[S-CG56] 海洋底地球科学

[SCG56-P12] 沖縄トラフ東奄西熱水フィールドでの浅層科学掘削

*熊谷 英憲¹、笠谷 貴史¹、戸塚 修平²、川口 慎介¹、町山 栄章¹、飯島 耕一¹、山本 浩文¹、金子 純二¹、大田 優介³、冨田 昇平³、小森 省吾⁴ (1.国立研究開発法人海洋研究開発機構、2.九州大学、3.京都大学、4.国立研究開発法人産業技術総合研究所)

キーワード：海底着座型掘削装置、自然電位異常、孔口付近の白色堆積物

A shallow seabed drilling was performed in February 2019 at Higashi Ensei Hydrothermal Field, Northern Okinawa Trough (Cruise ID: KM19-E01). Two localities were selected to investigate natures of sub-seafloor lithology with and without self-potential anomaly (SP anomaly) measured by near-bottom AUV survey. Here such a SP anomaly is to be resulted from a sub-seafloor orebody consisted of mainly sulfides. A seabed drilling apparatus, BMS (Boring machine system, Cellula Robotics Ltd.), was deployed twice from R/V Kaimei. At the first drilling in the cruise, the drilled hole reached to a formation 44m beneath the seafloor but stopped there due to significant venting through the drilled hole. Volcaniclastics with and without sulfide blocks or veins were sampled even poor recovery in the shallow part of the hole. Contrasting to it, the second drilled hole reached to 10 m beneath the seafloor where intact mafic-intermediate lava flow, i.e. volcanic basement, was sampled. In the second hole, little sulfide were retrieved except orange-colored one, probably realgar associating with orpiment and stibnite, in the first core, shallower than 1.5mbsf. On board IP measurement both as well as standard MSCL and visual core description were performed for the cores from the first hole. Further, an ROV dive observation was conducted within 16.5 hours after the drilling of the first hole. An exotic white sediment was recognized in the vicinity of the hole, similarly to the IODP exp.331 at Iheya-North Knoll, and successfully sampled. In this presentation, retrieved drilled samples as well as those sampled by ROV will be reported.