Subduction and melting of biogenic and ferromanganese sediments as evidenced by sub-Moho granitoids

Mantle-hosted granitoids (MHG) from the supra-subduction Samail ophiolite in Oman and the United Arab Emirates exhibit diverse compositions, highlighting variations in petrogenesis and source contributions. Previous isotopic data indicate these MHG originated through the interaction of sediment-derived with basaltic melts from an underthrust oceanic plate within the mantle wedge. The sedimentary contribution was attributed to the partial melting of pelitic to siliceous (bio-siliceous) material atop the subducted plate based on elevated zircon δ¹⁸O values (∼14–28 ‰). To further evaluate this hypothesis on Samail MHG petrogenesis and source contribution, we present new and compiled radiogenic (Sr-Nd-Hf-Pb) and stable (O-Li-H) isotopes, along with zircon trace element analyses. The variable Sr and Pb isotopic signature support a mixed origin involving altered mafic and sedimentary sources in the formation of the MHG. Negative whole-rock εNd, coupled with elevated δ⁷Li in muscovite suggest the involvement of sedimentary sources and particularly those resembling deep-sea ferromanganese-rich sediments. We propose a new model identifying ferromanganese sediments as a potential source given their widespread distribution across the ocean floor, broad range of δ¹⁸O (up to 29.5 ‰), slightly positive Hf values, seawater-like δ⁷Li signatures (median of ∼27 ‰), and zircon trace element compositions lacking a signature of monazite co-precipitation, which match the signatures required for the genesis of the Samail MHG. Preservation of oceanic lithosphere in the geological record is limited, and MHG in ophiolites are uncommon. Therefore, the Samail MHG are key examples of crustal materials transported to the mantle, with implications for mantle heterogeneity and arc mantle redox budget.