Application of Finite Strain Technique for Deformed Lithologies in Al Amar Suture, Eastern Arabian Shield

Abstract

Finite strain technique was applied for Abt schist, sheared granitoids and volcanosedimentary rocks exposed at Al Amar area, eastern Arabian Shield, in an attempt to decipher the relationship of these lithologies to nappe contacts and to clarify the nature of subhorizontal foliation pervasively recorded in the area. The R f /φ and Fry methods were utilized on quartz and feldspar porphyroclasts, as well as on mafic crystals, such as hornblende and biotite, in eighteen samples. The X/Z axial ratios ranged from 1.12 to 4.99 for R f /φ method and from 1.65 to 4.00 for Fry method. The direction of finite strain for the long axes displayed clustering along the WNW trend (occasionally N) with slight plunging. The Z axes were subvertical and associated with a subhorizontal foliation. The data revealed oblate strain symmetry (flattening) and the strain magnitudes showed no considerable increase towards the tectonic contacts. The obtained finite-strain data demonstrated that the sheared granitoids are mildly to moderately deformed. It is suggested that the accumulation of finite strain was not associated with any significant volume change. The penetrative subhorizontal foliation was concurrent with thrusting and showed nearly the same attitudes of tectonic contacts with the overlying nappes. Field relations and observations, together with finite stain data, are inconsistent with the proposed idea that nappes in orogens resulted from simple-shear deformation.