Figure F8. Th recycling at the Izu and Marianas subduction zones. A. Izu arc volcanics are deficient in Th relative to Marianas arc volcanics by a factor of ~5 (based on Th/Na). This deficiency in the Izu arc is anomalous with respect to the global array and the Th sediment input flux, based on drilling results reported here for ODP Site 1149 (Plank and Kelley, 2001). Volcanism in the backarc region of Izu, however, does have the appropriate Th concentrations, consistent with this region receiving the dominant sediment recycling flux. PM = primitive mantle, N-MORB = normal mid-ocean ridge basalt. B. This suggests a delayed delivery system for the Izu arc, possibly resulting from different dips of the cold Izu and Marianas slabs (cartoon after Straub, 2003). Global array after Plank and Langmuir (1993); Mariana arc data from Elliott et al. (1997); Izu arc data from Taylor and Nesbitt (1998); Izu backarc data from Hochstaedter et al. (2001). Izu Th sediment flux calculated from Site 1149 natural gamma logging data, which agree well with high precision core analyses (Fig. F4). VF = volcanic front.

Figure F8. Th recycling at the Izu and Marianas subduction zones. A. Izu arc volcanics are deficient in Th relative to Marianas arc volcanics by a factor of ~5 (based on Th/Na). This deficiency in the Izu arc is anomalous with respect to the global array and the Th sediment input flux, based on drilling results reported here for ODP Site 1149 (Plank and Kelley, 2001). Volcanism in the backarc region of Izu, however, does have the appropriate Th concentrations, consistent with this region receiving the dominant sediment recycling flux. PM = primitive mantle, N-MORB = normal mid-ocean ridge basalt. B. This suggests a delayed delivery system for the Izu arc, possibly resulting from different dips of the cold Izu and Marianas slabs (cartoon after Straub, 2003). Global array after Plank and Langmuir (1993); Mariana arc data from Elliott et al. (1997); Izu arc data from Taylor and Nesbitt (1998); Izu backarc data from Hochstaedter et al. (2001). Izu Th sediment flux calculated from Site 1149 natural gamma logging data, which agree well with high precision core analyses (Fig. F4). VF = volcanic front.