A palaeostress analysis of Precambrian granulite terrain of northern Tamil Nadu,
Peninsular India – A remote sensing study
S. BALAJI
Coastal Disaster Management, Department of Ocean studies & Marine biology, Pondicherry
University, Port Blair, Andaman Islands, India. Phone: 9933299064
Email:drbalaji64@gmail.com
Abstract
The tectonic evolution of Precambrian granulite terrain of northern Tamil Nadu evokes much
interest owing to its rich possession of natural resources and structural complications. The
efficacy of satellite remote sensing in tectonic mapping and analysis has been proved beyond
doubt owing to its spectral, spatial and temporal capabilities. The remote sensing analysis of
northern Tamil Nadu has displayed clear-cut structural trends, folds, mega and micro lineaments.
The analysis of fractures/lineaments in conjunction with the field data and the folds has resulted
in a schematic model to demonstrate the palaeostress pattern of Precambrian granulite terrain of
northern Tamil Nadu. The study further reveals that there are two phases of deformation namely
N-S and ENE-WSW compressions which have caused in the culmination of present
configuration of, structural trends and folds of northern Tamil Nadu contradicting the five phases
of deformation.
Key words: Paleostress, folds, lineaments, remote sensing, Nothern Tamil Nadu, India
1.Introduction
The understanding of structure and tectonics in an area is important as it sheds light on
the magmatism, metallogeny, ground water, seismicity and geothermal resources. The
Precambrian-Archaean rocks of Peninsular India exhibit polyphase metamorphism, multiple
deformation, repetitive folding and intense fracturing. These highly fragmented and widely
disseminated rock types show contrasting fold styles, multi variate linear and planar features.
These linear and planar features have controlled localization of minerals, ore bodies and
ultrabasics at several places. In addition, the linear features control major rivers like Cauvery,
Coleroon, Bhavani, Moyyar and reactivate frequently in the form of earth tremors along
Precambrian fractures (Balaji, 2000). Narayanaswamy (1966), Grady (1971), Sugavanam et al.
(1977), Katz (1978), Drury and Holt (1980), Ramasamy et al. (1987), Naga (1988), Ramasamy
and Balaji (1995) and Ramasamy et al. (1999) have studied the regional tectonic analysis of
southern Peninsular India. Among these geoscientists, Sugavanam et al. (1977) attributed five
phases of deformation and Narayanasamy (1966), Ramadurai et al. (1975), Katz (1978), Naga
(1988) and Ramasamy et al. (1999) advocated two phases of deformation responsible for the
tectonic evolution of Precambrian fold belts of southern Peninsular India. The northern Tamil
Nadu, which is a part of southern Peninsular India wherein tectonic studies were carried out at
few places and hence, disseminated information is available. A comprehensive and a wholistic
tectonic model for the evolution of Precambrian folds of this region is not available. Hence, the
present study has been taken to study all the structural features in detail using satellite imagery
amended with ground data and analyse them critically in a regional matrix to bring out a
schematic model for the tectonic evolution of Precambrian fold belts of northern Tamil Nadu.
2. Geological setting
The northern Tamil Nadu is bounded by northern latitude 10° 49″ 00′ and 13° 00″ 00′;
eastern longitude 77° 38″ 00′ and 80° 10″ 00′ which covers an area of nearly 75,000 sq.km
encompassing crystalline and sedimentary tracts. But, the present study is focussed on the
crystalline tract only (C, figure 1) excluding the sedimentary formations in the east (S, figure 1).
The Precambrian granulite terrain comprised of diversified rock types namely charnockites,
biotite gneiss, pyroxene granulite, granite, migmatite, granitoid gneiss, syenite and ultrabasics.
These rock types are traversed by dolerite and gabbro dykes at several places. Major hillocks
are Biligirirangan, Shevroy-Chitteri-Kalrayan and Kolli-Pachai. The Biligirirangan hills occupy the
western part (7, figure 1), the Javadi- Shevroy-Chitteri-Kalrayan hills covers the central part
(1,2,3 and 4, figure 1) and the Kolli-Pachai hills occur in the southern part of the study area (5
and 6, figure 1) are composed of charnockitic rocks.
3. Methods
3.1 Structural trendline mapping
Geological or topographical alignments usually straight and occasionally arcuate which
can be recognized on aerial photographs to consistently occur over a wide region. These have
been variously named as fracture zone, trendline and tectonic trends (Auden, 1954 and
Eremenko 1964). Bedding, foliation and lineation in rocks which are seem to be related to
tectonic trends. Drury and Holt (1980) have used Landsat satellite imagery to trace the
alignment of geological significance such as planar fabric and steep to vertical compositional
layering and they traced the regional scale folds and shears of South India from this. Ramasamy
et al. (1987) and Ramasamy et al. (1999) have used Indian Remote Sensing hereinafter called as
IRS, 1A satellite imagery to interpret the structural trendline and regional folds of South India.
Nair (1990) and Nair and Nair (2001) have interpreted structural trends using IRS 1A satellite
imagery based on tonal contrast, tonal linearity and elicited fold features such as F 1, F2 and F3
folds from structural trends. In the present study, the structural features of northern Tamil
Nadu were interpreted visually (figures 2, 3, and 4) using, False Colour Composite hereinafter
called FCC, Linear Imaging Self Scanning hereinafter called LISS 1 satellite data of 1987 on
1:250,000 scale on individual scene by adopting the same methodology of Auden (1954),
Eremenko (1964), Drury and Holt (1980), Ramasamy et al. (1987), Nair (1990), Ramasamy et al.
(1999) and Nair and Nair (2001). The whole area is covered in eight individual scenes. Landsat
satellite imagery Thematic Mapper (TM), band 6 data was used on 1:250,000 scale for thick soil
covered area. The interpreted each scene data were mosaiced on a planimetrically controlled
map which resulted in composite regional structural trendline pattern of northern Tamil Nadu.
The attitude of the beds measured in the field were incorporated in structural trends. The fold
styles were then determined from structural trendlines (Ramasamy et al. 1987), Nair (1990) and
Ramasamy et al. 1999) and based on the fold style pattern, different structural domains were
classified (Fig.5).
3.2 Lineament mapping
O’Leary et al. (1976) defined the term lineaments as mappable, simple or composite
linear feature of a surface, whose parts are aligned in a rectilinear or slightly curvilinear
relationship and which differs distinctly from the pattern of adjacent features and presumably
reflects a subsurface phenomenon. The lineaments were interpreted visually using IRS 1A, LISS
1, FCC satellite data of 1987 on 1:250,000 scale on several individual scene, based on the
morphological expression and anomalies such as straight sharp linear ridges, lithological
straightness, sharp lithological contact, offset of lithologies and structures identified by zones of
block displacements and truncation of structures along major faults (Brockmann et al. 1977),
long and linear fracture valley, soil tone linearities, vegetational alignment (figure 3) and
straight/ rectilinear drainages (figure 4 and Haman 1961, Bakliwal 1978, Ramasamy and Balaji
1993, Ramasamy and Balaji 1995 and Ramasamy et al. 1999). The whole study area is covered
in eight scenes and the interpreted eight scenes were mosaiced on a planimetrically controlled
map to get the composite regional lineament pattern of northern Tamil Nadu. The lineaments
falling in different structural domains were filtered separately and the lineament density map
(Fig. 6) was prepared by gridding each domain into 2.5 sq.cm grid (which is equal to 6.25 sq.km
/ grid on the ground). The total length of the lineaments falling in each grid area was measured,
plotted in the centre of the grid and contoured (Fig.6). The fold styles in conjunction with the
lineaments in each domain were critically analysed. Domainwise stress pattern and regional
stress pattern of northern Tamil Nadu were identified and finally, a schematic tectonic model
was built in.
4. Structural analysis of satellite imagery
4.1 Structural trends
The interpretation of structural trends using satellite imagery is already dealt with in section
3.1 and the structural trends of northern Tamil Nadu are shown in figure 1. These structural
trends have followed the regional trend of Eastern Ghats hill ranges. The structural trends fell in
five azimuthal frequencies viz N-S, NNE-SSW, NE-SW, E-W and NNW-SSE directions. The
structural trends show;

Long and linear N-S trending structural trend with dips 30° – 70° towards the east in
Biligirirangan area

NNE-SSW trending long, linear, broad, open, circular structural trends in Javadi-Kalrayan
area with dips 40° - 80° towards the east

N-S to NE-SW trending structural trends in Madras area with dips 45° - 60° towards the
east and

Circular, ovoidal, broad open structural trends in Kolli-Pachai area (Balaji, 1995 and
1996)
4.2 Fold styles and structural domains
Subsequent to the preparation of the structural trendline map of the study area, the types
of folding were deduced;

by analyzing the pattern and distribution of structural trends

through the integration of structural trends and drainage

through the integration of structural trends with the orientation of shadows and
highlights. For example, dip slope side of beds are relatively broad and bright displayed
in imagery and on the other hand, on the antidip scarp sides opposite to dipping side,
narrow and dark shadow appear in imagery because of low sun angle and

through the integration of structural trends with field strike/dip data
The types of folding and the position of fold axes were determined for all the structures in
the study area. The fold styles and fold axes so identified indicated the following characteristics
in each region (figure 5);

in Biligirirangan region, the folds are mostly tight, long, linear, overturned with N-S
trending axial traces and the folds are of alternating anticlines and synclines

the existence of long and upright open, isoclinals folds with NNW-SSE to NE-SW trending
axial traces in Javadi-Chitteri-Kalrayan region

broad open, elliptical doubly plunging domes and basin in Chengam-Madras region with
NE-SW trending axes and

the existence of domes and basins, upright anticlines and synclines in Kolli-Pachai hills
with NE-SW trending axis east of Namakkal, E-W trending axial traces in the centre and
WNW-ESE trending axial traces west of Namakkal area.
Based on the pattern of fold styles and fold axes, four structural domains have been
demarcated (1, 2, 3 and 4, figure 5). They are as follows and their characteristics were already
discussed as above.

Biligirirangan domain

Javadi-Kalrayan domain

Madras domain and

Kolli-Pachai domain
4.3 Lineaments
The lineaments of any region in general control minerals, ground water, ore bodies and
ultrabasics. The interpretation of lineaments using satellite imagery is dealt with in section 3.2.
The interpreted lineaments fell in six azimuthal frequencies namely NE-SW, NW-SE, N-S, E-W,
ENE-WSW and WNW-ESE directions. These Precambrian lineaments were deep seated (Grady
1971) and analysed for domainwise stress pattern. Bakliwal (1978) and Ramasamy and Bakliwal
(1988) have computed palaeostress for the tectonic evolution of folds in quartzites of Rajasthan
and Vindhyan basin of Rajasthan respectively from lineament density map. In the present
study, the interpreted lineaments were filtered for each domain separately and analysed
statistically from lineament density contours (Fig.6).
4.4 Lineament density
The preparation of lineament density contours was already discussed in section 3.2 and
was prepared for all the four structural domains. The lineament density contours of
Biligirirangan domain are in circular and elliptical shapes which varied from 2 to 8 km per unit
area (figure 6). From the lineament density contours and along the crest of lineament density
maxima contours, the lineament density maxima axes were drawn (figure 7). Similarly, along
the crest of such lineament density minima contours, the lineament density minima axes were
drawn (figure 7). The lineament density maxima axes indicated the axes of maximum strain and
lineament density minima axes indicated the minimum strain (Bakliwal 1978 and Ramasamy
and Bakliwal 1988). In a similar manner, the lineament density contours for Javadi-Kalrayan,
Madras and Kolli-Pachai hill domains were drawn and the axes of lineament density maxima
and minima were derived for these domains (figure 8).
5. Discussion
Domainwise stress analysis was done for all the four structural domains namely
Biligirirangan, Javadi-Chitteri, Madras and Kolli-Pachai domains. The axial traces of folds in
conjunction with the lineament density of each structural domain were scrutinized in detail to
identify the stress pattern in each domain separately. Accordingly, from principal elongation of
folds and lineament density contours, greatest principal stress for each structural domain was
derived (figure 8). The general axial traces of folds in Biligirirangan domain was observed in
NNE-SSW direction (figure 8). The greatest stress computed from the bulk strain or principal
elongation of folds (Hobbs et al. 1976) fell in N80°W –S80°E directions. But, the lineament
maxima/strain maxima axes fell in NE-SW, and WNW-ESE directions which are the Precambrian
dextral and sinistral faults respectively (Balaji, 1995) and hence, the greatest principal stress is
conceived in ENE-WSW direction along the acute bisector (Anderson, 1951) of these two
Precambrian faults. The folds in Biligirirangan domain are flexural slip folds (Balaji 1995) and the
bulk strain varies from place to place because of the adjustment of the folds with the basement
configuration. The greatest principal stress deduced from the bulk strain is considered as a local
phenomenon but the greatest principal stress deduced from the lineament anomaly axes
remain the same in the entire Biligirirangan domain and therefore the greatest principal stress
deduced from the lineament anomaly axes trending in ENE-WSW direction is taken as the stress
pattern for Biligirirangan domain (figure 8).
In Javadi-Kalrayan domain, the axial traces of folds were trending in N-S direction (figure
8) and hence, the greatest principal stress conceived from folds is in E-W direction. In the
eastern part of the same domain, the greatest principal stress is directed in WNW-ESE direction
and hence, the bulk strain varies from place to place within the domain. But, the lineament
anomaly axes are same in the entire domain and aligned in ENE-WSW direction (figure 9) which
is the acute bisector of NE-SW trending Precambrian dextral and WNW-ESE trending sinistral
faults. In Madras domain, the fold axes are trending in N-S in the northern part, NE-SW in the
central part and ENE-WSW in the southern part of the domain (figure 8) and these folds were
demonstrated to be flexuralslip folds (Balaji 1995). So, on the basis of principal finite elongation
of folds or bulk strain, the greatest principal stresses vary from place to place within the domain
in E-W direction in the northern part, NW-SE direction in the central part and NNW-SSE
direction in the southern part of the domain. But, the lineament anomaly axes are not varying
in the entire domain and maintain the same direction throughout the domain i.e in ENE-WSW
direction (figure 8). In Kolli-Pachai domain, the axes of folds are in NE-SW direction in
Manmedu, N-S direction south of Namakkal and NW-SE direction north of Namakkal but the
greatest principal stress deduced from the lineament anomaly axes is not varying but trending
in ENE-WSW direction which is the acute bisector of NE-SW trending Precambrian dextral and
WNW-ESE trending sinistral faults. The overall stress pattern for the entire northern Tamil Nadu
deduced from the bulk strain or the principal stresses deduced from bulk strain vary from place
to place in all the structural domains and is greately constrained by shallow and basement
irregularities. The greatest principal stresses deduced from the lineament anomaly axes do not
vary in all the structural domain and maintain the uniformity throughout the entire northern
Tamil Nadu of Peninsular India (figures 7, 8 and 9). The greatest principal stress derived from
the lineament anomaly axes directed in ENE-WSW trending Precambrian dextral faults is taken
as the regional stress pattern to cause the tectonic evolution of folds of northern Tamil Nadu
(Figure 9). Sugavanam et al. (1977) was of the opinion that Archaean-Precambrian piles of
southern Peninsular India have undergone five phases of deformation. Narayanasamy (1966),
Ramadurai et al. (1975), Katz (1978), Naga (1988) and Ramasamy et al. (1999) have suggested
two episodes of deformation for the tectonic evolution of folds of southern Peninsular India.
The newly presented tectonic model for northern Tamil Nadu, which is a part of southern
Indian Peninsula (figure 9) provided more evidence and supports the theory of two episodes of
deformation as postulated by (Ramasamy et al. 1999) for the tectonic evolution of whole of
southern Indian Peninsula.
6. Conclusion
The tectonic evolution of Precambrian granulite terrain of northern Tamil Nadu is
therefore attributed to two episodes of deformation. First compression is in N-S direction which
has caused cymatogenic arches and deeps from Cape-Comorin in the southern India upto the
Himalayas in the north (Ramasamy and Balaji 1995) and the second, most violent compression
trends in ENE-WSW direction, are responsible for the tectonic evolution of Precambrian fold
belts of northern Tamil Nadu.
Acknowledgement
The author is thankful to Prof.SM. Ramasamy, Vice-Chancellor, Gandhigram Central
University, Dindigul, India for his valuable guidance and suggestions.
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Tamil Nadu
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Structural trends
Tamil Nadu
Figure 1. Structural trends of northern Tamil Nadu (Interpreted from IRS - 1A satellite imagery)
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Figure 2. IRS 1A FCC satellite imagery of Attur valley
1. Doubly plunging fold 2.Structural trends 3.Vegetational alignments as lineaments
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Figure 3. IRS 1A FCC satellite imagery of Sankagiri dome
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6. Open fracture 7. Structural trends
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Figure 5. Fold styles of northern Tamil Nadu
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Legend
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Axes of isoclinal synclines
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Axes of isoclinal anticlines
12
00 '
Axes of lineament density maxima
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•
Axes of lineament density minima
Greatest principal stress computed from bulk
strain
Greatest principal stress computed from
lineament anomaly axes in ENE - WSW
78
00 '
Figure 7. Stress pattern in Biligirirangan domain
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80
N
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10
20 Km
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Dharmapuri
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B
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A
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C
12
00 ′
Chitteri
Shevroy
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13
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Javadi
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Madras
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13
00 ′
Kalrayan
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D
Manmedu
Namakkal
Kolli
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Pachai
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11
00 ′
11
00 ′
Legend
A
Biligirirangan domain
B
Javadi - Kalrayan domain
Domain boundaries
Greatest principal stress/Compressive force (From bulk strain)
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C
Madras domain
D
Kolli - Pachai domain
Hills
78
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Axial traces of synclines/Anticlines
Greatest principal stress in ENE – WSW (From lineament anomaly axes)
79
00 ′
Figure 8. Palaeostress environment of northern Tamil Nadu
80
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79
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80
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N
0
10
20 Km
13
00 ′
Madras
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13
00 ′
Vellore
Zone of domes and
basins and doubly
plunging folds
Zone of long and
linear tight to
moderate folds
Zone of tight isoclinal folds
Dharmapuri
•
12
00 ′
A
B
C
12
00 ′
11
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11
00 ′
Legend
A
B
C
Different structural domains
Domains boundaries
Greatest principal stress in ENE - WSW
Crystalline – sedimentary contact
Shoreline boundaries/continental margins
78
00 ′
79
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80
00 ′
Figure 9. Pattern of folds and regional stress field of northern Tamil Nadu