ダイヤモンドのドミノ効果は噴火スポットの秘密を説明する(Diamond domino effect explains eruption spot secrets)

地殻変動によるプレート分裂の発見が、将来の貴重な宝石の発見に火をつける可能性 Tectonic plate breakup discovery could spark future discoveries of precious gems

2023-07-26 バーミンガム大学

＜関連情報＞

• https://www.birmingham.ac.uk/news/2023/diamond-domino-effect-explains-eruption-spot-secrets
• https://www.nature.com/articles/s41586-023-06193-3

地殻キールの地殻変動がキンバーライト火山活動を促進する Rift-induced disruption of cratonic keels drives kimberlite volcanism

Thomas M. Gernon,Stephen M. Jones,Sascha Brune,Thea K. Hincks,Martin R. Palmer,John C. Schumacher,Rebecca M. Primiceri,Matthew Field,William L. Griffin,Suzanne Y. O’Reilly,Derek Keir,Christopher J. Spencer,Andrew S. Merdith & Anne Glerum
Nature  Published:26 July 2023
DOI:https://doi.org/10.1038/s41586-023-06193-3

Abstract

Kimberlites are volatile-rich, occasionally diamond-bearing magmas that have erupted explosively at Earth’s surface in the geologic past^1,2,3. These enigmatic magmas, originating from depths exceeding 150 km in Earth’s mantle¹, occur in stable cratons and in pulses broadly synchronous with supercontinent cyclicity⁴. Whether their mobilization is driven by mantle plumes⁵ or by mechanical weakening of cratonic lithosphere^4,6 remains unclear. Here we show that most kimberlites spanning the past billion years erupted about 30 million years (Myr) after continental breakup, suggesting an association with rifting processes. Our dynamical and analytical models show that physically steep lithosphere–asthenosphere boundaries (LABs) formed during rifting generate convective instabilities in the asthenosphere that slowly migrate many hundreds to thousands of kilometres inboard of rift zones. These instabilities endure many tens of millions of years after continental breakup and destabilize the basal tens of kilometres of the cratonic lithosphere, or keel. Displaced keel is replaced by a hot, upwelling mixture of asthenosphere and recycled volatile-rich keel in the return flow, causing decompressional partial melting. Our calculations show that this process can generate small-volume, low-degree, volatile-rich melts, closely matching the characteristics expected of kimberlites^1,2,3. Together, these results provide a quantitative and mechanistic link between kimberlite episodicity and supercontinent cycles through progressive disruption of cratonic keels.