JpGU-AGU Joint Meeting 2017

講演情報

[EJ] 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-CG71] [EJ] 海洋底地球科学

2017年5月24日(水) 13:45 〜 15:15 ポスター会場 (国際展示場 7ホール)

コンビーナ:沖野 郷子(東京大学大気海洋研究所)

[SCG71-P01] Results of physical property measurements obtained during the CHIKYU cruise CK16-05 of hydrothermal fields at the middle Okinawa Trough.

*正木 裕香1小森 省吾2斎藤 誠史1Kakda Kret3南出 奏4大野 正夫3山本 浩文1McIntosh Iona1谷川 亘1野崎 達生1熊谷 英憲1石橋 純一郎3前田 玲奈1CK16-05 乗船者一同 (1.海洋研究開発機構、2.産業総合研究所、3.九州大学大学院、4.京都大学大学院)

キーワード:海底熱水、ちきゅう、物性測定、伊是名

The middle Okinawa Trough, located along the Ryukyu-arc on the margin of the East China Sea, has several active hydrothermal fields. Cruise CK16-05 of D/V CHIKYU targeted one of the largest hydrothermal fields, the Izena hydrothermal field, and conducted coring operations. Site C9027 is located on the center part of the Northern sulfide mound. Four other sites where we can observe the subseafloor sulfide layer were drilled along an eastward transect from the Northern mound (Sites C9028, C9026, C9025 and C9032 from west to east). Two additional reference sites (C9029 and C9030) located to the north and northwest of Site C9027, where the subseafloor sulfide layer is not distributed, were
also drilled. Here, we present the results of physical property measurements obtained by using CHIKYU’s on-board laboratory.
Drilled core samples from the Northern mound (Site C9027) mainly consisted of sulfide-rich rocks. The total recovered core length was 5.09 m and core recovery rate was only 3.9 %, due to the difficulty of coring operations in this material. These core samples exhibited the highest thermal conductivity (18.37 W/m·K) and the highest P-wave velocity (7,613 m/sec) of all sites, which is consistent with an abundant occurrence of sulfide minerals.
The four sites along the eastward transect from the Northern mound (Sites C9028, C9026, C9025 and C9032) consisted of hemi-pelagic sediment, hydrothermal altered sediment, pumiceous gravel and sulfide layers. Conspicuous peaks in the results of physical property measurements such as a notably high grain density were observed within the cores from all four sites, suggesting that a large sub-seafloor sulfide layer is widely distributed in this area.
Core samples from the two reference sites (Sites C9029 and C9030) mainly consisted of pumiceous gravel and mud, and total recovered core lengths were 84.5 m and 61.4 m with recovery rates of 53.7% and 66.7%, respectively. Physical property data from these two sites did not exhibit the conspicuous peaks that were observed in the sites associated with the sub-seafloor sulfide layer.
Using whole physical property data, we will also present a first-order sub-seafloor physical property model for the Izena hydrothermal field in this presentation.