C-O-H-S fluids released by oceanic serpentinite in subduction zones: Implications for arc-magma oxidation

Two styles of Neoarchean slab subduction revealed by mantle oxygen fugacity

“…At sites of subduction with a steep slabdip, the release of oxidized materials (i.e., SO 4 2− and HSO 4 − ) is nearly 5.5 times higher than that in a at slab regime 19,20 . The impact of these oxidized species on the redox properties of arc mantle is signi cant 18,20 , suggestive of a close relationship between slab dip and mantle oxygen fugacity 18 (fO 2 , relative to the fayalite-magnetite-quartz buffer (ΔFMQ)). To date, our understanding of slab dip in the Archean is rudimentary.…”

“…Recent studies have highlighted that the amount of oxidizing C-H-O-S uids released from a subducting slab is positively correlated with slab dip, and uid in ux plays the principal role in oxidization arc mantle [18][19][20] . At modern subduction zones, a at slab is generally associated with a warm P-T path of the slab top 19,20,41 , leading to the shallow dehydration of serpentine and low e ciency of mantle metasomatism 19 . In contrast, a steep, cold slab generates deeper uids with more oxidized species at subarc depth 20,41,42 .…”

“…However, the thermal structure and geometry of Archean subduction and the differences or similarities with modern subduction remain a source of uncertainity 16,17 . In modern subduction zones, the dip of a downgoing slab is increasingly recognized as a crucial parameter that impacts the breakdown of altered oceanic crust (AOC) and peridotite, the nature of slab uids, and the delivery mechanism of slab uids into the mantle wedge [18][19][20] . At sites of subduction with a steep slabdip, the release of oxidized materials (i.e., SO 4 2− and HSO 4 − ) is nearly 5.5 times higher than that in a at slab regime 19,20 .…”

“…In modern subduction zones, the dip of a downgoing slab is increasingly recognized as a crucial parameter that impacts the breakdown of altered oceanic crust (AOC) and peridotite, the nature of slab uids, and the delivery mechanism of slab uids into the mantle wedge [18][19][20] . At sites of subduction with a steep slabdip, the release of oxidized materials (i.e., SO 4 2− and HSO 4 − ) is nearly 5.5 times higher than that in a at slab regime 19,20 . The impact of these oxidized species on the redox properties of arc mantle is signi cant 18,20 , suggestive of a close relationship between slab dip and mantle oxygen fugacity 18 (fO 2 , relative to the fayalite-magnetite-quartz buffer (ΔFMQ)).…”

Redox species and oxygen fugacity of slab-derived fluids: Implications for mantle oxidation and deep carbon-sulfur cycling

“…To evaluate whether the oxidized fluids from dehydrating AOC and serpentinite can oxidize the subarc mantle or not, Eqs 1. and 2, and 3 were used to estimate C-and S-related oxidation fluxes released by subducted slab and timescales for mantle oxidation. We assumed a subducted area of 2.45 km 2 /year (Jarrard, 2003) and densities of 3000 kg/m 3 for AOC (Bekaert et al, 2021) and 2800 kg/m 3 for serpentinite (Duan et al, 2022) with different thicknesses (Figure 5) in the calculation. Our results show that AOC-and serpentinite-related oxidation fluxes to subarc mantle are 18.6-43.3 × 10 12 mol/year and 0.67-7.64 × 10 12 mol/year for cold subduction and 21.3-49.8 × 10 12 mol/year and 0.45-5.13 × 10 12 mol/year for hot subduction.…”