نویسنده
گروه زمین شناسی، دانشگاه پیام نور، تهران، ایران
چکیده
کلیدواژهها
عنوان مقاله [English]
نویسنده [English]
The ophiolite sequence of Nain, located in the eastern microplate of central Iran, consists of harzburgite, dunite, chromitite layers, and lherzolite, with the primary minerals being olivine, orthopyroxene, clinopyroxene, and chromite. The studied chromites are classified into two groups: high chromium (Cr# > 0.6) and high aluminum (Cr# < 0.6, Al2O3 ≈ 17.5 wt%). Binary and ternary diagrams indicate that high-chromium chromites are located in the boninitic field, while high-aluminum chromites are more commonly associated with abyssal peridotites and mid-ocean ridge regions. The high Cr# content of the dunite and chromitite suggests that boninitic magmatism with a high magnesium content plays a key role in the formation of these rocks. It appears that high-aluminum harzburgites are derived from a mixture of boninitic and MORB (mid-ocean ridge basalt) melts. The studied chromites occupy the peridotite range of the supra-subduction zone (SSZ), with a tendency toward subduction-zone environments. Based on the supra-subduction characteristics of the ophiolite, it can be concluded that aqueous fluids with high oxygen fugacity, derived from a subducting slab, play a significant role in the evolutionary processes of the Nain ophiolite. The results of this study indicate that two types of melts play a role in the formation of the chromite-bearing ophiolitic assemblage in this region: one is derived from a subduction-zone origin, and the other from the supra-subduction zone.
کلیدواژهها [English]
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