Japan Geoscience Union Meeting 2019

Presentation information

[E] Oral

S (Solid Earth Sciences ) » S-CG Complex & General

[S-CG49] Hard-Rock Drilling Science: From Continental to Deep Sea Drilling, and Oman Project

Tue. May 28, 2019 10:45 AM - 12:15 PM A07 (TOKYO BAY MAKUHARI HALL)

convener:Katsuyoshi Michibayashi(Department of Earth and Planetary Sciences, Nagoya University), Eiichi TAKAZAWA(Department of Geology, Faculty of Science, Niigata University), Norikatsu Akizawa(Department of Ocean Floor Geoscience, Atmosphere and Ocean Research Institute, The University of Tokyo), Chairperson:Tomoaki Morishita(Kanazawa University), Katsuyoshi Michibayashi

11:00 AM - 11:15 AM

[SCG49-13] Petrophysical characteristics of serpentinized peridotites of Hole BA1B, BA3A and BA4A

*Kakihata Yuki1, Katsuyoshi Michibayashi2, Laura Crispini3, Bjorn Jamtveit4, Samuel Barbier5, Joe Aslin6, Manuel Menzel7, Marguerite Godard8 (1.Graduate School of Science, Shizuoka University, 2.Graduate School of Environmental Studies, Nagoya University, 3.University of Genova, 4.University of Oslo, 5.Claude Bernard University Lyon 1, 6.University of Liverpool, 7.Andalusian Earth Science Institute, 8.Géosciences Montpellier, CNRS, Univ. Montpellier)

Keywords:Oman Drilling Project, Peridotite, Crystal plastic fabric

Structural characteristics within peridotites of Hole BA1B, BA3A and BA4A have been described during the Oman Drilling Project Phase 2 from 5th August to 3rd September, 2018 on D/V Chikyu. The peridotites consisted of intensely serpentinized harzburgite and dunite, which exhibited foliations defined by elongation and alignment of constituent minerals. Crystal plastic fabrics in harzburgite were described prior to those in dunite because orthopyroxene grains are clearer than spinel grains in serpentinized peridotites at macro scale.

Harzburgites in BA1B show variously deformed textures ranging from pophyroclastic to protomylonitic textures in dependent on the depth. In BA3A, harzburgites with protogranular texture were observed in relatively shallow sections (10-90 m), whereas porphyroclastic to strongly foliated textures were dominant in deeper sections. Most of hartzburgites in BA4A show porphyroclastic texture, partly clear foliation and protomylonitic textures by strongly elongated orthopyroxene grains. Dip angles of measured foliations in BA1B are mostly 0-20°, which are nearly horizontal. Most of dip angles in BA3A are at around 30°, up to 50°. In BA4A, dip angles of orthopyroxene grains take various values between 10-50°. In BA3A and BA4A show similar dip angles, but significantly steeper than those in BA1B. In each hole, dip angles were nearly constant independent on the depth.

Pyroxene and spinel grains in strongly foliated to protomylonitic peridotites are intensely elongated and aligned, exhibiting clear foliation at thin section scale. In protogranular peridotites, pyroxene and spinel grains have rounded shapes and are not elongated and aligned, and foliations are unclear. Elongated pyroxene and olivine grains in protomylonitic peridotites show kink bands and wavy extinction, whereas few rounded pyroxene grains in protogranular peridotites show these features.