89. 海野 進, 2018. 日本人による世界のオフィオライト研究. 地質学雑誌, 124, 593 - 601.
The last quarter century is a period of world-wide activity of Japanese geologists. An increasing number of studies was conducted on ophiolites in the world by Japanese researchers, some of which were introduced in this paper. The Oman Mountains expose the world largest and best preserved ophiolite that provides insights into crustal and mantle processes below a fast-spreading system and transformation of oceanic lithosphere to subarc crust and mantle. The Mirdita Ophiolite exposes mantle peridotites covered by mid-ocean ridge basalt (MORB) to arc tholeiitic and boninitic lavas, which record a transition from a spreading to a subduction environment. The Luobusa Ophiolite is famous for its occurrences of ultrahigh-pressure minerals, such as coesite and micro-diamond inclusions in chromite. They are considered to represent the recycle of subducted slab deep into the mantle > 380 km in depth. The 5–3 Myr old ophiolites in Timor and Tanimbar Islands are the world youngest ophiolite, and are interpreted to have formed the forearc crust and mantle that collided and obducted onto the northern edge of Australian continent. Volcanic rocks have intermediate geochemical characteristics between arc tholeiite and MORB, although the mantle peridotites are not cognate with the overlying volcanic rocks. Another young ophiolite (6–5 Ma) of Taitao, South Chile, was a part of the eastern limb of the Chile Ridge, which was subducted and accreted in the accretionary complex along the western coast of Chile. In spite of their genuine mid-ocean ridge origin, the lavas and sheeted dikes of the ophiolite have geochemical characteristics that are typically shown by arc magmas. Both Isua and Pilbara have the world oldest accretionary complexes consisting of superposed slices of oceanic crust that form a duplex structure, indicating the beginning of plate tectonics in the early Archean.
Keywords: ophiolite, Oman, Mirdita, Luobusa, Timor-Tanimbar, Taitao, Isua, Pilbara
100周年以降の25年間は日本の地質学者が広く海外に活躍の場を拡げるとともに，新たな分析機器の導入や解析手法の開発により，オフィオライトを構成するマントルカンラン岩の精密な上昇プロセスやマントル中のマグマの移動・反応プロセス，マントルの流動・変形機構，マントル岩中の微小包有物の同定・分析などが勢力的に進められた．また，フィールド地質学の分野でも，詳細な地質調査に基づいて海洋地殻の形成プロセスや始生代の海洋地殻層序の復元などが行われた．本小論ではこれらの日本人によって行われた海外のオフィオライト研究のうち，世界で最も規模が大きく保存状態がよいとされるオマーン，島弧下マントルが露出するミルディータ，リサイクルしたスラブ由来の超高圧鉱物を含むルオブサ，世界で最も新しいチモールとタイタオ，世界最古の付加体からなるイスアとピルバラの各オフィオライトについて紹介した．
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