Strain Pattern Analysis of Mylonites From Sitampundi-Kanjamalai Shear Zone, Thiruchengode, South India

  • Thirukumaran V Department of Geology, Government Arts College, Salem-636 007, Tamil Nadu, India
  • Biswal T.K Department of Earth sciences, IIT Bombay, Poway, Mumbai, India.
  • Sundaralingam K Department of Geological Survey of India, Hyderabad, India.
  • Sowmya V Department of Geology, Government Arts College, Salem-636 007, Tamil Nadu, India
  • Boopathi S Department of Geology, Government Arts College, Salem-636 007, Tamil Nadu, India
  • Mythili R Department of Geology, Government Arts College, Salem-636 007, Tamil Nadu, India
Keywords: Mylonite, SASZ, Strain pattern, Vorticity, Kinematic analysis, Pure shear, Bulk strain


This study aims to investigate the petrography and strain pattern of mylonites from parts of N-S trending Sitampundi-Kanjamalai Shear Zone (SKSZ) around Thiruchengode. The petrographic study indicates the presence of recrystallized quartz, K-feldspar, plagioclase, biotite and some hornblende. The kinematic analysis of Mylonites was done with the help of shear sense indicators such as recrystallized type quartz (quartz ribbon) around the cluster of feldspar, S-C fabric shows dextral shear sense and some sinisterly shear sense in some parts of SASZ which can be considered as a product of partitioning of both strain and vorticity between domains. These all indicates the simple shear extension along E-W direction and the mylonitic foliation shows the pure shear compression along N-S direction. Further the study of bulk strain analysis by Flinn plot method using L and T section of mylonite shows k<1 which lies in the field of flattening zone of finite strain. The kinematic vorticity number is calculated by Rxz/β method which gives the value of 0.36 indicating the general shear. The rigid grain graph shows that the pure shear component is more ­­­­dominant than the simple shear component. The analysis leads to the conclusion that the mylonite has experienced a high temperature shearing of above 700°cat deep crustal level.


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R.H. Sibson, Fault rocks and fault mechanisms, J. Geol. Soc., 133 (1977) 191-213.

R. A. J. Trouw, C.W. Passchier, D.J. Wtersma, Atlas of Mylonites and related microstructures, Springer-Verlag Berlin Heidelberg, (2009)

Lister, Snoke, S-C Mylonite, J Struct Geol, 6 (1984) 617-638.

David C Greene, Richard A Schweickert, The Gem Lake shear zone: Cretaceous dextral transpression in the northern Ritter Range pendant, eastern Sierra Nevada, California, Tectonics. 14 (1995) 945-961.

T.H. Bell, M.A. Etheridge, Microstructure of mylonites and their descriptive terminology, Lithos. 6 (1973) 337-348.

N. B. W. Harris, M. Santosh, P. N. Talor, Crustal evolution in south India: Constraints from Nd isotopes, J. Geol, 102 (1994) 139-150.

Joy Gopal Ghosh, Maarten J. de Wit, and R. E. Zartman, Age and tectonic evolution of Neoproterozoic ductile shear zones in the Southern Granulite Terrain of India, with implications for Gondwana studies, Tectonics. 23 (2004) 1-38.

K.Naha, R.Srinivasan, Nature of the Moyar and Bhavani shear zones, with a note on its implication on the tectonics of the southern Indian Precambrian shield, Proceedings of the Indian Academy of Sciences - Earth and Planetary Sciences, (1996).

S.A. Drury, N.B.W. Harris, R.W. Holt, G.J. Reeves-Smith, R.T. Wightman, Precambrian tectonics and crustal evolution in South India, J. Geol, 92 (1984) 3-20.

K.S. Valdiya, Late Quaternary movement and landscape rejuvenation in SE Karnataka and adjoining TN in south Indian shield, Jour. Geol. Soc. India, 51 (1998) 139-166.

T. Yellappa, M. Santosh, T.R.K. Chetty, S. Kwon, C. Park, P. Nagesh, D.P. Mohanty, V. Venkatasivappa, A Neoarchean dismembered ophiolite complex from southern India: geochemical and geochronological constraints on its suprasubduction origin, Gondwana. Res, 21 (2012) 246-265.

C.W. Passchier, R.A.J. Trouw, (1996) Micro tectonics, Springer-Verlag, Berlin, Germany,

C.M. Bailey, E.L. Eyster, General shear deformation in the Pinaleño Mountains metamorphic core complex, Arizona, J. Struct. Geo., 25 (2003) 1883-1892.

J. F. Hippertt, F.D.Hongn, Deformation mechanisms in the mylonite/ultramylonite transition, J. Struct. Geo., 20 (1998) 1435-1448.

J.G. Ramsay, D. S. Wood, The geometric effects of volume change during deformation processes, Tectonophys. 13 (1973) 263-277.

C.M. Bailey, C. Simpson, D.G. De Paor, Volume loss and tectonic flattening strain in granitic mylonites from the Blue Ridge province, central Appalachians, J. of Struct. Geo. 16 (1993) 1403-1416.

P. Xypolias, Vorticity analysis in shear zones: A review of methods and applications, J. Struct. Geo. 32 (2010) 2072-2092.

W.D. Means, B.E. Hobbs, G.S. Lister, P.F. Williams, Vorticity and non-coaxialityinprogressive deformation, J. Struct. Geol, 2 (1980) 371-378.

R.Satheesh Kumar, V.Prasannakumar, Fabric Evolution in Salem- Attur Shear Zone, South India and its Implications on the kinematics, Gondwana Res. 16 (2009) 37-44.