A NEW TYPE OF GRANITE: EXPLORING THE PETROGENESIS OF SUB-MOHO GRANITES FROM THE SAMAIL OPHIOLITE

Granitoids with evolved chemical signatures, intrusive both in peridotite and mafic rocks, are well known in the Samail supra-subduction ophiolite of Oman and United Arab Emirates. In this study, we use major and trace element geochemical data to investigate their origin and better constrain relative contributions of sedimentary and mantle-derived sources. We compare granitoid composition based on intrusive loci, providing a baseline for understanding the petrogenesis of felsic intrusions in other ophiolite settings. Crust-hosted granitoids are predominantly ferroan, calcic, and metaluminous, resembling trondhjemites and ridge ‘tholeiitic’ granitoids with normal mid ocean ridge basalt (MORB)-like affinity formed by fractionation of mafic melt under fluid-present conditions from slab dehydration and partial melting of mafic rocks. Mantle-hosted granitoids are magnesian, calcic to calc-alkaline, and peraluminous, sharing similarities with cordierite- and muscovite-bearing peraluminous granitoids with enriched MORB-like affinity. Most mantle-hosted granitoids formed by mixing between amphibolite and sedimentary melts, with undetectable to minor mantle contribution. We hypothesize that the crust-hosted granitoids have a similar origin to trondhjemites in other ophiolite settings (e.g., Troodos) with a subduction-modified MORB source. The mantle-hosted felsic intrusions have divergent and unique geochemical signatures, and may represent a type of granite not accounted for in existing paradigms.