From the Valdivia Fracture Zone to the Villarrica volcanic complex - seismic evidence of a link between subducted oceanic faults and volcanism

Rabbel, Wolfgang, Dzierma, Yvonne, Thorwart, Martin, Wunderlich, Tina, Koulakov, I., Hoernle, Kaj and Wehrmann, Heidi (2012) From the Valdivia Fracture Zone to the Villarrica volcanic complex - seismic evidence of a link between subducted oceanic faults and volcanism [Talk] In: The Lübeck Retreat, Collaborative Research SFB 574 Volatiles and Fluids in Subduction Zones: Climate Feedback and Trigger Mechanisms for Natural Disasters, 23.-25.05.2012, Lübeck.

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The south-central Chilean subduction zone was investigated at 39-40°S by a passive seismic
experiment. The investigation area comprises the maximum slip of the great 1960 Mw 9.5 Valdivia
earthquake. The incoming Nazca plate is permeated by a number of major fault zones including the
Valdivia fault zone and the Mocha fault zone which seem to have behaved as a barriers for the
rupture propagation of large earthquakes in the past. The investigated sector is also home to the
Villarrica volcano - one of South America’s most active volcanoes. In the extension of the Valdiva fault
zone we observed a cluster of increased seismicity in the subducting plate at depths between 80 km
and 120 km, where dehydration of the subducting plate occurs. The focal plane solutions of this
cluster show predominantly strike-slip motion. Tomographic images show decreased P- and Svelocity
and increased ratio between the seismic cluster and the volcanic center of Villarrica,
Quetrupillán and Lanin, corresponding to an increased content of fluids or melt. Additional
geochemical investigations show that the magma of Villarrica volcano has an enhanced fluid signal
compared to the other volcanoes of the Southern Volcanic Zone of Chile. It can be assumed that the
Valdivia fault zone serves as the source for the fluids. Before the plate subducts, water can penetrate
the plate through faults within the Valdivia fault zone. Serpentinization would build the water into
minerals. Inside the subduction zone the Valdiva fault zone is reactivated by dehydration reactions at
a depth of about 100 km. The released fluids rise towards the volcanic center causing the
tomographic anomalies. At the end this leads to an increased degree of melting and a higher activity
of Villarrica volcano.

Document Type: Conference or Workshop Item (Talk)
Keywords: Geodynamics
Research affiliation: OceanRep > SFB 574 > C2
OceanRep > SFB 574 > A5
Kiel University
OceanRep > SFB 574
OceanRep > SFB 574 > A2
OceanRep > GEOMAR > FB4 Dynamics of the Ocean Floor > FB4-MUHS Magmatic and Hydrothermal Systems
Kiel University > Kiel Marine Science
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Date Deposited: 21 Sep 2012 10:26
Last Modified: 28 Feb 2013 12:38

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