Modification of fold geometry in Almora Crystalline Shear Zone, Lesser Himalaya, India

Abstract

The folds generally initiate at several discrete points along a layer or multilayer undergoing compressional forces. These compressional forces often lead to rotation of fold segments and in all such regimes, folds are strongly asymmetrical and are in complete agreement with the direction in which the force is applied and also with the related thrust sheet movement. This paper illustrates the progressive change in fold geometry with increasing compression and ductile shearing using natural example as studied in the Almora Crystalline Zone (ACZ).

The folds in the ACZ have started developing initially by the buckling processes as upright folds with varying degrees of inter-limb angles, which later on with increasing amount of ductile shearing modified in to tight to isoclinal and overturned to recumbent folds.

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References

  1. Agarwal, K.K. (1986) Some observations on the nature of the Almora Synform with special reference to the southern limb in Mukteshwar-Paharpani area, Kumaun Lesser Himalaya. Geosci. Jour., v. vii(1), pp.43–48.

    Google Scholar 

  2. Agarwal, K.K. (1994) Tectonic Evolution of the Almora Crystalline Zone, Kumaun Lesser Himalaya: A reinterpretation. Jour. Geol. Soc. India, v.43(1), pp.5–14.

    Google Scholar 

  3. Agarwal K.K. and Bali, R. (2008) Small-scale deformational structures as significant shear-sense indicators: An example from Almora Crystalline Zone, Kumaun Lesser Himalaya. Earth Sci. India, v. I(III), pp.161–172.

    Google Scholar 

  4. Agarwal, K.K. and Bhattacharya, A.R. (1987) Structural studies in the Almora Crystalline Zone of the Mukteshwar-Paharpani area, Kumaun Himalaya. In: V. K. Gairola (Ed.), Proc. Nat. Sem. Ter. Orogeny in Indian Subcontinent Varanasi, pp.1–9.

  5. Bali, R. and Agarwal, K.K. (1999) Microstructures of Mylonites in the Almora Crystalline Zone, Kumaun Lesser Himalaya. Gond. Res. Gr. Mem., v.6, pp.111–116.

    Google Scholar 

  6. Bali, R. and Bhattacharya, A.R. (1988) Geological and Structural studies of the rocks of the Dwarahat-Chaukhutia area, Kumaun Lesser Himalaya with special reference to the North Almora Fault. Geosci. Jour.,v.ix, pp. 215–230.

    Google Scholar 

  7. Berthe, D. and Brun, J.P. (1980) Evolution of folds during progressive shear in the South Armorican Shear Zone, France. Jour. Struct. Geol., v.2, pp. 127–133.

    Article  Google Scholar 

  8. Berthe, D., Choukroune, P. and Jegouzo, P. (1979) Orthogneiss, mylonite and noncoaxial deformation of granites: the example of South Armorican Shear Zone. Jour. Struct. Geol., v.1, pp.31–42.

    Article  Google Scholar 

  9. Bhattacharya, A.R. and Agarwal, K.K. (1985) Mylonites from the Kumaun Lesser Himalaya. Neu. Jahr. für Miner. Abh., v.152(1), pp.65–77.

    Google Scholar 

  10. Bhattacharya, A.R. and Agarwal, K.K. (1989) Strain analysis and fold shape modification in a crystalline complex of the Lesser Himalaya. Krystallinikum, v.20, pp.7–25.

    Google Scholar 

  11. Choukroune, P. and Gapais, D. (1983) Strain pattern in the Aar granite (Central Alps): orthogneiss developed by bulk homogeneous flattening. Jour. Struct. Geol., v.5, pp.411–418.

    Article  Google Scholar 

  12. Coward, M.P. (1976) Strain within ductile shear zones. Tectonophysics, v.34, pp.181–197.

    Article  Google Scholar 

  13. Gansser, A. (1964) Geology of Himalaya. Interscience, London, 289p.

    Google Scholar 

  14. Ghosh, S.K. and Sengupta, S. (1984) Successive development of plane non-cylindrical folds in progressive deformation. Jour. Struct. Geol., v.6(6), pp.703–709.

    Article  Google Scholar 

  15. Ghosh, S.K. and Sengupta, S. (1987) Progressive development of structures in a ductile shear zones. Jour. Struct. Geol., v.9(3), pp.277–287.

    Article  Google Scholar 

  16. Lister, G. S. and Williams, P. F. (1983) The partitioning of deformation in flowing rock masses. Tectonophysics, v.92, pp.1–33.

    Article  Google Scholar 

  17. Mehdi, S. H., Kumar, G. and Praksh, G. (1972) Tectonic evolution of Eastern Kumaun Himalaya: A new approach. Him. Geol., v.2, pp.481–501.

    Google Scholar 

  18. Merh, S.S. and Vashi, N.M. (1976) The problem of the South Almora Thrust. Him. Geol., v.6, pp. 508–516.

    Google Scholar 

  19. Misra, R.C. and Sharma, R.P. (1972) Structure of Almora Crystalline, Lesser Kumaun Himalaya. An interpretation. Him. Geol., v.2, pp.330–341.

    Google Scholar 

  20. Ramsay, J.G. and Graham, R.H. (1970) Strain variation in shear belts. Can. Jour. Earth Sci., v.7, pp.786–813.

    Google Scholar 

  21. Ramsay, J.G. and Huber, M.I. (1987) The techniques of modern structural geology. v.2: Folds and Fractures, 700p.

  22. Simpson, C. (1983) Strain and shape fabric variation associated with ductile shear zones. Jour. Struct. Geol., v.5, pp.61–72.

    Article  Google Scholar 

  23. Srikantia, S.V. (1988) Himalayan thrusts and structural belts. Jour. Geol. Soc. India, v.31(2), pp.210–229.

    Google Scholar 

  24. Srivastava, H.B. (2003) Estimation of strain from concentric folds. Tectonophysics, v.364, pp.237–241.

    Article  Google Scholar 

  25. Srivastava, H.B and Tripathy, N.R. (2005) Shear zone structures from the Main Central Thrust Zone of the Joshimath area Garhwal Himalaya. In: A.R. Bhattacharya, and K.K. Agarwal (Eds.), Himalayan Orogen Foreland Interaction. Pal. Soc. India, Spec. Publ., no.2, pp.53–64.

  26. Srivastava, H.B. and Tripathy, N.R. (2007) Geometric analysis of mesoscopic shear zones in the crystalline rocks of MCT Zone of Garhwal Higher Himalaya. Jour. Asian Earth Sci., v.30, pp.599–612.

    Article  Google Scholar 

  27. Srivastava, P. and Mitra, G. (1996) Deformation mechanism and inverted profile in the North Almora Thrust mylonite zone, Kumaon Lesser Himalaya, India. Jour. Struct. Geol., v.18, pp.27–39.

    Article  Google Scholar 

  28. Valdiya, K.S. (1979) An outline of the structural set-up of the Kumaun Himalayas. Jour. Geol. Soc. India, v.20, pp.145–151.

    Google Scholar 

  29. Valdiya, K.S. (1980) Geology of the Kumaun Lesser Himalaya. Wadia Inst. Him. Geol., Dehradun, 291p.

    Google Scholar 

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Correspondence to K. K. Agarwal.

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Agarwal, K.K., Jahan, N. & Agarwal, A. Modification of fold geometry in Almora Crystalline Shear Zone, Lesser Himalaya, India. J Geol Soc India 75, 411–414 (2010). https://doi.org/10.1007/s12594-010-0037-5

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Keywords

  • Fold geometry
  • Shear zones
  • Almora Crystalline Zone