日本地球惑星科学連合2018年大会

講演情報

[EE] Evening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-CG54] ハードロック掘削 オマーンから海洋リソスフェア,島弧形成+

2018年5月21日(月) 17:15 〜 18:30 ポスター会場 (幕張メッセ国際展示場 7ホール)

コンビーナ:高澤 栄一(新潟大学理学部地質科学科)、道林 克禎(名古屋大学大学院環境学研究科地球環境科学専攻地質・地球生物学講座岩石鉱物学研究室)、Peter B Kelemen (共同)、Damon A H Teagle (Ocean & Earth Science, National Oceanography Centre Southampton, University of Southampton, SO14-3ZH, Southampton, UK)

[SCG54-P06] Overview of Hole GT3A: The sheeted dike/gabbro transition

*阿部 なつ江1ハリス ミッシェル2道林 克禎3de Obeso Juan Carlos4ケレメン ピーター5高澤 栄一6ティーグル デーモン7カゴン ジュード7マター ヨルク4The Oman Drilling Project Phase I Science Party8 (1.国立研究開発法人海洋研究開発機構海洋掘削科学研究開発センター、2.Plymouth University、3.静岡大学、4.Lamont -Doherty Earth Observatory、5.Columbia University、6.新潟大学、7.University of Southampton, Ocean & Earth Science, National Oceanography Centre Southampton、8.University of Southampton, Oman Drilling Project Office)

キーワード:ICDPオマーン掘削、シート状岩脈群ー斑れい岩境界、地球深部探査船「ちきゅう」、海洋地殻

Hole GT3A (23.11409 N, 58.21172 E) was drilled by the Oman Drilling Project (OmDP) into Wadi Abdah of the Samail ophiolite, Oman and samples the sheeted dike-gabbro transition zone. OmDP is an international collaboration supported by the International Continental Scientific Drilling Program, the Deep Carbon Observatory, NSF, IODP, JAMSTEC, and the European, Japanese, German and Swiss Science Foundations, with in-kind support in Oman from the Ministry of Regional Municipalities and Water Resources, Public Authority of Mining, Sultan Qaboos University, and the German University of Technology. Hole GT3A was diamond cored in February to March 2017 to a total depth of 400 m. The outer surfaces of the cores were imaged and described on site before being curated, boxed and shipped to the IODP drill ship Chikyu, where they underwent comprehensive visual and instrumental analysis.

Hole GT3A recovered predominantly sheeted dikes and gabbros and has been sub-divided into 4 igneous groups based on the abundance of gabbro downhole. Group 1 (Upper Sheeted Dike Sequence), group II (Upper Gabbro Sequence), group III (Lower Sheeted Dike Sequence) and group IV (Lower Gabbro Sequence). Group II and IV are both associated with almost equal proportions of dikes to gabbroic lithologies, whereas group I & III have >95% dikes.

The sheeted dikes were logged as either basalt (46.9 %) or diabase (26.2 %) depending on the predominant grain size of the dike. Gabbroic lithologies include (most to least abundant) gabbro, oxide gabbro and olivine gabbro. Other lithologies present include diorite (7.5%) and tonalite and trondhjemite (1%). Tonalite and trondhjemite are present as cm-sized dikelets and are found within group II and IV. Gabbroic lithologies generally display a varitextured appearance and are characterised by the co-existence of poikilitic and granular domains. Detailed observations of chilled margins and igneous contacts reveal the relative timing of dike and gabbro intrusion, and identify that the Upper Gabbro Sequence intrudes into dikes, whereas the Lower Gabbro Sequence is intruded by dikes. Hydrothermal alteration is recorded throughout the hole and the mean alteration intensity is 54% (range = 10-100%) and mean vein density is 27 veins/m. The intensity of brittle deformation is generally low downhole with restricted intervals associated with fault zones.