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Sengupta, Siladitya
- Synchronous Development of Mylonite and Pseudotachylyte in Ductile Shear Zone: An Example from the Chitradurga Eastern Margin Shear Zone, Karnataka
Authors
1 Geological Survey of India, Eastern Region, Salt Lake City, Kolkata-700091, IN
2 Geological Survey of India, CGL, CHQ, Kolkata-700016, IN
3 Geological Survey of India, Antarctica Division, Faridabad-121001, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 72, No 4 (2008), Pagination: 447-457Abstract
The eastern margin of the Chitradurga schist belt is marked by a NNW-SSE trending sub vertical crustal scale ductile shear zone. The kinematic indicators indicate a predominant sinistral sense of strike-lip movement along the shear zone. Syntectonically emplaced granitic rocks are converted to mylonites and ultramylonites as a result of crystalplastic deformation in the shear zone. In contrast, there are localized zones of brittle failure with attendant functional heat generation exemplified by the development of thin but conspicuous bands and veins of pseudotachylytes, which are emplaced either subparallel with or transgressing the C-planes of the mylonites. From our field and petrographic studies it is interpreted that these two coexisting rock types, namely the mylonite and pseudotachylyte, which are the results of contrasting deformational mechanisms, have generated near synchronously in a progressively developed ductile shear zone. The pseudotachylytes represent the brief interlude of sudden increase in strain rate in an overall ductile regime.Keywords
Ductile, Brittle, Shear Zone, Mylonite, Pseudotachylyte, Chitradurga, Karnataka.
- Tectonic Amalgamation of Crustal Blocks along Gadag-Mandya Shear Zone in Dharwar Craton of Southern India
Authors
1 Geological Survey of India, 15 Kyd Street, Kolkata - 700 016, IN
2 Presidency University, Kolkata, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 80, No 1 (2012), Pagination: 75-88Abstract
The crustal scale Shear Zone that can be traced from Gadag in the north to Mandya in the south in Dharwar Craton of southern India is considered as the boundary between two subcratonic blocks namely the Eastern Dharwar Craton (EDC) and the Western Dharwar Craton (WDC) in published literature. The present study on the Gadag-Mandya Shear Zone (GMSZ) in the Javanahalli-Hagalvadi sector has brought out a detailed account on the disposition, geometry and kinematics of the shear zone, and also the distinctive structural patterns of the two adjacent supracrustal belts, namely the Chitradurga schist belt (CSB) in the west and Javanahalli schist belt (JSB) in the east. The JSB has an overall N-S striking and gentle easterly dipping geometry, the structural features of which are indicative of a predominant non-coaxial deformation and westward transportation of the supracrustal assemblage. In contrast, deformation in the CSB, which is defined mainly by a flattening type of strain, has produced an overall verticality of the structures (dominant foliation, axial planes of regional folds).
Difference in metamorphic grade is apparent from the mineral assemblages in the rocks of these two belts, while the JSB showing an amphibolite facies CSB is restricted to green schist facies mineral assemblages.
The 2 to 3 km wide, N-S striking, prominent ductile shear zone, GMSZ, has affected both CSB and JSB rocks and also the syntectonically emplaced Bukkapatna granite. The geometric and kinematic evidences from both the belts and the GMSZ point to an E-W horizontal compressional regime. The gentle dipping, amphibolite grade JSB and its underlying gneisses acted as an allochthon which got amalgamated with the subvertical, green schist grade CSB by a top-W thrusting along the GMSZ. The subvertical CSB impeded further up-dip movement of the eastern block, resulting in the subsequent development of N-S trending sinistral strike slip shear along the contact of the two contrasting belts to accommodate the continued E-W compression. The linear Bukkapatna Granite, synkinematically emplaced along GMSZ shows evidences of both magmatic stage and solid state deformation in the shear zone.
Keywords
Amalgamation, Shear Zone, Syntectonic Granite, Javanahalli, Chitradurga, Karnataka.References
- CHADWICK, B., RAMAKRISHNAN, M. and VISWANATHA, M.N. (1981a) The structure and stratigraphy of the Chitradurga Region: an illustration of cover-basement interaction in the Late Archaean evolution of Karnataka Craton, South India. Precambrian Res., v.16, pp.31-54.
- CHADWICK, B., RAMAKRISHNAN, M., VASUDEV, V.N. and VISWANATHA, M.N. (1989) Facies distributions and structure of a Dharwar volcanosedeimentary basin: evidence for Late Archaean transpression in southern India. Jour. Geol. Soc. London, v.146, pp.825-834.
- CHADWICK, B., VASUDEV, V.N. and HEGDE, G.V. (2000) The Dharwar Craton, Southern India, Interpreted as Late Archaean oblique convergence. Precambrian Res., v.99, pp.91-111.
- CHADWICK, B., VASUDEV, V.N. and HEGDE, G.V. (2003) The Chitradurga Schist Belt and its Adjacent Plutonic Rocks, NW of Tungabhadra, Karnataka: A Duplex in the Late Archaean Convergent Setting of the Dharwar Craton. Jour. Geol. Soc. India, v.61, pp.645-663.
- CHADWICK, B., VASUDEV, V.N., HEGDE, G.V. and NUTMAN, A.P. (2007) Structure and SHRIMP U/Pb Zircon Ages of Granites Adjacent to the Chitradurga Schist Belt: Implications for Neoarchaean Convergence in the Dharwar Craton, Southern India. Jour. Geol. Soc. India, v.69, pp.5-24.
- CHARDON, D., CHOUKROUNE, P.L. and JAYANANDA, M. (1996) Strain patterns, decollement and incipient sagducted greenstone terrains of Archaean Dharwar Craton, South India. Jour. Struct. Geol., v.18, pp.991-2004.
- CHARDON, D., CHOUKROUNE, P. and JAYANANDA, M. (1996) Sinking of the Dharwar Basin (South India): Implications for Archaean tectonics. Precambrian Res., v.91, pp.15-39.
- CHOUKROUNE, P., BOUHALLIER, H. and ARNDT, N.T. (1995) Soft lithosphere during periods of Archaean crustal growth or crustal reworking. In: M.P. Coward and A.C. Reis (Eds.), Early Precambrian processes. Geol. Soc. Spec. Publi., v.95, pp.67-86.
- CHOUKROUNE, P. LUDEN, J.N., CHARDON, D., CALVERT, and A.J. and BOUHALLIER, H. (1997) Archaean crustal growth and tectonic processes: a comparioson of the Superior Province, Canada and the Dharwar Province, India. In: J.P. Burge and M. Ford (Eds.), Orogeny through time. Geol. Soc. Spec. Publ., v.121, pp.63-98.
- DRURY, S.A. (1983) A regional tectonic study of the Archaean Chitradurga greenstone belt, based on LANDSAT interpretation. Jour. Geol. Soc. India, v.24, pp.167-184.
- DRURY, S.A. and HOLT, R.W. (1980) The tectonic framework of the south Indian craton: a reconnaissance involving LANDSAT imagery. Tectonophysics, v.65, pp.T1-T15.
- GHOSH ROY, A.K. and RAMAKRISHNAN, M. (1985) Stratigraphic status of Javanahalli belt in the Archaean geology of Karnataka. Jour. Geol. Soc. India, v.26, pp.567-579.
- JAYANANDA, M., MOYEN, J.F., MARTIN, H., PEUCAT, J. J., AUVRAY, B. and MAHABALESHWAR, B. (2000) Late Archaean (2550-2520 Ma) juvenile magmatism in the Eastern Dharwar craton, southern India: constraints from geochronology, Nd-Sr isotopes and whole rock geochemistry. Precambrian Res., v.99, pp.229-254.
- KAILA, K.L., ROY CHOWDHURY, K., REDDY, P.R., KRISHNA, V.G., NARAIN, H., SUBBOTIN, S.I., SOLLUGUB, V.B., CHEKUNOV, A.V., KHARETCHIKO, G.E., LAZARENKO, M.A. and ILCHENKO, T.V. (1979) Crustal structure along Kavali-Udupi profile in the Indian Peninsular shield from deep seismic soundings. Jour. Geol. Soc. India, v.20, pp.307-333.
- MUKHOPADHYAY, D. and BARAL, M.C. (1985) Structural Geometry of the Dharwar rocks near Chitradurga. Jour. Geol. Soc. India, v.26, pp.547-566.
- MUKHOPADHYAY, D., BARAL, M.C. and GHOSH, D. (1981) A tectonostratographic model of Chitradurga schist belt. Jour. Geol. Soc. India, v.22, pp.22-31.
- MUKHOPADHYAY, D. and GHOSH, D. (1983) Superposed deformation in Dharwar rocks in southern part of the Chitradsurga schist belt, Karnataka. In: S.M. Naqvi and J.J.W. Rogers (Eds.), Precambrians of South India. Mem. Geol. Soc. India, no.4, pp.275-292.
- NAHA, K., MUKHOPADHYAY, D., DASTIDAR, S. and MUKHOPADHYAY, R.P. (1995) Basement- cover relations between a granite gneiss body and its metasedimentary envelope: a structural study from the Early Precambrian Dharwar tectonic province, southern India. Precambrian Res., v.72, pp.283-429
- PASSCHIER, C.W. and TROUW, A.J. (2005) Micro-tectonics, 2nd Ed, Springer, Germany.
- ROLLINSON, H.R., WINDLEY, B.F. and RAMAKRISHNAN, M. (1981) Contrasting high and intermediate pressures of metamorphism in the Archaean Sargur schists of southern India. Contrib. Mineral. Petrol., v.75, pp.420-429.
- ROY, A., SENGUPTA, S. and MANDAL, A. (2008) Synchronous development of mylonite and pseudotachylyte: an example from the Chitradurga Eastern Margin Shear Zone, Karnataka. Jour. Geol. Soc. India, v.72, pp.447-457.
- SHACKLETON, R.M. (1995) Tectonic evolution of greenstone belts. In: M.P. Coward and A.C. Ries (Eds.), Early Precambrian Processes. Geol. Soc. Spec. Publi., no.95, pp.53-65.
- SHESHADRI, T.S., CHAUDHURI, A. HARINADHA BABU, P. and CHAYAPATHI, N. (1981) Chitradurga belt. In: Precambrian supracrustals of southern Karnataka. Mem. Geol Surv India, v.112, pp.163-198.
- SWAMI NATH, J., RAMAKRISHNAN, M. and VISWANATHA, M.N. (1976) Dharwar stratigraphic model and Karnataka craton evolution. Rec. Geol. Surv India, v.107, part 2, pp.149-175.
- VISWANATHA, M.N. and RAMAKRISHNAN, M. (1975) The Pre-Dharwar supracrustal Rocks of Sargur Schist Complex in southern Karnataka and their Tectono-Metamorphic Significance. Indian Mineralogist, v.16, pp.48-65.