Iron titanium oxyhydroxide as a water transporter into the Earths deep mantle

2019 Fiscal Year Final Research Report

• Project/Area Number: 17K05713
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Research Field: Petrology/Mineralogy/Economic geology
• Research Institution: Teikyo University of Science & Technology
• Principal Investigator: MATSUKAGE Kyoko N. 帝京科学大学, 総合教育センター/自然環境学科, 教授 (80343078)
• Project Period (FY): 2017-04-01 – 2020-03-31
• Keywords: 水 / 鉄チタン水酸化物 / 地球内部 / 海洋プレート / 高圧含水相 / 沈み込み帯 / マントル / 高温高圧実験

Outline of Final Research Achievements

We experimentally discovered new hydrous phases, FeTi oxyhydroxides (FeOOH-TiO2). To determine the phase relation of these phases in subducting basaltic system, we performed experiments of basalt + H2O system by using multi-anvil apparatus at 10-23 GPa and 750-1200°C. We found that the phase with α-PbO2 type crystal structure was stable at wide pressure range at deep upper mantle and mantle transition zone at slab temperatures. In this system, lawsonite is a major hydrous mineral in the upper mantle, although it dehydrates at ~10 GPa. Our study indicates that the FeTi oxyhydroxide represents the main carrier of water at depths beneath the lawsonite stability field. After dehydration of FeTi oxyhydroxide at ~19 GPa, CaTi perovskite was formed as a Ti-bearing phase, and Al-bearing phase D was stable as a hydrous phase. Our findings suggest that water transport in the Earth’s deep interior by basaltic crust is probably much more efficient than had been previously thought.

Free Research Field

地球惑星学

Academic Significance and Societal Importance of the Research Achievements

本研究の結論として、鉄チタン水酸化物が地球の深さ300～600kmで安定に存在しうること、この領域での主要な水成分の運び手及びリザバーであること、が示された。海洋地殻物質は元来我々研究者が考えていたよりも、効率的に水成分を地球深部に運搬・保持し、地球内部の化学進化過程に影響を与えていると考えられる。