The Kabr El-Bonaya mafic–ultramafic intrusion exposed along the southeastern border of Sinai Peninsula, the northernmost segment of the Arabian-Nubian Shield (ANS). It occurs as an elliptical intrusive body located along the major NE–SW trending fracture zones that prevail in the Kid metamorphic complex. The ultramafic rocks in the complex comprise ultramafic cumulates of peridotites (dunite, harzburgite and wehrlite) and pyroxenite. These rocks are generally unmetamorphosed and have intrusive contacts with their country rocks. Mineral chemistry and whole-rock chemical compositions of these ultramafic rocks are mostly consistent with those of residual mantle peridotites from refractory supra-subduction tectonic settings. Based on the variations of the major elements, the studied ultramafic rocks is conformable with supra-subduction zone mantle, as it seems to be melted at 1–2 GPa and 1300–1450 ° C. Linear variations of Al2O3, CaO, V and Ni with MgO, coupled with incompatible and rare-earth-element depletion and mineral compositions, suggest prior events of partial melting in both wehrlites and harzburgites. The LREE enrichment in the harzburgite, as well as the development of Cr-rich spinel is consistent with a history of melt–peridotite interaction. The calculated (Sm/Yb)N variations for the studied peridotites indicate general increasing addition of fluids with increasing degree of melting from the wehrlite (~13– 15 wt.%) of fluid in the source after initial spinel peridotite melting to the harzburgite (~20–25 wt.%) of fluid in the same source which is contrary to normal abyssal peridotites. The estimated equilibration temperature ranges from 1214 to 1321°C for the studied wehrlites and from 1297 to 1374°C for harzburgites. The Mg-rich nature of the analysed olivines from the studied ultramafic rocks (Fo = 81.41 to 91.77) reflecting their primary composition and are similar to olivines in Alaskan-type ultramafic rocks. The Fo content of the analyzed olivine decreases slightly from the dunite to the harzburgite to the wehrlite and to pyroxenite reflecting fractional crystallization trend. The high Cr# and very low TiO2 contents (0.03–0.12 wt.%) of the Cr-spinels from the studied peridotites are mostly consistent with modern highly refractory fore-arc peridotites indicating that these peridotites developed in a supra-subduction zone environment. |
