Date: 16:00 – 18:00, Friday, January, 20, 2023
Speaker：Konstantin Litasov
Title：Impact shock origin of diamonds in ureilite meteorites as revealed from observation and pulsed-heating high-pressure experiments
The origin of diamonds in ureilite meteorites is a critical topic in planetary geology as recent studies have proposed their formation at static pressures >20 GPa in a large planetary body, like diamonds formed deep within the Earth’s mantle. We investigated fragments of several diamond-bearing ureilites and found coexistence of different forms of carbon. In NWA 7983 we found an intimate association of large monocrystalline diamonds (up to at least 100 µm), nanodiamonds, nanographite, and nanometric grains of metallic iron, cohenite, troilite and likely schreibersite. The diamonds show a striking texture pseudomorphing inferred original graphite laths. The silicates in NWA 7983 record a high degree of shock metamorphism. The coexistence of large monocrystalline diamonds and nanodiamonds in a highly shocked ureilite can be explained by catalytic transformation from graphite during an impact shock event characterized by peak pressures possibly as low as 15 GPa for relatively long duration (on the order of seconds). The formation of “large” (as opposed to nano-) diamond crystals could have been enhanced by the catalytic effect of metallic Fe-Ni-C liquid coexisting with graphite during this shock event which is comparable with pulsed heating formation of microcrystalline diamonds in high-pressure experiments.
発表者：小林 大輝
Speaker：Hiroki Kobayashi
Title：A compass to “hidden places” on the phase diagram
「新しい氷を見つけたい！」これは私の研究の根底にある、何にも代え難い好奇心である。では、次の氷（ice XX）はどこにあるのだろうか？ これまで2回のGcRCセミナーでは、水素無秩序-秩序相転移に着目し、新しい水素秩序相の探索を報告してきた。しかし、水素結合で形作られるネットワーク構造は、秩序化によっては変化しないので、そういった観点でいえば、いわば「既存の氷に非常によく似た氷」を探索してきたことになる。
では、「全く違うネットワーク構造をもつ氷」はもう見つからないのだろうか？ 私には、とてもそうとは思えない。今回は、既報の理論計算の結果などを紹介しながら、「全く違うネットワーク構造をもつ氷」が相図のどこに存在するか、そしてその氷に到達するための戦略としてどのようなものがありえるか、予想してみよう。