Cambrian nepheline syenite complex at Jabal Sawda, Midyan region, Kingdom of Saudi Arabia

The only nepheline syenite complex presently known in the Arabian Shield is at Jabal Sawda, about 30 km S of Haql in the extreme NW of Saudi Arabia. It is a post-tectonic, composite intrusion with a crudely concentric structure. A core of leuco-nepheline syenite, a partial ring of mela-nepheline syenite, and an almost complete outer ring of alkali-feldspar syenite are the main rock units. Several mega-inclusions of porphyritic nepheline syenite, nepheline monzosyenite, malignite and ijolite are present in the leuco-nepheline syenite. The chemical composition is notable for very high values of Al₂O₃, Na₂O, Ba, La, Nb, Sr and Zr. UPb isotope dating indicates an emplacement age of 553 ± 4 Ma, one of an increasing number of reliable Cambrian isotope dates in the northern Red Sea region.