Jurassic–early cretaceous alkaline seamount volcanism in the batain nappes, eastern oman: petrology, geochemistry, and tectonic significance of the Ruwaydah volcanic unit

Abstract

The Ruwaydah Unit of the Batain Nappe, eastern Oman, preserves a complete record of Jurassic–Early Cretaceous intraplate seamount volcanism within the Eastern Oman Ophiolites. The Late Jurassic-Early Cretaceous unit comprises a volcanic-sedimentary sequence consisting of alkaline basaltic to trachytic lavas, pillow lavas, pillow breccias, pyroclastic deposits, volcanic breccias, radiolarian cherts, pelagic limestones, crinoidal limestones, Ammonitico Rosso facies, and shallow-water carbonate deposits. Field relationships indicate the development of submarine volcanic structures that evolved through repeated volcanic and sedimentary cycles within the Proto-Indian Ocean. The rocks display aphyric, porphyritic, pilotaxitic, and doleritic textures. Geochemically, the Ruwaydah volcanic suite exhibits alkaline affinities characterized by enrichment in high-field-strength elements (HFSE) and light rare earth elements (LREE), positive Nb-Ta anomalies, and strongly fractionated chondrite-normalized REE patterns. The volcanic rocks define a coherent differentiation trend from alkali basalt to trachyte through fractional crystallization of olivine, clinopyroxene, Fe-Ti oxides, apatite, and feldspar. Trace-element discrimination diagrams consistently place the Ruwaydah volcanic rocks within the ocean island basalt (OIB) and within-plate basalt fields. Rare earth element modelling indicates derivation from approximately 2–6% of partial melting of an enriched garnet-bearing lherzolite mantle source, with minor contributions from the garnet-spinel transition zone. The OIB-like geochemical characteristics, together with the absence of subduction-related signatures, indicate generation within an intraplate oceanic setting. The Ruwaydah volcanic complex formed during an Early Cretaceous tectono-magmatic event that affected the Eastern Oman Ophiolites approximately 10–15 million years after formation of the Jurassic oceanic crust. Volcanism was associated with lithospheric extension and localized asthenospheric upwelling, possibly influenced by the peripheral effects of the Marion hotspot in the southwestern Proto-Indian Ocean. However, the geochemistry demonstrates enriched intraplate mantle melting more securely than it demonstrates a particular plume source. The Ruwaydah Unit therefore represents a well-preserved example of oceanic seamount volcanism developed on mature oceanic lithosphere and provides insights into intraplate magmatism, mantle dynamics, and seamount evolution within the Proto-Indian Ocean prior to obduction of the Eastern Oman Ophiolites onto the Arabian continental margin.