HR: 1330h
AN: T12D-0494    [PDF]
TI: Detailed sub-surface structure of Atlantis Bank as derived from in-situ observation and seafloor gravimetry
AU: * Matsumoto, T
EM: takeshi@nme.co.jp
AF: Nippon Marine Enterprises, Ltd., 14-1 Ogawacho, Yokosuka, 238-0004 Japan
AU: Dick, H J
AF: Woods Hole Oceanographic Institution, Woods Hole Road, Woods Hole, MA 02543 United States
AB: Atlantis Bank was precisely surveyed by manned submersibles and ROV_fs since 1998 after the results from ODP Leg176 was compiled. In addition to the in-situ observation and rock sampling, seafloor gravimetry was carried out during the two cruises by Submersible SHINKAI6500 by use of gravity meters for on-land surveys. The observed gravity data were reduced into the free air anomaly on the sea surface and then Bouguer anomaly was calculated by 3-D terrain correction in order to estimate the average density of the basement rock underneath each gravity station. The result was compiled with the observed geological features, collected rock samples and precise seafloor topography obtained by the same cruises in order to describe the precise sub-surface structure and faulting of the bank. The average density of the basement rocks on the western slope of the bank was estimated as 3.0 g/cc in the lower part, 3.8 g/cc in the middle part and 3.1 g/cc in the upper part, corresponding to the collected mantle peridotite, oxide Fe-Ti gabbro and peridotite/oxide olivine gabbro, respectively. Results from swath bathymetry shows detachment faults sub-parallel to the ridge axis. The dive tracks which crossed these detachment faults showed an exposure of mantle peridotite above gabbro, as expected by the distribution of the low-angle normal faults. Considering also the seafloor observation and collected rock samples along the dive tracks nearby, the area is characterised by detachment of thin lower crust - mantle peridotite assemblage along the detachment faults. Seafloor gravimetry was also carried out on the eastern slope of Atlantis Bank. Average density of basement rock was estimated as 3.1 g/cc in the lower part and 2.6 g/cc in the middle part. The difference in estimated bedrock density is corresponding to the difference in seafloor observation: huge blocks of gabbroic massifs in the lower part and a steed escarpment covered with fault gauge in the middle part. The collected rock samples were mylonatised gabbros along the whole track.
UR: http://www.nme.co.jp
DE: 3035 Midocean ridge processes
DE: 8100 TECTONOPHYSICS
DE: 8120 Dynamics of lithosphere and mantle--general
DE: 8122 Dynamics, gravity and tectonics
DE: 9325 Atlantic Ocean
SC: Tectonophysics [T]
MN: 2003 Fall Meeting