地学雑誌 | Journal of Geography (Chigaku Zasshi)

2021 Vol.130 No.4

Drilling into Oman Ophiolite in the Middle of the Wadi Zeeb at the Wadi Tayin Massif, Sultanate of Oman: Core Sample of Ultramafic Rock (Dunite) (Corresponding to Part of the Mohorovicic Seismic Discontinuity, Which Was the Crust–Mantle Boundary) and View of the Drilling Site

The Oman ophiolite drilling project under the International Continental Scientific Drilling Program was carried out in 2016‒2018. A team of Japanese scientists led efforts to drill through the oceanic crust–mantle boundary that formed the ocean floor more than 100 million years ago. They succeeded in collecting continuous core samples from the gabbro sequence (the lowest part of the oceanic crust) through the Moho transition zone to the harzburgite sequence (the uppermost part of the mantle), and obtained fresh core samples (left photo) from the crust–mantle boundary. Many of the shiny particles that can be seen with the naked eye are crystals that were originally olivine under the mid-oceanic ridge and have been serpentinized by secondary alteration. Right photo: The drilling rig shown at the center of the photo was brought to the site, and core samples with a maximum length of 400 m were collected from two drilling holes. Two rotary holes were also drilled to measure physical properties in the holes. The core samples collected include gabbro, which constituted the lowermost part of the oceanic crust, through the Moho transition zone, and harzburgite, which constituted the uppermost part of the mantle. This crust–mantle boundary drilling is an important milestone in our ongoing project to drill into the mantle at the bottom of the ocean.

(Eiichi TAKAZAWA and Shigeaki ONO)

Special Issue: Hard-rock Drilling Science: Challenges of Mantle Drilling

Overview of the Special Issue
　“Hard-rock Drilling Science: Challenges of Mantle Drilling”

Shigeaki ONO

Journal of Geography (Chigaku Zasshi), 2021, 130(4), 453.

DOI:10.5026/jgeography.130.453

Introduction to the Special Issue
　“Hard-rock Drilling Science: Challenges of Mantle Drilling”

Shigeaki ONO

Journal of Geography (Chigaku Zasshi), 2021, 130(4), 457.

DOI:10.5026/jgeography.130.457

History of Deep-sea Ocean Basement Drilling Programs and Contributions
　to the Earth Sciences (Review Article)

Katsuyoshi MICHIBAYASHI

Journal of Geography (Chigaku Zasshi), 2021, 130(4), 461.

DOI:10.5026/jgeography.130.461

Crucial Scientific Issues in Earth Science Revealed Only by Mantle Drilling:
　Understanding the Current State of the Oceanic Plates of a Life-bearing Planet
　(Review Article)

Tomoaki MORISHITA, Gou FUJIE, Ken-ichi HIRAUCHI, Ikuo KATAYAMA,
Yui KOUKETSU, Jun-ichiro KURODA, Atsushi OKAMOTO, Shigeaki ONO,
Katsuyoshi MICHIBAYASHI, Yuki MORONO and Shinji YAMAMOTO

Journal of Geography (Chigaku Zasshi), 2021, 130(4), 483.

DOI:10.5026/jgeography.130.483

Achievements and Future Prospects of the ICDP Oman Drilling Project
　(Review Article)

Eiichi TAKAZAWA

Journal of Geography (Chigaku Zasshi), 2021, 130(4), 507.

DOI:10.5026/jgeography.130.507

Outcome of Hard Rock Drilling in the Izu‒Bonin Arc (Review Article)

Osamu ISHIZUKA

Journal of Geography (Chigaku Zasshi), 2021, 130(4), 527.

DOI:10.5026/jgeography.130.527

IODP Drilling at the Godzilla Megamullion:
　The Nature of the Backarc Basin Lower Crust and Upper Mantle (Review Article)

Yasuhiko OHARA

Journal of Geography (Chigaku Zasshi), 2021, 130(4), 543.

DOI:10.5026/jgeography.130.543

Testing the Ontong Java Nui Hypothesis: The Largest Supervolcano Ever on Earth
　(Review Article)

Takashi SANO, Maria Luisa G. TEJADA, Masao NAKANISHI,
Takeshi HANYU, Seiichi MIURA, Daisuke SUETSUGU, Takashi TONEGAWA,
Akira ISHIKAWA, Kenji SHIMIZU and Shoka SHIMIZU

Journal of Geography (Chigaku Zasshi), 2021, 130(4), 559.

DOI:10.5026/jgeography.130.559