Fig. 4: Redox front propagation.
From: Slab-derived devolatilization fluids oxidized by subducted metasedimentary rocks
a, Model in which relatively low \(f_{{{{\mathrm{O}}}}_2}\) (ΔFMQ −1) devolatilization fluids derived from deeper in the slab enter the base of an oxidizing metasedimentary rock sequence. The incoming fluids become oxidized as they reduce the rock. The time-integrated fluid flux increases with time. Consequently, as time progresses (t1–t3, from left to right), the boundary (or redox front) between the reduced rock (shaded grey) and the remaining oxidized rock (shaded red) moves upwards. Oxidized fluids will continue to leave the top of the system unless the front propagation distance L reaches the available thickness of metasediment, at which point the buffer capacity of the metasedimentary sequence is exhausted. b, Thicknesses of oxidizing metasedimentary sequences required to oxidize the slab devolatilization flux of 220 m3 m−2 for model O–H, C–O–H and S–O–H fluids. For each fluid composition, the red bars denote the minimum and maximum thicknesses considered, corresponding to reduction of 20 wt% and 2.5 wt% rock Fe2O3, respectively, for input fluids at ΔFMQ −1. Representative values for 5 wt% reduction are shown by the red squares. Two ranges for S–O–H fluids are shown; results for the molecular approach calculated herein give smaller values (~5–60 m) than the DEW approach21,41 (~20–200 m).
