古代の沈殿した海殻の存在は,大きな低剪定速度地域における地震異常に貢献している
Ewa Krymarys1, Motohiko Murakami1, Pinku Saha1
1Department of Earth and Planetary Sciences, Institute of Geochemistry and Petrology, ETH Zürich, Zürich, Switzerland.
まとめ
大規模な低切断速度地域 (LLSVPs) は,極端な熱ではなく,海殻の蓄積によって説明されます. コアマントルの境界圧力の新しい地震速度のデータはこれを支持し,数十億年にわたる深いマントルの起源を示唆しています.
科学分野:
- 地理学
- 鉱物物理学
- 地震学
背景:
- 核-マントルの境界付近にある大きな低切断速度領域 (LLSVPs) は謎めいた深層地球構造である.
- その構成は議論されているが,地震速度の予測によって挑戦されている.
- コア・マントルの境界圧力の地震速度の直接的な測定は欠けている.
研究 の 目的:
- 核-マントルの境界に関係する超高圧で主要なMORB相の切断波速度を測定する.
- LLSVPの組成と熱状態を制限する.
- 深層マントルに長期にわたって蓄積した物質を調査する.
主な方法:
- SiO2ポリモルフ (CaCl2型とα-PbO2型) の超高圧切断波速度測定を行った.
- 実験は,コア-マントルの境界にある圧力を上回る圧力で行われました.
- 結果はMORB蓄積の地力学モデルに統合された.
主要な成果:
- 密度の高いSiO2フェーズで測定された切断速度は,関連する圧力で以前に予測されたより7~14%低かった.
- これらの低速度は,海殻の23~33%を使用したLLSVPで観測された地震異常を説明します.
- この説明は,LLSVP内の極端な熱異常を必要としません.
結論:
- 海洋地殻 (MORB) は,数十億年にわたって蓄積することによって,LLSVPの地震特性を説明することができます.
- 発見は,LLSVPの構成と深層マントルの動態に関する重要な制約を提供します.
- 核-マントルの境界で長期にわたる物質の蓄積モデルを支持する.
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