1,2,- 1State Key Laboratory of Lithospheric and Environmental Coevolution, University of Science and Technology of China, Hefei 230026, China
- 2Department of Earth Science, Tohoku University, Sendai, Miyagi 980-8578, Japan
- 3Institute of Geosciences, Ruhr-University Bochum, 44780 Bochum, Germany
- 4College of Earth Science and Engineering, Shandong University of Science and Technology, Qingdao, 266590, China
Subduction zone fluids control mass transfer and crust-mantle evolution, yet their detailed sources and fluid-rock interaction processes remain debated. Jadeitite, formed either by direct precipitation from Na–Al–Si-rich fluids (P-type) or by metasomatic replacement of magmatic protoliths (R-type), serves as a unique archive of subduction zone fluids. We present high-precision Mg–Fe isotopic data for jadeitites and jadeite-rich rocks from the Rio San Juan Complex (RSJC), Dominican Republic. RSJC jadeitites exhibit low δ26Mg values (−0.92‰ to −0.16‰) that lack correlations with carbonate indicators (e.g., CaO/Al2O3, CaO/TiO2 and Sr/Nd), precluding a significant contribution from sedimentary carbonates. Instead, the coupling of light Mg isotopes with MgO–Ni–Cr enrichment indicates a substantial contribution from serpentinizing fluids. In contrast to the light Fe isotope signatures of Myanmar jadeitites, RSJC jadeitites display relatively high δ56Fe values (−0.08‰ to 0.29‰). Systematic covariations between δ56Fe values and redox-sensitive proxies (V/Sc, U/Th, Ce anomalies and Sb/As) suggest that Fe isotope heterogeneity is primarily controlled by fluid redox conditions. By integrating petrological and geochemical constraints, we propose that forearc serpentinization acts as a critical redox filter that governs the coupled Mg–Fe isotope heterogeneity of jadeitites. Olivine-dominated serpentinization generates reducing conditions that promote light Fe isotope fractionation, as recorded by Myanmar jadeitites, whereas orthopyroxene-involved serpentinization buffers the system under relatively oxidizing conditions, preserving heavier Fe isotopic signatures in RSJC jadeitites. Jadeitite-forming fluids are best explained as mixtures of altered oceanic crust-derived and serpentinizing fluid components. Consequently, forearc serpentinization exerts critical control on the redox state and chemical heterogeneity of fluids transferred to the mantle wedge and arc magmas.
How to cite: Chen, K., Chen, Y.-X., Tsujimori, T., Schertl, H.-P., Takahashi, N., Huang, F., and Maresch, W. V.: The impact of forearc serpentinization on the composition of subduction-zone fluids revealed by Mg–Fe isotopes in jadeitites, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4635, https://doi.org/10.5194/egusphere-egu26-4635, 2026.
