Quantifying Slab-Fluid Effects on Sulfide Stability and Metal Retention: Insights from Thermodynamic Modeling of the Yarlung-Zangbo Ophiolites

Ophiolitic peridotites preserve crucial records of material recycling throughout the Wilson cycle, from oceanic plate generation to subduction. However, quantitative constraints on the behavior of volatiles (notably S) and highly siderophile elements (HSE) during these processes remain limited. We integrate whole rock and mineral chemistry, HSE concentrations, and Re-Os isotope systematics of the Qunrang ophiolite with regional data from the Yarlung Zangbo Suture Zone (YZSZ) ophiolites, complemented by advanced thermodynamic modeling. This approach quantitatively simulates S and metal recycling in mantle residues formed under contrasting tectonic settings. Our results show that the Qunrang lherzolites formed via moderate degrees of polybaric continuous melting beneath a mid-ocean ridge (MOR). Thermodynamic modeling reveals that in this MOR setting, HSE remain sequestered in sulfides during decompression melting until abrupt sulfide exhaustion occurs at ~ 15% melt extraction, leading to rapid HSE depletion—a process quantitatively matched by the YZSZ lherzolite compositions. In contrast, the harzburgites originated in a suprasubduction zone (SSZ) setting, experiencing initial low-degree polybaric melting followed by a second stage of flux melting (up to 17%) triggered by slab sediment-derived aqueous fluids. Critically, our HSE migration modeling demonstrates that fluid influx does not destabilize sulfides through oxidation, contrary to prevailing models. Instead, H₂O addition combined with lower temperatures significantly decreases sulfur solubility, delaying sulfide exhaustion during partial melting. This novel mechanism of fluid-induced sulfide stabilization successfully reproduces the distinctive HSE enrichment observed in the YZSZ harzburgites. Broadly consistent ( ¹⁸⁷ Os/ ¹⁸⁸ Os) _125Ma compositions (lherzolites: 0.1193–0.1281; harzburgites: 0.1199–0.1286), alongside significant Al ₂ O ₃ depletion and elevated fO ₂ (higher V/Yb ratios) in the harzburgites, corroborate their SSZ flux melting origin by sediment-derived fluids shortly before obduction (~ 125 Ma). Ancient T _RD ages in YZSZ refractory components further indicate derivation from long-isolated, recycled materials. Collectively, our integrated study establishes a quantitative framework for tracking S and HSE recycling during crust-mantle interactions, fundamentally challenging the paradigm of ubiquitous fluid-induced sulfide destabilization in subduction zones and resolving key discrepancies in understanding deep volatile fluxes and metallogenesis.