2:45 PM - 3:00 PM
[SCG52-05] Recovering oceanic mantle rocks by the D/V Chikyu with riser-less drilling into the petit-spot pipe
Keywords:deep-sea drilling vessel (D/V) Chikyu, petit-spot pipe, riser-less oceanic mantle drilling, scientific ocean drilling,
Three potential drilling sites for IODP proposals using the riser drilling vessel (D/V) Chikyu; the Mohole to Mantle (M2M drilling project) have been proposed, but they have encountered a big difficulty, because provision of the riser pipe with about 4000m long seems to be no prospect. On the other hand, she has drill pipes of 12000m long. We would like to propose riser-less mantle drilling using the D/V Chikyu .
The Pacific Plate is subducting at the Japan Trench off NE Japan. Just immediately before the subduction, the new type volcanoes with young age(1.8-8.5Ma) and small edifice were found on the old ocean floor (130-135Ma), off Tohoku and named as petit-spot (Hirano et al. 2006).
The edifice has the following characters, according to the Sea Beam data, the crater rim is about 5700m deep (with about 5690m summit) and its diameter is about 600m. The crater bottom is about 5730m deep and flat, so shape is very smooth. It is topographically very similar to the Ichino-megata volcano in Yamagata prefecture, which is known as typical Maar in Japan.
Dredged samples are glassy vesicular basalts, mudstone, ferromanganese, pumice, and hemipelagic sediment containing basaltic fragments and glasses. Basalts is glassy, aphyric and very vesicular, Alkaline basaltic magma of petit-spot volcano is generated in the oceanic plate asthenosphere (approximately 60 km below the seafloor), passes through the Moho discontinuity (approximately 6 km below the seafloor), and rises to erupt and erupts as lavas, sills, and volcanic breccia (with a density of about 1.5) on the deep seafloor.
Petit-spot volcanoes on the oceanic plate are unique volcanoes like kimberlite volcanoes on the continental plate. Both volcanoes can directly bring materials from asthenosphere of ocean and continent, respectively. We can assume that petit-spot volcanoes have volcanic pipes (petit-spot pipes) like kimberlite pipes. Those volcanoes may be the best target for IODP riser-less mantle drilling using the D/V Chikyu. in the near future.
The petit-spot pipe, which is a volcanic vent, may have formed a nearly vertical tunnel with a natural casing down to the mantle, as a result of gaining regional stress relief and strong walls due to ascent and intrusion of magmas. We propose riser-less ultra-deep-sea Maar Crater drilling toward the Moho into the petit-spot pipe filled with volcanic breccia, which is also easy to drill by the riser-less drilling vessel.
The core barrel that can drill upwards should be developed for the riser-less drilling by the D/V Chikyu as shown by the author (Ishii et al., 2023). Sampling will be carried out by lateral and/or branch drilling, later.
Borehole locating near Japanese Island will be used for observatory against natural hazard. Many volcanic edifices similar to the petit-spot volcanoes have been recently reported from the deep sea floor in the all over the world.
References:
Hirano, N., Takahashi, E., Yamamoto, J., Abe, N., Ingle, S. P., Kaneoka, I., Kimura, J., Hirata, T., Ishii, T., Ogawa, Y., Machida, S. and Suyehiro, K. (2006): Volcanism in response to plate flexure. Science, 313, 1426–1428.
ISHII Teruaki, KANEKO Makoto, HIRANO Naoto, MACHIDA Shiki, MATSUMOTO Asako, AKIZAWA Norikatsu, SATO Yuki, YUTANI Taku, AZAMI Keishiro, KATSURAGI Yuki, SAKAI Shunta, NAKANO Yukihiko, MATSUZAKI Takuya (2019): Quick report of the R/V Shinsei-maru KS-18-9 dredge cruise on petit-spot volcanoes -Historical great discovery: explosion crater (Maar) in the Pacific abyssal plane, off Tohoku -, Annual Rep., Fukada Geol. Inst., 20, 105 –128 (in Japanese).
ISHII Teruaki, KANEKO Makoto, HIRANO Naoto, MACHIDA Shiki, AKIZAWA Norikatsu (2023): Riser-less drilling through the petit-spot pipe to recover oceanic mantle -New Project Mohole using the deep sea drilling vessel (D/V) CHIKYU-, Annual Rep., Fukada Geol. Inst., 24,119-138 (in Japanese).
The Pacific Plate is subducting at the Japan Trench off NE Japan. Just immediately before the subduction, the new type volcanoes with young age(1.8-8.5Ma) and small edifice were found on the old ocean floor (130-135Ma), off Tohoku and named as petit-spot (Hirano et al. 2006).
The edifice has the following characters, according to the Sea Beam data, the crater rim is about 5700m deep (with about 5690m summit) and its diameter is about 600m. The crater bottom is about 5730m deep and flat, so shape is very smooth. It is topographically very similar to the Ichino-megata volcano in Yamagata prefecture, which is known as typical Maar in Japan.
Dredged samples are glassy vesicular basalts, mudstone, ferromanganese, pumice, and hemipelagic sediment containing basaltic fragments and glasses. Basalts is glassy, aphyric and very vesicular, Alkaline basaltic magma of petit-spot volcano is generated in the oceanic plate asthenosphere (approximately 60 km below the seafloor), passes through the Moho discontinuity (approximately 6 km below the seafloor), and rises to erupt and erupts as lavas, sills, and volcanic breccia (with a density of about 1.5) on the deep seafloor.
Petit-spot volcanoes on the oceanic plate are unique volcanoes like kimberlite volcanoes on the continental plate. Both volcanoes can directly bring materials from asthenosphere of ocean and continent, respectively. We can assume that petit-spot volcanoes have volcanic pipes (petit-spot pipes) like kimberlite pipes. Those volcanoes may be the best target for IODP riser-less mantle drilling using the D/V Chikyu. in the near future.
The petit-spot pipe, which is a volcanic vent, may have formed a nearly vertical tunnel with a natural casing down to the mantle, as a result of gaining regional stress relief and strong walls due to ascent and intrusion of magmas. We propose riser-less ultra-deep-sea Maar Crater drilling toward the Moho into the petit-spot pipe filled with volcanic breccia, which is also easy to drill by the riser-less drilling vessel.
The core barrel that can drill upwards should be developed for the riser-less drilling by the D/V Chikyu as shown by the author (Ishii et al., 2023). Sampling will be carried out by lateral and/or branch drilling, later.
Borehole locating near Japanese Island will be used for observatory against natural hazard. Many volcanic edifices similar to the petit-spot volcanoes have been recently reported from the deep sea floor in the all over the world.
References:
Hirano, N., Takahashi, E., Yamamoto, J., Abe, N., Ingle, S. P., Kaneoka, I., Kimura, J., Hirata, T., Ishii, T., Ogawa, Y., Machida, S. and Suyehiro, K. (2006): Volcanism in response to plate flexure. Science, 313, 1426–1428.
ISHII Teruaki, KANEKO Makoto, HIRANO Naoto, MACHIDA Shiki, MATSUMOTO Asako, AKIZAWA Norikatsu, SATO Yuki, YUTANI Taku, AZAMI Keishiro, KATSURAGI Yuki, SAKAI Shunta, NAKANO Yukihiko, MATSUZAKI Takuya (2019): Quick report of the R/V Shinsei-maru KS-18-9 dredge cruise on petit-spot volcanoes -Historical great discovery: explosion crater (Maar) in the Pacific abyssal plane, off Tohoku -, Annual Rep., Fukada Geol. Inst., 20, 105 –128 (in Japanese).
ISHII Teruaki, KANEKO Makoto, HIRANO Naoto, MACHIDA Shiki, AKIZAWA Norikatsu (2023): Riser-less drilling through the petit-spot pipe to recover oceanic mantle -New Project Mohole using the deep sea drilling vessel (D/V) CHIKYU-, Annual Rep., Fukada Geol. Inst., 24,119-138 (in Japanese).