Hydrothermal alteration of lowermost crustal rocks at Hess Deep, East Pacific Rise

2015 Fiscal Year Final Research Report

• Project/Area Number: 25400515
• 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: Okayama University
• Principal Investigator: Toshio Nozaka 岡山大学, 自然科学研究科, 准教授 (80252948)
• Project Period (FY): 2013-04-01 – 2016-03-31
• Keywords: 海洋底 / 下部地殻 / 斑れい岩 / 変質 / ヘスディープ / 深海掘削

Outline of Final Research Achievements

Green spinel, corundum and diaspore were found in primitive troctolites recovered from Hess Deep, East Pacific Rise. This is the first discovery of these aluminous minerals from the in-situ oceanic crust. Petrological studies revealed that the aluminous minerals were formed by high-temperature acidic hydrothermal fluids and subsequent alteration during cooling of the magmatic lower crustal rocks. In addition, it was revealed that serpentinization took place at three-stage alteration by fluids with variable silica and oxygen activities, and that magnetite formed at multiple stages under high and low temperature conditions. All of these findings are important for further understanding of hydrothermal activities near the fast-spreading axes.

Free Research Field

岩石学