Document Type
Article
Publication Date
1-15-2020
Publication Title
Earth and Planetary Science Letters
Abstract
Tungsten is strongly incompatible during magmatic processes and is fluid mobile in subduction zones. Here we show that W isotope fractionation in arc lavas provide a powerful new tool for tracing slab dehydration and melting in subduction zones. Geochemically well characterized, representative arc-lavas from three subduction zones were chosen for this study to evaluate W isotope fractionation under different sub-arc conditions. Arc-lavas from SW Japan are produced by subducting a young, hot slab, and lavas from the volcanic front and rear arc of the Sangihe and Izu arcs are produced during subduction of a cold slab. The heaviest W isotope compositions (δ W∼0.06‰) are observed in fluid-rich samples from the volcanic fronts of the Sangihe and Izu arcs. With increasing distance from the volcanic front, more melt-rich samples are characterized by progressively lighter W isotope compositions. Enriched alkali basalts from SW Japan, thought to be the product of mantle melting at a slab tear, and adjacent shoshonites have the lightest W isotope compositions (δ W∼0‰). The correlation of W isotope fractionation with various indices of fluid release (e.g., Ce/Pb, Ba/Th) suggests that the heavy W isotope signatures record fluid recycling near the volcanic front due to dehydration of the subducted slab. Upon release of the heavy W, the residual slab preferentially retains isotopically light W, which is released during subsequent melting of drier lithologies in hot subduction zones, such as SW Japan. These data suggest that W isotopes can be used as a tracer of slab dehydration, potentially helping to determine the onset of cold subduction zone magmatism and hence, modern-style plate tectonics.
Keywords
arc volcanism, slab dehydration, stable tungsten isotopes, volatile recycling
Volume
530
DOI
10.1016/j.epsl.2019.115942
ISSN
0012821X
Creative Commons License
This work is licensed under a Creative Commons Attribution-NonCommercial-No Derivative Works 4.0 International License.
Rights
©2019 The Authors. Published by Elsevier B.V.
Recommended Citation
Mazza, Sarah E.; Stracke, Andreas; Gill, James B.; Kimura, Jun Ichi; and Kleine, Thorsten, "Tracing Dehydration and Melting of the Subducted Slab with Tungsten Isotopes in Arc Lavas" (2020). Geosciences: Faculty Publications, Smith College, Northampton, MA.
https://scholarworks.smith.edu/geo_facpubs/111
Comments
Archived as published. This is an open access article.