Relationship between finite strain and tectonic setting in the Ar-Ruwaydah area, eastern Arabian Shield, Saudi Arabia

Abstract

Our work deals with structural characteristics of the Ar-Ruwaydah area, which lie between the Al Amar–Idsas fault and the Halaban belt. Our goals are accomplished through field reconnaissance and finite strain analysis, as well as microstructural investigation to estimate the tectonic evolution and structures in the Ar-Ruwaydah area. Our strain data show that Abt schist, metavolcano-sedimentary rocks, and granitic gneiss are characterized by weak to moderate deformation, and the axial ratios for the XZ section range from 1.55 to 2.22. The long axes for ellipsoids (X) have NW–SE and W–E trend directions in the Ar-Ruwaydah area while their short axes (Z) are subhorizontal to subvertical foliations. The strain magnitude does not display any increase towards the tectonic contacts for varying rocks units. Most of the obtained data indicate a dominant oblate with minor prolate strain symmetries in the Abt schist and metavolcano-sedimentary and metagranite rocks. The strain data also display flattening with some constriction. It is concluded that Abt schist, granitic gneiss, and metavolcano-sedimentary rocks have the same deformation behavior. Our finite strain accumulated during the metamorphism which was investigated by thrusting activity in the studied rocks. Furthermore, the nappe contact for different types of rock formed during thrusting activity and intrusion of granitic plutons under semi-brittle to ductile deformation conditions in the Ar-Ruwaydah area.