Strain analysis using structural elements and geometry of surfaces of no finite longitudinal strain
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ORIGINAL PAPER
Strain analysis using structural elements and geometry of surfaces of no finite longitudinal strain Babak Samani
Received: 17 October 2014 / Accepted: 6 February 2015 # Saudi Society for Geosciences 2015
Abstract In this research, using structural elements and the geometry of surfaces of no finite longitudinal strain, crustal shortening and strain analyses have been carried out between two thrust faults in the Khon-Khoreh area in the north of Dehbid. The direction of the principal axes of the finite strain ellipsoid was defined using stereographic analyses of pole of foliation and lineation. With separation of shortening and longitudinal strain domains, the geometry of surfaces of no finite longitudinal strain was determined in 3D. The results of stereographic analyses and angular relations of surfaces of no finite longitudinal strain on the XZ and XY principal planes of strain ellipsoid show the amounts of 2Φ angle as: 48°< 2ΦXZ WK >0) (Passchier and Trouw 2005). Pure and simple shearing components contribute equally to the instantaneous flow at WK =0.71 (Law et al. 2004). There are several methods for determination of the kinematic vorticity number (Tikoff and Fossen 1995; Wallis 1995; Bailey and Eyster 2003). The northeastern and southwestern boundaries of the study area are coinciding to the thrust faults. The average strike of the thrust faults (N50°W) was assumed as reference lines. It is possible to determine the amount of kinematic vorticity number using (Rxz-θ) nomogram (Bailey et al. 1999). Rxz and θ are strain ratio in the XZ principal plane of strain ellipsoid and the angle between long axes of the strain ellipsoid related to the reference line, respectively. With application of (Rxz-θ-k-γ) nomogram (Tikoff and Fossen 1993) and using of Rxz and k values, the amounts of θ were determined between 3° to 12° (Fig. 10). Therefore, two basic parameters (Rxz and θ) for determination of the kinematic vorticity number were obtained. Finally, with application of (Rxz-θ) nomogram (Bailey et al. 1999), the amounts of WK were
determined (0.93≥WK ≥0.6) (Fig. 11) that show simple shear dominant strain in the study area. The significant shortening in the Zagros orogeny is related to convergence between AfroArabian continent and Iranian microcontinent. An analytical solution and graphical function to determination of shortening have been given by Wallis (1992) and Passchier (1988), respectively. Using the Rxz and WK values and application of the graphical function of (Stretch-Rxz-WK) (Passchier 1988), the amounts of shortening were determined between 0.4 and 0.7 (Fig. 12a). Figure 12b shows the percent amounts of the shortening in the area (30 to 60 %).
Fig. 9 Ellipsoid shape analyzed by plotting the finite strains for XY and YZ principal sections on a Ramsay diagram
Fig. 10 Determination of the angle θ with application of (Rxz-θ-k-γ) nomogram (Tikoff and Fossen 1993)
Discussion Finding the proper markers is the most important factor in the strain studies. In many cases, the lack of strain markers
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