鳥取県北東部，羽尾鼻に分布する下部鮮新統大羽尾溶岩

• Published in: The Journal of the Geological Society of Japan Vol. 131; no. 1; pp. 39 - 44
• Main Authors: 菅森, 義晃, 金山, 恭子, 羽地, 俊樹, 工藤, 崇
• Format: Journal Article
• Language: Japanese
• Published: 一般社団法人 日本地質学会 27.03.2025; The Geological Society of Japan
• Subjects: alkali basalt lava; K‒Ar age; major element composition; Zamclean
• ISSN: 0016-7630; 1349-9963
• DOI: 10.5575/geosoc.2025.0001

We propose the name ‘Obaneo Lava’ for Pliocene mafic volcanic rocks at Cape Haneobana, northeastern Tottori Prefecture. We undertook a geological survey of these rocks, measured their whole-rock major element compositions, and subjected them to plagioclase K‒Ar dating. The mafic volcanic rocks comprise at least three lava flows of clinopyroxene–olivine basalt and olivine basalt. Their chemical composition indicates they are alkali basalt. Their uniform compositions and the lack of evidence for dormancy indicate that they were derived from continuous volcanic activity. The plagioclase K‒Ar age of 4.28±0.11 Ma for the upper lava is older than the ages of surrounding Pliocene volcanic units (i.e., the Inabayama Basalt and rocks of Hamasaka Volcano). The Obaneo Lava is distinguished from these surrounding rocks on the basis of chemical composition and radiometric age.