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| Titel |
A model for the formation of volcanic gaps by slab advance |
| VerfasserIn |
Stéphane Rondenay, Laurent Montesi, Geoffrey Abers |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250046934
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| Zusammenfassung |
| Volcanic gaps are segments of subduction zones that lack the volcanic activity usually found
at these convergent margins. They are regions where the necessary conditions to produce melt
may appear favourable, but where volcanoes are surprisingly absent from the surface. In this
study, we present a new model that can explain the occurrence of such volcanic gaps. It is
based on seismic imaging and geodynamic modelling of the Denali volcanic gap, a
~400Â km-wide region at the eastern end of the Alaska-Aleutian subduction zone. Here, the
thick crust of the Pacific plate and Yakutat terrane subduct at shallow angle beneath North
America. A high-resolution seismic profile clearly images the subducting crust undergoing
progressive dehydration between 50–120Â km depth, and a negative sub-horizontal velocity
contrast at 60Â km depth in the overlying mantle wedge. We interpret this 60Â km
discontinuity as marking the top of a layer of partial melt that pools at the base of the
overriding plate. In steady-state subduction models, melt accumulates at the apex of a vaulted
mantle wedge, the ‘pinch zone’, from where it may break through the overlying lithosphere to
the surface. Beneath the Denali volcanic gap, the pinch zone is absent (or greatly reduced)
because shallow subduction of the Yakutat terrane progressively cools the system, and
causes the slab to advance and replace the hot core of the mantle wedge. This regime
can be seen as the opposite of subduction roll-back. It prevents the formation of a
pinch zone, reduces the length of the melting column and causes melt to pool at
the base of the overriding plate, thus inhibiting magma generation and extraction. |
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