A red-corundum-bearing vein in the Rai-Iz ultramafic rocks, Polar Urals Russia: the product of fluid activity in a subduction zone

The veins in the mantle wedge peridotite can record the activity of slab-derived melt/fluid, which is the reflection of the material circulation between crust and mantle. A red-corundum-bearing vein is present in the Rai-lz ultramafic rocks in the Polar Urals, Russia. The ultramafic rocks are harzburgite and dunite, and the red corundum bearing rocks consist of phlogopite, paragonite, oligoclase, red corundum, and chromian spinet. Red corundum occurs as prophyroblasts or fine grains that contain 92-98 wt% Al2O3 and 2-7 wt% Cr2O3. Chromian spinet has Cr# values ([100Cr/(Cr + Al)] atomic ratio) of 46-78. Oligoclase is characterized by An values of 20-30. Phlogopite is Ba-rich (BaO = 0.8-2.7 wt%) and paragonite is Sr-rich (SrO = 0.8-23 wt%). Zircons from the oligoclasite show oscillatory zoning and Th/U values of <0.2, indicating crystallization from fluid. A zircon weighted-mean Pb-206/U-238 age of 382 +/- 2 Ma and a phlogopite 40Ar/39Ar plateau age of 377 +/- 3 Ma indicate that the red-corundum-bearing vein formed at 380 Ma. The occurrence and formation age of the vein, structure and composition of vein minerals, and zircon epsilon Hf values (-11 to +13) suggest that the vein was the product of interaction between a subduction-zone-derived fluid and mantle wedge peridotite. (C) 2018 Elsevier B.V. All rights reserved.