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

Publication Type  Journal Article
Year of Publication  2004
Authors  Shillington, D. J.; Van Avendonk, H. J. A.; Holbrook, W. S.; Kelemen, P. B.; Hornbach, M. J.
Journal Title  Geochemistry Geophysics Geosystems
Volume  5
Pages  -
Journal Date  Oct 21
ISBN Number  1525-2027
Accession Number  ISI:000224875500001
Key Words  continental crust; crustal geophysics; island arc; major element geochemistry; exploration geophysics : computational methods, potential fields; geochemistry : composition of the crust; marine geology and geophysics : marine seismics; reflection travel-ti
Abstract  

[1] 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 similar to 10 - 20 km indicate an andesitic to basaltic composition. High lower-crustal velocities of 7.3 - 7.7 km/s over depths of similar to 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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URL  <Go to ISI>://000224875500001
DOI  Doi 10.1029/2004gc000715