1,2,6,7,9- 1China University of Geosciences, School of Earth Sciences, China (wcjiang@cug.edu.cn)
- 2School of Natural Sciences, Macquarie University, Sydney, New South Wales 2109, Australia
- 3State Key Laboratory of Critical Earth material Cycling and Mineral Deposits, School of Earth Sciences and Engineering, Nanjing, Jiangsu 210023, China
- 4Frontiers Science Center for Critical Earth Material Cycling, Nanjing University, Nanjing, China
- 6School of the Environment, Faculty of Science, The University of Queensland, Brisbane, St. Lucia campus, Queensland 4072, Australia
- 7Institute of Geochemistry and Petrology, ETH Zürich, Sonneggstrasse 5, CH-8092 Zürich, Switzerland
- 8State Key Laboratory of Ore Deposit Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, China
- 9School of Environment, University of Auckland, Auckland 1142, New Zealand
Arc magmatism plays a critical role in continental crustal growth and the formation of significant metal deposits, including granite-related tin (Sn) systems. However, the mechanisms governing Sn transport and isotopic fractionation at convergent margins remain poorly constrained due to a lack of systematic studies across spatial variations (arc-front to rear-arc) and magmatic-hydrothermal transitions. In this study, we present high-precision Sn isotopic data for lavas, pumices, and hydrothermal products from Whakaari (arc-front) and Taranaki (rear-arc) in the Kermadec system, alongside magmatic H2O concentrations estimated from clinopyroxene. Whakaari lavas exhibit significant variation (δ122/118Sn = –0.241‰ to 0.361‰). The heaviest values are attributed to extensive shallow degassing (>40%), with Rayleigh modeling indicating the preferential partitioning of light Sn isotopes into the vapor phase—a process corroborated by low magmatic water contents (avg. 0.83 wt.%). In contrast, Taranaki samples show limited variation (δ122/118Sn = 0.124 to 0.235‰). While amphibole and titanomagnetite fractionation may lower bulk-rock values, these processes cannot explain why both volcanoes are isotopically lighter than MORB (0.367 ± 0.087‰).
We propose that this light Sn signature originates from the subducted slab. Simulations suggest that the addition of 5–20% reduced, Cl-rich fluids derived from altered oceanic crust (AOC) can effectively lower arc magma δ122/118Sn. Regardless of the specific redox mechanism, slab-derived fluids dominate the Sn budget of the mantle wedge and the resulting arc magmas. Our results suggest that widespread light Sn isotope signatures serve as a diagnostic feature of fluid-mediated mass transfer in subduction zones. By combining spatial variations from arc-front to rear-arc, this study provides a robust geochemical framework to decipher slab-mantle interactions and the dynamic cycling of metals at convergent margins.
How to cite: Jiang, W., She, J., Davidson, A., Chen, C., Firth, C., Turner, S., Li, W., Ireland, T., Sossi, P., Wu, J., and Cronin, S.: Tin isotope fractionation in arc magmas controlled by degassing and slab input, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7076, https://doi.org/10.5194/egusphere-egu26-7076, 2026.
