Emplacement levels and pre-existing structures control mechanisms and host rock interactions of three granitic plutons, western Arabian Shield

Abstract

Field relations, structural measurements, and microfabric analyses are used to explain the emplacement mechanisms of granitic plutons in the Asir terrane. These circular-to-elliptical granitic intrusions are prominent plutons scattered across the Arabian–Nubian Shield. Various structural and tectonic fabrics affecting three plutons in the western Arabian Shield encouraged studying the effect of pre-existing structures and emplacement levels on the emplacement mechanisms and related solid-state deformation. Two of these plutons, called Al Sayl and Um Ar Raka, are circular and enveloped by ductile or brittle solid-state deformation. Pre- and post-emplacement tectonic fabrics controlled the distribution and superposition of the solid-state deformation. Lateral expansion of magma during the emplacement of these plutons induced significant radial shortening that was associated with either high or low heat transfer into the host rocks and developed brittle or ductile solid-state deformation, respectively. Heat transfer was controlled by the emplacement level and magma pressure of each pluton. The third, oval-shaped Al Hawiyyah pluton was structurally controlled, where magma was emplaced first into twofold hinges on both sides of a thrust fault under low-to-intermediate differential stress. Syn-emplacement shortening was accommodated mainly by upward and lateral magma flows. Continuous magma flow caused uplift of the pluton and its surrounding host rocks and developed stretching structures in these rocks.