ACKNOWLEDGEMENT
We are grateful to Prof. Anisha , Honourable Vice-Chancellor of
Pondicherry University for sponsoring the field training programme
from University grant. This field work and report would not be in its
present form without the excellent guidance and tremendous support
of Dr.Rajneesh Bhutani, Dr. Shreyas Managave, Dr. Nurul
Absarfaculties of Dept of Earth Science, Pondicherry University. We
are grateful that they never gave up on us and were very patient
throughout.
I thank all the non teaching staffs and research scholars who guided
us in the field and helped us in completing my field report. And, I also
thank my classmates for their immense support and encouragement.
Finally, I thank my friends and family members for their
encouragement and support and also offer my sincere thanks to the
Almighty for His blessings.
Field Report (2015-2016)
Page |1
INTRODUCTION
The Precambrian shield of southern India, of which the present study area forms a part has
been divided into cratonic nuclei of Dharwar, Singbhum and Bastar, surrounded by mobile
belts of successively younger ages (Radhakrishna and Naqvi, 1986). The Archaen terrain of
southern India records geological events that occurred essentially during 3.4 to 0.5 Ga. It
can be divided into two principal terrains based on the grade of metamorphism as: (1)
southern high-grade granulites terrain and (2) northern low grade granite-greenstone
terrain. The boundary between these two terrains is the fermour line or the palghat cauvery
shear zone.The northern lowgrade terrain is spread over major parts of Karnataka and Goa
and parts of Andhra Pradesh and is composed of several supracrustal (greenstone) belts
surrounded by gneisses and granitoids. The northern low-grade terrain has been referred to
variously as Dharwar Craton or Karnataka Craton and Dharwar Nuclei (Pichamuthu, 1985;
Drury et al., 1984; Rogers, 1985; Radhaakrishna and Naqvi, 1986 and Mukhopadhyay, 1986).
The central part consists of granite-greenstone terrain characterized by green schist to
lower amphibolite facies and is surrounded by a mobile belt consisting of granulite facies,
charnockite terrain and migmatitic gneisses, well exposed in the eastern portion of the
south Indian shield the south Indian Peninsular region includes representatives of all the
three principal rock associations which characterize Arachean terrains, say (i) the highgrade associations (granulites) of Tamilnadu and Kerala (ii) the granite-greenstone
association (older supracrustals) and, (iii) the Craton-basin association of (Dharwar). Perhaps
in no other part of the world, are the three associations brought together in such a well-knit
composite unit as in South India, affording excellent opportunities for a close study and
understanding of the stages in the evolution an Archean crust.
As a prelude to the observations of the study area a general idea about the geology of the
Dharwar craton is to be discussed.
THE DHARWAR CRATON
The Dharwar Craton (or the Karnataka craton) lying between longitude 72º 45´-80° and
latitudes 11º-19°is an elliptical region comprising of a number of subparallel supracrustal
belts and stringers, is set in a matrix of polyphasic gneisses and bordered by granulites in the
south and granites to the east (Radhakrishna and Naqvi, 1986; Radhakrishna and
Ramakrishnan, 1988). The available geochronological ages spanning between 3.4 and 2.0
b.y.a. highlights the major early Precambrian events in the Craton. The Karnataka Craton of
the South Indian shield exposes numerous linear greenstone belts covered by younger
Field Report (2015-2016)
Page |2
group of rocks in the North. The oldest group of rocks forming the Craton was considered till
recently as Dharwars, intruded extensively by granite of different ages (Pichamuthu, 1962).
The rocks of Super schist are characterized by high grade metamorphism from upper
amphibolites to transitional granulite facies and have suffered intensive deformation and
migmatisation.
The term Dharwar (Karnataka) Craton was introduced by the geological survey of India
(1978), to accommodate the already known Dharwar super group (Dharwar greenstone
granite) and recently established Sargur Schist complex (Sargur type high grade terrain). The
Dharwar Craton is split into Eastern and Western Cratons, with major differences in
lithology and ages of rock units. The dividing line being a steeply dipping mylonite zone or
listric structure, and as a low angle thrust which becomes shallow at depth. This listric fault
is named as Chithradurga boundary fault. The Closepet Granite is a good approximation of
the western boundary (Ramakrishnan and Vaidyanadhan).
FIG NO. 1 : Geology of the western and eastern Dharwar Craton (after Rogers, 1990).
Field Report (2015-2016)
Page |3
THE LITHOSTRATIGRAPHIC UNITS
The Dharwar Craton has been divided into Eastern Dharwar Craton (EDC) and Western
Dharwar Craton (WDC), based on the nature and abundance of supracrustal belts, crustal
thickness, lithological assemblage, grade of regional metamorphism and degree of melting.
Further, these schist belts of the craton have been divided into three stratigraphic groups
based on the stratigraphy, age and litho assemblage (Swaminath et al, 1976; Swaminath and
Ramakrishnan, 1981). In the WDC, the schist belts of Sargur Group (3.1 to 3.3 by) are
deformed with Peninsular Gneisses and are unconformably overlain by the younger
moderately deformed schist belts of Dharwar Supergroup (2.6 to 2.8 BY) (Peucat et al, 1995;
Nutman et al, 1996, Trendal et al, 1997). The Dharwar Supergroup unconformably overlies
Peninsular Gneiss and Sargur Group rocks, and is divided into lower Bababudhan Group and
an upper Chitradurga Group (Swaminath and Ramakrishnan, 1981). While the schist belts of
the Kolar Group from the EDC are coeval with the schist belts of Bababudhan Group (Walker
et al, 1990; Nutman et al, 1996; Balakrishnan et al, 1987). The metagreywackes are totally
absent in the Sargur Group and Bababudhan Group; they are either absent or present in
minor abundance in Kolar Group, while they constitute the most dominant lithounits in the
Chitradurga Group, especially in Gadag-Chitradurga and Dharwar-Shimoga Schist belts . The
metagreywackes belong to the Ranibennur Formation of the Chitradurga Group of DharwarShimoga belt.
Field Report (2015-2016)
Page |4
THE WESTERN DHARWAR CRATON
The Western Dharwar Craton (WDC) is located in southwest India and is bound to the easy
by the Eastern Dharwar Craton (EDC), to the west by the Arabian Sea, and to the south by a
transition into the “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). The western block of Karnataka Craton comprises of
Holenarsipur, Bababudan, Shimoga-North Kanara, and Chitradurga- Gadag belts
supracrustal (schist) belts. The supracrustal rocks and Peninsular gneisses are further
intruded by k-rich granites which are 2.5 Ga. old (Taylor et al,1984 ).
The younger Dharwar super group has been subdivided into
(a) the lower Bababudan group
(b) the upper Chitradurga group
(c) Shigegudda schist belts
based on the presence of a thin persistent oligomict quartz pebble conglomerate
horizon marking the unconformity between these two group.
FIG NO.2: Geological map of the Western Dharwar Craton (after Naqvi and Rogers, 1987;
Ramakrishnan and Vaidyanadhan, 2008)
Field Report (2015-2016)
Page |5
The supracrustal rocks of Sargur occur as thin inliers set in Peninsular gneiss and are mainly
confined to the southern fringes of the Dharwar Craton. The Sargur group consist of a
diversified group of volcanic and sedimentary lithologies, represented by ultramafic-mafic
volcanic rocks, pellites, quartzites, impure carbonates, iron formation and intrusive
ultramafic-mafic and gabbro-anorthosite complexes. The development of greenstone belts
in the western block of the Dharwar Craton proceeded through three major depositional
cycles of volcanism and sedimentation, terminating with the intrusion of syn- to postkinematic granites on minor scale.
Field Report (2015-2016)
Page |6
CHITHRADURGA
Field Report (2015-2016)
Page |7
TOPOGRAPHY:
Chitradurga gets its name from Chitrakaldurga, an umbrella-shaped lofty hill found there.
The whole district lies in the valley of the Vedavati River, with the Tungabhadra River
flowing in the northwest. Chithradurga group consists of the Vanivilas formation followed by
Ingaldhal formation and on top Hiriyur formation. Geomorphologically it comprises
denudational hills, residual hills, pediment, linear ridge, pediplain moderately weathered,
pediplain shallow weathered, pediplain deeply weathered, pediplain gullied, structural hills
and valley fills. Chithradurga schist belt consist of central anticline flanked by two syncline
on either side, this syncline is the earliest form which is refolded by a second generation
antiform structure at the centre of the belt. The Eastern margin of the schist belt is a major
thrust contact marked by a Strong mylontic zone. It is the line of suture between the WestArchean nucleus and East Younger gneissic complex. The Chithradurga Schist belt splits into
several narrow belts interlayered with Gneiss.
STRUCTURE AND TECTONICS:
Dharwar Craton is highly studied for ancient rocks and understanding of
tectonic/geodynamic processes of Mesoarchean to Paleoproterozoic. There are two
amalgamating cratons along the Chitradurga Shear Zone (CSZ). Western Dharwar crust is
much thicker, mainly due to domination of sedimentary deposition between greenstone
sequences Sargur group (>3 Ga) and Dharwar super group (2.9-2.5 Ga) sequences. The
tectonics of the Chithradurga shear zone is best described as juxtapositioning of east
dipping listric thrust fault between the eastern and western Dharwar craton.After the
accretionary process probably in an intracratonic rift basin/ possibly in an oceanic trench
lead to the formation of closely associated ultra basic to basic magmatic and volcanic rocks ,
with interaction of pelitic-silicious sediments, which actually forms the Sargur group and
represents the high grade of metamorphism called Older Green Stone Belt. Gorur gneiss and
Sargur group together formed the 3.4-3.2 Ga old nucleus of the craton. It was profusely
invaded in many phases by gneissic magmas, giving raise to the peninsular Gneiss around
3000Ma. After the gneissic terrain had stabilised the craton experienced extension,
resulting in sagging and rifting along the structural grains of the mesoarchaean crust.
Consequently the elongate basins of Dharwar sedimentation and volcanism was formed ,
which are represented by the Dharwar Supergroup. The basin attained the nature and the
shape of intra cratonic grabens. Syn-Sedimentary volcanism would have been the main
crustal process. Towards the close of NeoArchaean era there was a westward oblique
convergence of crustal blocks, this resulted in EW to NE-SW shortening of the basin, creating
a regime of thrusting and strike slip shearing. The transpression along NS line is
represented by Chitrdurga boundary fault. This phenomena led to the SW overturning of
folds in both the basement and cover. Possibly mantle plumes have become active during
Field Report (2015-2016)
Page |8
late NeoArchaean time, they brought up materials through deep shear zones and faults and
caused melting of basement rocks , particularly in the areas of East of Chithradurga belt.
This developement ended in the emplacement of closepet granite and the Dharwar
batholith along the northern part.
SEDIMENTOLOGY:
Conglomerate occurs at many levels in the formation and some are deposited along the
basement .i.e. Talya conglomerate.This is a glacio-marin deposits consisting of diamectite*
interbedded with mudstone and sand stone & is interpreted as glaciomarine conglomerate
.Talya conglomerate(~2700 Ma -Neo Archean) was deposited in a marine environment with
diamectite composed of IRD(ice rafted detritus) as per one view . The mud stone bearing
portion of the talya conglomerate was deposited upon the sand stone bearing portion as
sea further inundated the land mass due to glacial retreat and a decrease in glacial mass,
thereby resulting in the fining-upward nature of the Talya Conglomerate. Kaldurga
conglomerate is an equivalent of Talya conglomerate but is of glacio-fluvial environment.
This kaldurga conglomerate was brought up by upliftment of Bababudan group and got
eroded, before the formation of Chithradurga group. The difference in clast and matrix
composition suggest the striping of bababudan cover, which has contributed clasts to the
lower part of Kaldurga conglomerate. But this school of thought is still widely debated.
Vanivilas sub group (~2600 Ma) consists of Greywacke, Orthoquartzite, polymict
conglomerate ,Quartz arenite , Phyllites , limestone or Dolomite , Manganese formation and
BIF .Greywacke and BIF are locally rich in manganese oxide .Polymict conglomerate occur at
many levels and some were deposited on the basement .This Polymict sediments vary from
lenses to large complexes & are mostly unsorted .The matrix is mostly greywacke or arkosic
in composition. They appear to be deposited on progressively subsiding depression
between basement domes during the initial basin inversion . Composite units of
conglomerate-orthoquartzite are comparable to shallow alluvial or marine fans. Coarse
pebbles and large clast represent storm surge and debris flow deposits. Whereas the fine
conglomerates are probably sheet flow deposits .Herringbone cross bedding indicates
intertidal or near shore facies. This school of thought of marine turbidite deposits and facies
also have wide popularity.
Field Report (2015-2016)
Page |9
ECONOMIC SIGNIFICANCE:
Iron ore, manganese ore, copper ore, chromite, magnesite and gold are the important
economic assets of the area .The closepet granite, the Dharwar batholith, the peninsular
gneisses and the felsite and Porphry dikes are used as building material. BHQ & BMQ of the
BIF of the Dharwar super group host the iron ore deposits of the great valley in
Khuduramukh, Bababudan and Bellary belts. Manganese minerals are pyrolusite and
psillomalene occurring schist belt in association with limestone and BIF. Copper sulphide,
together with ZnS and PbS are found in pillow basalt and tuff of Jogimardi sequence of
Chithradurga group. The Auriferous schist belts are gold bearing. The kolar schist belt have
strong structural control on gold mineralisation. Gold occur in four parallel roads in
stratiform deposits of sulphides. Geochemistry indicates they have formed from submarine
hydrothermal exhalations. Chromite deposits occur in lensoid bodies of serpentine in
Nuggihalli belt of Sargur group. Magnesite occur in veins of serpentinised dunite in this
group.
Field Report (2015-2016)
P a g e | 10
FIELD OBSERVATIONS
Field Report (2015-2016)
P a g e | 11
DAY 1
LOCATION 1
STRIKE: 340/320
DIP: 49/80
MAJOR ROCK TYPE: GREEN COLOURED FUCHSITE QUARTZITE, PEGMATITE DIKES WITH MUSCOVITE
SPECIAL FEATURES:




Alternate bands of fuchsite and quartzite found.
At places pegmatitic intrusion shows muscovite mineralisation.
Two dominant joint planes identified
Close spaced foliation planes are schistose planes dipping at varying degrees
from 80, 79, 65 and 49.
 Micro folding in the schist beds.
LOCATION 2
LANDMARK: VILLAGE WATER TANK
MAJOR ROCK TYPE: GRANITIC GNEISS
SPECIAL FEATURES:
 Very close spaced gneissic planes defined by biotite
 More of quartz and feldspar in rock
LOCATION 3:
MAJOR ROCK TYPE: OLIGOMITIC QUARTZ PEBBLE CONGLOMERATE that later grades into
QUARTZITE
SPECIAL FEAUTES:
 Identified a marker horizon or the base of Bababudan.
 The rocks were found to be scattered and fallen over a large area.
Field Report (2015-2016)
P a g e | 12
LOCATION 4:
LANDMARK: A LINEAR RIDGE ALONG THE 340 STRIKE
STRIKE: 340
LAT/LONG: 10°,59.943/76°,17.714
MAJOR ROCK TYPE: METABASALTS, MAFIC SHIST
SPECIAL FEATURES:
 The rock dominantly contains plagioclase and pyroxene.
 The grain size of the basaltic rock progressively changes to the top of the
ridge.
 In the top part of the ridge the Meta basalts appeared to be perforated.
 The Meta basalt slowly grades into mafic schist along the other side of the
ridge.
LOCATION 5:
MAJOR ROCK TYPE: OLIGOMICTIC QUARTZ PEBBLE CONGLOMERATE
SPECIAL FEATURES:
 The rock found is in-situ and highly deformed.
 Base appears to be on the top part of the exposed outcrop.
 Could indicate a tight folding.
LOCATION 6:
MAJOR ROCK TYPE: META BASALTS
SPECIAL FEATURES:
 Meta basalts with large no of amphibolite grains found (needle shaped
hornblende crystals).
 Very well preserved vesicular Meta basalts found with larger perforations.
 Coarser basalts along the foot hills.
Field Report (2015-2016)
P a g e | 13
LOCATION 7:
MAJOR ROCK TYPE: DIAMICTIC CONGLOMERATE (TALYA CONGLOMERATE)
SPECIAL FEATURES:




Phyllite rock makes up the fine grained matrix.
Unsorted and large pebbles in the matrix
The size varies from 1cm to 10 cm in length and breadth.
The pebbles tend to be elongated and wrapping at ends.
DISCUSSIONS:
In location the mica and quartzite interlayer must have been formed due to the
metamorphism of alternate bands of shale and sandstone which can be interpreted from
the micro fold structure of the incompetent layer as can be seen in the fig. This deposit can
be probably interpreted as fluvial deposit and assumed to belong to the older Sargur group
which occurs as enclaves in the later observed peninsular gneisses of location 2. Here
moving along the strike younger beds are encountered. The QPC found as scattered
boulders are the marker horizon between the peninsular gneiss and Bababudan group,
called Neralkatte conglomerate. In location 4 the Meta basalts that vary in grain size and
show perforations can be interrupted as a sub aqueous or sub aerial volcanism and the
perforations in the top part of the ridge can be interpreted as the flow top vesicles. The
chlorotic schist on the eastern flank (younger side) may validate the subaqueous concept.
Strati graphically it can be called as a Bababudan formation. The repeated occurrence of
Meta basalt and QPC and observed overturning of the base of QPC can be interpreted as a
tight overturning fold. The presence of Talya conglomerate which is dimictic at location
seven is an indicator of another marker horizon between Bababudan and Vanivilas
formations. The speculation of the Talya conglomerate to be glacio-marine could not be
confirmed but the drop stones are highly unsorted.
Field Report (2015-2016)
DAY 2: GHATTI HOSAHALI VILLAGE
LOCATION 1:
STRIKE-350⁰
MAJOR ROCK TYPE: Quartz pebble Conglomerate, Mica Schist.
LOCATION 2:
STRIKE-330⁰
MAJOR ROCK TYPE: Metabasalt.
LOCATION 3:
STRIKE-167⁰
DIP-35⁰-40⁰ W
MAJOR ROCK TYPE: Talya Conglomerate.
READINGS: 1cm to 5 cm
 Clasts are elongated (deformed)
 Semi-major axis= 10 cm
 Semi-minor axis=15 cm
LOCATION 4:
STRIKE-330⁰
DIP- 35⁰ E
MAJOR ROCK TYPE: Conglomerate Quartz.
LOCATION 5:
MAJOR ROCK TYPE: Banded Iron Formation.
LOCATION 6:
MAJOR ROCK TYPE: Dolomite.
P a g e | 14
Field Report (2015-2016)
P a g e | 15
DISCUSSIONS:
In L1 New exposures of mica schist with patchy appearance around the road. In L2
Metabasalt found with specific orientation of Plagioclase along the regional strike. It
appears to have coarse plagioclase crystals. After micaceous schist, well preserved QPC has
been found on the opposite side of the ridge from almost top. In L3 Conglomerate is at high
energy condition. In L4 lot of quartzite toppled down. Micaceous quartz near temple are
Intruded by quartz viens, parasitic folds are all over showing incompetency during folding. In
L5 Normal folds and magnetic properties are observed. Folding axial plane, tilted west,
bedding dipping east.