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| Titel |
The halogen cycle in subduction zones: insight from back-arc basin basalts |
| VerfasserIn |
Deborah Chavrit, Lorraine Ruzié, Ray Burgess, David Hilton, Hirochika Sumino, John Sinton, Chris Ballentine |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250097487
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| Publikation (Nr.) |
 EGU/EGU2014-15734.pdf |
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| Zusammenfassung |
| The extent to which the subduction process preserves the volatile elements signature of the
downgoing slab and the mechanisms by which these elements are transferred into the mantle
wedge are not well understood. Halogens (Cl, Br, I) are good candidates to trace these
processes, due to their incompatibility and their relatively high concentrations in seawater and
marine sediments. A technique developed at the University of Manchester allows the high
precision measurements of these elements on neutron-irradiated samples using noble gas
mass spectrometry.
To better constrain the cycle of halogens in subduction zones, we analyzed
the halogens in 15 volcanic glasses (BABB) from three back-arc basins which are
known to contain slab-derived components viz Manus basin, Lau basin and Mariana
trough.
The three back-arc basins have relatively constant Br/Cl weight ratios (4.0±0.4x10-3)
which are 2x higher than the mid-ocean ridge basalts (MORB) value. The I/Cl weight ratios
(0.9 to 7.1x10-5) range from values close to seawater to MORB values. These results
suggest that the halogen composition of the BABB mantle source is affected by a
slab-derived component. However, the I/Cl ratios positively correlate with Ba/Nb ratios that
are between 5-33 (weight), which reflect the extent of the slab contribution. Thus,
it indicates the presence of an unknown end member with a MORB-like Ba/Nb
ratio and with low I/Cl and high Br/Cl ratios. It is notable that the halogen ratios of
this component are similar to that of the fluid phases trapped in altered oceanic
crust. Another component with higher Ba/Nb, higher I/Cl and lower Br/Cl ratios, is
consistent with the presence of a sedimentary-derived component. The possible
origins of the signature of the halogen BABB mantle source will be discussed by
comparing with the different components characterizing the subducted oceanic crust. |
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