日本地球惑星科学連合2019年大会

講演情報

[E] 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-CG49] ハードロック掘削科学~陸上掘削から深海底掘削、そしてオマーン~

2019年5月28日(火) 15:30 〜 17:00 ポスター会場 (幕張メッセ国際展示場 8ホール)

コンビーナ: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)、高澤 栄一(新潟大学理学部地質科学科)、秋澤 紀克(東京大学 大気海洋研究所 海洋底科学部門)

[SCG49-P03] Physical property of the fossilized crust-mantle transition zone from ICDP Oman Drilling Project Hole CM1A and CM2B measured onboard D/V Chikyu

*岡崎 啓史1阿部 なつ江1畠山 航平2赤松 祐哉2片山 郁夫2高澤 栄一3Damon Teagle4Peter Kelemen5Jude Coggon4The Oman Drilling Project Phase 2 Science Party (1.海洋研究開発機構、2.広島大学、3.新潟大学、4.サウサンプトン大学、5.コロンビア大学)

キーワード:オフィオライト、マントル、海洋地殻、モホ面

To understand physical properties of the oceanic crust and the mantle is fundamentally important to reveal the dynamics of plate tectonics, and the global circulations of H2O and CO2 fluids. We report results on physical property measurements of core samples from Oman Drilling Project (OmanDP) Holes CM1A and CM2B, which drilled from the lower igneous crust into the upper mantle in the Samail Ophiolite, Sultanate of Oman.



X-ray CT, bulk/grain density, porosity, magnetic susceptibility, P-wave velocity, electrical resistivity and thermal conductivity were measured onboard D/V Chikyu using whole-round cores and discrete samples for core sections from CM1A and CM2B.



The paleo-Moho in CM1A may not preserve the original structure due to minor faulting, possibly during obduction. The gabbro-dunite transition (paleo-Moho) in Hole CM1A is characterized by a sharp change in physical property data. For example, P-wave velocity decreases from ~6.7 km/s in the layered gabbro sequence to ~4.9 km/s in the MTZ. Low P-wave velocity and density (~2.6 g/cm3) in serpentinized dunites reflect the fact that olivine in the dunites is almost completely serpentinized. Serpentinization could have occurred during hydrothermal alteration near the spreading ridge axis, during subduction of 100’s of km of oceanic crust and sediment beneath the ophiolite, during obduction onto the Arabian continental margin, and/or during present-day weathering. In contrast to the paleo-Moho, the boundary between the Crust-Mantle Transition (CMT) sequences (i.e., dunites and dunites with gabbro lenses) and the underlying, residual mantle harzburgites is somewhat gradual. P-wave velocity gradually increases from ~4.9 km/s for dunite in the CMT to ~5.5 km/s for harzburgite in the mantle sequence. The thickness of the CMT is 50–70 m in Holes CM1A and CM2B. We also report on correlations between physical properties, especially electrical conductivity and magnetic susceptibility, and the fault intensity and alteration intensity from the core descriptions.