Trace Elements and Li Isotope Compositions Across the Kamchatka Arc: Constraints on Slab‐Derived Fluid Sources
Abstract Chalcophile elements and lithium (Li) isotopes were measured on lavas from a 220‐km transect across the Kamchatka arc in order to investigate the fluid variations below arc volcanoes and to trace the geochemical behaviour of Li in convergent plate margins. From the Eastern Volcanic Front (E...
| Published in: | Journal of Geophysical Research: Solid Earth |
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| Main Authors: | , , , , , , |
| Format: | Article in Journal/Newspaper |
| Language: | English |
| Published: |
2020
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| Subjects: | |
| Online Access: | https://resolver.sub.uni-goettingen.de/purl?gro-2/133789 https://doi.org/10.1029/2019JB019237 |
| Summary: | Abstract Chalcophile elements and lithium (Li) isotopes were measured on lavas from a 220‐km transect across the Kamchatka arc in order to investigate the fluid variations below arc volcanoes and to trace the geochemical behaviour of Li in convergent plate margins. From the Eastern Volcanic Front (EVF), through the Central Kamchatka Depression (CKD), into the Sredinny Range (SR) volcanic zones, chalcophile element ratios (e.g., As/Ce and Sb/Ce) show clear across‐arc variations, decreasing (e.g., As/Ce: 0.20 to 0.03 and Sb/Ce: 0.013 to 0.002) with increasing depth above the slab (110 to 400 km). This clearly indicates a gradually decreasing influx of slab‐derived fluids added to the mantle wedge as the slab subducts below Kamchatka. In addition, the anomalously high U/Th, La/Sm, and B/Nb ratios in the CKD lavas suggest lawsonite breakdown reaction dominates the fluid release in this area. However, Li/Y (0.07 to 1.78) and δ 7 Li (+1.8 to +5.4‰, with an exception of +8.6‰ in CKD) show limited variations and values similar to the MORB mantle. A dehydration model suggests that slab‐derived fluids, which are characterized by high Li concentration and high δ 7 Li, do not control the Li budget in Kamchatka arc lavas. Therefore, the isotopic heavy Li from slab‐derived fluids likely equilibrates in the sub‐arc mantle, which acts as a buffer for Li systematics. In addition, based on the Li isotopic signatures of Klyuchevskoy volcano, our study demonstrates insignificant Li isotopic fractionation during mantle melting and subsequent differentiation. Key Points The Kamchatka arc lavas show across‐arc variations in chalcophile elements, suggesting that the amount of fluid decreases with depth Slab‐derived fluids have a negligible contribution to the Li budget of the Kamchatka arc lavas CKD lavas have high U/Th, Li/Y, La/Sm, and B/Nb ratios, indicating that lawsonite breakdown reaction dominates the water release Funder: China Postdoctoral Science Foundation https://doi.org/10.13039/501100002858 Funder: Wenzhou Institute ... |
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