High-pressure (HP) interactions between aqueous fluids and subducting crustal and mantle rocks alter the deep volatile recycling and redox capacity of fluids migrating toward the overlying mantle wedge. Recent findings (Padrón-Navarta et al., 2023) show that reduced fluids derived from graphite-bearing metasediments can interact with serpentinites, (1) promoting antigorite breakdown and (2) modifying the redox capacity of the released deserpentinization fluids. The Cerro Pingano ultramafic body (Sierra de Baza, Spain) preserves a deserpentinization front oblique to the foliation, similar to the type locality of Cerro del Almirez massif (Padrón-Navarta et al., 2023) outcropping in Nevado-Filabride Complex (NFC) of Sierra Nevada. The ultramafics are hosted within a sequence of graphite-bearing metasediments and calcite-dolomite marbles of the Tahal formation (NFC) and together underwent Alpine HP metamorphism at ~16 kbar and ~660°C. A transition from Atg-serpentinite through Atg-Chl-Opx-Ol rock to Chl-harzburgite can be traced across a ~50 cm wide reaction front. The influx of reducing, C-bearing fluids along the reaction front is inferred from the decrease in the bulk Fe3+/ΣFe ratio and the appearance of magnesite in Chl-harzburgites. Thermodynamic models confirm that infiltration of less than 10 moles ( –1.0 contain a sufficiently high CO2 concentration and CO2/CH4 ratio to trigger coupled reduction and simultaneous carbonation of serpentinite. Our new reduction-carbonation model shows that serpentinite can capture carbon from CH4 and CO2 via redox-driven carbonate precipitation under high-pressure conditions along a hot subduction geotherm. While the reduction-carbonation model explains carbon capture within the downgoing slab, we propose that it can also be used as a proxy for mantle wedge processes at subarc depths.

Research funded by RUSTED project PID2022-136471N-B-C21 & C22 funded by MICIN/ AEI/10.13039/501100011033 and FEDER program, and “Juan de la Cierva” Fellowship JFJC2021-047505-I by MCIN/AEI/10.13039/501100011033 and CSIC

Comunicación oral presentada en en The 7th Orogenic Lherzolite Meeting, del 30 de septiembre al 6 de octubre de 2024, celebrado en Oviedo (España)