Abstract:

The Big Mantle Wedge (BMW), since first proposed in eastern China, has been extensively studied. The deep volatile cycling in the BMW system has a great impact on the redox state of the mantle. Here, we review geochemical data of the Cenozoic intraplate basalts and enclosed mantle xenoliths from eastern China, and find that the intraplate basalts are highly oxidized, with their oxygen fugacity higher than the lithospheric mantle as represented by the mantle xenoliths, based on metal stable isotope geochemistry, V-in-olivine oxybarometry, and bulk rock Fe³⁺/∑Fe. Therefore, we propose that the BMW has experienced one or multiple oxidation events, whose trigger mechanism is closely linked to the deep carbon cycle. The subduction of western Pacific slab has delivered a large amount of sedimentary carbonates into the deep mantle, facilitating carbon-iron redox reaction in the mantle transition zone. The diamond produced during the carbon-iron redox reaction in mantle transition zone due to its high density, making the resulting melts highly enriched in Fe³⁺/∑Fe, and the forming the highly oxidized mantle endmember (HOME), likely serving as a crucial medium for the transportation of precious metals and sulfides in the deep mantle.

Key words: big mantle wedge, intraplate basalt, deep carbon cycle, oxidation