Document Type : Original Research Paper


Assistant Professor, Department of Mining Engineering, Faculty of Mining, Civil and Chemistry, Birjand University of Technology, Birjand, Iran


The Bahlgerd shear zone in the northern margin of Bagheran Mountain is separated Eocene flysch from the Cretaceous ophiolite sequence and Quaternary sediments by southern Birjand and Bahlgerd faults. In the deformation evaluation , sigmoidal array arrays located in sandstone units have been used as strain markers. Based on the geometry of these arrays, the mathematical equations and R-θ' diagrams of the strain parameters were estimated. The mean values of shear strain (γ), volume change (∆) and convergence across the zone (K) are 0.45, -0.26 and 0.85, respectively. The plotting strain ellipses on the logarithmic Flinn diagram are in the field of flattening, which indicates the simultaneous simple shear and compaction in the region and show a volume reduction of up to 30%. Also, in the Bahlgerd shear zone, the value of θ'> 45 ° and cleavages are created in the direction perpendicular to the opening of the veins, which conforms to the characteristics of the compactional simple shear model. The horizontal strain parameters in the transpression model have similar values the compactional simple shear model. Based on the calculated convergence parameter (0.39), Behlgard shear zone is in the category of slightly convergence zones in which the amount of shortening


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Baird, G. B. and Hudleston, P., 2007- Modeling the influence of tectonic extrusion and volume loss on the geometry, displacement, vorticity, and strain compatibility of ductile shear zones. Journal of Structural Geology, Vol. 29, pp. 1665–1678,
Bhattacharyya, P. and Hudleston, P., 2001- Strain in ductile shear zones in the Caledonides of northern Sweden: a three-dimensional puzzle. Journal of Structural Geology, Vol. 23, pp. 1549e1565,
Coward, M. P., 1976- Strain within ductile shear zones. Tectonophysics, Vol. 34, pp. 181–197,
Davis, G.H., Reynolds, S.J. and Kluth, Ch.F., 2012- Structural geology of rocks and regions. J. Wiley and Sons press, 861 p.
Eftekhar Nezhad, J., Ohanian, T., Tatevosian, S., Manouchehri, M., Afaghi, A., Hosseini, Z., Qomashi, A., Afsharian Zadeh, A. and Etemadi, N., 1986- Geological Map of Birjand, Scale: 1:100,000, Geological Survey of Iran, Tehran,
Flinn, D. 1962- On folding during three-dimensional progressive deformation. Quarterly Journal of the Geological Society of London, Vol. 118, pp. 385-433,
Fossen, H. and Tikoff, B., 1998- Extended models of transpression and transtension, and application to tectonic settings. Geological Society, London, Special Publications, Vol. 135, pp. 15–33,
Fossen, H. and Tikoff, B., 1993- The deformation matrix for simultaneous simple shearing, pure shearing, and volume change, and its application to transpression/transtension tectonics. Journal of Structural Geology, Vol. 15, pp. 413–422,
Krantz, R.W., 1995- The transpressional strain model applied to strike-slip, oblique-convergent and oblique-divergent deformation. Journal of Structural Geology, Vol. 17, pp. 1125–1127,
Lisle, R. J., 2013- Shear zone deformation determined from sigmoidal tension gashes. Journal of Structural Geology, Vol. 50, pp. 35-43,
Lister, G. S. and Snoke, A. W., 1984- S-C mylonites. Journal of Structural Geology, Vol. 6, pp. 617–638,
Nicholson, R. and Pollard, D., 1985- Dilation and linkage of echelon cracks. Journal of Structural Geology, Vol. 7, pp. 583-590,
Passchier, C.W., 1986- Flow in natural shear zones - the consequences of spinning flow regimes. Earth and Planetary Science Letters, Vol. 77, pp. 70–80,
Ramberg, H., 1975- Particle paths, displacement and progressive strain applicable to rocks. Tectonophysics, Vol. 28, pp. 1–37,
Ramsay, J. G. and Graham R.H., 1970- Strain variation in shear belts. Canadian Journal of Earth Sciences, Vol. 7, pp. 786-813,
Ramsay, J.G. and Huber, M.I., 1983- The techniques of modern structural geology. Volume1: Strain analysis. Academic Press, London, 307 p,
Ramsay, J. G., 1980- Shear zone geometry: a review. Journal of Structural Geology, Vol. 2, pp. 83–99,
Sanderson, D. and Marchini, R.D., 1984- Transpression. Journal of Structural Geology, Vol. 6, pp. 449–458,
Sibson, R. H., 1977- Fault rocks and fault mechanisms. Journal of the Geological Society, Vol. 133, pp. 191–213,
Simpson, C. and De Paor, D. G., 1993- Strain and kinematic analysis in general shear zones. Journal of Structural Geology, Vol. 15, pp. 1-20,
Tikoff, B. and Fossen, H., 1993- Simultaneous pure and simple shear: the unified deformation matrix. Tectonophysics, Vol. 217, pp. 267–283,
Walker, R. and Khatib, M. M., 2006- Active faulting in the Birjand region of NE Iran: Tectonics, Vol. 25, TC4016,
Wilson, G. and Cosgrove, J. W., 1982- Introduction to Small-scale Geological Structures. Allen and Unwin, London. 128 p,
Zarrinkoub, M. H., Pang, K. N., Chung, S. L., Khatib, M. M., Mohammadi, S. S., Chiu, H. Y. and Lee, H. Y., 2012- Zircon UPb age and geochemical constraints on the origin of the Birjand ophiolite, Sistan suture zone, eastern Iran. Lithos, Vol. 154, pp. 392–405,