HR: 0800h
AN: T31A-0475    [Abstracts]
TI: Spreading evolution in the southern Lau Basin based on geophysical surveys
AU: * Watanabe, M
EM: mizuki@ori.u-tokyo.ac.jp
AF: Ocean Research Institute The University of Tokyo, 1-15-1 Minamidai, Nakano-ku, Tokyo-to, Tokyo, 164-8639 Japan
AU: Okino, K
EM: okino@ori.u-tokyo.ac.jp
AF: Ocean Research Institute The University of Tokyo, 1-15-1 Minamidai, Nakano-ku, Tokyo-to, Tokyo, 164-8639 Japan
AU: Kodera, T
EM: kodera@nme.co.jp
AF: Nippon Marine Enterprise, 14-1, Nissei Yokosuka Center Building8F, Ogawa-cho, Yokosuka-shi, Kanagawa-ken, Yokosuka, 238-0004 Japan
AU: Takai, K
EM: kent@jamstec.go.jp
AF: Japan Agency for Marine-Earth and Technology, 2-15, Natushima-cho, Yokosuka-shi, Kanagawa-ken, Yokosuka, 237-0061 Japan
AB: Lau Basin and Havre Trough are back-arc basins related to Pacific-Australian plate convergence. Seafloor spreading occurs in the Lau Basin and Havre Trough is in a rifting stage. At present, the spreading propagator has a tectonic tip at the southern end of the Valu Fa Ridge(VFR)(22°40S). This tip has advanced at the rate of 120mm/yr. South of the tip, well defined linear feature of VFR loses it_fs morphological identity and the topography changes into a disordered rough area. New bathymetry data revealed that this area can be divided into three zones across the basin. The westernmost zone has flat topography indicating sedimented basement. The central part lies in the extended area of the topographic high in the northern Havre Trough(23°30S~24°30S). The easternmost zone is deeper compared to the west and has grabens divided by short narrow ridges. A deep graben of depth 3400m~3500m has been observed. This graben is located about 10km east from the extended area of VFR. The trend of this graben can be extended southward to another deep graben in the northern Havre Trough. Side-scan data obtained by SeaBeam2112 show intensity difference between the zones. Strong intensity comes from the eastern zone indicating active rifting. Within this active zone, strongest intensity comes from two segmented areas:1)VFR and it_fs southern extension, 2)along the graben 10km offset from VFR trend. This indicates segmented rifting occurring in the active zone. The rifting may connect the propagating spreading at VFR with the deep graben in the Havre Trough. Gravity anomaly and sea surface magnetic anomaly data are also presented. High Bouguer anomaly is observed around the eastern graben. This may be due to thinner crust. Variations in magnetic intensity will be presented to show whether basaltic intrusions can be suggested.
DE: 8150 Plate boundary: general (3040)
SC: Tectonophysics [T]
MN: Fall Meeting 2005