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Island Arc Magmatism

Island Arc Magmatism. Eruption of Anatahan Volcano, Northern Mariana Is, June 10, 2003. Subduction Factory. Arc lavas contain signature of subducted sediments. Decompression Melting. This model includes a backarc spreading center and shows contours of decompression melt production.

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Island Arc Magmatism

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  1. Island Arc Magmatism Eruption of Anatahan Volcano, Northern Mariana Is, June 10, 2003

  2. Subduction Factory

  3. Arc lavas contain signature of subducted sediments

  4. Decompression Melting This model includes a backarc spreading center and shows contours of decompression melt production Conder et al., 2002

  5. Mantle water as a function of distance from the Trench Kelley et al [2006]

  6. Amphibole dehydration model(Davies & Stevenson 1992)

  7. Modeling water transport and magma productionin the arc • Water is extremely important in arc processes • Water produces flux melting in the hot part of the arc • One goal of geophysical imaging is to provide constraints on these processes Cagniocle et al., 2007

  8. Development of Arc Crust

  9. Ocean Bottom Seismographs (OBS) Long Term Lamont-Doherty OBS OBS deployment from R/V Kaiyo, June, 2003

  10. 1994 Tonga-Lau 2003-2004 Mariana Seismic Studies of Arc-Backarc Systems Joint US-Japan project 58 OBSs deployed for 11 months 20 land broadband stations 30 OBSs recording for 3 months 11 land broadband stations

  11. Comparison with Basalt Geobarometry = maximum anomaly • Si & Mg thermobarometry suggest a final equilibration depth of magma: 21-34 km for the backarc spreading center 34-87 km for the volcanic arc [Kelley et al., in press] • Corresponds perfectly with the strongest anomalies beneath the backarc and arc • Shows that velocity and Q anomalies delineate the melt production region • Anomalies result from small fractions of in-situ melt

  12. Comparison of P Velocity and Attenuation Anomalies • The images are generally very similar • Attenuation image shows backarc anomaly narrower and centered on the spreading ridge • Some differences in the forearc

  13. Comparison to Resistivity Structure fromOcean Bottom MT Survey Matsuno, Seama et al., in press • High conductivity above the slab up to depths of 60 km beneath the arc • Suggests the presence of connected melt and/or other fluids • Low conductivity beneath the spreading center • Any melt beneath the spreading center is disconnected or distributed discontinuously along the ridge

  14. Seismic and Geochemical Evidence for Mantle Flow - Lau Shear wave splitting Helium isotope anomalies Mantle flow diagram Smith et al., [2001] After Turner and Hawkesworth, 1998

  15. TUCAN Broadband Seismic Experiment

  16. Nicaragua vs Costa Rica Attenuation – More Water? Rychert et al. [2008] • Nicaragua shows significantly higher attenuation than Costa Rica • Geochemical/petrologic constraints suggest similar mantle temperatures • The greater attenuation is consistent with higher mantle water contents and extents of melting inferred from geochemistry and melt inclusions.

  17. Nicaragua Attenuation & Vp/Vs Ratio – evidence of magma ascent? Attenuation (from Rychert et al. 2008) Vp/Vs ratio (from Syracuse et al. 2008)

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