Variation of hydrothermal alteration in deep levels of the oceanic crust

2023 Fiscal Year Final Research Report

• Project/Area Number: 20K04107
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Review Section: Basic Section 17040:Solid earth sciences-related
• Research Institution: Okayama University
• Principal Investigator: Nozaka Toshio 岡山大学, 環境生命自然科学学域, 准教授 (80252948)
• Project Period (FY): 2020-04-01 – 2024-03-31
• Keywords: 海洋リソスフェア / 下部地殻 / 上部マントル / 斑れい岩 / かんらん岩 / 蛇紋岩 / 変質作用

Outline of Final Research Achievements

This study focused on the analyses of mode of occurrence, chemical compositions and the composition-paragenesis relationships between typical alteration minerals including serpentine, epidote, prehnite, talc, and other coexisting minerals in the oceanic lower crust, and mainly obtained some significant findings as follows: Incompatibility between serpentinization of olivine and epidote formation after plagioclase, indicating redox conditions of hydrothermal alteration; usefulness of cuttings formed by onboard sample processing during ocean drilling for revealing the average modal compositions of alteration minerals; formation of Fe-monticellite during serpentinization; and formation of Na-rich talc in meta-serpentinites. They are promising indicators for the cause of variation of hydrothermal alteration in the oceanic lower crust and upper mantle.

Free Research Field

岩石学

Academic Significance and Societal Importance of the Research Achievements

地球における岩石圏と水圏の間の最大の境界層である海洋リソスフェアの変質作用は，地球システム全体における物質とエネルギーの循環に大きな役割を果たし，人類を取り巻く環境と地球全体の過去・現在・未来の姿を正しく理解するための鍵となる。本研究では蛇紋岩中からモンチセリ石とNaに富む滑石を世界で初めて発見した。これらの鉱物のほか，蛇紋石，緑簾石，ブドウ石など，海洋下部地殻と上部マントル起源の岩石に産する変質鉱物の生成条件を明らかにした。