地球の初期の大陸地殻は,湿気と酸化する弧のマグマから形成された
Rong-Feng Ge1, Simon A Wilde2, Wen-Bin Zhu3
1State Key Laboratory for Mineral Deposits Research, Institute of Continental Geodynamics, Frontiers Science Center for Critical Earth Material Cycling, School of Earth Sciences and Engineering, Nanjing University, Nanjing, People's Republic of China. gerongfeng@nju.edu.cn.
Nature
|September 27, 2023
まとめ
初期の地球の大陸の殻は,現代の弧に似た酸化した,水に富んだマグマによって証明されている. これは40億年前の プレート構造と沈殿の始まりを示唆しています
科学分野:
- 地理科学
- ペトロロジー
- 構造学
背景:
- 初期の地殻の形成は 基本的な地質学的な問題です
- 初期の地殻形成を理解することは 資源と惑星の進化の鍵です
- 過去のモデルは,古代の変形岩を分析する際の課題のために議論されています.
研究 の 目的:
- 初期の大陸地殻のマグマの酸素流動性 (fO2) と水分 (H2O) を決定する.
- 早期の地殻形成における潜水作用をテストする.
- 潜水開始のタイミングを調査する
主な方法:
- 2つのジルコンの酸素度計を用いて,マグマのfO2とH2Oを同時に測定した.
- 初期の大陸の地殻を支配する 古代の花岩類を分析した.
- マグマ形成の推定深さと相関するマグマ特質.
主要な成果:
- 古代のグラニトイドマグマは,周囲のマントル由来マグマよりも著しく酸化していた.
- これらのマグマは高濃度のH2O (6-10 wt%) と高濃度のH2O/Ce (>1,000) を有していた.
- マグマのfO2,H2O含量,H2O/Ce比率はマグマ形成の深さと正に相関している.
結論:
- 観測されたマグマ特性は,初期の地殻形成の潜水駆動モデルを強く支持しています.
- これらの発見は非潜水モデルと調和することが困難である.
- 40億年から36億年前のマグマのfO2とH2Oの含有量の増加は,沈殿の始まりを示唆しています.
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