Neoproterozoic crustal growth at the margin of the East Gondwana continent – age and isotopic constraints from the easternmost inliers of Oman

The Jebel Ja’alan and Qalhat inliers of Oman represent the easternmost exposures in the Arabian peninsula of the Neoproterozoic basement associated with the East African Orogen (EAO) and the assembly of East and West Gondwana. These inliers expose tonalitic gneisses and metasediments intruded by granodiorites and granites of the Ja’alan batholith. Zircons from the gneisses yield U–Pb SIMS ages of ca. 900–880 Ma, which are interpreted as crystallization ages. These represent the oldest magmatic events associated with the closure of the Mozambique Ocean reported to date. Zircon of this age is also the dominant component in the metasediments. The Ja’alan batholith yields ages of ca. 840–825 Ma. Nd isotopes indicate that both the gneisses and the batholith range from juvenile to slightly more evolved, with ε_Nd(t) of +6 to +1.5 interpreted to reflect variable contamination by older, evolved continental material; this is also indicated by >900 Ma detrital zircon from the metasediments. The Nd data also contrast with the uniformly juvenile signature of younger, ca. 840 Ma, rocks of the Marbat region of southern Oman that lie structurally to the west. The Ja’alan and Qalhat inliers thus document eastward increasing age and continental influence, consistent with the progressive development of arc rocks onto the western margin of East Gondwana, although the location and nature of the eastern continental block remain elusive.