JpGU-AGU Joint Meeting 2017

講演情報

[EE] ポスター発表

セッション記号 S (固体地球科学) » S-CG 固体地球科学複合領域・一般

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

2017年5月24日(水) 15:30 〜 17:00 ポスター会場 (国際展示場 7ホール)

コンビーナ:田村 芳彦(海洋研究開発機構 海洋掘削科学研究開発センター)、道林 克禎(静岡大学理学部地球科学科)、高澤 栄一(新潟大学理学部地質科学科)、Katy Jane Chamberlain(JAMSTEC)、森下 知晃(金沢大学理工研究域自然システム学系)、Henry JB Dick(Woods Hole Oceanographic Institution)、Mark K Reagan(University of Iowa)、Susanne M Straub(Lamont Doherty Earth Observatory of Columbia University)

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

*佐藤 智紀1宮崎 隆1田村 芳彦1Gill James2Jutzeler Martin3,4仙田 量子5,1木村 純一1 (1.国立研究開発法人海洋研究開発機構、2.カリフォルニア大学サンタクルーズ校、3.ナショナルオセアノグラフィーセンター、4.タスマニア大学、5.九州大学)

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.