GEOLOGICAL MAPPING, PETROGRAPHIC STUDY and FIELD RELATION OF KARIGHATTA SCHIST BELT, DHARWAR CRATION, SOUTH INDIA.

1. PRESENTED BY
PRAMODA G
GEOLOGY
Presentation on
GEOLOGICAL MAPPING, PETROGRAPHIC
STUDY and FIELD RELATION OF KARIGHATTA
SCHIST BELT, DHARWAR CRATION, SOUTH
INDIA.

2. CONTENTS:
• Introduction
• literature review
• Methodology
• Petrographic studies
• Results and Conclusion
• Reference

3. INTRODUCTION:
Karighatta is one of the oldest rocky in south India, which
could be considered very much for geological studies. These
rocks come under granite – green stone belt. The rock types
are meta-volcanic which were deposited in the ocean and later
metamorphosed. The Karighatta has housed variety of rocks
both igneous & metamorphic.
The study of the Granite-Greenstone belts has attracted
the attention of many Geologists as it offers an excellent
opportunity to understand the Crust forming process during the
early period of the Earth’s history. The Dharwar Craton in
Southern India exposes crustal segments in which geological
activity can be traced continuously throughout the Pre-
Cambrian.

4. Location
11°30' North and 18°30'
North latitudes
74° East and 78°30' East
longitude.

5. Geology of Karnataka is a fascinating subject. Oldest
rocks exposed in Gorur area, Hassan district, Karnataka date
back to about 3300 million years. The Precambrian craton of
Karnataka is made up of western and eastern segments. The
Precambrian of Karnataka have been divided into older
Sargur supracrustals (about 3300 to 3000 million year old)
and younger Dharwar supracrustals(about 3000 to 2600
million year old. The Dharwar supracrustals Supergroup has
been further divided into older Bababudan Group(ca.3000 to
2700 million years) and younger Chitradurga Group(ca.2700
to 2500 million years). The schist belts of the Eastern craton,
like Kolar,Hutti,Sandur etc., appear to be approximately
equivalent to the Chitradurga Group.
GEOLOGY OF KARNATKA

6. GEOLOGY OF DHARWAR CRATON
The Dharwar or
Karnataka Craton in
South India presents
a natural cross-
section of late-
Archaean continental
nuclei lying between
longitude 72°45´–80°
and
latitudes 11°–19°.

7. Dharwar Craton is one of the best studied terrains of
Peninsular India and is renowned for its Greenstone Schist
Belt, Grey-Gneisses, Charnokites, and younger Granites .
The Craton is divided into two tectonic blocks after
Swaminath et. al. (1976), viz. the Western Block renamed
respectively as the Western Dharwar Craton (WDC), and
Eastern Dharwar Craton (EDC) are separated by
Chittradurga Shear Zone which is situated at the Eastern
margin of Chittradurga Schist Belt, not far from the Western
margin of Closepet –Granite.
GEOLOGY OF DHARWAR CRATON

8. The contact between WDC and EDC is not sharp, and there
is a Transition Zone between Chittradurga Shear Zone and
Closepet Granite. The Grey-Gneiss complex covering the entire
Craton was formerly known is Peninsular Gneiss in the view of
its critical differences in age, composition and mutual relation
with associated Supracrustal Rocks and Geographic distribution
in separate Tectonic Blocks. Dominantly, Granitic terrain of EDC
is Called Dharwar Batholiths (>2500m.a.) after Chadwick et al.
(2000). According to Ramakrishnan and Swaminath
(1981), Dharwar Craton has been divided into two.
1. Eastern Dharwar Craton (EDC)
2. Western Dharwar Craton (WDC)

9. EASTERN DHARWAR CRATON (EDC)
The EDC is bounded to the north by the Deccan
Traps and the Bastar Craton, to the east by the
Eastern Ghats Mobile Belt, and to the south by the
Southern Granulite Terrain (Balakrishnan et al.,
1999). The Craton is composed of the Dharwar
Batholith (dominantly granitic), greenstone belts,
intrusive volcanic, and middle Proterozoic to more
recent sedimentary basins (Ramakrishnan and
Vaidyanadhan, 2008).

10. Geological Map of Eastern
Dharwar Craton (Modified from
Naqvi and Rogers, 1987)
EASTERN
DHARWAR
CRATON (EDC)

11. The Western Dharwar Craton (WDC) is located in
southwest India and is bound to the east by the Eastern
Dharwar Craton (EDC), to the west by the Arabian Sea,
and to the south by a transition into the so-called
“Southern Granulite Terraine”. The remaining boundary
to the north is buried under younger sediments and the
Cretaceous Deccan Traps. The division between the
Western and Eastern Dharwar Cratons is based on the
nature and abundance of greenstones, as well as the
age of surrounding basement and degree of regional
metamorphism (Rollinson et al., 1981).
WESTERN DHARWAR CRATON (WDC)

12. Geological map of the Western Dharwar
Cratons (after Naqvi and Rogers, 1987;
Ramakrishnan and Vaidyanadhan, 2008).

13. WDC EDC
SCHIST BELT LARGE WITH
VOLCANICS, SUBORDINATE
SEDIMENTS.
NARROW, WITH GREENSTONE
BELTS. PILLOW BASALTS.
BASEMENT IS PENINSULAR
GNEISS. UNCONFORMITY
MARKED BY QPC.(<3000MY)
DHARWAR BATHOLITH INTRUSIVE
ON ALL SIDES .(2500-2700 MY)
OLDER SEQUENCE (SARGUR
GROUP)AS NARROW BELTS AND
ENCLAVES, ABUNDANT IN THE
SOUTH.
OLDER SEQUENCE(WARANGAL
GROUP) MOSTLY AS ENCLAVES IN
THE NORTH.
INTER MEDIATE PRESSURE
METAMORPHISM.
LOW PRESSURE METAMORPHISM.
Comparison between WDC and EDC

14. Karighatta Schist belt is the southernmost part of
Chittradurga Schist Belt characterized by Peninsular
Gneiss, Quartzites (± Fuchsite), Garnet-Biotite-
Schist, Amphibolites, BIF, Pyroxenite, Pegmatite, etc.
These rocks are intruded by Dykes like Diorite
Porphyry and surrounded by Gneisses belonging to
Peninsular Gneisses Complex. The Relict
Sedimentary Structures like bedding, lamination,
current bedding, or less cross bedding can be noticed
in the Metasediments.
KARIGHATTA SCHIST BELT

16. AIM AND SCOPE OF PRESENT STUDY
The aims of the investigations are:
* To prepare geological map of Karighatta Schist Belt of the
scale 1:500 and to bring out field relationships of the various
rock types.
* To record petrography features of different rock types, their
textures and mineral assemblages. The geology and
tectonic activity of the area.
* To Elements of geological map. Basics of construction of
geological maps and cross-sections.
* Obtaining and marking samples and describing and
measuring where they came from in an outcrop;
* Measuring and recording orientation (i.e., altitude) of strata
or other planar features;

18. Field mapping can be physically and mentally challenging.
Hundreds of questions arise, dictating that hundreds of
decisions must be made during the course of a single day.
Where should I go? What unit is this? Why does this? bed
abruptly end? Thus, field mapping is the ultimate application of
the scientific method – a good field mapper is constantly testing
predictions about the next outcrop and evaluating multiple
hypotheses about the structure. In the midst of this mental
workout, it is important to maintain your focus and purpose by
remembering the goals of your project or research. Try to
maintain a good sense of humor and enjoy the day. After all,
didn’t most of us decide to go into geology because we like
being outdoors and we like thinking about the Earth?
GEOLOICAL MAPPING

19. PLANNING OF FIELD WORK
Each mapping/structural field project in geology requires the
following deliverables (i.e., products to be turned in), typically
at a designated time/place on the evening of the last day of
the project:
 Geologic map – lightly colored and burnished
 Structural cross-section(s) – lightly colored and burnished
 Key or explanation that describes all rock units and
explains structural symbols, etc.
 Written report, usually based on a set of questions posed
at the onset of the project; some reports may require
accompanying stereonets
 Field notebook

20. LOCATION FIELD DATA
A geological map is prepared by locating many points,
lines and data on a base map. Points on a map by a number
of methods, the most suitable for which must be chosen
depending on the base map, the map itself has to be oriented
with reference to “North” direction.
Data can be plotted directly by inspection when the
configuration of surface features makes it possible to identify
them positively on the map. Examples of such points are
distinctive turns or interaction in steams, roads of rid
characteristic topography, etc.

21. LOCATION BY OBSERVATION AND A BEARING
LINE
Data along liner features, such as bridges, roads, or steams can often
be located by taking a bearing from a point that can be identified exactly on
the map, then plotting the back bearing from that point to intersect the linear
feature on which the observation stands.
LOCATING BY INTERSECTION OF BEARING
LINES
When the features that can be identified on the base map are too
distant for facing bearing to two such features from the required point is read
and the back bearing lines are plotted. The intersection point of the bearing
lines will indicate the location of the required point on the base map. They
include angle between the bearing lines should not be very acute or obtuse.

22. LOCATION
The area selected for present study is situated North of Mysore City
Karighatta( 12°25'05''N and 76°43'17''E, Toposheet - 57D/11) is a hill situated
a few kilometer’s outside the ‘island’ town of Srirangapatna, on SH NO.17,
Mysore-Bangalore Road, representing a narrow linear schist belts around
Karighatta, termed as Karighatta Schist Belt.

23. Our base Map for geological field work of Karighatta

24. Traverse pattern

25. FIELD SETTING
AND
PETROGRAPHY

26. Basic Job Description:
Study composition, structure, and history of the earth's
crust; examine rocks, minerals, and fossil remains to
identify and determine the sequence of processes
affecting the development of the earth; apply knowledge
of chemistry, physics, biology, and mathematics to explain
these phenomena and to help locate mineral and
petroleum deposits and underground water resources;
prepare geologic reports and maps; and interpret research
data to recommend further action for study.
FIELD DESCRIPTION AND PETROGRAPHY

27. Petrography
Petrography is a branch of petrology that focuses on detailed
descriptions of rocks. The mineral content and the textural
relationships within the rock are described in detail. The classification
of rocks is based on the information acquired during the petrographic
analysis. Petrographic descriptions start with the field notes at the
outcrop and include macroscopic description of hand specimens.
However, the most important tool for the petrographer is the
petrographic microscope. The detailed analysis of minerals by optical
mineralogy in thin section and the micro-texture and structure are
critical to understanding the origin of the rock. Electron microprobe
analysis of individual grains as well as whole rock chemical analysis
by atomic absorption or X-ray fluorescence are used in a modern
petrographic lab. Individual mineral grains from a rock sample may
also be analyzed by X-ray diffraction when optical means are
insufficient.

28. PENINSULAR GNEISS GPS Coordinates
Latitude - 12°25'25''
Longitude - 76°41'47''
Elevation – 2232 ft
In thin section, the Peninsualar
Gneisses exhibits Gneissosity
which are alternate layers of Sialic
and Mafic rich bands are observed
and the thickness of the bands are
variable. Sialic rich bands consist
of feldspar and quartz, whereas
mafic parts are made up of Biotite
and Hornblende.
Under microscopic thin
section

29. Peninsular Gneiss
having trend of N400E
Elevation:662mts

30. Peninsular Gneisses occupy in the low land
area in Karighatta schist belt. They are
medium to course grained rocks that
exhibits gneissic fabric which consists of
alternate layers of light and dark bands of
minerals. They are well foliated along the
strike direction ranging from N-S to N40˚E
and an amount of dip varies from 80˚ to
almost sub vertical. Pegmatite or Quartz
feldspathic veins are found parallel to the
banding. Furthermost amphibolites and
some pure white quartz are also found.
There are some pegmatite veins which
occurred between amphibolites and
peninsular gneiss. The minerals which are
found in Peninsular Gneiss are quartz,
plagioclase, K-feldspar, biotite etc.
Peninsular Gneiss exposed
in Kaveri River.

31. Quartzites:GPS Coordinates
Latitude - 12°25'29''
Longitude - 76°43'10''
Elevation – 2482 ft
Under microscopic thin
Quartzite (from German: Quarzit)
is a hard, non-foliated
metamorphic rock which was
originally pure quartz sandstone.
Sandstone is converted into
quartzite through heating and
pressure usually related to
tectonic compression within
orogenic belts. Pure quartzite is
usually white to grey, though
quartzites often occur in various
shades of pink and red due to
varying amounts of iron oxide
(Fe2O3). Other colors, such as

32. Fuchsite Quartzite having
strike N500Ewith dip of 550
towards west
Elevation:762mts

33. AMPHIBOLITE
GPS Coordinates
Latitude - 12°25'30''
Longitude - 76°a43'19''
Elevation – 2475 ft
Medium to fine grained containing
Hornblende, Garnet, plagioclase,
etc. The general strike direction of
Amphibolites is N-S to N600E
dipping with an amount of 400W to
almost sub-vertical. Amphibolites
are traversed by white massive
quartz veins and loose garnets are
found. The width of the amphibolites
ranges from 0.5 to 2m. There is a
contact between amphibolites and
pegmatite vein

34. Amphibolite
Direction of trending
N650E
Elevation:760mts

35. In thin section, Plagioclase + Hornblende +
opaque are seen. Hornblende grains are
prismatic and cleavages not distinct, It
shows inclined extinction with high order
interference colour. The pleochroic colours
ranges from yellowish green to green. Few
grains consist of inclusions of plagioclase.
No alteration observed. Plagioclase is
colourless without cleavage and untwined. It
is tabular showing inclined extinction. Some
of the Plagioclase grains exhibit
characteristic multiple twinning. In some of
the sections, the granulation of individual
grains is noticed.
Under microscopic thin
section

36. DIORITE PORPHYRY:
GPS Coordinates
Latitude - 12°25'53''
Longitude - 76°43'17''
Elevation – 2502 ft
Diorite porphyry exhibits 3 sets
of color’s from dark grey, pale
pink to chocolate brown colour.
The phenocryst often due to the
alteration of feldspar grains with
the release of Iron Oxide and
the groundmass is of pink
colour. The general strike
direction is N450E with an
amount of dip of almost vertical.

37. Diorites
Extended 310mts long
Direction of extension N450E
Elevation:769mts

38. In thin section, there is a porphyritic texture
where two modes of mineralogy are observed. It
consists of bigger grains forming phenocrysts
and smaller fine grains forming ground mass. It
consists of plagioclase Feldspar Hornblende +
Opaque. Plagioclase Feldspar is tabular,
colourless, indistinct, non-pleochroic. It shows
inclined extinction with multiple twinning and low
order interference colour. It is found as
phenocrysts showing alteration to Sericite along
the grain boundaries and cleavage plains. Some
of the Feldspar grains are traversed by irregular
fractures. Hronblende is green in colour,
prismatic and shows inclined extinction. It shows
high order interference colour and pleochroic
colour varies from green to yellowish green.
Cleavages are not distinct. Opaque’s are dark
colour, isotropic and grains are present as
accessorie
Under microscopic thin
section

39. Garnets:
GPS Coordinates
Latitude - 12°25'39''
Longitude - 76°43'14''
Elevation – 2492 ft.
We have found good crystals of garnets
on the next stage after the Amphibolite.
The Garnets what we have found in
Karighatta area varies from 1-5cm in
diameter. These Garnets are showing
Dodecahedral crystals. The colors of the
Garnets are dark pink. It is hardly
scratched by pen knife, Diaphaneity
opaque, luster dull. Garnets generally
have indistinct cleavage planes, uneven
fracture. Garnets can be used as Gem
minerals.
Under microscopic thin
section

40. Garnetiferrous Mica
Schist
Direction of trending
N27ᴼW
Elevation:778-785mts

41. Current beddings:
Just after the Diorite extension, we saw current beddings
having thin lamination.

42. Pegmatite + Quartz Vein ………. Quartz + Plagioclase + K-Feldspar
Mica Schist ………….………… Garnet + Biotite + Plagioclas + Muscovite +
Sericite + Quartz
Diorite Porphyry ….………… Plagioclase + Hornblende+ Orthoclase+CPx
Amphibolite……………………Hornblende + Plagioclase + CPx + Garnet
Fuchsite Quartzite ………………… Quartz + Silliminite +
Fuchsite
Peninsular Gneiss ………………….. Quartz + mica + Biotite +
Hornblende
LITHOSTRATIGRAPHIC SUCCESSION

43. Karighatta Succession
1.Banded peninsular gneiss(Age 2.8 B.Y)
2.Larger boulder Quartzites
3.Huge Fuchsite quartzite(Joined and Huge )
4.Diorite Porphyry
5.Amphibolite
6.Garnet Biotite Schist

44. CONCLUSION
The Dharwar Craton in Southern India is composed of extensive linear Granite-
Greenstone Belts called as the Gneissic-Granulite belt occupy large area of the
craton.
The study area Karighatta Schist Belt consist of Banded Peninsular gneiss
which are look like large boulder, Fuchsite quartzite if joined trending N55E.
After the formation of Fuchsite quartzite Diorite Porphyry it indicates later
volcanic activity, this followed by Amphibolite later Garnet Biotite Schist.
In the study are micaceous enclaves also seen and Shielding also visible.
In lower regions Feldspar is alternated into epidote.
Ripple marks and Cross bedding also seen in hill lock region this indicates that
paleoclimate condition is marine.
The occurrence of Garnet in many of the rock type indicates “Prograde
Metamorphism”. The entire area was subjected to Upper Amphibolites to Lower
Granulites Facies of Metamorphism and the sediments are now found as
Quartzites trending NE.

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REFERENCE