14:00 〜 14:15
[MIS02-14] Overview of drilling of crust-mantle boundary of Oman ophiolite: the ICDP Oman Drilling Project
キーワード：オマーンオフィオライト、国際陸上科学掘削プログラム、オマーン掘削プロジェクト、地殻-マントル境界、モホ遷移帯
From the winter of 2017 to 2018 the drilling of crust-mantle transition zone (MTZ) was conducted at Wadi Zeeb (CM1&2 sites) in Wadi Tayin massif by the International Continental Scientific Drilling ProgramOman Drilling Project [6]. The MTZ of Oman ophiolite has been characterized by thick dunites accompanied by thin veins or clots of plagioclase and clinopyroxene and several centimeters to meters thick gabbro sills and wehrlite intrusions. The origin of MTZ is still under debate [2-5]. To clarify this origin, more detailed research by continuous core through MTZ is necessary.
Geological mapping on ground associated with information from the recovered cores in CM1&2 sites the thickness of the MTZ is estimated as about 150 m. The upper and lower boundaries of the MTZ has a strike in the east-west direction, and it is inclined about 30 degrees south. In the summer of 2018, the drilled cores were carefully described by scientists on the deep-sea drilling vessel "CHIKYU". The stratigraphy has been divided into four igneous sequences based on the abundance of different lithologies: Layered Gabbro Sequence, Dunite Sequence, Dunite with Gabbro Sequence, and Mantle Sequence. Dunite Sequence and Dunite with Gabbro Sequence are summarized as Crust - Mantle Transition.
Hole CM1A is inclined 60° northward. The upper 160 m of the core is the Layered Gabbro Sequence, mostly composed of olivine gabbro, interlayered with gabbro and a small amount of wehrlite, dunite, anorthosite and troctolite. From 160 to 310 m the Crust-Mantle Transition is divided into an upper 90 m Dunite Sequence and a lower 60 m Dunite with Gabbro Sequence containing small lenses of gabbro, troctolite and wehrlite. The dunites are highly serpentinized, and rodingite and diopsidite commonly replace minor gabbroic rocks in these sequences. The lower 80 m of the hole is the Mantle Sequence, with alternating layers of dunite and increasingly abundant, residual mantle harzburgite.
Hole CM2B is a vertical hole located 400 m north of CM1A, and samples the Crust-Mantle Transition and the Mantle Sequence. As in CM1A, the transition is divided into an upper Dunite Sequence and a lower Dunite with Gabbro Sequence. In contrast to Hole CM1A, a small amount of olivine has escaped complete serpentinization in the lower portions of the CM2B transition zone. In the Mantle Sequence, harzburgite is dominant. Dunite accounts for about 25% of this Sequence, less than in CM1A. The lowermost peridoties in Hole CM2B are strongly altered to talc+carbonate.
[1] Boudier and Nicolas, 1995, J. Petrol., 36, 777-796, [2] Pallister and Hopson, 1981, J. Geophys. Res., 86, 2593-2644, [3] Kelemen et al., 1995, Nature, 375, 747-753, [4] Abily and Ceuleneer, 2013, Geology, 41, 67-70, [5] Rospabé et al., 2017, Geol. Soc. Am., Data Rep. 2017139, [6] Kelemen et al., 2013, Scientific Drilling, 15, 64-71.
Geological mapping on ground associated with information from the recovered cores in CM1&2 sites the thickness of the MTZ is estimated as about 150 m. The upper and lower boundaries of the MTZ has a strike in the east-west direction, and it is inclined about 30 degrees south. In the summer of 2018, the drilled cores were carefully described by scientists on the deep-sea drilling vessel "CHIKYU". The stratigraphy has been divided into four igneous sequences based on the abundance of different lithologies: Layered Gabbro Sequence, Dunite Sequence, Dunite with Gabbro Sequence, and Mantle Sequence. Dunite Sequence and Dunite with Gabbro Sequence are summarized as Crust - Mantle Transition.
Hole CM1A is inclined 60° northward. The upper 160 m of the core is the Layered Gabbro Sequence, mostly composed of olivine gabbro, interlayered with gabbro and a small amount of wehrlite, dunite, anorthosite and troctolite. From 160 to 310 m the Crust-Mantle Transition is divided into an upper 90 m Dunite Sequence and a lower 60 m Dunite with Gabbro Sequence containing small lenses of gabbro, troctolite and wehrlite. The dunites are highly serpentinized, and rodingite and diopsidite commonly replace minor gabbroic rocks in these sequences. The lower 80 m of the hole is the Mantle Sequence, with alternating layers of dunite and increasingly abundant, residual mantle harzburgite.
Hole CM2B is a vertical hole located 400 m north of CM1A, and samples the Crust-Mantle Transition and the Mantle Sequence. As in CM1A, the transition is divided into an upper Dunite Sequence and a lower Dunite with Gabbro Sequence. In contrast to Hole CM1A, a small amount of olivine has escaped complete serpentinization in the lower portions of the CM2B transition zone. In the Mantle Sequence, harzburgite is dominant. Dunite accounts for about 25% of this Sequence, less than in CM1A. The lowermost peridoties in Hole CM2B are strongly altered to talc+carbonate.
[1] Boudier and Nicolas, 1995, J. Petrol., 36, 777-796, [2] Pallister and Hopson, 1981, J. Geophys. Res., 86, 2593-2644, [3] Kelemen et al., 1995, Nature, 375, 747-753, [4] Abily and Ceuleneer, 2013, Geology, 41, 67-70, [5] Rospabé et al., 2017, Geol. Soc. Am., Data Rep. 2017139, [6] Kelemen et al., 2013, Scientific Drilling, 15, 64-71.