HR: 1340h
AN: GP23A-0027    [Abstracts]
TI: Seafloor Dating Within The Brunhes Period With Deep-Sea Vector Magnetic Anomalies
AU: * Kitazawa, M
EM: mitsu@ipgp.jussieu.fr
AF: IPGP, Laboratoire de geosciences marines, 4 Place Jussieu, Paris, 75005 France
AU: * Kitazawa, M
EM: mitsu@ipgp.jussieu.fr
AF: ERI, Ocean Hemisphere Research Center, University of Tokyo, Yayoi 1-1-1, Bunkyo-ku, Tokyo, 113-0032 Japan
AU: Dyment, J
EM: jdy@ipgp.jussieu.fr
AF: IPGP, Laboratoire de geosciences marines, 4 Place Jussieu, Paris, 75005 France
AU: Chauvin, A
EM: annick.chauvin@univ-rennes1.fr
AF: Geosciences Rennes UMR-CNRS, Universite de Rennes I, 263 Ave du General Leclerc CS 74205, Rennes, 35042 France
AU: Horen, H
EM: hhoren@geologie.ens.fr
AF: ENS, Departement de geologie, 24 rue Lhomond, Paris, 75005 France
AU: Utada, H
EM: utada@eri.u-tokyo.ac.jp
AF: ERI, Ocean Hemisphere Research Center, University of Tokyo, Yayoi 1-1-1, Bunkyo-ku, Tokyo, 113-0032 Japan
AU: Tamaki, K
EM: tamaki@geosys.t.u-tokyo.ac.jp
AF: Department of Geosystem Engineering, University of Tokyo, Yayoi 1-1-1, Bunkyo-ku, Tokyo, 113-0032 Japan
AU: Hemond, C
EM: chhemond@univ-brest.fr
AF: Domaines Oceaniques, IUEM, Place Nicolas Copernic, Plouzane, 29280 France
AB: Marine magnetic anomalies provide a robust record of the past geomagnetic reversal. Classical sea-surface magnetic anomaly studies are generally restricted to the analysis of polarity reversals, although a systematic secondary signal, made of shorter wavelength and lower amplitude anomalies, superimposes to the major anomalies. The consistent pattern of these tiny wiggles worldwide strongly suggests a geomagnetic origin for these anomalies, either short polarity intervals or large-scale fluctuations in the past geomagnetic field intensity. If they are precisely dated, these short wavelength geomagnetic variations provide a new tool to determine the age of the seafloor with a high resolution, especially for young mid-ocean ridge basalt. In order to collect high resolution magnetic data within the Brunhes period, a deep-sea vector magnetic survey was carried out across the Central Indian Ridge (CIR, 19° S) with the French submersible Nautile. We correct the magnetic effects of the submersible and obtain four magnetic anomalies profiles from ridge axis to the Brunhes-Matuyama boundary. We estimate the seafloor magnetization by comparing the deep-sea magnetic anomalies to synthetic anomalies computed with a realistic geometry (topography, submersible path). This estimated magnetization is generally similar to the Natural Remanent Magnetization (NRM) measured on the rock samples that were collected during Nautile dives, suggesting that the seafloor magnetization deduced from the deep-sea magnetic anomalies is reliable. Beyond the NRM measurements, rock magnetic measurements show that the samples are petrologically and magnetically homogenous, with pseudo-single domain tetanomagnetite. Variations within pillow lavas are minimized by coring the samples at a constant distance from the glassy rim. Although varying alteration degrees result in scattered data, the NRM and paleointensity obtained by Thellier method are well correlated and suggest that variations in magnetization are mostly due to the fluctuations of paleointensity. The seafloor magnetization variations obtained across the CIR compares well with the geomagnetic paleointensity curve obtained from sediment cores for the Brunhes period (Guyodo and Valet, Nature 1999). Similar patterns are clearly recognized on both, suggesting that the seafloor can be dated at very high resolution through the geomagnetic intensity variations.
DE: 1517 Magnetic anomalies: modeling and interpretation
DE: 3005 Marine magnetics and paleomagnetics (1550)
DE: 3035 Midocean ridge processes
SC: Geomagnetism and Paleomagnetism [GP]
MN: Fall Meeting 2005