Magnetization process of serpentine

2013 Fiscal Year Final Research Report

• Project/Area Number: 23654173
• Research Category: Grant-in-Aid for Challenging Exploratory Research
• Allocation Type: Multi-year Fund
• Research Field: Geology
• Research Institution: Kobe University
• Principal Investigator: OTOFUJI Yo-ichiro 神戸大学, 理学(系)研究科(研究院), 教授 (90160895)
• Co-Investigator(Kenkyū-buntansha): UNO Koji 岡山大学, 大学院・教育学研究科, 准教授 (10510745) ; SATO Eiichi 神戸大学, 大学教育推進機構, 助教 (40609848)
• Project Period (FY): 2011 – 2013
• Keywords: 蛇紋岩 / 古地磁気学 / 岩石磁気学 / 西南日本弧 / 東北日本弧

Research Abstract

Serpentine is collected at four areas in Southwest Japan (Oheyama,Kuzuryu-river, Hakuba, Oyashirazu) and at Hitachi Ohta in Northeast Japan. Remanent magnetization of serpentine is carried by magnetite. Remanent magnetization of serpentine is probably acquired by magnetite which occurrs during hydro-thermal alteration of periodite.
Remanent magnetizations of serpentine at Sakurae, Oheyama and Kuzuryu-river show easterly deflected directions from the north (D=60-90 degree; I=50 degree) which is parallel to the remanent magnetization of igneous rocks in Southwest Japan with ages older than 15Ma. Serpentine at these areas acquired the remanent magnetization before Southwest Japan experienced clockwise rotation. Serpentine from other areas reveal variable directions in the remanent magnetizaiton; such as, present geomagnetic field direction and reversed directions. We conclude that serpentinization occurrs at many times in various periods prior to 15 Ma and between 15Ma and present.