大陸の裂け目で移動したクレートンマントルは,深い炭素を集約する
James D Muirhead1,2, Tobias P Fischer3, Sarah J Oliva4
1Department of Earth Sciences, Syracuse University, Syracuse, NY, USA. james.muirhead@fulbrightmail.org.
Nature
|June 5, 2020
まとめ
大陸の裂け目がマントルから二酸化炭素 (CO2) を放出する. 石層の差異は深層の炭素を濃縮し,CO2の流れを増加させ,東アフリカの裂け目系におけるマグマ形成に影響を与えます.
科学分野:
- 地化学
- 構造学
- 地力学
背景:
- 大陸の裂け方はマントルの二酸化炭素 (CO2) 排出量の重要な源です.
- リトスフィアのマントルの深層の炭素貯蔵は,溶融と揮発性輸送を通じて二酸化炭素の流れに影響を与えます.
- 岩層の組成と厚さの変動が深層の炭素流に与える影響は十分に理解されていません.
研究 の 目的:
- 古代とプロテロゾイク時代の石層の組成と厚さの違いが深層の炭素流動にどのように影響するかを調査する.
- 東アフリカ・リフト・システムの下の タンザニア・マントルの 炭素濃縮の仮説を検証する
主な方法:
- 東アフリカ・リフト・システムを横断する350キロメートルの経路に沿った二酸化炭素とヘリウム源と流れを調べた.
- アーケイア・プロテロゾイク期の石層界を越えて拡散したCO2脱ガスとヘリウム同位体比 (3He/4He) を分析した.
- クレトン縁の近くの活性炭酸塩のマグマティズムを調査した.
主要な成果:
- マントルのCO2流量と3He/4He比は,裂け目がアルカイアからプロテロゾイク層に通過するにつれて増加する.
- 拡散したCO2脱気は,クレートンからオロゲン岩層への移行地域ではより高い.
- アクティブ・カーボナイト・マグマティズムは,クレートン・エッジの近くで見られる.
結論:
- 薄いプロテロゾーイク石層の下にある厚いアルカイアン石層の横向きのアドベクションは,深い炭素を集約する.
- このプロセスは 大陸の裂け目に 二酸化炭素の流れを高めます
- 炭酸塩が豊富なマグマの生成と位置を制御する役割を果たします.
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