Subduction zones are fundamental for element recycling and chemical exchange between the Earth¿s surface and mantle. Prograde metamorphic reactions, particularly deserpentinization, release fluids that ascend into the mantle wedge, playing a key role in the geochemical composition of arc magmas. Arc basalts are typically depleted in high-field-strength elements (HFSE: Ti, Zr, Hf, Nb, Ta) relative to MORB, although some studies suggest these elements can be fluid-mobile under slab devolatilization conditions [1]. Titanium isotopes provide a promising tool for tracing the processes responsible for Ti depletion in arc magmas, with potential implications for other HFSE.b. Our results highlight the role of deserpentinization and associated oxide crystallization in modifying the Ti budget of slab-derived fluids, ultimately shaping the geochemical signature of arc mag Here, we present new Ti isotopic data from ultramafic rocks of the Cerro del Almirez massif (Betic Cordillera, Southeast Spain), a paleo-subduction terrain that preserves a unique deserpentinization front within a serpentinized oceanic lithosphere. The studied samples include antigorite serpentinites and their dehydration products, chlorite harzburgites. Our data reveal a systematic shift towards heavier Ti isotopic compositions in chlorite harzburgites compared to serpentinites, with correlations between δ49/47Ti values and several major and trace elements (e.g., Fe, Mg, Mn, Cr). The heavier Ti isotopic compositions cannot be accounted for by fractionation inherited from their oceanic mantle protoliths. We propose that the dissolution-precipitation of Fe-Ti oxides (e.g., magnetite, hemato-ilmenite, ilmenite) during deserpentinization plays a key role in the observed isotopic shift [2]. This process also acts as a mechanism for Ti capture in the subducting slab. Our results highlight the role of deserpentinization and associated oxide crystallization in modifying the Ti budget of slab-derived fluids, ultimately shaping the geochemical signature of arc magmas.

Funding: Pre-doctoral contract PREDOC_00939 granted by the Junta de Andalucía and Project PID2022-136471NB-C21 “RUSTED” funded by MCIN/AEI/10.13039/501100011033.

Póster presentado en Goldschmidt (2025), celebrado en Praga del 6 al 11 de julio de 2025