Age and petrochemistry of bahrah granodiorite-granite complex, Jeddah-Makkah Region, Saudi Arabia

الملخص EN

The Buhrah granodiorite-granite complex is an oval intrusion oriented NE-SW forming a negative geomorphologic feature at the intersection of Wadi Fatima to the west and Wadi AI-Shumaysi to the east.

It is bound to the west by Jeddah group metavolcanics and Bahah group paraschist, To the cast, it is in contact with Jcddah group mcravolcanics and intruded quartz-diorites.

The complex is traversed by fine grained basic dik es trending E-W .

The rock types range from gabbroic to granitic .

The main rock type is medium to coarse grained biotite and sometimes biotite-hornblende granile .

The quartz-diorite and granodiorite facies near the eastern borders of the complex arc slightly foliated and contain abundant mafic xenoliths, indicating an emplacement mechanism by stoping, The intrusion is peraluminous calc-alkaline in nature and highly depleted in LIL-c1ements suggesting a subduction related origin of the magma .

The RbfSr age obtained is 665 :!: 12 Ma , and is interpreted as the age of emplacement during post-Fatima group time whose age is 690-6iiOMa.

This is the time-equivalent of the post-Hal aban-Hulayfah tectono-plutonic cycle widely spread in the Arabian Shield.