c l i n o p y r o x e n e r a n g e s f r o m (Ens45 Fs4 Wo47)t o ( Ens48 F s9 W o49) . Th e c l i nopy r oxe n i t e c on ta in s a d -c u m u l u s c o a r s e g r a i n e d e u h e d r a l ( 1 -8 . 5 r a m ) c l i n o p y -r o x e n e s .T h e m a f i c c u m u l a t e s c o n s i s t i n g m a i n l y o f g a b b r o ,l e u c o g a b b r o , o l i vi n e g a b b r o a n d a n o r t h o s i t e c o n s t i t u t ea l m o s t t w o t h i r d s o f w h o l e c u m u l a t e s e c ti o n . T h e m a f icc u m u l a t i v e r o c k s a r e v e r y f r e sh a n d t h e y p r e s e n t a d c u -m u l a t e , m e s o c u m u l a t e a n d o r t h o c u m u l a t e t e x t u r e . T h ega bb r os c ons i s t m a in ly o f 50 - 55 vo l . % c a l ci c p la g io -c l a se (A n95_91) w i th t he g r a in s i z e be tw e e n 1 - 3 r a m , 35 -4 5 v o l .% c l i n o p y r o x e n e (En40_45 Fs8_12 W 046~7) w i th0 . 5 - 2 m m g r a i n s i z e a n d i n t e r c u m u l u s a n h e d r a l 2 -5 vo l . % o r th op y r o xe n e w i th g r a in s i z e o f 0 . 5 -0 . 8 r a m .T h e g a b b r o w i t h o l i v i ne c o n t a i n s c u m u l u s 2 0 - 2 5 v o l .%o l iv ine ( F oso - 81 ) w i th g r a in s i ze o f 0 . 8 -2 . 5 m m , 55 -60vo1 . % p la g ioc l a se a nd 15 - 20vo1 . % c l inopy r o xe ne .T h e l e u c o g a b b r o s a r e m a d e o f 6 5 -7 0 v o 1 .% c u m u l u sp la g ioc l a se a nd 30 - 35 vo l . % c l inopy r ox e ne . Th e a no r -

t h o s i te c o n t a i n s a d c u m u l a t e ( 99 v o l .% ) e u h e d r a l h i g h l ycalcic plagio clase (An91.6-95.6) wi th t he gra in size b e-tw e e n 2 a nd 5 .2 m m a nd 1 vo l . % c l inop y r ox e ne f il l ingthe i n t e r s t i c e s o f t he c um ulus p l a g ioc l a se s a s pos t - c u -m u l u s m i n e r al .

Analyt ical techniqueA to t a l o f 21 s a m p le s f r om u l t r a m a f i c a nd m a f i c c um u-l a te s h a v e b e e n a n a l y s e d in t e r m s o f m a j o r a n d t r a c ee l e m e n t c o n c e n t r a t i o n s . M a j o r a n d t r a c e e l e m e n t a n a -l y se s h a v e b e e n c a r r i ed o u t b y X R F i n t h e M i n e r a l o g yD e p a r t m e n t a t t h e U n i v e r s i t y o f G e n e v a . M a j o r a n dt r a c e e l e m e n t c o m p o s i t i o n s w e r e d e t e r m i n e d o n g l a s sb e a d s f u s e d f r o m i g n i t e d p o w d e r s t o w h i c h Li2B407w a s a dd e d ( 1 :5 ) , i n a go ld - p l a t i num c r uc ib l e a t 1150~A to t a l o f 30 r e p r e se n ta t i v e t h in s e c tions w e r e u se d f o rm i c r o p r o b e a n a l y s i s o n a C a m e b a x S X - 5 0 i n t h e M i -n e r a l o g y D e p a r t m e n t a t L a u s a n n e U n i v e r s i ty . T h e a n a -l y t i c a l c o n d i t i o n s f o r t h e e l e m e n t s [ ( K = O r t h o s e ) ,( S i = D i o p s i d e , O l i v in e , A l b i t e ) , ( M g = D i o p s i d e , O l iv -ine ) , ( C a = W ol l a s ton i t e , A n or th i t e ) , ( A 1 = Ja de i t e ,A n o r t h i t e ) , ( N a = J a d e i t e , A l b i t e ) , ( M n = M n s l ,M nT iO 3) , ( C r = C r 203 ) , ( T i : I lm e n i t e , M nT iO 3) ,( F e = H e d e n b e r g i t e , F e 2 03 ), ( N i = N i O ) ] w e r e 20 s o fc o u n t i n g i nt e rv a l , b e a m c u r r e n t - 2 0 m A a n d a c c e l e r a -t i on vo l t a ge - 15 kV .

W hole- rock chemist ryT h e c u m u l a t i v e r o c k s i n t h e M e r s i n o p h i o l i t e r a n g ef r o m h i g h l y m a g n e s i a n ( 4 0 -1 7 w t . % ) i n d u n i t es , w e h r -l i te s a nd c l i nopy r oxe n i t e t o l es s m a gne s i a n ( 5 - 10 w t . % )in m or e e v o lve d r oc ks suc h a s ga bb r o , ga bb r o w i th o l iv -i n e a n d a n o r t h o s i t e c h a r a c t e r i z e d b y h i g h C a O ( 1 5 -1 8 w t . % ) a n d A 1 20 3 ( 3 4 - 1 8 w t . % ) c o n t e n t s ( T a b l e 1 ).T h e o v e r a ll t r e n d f r o m M g - r ic h t o C a - a n d A l - r i ch c u -m u la t e s i s d i r e c t ly a s soc i a t e d w i th t he f o r m a t ion o f t hel a y e r e d s e q u e n c e s b y m a g m a t i c a c c u m u l a t i o n o f o l i v -ine s , c l i nopy r oxe ne s a nd p l a g ioc l a se s i n t he M e r s ino p h i o l i t e m a g m a c h a m b e r . M a j o r e l e m e n t c o m p o s i -t io n s o f t h e u l t r a m a f i c a n d m a f i c c u m u l a t e s a r e p l o t t e di n t h e A F M d i a g r a m ( B e a r d 1 9 8 6 ) : T h e d u n i t e s a n dw e h r l i te s s h o w M g e n r i c h m e n t , w h e r e a s g a b b r o s a r e o nthe a r c - c um ula t e ga bb r o f i e ld ( Fig. 2 ) ; how e ve r , tw os a m p l e s f r o m t h e u l t r a m a f i c c u m u l a t e s p l o t o n t h e a r c -c u m u l a t e g a b b r o f ie l d. T r a c e e l e m e n t a b u n d a n c e s v a r yw i t h b o t h m o d a l m i n e r a l o g y ( in c l u d in g a m o u n t o f p o st -c u m u l u s m i n e r a l ) a n d M g n u m b e r o f r o c k u n i ts ( J a q u e se t a l . 1983 ) . T r a c e e l e m e n t c onc e n t r a t i ons i n t he u l t r a -m a f i c a n d m a f ic c u m u l a t e s o f t h e M e r s i n o p h i o l i t e a r ew e l l c o r r e l a t e d w i th t he f r a c t io na t ion o f o l i v ine , c h r om -sp ine l , py r oxe ne a nd C a - p l a g ioc l a se . C r a nd N i c on -t e n t s a r e h igh in t he dun i t e s a nd w e hr l i t e s ( 1900 -200 ppm N i , 7500 - 1500 ppm C r ; F ig . 3 ) a n d de c r e a sel o w e r v a l u e s in g a b b r o i c r o c k s ( N i < 6 0 p p m , C r< 25 0 p p m ) . S r c o n c e n t r a t i o n s i n c r e a s e w it h t h e m o d a l


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R

WhD

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G

G+ovWhWhA

N

1

1

1

11

1

1

1

2

2

2

2

2

2

2

3

3

3

3

4

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SO

543353413034555658424640484946474948455541

TO

00000000000000000000

0000000000000000

000000

A1

11021110020218252413

2212111722261926

351337

FO

42864450947749514241

5054656962355425154407

MgO22452725474322181413

1129151675771156222102

MnO

01010101010101010100

0101010101000100

010100

CO

1316191611051213291318.6610151816151213

812310

NO

0000

mineral chemistry of ultramafic and mafic cumulates as an indicator

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