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

Osama M. K. Kassem, Abdel Aziz M. Al Bassam, Faisal K. Zaidi

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.

Keywords


Finite strain, Microstructural, Mahd Ad Dahab area, Arabian Shield, Saudi Arabia

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