Constraints on the composition of the Aleutian arc lower crust from V P/VS

Donna J. Shillington, Harm J.A. Van Avendonk, Mark D. Behn, Peter B. Kelemen, Oliver Jagoutz

Research output: Contribution to journalArticlepeer-review

22 Scopus citations


Determining the bulk composition of island arc lower crust is essential for distinguishing between competing models for arc magmatism and assessing the stability of arc lower crust. We present new constraints on the composition of high P-wave velocity (VP = 7.3-7.6 km/s) lower crust of the Aleutian arc from best-fitting average lower crustal VP/VS ratio using sparse converted S-waves from an along-arc refraction profile. We find a low VP/VS of ∼1.7-1.75. Using petrologic modeling, we show that no single composition is likely to explain the combination of high VP and low VP/VS. Our preferred explanation is a combination of clinopyroxenite (∼50-70%) and alpha-quartz bearing gabbros (∼30-50%). This is consistent with Aleutian xenoliths and lower crustal rocks in obducted arcs, and implies that ∼30-40% of the full Aleutian crust comprises ultramafic cumulates. These results also suggest that small amounts of quartz can exert a strong influence on VP/VS in arc crust.

Original languageEnglish (US)
Pages (from-to)2579-2584
Number of pages6
JournalGeophysical Research Letters
Issue number11
StatePublished - Jun 16 2013
Externally publishedYes


  • V/V
  • island arc
  • lower crust

ASJC Scopus subject areas

  • Geophysics
  • General Earth and Planetary Sciences


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