Volatile contents of melt inclusions of tephras along and across the Southern Volcanic Zone, Chile – preliminary results

Freundt, Armin, Kutterolf, Steffen, Burkert, Cosima, Gilbert, David, Lara, L. and Naranjo, J. (2010) Volatile contents of melt inclusions of tephras along and across the Southern Volcanic Zone, Chile – preliminary results [Talk] In: SFB 574 Subduction Workshop, 04.-07.11.2010, Pucon, Chile.

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Abstract

Rapidly quenched melt inclusions potentially preserve the pre-eruptive volatile concentrations of magmatic melts. We analyze melt inclusions, matrix glasses, phenocrysts and bulk rocks of tephras in order to reveal (1) how magmatic volatile contents are determined by petrogenetic processes, (2) in how far the triggering, intensity and magnitude of explosive volcanic eruptions are controlled by the volatile contents, and (3) how much of the volatiles is actually released into the atmosphere where they may affect atmospheric chemistry and climate.
Presently available results show that volatiles (H2O, S, Cl, F) are significantly more enriched relative to incompatible K2O in the tephras from the volcanic
front than in those from the back-arc region. Moreover, volatile/K2O ratios vary along the arc such that they converge from both N and S toward a maximum around 38.5°S. This along-arc variation mimicks that of bulk-rock
Ba/Th and is a mirror-image of the La/Yb pattern. Thus peak volatile/K2O values coincide with maximum slab-fluid metasomatism (max. Ba/Th) in the mantle source of the magmas and with the highest degree of partial melting
(min. La/Yb). Melt inclusions in compositionally zoned tephras show S contents decreasing to higher glass K2O contents, evidence that sulphur exsolution into a fluid
phase occurred during progressive crystal fractionation. Melt inclusions in all highly evolved tephras have very low S contents. However, for some of these tephras the H2O and Cl to K2O ratios of melt inclusions decrease to more evolved compositions, suggesting that degassing occurred in the magma chamber and potentially triggered the eruption. Ongoing thermobarometric modelling, however, is needed to better constrain degassing conditions.

Document Type: Conference or Workshop Item (Talk)
Keywords: Geodynamics; Volcanology; Southern Volcanic Zone, Chile
Research affiliation: OceanRep > SFB 574 > C4
OceanRep > GEOMAR > FB4 Dynamics of the Ocean Floor > FB4-MUHS Magmatic and Hydrothermal Systems
OceanRep > SFB 574
Date Deposited: 13 Dec 2010 11:56
Last Modified: 05 Jul 2012 03:59
URI: http://eprints.uni-kiel.de/id/eprint/10471

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