Age and evolution of the southern part of the Arabian Shield

Rb–Sr studies of Precambrian volcanic and plutonic rocks of the Arabian Shield document an early development of continental lithosphere in the Arabian Peninsula between 900 and 680 Ma ago. Geologic studies indicate an intraoceanic island-arc environment characterized by andesitic (dioritic) magmas, volcaniclastic sedimentation, rapid deposition, and contemporaneous deformation along north- or N.W.-trending axes. The earliest plutonic units are diorite to trondhjemite batholiths ranging from 900 to 800 Ma in age that occur in the western and southwestern parts of Saudi Arabia. Younger units, ranging from 750 to 680 Ma in age, vary in composition from quartz diorite to granodiorite and become more abundant in the south-central and eastern parts of the Arabian Shield.