Strain analysis and deformation history of Zalm area, Arabian shield, Saudi Arabia

Abstract

The present work deals with the strain analysis and deformation of the Zalm area which is located in the central part of the central Nabitah suture belt, which separates the continental Afif terrane from the ensimatic arc terranes of the western Arabian Shield. This study carried out through field investigation, strain parameters, and microscopic examination for understanding the nature of deformation in the Zalm area. On the basis of the field investigation and the geometry of the contact, it is more likely that the contact between ultramafic rocks and gabbroic rock complex is low-angle thrust faulting. The granitoid rocks are divided into the quartz monzodiorite, monzogranite, alkali-feldspar granite and leucocratic-granodiorite. The Rf/ϕ and Fry techniques on feldspar and mafic grains from 53 samples representative of each rock type were collected in the field. Strain data shows that the deformation of the granitic, metavolcanic and amphibole schist samples range from high to moderate. The axial ratios (XZ section) range from 1.60 to 4.10 for the Rf/ϕ method and 2.80 to 4.90 for the Fry method. Furthermore, the finite strain data does not dispay any significant difference in the deformation behavior between Rf/ϕ and Fry methods. We concluded that the strain magnitude has the same order of deformation in the deformed granitoid and amphibole schist rocks. The majority of samples are in a zone of flattening symmetry, while a few samples are showing constrictional symmetry. In addition, it is noted that the short axes (Z) are sub-perpendicular related with a sub-parallel foliation. Furthermore, the nappe contact are designed during the intrusion of plutons associated with faults in the Zalm regions under brittle to semi-ductile deformation conditions.