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Preliminary geochronological results of a suite of granulites from Eastern Ghats, India
XII
from the supracrustal terrain of the Kerala Khondalite belt, in the southern part of the granulite terrain, has led to the re-evaluation of the source and role of CO, (cf Harley and Santosh, 1995; Satish-Kumar et a/. , 1995, in press). Calc-silciate rocks in the Kerala Khondalite belt occur as bands and layers concordant with the regional structural trends of the associated gneisses, and varying in thickness from less than a meter to more than tens of meters. Mineralogically, all the occurrences are comprised dominantly of wollastonite-scapolite-clinopyroxene assemblages with grossular in a few localities. The grossular-absent assemblages are commonly associated with charnockites. The peak metamorphic granoblastic textures in these rocks have been overprinted by a variety of retrograde reaction textures. These textures are of great importance since they provide information on the pressure-temperature-fluid histories of the talc-silicate rocks (cf Harley and Buick, 1992; Harley et a/., 1994). Important reaction textures in grossular-absent assemblages from KKB include wollastonite breaking down to calcite and quartz, scapolite breaking down to calcite, anorthite and quartz, and scapolite-quartz symplectites after wollastonite and feldspars (Satish-Kumar et al., in press). Some of these reaction textures indicate a post-peak infiltration of CO,. From the classic locality, Nuliyam at the southern margin of KKB, Harley and Santosh (1995) showed that the wollastonite bearing assemblages preserve retrograde textures supporting CO, influx during post-peak metamorphism and isothermal uplift, resulting in the dehydration of the associated gneisses into charnockites. In grossular-bearing assemblages, the textures include the breakdown of scapolite into calcite, anorthite and quartz, formation of grossular-quartz coronas between wollastonite and anorthite, and formation of grossular from the anorthitecalcite-quartz. All these reactions indicate an initial cooling of these rocks (Satish-Kumar et a/., in press). These reactions also indicate that the rocks have acted as closed systems with an internal fluid buffering. The general conclusions derived from the study of talc-silicate rocks from the Kerala Khondalite belt are the following: i) the occurrence of wollastonite-bearing assemblages does not necessarily restrict the possibility of CO, influx for charnockite formation in the terrain, but a pervasive influx of carbonic fluids in the terrain is unsupported;
j.i) an internally controlled fluid composition (mostly vapor-free) existed during the peak metamorphic conditions in the terrain; iii) the terrain underwent an initial cooling before decompression; and iv) during the decompressional regime, there was local influx of carbonic fluids, resulting in the formation of charnockites and also partially wollastonite bearing retrograding the assemblages. REFERENCES Harley, S. L. and Buick, I. S. 1992. Journal Petrology 33, 693 -728. Harley, S. L. and Santosh, M. 1995. Contributions Mineralogy Petrology 120, 139-l 50. Harley, S. L. et al. 1994. Precambrian Research 66, 309-323. Lamb, W. M. and Valley, J. W. 1984. Nature 312, 56-58. Newton, R. C. et al. 1980. Nature 288, 45-50. Santosh, M. et al. 1991. Contributions Mineralogy Petrology 108, 318-330. Satish-Kumar, M. et al. 1995. Current Science 68, 813-819. Satish-Kumar, M. et al. (In press) Journal Southeast Asian Earth Sciences.
Preliminary geochronological results of a suite of granulites from Eastern Ghats, India R. K. SHAW,’ M. ARIMA’
and H. KAGAM12
‘Geological Institute, Yokohama National University, Yokohama, Japan %stitute for Study of Earth’s Interior, Misasa, Tottori, Japan
A suite of granulites (metapelites, quartzites and talc-silicate rocks, mafic (two-pyroxene) granulites, opx granulites (charnockite), leptynites and sillimanite granites) are exposed in Rayagada, the north-central part of the Eastern Ghats belt of Peninsular India. Structural studies show that the area suffered at least three deformation events, giving rise to three distinct types of folding. Petrography, textural relations among different phases and thermobarometric calculations suggest a maximum temperature of 950°C at 9 kbar for the conditions of metamorphism of the metapelites, which has been correlated with the second deformation. The peak metamorphic condition might have been in a higher P-T regime.
XIII
In the
present
preliminary of
five
communication,
results different
implication An
rock-types
to Gondwana
attempt
has
chronological
opx
sillimanite
granites.
whole
Mafic give
and
and
been
made
of
granulites, and
1023?93
Rb-Sr
whole
ages Ma,
leptynites,
metapelites
are 958 & 16, 1388
and
84
whereas 781 * 39 rsochron give
and
an age
Rb-Sr
833
(of
t 10
granites
and
rock)
ages
Ma.
rock) metapelites
(grt-fel-whole
1067+43,
rock)
of
Rb-Sr
(bt-fel-whole
Summarizing that
the
four different at -1000
events: Ma
and -500
and
other
formation
are
is characterized
The two
other
at 500
can
mainly
events,
Ma, another
event, from
and
the
granite-
orthogneiss complex Ma:
of
Holzl
of Cuamba 26,
et
Unit
842_+50
500
other
several
present
four
described
major
Ma;
age-data
from
clusters;
1450,
Ma.
Among
the
four
age
above,
except
the
800
Ma
events
parts
are
well
of Eastern
documented
Ghats.
However,
geochronological more
Eastern
clear
Ghats
studies
picture
are
of evolution
belt.
REFERENCES
and
1000
Aftalion, H. et al. 1988. Journal Geology 96, 663-676. Grew, E. S. and Manton, W. I. 1986. Precambrian Research 33, 123-l 37. Precambrian Research 66, Holzl, S. et al. 1994. 123-149. Paul, D. K. et al. 1990. Journal Geology 98, 253-263. Pinna, P. et al. 1993. Precambrian Research 62, l-59. Sarkar, A. et al. 1994. Abstract, Workshop on Eastern Ghats
Ma
Ma event
the
Mobile
Belt,
Visakhapatnam,
India.
Shiraishi, K. et al. 1994. Journal Geology 102, 47-65. Yoshida, M. et al. 1995. Abstracts VII International Symposium,
Antartic
Earth
Science,
Siena
416
Ma
by charnockites.
one at 800
Ma are possibly
be
at -800
magmatism
whereas
800
leptite (837k
have
of
at least
The 1400
of leptynite,
1000,
19941,
771 + 17/-14
the
Ghats
clusters
e.g.
from
of East Antarctica
of Wanni
belt
from
found
1993).
et a/.,
of the
ages are it
two
mafic
Mozambique
Pinna
been
al.,
and granitic
Sm-Nd
554+52
rock)
one at -1450
by
1994)
to have
samples and
results,
Ma, respectively.
et
orthogneiss
needed
mineral
area underwent
the
is characterized event
above
the present
Shiraishi
give
534 + 3 and 498 + 40 Ma. stated
Ma: granitic
is also
573 + 12 Ma
four
500+54
Ma, whereas
(770 and
(793&4,
There Ma event
Gondwana, complex
Gondwana
rock)
Sm-Nd
613+20,
of East
intensive
and that
give
has
of Rayner
further
samples) Internal
of
on 800
which
Ma,
(grt-fel-opx-whole
(grt-fel-whole
567 +63
Sm-
of 946+30
815 + 9 Ma and 808 & 64 Ma,
leptynite
and f 94
Internal
two
parts
1994).
et a/.,
pegmatite
Eastern
opx
1165
Ghats,
several
and other
data
In conclusion,
of
+ 63,
Ma.
of px granulites
(Shiraishi reliable
of
+ 80,
of Antarctica
no recent
Sri Lanka
isochrons
(hbl-pxn-fel-whole
gives of
of
respectively,
respectively.
isochron that
and
ages
sillimanite
Ma,
granulite
the mafic
of 1455
rock
parts
fragments
al.,
granulites,
Nd mineral
reveal
and opx granulites
rock
1464+63
mafic
to
mineral
leptynites whole
several
Eastern
system.
whereas
1069_+
possible
are the results
and internal
an Sm-Nd
its
leptynites
Following
Rb-Sr
the
studies
metapelites,
granulites,
rock
of Sm-Nd
report
correlation.
history
granulites, both
we
of our geochronological
On the origin of the Eppawala
Ma and other
younger
metamorphic
deposits,
apatite
Sri Lanka
events. Published
data
Ghats
suggest
in this
belt,
1986);
(1176 + 200 Ages of
from
Eastern
(1436+58 1994).
augen
et
syenitic
Ghats Ma,
cluster 1413+23
On the other
although
not
Ma:
and
leptynite
Ma,
1088
and
and
+ 26/-l
7
charnockite
plutons around Ma:
hand,
reported
Grew
Ma: Paul et a/. , 1990).
Ma, 985 15 several
D. J. A. C. HAPPURACHCHI
event and
gneiss, 1988)
al.,
of Eastern
charnockite
(1000
(I 159 + 59/-30
Aftalion
parts
Ma is a major from
granulites
charnockite Ma:
several
1000
as evidenced
sapphirine Manton,
from that
from
parts
1400
Sarkar
et
from
19951,
has
been
widely
reported
Although
the has been
origin
has always
has been deposit rock
from
at
apatite
referred
some may
According
the
Eppawala
Lanka
Ma
Eastern Ghats except for two Sm-Nd garnetwhole rock ages (Paul et al., 1990; Yoshida et a/.,
Old Kasbewa Road, Nugegoda,
al.,
the ca 500 Ma event, extensively
48/14,
isotopic
to Hoernes Eppawala
in
deposit
in Sri
to as a carbonatite,
been enigmatic.
not
Sri Lanka
data fact
to show be
et a/. (1994),
show
its
Recently
there
that
the
a carbonatite. the carbonate
6180 = + 15.3560
613C=-1 .8’%0, which are much higher than for unaltered carbonatites (6”O = + 6 to
and those +8%
and 6j3C =-5.1 & 1.4%0). Carbon and oxygen isotopic compositions of Sri Lankan marbles are typical
for carbonate
sediments
(6’*0
> + 20%).
from the supracrustal terrain of the Kerala Khondalite belt, in the southern part of the granulite terrain, has led to the re-evaluation of the source and role of CO, (cf Harley and Santosh, 1995; Satish-Kumar et a/. , 1995, in press). Calc-silciate rocks in the Kerala Khondalite belt occur as bands and layers concordant with the regional structural trends of the associated gneisses, and varying in thickness from less than a meter to more than tens of meters. Mineralogically, all the occurrences are comprised dominantly of wollastonite-scapolite-clinopyroxene assemblages with grossular in a few localities. The grossular-absent assemblages are commonly associated with charnockites. The peak metamorphic granoblastic textures in these rocks have been overprinted by a variety of retrograde reaction textures. These textures are of great importance since they provide information on the pressure-temperature-fluid histories of the talc-silicate rocks (cf Harley and Buick, 1992; Harley et a/., 1994). Important reaction textures in grossular-absent assemblages from KKB include wollastonite breaking down to calcite and quartz, scapolite breaking down to calcite, anorthite and quartz, and scapolite-quartz symplectites after wollastonite and feldspars (Satish-Kumar et al., in press). Some of these reaction textures indicate a post-peak infiltration of CO,. From the classic locality, Nuliyam at the southern margin of KKB, Harley and Santosh (1995) showed that the wollastonite bearing assemblages preserve retrograde textures supporting CO, influx during post-peak metamorphism and isothermal uplift, resulting in the dehydration of the associated gneisses into charnockites. In grossular-bearing assemblages, the textures include the breakdown of scapolite into calcite, anorthite and quartz, formation of grossular-quartz coronas between wollastonite and anorthite, and formation of grossular from the anorthitecalcite-quartz. All these reactions indicate an initial cooling of these rocks (Satish-Kumar et a/., in press). These reactions also indicate that the rocks have acted as closed systems with an internal fluid buffering. The general conclusions derived from the study of talc-silicate rocks from the Kerala Khondalite belt are the following: i) the occurrence of wollastonite-bearing assemblages does not necessarily restrict the possibility of CO, influx for charnockite formation in the terrain, but a pervasive influx of carbonic fluids in the terrain is unsupported;
j.i) an internally controlled fluid composition (mostly vapor-free) existed during the peak metamorphic conditions in the terrain; iii) the terrain underwent an initial cooling before decompression; and iv) during the decompressional regime, there was local influx of carbonic fluids, resulting in the formation of charnockites and also partially wollastonite bearing retrograding the assemblages. REFERENCES Harley, S. L. and Buick, I. S. 1992. Journal Petrology 33, 693 -728. Harley, S. L. and Santosh, M. 1995. Contributions Mineralogy Petrology 120, 139-l 50. Harley, S. L. et al. 1994. Precambrian Research 66, 309-323. Lamb, W. M. and Valley, J. W. 1984. Nature 312, 56-58. Newton, R. C. et al. 1980. Nature 288, 45-50. Santosh, M. et al. 1991. Contributions Mineralogy Petrology 108, 318-330. Satish-Kumar, M. et al. 1995. Current Science 68, 813-819. Satish-Kumar, M. et al. (In press) Journal Southeast Asian Earth Sciences.
Preliminary geochronological results of a suite of granulites from Eastern Ghats, India R. K. SHAW,’ M. ARIMA’
and H. KAGAM12
‘Geological Institute, Yokohama National University, Yokohama, Japan %stitute for Study of Earth’s Interior, Misasa, Tottori, Japan
A suite of granulites (metapelites, quartzites and talc-silicate rocks, mafic (two-pyroxene) granulites, opx granulites (charnockite), leptynites and sillimanite granites) are exposed in Rayagada, the north-central part of the Eastern Ghats belt of Peninsular India. Structural studies show that the area suffered at least three deformation events, giving rise to three distinct types of folding. Petrography, textural relations among different phases and thermobarometric calculations suggest a maximum temperature of 950°C at 9 kbar for the conditions of metamorphism of the metapelites, which has been correlated with the second deformation. The peak metamorphic condition might have been in a higher P-T regime.
XIII
In the
present
preliminary of
five
communication,
results different
implication An
rock-types
to Gondwana
attempt
has
chronological
opx
sillimanite
granites.
whole
Mafic give
and
and
been
made
of
granulites, and
1023?93
Rb-Sr
whole
ages Ma,
leptynites,
metapelites
are 958 & 16, 1388
and
84
whereas 781 * 39 rsochron give
and
an age
Rb-Sr
833
(of
t 10
granites
and
rock)
ages
Ma.
rock) metapelites
(grt-fel-whole
1067+43,
rock)
of
Rb-Sr
(bt-fel-whole
Summarizing that
the
four different at -1000
events: Ma
and -500
and
other
formation
are
is characterized
The two
other
at 500
can
mainly
events,
Ma, another
event, from
and
the
granite-
orthogneiss complex Ma:
of
Holzl
of Cuamba 26,
et
Unit
842_+50
500
other
several
present
four
described
major
Ma;
age-data
from
clusters;
1450,
Ma.
Among
the
four
age
above,
except
the
800
Ma
events
parts
are
well
of Eastern
documented
Ghats.
However,
geochronological more
Eastern
clear
Ghats
studies
picture
are
of evolution
belt.
REFERENCES
and
1000
Aftalion, H. et al. 1988. Journal Geology 96, 663-676. Grew, E. S. and Manton, W. I. 1986. Precambrian Research 33, 123-l 37. Precambrian Research 66, Holzl, S. et al. 1994. 123-149. Paul, D. K. et al. 1990. Journal Geology 98, 253-263. Pinna, P. et al. 1993. Precambrian Research 62, l-59. Sarkar, A. et al. 1994. Abstract, Workshop on Eastern Ghats
Ma
Ma event
the
Mobile
Belt,
Visakhapatnam,
India.
Shiraishi, K. et al. 1994. Journal Geology 102, 47-65. Yoshida, M. et al. 1995. Abstracts VII International Symposium,
Antartic
Earth
Science,
Siena
416
Ma
by charnockites.
one at 800
Ma are possibly
be
at -800
magmatism
whereas
800
leptite (837k
have
of
at least
The 1400
of leptynite,
1000,
19941,
771 + 17/-14
the
Ghats
clusters
e.g.
from
of East Antarctica
of Wanni
belt
from
found
1993).
et a/.,
of the
ages are it
two
mafic
Mozambique
Pinna
been
al.,
and granitic
Sm-Nd
554+52
rock)
one at -1450
by
1994)
to have
samples and
results,
Ma, respectively.
et
orthogneiss
needed
mineral
area underwent
the
is characterized event
above
the present
Shiraishi
give
534 + 3 and 498 + 40 Ma. stated
Ma: granitic
is also
573 + 12 Ma
four
500+54
Ma, whereas
(770 and
(793&4,
There Ma event
Gondwana, complex
Gondwana
rock)
Sm-Nd
613+20,
of East
intensive
and that
give
has
of Rayner
further
samples) Internal
of
on 800
which
Ma,
(grt-fel-opx-whole
(grt-fel-whole
567 +63
Sm-
of 946+30
815 + 9 Ma and 808 & 64 Ma,
leptynite
and f 94
Internal
two
parts
1994).
et a/.,
pegmatite
Eastern
opx
1165
Ghats,
several
and other
data
In conclusion,
of
+ 63,
Ma.
of px granulites
(Shiraishi reliable
of
+ 80,
of Antarctica
no recent
Sri Lanka
isochrons
(hbl-pxn-fel-whole
gives of
of
respectively,
respectively.
isochron that
and
ages
sillimanite
Ma,
granulite
the mafic
of 1455
rock
parts
fragments
al.,
granulites,
Nd mineral
reveal
and opx granulites
rock
1464+63
mafic
to
mineral
leptynites whole
several
Eastern
system.
whereas
1069_+
possible
are the results
and internal
an Sm-Nd
its
leptynites
Following
Rb-Sr
the
studies
metapelites,
granulites,
rock
of Sm-Nd
report
correlation.
history
granulites, both
we
of our geochronological
On the origin of the Eppawala
Ma and other
younger
metamorphic
deposits,
apatite
Sri Lanka
events. Published
data
Ghats
suggest
in this
belt,
1986);
(1176 + 200 Ages of
from
Eastern
(1436+58 1994).
augen
et
syenitic
Ghats Ma,
cluster 1413+23
On the other
although
not
Ma:
and
leptynite
Ma,
1088
and
and
+ 26/-l
7
charnockite
plutons around Ma:
hand,
reported
Grew
Ma: Paul et a/. , 1990).
Ma, 985 15 several
D. J. A. C. HAPPURACHCHI
event and
gneiss, 1988)
al.,
of Eastern
charnockite
(1000
(I 159 + 59/-30
Aftalion
parts
Ma is a major from
granulites
charnockite Ma:
several
1000
as evidenced
sapphirine Manton,
from that
from
parts
1400
Sarkar
et
from
19951,
has
been
widely
reported
Although
the has been
origin
has always
has been deposit rock
from
at
apatite
referred
some may
According
the
Eppawala
Lanka
Ma
Eastern Ghats except for two Sm-Nd garnetwhole rock ages (Paul et al., 1990; Yoshida et a/.,
Old Kasbewa Road, Nugegoda,
al.,
the ca 500 Ma event, extensively
48/14,
isotopic
to Hoernes Eppawala
in
deposit
in Sri
to as a carbonatite,
been enigmatic.
not
Sri Lanka
data fact
to show be
et a/. (1994),
show
its
Recently
there
that
the
a carbonatite. the carbonate
6180 = + 15.3560
613C=-1 .8’%0, which are much higher than for unaltered carbonatites (6”O = + 6 to
and those +8%
and 6j3C =-5.1 & 1.4%0). Carbon and oxygen isotopic compositions of Sri Lankan marbles are typical
for carbonate
sediments
(6’*0
> + 20%).