The characterization of fluids involved in the gneiss-charnockite transformation in southern Kerala are discussed. Using a variety of techniques, including microthermometry, Raman laser probe analysis, and mass spectrometry, it was concluded that the CO2-rich, N2-bearing metamorphic fluids in these rocks were internally-derived rather than having been introduced by CO2-streaming

Hoernes, S.

Klatt, E.

Raith, M.

Welsh 

NASA Technical Reports Server

CHARACTERIZATION 
TRANSFORMATION IN 
N89- 22 2 17 
f,3 81 
OF FLUIDS INVOLVED IN THE GNEISS-CHARNOCKITE 
7dYO 
SOUTHERN KERALA (INDIA) 
b7 E. K l a t t ,  Hoe rnes ,  S. a n d  R a i t h ,  M. 
Mineralogisch-Petrologisches I n s t i t u t ,  U n i v e r s i t a t  Bonn, FRG 
Most i m p r e s s i v e  e x a m p l e s  o f  ' i n - s i t u '  c h a r n o c k i t i z a t i o n  
o c c u r  i n  t h e  P r o t e r o z o i c  c r u s t a l  s e g m e n t  s o u t h  o f  t h e  Achankov i l  
s h e a r  b e l t  ( P o n  Mudi  u n i t  ( 1  11, w h e r e  m i g m a t i c  g a r n e t - b i o t i t e  
g n e i s s e s  h a v e  been  p a r t i a l l y  c o n v e r t e d  t o  c o a r s e - g r a i n e d  c h a r n o -  
c k i t e  s.str. a l o n g  a s y s t e m  of  c o n j u g a t e  f r a c t u r e s  a b o u t  550 m.y. 
ago. To  charac te r i se  t h e  c o m p o s i t i o n  o f  pore  f l u i d s  a n d  t o  
u n d e r s t a n d  t h e i r  r o l e  i n  t h e  process o f  ' i n - s i t u '  c h a r n o c k i t e  
f o r m a t i o n ,  f l u i d  i n c l u s i o n s  i n  s p a t i a l l y  r e l a t e d  g n e i s s e s  a n d  
c h a r n o c k i t e s  w e r e  s t u d i e d  by  microther m e t r y ,  Raman-Laser-Probe 
a n a l y s i s  a n d  mass s p e c t r o m e t r y  ( 2 ) .  
work a n d  ( 3 ) )  a n d  f l u i d  i n c l u s i o n s  i n  q u a r t z  ( 4 )  as w e l l  a s  6 0 
whole rock data  provided i m p o r t a n t  i n f o r m a t i o n  on t h e  o r i g i n  o f  
t h e  f l u i d s .  
HS &*'C d a t a  on g r a p h i t e  ( t  
T h e  f l u i d  i n c l u s i o n  c h a r a c t e r i s t i c s  o f  t h e  g n e i s s e s  a n d  
associated c h a r n o c k i t e s  a re  s imi l a r  a n d  reveal a comparable a n d  
c o m p l e x  e v o l u t i o n  o f  t h e  pore f l u i d s .  Rare  b r i n y  i n c l u s i o n s  ( +  
s a l t )  a r e  c o n s i d e r e d  t o  r e p r e s e n t  r e l i c s  o f  e a r l y  metamorphic  
f l u i d s  w h i c h  s u r v i v e d  h i g h - g r a d e  r e g i o n a l  m e t a m o r p h i s m  and 
s u b s e q u e n t  c h a r n o c k i t i z a t i o n .  The common t y p e  of f l u i d  i n c l u s i o n s  
are medium- t o  l o w - d e n s i t y  c a r b o n i c  i n c  u s i o n s  (Th: +15 t o  +27 OC 
Tm: -60.0 t o  -56.6 OC; pO.70-0.86 g/cm ) w h i c h  o c c u r  i n  s eve ra l  
se t s  o f  h e a l e d  f r a c t u r e s .  T h e  m i c r o t h e r m o m e t r i c  d a t a  i n d i c a t e  
p a r t i a l  t o  comple te  p h y s i c a l  e q u i l i b r a t i o n  o f  these  f l u i d s  b y  
p r o g r e s s i v e  l e a k a g e  a n d  repeated r e e n t r a p m e n t  as  a c o n s e q u e n c e  
o f  n e a r - i s o t h e r m a l  u p l i f t  o f  t h e  r o c k  complex. The  c a r b o n i c  
f l u i d s  c o n t a i n  up  t o  1 4  m o l %  o f  n i t r o g e n  b u t  less 1 m o l %  hydro -  
c a r b o n s  (CH a n d  C2H6).  N i t r o g e n  i n c l u s i o n s  (Th -152 t o  -130 OC; 
b o t h  t h e  g n e i s s e s  a n d  c h a r n o c k i t e s  a n d  a t  severa l  l o c a l i t i e s  
p r e d o m i n a t e .  A g e n e r a t i o n  o f  t h e s e  f l u i d s  by  d e v o l a t i l i z a t i o n  of 
NH4-bearing K - f e l d s p a r  a n d  i o t i t e  i s  l i k e l y .  The p r e s e n c e  of 
a n d  c h a r n o c k i t e s  p o i n t s  t o  t h e  s e d i m e n t a r y  n a t u r e  of t h e  proto- 
l i t h s .  Medium-de s i t y  w a t e r y  i n c l u s i o n s  o f  l o w  s a l i n i t y  
( p 0 . 8 9  - 0.94 g/cm'; < 4 m o l %  e q u i v .  N a C l )  a r e  t h e  t e x t u r a l l y  
la tes t  e n t r a p p e d  metamorphic pore f l u i d s .  Where t h e y  cross t r a i l s  
o f  c a r b o n i c  i n c l u s i o n s ,  mixed HZ0-CO2 i n c l u s i o n s  ( f o r m i n g  
c l a t h r a t e  ices) developed. Bu lk  f l u i d  a n a l y s i s  b y  mass spectro- 
m e t r y  on  q u a r t z  c o n c e n t r a t e s ' s h o w e d  t h e  c h a r n o c k i t e s  t o  be h i g h e r  
i n  N 2 ,  CH4 and  H20 b u t  lower i n  H2 i n  c o m p a r i s o n  t o  t h e  g n e i s s e s .  
C 0 2  and  A r  h a v e  s imi l a r  abundances  i n  both rock t y p e s .  
The f l u i d  i n c l u s i o n  c h a r a c t e r i s t i c s  s u g g e s t  t h a t  t h e  compo- 
s i t i o n  of m e t a m o r p h i c  pore f l u i d s  i n v o l v e d  i n  h i g h - g r a d e  r e g i o -  
n a l  metamorphism a n d  s u b s e q u e n t  c h a r n o c k i t i z a t i o n  can '  be model led 
3 
u p  t o  1 6  m o  f % h y d r o c a r b o n s ,  n i l  c a r b o n  d i o x i d e )  commonly o c c u r  i n  
6 19 C -15 t o  -20 per m i l )  i n  t h e  g n e i s s e s  n i t r o g e n  a n d  g r a p h i t e  ( 
https://ntrs.nasa.gov/search.jsp?R=19890012846 2020-03-20T02:32:17+00:00Z
CHARACTERIZATION OF FLUIDS 
82 Klatt, et al. 
by g r a p h i t e - f  l u i d  e q u i l i b r i a  i n  t h e  C-0-H-N sys t em.  A c c o r d i n g l y ,  
t h e  pore f l u i d s  i n  t h e  g n e i s s e s  a n d  c h a r n o c k i t e s  w e r e  i n t e r n a l l y  
b u f f e r e d  towards s t r o n g l y  water d e f i c i e n t  and  r e d u c e d  compos i -  
t i o n s .  Oxygen f u g a c i t i e s  c lose o r  l o w e r  t h a n  d e f i n e d  b y  t h e  QFM 
b u f f e r  are i n  a c c o r d a n c e  w i t h  t h e  s i l i c a t e - o p a q u e  m i n e r a l  assem- 
b l a g e s  a n d  m i n e r a l  c h e m i s t r y  data  ( 1 , 7 ) .  
F u r t h e r  e v i d e n c e  f o r  a n  i n t e r n a l  g e n e r a t i o n  and  b u f f e r i n g  o f  
t h e  pore f l u i d s  comes f r o m  t h e  6I3C d a t a  on g r a p h i t e  a n d  carbo- 
n i c  f l u i d  i n c l u s i o n s :  Grypite f r o m  t y p i c a l  g a r n e t - b i o t i t e - ( s i l l ,  
cord) g n e i s s e s  e x h i b i t  6 C v a l u e s  be tween  -14'/00 a n d  -17%0 
(see a l s o  ( 3 ) )  a n d  o b v i o u s l y  w a s  d e r i v e d  f r o m  t h e  d e g r a d a t i o n  
o f  r g a n i c  m a t t e r  (-2OVo0 t o  -35%0 ; d a t a  f o r  k e r o g e n ) .  Repor ted  
b ''C v a l u e s  f o r  c a r b o n  d i o x i d e  trapped i n  t h e  f l u i d  i n c l u s i o n s  
o f  comparable g n e i s s  a m p l e s  v a r y  b e t w e e n  -100/oand -15%0 ( 4 ) .  The 
d i f f e r e n c e  i n  t h e  S C v a l u e s  o f  g raph i t e  and  c a r b o n i c  f l u i d s  (5 
t o  7%0 1, i n  a g r e e m e n t  w i t h  t h e  e x p e r i m e n t a l  f r a c t i o n a t i o n  data  
f o r  t h e  g r a p h i t e - C 0 2  s y s t e m  (51 ,  i n d i c a t e s  a t t a i n m e n t  o f  i s o t o p i c  
e q u i l i b r i u m  n e a r  p e a k  m e t a m o r p h i c  t e m p e r a t u r e s  ( <  7 0 0  O C ) .  
G r a p h i t e  a n d  c a r b o n i c  f l u i d s  i n  c o a r  e - g r a i n e d  m a s s i v e  
' i n c i p i e n t '  c h a r n o c k i t e s  s h o w  s i m i l a r  6 f 3 C  s y s t e m a t i c s .  T h e  
1 5  
g r a p h i t e s  a r e  i s o t o p i c a l l y  l i g h t e r  (-19Y00 -22%0 ) t h a n  t h e  
c a r b o n i c  f l u i d s  (-7%0 t o  -15%0 ; d a t a  r e p o r t  i n  ( 4 ) ) .  G r a p h i t e  
o f  o n e  c h a r n o c k i t e  sample, however ,  h a s  a 6 v a l u e  o f  - 1 2 Y 0 0 ,  
much s i m i l a r  t o  t h e  v a l u e s  o b t a i n e d  f o r  g r a p h i t e  (-10%0 t o  
-13%0 t h i s  w o r k  a n d  ( 3 ) )  f r o m  g a r n e t  a n d  c o r d i e r i t e - b e a r i n g  
pegmatites which  c u t  across t h e  g n e i s s e s  b u t  are older t h a n  t h e  
c h a r n o c k i t e s .  T h e  d a t a  c o u l d  i n d i c a t e  t h a t  g r a p h i t e s  i n  t h e s e  
samples c r y s t a l l i s e d  from i s o t o p i c a l l y  h e a v i e r  c a r b o n i c  f l u i d s  ( <  
- 5 % 0  1. m e a n i n g f u l  i n t e r p r e t a t i o n ,  h o w e v e r ,  i s  n o t  p o s s i b l e  
u n l e s s  6 C da t a  o n  t h e  associated f l u i d s  are  avai lable .  e 3  
A de t a i l ed  s t u d y  o f  oxygen  isotopes w a s  carried o u t  on  o n e  
t y p i c a l  e x p o s u r e  o f  ' i n - s i t u '  c h a r n o c k i t i z a t i o n  ( K o t t a v a t t a  
G n e i s s e s  a n d  a s s o c i a t e d  c h a r n o c k i t e s  e x h i b i t  i d e n t i c a l  6 
v a l u e s  o f  l O . 3  YOO which  are  t y p i c a l  o f  psammo-pelitic m e t a s e d i -  
m e n t s .  T h i s  f i n d i n g s  p r o v i d e  f u r t h e r  e v i d e n c e  o n  t h e  i n t e r n a l  
n a t u r e  o f  c a r b o n i c  f l u  I n f l u x  o f  c a r b o n i c  f l u i d s  w i t h  m a n t l e  
is@opic s i g n a t u r e  ( 6 i0E*w8)  would  have  s h i f t e d  t h e  c h a r n o c k i t e  
6 0 t o  lower v a l u e s .  
I n  t h e  l i g h t  o f  t h e  f l u i d  i n c l u s i o n  a n d  s tab le  isotope da ta  
it t h u s  a p p e a r s  u n l i k e l y  t h a t  c h a r n o c k i t i z a t i o n  i n  s o u t h e r n  
Kerala w a s  c a u s e d  b y  t h e  i n f l u x  o f  e x t e r n a l l y  d e r i v e d  c a r b o n i c  
f l u i d s  a n d  t h e  concommi tan t  decrease i n  water a c t i v i t y  a s  sugges -  
t e d  b y  t h e  p r o p o n e n t s  o f  t h e  C 0 2 - s t r e a m i n g  h y p o t h e s i s  (6). An 
a l t e r n a t i v e  m e c h a n i s m  h a s  b e e n  r e c e n t l y  proposed f o r  ' i n - s i t u '  
c h a r n o c k i t i z a t i o n  i n  s o u t h e r n  Kerala ( 1 )  a n d  i s  d i s c u s s e d  i n  a n  
other c o n t r i b u t i o n  t o  t h e  workshop  ( 7 ) .  
( 1 )  S r i k a n t a p p a ,  C., R a i t h ,  M .  a n d  S p i e r i n g ,  B. ( 1 9 8 5 )  J. G e o l .  
SOC. I n d i a  26, 849-872 
( 2 )  K l a t t ,  E. a n d  R a i t h ,  M.  ( 1 9 8 7 )  E u r o p e a n  C u r r e n t  R e s e a r c h  o n  
F l u i d  I n c l u s i o n s ,  9 t h  Smposium, U n i v e r s i t y  o f  P o r t o ,  P o r t u g a l  
Abs t rac ts  
CHARACTERIZATION OF FLUIDS 
K l a t t ,  e t  al. 83 
( 3 )  Soman, K., Lobzova, R.V. a n d  S i v a d a s ,  K.M. ( 1 9 8 5 )  E c o n o m i c  
Geology 81, 997-1002 
( 4 )  J a c k s o n ,  D.H., M a t t e y ,  D.P., Har r i s ,  N.B.W. a n d  S a n t o s h ,  M.  
( 1 9 8 7 )  Nato Advanced R e s e a r c h  Workshop,  L i n d a s ,  Norway,  
A b s t r a c t s  
( 5 )  B o t t i n g a ,  Y. (1968) Ph. D. T h e s i s ,  C a l i f o r n i a  U n i v e r s i t y  a t  
San Diego 
(6) H a n s e n ,  E.C., J a n a r d h a n ,  A.S., N e w t o n ,  R.C., P r a m e ,  W.K.B.N. 
a n d  R a v i n d r a  K u m a r ,  G.R. ( 1 9 8 7 )  C o n t r i b .  M i n e r .  P e t r o l .  9 6 ,  
( 7 )  R a i t h ,  M . t  K l a t t ,  E., S p i e r i n g ,  B., S r i k a n t a p p a ,  C. a n d  
225-244 
S t a h l e ,  H . J .  (1988) Abstract  t h i s  workshop 


Characterization of fluids involved in the Gneiss-Charnockite transformation in Southern Kerala (India)

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server