Structural and Mechanical Controls on Intrusion Related to Mahd Ad Dahab Area, Arabian Shield, Saudi Arabia

Abstract

Mahd Ad Dahab area is located on the western side of the Arabian Precambrian Shield. In the study area, Mahd group rocks are deposited along margin of active extensional volcanotectonic basin. These rocks are associated with the major geologic structures which are attributed to various deformational stages of the Precambrian basement. Field geology, finite strain and microstructural studies were carried out and the relationships between the lithological contacts and major/minor structures have been studied. The Rf/φ and Fry methods on the metavolcano-sedimentary samples from 3 andesite samples, 2 lower agglomerate samples, 7 lower rhyolite samples, 3 upper agglomerate, 1 upper tuff sample and 2 rhyolite porphyry samples were used in Mahd Ad Dahab area. Finite-strain data shows that a low to moderate range of deformation of the metavolcanosedimentary samples and axial ratios in the XZ section range from 1.10 to 2.50 for the Rf/φ method and from 1.15 to 2.35 for the Fry method. Furthermore, the short axes are subvertical associated with a subhorizontal foliation. We conclude that finite strain in the deformed rocks is of the same order of magnitude for all units of metavolcano-sedimentary rocks. Furthermore, contacts formed during intrusion of plutons with some faults in the Mahd Ad Dahab area under brittle to semi-ductile deformation conditions. In this case, finite strain accumulated during superimposed deformation on the already assembled nappe structure. It indicates that the nappe contacts formed during the accumulation of finite strain.