granitos classificacao petrogenesis tectonica
TRANSCRIPT
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GRANITESClassification, Petrogenesis and
Tectonic Discriminations
Presented By:
Samir Kumar ari!
"#$Sc % IIT om&a'(Pro)ect *ello+
Geocronolog' Di-$
CSIR.NGRI, /'dera&ad
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Granite
#ineralogicall'0Essential minerals - Quartz , Feldspar
Accessor' minerals Biotite, muscovite , amphibole.Other accessories are 1ircon, a2atite, ilmenite, magnetite, s2ene,
2'riteetc.
Te3turall'0
Medium to coarse grained crystalline rock generally ehibiting/'2idiomor2ic te3ture and Intergro+t te3tures !perthite,
"ntiperthite, Myrmekite, #raphic, #ranophyric, rapakivi$.
%he term 4Granite4 is derived &rom latin 'ord "Granummeaning (grain( because o& its granular nature.
Cemicall' 0 )iO* - + , !other oides vary$
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Classification of Granitoids0
#ineralogical classifications !/0#) classi&ication$
Cemical classification !alumina saturation, )-/-"-M
classi&ication etc.$
Tectonic classification !Based on plate tectonic setting$
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5.A.P classification of Granitoids
" a 2art of 5AP* classification(
Fig.1. "&ter /0#) !1234$
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Granite classification &ased on alumina
Saturation "&' Sand(0
Fig *. "lumina saturation classes based on the molarproportions o& "l*O
45!6aO78a
*O79
*O$ !:"5689;$
a&ter )hand !12*3$.
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Al2a&etic "S.I.A.#( Classification of
Granitoids0
' Ca22ell and 6ite "789:(
S.t'2e Granitoid "sedimentary protolith$
I.t'2e Granitoid!igneous protolith$#.t'2e Granitoid !direct mantle source$
' ;oiselle and 6ones "7898(
A.t'2e Granitoid !anorogenic type$
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S.T'2e Granitoids0
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I.T'2e Granitoids0
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#.T'2e Granitoids0
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A.T'2e Granitoids0
"-type granites are emplaced in either 'ithin plate anorogenic
settings or in the &inal stages o& an orogenic event.
Caracterised &'0
?igh )iO* "7?(?igh F contents "@ to > 22m(Cresence o& fluorite is an important characteristic o&
"-type granites.
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S.I.A. # Classification of Granitoids0
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Classification of Granitoid Rroc!s
&ased on Tectonic Setting0
BRBGENIC0Mountain building resulting &rom compressive stresses
associated 'ith subduction.
e$g$ 6ontinental collision granites- ?imalayas.
Fig.E. " 6lassi&ication o& #ranitoid ocks Based on %ectonic )etting. "&ter Citcher !124$ in 9. G. ?sH !ed.$, Mountain
Building Processes, "cademic Cress, IondonJ Citcher !1224$, The Nature and Origin of Granite, Blackie, IondonJ and
Barbarin !122K$ Geol. Journal, *, **3-*4. Linter !*KK1$ "n /ntroduction to /gneous and Metamorphic Cetrology.
Crentice ?all.
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Classification of Granitoid Rroc!s
&ased on Tectonic Setting0
Fig.. " 6lassi&ication o& #ranitoid ocks Based on %ectonic )etting. "&ter Citcher !124$ in 9. G. ?sH !ed.$, Mountain
Building Processes, "cademic Cress, IondonJ Citcher !1224$, The Nature and Origin of Granite, Blackie, IondonJ and
Barbarin !122K$ Geol. Journal, *, **3-*4. Linter !*KK1$ "n /ntroduction to /gneous and Metamorphic Cetrology.
Crentice ?all.
ANBRBGENIC0Magmatism 'ithin plate or at a spreading plate margin.?ere magmatism occurs in settings that are not genetically
related 'ith compressive orogeny.
e.g. ello'stone-snake river plain in 0)"
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TRANSITIBNA; PBST.BRBGENIC 0Magmatism takes place a&ter the main orogenic event. ! because it
needs a precursor orogeny t'o diverse groups eist 'hether they are
orogenic or anorogenic$.
e.g. Iate 6aledonian plutons o& Britain
Classification of Granitoid Rroc!s
&ased on Tectonic Setting0
Fig.. " 6lassi&ication o& #ranitoid ocks Based on %ectonic )etting. "&ter Citcher !124$ in 9. G. ?sH !ed.$, Mountain
Building Processes, "cademic Cress, IondonJ Citcher !1224$, The Nature and Origin of Granite, Blackie, IondonJ and
Barbarin !122K$ Geol. Journal, *, **3-*4. Linter !*KK1$ "n /ntroduction to /gneous and Metamorphic Cetrology.
Crentice ?all.
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Geocemical "trace element(
Discrimination Plots of Granitoids0
Fig. 3. %ectonic discrimination plots o& b!8b7$ and 8b !Cearce et al.12E$. Fields &or
syn-collision !6OI#$, volcanic arc !N"#$, 'ithin plate !LC#$ and ocean ridge !O#$ granites.
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Petrogenesis0
Magmatic Origin
Metasomatic %rans&ormation !#ranitisation$
o+ensstudies sho'ed that a basaltic magma can give rise toacid magma !granitic$ due to di&&erentiation.
tensive &ield studies , in high grade terranes, sho'ed that
etensive metasomatic trans&ormation 'as capable o& bringingabout compositional changes insitu o& a variety o& pre-eisting
rocks to create granites "/$/$Read($
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Most granitoids o& signi&icant volume occur in areas 'here the
continental crust has been tic!ened by orogeny, eithercontinental arc subduction or collision.
Because the crust is solid in its normal state, some termaldistur&anceis reDuired to &orm granitoids.
Most 'orkers are o& the opinion that the ma@ority o& granitoidsare derived by crustal anate3is, but that the mantle ma' also&e in-ol-ed. %he mantle contribution may range &rom that o& asource of eat &or crustal anateis, or it may be the source of
material as +ell$
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Many 'orkers believed there are
more than one origin &or granites P the
term GRANITES F GRANITES
'as coined.
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*uture 6or!0
)tudy about #ranite #eochemistry 'ith special re&erence to
Larangal and 8algonda
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