HR: 0800h
AN: GP41A-0866    [Abstracts]
TI: Ultra-fine scale magnetostratigraphy of Mn crust with SQUID microscope
AU: * Oda, H
EM: hirokuni-oda@aist.go.jp
AF: Geological Survey of Japan, AIST, Central 7, 1-1-1 Higashi, Tsukuba, 305-8567 Japan
AU: Joshima, M
EM: m-joushima@aist.go.jp
AF: Geological Survey of Japan, AIST, Central 7, 1-1-1 Higashi, Tsukuba, 305-8567 Japan
AU: Usui, A
EM: a-usui@cc.kochi-u.ac.jp
AF: Kochi University, 2-5-1 Akebono-cho, Kochi, 780-8520 Japan
AU: Weiss, B P
EM: bpweiss@mit.edu
AF: Massachusetts Institute of Technology, 54-724 77 Massachusetts Avenue, Cambridge, MA 02139 United States
AU: Fong, L E
EM: luis.e.fong@vanderbilt.edu
AF: Vanderbilt University, 6301 Stevenson Center, Box 1807 Station B, Nashville, TN 37235 United States
AU: McBride, K K
EM: krista@femto.cas.vanderbilt.edu
AF: Vanderbilt University, 6301 Stevenson Center, Box 1807 Station B, Nashville, TN 37235 United States
AU: Baudenbacher, F J
EM: franz.j.baudenbacher@vanderbilt.edu
AF: Vanderbilt University, 6301 Stevenson Center, Box 1807 Station B, Nashville, TN 37235 United States
AB: We have conducted ultra-fine scale magnetostratigraphy on a Mn crust sample D96-m4 from northwest Pacific (38°48.7'N, 138°19.14'E, water depth 1940 m) with a high-resolution SQUID microscope at Vanderbilt University. Various rock-magnetic techniques delineate the presence of well dispersed single domain magnetic mineral with coercivity of about 30 mT and Curie temperature of about 550-570°C. However, low temperature measurement did not show Verwey transition characteristic of magnetite and X-ray diffractometry on magnetic separate did not show any peaks of magnetite or maghemite. Two thin sections of 5 mm width x 35 mm length x 0.2 mm thickness were taken from a Mn crust, which are perpendicular to each other. The slices were subjected to SQUID scanning on 85 microns grids with a spatial resolution of about 100 microns for NRM, and after 10 and 20 mT AF demagnetization. The SQUID microscopy revealed fine scale magnetic anomaly parallel to the growth pattern. The identification of polarity boundaries made it possible to estimate growth rate of the Mn crust as 4.5 mm/Myr. The result is much less than the previous estimate on the same Mn crust block (Joshima and Usui, 1998; 14 mm/Myr), however, it is rather consistent with the estimate by ¹⁰Be/⁹Be (5.9 mm/Myr).
DE: 1520 Magnetostratigraphy
DE: 1540 Rock and mineral magnetism
DE: 1594 Instruments and techniques
SC: Geomagnetism and Paleomagnetism [GP]
MN: Fall Meeting 2005