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8/10/2019 03 - glaucophane-lawsonite schists - CMP 1980.pdf
1/13
Contrib. Mineral. Petrol. 72, 243-255 (1980)
o n t r i b u t i o n s to
i n e ra lo g y an d
P et ro l o g y
9 by Springer-Verlag 1980
M ineralogy Petrology and Phase Relat ions
of G laucophane-Lawsonite Zo ne Blueschists
From the Tavsanh Region Northw est Turkey
A . I . O k a y
Department o f M ineralogy and Petrology, Downing Place, Cambridge CB2 3EW , England
Abstrac t G l a u c o p h a n e - l a w s o n i t e f a c i e s b l u e s c h i s t s
r e p r e s e n ti n g a m e t a m o r p h o s e d s e q u e n c e o f b a s i c ig -
n e o u s r o c k s , c h e r t s a n d s h a l e s h a v e b e e n i n v e s t i g a t e d
n o r t h e a s t o f t h e d i s tr ic t o f T a v s a n l i i n N o r t h w e s t
T u r k e y . S o d i c a m p h i b o l e s a r e r i ch i n m a g n e s i u m r e -
f l e c ti n g t h e g e n e r a l l y h i g h o x i d a t i o n s t a te s o f t h e
b l u es c h is t s. L a w s o n i t e h a s a v e r y u n i f o r m c o m p o s i -
t i o n w i t h u p t o 2 .5 w t . %
Fe203
S o d i c p y r o x e n e s
s h o w a n e x t e n s iv e r a n g e o f c o m p o s i t i o n s w i t h a ll th e
e n d - m e m b e r s r e p r e s en t e d . C h l o r i te s a r e u n i f o r m i n
t h ei r A 1 / ( A I + F e + M g ) r a ti o b u t sh o w v a r ia b l e Fe /
( F e + M g ) r a ti o s . G a r n e t s f r o m m e t a c h e r t s a r e r i ch
i n s p e s s a rt in e ( > 5 0 % ) w h e r e a s t h o s e f r o m m e t a b a -
s i t es a r e l a r g e l y a l m a n d i n e . P i s t a c i t e r ic h e p i d o t e i s
f o u n d i n m e t a c h e r t s c o e x i s t i n g w i t h la w s o n i t e . P h e n -
g i t e s a r c d i s t i n c t l y h i g h e r i n th e i r F e , M g a n d S i
c o n t e n t s t h a n t h o s e f r o m g r e e n s c h i s t f a c ie s . H e m a t i t e s
w i t h l o w T i O z a r e u b i q u i t o u s i n m e t a c h e r t s .
F e 2 + / M g p a r t i ti o n i n g b e t w e e n c h l o r it e a n d s o d ic
a m p h i b o l e i s s t ro n g l y c o n t r o l le d b y t h e c a l c i u m c o n -
t e n t o f t h e s o d i c a m p h i b o l e a n d r a n g e s f r o m 1 .1 f o r
l o w c a l c i u m s u b s t i t u t i o n t o 0 . 8 f o r h ig h e r c a l c i u m
s u b s t i t u t i o n . T h e A 1 / F e 3 + p a r t i t i o n c o e f f i c ie n t b e -
t w e e n s o d i c a m p h i b o l e a n d s o d i c p y r o x e n e is 2 .1 .
A m o d e l s y s t e m h as b e e n c o n s t r u c t e d i n v o l v i n g
p r o j e c t io n s f r o m l a w s o n it e , i r o n - o x i d e a n d q u a r t z
o n t o a t e t r a h e d r o n w i t h N a , A 1 , F e 2 + a n d M g a t
i t s a p i c e s . C a l c i t e i s t r e a t e d a s a n i n d i f f e r c n t p h a s e .
T h e m o d e l s y s t e m i ll u s tr a te s t h e i n c o m p a t i b i l it y o f
t h e s o d i c p y r o x e n e w i t h c h l o r i te i n th e g l a u c o p h a n e -
l a w s o n i t e f a c i e s ; t h i s a s s e m b l a g e i s r e p r e s e n t e d b y
s o d ic a m p h i b o l e .
S o d i c a m p h i b o l e c o m p o s i t i o n s a re p l o t t e d i n
t e r m s o f c o e x i st i n g fe r r o m a g n e s i a n m i n e ra l s . F i v e m a -
j o r a r e a s o n t h e s o d ic a m p h i b o l e c o m p o s i t i o n a l f i e ld
a r e d e l in e a t e d , e a c h a s s o c i a t e d w i t h o n e o f th e f o l l o w -
i n g m i n e r a l s : c h l o r it e , s t i l p n o m e l a n e , t a l c, a l m a n d i n e ,
d e e r i t e .
Introduct i on
I n N o r t h w e s t T u r k e y b l u e s c hi s ts f o r m a c o h e r e n t ,
d i s c o n t in o u s l y e x p o s e d m e t a m o r p h i c b e lt a b o u t
2 0 k m i n w i d t h a n d 3 0 0 k m i n l e n g t h ( F i g . 1 , i n s e t) .
T h e y f l a n k th e n o r t h e r n m a r g i n s o f t h e l a r g e u l tr a m a -
f ic m a s s i f s i n t h e e a s t e r n p a r t o f th e I z m i r - A n k a r a
o p h i o l i t e z o n e ( B r i n k m a n n 1 9 72 ) f o r m i n g a re g i o n a l l y
m e t a m o r p h o s e d e u g e o s y n c l i n a l s e q u e n c e o f b a si c
v o l c a n i c r o c k s , c h e rt s , s h a le s a n d m i n o r g a b b r o i c i n -
t r u s i o n s .
A l t h o u g h t h e e x is t e n c e o f b l u e s c h i s ts i n T u r k e y
h a v e b e e n k n o w n f o r o v e r s e v e n t y y e a r s ( c f . v a n d e r
K a a d e n 1 9 66 ), t h e fi r st d e ta i l e d s t u d y o n t h e i r p e t r o l -
o g y w a s n o t p u b l i s h e d u n t i l 1 96 7 b y C o g u l u . H e
w o r k e d i n t h e e a s te r n p a r t o f th 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 b e l t i n t h e r e g i o n o f M i h a l l i~ i k , a n d d i s -
t i n g u is h e d t h r e e m e t a m o r p h i c z o n e s : l a w s o n it e , l a w -
s o n i t e -c r o s s i te , a n d e p i d o t e - c r o s s i t e w i t h a n i n c r e a s e
i n g r a d e n o r t h w a r d s . H e a l s o o b t a i n e d a g e s f o r b l u e -
s c h is t m e t a m o r p h i s m o f 6 0 - 8 0 M a ( @ o ~ ul u a n d K r u m -
m e n a c h e r 1 9 6 7 ) . L t i n e l ( 1 9 6 7 ) s t u d i e d a s m a l l a r e a
o f g l a u c o p h a n e - l a w s o n i t e f a c ie s b l u e s c h i s t s s o u t h o f
E s k i s e h i r ( F i g . 1 , i n s e t ) w i t h s p e c i a l r e f e r e n c e t o t h e
b u l k r o c k c h e m i s t r y a n d s t r u c t u r e . K a y a ( 19 7 2 )
w o r k e d o n t h e is o l a t e d s m a l l b lu e s c h i s t o u t c r o p s
s o u t h o f T a v s a n h .
Geo l o g y
Throughout the N W Turkish blueschist/ultramafic belt the out-
crops are separated by an extensive Neogene cover. A large area
(20 to 45 kin ) of blueschists, ultramafics and ma rble s protrudes
from under the N eogene northeast o f the d istrict of Tav~an h (Fig.
1, inset) . During the co urse of the pre sent study, part of this
extensive area (30 to 13 km) of blueschists and ultramafics was
map pcd in d etail and ov er 700 rock specim ens were collected for
petrological investigations. In the studied area glaucophane-lawso-
nite zone blueschists form a coheren t, complexly deform ed regional
O010-7999/80/0072/0243/ 02.60
8/10/2019 03 - glaucophane-lawsonite schists - CMP 1980.pdf
2/13
244 A.I. Okay: Glaucopha ne-Lawsoni te Zone Blueschists Fro m NW Turkey
t
i
i
i
. , t. 73
s s
~ - 7 2 0
N
. 7 2 1
4 6 0
4 5 9
' v.
. 4 5 2 6 4 3
X
3 9 4
. 3 9 3
l / / / / .--,
/ / / / > / / /
/ / / i / ' / /
2-~ / /
\: 5 0 ) w i t h v e r y l o w v a l u e s o f p y r o p e (a v . 1 ) .
G a r n e t s o f th i s t y p e a r e c o m m o n i n t h e F r a n c i s c a n C o m p l e x ( E r n s t
e t a l . 1970) a nd i n N e w Ca l e don i a ( B l a c k 1973) .
T h e s e c o n d a n d m u c h r a r e r t y p e o f g a r n e t is f o u n d i n r o c k s
o f b a si c i g n eo u s c o m p o s i t i o n . T h e s e t e n d t o b e m u c h l a rg e r i n
s i ze ( 1 3 m m ) a n d m o r e s p o r a d i c i n o c c u r r e n c e t h a n t h e f i r s t t y p e .
T h e y c o n s i s t d o m i n a n t l y o f a l m a n d i n e - g r o s s u l a r c o m p o n e n t s w i t h
l e ss e r p y r o p e ( 8 - 1 0 ) a n d s p e s s a rt i n e ( 1 - 5 ) ; a n d a re s i m i la r
i n c o m p o s i t i o n t o t h e g a r n e t s f r o m t y p e I I I m e t a b a s i t e s f r o m t h e
Ca z a de r o a r e a i n Ca l i f o r n i a ( L e e e t a l . 1963) .
G a r n e t s f r o m 1 0 m e t a c h e r t s a n d 5 m e t a b a s i te s a r e p l o t t e d
i n F i g . 6 in t e r m s o f g r o s s u l a r , s p e s s a r t i n e a n d a l m a n d i n e + p y r o p e
e n d - m e m b e r s ; s ix g a r n e t a n a ly s e s , th r e e f r o m m e t a b a s i t es a n d t h r e e
f r o m m e t a c h e r t s , a re s h o w n i n T a b l e 4 . G a r n e t s f r o m t h e D e v l e z
a r e a s h o w c o m p l e t e s o li d s o l u ti o n b e t w e e n a l m a n d i n e a n d s p e s s ar -
t i ne .
Z o n i n g i n t h e s p e s s a r t i n e - r i c h g a r n e t s f r o m t h e m e t a c h e r t s
i s d if f i c u lt to o b s e r v e b e c a u s e o f t h e v e r y s m a l l s i z e o f t h e g r a i n s .
H o w e v e r , a n a l y s e s o f s e p a r a t e g a r n e t g r a i n s i n a s i n g l e th i n s e c t i o n
u s u a l l y r e v e a l v a r i a t io n s i n c o m p o s i t i o n b e t w e e n 2 0 3 0 m o l .
s p e s s a r t i n e - a l m a n d i n e w i t h a f a i rl y c o n s t a n t g r o s s u l a r i t e c o n t e n t .
T h e g r o s s u l a r i t e c o n t e n t s o f a l l a n a l y s e d s p e s s a r t i n e g a r n e t s a r e
r e l a ti v e l y c o n s t a n t ly i n g b e t w e e n 1 0 - 2 0 m o l . ( F i g . 6 ). O n l y g a r -
n e t s f ro m o n e m e t a b a s i t e o u t o f f iv e s h o w e d z o n i n g i n v o l v i n g
a n i n c r e a s e O f a l m a n d i n e t o w a r d s t h e r i m ( F i g . 6 , T a b l e 4 ) .
Epidote
E p i d o t e i s a r a r e m i n e r a l i n t h e a r e a ; i t m a i n l y o c c u r s i n s o m e
m e t a c h e r t s i n a s s o c i a t i o n w i t h h e m a t i t e a n d l a w s o n i t e . T w e n t y -
t h r e e e p i d o t e s fr o m 4 m e t a c h e r t s a n d 3 m e t a b a s i te s w e r e a n a l y s e d
a n d t h e s e a r e s h o w n o n a h i s t o g r a m i n F i g . 7 a . E p i d o t e s f r o m
m e t a c h e r t s a r e i n v a r i a b l y p i s t a c i t e - r i c h ( 2 7 - 3 5 p i s t a c i te ) , a n d
o c c u r i n m u c h l e s s a b u n d a n c e t h a n t h e a c c o m p a n y i n g l a w s o n i t e .
I n m e t a b a s i t e s , e p i d o t e i s u s u a l l y f o u n d a s s m a l l , r o u n d e d i n c l u -
s i o n s in l a w s o n i t e p o r p h y r o b l a s t s , s u g g e s t i n g t h a t i t i s a r e li c t
p h a s e f r o m a s p i l it i c p r o t o l i t h . E p i d o t e s f r o m m e t a b a s i t e s a r e l e s s
p i s t a c i t e - r i c h t h a n t h o s e f r o m m e t a c h e r t s , w i t h p i s t a c i t e c o m -
p o n e n t s o f 2 0 2 8 . A l l e p i d o t e s c o n t a i n s m a l l a m o u n t s o f M n
w h i c h s u b s t i t u t e s f o r C a .
T h e a s s e m b l a g e e p i d o t e -l a w s o n i t e - h e m a t i te , a s f o u n d i n t w o
m e t a c h e r t s ( T a b l e 3 ), is c o m p o s i t i o n a l l y i n v a r i a n t a t c o n s t a n t
P a n d T in t h e s y s t e m C a - A 1 - F e 3 + ; n e g le c t in g s m a l l a m o u n t o f
M n i n e p i d o t e ( 0 .0 7 p e r f o r m u l a u n i t ) a n d T i i n h e m a t i t e ( 0 .0 7
p e r f o r m u l a u n i t ). T h e p i s t ac i t e c o m p o n e n t o f t h e e p i d o t e a n d
t h e f er ri c c o n t e n t o f l a w s o n i te m u s t b e a m a x i m u m f o r t h i s i n v a -
r i a n t a ss e m b l a g e u n d e r t h e p a r t i cu l a r c o n d i t i o n s o f m e t a m o r p h i s m
( F i g . 7 b ) . E p i d o t e s f r o m t h e t w o m e t a c h e r t s h a v e v e r y s i m i l a r
p i s t a c i te c o m p o n e n t s ( 3 1 a n d 3 2 ) ; t h e l a w s o n i t e s h a v e r e l a -
t i v el y h i g h i r o n c o n t e n t s ( a v. 0 . 0 8 p e r f o r m u l a u n i t ) c o n f i r m i n g
t h e i n v a r i a n c e o f t h e s u b a s s e m b l a g e .
Phengite
P h e n g i t e i s t h e o n l y m a j o r K - b e a r i n g p h a s e i n t h e D e v l e z b l u e -
s c h i s t s . I t i s a n i m p o r t a n t c o n s i t u e n t i n t h e m e t a c h e r t s , a n d i s
c o m m o n a s a m i n o r p h a s e i n m e t a b a si t e s. S i x t y - tw o p h e n g i t e a n a l -
y s e s f r o m 1 5 m e t a b a s i t e s a n d 1 1 m e t a c h e r t s a r e s h o w n i n t h e
A 1 - F e - M g d i a g r a m i n F i g . 8 , s ix o f t h e s e a r e g iv e n in T a b l e 4.
T h e D e v l e z p h e n g it e s a r e ri c h e r in F e , M g a n d S i th a n t h o s e o f
t h e g r e e n s c h i s t f a ci e s ( c f. B r o w n 1 9 6 7 ). I n t h o s e f r o m t h e m e t a b a -
s i t e s t h e r e i s n o t e v e n a n o v e r l a p b e t w e e n t h e b l u e s c h i s t a n d g r e e n -
s c h i s t c o m p o s i t i o n s ( F ig . 8 ) . A l l a n a l y s e d p h e n g i t e s s h o w v e r y l i m -
i t e d s o l i d s o l u t i o n t o w a r d s C a - m i c a ( < 1 t o o l . ) a n d n o s o l i d s o l u -
t i o n w i t h p a r a g o n i t e .
Hematite
H e m a t i t e is a n e s s e n t i a l p a r t o f t h e m e t a c h e r t m i n e r a l a s s e m b l a g e .
I t o c c u r s a s a b u n d a n t , s m a l l p l a t e l e t s c l o s e l y a s s o c i a t e d w i t h t h e
o t h e r f e r r o m a g n e s i a n m i n e r a l s i n t h e r o c k ( F i g . 2) . F o u r t e e n a n a -
l y s e d h e m a t i t e s f ro m 9 m e t a c h e r t s a n d 2 m e t a b a s i t e s c o n t a i n u p
t o 4 w t . T i O z a n d 0 . 2 w t . V 2 0 3 .
O p a q u e m i n e r a l s a r e m u c h s c a r c e r i n t h e m e t a b a s i t e s . T h e y
t e n d t o b e e i t h e r p y r i t e o r m a g n e t i t e . M a g n e t i t e o f t e n s h o w s l a t e
s t a g e a l t e r a t i o n .
Aragonite Caleite
C a l c i t e o r a r a g o n i t e p a r t i a l l y a l t e r e d t o c a l c i t e o c c u r s i n s o m e
m e t a b a s i t e s a s i n t e r s t i ti a l g r a i n s o r v e i n s . I n s o m e c a s e s it p s e u d o -
m o r p h s l a w s o n i t e . N o o t h e r c a r b o n a t e w a s f o u n d i n t h e a r e a .
I n t h e D e v l e z a r e a o n l y o n e s p e c i m e n ( 3 9 4 / 3 ) w a s f o u n d t o
c o n t a i n
pumpelIyite
i n a l a m e l l a r i n t e r g r o w t h w i t h l a w s o n i t e .
T a / c
T a l c w a s o n l y fo u n d i n o n e o f t h e a n a l y s e d s p e c i m e n s (3 5 6) c o e x i s t -
i n g w i t h c h l o r i t e a n d s o d i c a m p h i b o l e ( T a b l e s 2 a n d 4 ) .
Quartz
Q u a r t z i s th e d o m i n a n t p h a s e i n m e t a c h e r t s a n d i s p r e s e n t i n
s m a l l a m o u n t s i n m a n y m e t a b a s i t e s ( T a b l e s 2 a n d 3 ) .
Albite
A l b i t e i s a v e r y r a r e m i n e r a l . I t w a s o n l y f o u n d i n t w o m e t a b a s i t e s
w h e r e i t i s p u r e a l b i t e w i t h n o d e t e c t a b l e a n o r t h i t e c o m p o n e n t .
I n t h e b l u e s c h i s t f a c i e s s o d i c a m p h i b o l e s a n d p y r o x e n e s t a k e
u p o n l y t r a ce a m o u n t s o f t i t a n i u m ; s u b s e q u e n t l y sphene b e c o m e s
a u b i q u i t o u s a c c e s s o r y m i n e r a l i n m e t a b a s i t e s . It i s l e s s c o m m o n
i n m e t a c h e r t s ( T a b l e 2) w h e r e t i t a n i u m e n t e r s h e m a t i t e i n s t e a d
o f f o r m i n g s p h e n e . S p h e n e o c c u r s a s p o o r l y c r y s t a ll i n e d u s t y b r o w n
a g g r e g a t e s . R u t i l e i s n o t f o u n d i n t h e a r e a . B l u e s c h i s t m i n e r a l s
n o t a b l e i n t h e i r a b s e n c e i n t h e D e v l e z a r e a i n c l u d e s t i l p n o m e l a n e
a n d d e e r i t e . T h e a b s e n c e o f t h e s e t w o m i n e r a l s c a n b e r e l a t e d
t o t h e l a c k o f s u i t a b l e i r o n - r i c h r o c k c o m p o s i t i o n s a n d t o t h e
g e n e r a l ly h i g h o x i d a t i o n s t a t e s o f th e b l u e s c h i s t s . H o w e v e r , a s
stilpnomelane
i s a n i m p o r t a n t m i n e r a l i n t h e m o r e r e d u c e d b l u e -
s c h i s t s , s u c h a s F r a n c i s c a n m e t a c h e r t s , f i v e s t i l p n o m e l a n e - b e a r i n g
m i n e r a l a s s e m b l a g e s w e r e a n a l y s e d : o n e f r o m a m e t a - a c i d i c r o c k
8 k m s o u t h o f t h e a r e a s h o w n i n F i g . 1 , a n d f o u r F r a n c i s c a n
m e t a c h e r t s ( f r o m H e a l d s b n r g , T i b u ra n , P a c h e c o P a s s , a n d P a n o c h e
P a s s ) . T h e e s s e n t i a l m i n e r a l a s s e m b l a g e i n F r a n c i s c a n m e t a c h e r t s
i s ' q u a r t z + s o d i c a m p h i b o l e
c h l o r i te ' a n d i n t h e m e t a -a c i d i c r o c k f r o m T a v s a n l i ' a l b i t e +
s t i l p n o m e l a n e + s o d i c a m p h i b o l e + q u a r t z + i l m e n i t e + l a w s o n i t e ' .
S o d i c a m p h i b o l e s c o e x i s ti n g w i t h s t i lp n o m e l a n e h a v e c o m p o -
s i t i o n s w i t h F e 2 + / F e 2 + + M g r a t i o s g r e a t e r t h a n 0 . 5 ( F i g . 1 2 a )
c h a r a c t e r i s t i c o f r e d u c e d m i n e r a l a s s e m b l a g e s w h i c h r e c r y s t a l li z e d
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248
Table 4. Com pos i t ions of m ine ra l s
A . I . Oka y: G la uc opha ne -La wsoni te Zone B lue sc hi s t s From NW Turke y
Sodic a m phibo le s Sodic pyroxe ne s
357/1 643]2 182 380 381 460 473 33 471 643/2 182 381 395
c ore r im
S iO z 5 7.3 6 5 6 . 7 1 5 5 . 9 9 5 8.2 0 5 7.5 4 5 6 .5 2 5 7 . 9 1 5 8.7 0 5 3 . 4 2 5 3 . 7 5 5 3.5 7 5 5 . 1 3 5 2 . 6 9 5 8.3 7
AI20 ~ 11.00 7.83 6.46 7.72 4.87 3.80 5.72 6.70 4.52 5.58 5.47 8.50 3 _77 19 .59
TiO 2 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.19 0.00 0.00 0.00
F e O* 1 0 . 47 1 5 . 1 2 1 6 . 7 1 1 1 . 6 5 1 6 . 5 2 2 3.8 7 1 5 . 0 0 8 .1 8 1 7 . 7 4 1 3 . 8 5 1 4 . 8 8 1 8 . 4 4 2 2.9 7 7 .5 5
M nO 0.00 0.00 0.15 0.20 0.16 0.13 0.27 0.45 0.23 0.30 0.00 0.00 0.00 0.00
Mg O 9 .86 8 .89 8 .79 1 1 .1 6 10 .3 9 6 .57 1 0 .6 7 14 .0 0 4 .00 5 .55 4 .93 0 .91 1 .52 0 .00
Ca O 1.07 0.44 0.72 0.09 0.86 0.22 0.69 0.89 8.10 13 .3 6 9.19 1.92 4.07 0.09
Na 20 6 .72 7 .23 6 .97 7 .76 6 .84 7 .46 7 .22 7 .26 9 .16 6 .36 8 .81 1 3 .1 3 1 1 .5 6 14 .3 8
To ta l 96.48 96.22 95,80 96.79 97.18 98.58 97,49 96.18 97.15 98.75 9 7 .0 3 98,02 96.58 99.97
* Tota l i ron a s Fe O
Si
A1~v
A Iv~
T i
Fe 3 +
Fe 2 +
M n
M g
Num be r of c a t ions pe r 23 oxyge ns Num be r of c a t ions pe r 6 oxyge ns
7.97 8.00 7.99 8.01 8.07 8.03 8.04 8.02 2.01 2.00 2.00 2.01 2.00 2.01
0.03 0.00 0.01 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
1.77 1.30 1,08 1.25 0.81 0.64 0.94 1.08 0.20 0.25 0.24 0.37 0.17 0.80
0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.01 0,00 0.00 0.00
0.22 0.67 0.86 0.70 1.11 1.37 0.95 0.80 0.46 0.21 0.40 0.56 0.68 0.16
1.00 1.11 1.14 0.64 0.83 1.47 0.79 0.13 0.10 0.22 0.07 0.00 0.05 0.06
0.00 0.00 0.02 0.02 0.02 0.02 0.03 0.05 0.01 0.01 0.00 0.00 0.00 0.00
2.04 1.87 1.87 2.29 2.17 1.39 2.21 2,85 0.22 0.31 0.28 0.05 0,09 0.00
~2 5.03 4.95 4.97 4.90 4.94 4.89 4.92 4.92 0.99 1.00 1.00 0.98 0.99 1.02
Ca 0.16 0.07 0.11 0.01 0.13 0.03 0.10 0.13 0.33 0.54 0.37 0.08 0.i7 0.00
N a 1.81 1.98 1.93 2.07 1.86 2.06 1.94 1,92 0.66 0.46 0.64 0.93 0.85 0.96
~2 1.97 2.05 2,04 2.08 1.99 2.09 2.04 2.05 0.99 1.00 1.01 1.01 1.02 0.96
Jd 20 25 2 4 37 17 80
Ac 46 21 40 56 68 20
Au 34 54 36 7 15 0
well within the mag neti te s tabi l i ty f ie ld Okay , in press). W ith
the se c om pos i t ions the who le sodic a m phibole f ie ld , w i th the e xce p-
t ion of a n a re a a round the g la uc op ha ne e nd-m e m be r , c a n be
inferred to be potentia l ly s table in the glaucophane-lawsonite fac ies .
l e m e n t P a r t i t io n i n g
T h e v a r i a b l e f e r r o m a g n e s i a n r a t i o s o f p h e n g it e s a n d
s o d i c p y r o x e n e s w i t h i n a s i n g le s e c t i o n a n d t h e i r
r e s t r i c t e d r a n g e d o n o t a l l o w r e l i a b l e d i s t r i b u t i o n
c o e f f i c i en t s b e t w e e n t h e m a n d o t h e r m i n e r a l s t o b e
d e t e r m i n e d . D i s c u s s i o n o n e l e m e n t p a r t i t i o n i n g i s
c o n s e q u e n t l y r e s t r ic t e d to t h e F e Z + / M g d i s t r i b u t i o n
b e t w e e n c h l o r i t e a n d s o d i c a m p h i b o l e a n d A 1 / F e 3 +
d i s t r ib u t i o n b e t w e e n s o d i c a m p h i b o l e a n d s o d i c p y -
r o x e n e ,
Chlorite Sodic Amphibole
F e 2 + / M g r a t i o s f o r s e v e n t e e n c o e x i s t in g h o m o g e n -
e o u s s o d i c a m p h i b o l e s a n d c h l o r i t e s a r e s h o w n i n
F i g . 9 a . T h i r t e e n o f t h e p a ir s c o m e f r o m D e v l e z ,
2 f r o m G f i m e l e L i i n e l 19 6 7) , o n e f r o m M i h a l l i c i k
~ o g u l u 1 9 67 ) a n d o n e f r o m P a n o c h e P a s s , C a l i f o r -
n i a . T h e m a i n e r r o r s i n t h e d e t e r m i n a t i o n o f t h e p a r t i -
t i o n c o e f f i c i e n t K D a r is e f r o m t h e u n c e r t a i n t y o f f e r r i c /
f e r r o u s r e c a l c u l a t i o n i n s o d i c a m p h i b o l e m i c r o p r o b e
a n a l y s e s a n d t h e m i n o r u n d e t e r m i n e d f e rr i c i o n i n
c h l o r i t e ,
T h e F e a + / M g d i s t r i b u t i o n c o e f f i c i e n t i s s t r o n g l y
d e p e n d e n t o n t h e c a l c i u m c o n t e n t o f t h e s o d ic a m p h i -
b o l e a n d r a n g e s f r o m 1 .1 f o r l o w c a l c i u m s u b s t i t u t i o n
0 . 0 0 < C a / C a + N a < 0 . 0 3 ) t o 0 .8 f o r i n c r e a s e d c a l-
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A . I . O k a y : 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 es c h is t s F r o m N W T u r k e y
T a b l e 4 C o n t i n u e d )
2 4 9
C h l o r i t e s T a l c G a r n e t s
2 7 3 3 3 5 6 1 8 2 3 5 6 3 5 7 / 1 4 7 1 3 8 0 4 6 0 4 7 3
c o r e r i m
S i O / 2 7 . 7 5 2 7 . 6 8 2 8 . 7 7 2 9 . 1 7 6 1 . 2 8 3 8 . 1 4 3 7 . 8 5 3 7 . 8 7 3 6 . 9 9 3 7 . 2 5 3 7 . 5 7
A 1 2 0 3 1 7 . 5 8 1 7 . 5 6 1 8 , 5 2 2 0 . 3 9 0 . 0 0 2 1 . 9 9 2 1 . 3 1 2 1 . 3 8 1 9 . 7 4 2 0 . 7 7 2 0 . 1 9
T i O 2 0 . 0 0 0 . 0 0 0 . 0 0 0 . 0 0 0 . 0 0 0 . 2 0 0 . 0 0 0 . 0 0 0 . 2 5 0 . 3 3 0 . 2 8
F e O * 2 2 . 9 9 2 1 . 6 2 1 8 . 2 8 1 0 . 7 7 8 . 1 8 2 8 . 4 0 1 5 . 3 4 2 2 . 3 4 9 . 4 9 7 . 4 0 2 . 9 8
M n O 0 . 6 9 1 . 2 3 0 , 3 2 0 . 5 2 0 . 0 0 0 . 8 4 1 3 . 7 t 7 , 2 9 2 6 . 1 7 3 0 . 6 4 3 3 . 8 5
M g O 1 7 . 6 7 1 9 . 1 9 2 1 . 4 7 2 5 . 1 2 2 5 . 7 2 2 . 2 5 0 . 0 0 0 . 3 2 0 . 2 7 0 . 2 7 0 . 2 9
C a O 0 . 0 9 0 . 0 0 0 . 0 8 0 . 0 0 0 . 0 0 9 . 0 8 1 3 . 1 2 1 1 . 7 8 7 . 3 3 5 . 7 4 0 , 5 6
T o t a l 8 6 . 7 7 8 7 . 2 6 8 7 . 4 4 8 6 . 1 1 9 5 . 1 9 1 0 0 . 8 9 1 0 1 . 3 4 1 0 0 , 9 7 1 0 0 . 2 5 1 0 2 . 3 0 1 0 1 . 7 2
N u m b e r o f c a t io n s p e r :
2 8 o x y g e n s 2 2 o x y g e n s 8 o x y g e n s
S i 5 . 8 5 5 , 7 8 5 . 8 4 5 . 7 8 8 , 0 4 2 , 9 9 2 . 9 8 3 . 0 0 2 , 9 9 2 . 9 6 3 . 0 0
A 1 ~ 2 , 1 5 2 . 2 2 2 . 1 6 2 . 2 2 0 . 0 0 0 . 0 1 0 . 0 2 0 . 0 0 0 . 0 1 0 . 0 4 0 . 0 0
A1 v l 2 . 2 2 2 . 1 0 2 . 2 7 2 . 5 4 0 . 0 0 2 . 0 2 1 . 9 6 2 . 0 0 1 . 8 7 1 .9 1 1 . 9 0
F e 3 . . . . . 0 .0 0 0 . 0 4 0 .0 0 0 .1 3 0 .0 9 0 .1 0
F e 2 + 4 . 0 5 3 . 7 8 3 . 1 0 1 . 7 8 0 . 9 0 1 . 8 5 0 . 9 7 1 .4 8 0 . 5 1 0 . 4 0 0 . 1 0
T i 0 . 0 0 0 . 0 0 0 , 0 0 0 . 0 0 0 . 0 0 0 . 0 1 0 . 0 0 0 . 0 0 0 . 0 1 0 . 0 1 0 . 0 2
M n 0 . 1 2 0 . 2 2 0 . 0 6 0 . 0 9 0 . 0 0 0 . 0 6 0 . 9 2 0 . 4 9 1 . 7 9 2 . 0 6 2 . 2 9
M g 5 . 5 5 5 . 9 7 6 . 5 0 7 . 4 1 5 . 0 3 0 . 2 6 0 . 0 0 0 . 0 4 0 . 0 3 0 . 0 3 0 . 0 3
C a 0 . 0 2 0 . 0 0 0 . 0 2 0 . 0 0 0 . 0 0 0 . 7 6 1 . 11 1 . 0 0 0 . 6 4 0 . 4 9 0 . 5 6
T o t a l 1 9 . 9 7 2 0 . 0 6 1 9 . 9 5 1 9 . 8 4 1 3 . 9 7 7 . 9 8 8 . 0 0 8 . 0 1 8 . 0 0 8 . 0 0 8 . 0 0
* T o t a l i r o n a s F e O
A i m . 6 3 3 2 4 9 1 7 1 3 3
Spe ss . 2 31 17 60 69 76
Pyr . 9 0 1 1 1 1
G r o s s . 2 6 3 7 3 3 2 2 1 7 1 9
P h e n g i t e s
3 3 3 5 7 / 1 3 8 0 4 6 0 4 7 3 3 9 5
S i O 2 5 1 . 4 3 5 1 . 7 1 5 2 . 2 0 5 2 . 1 5 5 1 . 5 0 4 7 . 7 5
A 1 / O 3 2 2 . 5 0 2 2 . 9 5 2 3 . 0 0 2 3 . 2 7 2 4 . 9 6 3 0 . 0 4
T i O 2 0 . 0 0 0 . 2 0 0 . 2 2 0 . 0 0 0 . 1 4 0 . 0 0
F e O * 4 . 9 5 3 . 9 3 4 . 5 0 4 . 4 5 2 . 7 8 3 . 9 3
M n O 0 . 0 0 0 . 0 0 0 . 1 8 0 . 1 2 0 . 1 3 0 . 3 4
M g O 3 . 7 5 3 . 7 8 3 . 8 8 3 . 8 3 3 . 7 1 0 . 9 4
C a O 0 . 0 0 0 . 1 6 0 . 0 0 0 . 0 0 0 , 0 0 0 . 0 0
N a 2 0 0 . 0 0 0 , 0 0 0 . 0 0 0 . 0 0 0 , 0 0 0 . 0 0
K 2 0 1 0 . 8 3 1 0 . 8 0 1 0 , 8 6 1 0 . 8 1 1 0 , 5 0 1 0 . 0 5
T o t a l
9 3 . 4 5 9 3 . 5 2 9 4 . 8 4 9 4 . 6 4 9 3 , 7 2 9 3 . 0 5
N u m b e r o f c a t i o n s p e r 2 2 o x y g e n s
33 357 /1 380 460 4 73 395
S i 7 . 1 0 7 . 1 0 7 . 0 9 7 . 0 9 6 . 9 9 6 . 5 7
A1 v 0 .90 0 .90 0 .91 0 .91 1 ,01 1 .43
A W 2 . 7 6 2 . 8 1 2 . 7 7 2 . 8 2 2 . 9 9 3 . 4 4
T i 0 . 0 0 0 . 0 2 0 . 0 2 0 . 0 0 0 . 0 1 0 . 0 0
Fe 2+ 0 .57 0 .45 0 .51 0 .51 0 .32 0 .45
M n 0 . 0 0 0 . 0 0 0 . 0 2 0 . 0 1 0 . 0 2 0 . 0 4
M g 0 . 7 7 0 . 7 7 0 . 7 9 0 . 7 8 0 . 7 5 0 . 1 9
4 . 1 0 4 . 0 6 4 . 1 1 4 . 1 2 4 , 0 9 4 . 1 2
C a 0 . 0 0 0 . 0 2 0 . 0 0 0 , 0 0 0 , 0 0 0 . 0 0
N a 0 . 0 0 0 . 0 0 0 , 0 0 0 . 0 0 0 , 0 0 0 . 0 0
K 1 .91 1 .89 1 .88 1 ,87 1 .82 1 .76
T o t a l 1 4 . 0 l 1 3 . 9 7 1 3 . 9 9 1 3 , 9 9 1 3 . 9 1 t 3 . 8 8
* T o t a l i r o n a s F e O
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2 5 0 A . I . O k a y : 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 s ch i s ts F r o m N W T u r k e y
c
o o c~
o o o 9
0 o
u Jd
Fi g . 4 . C o mp o s i t i o n s o f so d i c p y ro x e n e s p l o t t e d o n a c mi t e - j a d e i t e -
a u g i t e d i a g r a m . S o d i c p y r o x e n e s f r o m m e t a c h e r t s , f i l l e d c i r c l e s ;
f r o m m e t a b a s i t e s , o p e n c i r c l e s ; f r o m m e t a k e r a t o p h y r e s , f i l l e d
s q u a r e s
O 4
X _
O . 2
I I I I l l
o o . 0 . 2 o . 3 o 4 o ~ o . 6
Fe/Fe Mg Mn
F i g . 5 . C o m p o s i t i o n o f c h l o r i t e s f r o m N o r t h e a s t T a v s a n h p l o t t e d
i n t e r m s o f t h e i r F e / ( F e + M g + M n ) a n d A 1 /( A 1 + F e + M g + M n )
ra t i o s
9 - . . o ~ o = o o ; \
.
oO 9 9 - 9 ~ 9
/
V V V V
" - /
v ,.]
Sp lm
Fi g . 6 . Ga rn e t c o m p o s i t i o n s p l o t t e d o n sp e ssa r t i n e -g ro ssu l a r - (a l -
m a n d i n e d i a g r a m ; a l l p y r o p e c o n t e n t s b e l o w 9 . G a r -
n e t s f r o m m e t a c h e r t s f i l l e d c i rc l e s; f r o m m e t a b a s i t es , o p e n c i r c l e s
a Mo t. Ea2Fe3Si3012(OH)
_>.
~ 3
~
E a A t
Fi g . 7 . a C o mp o s i t i o n s o f 23 e p i d o t e s f ro m 7 b l u e sc h i s t s p l o t t e d
i n t e rms o f t h e i r p i s t a c it e c o m p o n e n t s , b Th e c o m p o s i t i o n a l l y i n v a -
r i a n t e p i d o t e - l a w so n i t e -h e m a t i t e a s se mb l a g e i n th e C a - Fe 3+ - A1
s y s t em f r o m t w o m e t a c h e r t s ( 38 0 a n d 4 5 9 )
L
~
e g
F i g . 8 . P h e n g i t e c o m p o s i t i o n s p l o t t e d o n A 1 - F e - M g d i a g r a m .
P h e n g i t e s f r o m m e t a c h e r t s ,
f i l l e d c i r c l e s ;
f r o m m e t a b a s i t e s ,
o p e n
circles.
C o m p o s i t i o n a l f i e ld o f p h e n g i t e s f r o m E a s t e r n O t a g o
g re e n sc h i s t s (B ro wn 1 9 6 7 ) a re sh o wn b y
d a s h e d l i n e s
c i u m s u b s t i t u t i o n 0 .0 3 < X c a < 0 .1 0 ) i n s o d i c a m p h i -
bo le . A decrease in the par t i t ion coeff ic ien t , wi th in -
creas ing ca lc ium con ten t in sod ic am phibo le , i s to
be expe c ted as the KD fo r ac t ino l i t e /ch lo r i t e pa i rs i s
0 .58 Ka wa ch i 1975 ; Co om bs e t a l. 1976) .
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A.I. Okay: Glaucophan e-Lawsonite Zone Blueschists Fro m NW Turkey 251
1.6
~.2
OA
0 0
0 0
' o i ~ o 1 8 1 : 2 ' 6
F e / M g ) c h l o r i t e
1 6
,~I,2
=
~
0B
0.0
o . o o o 1 8 1 . (
b (At/Fe3 ]sodic.,
y r o x e n e
Ok,
Fig. 9. a Fe 2 +/Mg ratios in coexisting sodic amphib ole an d chlorite,
where Fe =to tal Fe, Sodic amphiboles with Xca< 0.03, o p e n c i r -
c l e s ; sodic amphibo les with 0.03 < Xca < 0.1, i l l e d c i r c le s b A1/Fe 3+
ratios in coexisting sodic amphibole and sodic pyroxene
T h e C o m p o s i t i o n o f t h e F l u i d P h a s e a n d t h e S t a t u s
o f C 2
The abundance of hydrous bluescbist minerals, such
as lawsonite and/or sodic amphibole, in the initially
anhydrous basic igneous rocks is prima facie evidence
for the presence of fluid phase during the regional
metamorphism. The lack of graphite in the blueschists
suggests that the two main components of the fluid
phase were H20 and CO2. The common occurrence
of lawsonite-quartz and phengite-sphene subassem-
blages indicate that the fluid was dominated by H20
Xco2
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252 A.I. Okay: Glaucophan e-Lawsonite Zone Blueschists Fro m NW Turkey
a A t
/ / ~
* Q u o r t z
/ / \ +Lo.wsonife
/ / ~ +Iron-oxide
1 \
A l b i f e L / \
A ~ to /:: ~ / L 6 - - - : - - - ~
A[bil'e
Jadeite
. t
0.2
AcmiteN
AI9
~ S Quartz
9Lowsonite
*Iron-oxide
*H20
[orite
f i l p n o m e l o n e
R/MR
0 4
Ornphacite
F i g 10. a NAFM projection of mineral
compositions from quartz, lawsonite
and iron-oxide hematite) onto the
tetrahedra Na- AI *- Fe 2+ -M g. Only
some of the tie lines are indicated.
AI* = A1-2 Ca) . b Projection of
mineral compositions from quartz,
lawsonite, HzO and iron-oxide
hematite) onto the plane
Na -A I* - Fe z+, Mg). The jadeite and
augite contents of sodie pyroxenes are
also indicat ed. A1 * = A1 - 2Ca)
assemblages may be recognizable. However, the es-
tablishment of the ideal phase compatibilities at dif-
ferent P- T -X va lu es is important in understanding
the evolution of mineral assemblages through meta-
morphism. Phase relations established from equili-
brated mineral assemblages can then be used to un-
derstand the nature of frozen reactions and zoning
in minerals.
Metamorphic minerals are assumed to have
reached equilibrium in equigranular, schistose meta-
cherts (see Fig. 2) and metabasites. Rocks with reac-
tion textures involving replacement of sodic pyroxene
by sodic amphibole are interpreted to be in disequili-
brium.
At
/ / ~ * Q u a r t z
/ \ +Lawsonife
/ \ +Iron-oxide
A[bite~ ~ .1"120
(Jnd e i f e ) ~ . . . _ ..~ ~ i r e
Fig. 11. Model phase relations in the gla ucophane-lawson ite facies
for moderat e Fe2 +/F e2+ +Mg values 0.30-0.50) in the rock,
shown on a NAF diagram. Sodic pyroxene field is s t i pp l e
h a s e R e l a t io n s
The minerals considered in this study can be rep-
resented to a first approximation in the system
Na20 - K2 0 - CaO - MgO - FeO - MnO - Fe203
-A1203-TiO2-SiO2-H20. K20, MnO and TiOa
are assumed to affect only the formation of the
phases phengite, spessartine and sphene respectively.
By considering quartz-bearing assemblages SiO2 is
regarded as an excess component, and H20 is
taken as a perfectly mobile component. The chemo-
graphic relationships are further simplified by pro-
jecting from lawsonite for CaO and from hematite
for Fe203 into the system Na20-MgO-FeO-
AlzO3 (NAFM). All projections are made from hema-
tite although part of the sodic amphibole field, as
well as almandine and stilpnomelane are only stable
with magnetite. However, projecting from magnetite
will only slightly alter the coordina tes of sodic pyrox-
enes and amphiboles in the NAFM system but will
not have any effect on the topology. The algebraic
procedure used for projecting phases is that given
by Greenwood (1975).
Phase relations in the glaucophane-lawsonite
facies between the minerals sodic amphibole,
chlorite, albite, sodic pyroxene, almandine, stilpno-
melane and talc are shown in Fig. 10 a. In the NA FM
diagram sodic pyroxenes project into an open ended
beak shaped volume with the calcic end-members
plotting below the A1 -F e 2 + - M g plane. The posi-
tions of different sodic pyroxene end-members are
shown in a NAF triangular diagram (Fig. 10 b) where
Fe 2 + and Mg are treated as a single component . The
advantage of the NAF diagram lies in the precision
with which actual sodic pyroxene and sodic amphi-
bole compositions can be plotted.
Figure 11 shows an NAF diagram for moderate
Fe2+ /Fe2++Mg values (0.3-0.5), where chlorite is
the stable ferromagnesian phase. Here, the important,
compositionally invariant assemblage is albite
(jadeite)-chlorite-sodic amphibole plus the projected
phases. Such assemblages are found in Northwest
Turkey, in New Caledonia (Black 1973, p. 224) and
in many other areas.
At lower Fe2+/Fe2++Mg values (0.55) stillp-
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A.I. O kay: G laueophane-LawsoniteZone Blueschists From NW Turkey 253
. . . . . .
R
u
e
o o o S T I L P N O H E L N E
i / l l / / / i / / / / / / , / / / / / / /~r~l~}//I//////11///11/i////////;,,, . . . , , , ,
9 : , ~ ' : : " 9 ~ , l l , , , ~ l l , , 7 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 ~ ' i l , 'l l ll / # l l ,, i ll i l, I / ,v / I / l l
I l l l
i l l I I ~ O I "
m m 9 ~ m 9 m m 9
o
: , 9 #
9
_
o ~ . . . . . , . ~ : . : J , - - , .
' ; / i / tt / l i, i D ; : i ' ll t i, , Y i
T L E
I I I I _ _ I I ~ i
t _ _ I ~ ]
I I . . . . 1 | | I - I I . 1
M R M R
Fig. 12. a So dic amphibole composition n re lation to the mineral assemblage. Sodic amphibole with ch lorite, solid squares; with stilpnome~
lane, open squares; wi th chlorite and stilpnomelane, half-filled squares; with almandine,open circles; with talc and chlorite, open trzkmgles.
ll Phase relations o f sod ic amphibo le in the glaucophane-lawsonite facies. Sodic amphibo le compositions which may coexist with two
ferromagnesian minerals are ruled. Iron-o xides most probably can coexist with all so dic amp hibole compositions. Albite is restricted
to glaucophane-ferroglalscophane olid solution
n o m e l a n e a r e t h e s t a b l e f e r r o m a g n e s i a n m i n e r a l s
c o e x i s t in g w i t h s o d i c a m p h i b o l e . T h e c h a n g e f r o m
o n e f e r r o m a g n e s i a n m i n e r a l t o a n o t h e r o c c u r s a t a p -
p r o x i m a t e l y c o n s t a n t F e 2 + / F e z + + M g a n d t h e r e f o r e
c a n n o t b e s u c c e s sf u l ly il l u s tr a t e d o n t h e N A F d i a -
g r a m .
A p e c u l i a r p r o b l e m i n t h e D e v l e z a r e a i s t h e p r e s -
e n c e o f a l m a n d i n e g a r n e ts w i t h 2 5 - 3 5 g r o s su l a r
c o m p o n e n t c o e x i s ti n g w i t h A l - r ic h a m p h i b o l e s . W h e n
p r o j e c t e d f r o m l a w s o n i te f o r C a o n t h e N A F p l a n e,
t h e g a r n e t s p l o t n e a r t h e F e 2 + , M g ( F ) a p e x ; s i nc e
c h l o r i t e c o e x i s t s w i t h c o m p a r a t i v e l y A l - p o o r s o d i c
a m p h i b o l e , g a r n e t - a m p h i b o l e a n d c h l o r i te - a m p h i b o l e
t i e l ines c ros s .
T h e r e i s n o t e x t u r a l e v i d e n c e f o r a n y d i s e q u i l i -
b r i u m b e t w e e n c o e x i s t in g l a w s o n i t e a n d g a r n e t . F u r -
t h e r m o r e g a r n e t s f r o m t h e C a z a d e r o a r e a m e t ab a s it e s,
c o e x i s t i n g w i t h l a w s o n i t e a n d a l m n i n o u s s o d i c a m p h i -
b o l e ( C o l e m a n a n d P a p i k e 1 9 6 8 , p . l 1 1 ), h a v e s i m i l a r
g r o s s u l a r c o m p o n e n t s ( 2 5 - 3 0 ; L e e e t a l. 1 96 3 ,
p . 4 7 2 ) . I t s e e m s t h a t t h e b l u e s c h i s t s o f t h e D e v l e z
a r e a r e c r y s t a l li z e d a t t h e c r i ti c a l P - T c o n d i t i o n s c o r -
r e s p o n d i n g t o t h e c h l o r i t e - g a r n e t t r a n s i t i o n .
I n s t a b i l i ty o f S o d i c P y r o x e n e C h l o r i te
S o d i c p y r o x e n e s c o n t a i n p r o p o r t i o n a t e l y h i g h er
a m o u n t s o f N a + C a t h a n s o d i c a m p h i b o l e s , c o n s e -
q u e n t l y t h e y a r e r e s t r i c t e d t o t h e s o d i u m - r i c h c o r n e r
o f t h e N A F M d i a g ra m . T h e y a re s e p a ra t e d f r o m t h e
f e r r o m a g n e s i a n m i n e r a l s b y t h e i n t e r v e n i n g s o d i c a m -
p h i b o l e c o m p o s i t i o n a l f i e l d a n d a l b i t e -s o d i c a m p h i -
b o l e t i e l i n e s ( F i g . 1 0 a ) . T h u s a c m i t e - a n d j a d e i t e - r i c h
s o d i c p y r o x e n e s c a n n o t c o e x i s t w i t h f e r r o m a g n e s i a n
m i n e r a l s, i n s t e a d s o d i c a m p h i b o l e i s t h e s t a b le p h a s e .
O b v i o u s l y s o d i c p y r o x e n e c a n c o e x i s t s t a b ly w i t h s o -
d i c a m p h i b o l e i n a s s e m b l a g e s f r e e o f a n y f e r r o m a g n e -
s i a n m i n e r a l s , a s i n t h e s o d i u m - r i c h m e t a c b e r t 3 8 1
(Table 3 ) .
T h e c o e x i s t e n c e o f s o d i c p y r o x e n e w i t h c h l o r i t e
a n d s o d i c a m p h i b o l e i n m a n y b l u e s c h i s t m e t a b a s i t e s
f r o m t h e D e v l e z a r e a is d u e t o a n i m c o m p l e t e p r o -
g r a d e s o d i c a m p h i b o l e p r o d u c i n g r e a c t i o n i n v o l v i n g
s o d i c p y r o x e n e a n d c h l o r i t e ( O k a y i n p r e p a r a t i o n ) .
T h e C o m p o s i ti o n o f S o d i c A m p h i b o l e
i n R e l a t i o n t o M i n e r a l A s s e m b l a g e
A l l p h a s e s i n t h e N A F M s y s t e m h a v e t ie l in e s e x t e n d -
i n g t o t h e s o d ic a m p h i b o l e f i e ld ; t h e r e f o r e t h e c o m p o -
s i t i o n a l f i e l d o f s o d i c a m p h i b o l e s c a n b e u s e d a s a
p l a n e o n w h i c h o t h e r p h a s e s a r e p r o j e c t e d i n t e r m s
o f a c tu a l s o d i c a m p h i b o l e c o m p o s i t i o n s ( B r o w n
1974).
I n q u a r t z - b e a r i n g r o c k s , s o d i c a m p h i b o l e c a n b e
8/10/2019 03 - glaucophane-lawsonite schists - CMP 1980.pdf
12/13
254 A.I. Ok ay: Glaucophane-Lawsonite Zone Blueschists Fro m NW Turkey
r e g a r d e d a s c o n s is t in g o f fi ve m a j o r c o m p o n e n t s
( N a 2 0 , M g O , F e O , A 1 2 03 , F e 2 O a ) , c o n s e q u e n t l y a n y
t h r ee p h a s es in t h e N A F M d i a g r a m p l u s ir o n - o x i d e
s h o u l d c o e x i s t w i t h a s i n gl e c o m p o s i t i o n o f s o d i c a m -
p h i b o l e . S o d i c a m p h i b o l e c o e x i s t i n g w i t h t w o o t h e r
p h a s e s i n t h e N A F M d i a g r a m p l u s i ro n - o x i d e s h o u l d
b e c o m p o s i t i o n a l l y u n i v a r i a n t; t h e c o m p o s i t i o n
s h o u l d v a r y a l o n g a l in e o n t h e M i y a s h i r o d i a g r a m .
I n F i g . 1 2 a s o d i c a m p h i b o l e s a r e s h o w n i n t e r m s
o f c o e x i s t in g m i n e r a l s ; t h e f i g u r e in c l u d e s s o d i c a m -
p h i b o l e s f r o m G t i m e l e ( L f i n e l 1 9 67 ) a n d f r o m s t i lp n o -
m e l a n e - b e a r i n g F r a n c i s c a n m e t a c h e r t s , a s w e l l a s so -
d i c a m p h i b o l e s f r o m t h e D e v l e z a r ea . T h e s o d i c a m -
p h i b o l e c o m p o s i t i o n a l f i e ld is d i v i d e d i n t o f o u r m a j o r
r e g i o n s e a c h a s s o c i a t e d w i t h o n e o f t h e f o l l o w i n g f e r -
r o m a g n e s i a n m i n e r a l s : c h l o r i te , a l m a n d i n e , t a l c a n d
s t i l p n o m e l a n e ; a f i ft h d e e r i t e r e g i o n i s p r e s e n t
a r o u n d t h e r i eb e c k it e e n d - m e m b e r ( M u i r W o o d 1 97 7,
p . 256 ) .
S p e s s a r t i n e - r i c h g a r n e t s a r e s t a b l e w i t h a l l s o d i c
a m p h i b o l e c o m p o s i t i o n s a s a n ex t r a M n - b e a r i n g
p h a s e ; o n l y a l m a n d i n e w i t h n e g l i g ib l e s p e s s a r ti n e
c o m p o n e n t i s r e s t r ic t e d t o g l a u c o p h a n e (s.1 .) b e a r i n g
a s s e m b l a g e s ( 3 5 7 / 1 a n d 5 3 6 ) . H o w e v e r , a s d i s c u s s e d
e a r li e r, a l m a n d i n e m i g h t r e p r e s e n t a h i g h e r g r a d e o f
m e t a m o r p h i s m . S o d i c p y r o x e n e s a re n o t s h o w n a s
t h e y d o n o t c o e x i s t s t a b l y w i t h th e o t h e r f e r r o m a g n e -
s i a n m i n e r a ls , l y i n g o n t h e o p p o s i t e s id e o f t h e s o d i c
a m p h i b o l e c o m p o s i t i o n a l f ie l d ( F i g . 1 0 a ).
T h e p o s i t io n o f u n i v a r i a n t l in e s o n t h e s o d i c a m -
p h i b o l e f i e l d w i ll d e p e n d t o s o m e e x t e n t o n t h e c a l -
c i u m c o n t e n t o f t h e s o d ic a m p h i b o l e w h i c h h a s a n
i m p o r t a n t e f fe c t o n t h e F e Z + / M g p a r t i ti o n i n g b e -
t w e e n s o d i c a m p h i b o l e a n d o t h e r m i n e r al s . V a r i a ti o n s
i n t h e c a lc i u m c o n t e n t o f so d i c a m p h i b o l e a n d u n c e r -
t a i n t i e s i n t h e f e r r i c / f e r r o u s r e c a l c u l a t i o n w i l l r e s u l t
i n c o m p o s i t i o n a l b a n d s , r a t h e r t h a n l i n es , o n t h e s o d i c
a m p h i b o l e f i el d , m a r k i n g t h e c o e x i s te n c e o f t w o f e r r o -
m a g n e s i a n m i n e r a l s (F i g . 1 2 b ).
B r o w n ( 1 9 7 4 ) f i rs t r e l a t e d s o d i c a m p h i b o l e c o m -
p o s i t i o n t o c o e x i s t in g m i n e r a l s i n t h e b l u e s c h is t s f r o m
S h u k s a n . T h e m a i n d i ff e re n c e b e t w e e n t h e d i a g r a m
h e r e a n d B r o w n s d i a g r a m ( 1 9 74 , F i g . 1 1) i s i n t h e
t r e a t m e n t o f i r o n - o x id e s ; a s m a n y o f B r o w n s a m p h i -
b o l e a s s e m b l a g e s l a c k e d ir o n - o x i d e s , h e a s s u m e d t h a t
i r o n -o x i d e s w e r e n o t s t ab l e w i t h f e r r o g l a u c o p h a n e
a n d g l a u c o p h a n e c o m p o s i t i o n s . H o w e v e r , s o d i c a m -
p h i b o l e c o m p o s i t i o n s f r o m N o r t h w e s t T u r k e y d e -
m o n s t r a t e t h a t t h i s i s n o t t h e c a s e ( O k a y , i n p r e s s );
t h e a b s e n c e o f i r o n - o x i d e s i n s o m e a s s e m b l a g e s i s
p o s s i b l y d u e t o l o w a m o u n t s o f fe r r ic i o n i n th e r o c k
g i v in g i n c re a s e d c o m p o s i t i o n a l f r e e d o m .
Acknowledgements I thank S .O . Ag rell , E.H. Brown, G.T.R.
Droop, J.G. Spray, and R. Muir Wood for reviewing the manu-
script. Probe facili t ies were provided by the Department of M ineral-
ogy and Petrology in Camb ridge. This work was carried out w hile
in receipt of a grant from the Mineral Research and Exploration
Institute of Turkey (M.T.A.), w hich is gratefully acknowledged.
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