Age of initial oceanic magmatism in the Late Proterozoic Arabian Shield

Lead isotopic data for zircons from a dacite clast in a volcanic breccia of the oldest oceanic assemblage (immature arc or oceanic plateau) of the southwestern Arabian Shield (Baish group), acquired with the single-grain evaporation technique, yielded a mean 207 Pb/ 206 Pb age of 842 ±17 Ma. Earlier published Rb-Sr data for Baish rocks yielded a three-point isochron of 1165 ±110 Ma. This age has been repeatedly cited as evidence for pre-1 Ga arc magmatism in the Arabian Shield. However, more recent Rb-Sr data and zircon ages for clastic metasedimentary rocks are in agreement with our new zircon age, suggesting that initial oceanic magmatism in the Arabian Shield did not begin until after 90…