Finite strain analysis for deformed Neoproterozoic rock associations of the Al Amar fault zone, Eastern Arabian Shield, Saudi Arabia

Abstract

The Al Amar area has played important role to effect the Al Amar–Idsas fault zone, which consists of a sequence of volcanic rocks and sedimentary detrital. Also, it is characterized by a difference in facies with intruded granitoid bodies. The present work has used the finite strain techniques to investigate the relationship of the different lithologies and nappe contacts, which recorded in the Al Amar area. Furthermore, the microstructural analysis has investigated the Abt schist, deformed granitoids, and metavolcanic-sedimentary rocks, which represented the Al Amar area. The axial ratio results average from 1.55 to 2.87 for the Rf/φ method and 1.43 to 7.51 for the Fry method in the XZ sections for metamorphic rocks. In the finite strain data, the long axes direction (X) displays grouping along a NW–SE trend with shallow plunging. The direction of short axes (Z) displays subvertical and accompanied with a subhorizontal foliation. Our strain measurement reveals that strain symmetry shows an oblate shape (flattening) and the strain magnitudes do not display any valuable increasing towards the tectonic nappe contacts. Also, it is indicated that the volume change in the different rock units was unassociated with the accumulation of finite strain. In the investigated area, the subhorizontal foliation in the different lithologies was parallel to thrusting. Furthermore, it shows mainly the similar attitudes for tectonic contact nappes. In the present work, it is suggested that the ductile strain is accumulated during thrusting and involves as vertical shortening component with the subhorizontal foliation. The field observations with finite stain data are not sufficient to decide that the tectonic contact in the orogeny is formed as the simple-shear deformation.