Date post: | 02-Jun-2018 |
Category: |
Documents |
Upload: | mastergeo35 |
View: | 219 times |
Download: | 0 times |
of 7
8/10/2019 07 - incipient metamorphism - CMP 1982.pdf
1/7
Co ntrib M ineral Petrol (1982) 79:361-367
ontr ibut ions to
M i n e r a lo g y a n d
P e t r o l o g y
9 Springe r-Verla g 1982
Incipient Blueschist M etamorphism and M etasomatism
in the Tav~anll Re gion Northwest Turkey
A . I . O k a y *
De partm ent of Earth Sciences, Downing Place, Cambridge CB2 3E, England
Abs t r a c t V o l c a n o - s e d i m e n t a r y r o c k s i n a n i m b r i c a t e t e c -
t o n i c z o n e a r o u n d a p e r i d o t i te m a s s i f h a v e b e e n s t u d i e d
n o r t h e a s t o f t h e t o w n o f T a v ~ a n h in N o r t h w e s t T u r k e y .
B a s i c v o l c a n i c r o c k s , w h i c h a r e t h e d o m i n a n t r o c k t y p e
i n t h i s z o n e , s h o w i n c i p i e n t 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
a s s o c i a t e d m e t a s o m a t i s m . W h i l e t h e ig n e o u s t e x t u r e s o f t h e
v o l c a n i c r o c k s a r e r e t a i n e d , a u g i t e s a r e p a r t i a l l y t o c o m -
p l e t e ly r e p l a c e d b y s o d i c p y r o x e n e , a n d p l a g i o c l a s e is a l b i t-
i s ed r e s u lt i n g i n r o c k s w i th 6 8 w t . % N a 2 0 . T h e v o l c a n i c
r o c k s a r e c r o s s - c u t b y n u m e r o u s v e i ns o f c a l ci te , a r a g o n i t e ,
q u a r t z , p u m p e l l y i t e , a l b i t e , l a w s o n i t e a n d s o d i c p y r o x e n e .
P e l a g i c l i m e s t o n e s , w h i c h a r e i n t e r b e d d e d w i t h t h e b a s i c
v o l c a n i c r o c k s , c o n s is t o f c o a r s e a r a g o n i t e g r a i n s s h o w i n g
p a r t i a l r e p l a c e m e n t b y c a l ci te . T h e o c c u r r e n c e o f a r a g o n i t e ,
l a w s o n i t e a n d a l b it e i n d i c a te s 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 o r t h e w h o l e z o n e i n t h e r a n g e o f 5 8 k b a n d 1 5 0 -2 0 0 ~ C .
M e t a s o m a t i s m , p r o b a b l y r e l a t e d t o h i g h p r e s s u r e s e r p e n t i n -
i z a t i o n , h a s o c c u r r e d c o n t e m p o r a n e o u s l y w i t h t h e i n c i p i e n t
h i gh p r e s s u re m e t a m o r p h i s m .
P r e s e n t a d d r e s s :
Temel Ara~tirmalar, M ineral Research and E x-
p lorat ion Insti tu te (MTA), A nkara, Turkey
I n t r odu c t i o n
Th i s i s t h e t h i rd i n a seq u en ce o f p ap e r s d esc r i b in g t h e
b l u e s c h i s t f a c i e s r o c k s f r o m N o r t h w e s t T u r k e y . T h e t w o
p r e v i o u s p a p e r s ( O k a y 1 98 0 a , b ) h a v e d e s c r i b e d t h e g l a u c o -
p h a n e - l a w s o n i t e a n d l a w s o n i t e z o n e b l u e s c h i s t s i n t h e
T a v ~ a n h r e g i o n . T h i s p a p e r d e a l s w i t h t h e v o l c a n o - s e d i m e n -
t a r y r o c k s , w h i c h a r e t h e p r o t o l i t h s o f t h e b l u e s ch i s ts a n d
s h o w i n c i p i e n t h i g h p r e s s u r e , l o w t e m p e r a t u r e m e t a m o r -
p h i s m a n d a s s o c i a te d m e t a s o m a t i s m .
As sh o wn in F ig . 1 sev era l eas t -wes t o r i en t ed t ec to n i c
z o n e s c a n b e r e c o g n i s e d i n N o r t h w e s t T u r k e y . I n t h e s o u t h
is a d o m e s h a p e d H T / L P m e t a m o r p h i c c o m p l e x ( M e n d e r e s
Mas s i f ) wi th a g n e i s si c co re an d a co v er o f g reen sch i s t f ac i es
r o c k s . T o t h e n o r t h t h e M e n d e r e s M a s s i f i s i n te c t o n i c c o n -
t a c t w i t h a 2 0 k m w i d e p e r i d o t i t e z o n e c o n s i s t in g l a r g e l y
o f h a r z b u r g i te s a n d d u n i t e s w i t h v e r y m i n o r g a b b r o b o d i e s
(L i sen b ee 1 9 7 1 ; Ok ay 1 9 8 0 c) . Th e p e r id o t i t e s a r e cu t b y
a s w a r m o f g a b b r o i c d y k e s , n o w a l l b o u d i n a g e d a n d s a u s -
s u r it i se d , a n d a r e t h r u s t o v e r a t e c t o n i s e d c o m p l e x o f s p i -
l i t e s , ch er t s , i so l a t ed se rp en t i n i t e b o d i es , g r ey wack es an d
sh a l es . P a l a eo n to lo g i ca l (Oz k o g ak 1 9 6 9, p . 7 6 ; L i sen b e e
1 9 7 1 , p . 3 5 5 ) a n d r a d i o m e t r i c ( ~ o ~ u l u a n d K r u m m e n a c h e r
Fig. 1. Generalised geotectonic
map of Northwest Turkey ,
compiled from the geological
maps of Turkey (Maden
Tetkik ve Arama Enst. 1963,
1964) and the author's own
observations
0010-7999/82/0079/0361/$01.40
8/10/2019 07 - incipient metamorphism - CMP 1982.pdf
2/7
36
ZA - W S O N / T E
Z~VE_BLUES_CHISTS ._
~ v
9 - ' ~ / (
9 9 o
9 ~ ~
9 O g e o o . O ~ G R E E N S C H I S T S - - / 9
9 ~ ~
_ _ - ~ - . . . 9
G~m~yenik~y ~ 9 Iv v
v v.~i/VWv ~
Fig. 2. Simplified geological ma p of the Giimii~yenik6y
area, Tav~anll , Northwest Turkey. Only the m ajor shear
zones and large serpentinite outcrops are shown. Blank
areas consist of closely intercalated pelagic sediments, basic
volcanic rocks an d serpentinite, al l o f which are incipiently
metam orphosed and metasomat ised. Circles indicate
specimen loca l i t ie s ; f i l led c irc les augite partially or
completely replaced by sodic pyroxene; open circles no
such replacement. N u m b e r s of the analysed specimens are
also indicated
1 9 6 7 ) d a t a i n d i c a t e a n U p p e r C r e t a c e o u s d e p o s i t i o n a l a g e
f o r s o m e o f th e s e r o c k s . B l u e s ch i s t m e t a m o r p h i s m i s n o t
e v i d e n t i n th i s v o l c a n o - s e d i m e n t a r y se q u e n c e a n d H P / L T
m i n e r a l s , s u c h a s la w s o n i t e a n d a r a g o n i t e , o c c u r in t h e
a m y g d a l e s a n d v e i n s i n t h e v o l c a n i c r o c k s . T h e i n c i p i e n t
n a t u r e o f th i s b lu e s c h is t m e t a m o r p h i s m i n t h e T a v ~ a n h r e -
g i o n i s t h e s u b j e c t o f t h i s p a p e r .
L a w s o n i t e a n d 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 c h i s t s
a r e p r o d u c e d b y t h e p r o g r e ss i v e m e t a m o r p h i s m o f th e s e
v o l c a n o - s e d i m e n t a r y r o c k s . T h e y f o r m a n e x t e n s i v e m e t a -
m o r p h i c b e l t o f v a r y i n g t h i c k n e s s a n d l ie o n a v e r y t h i c k
m a r b l e s e r i e s . T h e i n t e r f o l d e d b l u e s c h i s t - m a r b l e c o n t a c t s ,
t h e p a r a l l e l l i n e a t io n d i r e c t io n s i n m a r b l e s a n d b l u e s c h is t s,
a n d s m a l l i n li e rs o f b lu e s c h i s ts in t h e m a r b l e O k a y 1 9 8 0 b ,
1 98 1 ) a l l s h o w t h a t t h e m a r b l e s h a v e u n d e r g o n e t h e s a m e
H P / L T m e t a m o r p h i s m a s t h e b l u e s c h i s t s . M a s s i v e , w h i t e
m a r b l e i s i n s t e e p t e c t o n i c c o n t a c t , m a r k e d b y e x t e n s i v e
b r e c c i a t i o n , l i n e a r s e r p e n t i n i t e s a n d T e r t i a r y d a c i t e i n t r u -
s io n s, w i t h a h ig h t e m p e r a t u r e / m o d e r a t e p r e s s u r e m e t a m o r -
p h i c b e l t . T h e m a j o r r o c k t y p e s i n t h i s b e l t a r e b a s i c v o l -
c a n i c r o c k s , p e l i t e s a n d l i m e s t o n e s . P r o g r e s s i v e m e t a m o r -
p h i c z o n e s f r o m z e o l i t e t o a m p h i b o l i t e f a c i e s h a v e b e e n
m a p p e d i n th i s b e l t n e a r S 6 g f i t Y i l m a z 1 9 79 ). A s t h e m e t a -
m o r p h i c a g e o f t h e H T / M P m e t a m o r p h i c b e l t i s n o t w e ll
e s t a b l i s h e d , i t i s n o t y e t c l e a r w h e t h e r i t f o r m s a p a i r e d
m e t a m o r p h i c b e l t t o g e t h e r w i th t h e U p p e r C r e t a c e o u s
b l ue s ch i st s. T h e H T / M P m e t a m o r p h i c b e l t is i n t h r u s t c o n -
t a c t t o t h e n o r t h w i t h t h e g r a n i ti c b a s e m e n t o f t h e M i d d l e
S a k a r y a Z o n e . T h e M i d d l e S a k a r y a Z o n e c o n s i s ts o f a n
a u t o c h t h o n o u s e p i c o n ti n e n t a l s e d i m e n t a r y s eq u e n c e r a n g -
i n g i n a g e f r o m P e r m i a n t o E o c e n e A l t in l i 1 9 7 5 ; S a n e r
1980).
T h e r e a r e T e r t i a r y g r a n o d i o r i t e i n t ru s i o n s s u p e r i m p o s e d
o n t h is e a s t - w e s t o r i e n t e d t e c t o n i c p a t t e r n A t a m a n 1 9 7 4)
a n d a n e x t e n s iv e c o v e r o f N e o g e n e l a c u s t ri n e s e d i m e n t s a n d
vo l can i cs .
e o l o g y a n d R o c k T y p e s
V o l c a n o - s e d i m e n t a r y s e q u e n c e s w i t h s m a l l s e r p e n t i n i t e
b o d i e s c h a r a c t e r i s e d b y a c h a o t i c in t e r n a l s t r u c t u r e a r e c o m -
m o n a l o n g t h e m a r g i n s o f th e p e r i d o ti t e m a s s if s in N o r t h -
w e s t T u r k e y . A l t h o u g h s u c h s e q u e n c e s a r e c a l l e d o p h i o l i t e
o r o p h i o l it i c m e l a n g e b y s o m e w o r k e r s L i s e n b e e 1 97 1 ;
K a y a 1 9 72 ), t h e r e p e a t e d i n t e r c a l a t i o n o f s e d i m e n t a r y a n d
v o l c a n ic r o c k s , l a c k o f s h e e te d d y k e c o m p l e x e s a n d g a b b r o s
d o e s n o t m e r i t t h e c u r r e n t u s a g e o f t h e t e r m o p h i o l it e f o r
t h e se r o c k s . T w o m a j o r a r e a s o f s u c h r o c k s h a v e b e e n r e -
c o g n i s e d i n th e T a v ~ a n h a r e a : t h e o n e n o r t h o f th e v i l la g e
o f K e t e n l i k o c c u r s a s a t e c to n i c k l i p p e a m o n g t h e l a w s o n i t e
z o n e b l u e s c h is t s O k a y 1 9 8 0 b , Y e n i k 6 y G r o u p o f F i g . 5 ).
A l a r g e r a r e a l ie s t o t h e s o u t h a r o u n d t h e v i ll a g e o f G f i m f i -
~ y e n i k 6 y . T h i s p a p e r d e a l s m a i n l y w i t h t h e v o l c a n o - s e d i -
m e n t a r y r o c k s i n t h e G f i m i i~ y e n ik 6 y a re a , a l t h o u g h b o t h
a r e a s a r e l i th o l o g i c a l ly a n d s t r u c t u r a l l y v e r y s i m i l a r.
T h e v o l c a n o - s e d i m e n t a r y r o c k s o f t h e G f i m i i~ y e n ik 6 y
a r e a o c c u r d i r e c t l y b e l o w a l a r g e p e r i d o t i te m a s s i f i n a n
i m b r i c a t e t e c t o n i c z o n e o f 2 - 3 k m w i d t h F i g . 2) . T h e d o m i -
n a n t l i t h o lo g i e s in t h i s z o n e a r e r o c k s o f t h e S t e i n m a n n
t r i n i t y : b a s i c v o l c a n i c r o c k s , r a d i o l a r i a n c h e r t s a n d s e r p e n -
t in i t es i n c o n j u n c t i o n w i t h r e d a n d g r e e n s h a l es , g r e y w a c k e s ,
m a n g a n e s e d e p o s i t s , p i n k t h i n l y - b e d d e d l i m e s t o n e s , k e r a t o -
p h y r e s a n d e x o t i c b lo c k s o f w h i t e li m e s t o n e . T h i s g r o u p
o f r o c k s i s c h a r a c t e r i s e d b y a r i c h l i t h o l o g ic a l v a r i e t y ; s e v e r -
a l d i f f e r e n t r o c k t y p e s c a n o f t e n b e s e e n i n t e r b e d d e d o v e r
a d i s t a n c e o f t e n m e t e r s , a n y s i n g l e li t h o l o g y i s r a re l y m o r e
t ha n t en me t e r s t h i ck c f. Oka y 1981 , F i g . 4 ). T he whol e
z o n e i s s t r o n g l y t e c t o n i s e d w i t h l a r g e n u m b e r s o f s h e a r
z o n e s m a r k e d b y s e r p e n t i n i t e a n d t a l c o u t c r o p s ; s l i v e r s o f
g r e e n s c h i s t s o c c u r a s f a u l t - b o u n d e d b l o c k s . O n l y t h e m a j o r
s h e a r z o n e s a n d t h e l a r g e r s e r p e n t i n i t e b o d i e s a r e s h o w n
i n F ig . 2 . T h e s t r o n g t e c t o n i s m a n d l i t h o l o g i c a l h e t e r o g e n e -
i ty m a k e s t h e m a p p i n g o f i n d iv i d u a l r o c k t y p e s i m p o s s i b le
on a 1 : 250 00 sca l e c f . K ay a 1972 , F i g . 10).
I n t h e f i e ld t h e r o c k s o f t h e v o l c a n o - s e d i m e n t a r y s e -
q u e n ce a p p e a r u n m e t a m o r p o s e d a n d d o n o t s h o w p e n e tr a -
t iv e d e f o r m a t i o n . V o l c a n ic r o c k s a r e th e m o s t c o m m o n r o c k
t y p e . T h e y f o r m m a s s i v e g r e e n f l o w s i n t e r b e d d e d w i t h r a -
d i o l a r i a n c h e r t s a n d r e d g r e e n s h a l e s , a n d i n c l u d e d o l e r i t e s ,
s p i li te s , p y r o c l a s t i c s a n d m i n o r a m o u n t s o f k e r a t o p h y r e s ,
t r a c h y b a s a l t s a n d m o r e a c i d i c d i f f e r e n t i a t e s . P i l l o w l a v a s
a r e v e r y r a r e . C l i n o p y r o x e n e c o m p o s i t i o n s f r o m t h e v o l -
c a n i c r o c k s i n d i c a te t h a t m o s t o f t h e m w e r e s u b a l k a l in e ,
a l t h o u g h s o m e k a e r s u t i t e - b e a r i n g s p i l i t e s a n d p y r o c l a s t i c s
h a v e m a r k e d a l k a l i n e a f f in i t ie s O k a y J9 8 0 c ) .
S e r p e n t i n i t e o c c u r s a s b o d i e s o f v a r i o u s s i z e s r a n g i n g
8/10/2019 07 - incipient metamorphism - CMP 1982.pdf
3/7
363
Fig. 3a--d. Pho tom icrog raph s from the incipiently metam orp hose d zone: a Augite partially replaced by sodic pyroxene px, dark areas)
with leucoxene and albite ab) in a dolerite K48). b Completely metasomatised dolerite K92 0) with sodic pyroxene pseud om orph s
px) after augite, albite
ab)
and interstitial chlorite
chl). c
Lawsonite laths
lw),
fibrous pumpellyite pp) and chlorite
chl)
in an amygdale
of a fine-grained spilite K864). The grou ndm ass shows no signs of any m etam orpism , d Aragonite m arb le; a large aragonite grain
in extinction position) is expitaxically and partially replaced b y elongate lamellae of calcite cc). Aragonite shows the characteristic
110) multiple twinning parallel to the replacing calcite lamellae
f rom a few mete rs to a few k i lomete rs concent ra t ed a long
the shear zones . In the few samples examined, ant igori te
is the main serp ent ini te mineral . Veins of andradi te garnet
occur frequent ly in these serpent ini tes .
Greenschis ts associa ted with serpent ini tes occur in two
wedge shaped a reas . Wel l -marked thrus t p l anes s epa ra t e
them f rom the vo lcano-sed imenta ry rocks . The dominant
rock type is a s t rongly fol ia ted metabas i te wi th a mineral
assemb lage of act inol i te + epidote + chlori te + a lbi te +
quartz . Some greenschis t metabas i tes contain re l ic t lawson-
i te or pumpel lyi te .
Petrography and ineralogy
Fifty-f ive specimens o f bas ic volcanic rocks , including p y-
roclas t ic f lows, doler i tes and spi l i tes , f rom the vic ini ty of
the vi l lage of Gfimfi~yenik6y were inves t igated petr ogra phi-
cal ly Fig. 2). Al l re ta in thei r igneous textures and their
essent ia l mineralogy consis ts of augi te a l ter ing to sodic py-
roxene, a lbi te Ano), chlori te and leucoxene. In ma ny speci-
mens pumpel lyi te occurs as i r regular s t r ingers in large a lbi t -
ised plagioclase grains . Epidote and act inol i te character is t ic
of man y spi l i tes , are absent .
ethod
Minera l compos i t ions were de te rmined for twe lve e lement s
Na, Ca, K, Fe, Mg, Mn, V, Ni , Cr, Ti , A1, Si) us ing an
energy dispers ive e lect ro npro be with a Harw el l Si Li) de-
t ec tor and pul se proces sor . The cor rec t ion procedures a re
g iven by Swea tmann and Lon g 1969) . The me th od for
es t imat ing ferr ic i ron in sodic pyr oxen e is given in an earl ier
pape r Okay 1978). Who le rock ana lys i s were mad e on an
X-ray spectrometer us ing fused discs wi th a l i thium te t ra-
bora t e f lux . Na and K were de te rmined by f l ame photo -
me t ry and FeO by t i t r a t ion .
Topotactic Replacement of Augite by Sodic Pyroxene
The rep lacement o f augi te by green i sh-ye llow sodic pyrox-
ene in the volcanic rocks is variable in extent , ranging from
thin r ims and ve ins F ig. 3a ) to comple te pseudom orphs
Fig. 3 b) . On a region al scale 44 ou t of 55 spil i tes contain
such replacem ent textures Fig. 2). The replacem ent of au-
g i t e by sodic pyroxene has occur red topotac t i ca l ly , on an
ion by ion bas is, leaving the igneous texture intact Carp en-
ter and Okay 1978). This replacement process seems to be
control led by the avai lable mineral s t ructure; in an a lkal i
basa l t kae rsu t i t e has r ims of b lue sodic amphibole , whereas
t i tanaugi te in the same rock has been replaced by sodic
8/10/2019 07 - incipient metamorphism - CMP 1982.pdf
4/7
364
Table l. Representative mineral analyses
Sodic Pyroxene Pumpellyite Albite Lawsonite Chlorite Garnet
K48 K860 K919/2 K160 K733/1 K733/1 K30t K960 K36 K48 K485/2 K3 01
vein vein
core rim
SiO 2 52.75 53 .46 57. 00 52.54 37.04 37.93 68.17 38.30 37,17 30.31 30. 81 30.67 38.00 35.76
TiOz 0.00 0.28 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0. 00 0.00 0.00 0.00 0.00
A120 3 0.61 2.39 8.01 2.11 21.97 24.17 19.41 27.92 29.72 14.39 13 .5 3 14.37 9.91 1.54
FeO* 26.18 24 .2 4 18 .6 1 22.19 8.59 6.01 0.00 5.25 2.23 24.57 24 .2 9 23.59 16.12 27.29
MgO 1.84 1.14 0.77 2.91 2.26 2,40 0.00 0.00 0.00 16.93 14 .5 6 16.06 0.00 0.00
MnO 0.36 0.24 0.00 0.22 0.17 0.25 0.00 0.00 0.00 0.23 0.25 0.32 0.44 0.23
CaO 6.90 3.53 2.26 7.36 22.31 23.07 0.11 17.32 16.99 0.24 0.80 0.83 34.95 33.69
NazO 10 .13 12 .7 3 13.81 9.92 0.00 0.00 12.23 0.00 0.00 0. 00 0.00 0.00 0.00 0.00
K20 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0. 00 0.24 0.00 0.00 0.00
Total 98 .7 7 98.0 1 100.46 97.25 92.34 93.83 99.92 88.79 86.11 86.67 84. 48 85.84 99.42 98.51
Number of cations per
4 cations 16 cations 8 0 5 cations 28 oxygens 12 cations
Si 2.00 1.99 2.03 2.00 6.07 6.07 2.99 2.03 2.01 6.41 6.70 6.51 3.01 2.97
A14 0 .0 0 0 .0 1 0 .0 0 0 .0 0 0 .0 0 0 .0 0 0 .0 1 0 .0 0 0 .0 0 1 .5 9 1 .3 0 1 .4 9 0 .0 0 0 .0 3
A16 0.03 0.10 0.34 0.10 4.25 4.56 0.99 1.75 1.90 1.99 2.17 2.11 0.92 0.08
Ti 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 0,00
Fe 3+ 0.71 0.76 0.55 0.63 0.75 0.44 0.00 0.23 0.10 4.34 4.42 4.19
1 .0 8 1 .8 9
Fe z+ 0.12 0.00 0.00 0.07 0.43 0.37 0.00 0.00 0.00 0.00 0.00
Mg 0.10 0.06 0.04 0.16 0.56 0.57 0.00 0.00 0.00 5. 33 4.72 5.08 0.00 0.00
Mn 0 .0 1 0 .0 1 0 .0 0 0 .0 1 0 .0 2 0 .0 3 0 .0 0 0 .0 0 0 .0 0 0.04 0.05 0.06 0.03 0.03
0 .9 7 0 .9 4 0 .9 3 0 .9 7 6 .0 1 5 .9 7 1 .9 8 2 .0 0
Ca 0.28 0.14 0.08 0.30 3.92 3.96 0.005 0.99 0.99 0.06 0.19 0.19 2.96 3.00
Na 0.74 0.92 0.99 0.73 0.00 0.00 1.04 0.00 0.00 0.00 0.00 0.00 0.00 0.00
K 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
1 .0 2 1 .0 6 1 .0 7 1 .0 3 3 .9 2 3 .9 6 5 .0 4 0 .9 9 0 .9 9 1 9 .7 6 1 9 .6 2 1 9 .6 3 2 .9 9 3 .0 3
Jd 3 10 34 t0 * Tot ali ron Andr. 54 96
Ac 71 76 55 63 as FeO Gross . 46 4
Au 26 14 11 27
pyroxene. Sodic pyroxene also occurs as acicular crystalls
in monom ineralic veins.
Sodic pyroxene compositions from eight rocks are plot-
ted in the acmite-jade ite-augi te ternary diagr am in Fig. 4
and four sodic pyrox ene analyses are sho wn in Table 1.
Sodic pyroxenes from the incipiently metamorphosed zone
have high acmite compon ents (generally over 50 ) and
are compositionally similar to the sodic pyroxenes from
the lawsonite zone metabasites. Conversely sodic pyroxenes
from the glaucophane-lawsonite zone metabasites show a
wider range of compositi ons (Fig. 4). A lack of omphacit ic
compositions is characteristic of all three metamorphic
zones in the Tav~anh region.
The main chemical changes involved in the constant
volume replacement of augite by sodic pyroxene are an
increase in sodium and ferric iron, and a concomitant de-
crease in calcium and magnesium. For a specific case (sam-
ple K48):
100 g augi te + 9.44 g Na2 0 + 13.52 g Fe20 3 + 2.65 g SiO2
+0.08 g A1203+0.38 g 02
= 103.85 g sodic pyroxene (JdsAcs9Au33)+ 9.90 g CaO
+11.88 g MgO+ 0. 59 g TiO z.
However, as the composition of the replacing sodic pyrox-
ene changes (Fig. 4), the chemical balance in the isovolume
replacement is variable.
c
Au Jd
Fig. 4. Sodic pyroxene compositions from the incipiently metamor-
phosed basic volcanic rocks plotted on the acmite-jadeite-augite
diagram. Subscript v indicates compositions of sodic pyroxenes
from the veins. Compositional fields of sodic pyroxenes from the
lawsonite zone
co n t i n u o u s l i n e s )
and glaucophane-lawsonite zone
d a sh ed l i n e s ) metabasites are also indicated
8/10/2019 07 - incipient metamorphism - CMP 1982.pdf
5/7
365
Table 2. Analyses o f three metasomatised basic volcanic rocks. Ox-
ides are normalised to 100 wt.
K960 K775 K920
SiOz 50.02 50.66 53.82
TiO2 0.97 2.10 1.57
A120 3 16.10 16.22 14.79
F O3 5.63 5.52 5.03
FeO 3.74 3.81 6.05
MgO 5.92 4.89 4.69
MnO 0.15 0.19 0.21
CaO 7.05 5.04 2.90
Na20 6.09 6.19 7.79
KzO 0.20 0.14 0.20
P205 0.11 0.75 0.10
HzO 4.02 4.49 2.85
3 t ~
X t
0.2
0 1 . 0 0 J , 1 0 1 2 0 M . 3 0 , 4 0 1 . 5 0 1 6
Fe/Fe Mg
Fig. 5. Chlorite compositions from the incipiently metamorphosed
basic volcanic rocks plo tted in terms of their F e/Fe + Mg and A1/
AI + Fe + M g ratios. C ompositional fields of chlorites from the law-
sonite zone metabasites are also indicated
T h r e e a n a l y s e s o f s t r o n g l y m e t a s o m a t i s e d b a s i c v o l c a n i c
r o c k s a r e s h o w n i n T a b l e 2 . C o m p a r e d w i t h b a s a l ts o r s p i-
l it e s, t h e a n a ly s e s s h o w i n c r e as e s in N a 2 0 ( f r o m 1 4 .5 w t .
i n b a s a l ts a n d s p il it e s t o 6 - 8 w t . ) , S i O 2 a n d F e 2 0 3 , b u t
d o n o t i n d i c a t e a m a r k e d c h a n g e i n t h e t o t a l i r o n c o n t e n t .
M a g n e t i t e i s a b s e n t i n t h e s e r o c k s , a n d i r o n s e em s t o h a v e
b e e n r e d i s t r ib u t e d t o s o d i c p y r o x e n e . T h e r e a r e c o r r e s p o n d -
i n g d e c r e a s e s i n C a O a n d M g O . A 1 2 0 3 a n d T i O 2 h a v e a p -
p a r e n t l y s t a y e d f a i r l y c o n s t a n t . T i O 2 a n d s o m e o f t h e r e -
l e a se d c a l c i u m i s r e t a i n e d i n l e u c o x e n e , w h i c h f o r m s s m a l l
i n c l u si o n s i n s o d ic p y r o x e n e p s e u d o m o r p h s .
Chlorite i s t h e m a j o r s e c o n d a r y m i n e r a l f o u n d i n t h e
in te rs t i ces o f p lag ioc la se a nd py rox ene c ry s ta l s (F ig . 3 b ) ,
and in a m yg da les (F ig . 3 c ). I t fo rm s f ine -gra ined aggreg a tes
o r b l a d e d c r y s ta l s . S o m e o f t h e c h l o r i t e s s h o w r e l a t i v e ly
h i g h i n t e r f e r e n c e c o l o u r s a p p a r e n t l y r e l a t e d t o t h e i r r e l a -
t i v e ly h i g h p o t a s s i u m a n d c a l c i u m c o n t e n t s ( T a b l e 1 ) . C o m -
p o s i t i o n a l l y , c h l o r i t e s f r o m t h e i n c i p i e n t l y m e t a m o r p h o s e d
b a s i c v o l c a n i c r o c k s a r e s l i g h t l y l e s s a l u m i n o u s a n d m o r e
s i l i c e o u s t h a n l a w s o n i t e a n d g l a u c o p h a n e - l a w s o n i t e z o n e
ch lor i t e s (F ig . 5 , Tab le 1 ) . P hengi te i s absen t in these roc ks
a n d o n l y a p p e a r s i n t h e l a w s o n i t e z o n e m e t a b a s i t e s a s
s lende r c rys ta l s em bedded in ch lor i t e .
Al l p lag ioc la se in the vo lcan ic rocks i s com ple te ly a lb i t-
i s ed . Alb i t i s ed p lag ioc la se i s c loudy and qu i te d i s t inc t ive
f rom the f re sh , inva r iab ly twinned a lb i t e in the ve ins . I t
h a s le ss t h a n 1 a n o r t h i t e c o m p o n e n t a n d m i n o r a m o u n t s
o f F e O ( 0 . 1 t o 0 .5 w t . ) .
Mineralogy of the Veins and mygdales
in the Basic Volcanic Roeks
T h e b a s i c v o l c a n i c r o c k s a r e c r o s s - c u t b y n u m e r o u s v e i n s
o f c a l c i u m c a r b o n a t e ( i n 26 sa m p l e s o u t o f 5 5 ), q u a r t z ( i n
18), pumpellyi te ( in 18), a lbi te ( in 13), lawsonite ( in 6) ,
sod ic pyroxene ( in 4 ) and ga rne t ( in 2 ) . Com pos i t e ve ins
c o n t a i n i n g t w o t o f o u r m i n e r a l s a r e f a i r l y c o m m o n w i t h
q u a r t z - c a r b o n a t e a n d c a r b o n a t e - a l b i t e b e i n g t h e m o s t f r e -
q u e n t c o m b i n a t i o n s . M o r e c o m p l e x v e i n s o f p u m p e l l y i te -
l a w s o n i t e - q u a r tz - c a l c i te ( K 2 6 5 ) , p u m p e l l y i t e - g a r n e t ( K 3 0 1 )
a n d a l b i te - l a w s o n i t e a re a l s o p r e s e n t . C a r b o n a t e m i n e r a l s,
p u m p e l l y i t e , c h l o r i t e a n d l a w s o n i t e a l s o o c c u r f r e q u e n t l y
in a m yg da les (F ig . 3 c ) .
ragonite w a s i d e n t i f i e d a s t h e p r i m a r y C a C O 3 p o l y -
m o r p h i n 1 2 s p e ci m e n s f r o m i t s m u l t i p l e ( 11 0 ) t w i n l a m e l la e
( F ig . 3 d ) ; i t f o r m s l a rg e ( l - 1 0 m m ) c r y s t a ls i n t h e v e in s
and am ygda les , and i s be ing rep laced by sm a l l , i r regu la r
s t ri n g e r s o f c al c it e . In s o m e r o c k s e x t r a o r d i n a r y a n a s t o m o s -
i n g v e i n s c o m p o s e d o f s i n g l e c r y s t a l s o f a r a g o n i t e u p t o
2 6 m m l o n g a n d o n l y 0 .1 m m w i d e a r e p r e s e n t.
Pumpellyite i s p r e s e n t in a l m o s t e v e r y s a m p l e e i t h e r i n
am y gda les (F ig . 3 c ) , in ve ins o r a s pa le ye l low m ic ro gran u-
l a r p a t c h e s o v e r g r o w i n g t h e g l a s s y m a t r i x o f t h e v o l c a n i c
r o c k s ; in s o m e g l as s y v o l c a n i c r o c k s i t m a k e s u p 7 0 o f
t h e m o d e . I n v e i n s a n d a m y g d a l e s i t f o r m s a g g r e g a t e s o f
r a d i a t i n g a c i c u l a r c ry s t a l s s h o w i n g a n o m a l o u s i n t e r f e r e n c e
c o l o u r s . P u m p e l l y i t e s h a v e v i r t u a l l y c o n s t a n t M g c o n t e n t s
and show res t r i c ted A1 for F e 3+ su bs t i tu t ion (Tab le 1 ) .
C o m p o s i t i o n a l l y t h e y a r e s i m i l a r t o a n a l y s e d p u m p e l l y i t e s
f r o m o t h e r l o w - g r a d e m e t a m o r p h i c t e r r a i n s ( c f . C o o m b s
et al. 1976).
lbite
in the ve ins occurs a s f re sh id iob las t i c c rys ta l s
inva r iab le showing s im ple o r m ul t ip le twinn ing . I t has l e s s
t h a n 1 a n o r t h i t e c o m p o n e n t ( T a b l e 1 ).
Lawsonite
a p a r t f r o m i t s u s u a l t a b u l a r s h a p e , d i s p l a y s
unusua l ac icu la r and bow- t i e hab i t s in the ve ins . I t i s found
i n t h e a m y g d a l e s o f a v o l c a n i c r o c k , t h a t o t h e r w i s e a p p e a r s
u n m e t a m o r p o s e d , i n a s s o c i a t i o n w i t h c h l o r i t e a n d p u m p e l -
ly i t e (F ig . 3 c ) . An a lysed l awsoni te s f r om the inc ip ien t ly m e-
t a m o r p h o s e d z o n e h a v e c o n s i s t e n t l y h i g h e r F e 2 0 3 c o n t e n t s
( 1 . 5 -5 . 5 w t . ) t h a n l a w s o n i te s f r o m t h e g l a u c o p h a n e - l a w -
son i te and l awsoni te zones (Tab le 1 ) .
Garnets
o f t h e a n d r a d i t e - g r o s s u l a r s e r i e s o c c u r i n t w o
s t r o n g l y m e t a s o m a t i s e d v o l c a n i c r o c k s i n a s s o c i a t i o n w i t h
p u m p e l l y i t e a n d s o d i c p y r o x e n e . T h e y s h o w d i s c o n t i n u o u s
z o n i n g p r o f i l e s w i th i n t e r m e d i a t e a n d r a d i t e - g r o s s u l a r c o r e s
a n d p i n k a n d r a d i t e r i m s ( T a b l e 1 ) . G a r n e t s o f s i m i l a r c o m -
p o s i t i o n a r e a l s o f o u n d i n t a l c s a n d s e r p e n t in i t e s o f t h e
i n c i p i en t l y m e t a m o r p h o s e d z o n e a n d o f th e l a w s o n i t e z o n e
( O k a y 1 9 8 0 b ) .
ragonitised Limestone
I f t h e a m b i e n t p r e s s u r e s i n t h e v o l c a n o - s e d i m e n t a r y r o c k s
w e r e h i g h e n o u g h t o s t a b i l i z e a r a g o n i t e i n t h e v e i n s a n d
a m y g d a l e s o f b a s ic v o l c a n i c r o c k s , t h e n o n e w o u l d s i m i la r l y
e x p e c t c a l c i t e i n l i m e s t o n e s , w h i c h a r e o f t e n i n t e r b e d d e d
w i t h b a s i c v o l c a n i c r o c k s , t o h a v e t r a n s f o r m e d t o a r a g o n i t e .
I n d e e d , a l l t h e p e t r o g r a p h i c a l l y e x a m i n e d l i m e s t o n e s c o n s i st
o f c o a r s e c r y s t al s o f a r a g o n i t e s h o w i n g v a r i o u s d e g r e e s o f
r e p l a c e m e n t b y c a lc i te .
T w o t y p e s o f a r a g o n i t i s e d l i m e s t o n e h a v e b e e n r e c o g n -
i s ed p e t r o g r a p h i c a l l y . I n t h e f i r s t t y p e t h e s e d i m e n t a r y f a b -
r i c o f t h e l i m e s t o n e w i t h t h e r a d i o l a r i a t e st s, f o s si l fr a g m e n t s
a n d c l a y f r a c t i o n is p e r f e c t ly p r e se r v e d . H o w e v e r , t h e w h o l e
b i o m i c r i t i c g r o u n d m a s s n o w c o n s is t s o f s e v e r al c e n t i m e t e r s
l a r g e g r a in s o f a r a g o n i t e . I n t h e s e c o n d t y p e t h e l i m e s t o n e
i s rec rys ta l l i s ed and cons i s t s o f ve ry l a rge c lea r a ragoni te
8/10/2019 07 - incipient metamorphism - CMP 1982.pdf
6/7
366
g r a i n s p a r t i a l l y a n d e p i t a x i a l l y r e p l a c e d b y s m a l l e r g r a i n s
o f ca l c i t e (F ig . 3 d ) .
i scuss ion
T h e p r e s e n c e o f a r a g o n i t e a s w e l l r e c r y st a l li s e d l a r g e g r a i n s
i n t h e v o l c a n i c r o c k s a n d l i m e s t o n e s o f t h e T a v ~ a n h r e g i o n
a n d i ts a s s o c i a t i o n w i t h l a w s o n i t e a n d s o d i c p y r o x e n e i n d i-
c a t e t h a t t h e v o l c a n o - s e d i m e n t a r y s e q u e n c e h a s u n d e r g o n e
a n i n c ip i e nt H P / L T m e t a m o r p h i s m . T h e a b s e n c e o f j a d e it e
a n d z e o l it e s a n d t h e p r e s e n c e o f a r a g o n i t e , a l b i t e a n d l a w -
s o n i te i n s o m e o f t h e b a s i c v o l c a n i c r o c k s i n d i c a t e s p r e s -
s u r e s o f 5 t o 8 k b a r s a n d t e m p e r a t u r e s 1 5 0 - 20 0 ~ C d u r i n g
t h e i n c i p i e n t m e t a m o r p h i s m ( N e w t o n a n d S m i t h 1 9 6 7 ;
H l a b s e a n d K l e p p a 1 9 6 8 ; J o h a n n e s a n d P u h a n 1 97 1) .
I n t h e i n c i p i e n t l y m e t a m o r p h o s e d v o l c a n i c r o c k s m e t a -
s o m a t i s m i s e v id e n c e d b y t h e s o d ic p y r o x e n e p s e u d o m o r p h s
a f t e r a u g i t e c o e x i s t in g w i t h a l b i t e a n d c h l o ri t e . T h e p r e s e n c e
o f s i m i la r s o d ic p y r o x e n e p s e u d o m o r p h s a f t e r a u g i te i n la w -
s o n i te z o n e m e t a b a s i t e s , w h i c h o c c u r n o r t h o f t h e m a i n
eas t -w es t t r en d in g t h ru s t (F ig . 2 ), p o in t o u t t o t h e c lo se
r e l a t i o n s h i p b e t w e e n H P / L T m e t a m o r p h i s m a n d m e t a s o -
m a t i s m . H o w e v e r , i n t h e l a w s o n i t e z o n e m e t a b a s i t e s , w h e r e
l a w s o n i t e is a b u n d a n t a n d a l b i te a b s e n t , t h e r e i s n o e v i d e n c e
o f s od i u m m e t a s o m a t i s m .
Th e p resen ce o f g reen sch i s t t ec to n i c s l i ces wi th in t h e
v o l c a n o - s e d i m e n t a r y s e q u e n c e ( F i g . 2) i n d ic a t e t h a t t h e i n -
c i p ie n t H P / L T m e t a m o r p h i s m a n d m e t a s o m a t i s m ha s o c -
c u r r e d p r i o r t o t h e s t r o n g t e c t o n i s m . T h e i m b r i c a t i o n o f
t h e w h o l e s e q u e n c e c a n b e r e l a t e d t o t h e e m p l a c e m e n t o f
t h e l a r g e u l t ra m a f i c s l a b ( F ig . 1 ) o n t h e v o l c a n o - s e d i m e n t a -
r y r o c k s . T h e r e i s a n i m p o r t a n t d i f f e r e n c e b e t w e e n t h e m a i n
b o d y o f p e r id o t i t e , w h i c h i s o n l y p a r t i a l ly s e r p e n t i n i se d a n d
h a s c h r y s o t i l e a s t h e m a i n s e r p e n t i n e m i n e r a l , a n d t h e
s m a l l e r c o m p l e t e l y s e r p e n ti n i s e d b o d i e s w i t h i n t h e v o l c a n o -
s e d i m e n t a r y s e q u e n c e , w h i c h c o n t a i n a n t i g o r i t e . S e v e r a l
m e t e r s t h i c k r e a c t i o n z o n e s o f p u m p e l l y i t e , a l b it e , s o d i c
p y r o x e n e , c h l o r i te e t c . h a v e b e e n f o u n d a t t h e c o n t a c t z o n e s
o f s e r p en t i n it e s in N o r t h w e s t T u r k e y ( O k a y 1 9 8 0c ) a n d
i n C a l i f o r n i a ( C h e s t e r m a n 1 9 60 ; L e o n a r d e s a n d F y f e 1 96 7) .
I f t h e s m a l l u l t r a b a s i c b o d i e s i n t h e T a v ~ a n l l re g i o n w e r e
p a r t o f t h e v o l c a n o - s e d i m e n t a r y s e q u e n c e a n d w e r e s e r p e n -
t in i se d d u r i ng t h e H P / L T m e t a m o r p h i s m , t h e n t h e y w o u ld
b e e x p e c t e d t o p r o d u c e s i m i l a r m e t a s o m a t i c z o n e s d u r i n g
t h e i r s e r p e n t i n i z a t i o n . T h i s m i g h t e x p l a i n t h e p r e s e n c e o f
e x t r e m e l y m e t a s o m a t i s e d p u m p e l l y i t e - a n d r a d i t e r o c k t y p e s
o r u n m e t a s o m a t i s e d s p il it es , w h i c h b y a n a l o g y m u s t
h a v e f o r m e d r e s p e c t i ve l y n e a r o r f a r a w a y f r o m t h e s e r p e n -
t i n i t e c o n t a c t s . H o w e v e r , t h e s t r o n g l a t e t e c t o n i s m h a s
m o s t l y o b l i t e r a t ed t h e f i e l d ev id en ce l i n k in g t h ese ro ck s t o
se rp en t i n i t e co n t ac t s .
M e t a s o m a t i s m h a s o f t e n b e e n c i t e d a s a n a c t i v e a g e n t
i n t h e fo rm at io n o f t h e b lu esch i s t s ( e .g . Gresen s 1 96 9 ). T h u s
T a l i a f e r r o ( 1 9 4 3) a s c r i b e d t h e f o r m a t i o n o f b l ue s c h i s ts t o
t h e l o c a l i n t r o d u c t i o n o f s o d a , i r o n a n d m a g n e s i u m i n t o
s a n d s t o n e s , s h a l e s , c h e r t s a n d b a s a l t s n e a r c o n t a c t s w i t h
u l t r a b a s i c i n t r u s i o n s . H o w e v e r , e x p e r i m e n t a l s t u d i e s h a v e
d e m o n s t r a t e d c o n v i n c i n g l y t h e h i g h p r e s s u r e s t a b i li t ie s o f
b lu esch i s t m in era l s , an d i n g en era l i t i s t r u e t h a t b lu esch i s t
m e t a m o r p h i s m i s i s o c h e m i c a l . N e v e r t h e l e s s , a s d o c u m e n t e d
h e r e , v e r y l o w - g r a d e i n c i p i e n t l y h i g h p r e s s u r e m e t a m o r -
p h o s e d r o c k s s h o w e x t e n s i v e m e t a s o m a t i c e f f e c t s . I t s e e m s
t h a t a l t h o u g h b l u e s c h is t s a r e n o t p r o d u c e d b y m e t a s o m a -
t i s m , m e t a s o m a t i s m i s w i d e s p r e a d i n l o w - g r a d e b l u e s c h i s t
f a d e s c o n d i t io n s .
Summary o f the Blueschist Metamorphic Zones
in the Tav~anh Region
I n N o r t h w e s t T u r k e y a t h i c k s e qu e n c e o f i n t e r c a l a t e d b a s i c
v o l c a n i c r o c k s , c h e r t s a n d s h a l e s h a s u n d e r g o n e b l u e s c h i s t
m e t a m o r p h i s m . B a s e d o n t h e m e t a b a s i c m i n e r a l a s s e m b l a g e
a n d t e x t u r e s , o b s e r v e d b o t h i n t h e f i e l d a n d u n d e r t h e m i -
c r o s c o p e , t h r e e b l u e s c h i s t m e t a m o r p h i c z o n e s h a v e b e e n
d i f f e r en t i a t ed i n t h e Tav ~an l l r eg io n .
T h e l o w e s t g r a d e z o n e , d e c r i b e d i n t h i s p a p e r , c o n s i s t s
o f a c l o se l y i n t e r c a l a t e d v o l c a n o - s e d i m e n t a r y s e q u en c e . T h e
h i g h p r e s s u r e m e t a m o r p h i s m w a s i n c i p i e n t a n d i s c h i e f l y
e v i d e n c e d i n t h e v e i n a n d a m y g d a l e m i n e r a l o g y , w h i c h i n -
c lu d es p u m p el ly i t e , a r ag o n i t e , l awso n i t e , a l b i t e an d so d i c
p y r o x e n e . A s s o c i a t e d w i t h t h i s i n c i p i e n t m e t a m o r p h i s m ,
t h e r e h a s b e e n e x t e n s i v e s o d i u m m e t a s o m a t i s m i n v o l v i n g
t o p o t a c t i c r e p l a c e m e n t o f a u g i te b y s o d i c p y r o x e n e .
T h e i n c i p i e n t l y m e t a m o r p h o s e d v o l c a n o - s e d i m e n t a r y
ro ck s t ec to n i ca l l y o v er l i e t h e l awso n i t e zo n e b lu esch i s t s .
R o c k t y p e s i n t h e l a w s o n i t e z o n e a r e s i m i l a r t o t h o s e o f
t h e i n c i p i e n t l y m e t a m o r p h o s e d z o n e a n d a p p e a r s i m i l a r l y
u n m e t a m o r p h o s e d i n t h e f i e l d . H o w e v e r , u n d e r t h e m i c r o -
s c o p e t h e m e t a b a s i c r o c k s c o n s i s t o f s o di c p y r o x e n e p s e u d o -
m o r p h s a f t e r a u g i t e , l a w s o n i t e a n d c h l o r i t e . T h e o r i g i n a l
t ex tu re h as b een l a rg e ly r e t a in ed an d t h e re i s l i t t l e p en e t r a -
t i v e d e f o r m a t i o n ( O k a y 1 9 8 0 b ) .
M e t a b a s i t e s o f th e l a w s o n i te z o n e p a s s a l o n g a m a p p e d
i s o g r a d i n t o t h e r o c k s o f th e g l a u c o p h a n e - l a w s o n i t e z o n e
w i t h t h e d e v e l o p m e n t o f s o d i c a m p h i b o l e f r o m a r e a c t i o n
i n v o l v in g c h l o ri t e, s o d i c p y r o x e n e a n d q u a r t z . M e t a b a s i t e s
o f t h e g l a u c o p h a n e - l a w s o n i t e z o n e h a v e l o s t a ll t h e ir p r i m a -
r y i g n e o u s f e a t u r e s a n d a r e o f t e n s c h i st o se . T h e y a r e c h a r a c -
t e ri s ed b y t h e d o m i n a n c e o f s od i c a m p h i b o l e + l a w s o n i t e
i n t h e m i n e r a l a s s e m b l a g e ( O k a y 1 9 8 0 a ) . T h e c o m m o n o c -
c u r r e n c e o f r e li c t s o d ic p y r o x e n e , o f t e n i n r e a c t i o n r e l a t i o n
t o s o d i c a m p h i b o l e , i n d i c a t e s t h a t t h e g l a u c o p h a n e - l a w s o n -
i t e z o n e r o c k s h a v e p a s s e d t h r o u g h t h e l a w s o n i t e z o n e s t a g e .
A l t h o u g h t h e r e i s a m p l e e v i d e n c e t h a t l a w s o n i t e a n d
g l a u c o p h a n e - l a w s o n i t e z o n e s r e p r e s e n t a p r o g r e s s i v e i n -
c r e as e in m e t a m o r p h i c g r a d e, t h e u b i q u it o u s m e t a s o m a t i s m
i n t he i n c i p ie n t l y m e t a m o r p h o s e d r o c k s i n d ic a t e s t h a t t h e s e
r o c k s u n d e r w e n t a d i f f e r e n t s e t o f p h y s i c a l c o n d it i o n s .
Acknowledgements
I thank R. Colston and J. Spray for reviewing
the manuscript. This work was carried o ut w hile in receipt of a
grant from the Mineral Research and E xploration Institute o f Tur-
key (MTA), which is gratefully acknowledged.
References
Altmh E (1975) Geology of the Middle Sakarya River (Turkey).
In: Congress of Earth Sciences. MTA Publications, Ankara,
pp 161-197
Ata m an G (1974) Revue g$ochronologique des massifs plutoniques
et m6tamorphiques de l 'Anatolie. Hac ettepe Bull Na tl Sci Eng
3 : 75-88
Carpenter MA, Okay AI (1978) Topotactic replacement of augite
by omphacite in a blueschist rock from NW Turkey. Mineral
Mag 4 2 :4 3 5 4 3 8
Chesterm an C W (1960) Intrusive ultrabasic roc ks and their m eta-
morp hic relationships at Leach L ake Mountain, Mendocino
County, California. Rep t Intern Geo l Congr 21st Session No r-
den 13:208-215
8/10/2019 07 - incipient metamorphism - CMP 1982.pdf
7/7
367
C o o m b s D S , N a k a m u r a Y , V u a g n a t M ( 19 76 ) P u m p e l l y it e - a c t in o -
l i t e f ac ies sch i s t s o f the Taveyanne fo rmat ion nea r Loeche , Va-
la i s , Swi tze r land . J Pe t ro l 17 :440-471
~ o g u t u E , K r u m m e n a c h e r D ( 1 9 6 7 ) P r o b l ~ m e s g + o c h r o n o m 6 -
t r iq u e s d a n s l a p a t t i e N W d e l A n a t o l i e C e n tr a l e ( T u r q u ie ) .
Schweiz Minera l P e t rogr M i t t 47 : 825-833
Gresens RL (1969) B luesch i s t a l t e ra t ion dur ing se rpen t in iza t ion .
Con t r ib M inera l Pe t ro l 24 : 93 113
H l a p s e T , K l e p p a O J ( 19 68 ) T h e t h e r m o c h e m i s t r y o f j a d e i t e . A m
M i n e r a l 5 3 : 1 2 3 - 1 3 3
Johannes W , Puhan D (1971) The ca lc i t e -a rago n i te t r ans i t ion , r e in -
v e s t ig a t e d . C o n t r i b M i n e r a l P e t r o l 3 1 : 2 8 - 3 8
Ka ya O (1972) Out l ines o f the op h io l i t e ques t ion in the Tav~anh
reg ion ( in Turk i sh ) . Bu l l Geo l Soc Tu rk 15 : 26-108
Leo nardo s OH, Fyfe WS (1967) Serpen t in i t e s and asso c ia ted a lb i -
t i t e s Mo ccos in Qua drang le , Ca l i fo rn ia . Am J Sc i 265 :609 618
Lisenbee A (1971) The O rhane l i u l t r am af ic -ga bbro th rus t shee t
a n d i t s s u r r o u n d in g s . I n : C a m p b e l l A S ( e d ), G e o l o g y a n d h i s t o -
ry o f Turkey . Pe t r Exp l Soc L ibya , Tr ipo l i , pp 349-368
M a d e n T e t k i k v e A r a m a E n s t ( 19 6 3) G e o l o g i c a l m a p s o f T u r k e y ;
A n k a r a s h e et . M T A P u b l i c a t io n s , A n k a r a
M a d e n T e t k i k v e A r a m a E n s t ( 1 9 64 ) G e o l o g i c a l m a p s o f T u r k e y ;
[ s t a n b u l , Z o n g u l d a k , I z m i r s h e et s. M T A P u b l i c a t io n s , A n k a r a
New ton R C, Sm i th JV (1967) Inves t iga t ion s concern ing the b reak-
dow n of a lb i t e a t dep th in the ea r th . J Ge o l 75 : 268-286
Okay AI (1978) Sod ic pyroxenes f rom metabas i t e s in the eas te rn
M e d i t e r r a n e a n . C o n t r i b M i n e r a l P e t r o l 6 8 : 7 - i 1
O k a y A I ( 1 9 8 0 a ) M i n e r a l o g y , p e t r o l o g y a n d p h a s e r e l a t io n s o f
g laucoph ane- laws on i te zone b luesch i s t s f rom the Tav~anh re -
g i o n , N o r t w e s t T u r k e y . C o n t r i b M i n e r a l P e t r o l 7 2 : 2 4 3 -2 5 5
Ok ay AI (1980b) Law soni te zone b luesch i s t s and a sod ic amph i -
b o l e p r o d u c i n g r e a c t i o n i n t h e T a v ~ a n h r e g i o n , N o r t h w e s t T u r -
k e y . C o n t r i b M i n e r a l P e tr o l 7 5 : 1 7 9 - 1 8 6
O k a y A I ( 1 9 80 c ) T h e p e t r o l o g y o f b l ue s c h is t s i n N o r t h w e s t T u r -
key , No r theas t o f Tav~an ll . Ph D T hes i s (unpnb l ) . Un ivers i ty
o f C a m b r i d g e
O k a y A I ( 19 8 1) T h e g e o l o g y an d b l u e s ch i s t m e t a m o r p h i s m o f t h e
o p h i o l i te s i n N o r t h w e s t T u r k e y ( T a v ~ a n h - K i i t a h y a ) ( in T u r k -
i sh ) . Bu l l Geo l Soc Turk 24 :85-95
( ) z k o g a k O ( 19 6 9) E t u d e g 6 o l og i q u e d u m a s s i f u l t r a b a s ic d O r h a n -
e li e t de sa p roche b ordure . These (unpub l ) . U nivers i ty o f Pa r i s
S a n e r S ( 19 8 0) T h e p a l e o g e o g r a p h i c a l i n t e r p r e t a ti o n o f t h e M u -
d u r n u - G 6 y n i i c e k b a s i n b a s e d o n t h e d e p o s i t i o n a l f e a t u r e s o f
the Ju rass ic and la te r sed iments ( in Turk i sh ) . Bu l l Geo l Soc
Tur k 23 : 39-52
S w e a t m a n R R , L o n g J V P ( 1 9 69 ) Q u a n t i t a t i v e e le c t r o n p r o b e m i c r o -
ana lys i s o f rock fo rming minera l s . J Pe t ro l 10 :332-379
T a l i a f e r r a W L ( 19 4 3) F r a n c i s c a n - K n o x v i l l e p r o b l e m . A m A s s o c
Pe t ro leum Geo l Bul l 27 :109 219
Yl lm az Y (1979) Po lyp hase metam orph ism o f the S6~i i t -B i lec ik
reg ion and i t s t ec ton ic impl ica t ions . Bu l l Geo l Soc Turk
22 : 85-100
Accep ted May 13 , 1982