[M-IS46] Marine manganese deposits: Origin, growth processes, and environment

[MIS46-04] Paleomagnetic study on the ferromanganese crusts recovered from northewest Pacific

*Atushi NOGUCHI¹, Yuhji YAMAMOTO², Keisuke NISHI³, Akira USUI⁴ (1.Graduate School Of Integrated Arts and Sciences, 2.Center for Advanced Marine Core Research, Kochi University, 3.Kochi University, 4.Geology Dept., Kochi Univ.)

Keywords:ferromanganese crust, paleomagnetic polarity, growth rate

We have conducted paleomagnetic measurements on the ferromanganese crusts recovered from five different locations in the northwest Pacific. The analyses were made on a series of the thin slices (0.5-1.0 mm in thickness) cut perpendicular to the growth layers of the crusts, from surface to the interior. We recognized 2-8 polarity reversals in the crusts, and the most surficial layers were commonly characterized by normal polarities. Assuming that these layers were grown constantly in Brunhes normal polarity chron (0-0.78 Ma), growth rates were estimated as 2.1-5.0 mm/Ma. These rates are consistent with those estimated by the ¹⁰Be/⁹Be method except for one location.