Japan Geoscience Union Meeting 2025

Presentation information

Print

[E] Poster

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

[S-CG51] Hard-Rock Drilling Science: Continental and Deep-Sea Drilling, and Ophiolite

Mon. May 26, 2025 5:15 PM - 7:15 PM Poster Hall (Exhibition Hall 7&8, Makuhari Messe)

convener:Takashi Hoshide(Faculty of International Resource Sciences, Akita University), Yumiko Harigane(Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology (AIST)), Keishi Okazaki(Earth and Planetary Systems Science Program, Hiroshima University)

5:15 PM - 7:15 PM

[SCG51-P07] Mylonitized plagioclase lherzolite from Uenzaru peridotite complex in the Hidaka Metamorphic Belt, Hokkaid

*So Inoue1, Katsuyoshi Michibayashi1,2 (1.Department of Earth and Planetary Sciences, GSES, Nagoya University, 2.Volcanoes and Earth's Interior Research Center, IMG, JAMSTEC)


Keywords:Uenzaru peridotite complex, Hidaka metamorphic belt, peridotite, mylonite, phase transformation, spinel

The Uenzaru peridotite complex, located in the northern part of the Hidaka metamorphic belt in central Hokkaido, contains mylonitized plagioclase lherzolite. Mylonitization appears to occur because of a subsolidus phase transformation reaction from spinel lherzolite to plagioclase lherzolite[1]. In this study, we focused on the mylonitization of plagioclase lherzolite in the Uenzaru peridotite complex using polarized light microscopy and scanning electron microscopy with electron backscatter diffraction (SEM-EBSD). We analyzed an oriented plagioclase lherzolite sample. Polished thin sections were made in a plane normal to foliation and parallel to lineation (XZ plane). Plagioclase lherzolite shows a porphyroclastic texture with porphyroclasts consisting of olivine, highly elongated orthopyroxene (ca. 15 mm), clinopyroxene, and spinel in a fine-grained matrix of olivine, orthopyroxene, clinopyroxene, plagioclase, spinel, and amphibole. Symplectites, composed of vermicular olivine and plagioclase, occur between the orthopyroxene and spinel porphyroclasts. Furthermore, fine-grained plagioclase grains were observed around the margins of spinel porphyroclasts. The SEM-EBSD analysis showed that the amphibole modal ratio was approximately 3 %. The crystallographic preferred orientation of olivine was (001)[100] slip (E-type). The spinel porphyroclasts were locally ductilely elongated and showed a boudin texture with small grains in the necking zone. Based on these results, we discuss the microstructural development of the mylonitized plagioclase lherzolite in the Uenzaru peridotite complex.

[1] Furusho & Kanagawa 1999 Tectonophysics.