JpGU-AGU Joint Meeting 2017

Presentation information

[EE] Poster

S (Solid Earth Sciences) » S-CG Complex & General

[S-CG63] [EE] Crust-Mantle Connections / Hard-Rock Drilling

Wed. May 24, 2017 5:15 PM - 6:30 PM Poster Hall (International Exhibition Hall HALL7)

[SCG63-P01] The earliest stage of Izu rear arc volcanism revealed by drilled cores at Site U1437, IODP Expedition 350

*Tomoki Sato1, Takashi Miyazaki1, Yoshihiko Tamura1, James B. Gill2, Martin Jutzeler3,4, Ryoko Senda5,1, Jun-Ichi Kimura1 (1.Japan Agency for Marine-Earth Science and Technology, 2.University of California Santa Cruz, 3.National Oceanography Centre, 4.University of Tasmania, 5.Kyushu University)

The present Izu arc system consists of three types of volcanic structures, which are (1) the Quaternary volcanic front, (2) the rear-arc seamount chains and (3) bimodal rift-type volcanoes in a back-arc knoll zone and an active rift area, situated between the volcanic front and the rear-arc seamount chains. Ishizuka et al. (2003) show that the Izu rear arc volcanism migrated from eastward after the cessation of the Shikoku Basin opening (25-15 Ma; Okino et al., 1999). The rear-arc seamount chains volcanism began at 17 Ma and continued until 3 Ma, and was followed by rift type volcanism from 2.8 Ma to present (Ishizuka et al., 2003).

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.