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Composition and structure of the central Aleutian island arc from arc-parallel wide-angle seismic data

Record type: Article

New results from wide-angle seismic data collected parallel to the central Aleutian island arc require an intermediate to mafic composition for the middle crust and a mafic to ultramafic composition for the lower crust and yield lateral velocity variations that correspond to arc segmentation and trends in major element geochemistry. The 3-D ray tracing/2.5-D inversion of this sparse wide-angle data set, which incorporates independent phase interpretations and new constraints on shallow velocity structure, produces a faster and smoother result than a previously published velocity model. Middle-crustal velocities of 6.5–7.3 km/s over depths of ~10–20 km indicate an andesitic to basaltic composition. High lower-crustal velocities of 7.3–7.7 km/s over depths of ~20–35 km are interpreted as ultramafic-mafic cumulates and/or garnet granulites. The total crustal thickness is 35–37 km. This result indicates that the Aleutian island arc has higher velocities, and thus more mafic compositions, than average continental crust, implying that significant modifications would be required for this arc to be a suitable building block for continental crust. Lateral variations in average crustal velocity (below 10 km) roughly correspond to trends in major element geochemistry of primitive (Mg # > 0.6) lavas. The highest lower-crustal velocities (and presumably most mafic material) are detected in the center of an arc segment, between Unmak and Unalaska Islands, implying that arc segmentation exerts control over crustal composition.

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Citation

Shillington, Donna J., Van Avendonk, Harm J.A., Holbrook, W. Steven, Keleman, Peter B. and Hornbach, Matthew J. (2004) Composition and structure of the central Aleutian island arc from arc-parallel wide-angle seismic data Geochemistry, Geophysics, Geosystems, 5, (10), pp. 1-32. (doi:10.1029/2004GC000715).

More information

Published date: 2004
Keywords: continental crust, crustal geophysics, island arc, major element geochemistry

Identifiers

Local EPrints ID: 15819
URI: http://eprints.soton.ac.uk/id/eprint/15819
ISSN: 1525-2027
PURE UUID: c7175c9b-f187-448c-a357-46ec3a5af300

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Date deposited: 02 Jun 2005
Last modified: 17 Jul 2017 16:46

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Contributors

Author: Donna J. Shillington
Author: Harm J.A. Van Avendonk
Author: W. Steven Holbrook
Author: Peter B. Keleman
Author: Matthew J. Hornbach

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