Distribution and tectonic setting of plutonic rocks of the Arabian Shield

Abstract

Although it is still not possible to model in detail the tectonic evolution of the Arabian Shield, its evolution can be interpreted in terms of the classic pattern of Phanerozoic plate tectonics (the ‘Wilson cycle’). During the first stage of evolution (900-630 Ma), plutonism was dominated by intermediate plutonic rocks (diorite, quartz diorite, tonalite and trondhjemite) and involved a progressive evolution from primitive tholeiitic series are rocks to mature calc-alkaline series rocks. These rocks formed in both ensimatic island arc and continental—marginal arc environments. The magmatic-arc stage was terminated by two collisions (680-630 Ma); between an accreted ensimatic arc terrane and a continental microplate and between the microplate and a continental(?) plate. These collisions resulted in a shift from arc magmatism dominated by intermediate plutonic rocks to collision-related granitic (granodiorite to monzogranite) magmatism (660-610 Ma). The final phase of plutonism within the Shield (610-510 Ma) was the formation of widespread postorogenic intracratonic evolved peraluminous to peralkaline alkali-feldspar granites. Such granites typically form during the terminal relaxation phase of continental collisions. Although minor amounts of evolved peraluminous granites are present in the eastern part of the Shield, well-developed S-type granites (tourmaline- or cordierite-bearing granite) appear to be lacking. Minor amounts of syenitic plutonic rocks were also emplaced throughout the Shield from about 620 to 550 Ma. The plutonic rock assemblage of the Arabian Shield is composed of approximately 37% granite, 19% granodiorite, 17% tonalite and trondhjemite, 1.3% dioritic rocks, 7% alkali-feldspar granite (including 2.3% alkali granite and 1.3% aluminous granite), 6% gabbro, and 1% syenitic rocks. Plutonic rocks compose approximately 55% of the outcrop area of the Shield.