Fluids inclusion of metamorphic rocks

1. Fluid inclusion in metamorphic rockFluid inclusion in metamorphic rock

2. ContentsContents
 Introduction about fluid inclusionIntroduction about fluid inclusion
 Mode of formation of inclusionMode of formation of inclusion
 Changes in inclusion after trappingChanges in inclusion after trapping
 Fluids in metamorphic rockFluids in metamorphic rock
 Fluid pressureFluid pressure
 Massive banded charnockitesMassive banded charnockites
 Origin of fluidOrigin of fluid
 ReferenceReference
 ConclusionConclusion

3. Bubble of liquid or gas trapped inside a solid
mineral-phase, usually formed during
crystallization of the mineral in the presence of a
fluid phase. Tiny cavities 1.0-100 microns in
diameter. Containing liquid or gas, formed by the
entrapment of fluid in crystal irregularities. Fluid
inclusion provide information on the
temperature, pressure and chemical composition
of the fluids or gases trapped at the time of
mineral formation.

4. MODE OFMODE OF FORMATIONFORMATION OF INCLUSIONSOF INCLUSIONS
• Most of the crystal grew or recrystallize in a fluid medium ofMost of the crystal grew or recrystallize in a fluid medium of
any kind. During crystal growth, growth irregularities results inany kind. During crystal growth, growth irregularities results in
trapping of small portion of the fluids in solid crystals. Suchtrapping of small portion of the fluids in solid crystals. Such
growth irregularities may be sealed off during growth of thegrowth irregularities may be sealed off during growth of the
surrounding part of the host crystal, yieldingsurrounding part of the host crystal, yielding PRIMARYPRIMARY
INCLUSIONS (P)INCLUSIONS (P) Although most of these inclusions will beAlthough most of these inclusions will be
intracrystalline (with in the grains) there are inclusions whichintracrystalline (with in the grains) there are inclusions which
are intercrystalline (between the grains).are intercrystalline (between the grains).
• SECONDARY INCLUSIONSSECONDARY INCLUSIONS (S)(S) are those that have formedare those that have formed
by any process after crystallization of the bulk of the hostby any process after crystallization of the bulk of the host
mineral.mineral.
• PSEUDO SECONDARYPSEUDO SECONDARY (PS):(PS): inclusions are those that areinclusions are those that are
trapped along a fracture developed in the crystal during itstrapped along a fracture developed in the crystal during its
growth. Instead of being trapped as primary inclusion in thegrowth. Instead of being trapped as primary inclusion in the
rim of the crystal.rim of the crystal.

5. Changes in inclusions after trappedChanges in inclusions after trapped::
From the time the fluid inclusions are trapped within theFrom the time the fluid inclusions are trapped within the
crystal they tend to change significantly exhibiting thecrystal they tend to change significantly exhibiting the
development of various phases. Normally, a singledevelopment of various phases. Normally, a single
homogeneous fluid will be trapped originally. But at roomhomogeneous fluid will be trapped originally. But at room
temperature multiple phases are present.temperature multiple phases are present.
A common feature observed in most of the inclusions we studyA common feature observed in most of the inclusions we study
is the presence of a vapor or gas bubble that may move underis the presence of a vapor or gas bubble that may move under
the influence ofthe influence of gravity or due to thermal gradientgravity or due to thermal gradient withwith
in the inclusions. When the pressure in the inclusion dropsin the inclusions. When the pressure in the inclusion drops
below the saturation vapor pressure of the contained fluid atbelow the saturation vapor pressure of the contained fluid at
that temperature (and hence the equilibrium volume of thethat temperature (and hence the equilibrium volume of the
fluid becomes less than that of inclusion) the fluid will splitfluid becomes less than that of inclusion) the fluid will split
into two phases. Liquid and vapor phases. The relative amountinto two phases. Liquid and vapor phases. The relative amount
of these two phases vary with the original fluid density. Byof these two phases vary with the original fluid density. By
heating inclusions up to the temperature of disappearance ofheating inclusions up to the temperature of disappearance of
bubble (Th) and by adding a pressure correction, we couldbubble (Th) and by adding a pressure correction, we could
obtain the trapping temperatures (Tt).obtain the trapping temperatures (Tt).

6. Fluid inclusion in metamorphicFluid inclusion in metamorphic rock:rock:
Fluids in metamorphic rocks could either be generatedFluids in metamorphic rocks could either be generated
in the rock during metamorphism or introduced duringin the rock during metamorphism or introduced during
or after the peak of metamorphism, duringor after the peak of metamorphism, during
cooling/uplift history.cooling/uplift history.

7. Fluid pressureFluid pressure
 Fluid present in pore spacesFluid present in pore spaces
PPff=P=PHH22OO+P+PCOCO22 +P+PHH+P+POO+P+P(S,B,F…)(S,B,F…),NaCl,KCl.,NaCl,KCl.
Different mineral reaction in metamorphic rocks isDifferent mineral reaction in metamorphic rocks is
sensitive to fluid composition .sensitive to fluid composition .
When rocks are dry fluid pressure is zero and Pl will beWhen rocks are dry fluid pressure is zero and Pl will be
activeactive
When fluids are present results in the high fluid press.When fluids are present results in the high fluid press.

8. Fluid pressureFluid pressure
 Pl is litho pressurePl is litho pressure
 Pf is fluid pressurePf is fluid pressure
 Where σA is StressWhere σA is Stress
due to Pldue to Pl
 σB is Lateral StressσB is Lateral Stress
When σA = σB Pl holdsWhen σA = σB Pl holds
the grains together.the grains together.
When Pf >Pl fluid willWhen Pf >Pl fluid will
tend to push the rocktend to push the rock
apart causing cracks.apart causing cracks.
Pf
Pl Pl
Pl Pl
σA
σA
σBσB

9. TheThe Study of fluid inclusions in metamorphic rocks,Study of fluid inclusions in metamorphic rocks,
apart from revealing the P-T-t paths, will provideapart from revealing the P-T-t paths, will provide
information on theinformation on the nature and compositionnature and composition of theof the
fluid phase present and its evolutionfluid phase present and its evolution duringduring
deformation/metamorphismdeformation/metamorphism fluids play anfluids play an
important role inimportant role in controlling mineral stabilitycontrolling mineral stability, heat, heat
flow, element transport, melting and deformationflow, element transport, melting and deformation
of rocks. Information on the nature andof rocks. Information on the nature and
composition of fluids present in rocks can becomposition of fluids present in rocks can be
estimated by calculation of fluid-mineralestimated by calculation of fluid-mineral
assemblages present in metamorphic rocks,assemblages present in metamorphic rocks,
stable isotopic distribution pattern, fluid inclusionsstable isotopic distribution pattern, fluid inclusions
as well as field evidences of fluid pathways (cf.as well as field evidences of fluid pathways (cf.
Newton, 1992). Fluids in metamorphic rocks couldNewton, 1992). Fluids in metamorphic rocks could
either be generated in the rock duringeither be generated in the rock during
metamorphism, during cooling/uplift history.metamorphism, during cooling/uplift history.

10. Fluids in south Indian GranulitesFluids in south Indian Granulites
Fluid inclusion studies in metamorphic rocks form India areFluid inclusion studies in metamorphic rocks form India are
relatively recent and most of the data reported are formrelatively recent and most of the data reported are form
the granulite facies rocks from southern Peninsular Indiathe granulite facies rocks from southern Peninsular India
Fluid inclusion studies from south Indian granulites inFluid inclusion studies from south Indian granulites in
have shown that COhave shown that CO22 – rich fluids are the common and– rich fluids are the common and
probably the most characteristic feature of the deepprobably the most characteristic feature of the deep
crustal rocks (Table-1). Apart from COcrustal rocks (Table-1). Apart from CO22in granulites,in granulites,
occurrence of pure Nitrogen bearing inclusions andoccurrence of pure Nitrogen bearing inclusions and
some amount of methane associated with COsome amount of methane associated with CO22 has beenhas been
reported form the Kerala Khondalite Belt Table-1.reported form the Kerala Khondalite Belt Table-1.

12. Table-1:Age P-T Condition and CompostionTable-1:Age P-T Condition and Compostion
of deep crustal Fluids of the Precambrianof deep crustal Fluids of the Precambrian
rocks of Southern India.rocks of Southern India.
Sl.NoSl.No RocksRocks Age ofAge of
MetamorpMetamorp
hismhism
P (Kb)P (Kb) T (‘C)T (‘C) XfXf
a.a. MASSIVE/BANDED CHARNOCKITEMASSIVE/BANDED CHARNOCKITE
Mercara Granulites (MEG)Mercara Granulites (MEG)
2.52.5 7 TO 8.57 TO 8.5 700700
TO 880TO 880
CO2 (0.90 toCO2 (0.90 to
1.11 g/cc)1.11 g/cc)
Biligirirangan Granulites (BRG)Biligirirangan Granulites (BRG) 2.52.5 7 to 8.97 to 8.9 710 to 890710 to 890 CO2 (1.00 toCO2 (1.00 to
1.12 g/cc)1.12 g/cc)
MM hill granulites(MMG)MM hill granulites(MMG) 2.52.5 7 to 8.27 to 8.2 550 to 860550 to 860 CO2 (0.90 toCO2 (0.90 to
1.12 g/cc)1.12 g/cc)
Satnur-Halagur granulites (SHG)Satnur-Halagur granulites (SHG) 2.52.5 6 to 6.56 to 6.5 700 to 720700 to 720 CO2 (0.90 toCO2 (0.90 to
1.04 g/cc)1.04 g/cc)
Nilgiri GranulitesNilgiri Granulites 2.52.5 7 to 10.57 to 10.5 720 to 810720 to 810 CO2 (1.10 toCO2 (1.10 to
1.15 g/cc)1.15 g/cc)
CHCH44
Kodaikanal Granulites (KKG)Kodaikanal Granulites (KKG) 0.550.55 6 to 96 to 9 710 to 790710 to 790 CO2 (0.80 toCO2 (0.80 to
1.10 g/cc)1.10 g/cc)

13. MASSIVE/BANDED”CHARNOCKITEMASSIVE/BANDED”CHARNOCKITE
With in the south IndianWith in the south Indian
Precambrian terrain, two types ofPrecambrian terrain, two types of
acid granulites viz., the massiveacid granulites viz., the massive
/banded charnockite (MBC) and/banded charnockite (MBC) and
incipient charnockites (IC) haveincipient charnockites (IC) have
been recognizedbeen recognized

14. MASSIVE/BANDED CHARNOCKITES (MBC)MASSIVE/BANDED CHARNOCKITES (MBC)
The MBC are generally massive (look homogeneous inThe MBC are generally massive (look homogeneous in
outcrop), occur as mappable units covering large areas andoutcrop), occur as mappable units covering large areas and
generally occupy upland regions (could be uplifted masses).generally occupy upland regions (could be uplifted masses).
Many of these massive looking charnockitic rocks on closerMany of these massive looking charnockitic rocks on closer
observation in the field show typical banded nature withobservation in the field show typical banded nature with
alternate bands of charnockitic granulites with two pyroxenealternate bands of charnockitic granulites with two pyroxene
+/- garnet bearing basic granulite (Fig 2a and 2b). These+/- garnet bearing basic granulite (Fig 2a and 2b). These
rocks show evidence of at least two periods of deformation asrocks show evidence of at least two periods of deformation as
seen in BRG, MEG, MMG and NG in the NGT. The regionalseen in BRG, MEG, MMG and NG in the NGT. The regional
foliation in these rocks is defined by stretching offoliation in these rocks is defined by stretching of
orthopyroxene, quartz and feldspars. Generation of minororthopyroxene, quartz and feldspars. Generation of minor
amounts of partial melts is noticed in these granulites with theamounts of partial melts is noticed in these granulites with the
formation of orthopyroxene neo-blasts, within the coarse-formation of orthopyroxene neo-blasts, within the coarse-
grained quartz + plagioclase rich matrix.grained quartz + plagioclase rich matrix.

15. Banded Charnockites with alternate bands of acidic
Charnockites

16. Massive enderbitic-charnockitic
granulites with leucocratic
quartz+feldsbar rich layers

17. MBC are medium to coarse-granied rocksMBC are medium to coarse-granied rocks
with fresh to altered orthopyroxenes.with fresh to altered orthopyroxenes. K-K-
feldspar bearing acid granulites arefeldspar bearing acid granulites are
classified asclassified as charnockitescharnockites andand K-feldsparK-feldspar
free, andfree, and plagioclase rich rocks are termedplagioclase rich rocks are termed
asas enderbitic granulitesenderbitic granulites. Such. Such
classification has to be followed inclassification has to be followed in
identifying different types of acidicidentifying different types of acidic
granulites in the field..granulites in the field..

18.  TThe P-T conditions of regional high-gradehe P-T conditions of regional high-grade
metamorphsim (M1) estimated based on the minerealmetamorphsim (M1) estimated based on the minereal
chemistry of co-existing mineral pairs in thechemistry of co-existing mineral pairs in the
charnockites and in the basic granulites for the MBC incharnockites and in the basic granulites for the MBC in
both the NGT and SGT is presented in Table-1. Theseboth the NGT and SGT is presented in Table-1. These
rocks show a range of pressure estimates from 5 torocks show a range of pressure estimates from 5 to
10.5 Kb, indicating a depth of burial of these rocks10.5 Kb, indicating a depth of burial of these rocks
about 12 to 35 km.about 12 to 35 km.

19. During the regional granulite faciesDuring the regional granulite facies
metamorphism. Metamorphic temperatures varymetamorphism. Metamorphic temperatures vary
from 550 to 850 ‘C. Most of the granulitiesfrom 550 to 850 ‘C. Most of the granulities
exposed in the NGT, particularly the MBC showexposed in the NGT, particularly the MBC show
an isobaric cooling P-T-t paths (IBC) with peak Tan isobaric cooling P-T-t paths (IBC) with peak T
followed by peak P. In contrast, most of thefollowed by peak P. In contrast, most of the
granulites in the SGT as well as the IC showgranulites in the SGT as well as the IC show
isothermal decompression (ITD) paths, withisothermal decompression (ITD) paths, with
peak P followed by peak T.peak P followed by peak T.

20. FLUIDS IN SOUTH INDIAN GRANULITES

21. The deformed and often recrystallised quartz in theThe deformed and often recrystallised quartz in the
matrix contain primary as well as pesudosecondarymatrix contain primary as well as pesudosecondary
COCO22 – rich inclusions whose ranges of densities are– rich inclusions whose ranges of densities are
very narrow and generally higher (1.10 to 1.15 g/cc)very narrow and generally higher (1.10 to 1.15 g/cc)
When compared to COWhen compared to CO22 inclusions in qtz I andinclusions in qtz I and
garnet. COgarnet. CO22 – rich fluids in plagioclase in– rich fluids in plagioclase in
charnockites vary in density from 1.07 to 1.08 g/cccharnockites vary in density from 1.07 to 1.08 g/cc
and are comparable with COand are comparable with CO22 densities in qtz II.densities in qtz II.
Utilizing the fluid inclusion as well as mineral P-TUtilizing the fluid inclusion as well as mineral P-T
estimates on the very same set of samples studiedestimates on the very same set of samples studied
for fluid inclusions, an IBC path for the evolution onfor fluid inclusions, an IBC path for the evolution on
fluids has been recorded for the Nilgiri granulates.fluids has been recorded for the Nilgiri granulates.

22. Origin of fluids:Origin of fluids:
 Internal sourceInternal source: when metamorphic: when metamorphic
rocks interact only with initial porerocks interact only with initial pore
fluids modified by progressivefluids modified by progressive
devolatization reaction.devolatization reaction.
 ExternalExternal sourcesource:granitic:granitic
bodies,syenites orbodies,syenites or
diorites,Decorbonisation of upperdiorites,Decorbonisation of upper
mantle,degassing of underseatedmantle,degassing of underseated
basaltic intrusionsbasaltic intrusions

23. Metamorphic petrology is perhaps one of the fields where fluid inclusion
study has recently been taken up with great deal of enthusiasm, primarily
because it has aided considerably in gathering first-hand information on fluid
rock interaction process predicted by theoretical model, and the tracing of
uplift paths.
 Paleo pressure for the massive charnokite terrain of southern Karnataka and
Tamilnadu.
Based on stable isotope results the source of carbonic fluids is also evaluated.
Carbonic fluids however, need not always represent traces of sys-metamorphic
fluids.
Fluid inclusion in charnokite occurs as isolated or as oval to negative crystal
shape found in healed fractures, they vary in size from 5 to 10 meumicron.
Fluids in charnokites are generally monophase.
Predominence of CO2 inclusion in charnokite indicate anhydrous conditions
and help in the stability of minerals like Garnet,Hypersthene and Plagoioclase

24. Reference
Websites;
en.wikipedia.org/wiki/Fluid_inclusions - Cached
www.geology.wisc.edu/flincs/fi.html - Cached
Books
Encyclopedic dictionary of geography(vol I),Girish Chopra ,
p.no.277.
Metamorphic petrology ,Turner F.J , p.no.60,244,351.
Igneous and metamorphic petrology , Turner F.J ,
p.no.481,482,486.