2026-01-15 京都大学
(a) マントル捕獲岩とは、マグマが地表に上昇する際に通過する火道の内壁の岩石がマグマ中に取り込まれ、地表に運ばれてきた岩石のことである。 (b) 今回分析した包有物の放射光X線ナノCT画像。マントル捕獲岩の構成鉱物である単斜輝石の中に白金族鉱物、Fe-Ni-Cu硫化鉱物、ケイ酸塩ガラス、CO₂+CO+有機物から成る包有物が観察される。
＜関連情報＞
- https://www.kyoto-u.ac.jp/ja/research-news/2026-01-15-1
- https://www.kyoto-u.ac.jp/sites/default/files/2026-01/web_2601_Scientific%20Reports_mitsukawa_ver4-2219762fead4f069eb14b2e9526115c7.pdf
- https://www.nature.com/articles/s41598-025-32798-x
海洋底マントル起源の非生物的多環芳香族炭化水素 Abiotic polycyclic aromatic hydrocarbons originating from the sub-oceanic mantle
Itaru Mitsukawa,Akira Miyake,Yohei Igami,Tetsu Kogiso,Norikatsu Akizawa,Junya Matsuno,Megumi Matsumoto,Akira Tsuchiyama,Kentaro Uesugi,Masahiro Yasutake,Tomoki Taguchi,Yoshio Takahashi,Shohei Yamashita & Shota Okumura
Scientific Reports Published:14 January 2026
DOI:https://doi.org/10.1038/s41598-025-32798-x
Abstract
Experimental studies have demonstrated that petroleum may form from abiotic organic compounds synthesised in the Earth’s upper mantle. However, the most direct evidence of mantle-derived organics, as obtained from whole-rock analyses, indicates ambiguous origins. Although inclusions containing organic matter have been reported in minerals from kimberlite pipes, such occurrences have not previously been documented in mantle xenoliths derived from the sub-oceanic upper mantle, which represent the predominant lithology of the Earth’s upper mantle. In this study, we identified polycyclic aromatic hydrocarbons (PAHs)-bearing melt inclusions within a spinel-bearing unaltered harzburgite xenolith from Tahiti Island. The inclusions consisted of platinum-group minerals, base metal sulphides, silicate glass, and C–O–H phases. Our comprehensive sub-micrometre-scale analyses revealed the presence of PAHs in the C–O–H phases. These PAHs contained few functional groups or aliphatic chains and coexisted with CO and CO₂. They likely formed under reducing conditions in deeper regions of the upper mantle without serpentinisation. Our findings demonstrate abiotic organic matter formation in the sub-oceanic mantle and suggest widespread abiotic organic synthesis in the sub-oceanic mantle.
