shear zone in the area are described

1. TECTONIC
AMALGAMATION OF
CRUSTAL BLOCK IN
DHARWAR CRATON
Along Gadag
Mandya Shear
Zone

2. INTRODUCTION
Dharwar Craton:
 The term Dharwar(Karnataka) was
introduced by GSI in 1978
 Covers an area of about 450,000 km.sq
 Age: 3.6-2.5 billion years ago (Archean)
 Location: . It is bounded to the south by
the Pandyan mobile belt (PMB), to the north
by the Deccan Traps.
 Owing to lithological differences Dharwar
craton is divided into :
Eastern Dharwar Craton (EDC) and the
Western Dharwar Craton (WDC)

3.  The boundary between EDC and WDC can be
traced from Gadag in the north to Mandya in
the south.
 Known as Gadag- Mandya Shear Zone
(GMSZ)
 The area of study is in (GMSZ) in the
Javanahalli-Hagalvadi sector.

4. It is also called Chitradurga Eastern Boundary Fault,
Chitradurga Eastern Boundary Thrust or Eastern
Margin Shear Zone by various authors.
It has a strike length of about 400 km.
The Study area, Javanahalli – Hagalvadi sector
covers a rectangular area of about 700 sq. Km
The GMSZ is between Javanahalli Schist Belt (JSB) in
the east and Chitradurga Schist Belt (CSB) in the
west.

6. Figure 2

7. STRUCTURE
Disposition of components shown in fig 2
Granitic and magmatic gneisses underlie rocks of JSB
Both JSB and CSB contain volcano sedimentary sequence by t have
distinctly different association.

8. GNEISSES UNDERLYING JSB
•Well banded and foliated quartzofeldspathic gneisses.
•In general altered composed of biotite rich quartzo feldspatic band.

9. JSB
Lithounit:Amphibolite,calc-silicate,crystalline
Limestone,Quartzite,BIF,Quartz Biotite Schist,Corderite,Anthophyllite
rock and Quartz Siliminate Schist.
•Dominant:Amphibolite
•Garnet is rare.
•Relict Gabbroic structure can be recognized.
•Coarse medium sized metamorphic assemblage obscured or replaced
by strong fine grained mylonitic rock(characteristic of shear zone)
•Well banded calc-silicate rock are intercalated with amphibolite.

10. •Crystalline limestone occurs as narrow bands in amphibolite(grey
,banded,hard,crystalline and occasionally contains alternating centimeters
wide chert bands).
•BIF rare within amphiboles of JSB.
•Quartzite occur in association show well developed banding(Manchaldore
and Muchhavirahalli areas
•Amphibolite acts as lower marker.
•Quartzite:Quartz with little muscovite with or without Fucshite.
•Corderite-Anthophyllite rock recorded in minor quantities as small patch
within BIF and amphibolite.
•Rock type of JSB indicate middle amphibolite grade of metamorphism.

11. CHITRADURGA SCHIST BELT(CSB)
•Dominant rock type: Metabasalt and Metagreywacke-argillite
sequences interspersed with bands of quarzite,polymict
conglomerate and BIF.
•Metaultramafites and metabasic intrusives occur in west of Janakallu.
•Metabasalt occur at core of an antiformal closure defined by the BIF
bands that seprate the unit from the argillite-greywacke unit.
•Argillite-metagreywacke unit is well bedded,soft,friable schistose
rock composed mainly of Quartz and Chlorite with minor Sericite.
•A number ofv bedded carbonate layers occur as intercalations within
argillite-metagreywacke sequence.

12. •A narrow lensoid body of polymict conglomerate,composed of large
cobble and pebbles of quartzite and BIF embedded in argillitic matrix.
•There are two three bands of well bedded quartzite assocoiated with
metabasalt and argillite in eastern most part of CSB.
•Minerological constituent include quarz,muscovite with or without
fuchsite.
•Cross lamination recoginised at places.
•Metaultramafics occurring as small lensoid patches.
•The large lensoid metagabbro bands within metabasalts and argilites are
coarse and crudely foliated.
•CSB indicates a low grade greenschist facies of metamorphism.

13. INTRUSIVE BUKKPATNA GRANITE
•Emplaced sheet like body showing a N-S disposition between CSB ans
JSB.
•Extending from Javanhalli in the north to beyond Hagalvadi in south.
•Porphyritic in nature megacryst of k-feldspar and ocassional
plagioclase embedded in groundmass of quartz, K-
felspar,plagioclasde and biotite.

14. OTHER INTRUSIVES
•There are several other minor granite intrusives are observed around
Ranganthapura,Hudyilore,Sakshihalli,Tuppadakona areas..
•Fine to medium grained.
•Composed of quartz,K-felspar,plagioclase and occasionally
hornblende.
•Regarded as products of remobilization of basement gneisses in
zones of higher grade of metamorphism.

15. THANK YOU
Presented by,
Anagha R
Jayalakshmi J
Meenakshi A