The Nabitah fault zone, Saudi Arabia: A Pan-African suture separating juvenile oceanic arcs

U-Pb zircon ion-microprobe geochronology, whole rock geochemistry and feldspar Pb and Sm-Nd isotopic analyses carried out on granitoid rocks along a transect across the Nabitah fault zone suggest that it separates two juvenile oceanic arc terranes which differ in age and geochemical character. The Tathlith–Malahah terrane situated to the east of the fault zone comprises the Tathlith arc which developed through an older volcanic and sedimentary succession. Plutonic rocks associated with the Tathlith arc formed between c. 700–670 Ma and are younger than those from the 750–720 Ma Tarib arc within the Al Qarah terrane, situated to the west of the fault zone. Intrusions from both the Tarib and Tathlith arcs have positive ɛNd values and feldspar Pb signatures that are consistent with juvenile crustal additions. A tectonic model is presented for the evolution of the Nabitah fault zone: the Tathlith arc developed on and through the Tarib fore arc as a consequence of subduction roll back. Back arc spreading, promoted by collision of a continental mass to the south, created a separate Tathlith–Malahah terrane. Continued convergence of the continent inverted the back arc basin and counter-clockwise rotation formed the Nabitah fault zone. The fault zone does not represent a major suture zone between the western juvenile arc terranes and the more evolved eastern arc and continental terranes, as had previously been speculated.