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Shear-wave velocity structure of the Chilean subduction zone (39–40°S) based on Rayleigh wave dispersion: evidence of fluid release and melts in the mantle beneath the Villarrica volcano

By
Martin Thorwart
Martin Thorwart
1
Christian-Albrechts-University Kiel, Institute of Geosciences, Otto-Hahn-Platz 1, D-24118 Kiel, Germany
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Yvonne Dzierma
Yvonne Dzierma
1
Christian-Albrechts-University Kiel, Institute of Geosciences, Otto-Hahn-Platz 1, D-24118 Kiel, Germany
2
Department of Radiation Oncology, Saarland University Medical Centre, D-66421 Homburg, Germany
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Kathrin Lieser
Kathrin Lieser
3
GEOMAR Helmholtz-Centre for Ocean Research Kiel, Wischhofstraße 1-3, D-24148 Kiel, Germany
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Heiko Buhs
Heiko Buhs
1
Christian-Albrechts-University Kiel, Institute of Geosciences, Otto-Hahn-Platz 1, D-24118 Kiel, Germany
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Wolfgang Rabbel
Wolfgang Rabbel
1
Christian-Albrechts-University Kiel, Institute of Geosciences, Otto-Hahn-Platz 1, D-24118 Kiel, Germany
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Published:
January 01, 2015

Abstract

A seismic network operated from December 2008 to November 2009 in south-central Chile covering the Chile subduction zone from c. 39°S to 40°S. This segment of the subduction zone includes the highly active Villarrica volcano and the maximum slip area of the 1960 Mw 9.5 earthquake. We applied surface wave dispersion analysis to data from a linear array of broadband stations and to records of four areal sub-arrays. Fifty regional and teleseismic events were used to produce dispersion curves of Rayleigh waves. From the dispersion curves, we determined depth functions of the shear-wave velocity for 4 subregions of the subduction zone: the Coastal Range, the Central Valley, the Volcanic Arc and the Back-arc Region in Argentina. The resulting models reveal the structure of the crust and the depth of the Moho discontinuity. Below the volcanic arc, the shear-wave velocities of the continental mantle are reduced by c. 7% with respect to a background value of 4.3 km s−1. This low-velocity zone coincides with a zone of reduced electrical resistivity that was previously determined from magnetotelluric measurements. The combined occurrences of minima in the S-wave velocity and resistivity can be interpreted as an indicator of partial melts.

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Geological Society, London, Special Publications

The Role of Volatiles in the Genesis, Evolution and Eruption of Arc Magmas

G. F. Zellmer
G. F. Zellmer
Massey University, New Zealand
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M. Edmonds
M. Edmonds
University of Cambridge, UK
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S. M. Straub
S. M. Straub
Columbia University, USA
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Geological Society of London
Volume
410
ISBN electronic:
9781862396982
Publication date:
January 01, 2015

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