Age and Stratigraphic Relationships of Structurally Deepest Level Rocks, Oman Mountains: U/Pb SHRIMP Evidence for Late Carboniferous Neotethys Rifting

Abstract

Igneous zircons in felsic schist, or metatuff, infolded with mafic schist, calcschist, and quartz mica schist of the As Sifah lower plate window, NE Oman, have yielded a U/Pb SHRIMP crystallization age of $$298\pm 3$$ Ma. The metatuff was previously considered to represent Permian bimodal volcanism, but these data indicate that the magmatism is older and suggest that Neotethys intracontinental rifting on the Oman part of the Gondwana northern margin was initiated in the Late Carboniferous. This, combined with δ13C values of calcschists indicating a predominantly pre–Late Permian age for the basal lower plate metacarbonates, suggests that passive margin carbonate ramp development occurred in the Late Carboniferous/Early Permian during Neotethys oceanic spreading and not just in the Late Permian, as previously thought. The restricted occurrence of the metatuff to the Saih Hatat lower plate, a unique lower plate stratigraphy, and the unique δ13C values of the calcschists all suggest that the lower plate was certainly distal, and possibly exotic, to the Arabian Peninsula. The felsic schist sample was entrained within an eclogite megaboudin at As Sifah. The age relationships therefore suggest that the high‐P rocks that reached pressures of up to 20 kbar and are now part of the lower plate of Gregory and coworkers were either part of a subducted Florida‐style promontory as part of the attenuated leading edge of the Arabian platform or part of a subducted microplate that was originally caught in the developing southern Neotethys ocean some 1300 km from the margin.