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| Titel |
Variations of water, sulphur, and chlorine in mafic to intermediate tephras along the Chilean Southern Volcanic Zone |
| VerfasserIn |
Heidi Wehrmann, Kaj Hoernle, Guillaume Jacques, Dieter Garbe-Schönberg, Robert Trumbull, Michael Wiedenbeck |
| 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 |
250096277
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| Publikation (Nr.) |
 EGU/EGU2014-11773.pdf |
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| Zusammenfassung |
| Relating along-arc variations in melt volatile concentrations to differences in the tectonic
parameters of a subduction system can help to identify processes influencing the volatile
inventories of arc magmas. Here we present pre-eruptive water, sulphur, and chlorine
concentrations in olivine-hosted melt inclusions in mafic to intermediate tephras along the
volcanic front of the Chilean Southern Volcanic Zone (SVZ) between 33°S and 43°S,
determined by SIMS and electron microprobe. Additionally, melt water abundances were
estimated by plagioclase-melt hygrometry.
We observe systematic along-arc variations in water content, H2O/K2O, and
ratios of highly fluid-mobile to less fluid-mobile trace elements (e.g. Ba/Nb, Pb/Ce),
with a peak observed in the Central (C)SVZ (38°S to 42°S). This suggests a strong
involvement of slab fluids in these melts. Ratios of more incompatible to less incompatible
trace elements, such as La/Yb, La/Sm, or Sm/Lu, are lower in the CSVZ, reflecting
higher degrees of mantle melting. The higher-degree, hydrous flux melting beneath
the CSVZ, as revealed from volatile and trace element geochemistry, coincides
with peak volumes of extruded material in this arc segment, which is indicative of
large magma production rates (Völker et al., 2011). Furthermore, a low-velocity
seismic anomaly and high Vp/Vs ratios in this region have been interpreted by
Dzierma et al. (2012) as the result of elevated fluid infiltration into the mantle wedge,
originating from the subducting Valdivia Fracture Zone. Integration of the geophysical,
morphological, and geochemical data suggests that the increased transport of water
into the system through hydration of the incoming plate at fracture zones and bend
faults leads to a generation of large amounts of water-rich, higher-degree melts, and
subsequently to intense volcanic activity with respect to volcano volumes and eruption
frequency.
An inverse along-arc trend is displayed by the melts’ S and Cl concentrations, showing
low values in the CSVZ and higher values towards the north and the south. Chlorine
concentrations correlate with trace element indicators for the degree of melting and/or source
enrichment, showing that the lowest Cl contents are generated through dilution in high-degree
melts from the most depleted mantle sources. |
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