Origin and crystallization mechanism of polycrystalline diamonds in the deep Earth

2016 Fiscal Year Final Research Report

• Project/Area Number: 26287138
• Research Category: Grant-in-Aid for Scientific Research (B)
• Allocation Type: Partial Multi-year Fund
• Section: 一般
• Research Field: Petrology/Mineralogy/Economic geology
• Research Institution: Ehime University
• Principal Investigator: Ohfuji Hiroaki 愛媛大学, 地球深部ダイナミクス研究センター, 教授 (80403864)
• Co-Investigator(Kenkyū-buntansha): 井上 徹 愛媛大学, 地球深部ダイナミクス研究センター, 教授 (00291500) ; 鍵 裕之 東京大学, 理学(系)研究科(研究院), 教授 (70233666)
• Research Collaborator: SUMIYA Hitoshi ; KURIO Ayako ; KOJIMA Yohei ; TAKEDA Yuhei ; ASANO Natsuko ; YAMASHITA Tomoharu ; NAKAYA Motosuke ; ISOBE Futoshi ; Konstantin D. Litasov ; Valentn P. Afanasiev ; Nikolai P. Pokhilenko ; Alexander P. Yelisseyev
• Project Period (FY): 2014-04-01 – 2017-03-31
• Keywords: 多結晶ダイヤモンド / バラス / カーボナード / 包有物

Outline of Final Research Achievements

We studied the microtexture and inclusions of polycrystalline diamonds (ballas and carbonado) to understand their origin and formation mechanism in the deep mantle. We found that most of them were formed in the subduction zone where crustal (oceanic) materials are supplied by slab subduction and C-H-O fluid (highly supersaturated with carbon) is dominated. The crystal growth and resulting microtexture seem to depend largely on the hydrodynamics (still or advective) of the growth media. Furthermore, we found, for the first time, a natural counterpart of nano-polycrystalline diamond, which is synthesized by high pressure and high temperature experiment and known to have superior hardness and mechanical properties, from a large impact crater in Russia and revealed the formation mechanism.

Free Research Field

鉱物学