High-precision determination of stable chlorine isotopes: Insights into recycling processes beneath volcanic arcs

Frische, Matthias, Fietzke, Jan, Wehrmann, Heidi, Hansteen, Thor and Kutterolf, Steffen (2010) High-precision determination of stable chlorine isotopes: Insights into recycling processes beneath volcanic arcs [Talk] In: SFB 574 Subduction Workshop, 04.-07.11.2010, Pucon, Chile.

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Volatile induced melting processes at mantle depth of convergent margins are triggered by sequential devolatilizing of the subducting oceanic slab. We show
that stable chlorine isotopes (37Cl, 35Cl, expressed as 37Cl) can be used to trace each volatile source involved in melt generation and arc volcanism: During dewatering processes in subduction zones, chlorine is strongly
partitioned into the aqueous fluid phase, while preserving the distinct ᵟ37Cl values of its volatile sources; Chlorine-isotope fractionation is marginal at high (magmatic) temperatures or during subduction metamorphism and is
apparently limited to low temperature processes.
Due to limited range of ᵟ37Cl-values in silicate rocks (about ± 2‰) and the relatively imprecise analytical data in earlier studies, few convincing geochemical trends for stable chlorine isotopes have been published so far.
To archive the required analytical precision, we developed an alternative and more exact (~0.05‰ 2#) method for ᵟ37Cl determination via LA-MC-ICP-MS. Here we present high-precision ᵟ37Cl data of basaltic to rhyolitic volcanic
glasses collected about 700 km along the Central America Volcanic Arc (CAVA). The observed systematic isotopic variations spans a relatively small range in !37Cl values of -1.15 to +0.96‰ and represent systematic changes in
volatile sources and depth-dependent zones of fluid release. Our results confirm models for continuous slab dewatering and melt generation and highlight the conservative behavior of stable chlorine isotopes during recycling processes in subduction zones.

Document Type: Conference or Workshop Item (Talk)
Keywords: Geodynamics; Volcanology; Biogeochemistry; stable chlorine isotopes; volcanic arcs; subduction
Research affiliation: OceanRep > SFB 574 > C4
OceanRep > GEOMAR > FB2 Marine Biogeochemistry > FB2-MG Marine Geosystems
OceanRep > SFB 574 > B5
OceanRep > GEOMAR > FB4 Dynamics of the Ocean Floor > FB4-MUHS Magmatic and Hydrothermal Systems
OceanRep > SFB 574 > C2
OceanRep > SFB 574
Date Deposited: 10 Dec 2010 13:19
Last Modified: 23 Feb 2012 05:52
URI: http://eprints.uni-kiel.de/id/eprint/10429

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