Rb-Sr isotope study of latest Proterozoic volcano-sedimentary belts in the Central Arabian Shield

Five new Rb-Sr whole-rock isochrons for volcanic successions assigned to 9sequence9 A in the Central Arabian Shield indicate that very late Precambrian c .690–570 Ma volcanicity was an important event in the evolution of the shield. The following ages are considered to define or approximate to the age of lava extrusion: Fatimah group— 688 ± 30 Ma; Jahhad unit—616 ± 13 Ma; Juqjuq formation— 612 ± 22 Ma; Arfan formation— 608 ± 9 Ma; Hummah unit— 572 ± 23 Ma. Initial 87 Sr/ 86 Sr ratios range from 0.7027 to 0.7036, and Rb/Sr ratios are uniformly low ( 87 Srl 86 Sr ratio for the Jahhad and Hummah samples reflects the involvement of less-depleted mantle or possibly slight crustal contamination.