[SCG63-P01] The earliest stage of Izu rear arc volcanism revealed by drilled cores at Site U1437, IODP Expedition 350
IODP Expedition 350 Site U1437 is located in the boundary area of the back-arc knoll zone and rear-arc seamount chains and drilled between the Enpo and Manji rear-arc chains. The first complete sequence of rear-arc rocks dated <15 Ma (Schmitt et al., in preparation) were recovered at this Site (Tamura et al., 2015), and develop over Unit I (top) to Unit VII (bottom).
The major and trace element compositions collected from the deepest parts of the Hole (Unit V and VII) show different types of magmatism. The lowermost Unit VII (~15 Ma) shows rift-type magmatism which have a relatively flat REE patterns, and Unit V (8 Ma) shows rear-arc seamount chains type with LREE-enriched patterns. This suggests that the area around Site U1437 used to be an extensional zone following the Shikoku Basin opening. At 17-8 Ma, volcanism in the Izu back-arc side occurred only in the western part of the seamount chains (Ishizuka et al., 2003) and in the eastern part of the Shikoku Basin (e.g. Kinan Escarpment; Ishizuka et al., 2009). Simultaneously rift-type volcanism occurred in the eastern part of the present seamount chains region.
The difference between the Unit VII and V indicates the temporal change of the subduction components with time. It is suggested that the subducting slab below Site U1437 had deepened with time.