B. Taylor, J. Mutter, F. Martinez, A. Goodliffe, G. Abers, C. Mutter, R. Binns, H. Davies, and S. Scott
Staff Scientist: Adam Klaus
Co-Chief Scientists: Brian Taylor and Philippe Huchon
ABSTRACT
The lateral variation from active continental rifting to seafloor spreading within a small region makes the western Woodlark Basin an attractive area to investigate the mechanics of lithospheric extension. Earthquake source parameters and seismic reflection data indicate that low-angle (~25°) normal faulting is active in the region of incipient continental separation. A low-angle normal fault emerges along the northern flank of Moresby Seamount, a continental crustal block with green schist metamorphic basement. Asymmetric basement fault blocks overlain by only minor ponded sediments characterize the margin to the south, whereas the margin to the north has a down-flexed pre-rift sedimentary basin and basement sequence unconformably onlapped by synrift sediments.
Leg 180 will drill a transect of sites just ahead of the spreading tip: ACE-1c and ACE-7b on the down-flexed northern margin; ACE-8a through the rift basin sediments, the low-angle normal fault zone, and into the footwall; and ACE-3c near the crest of Moresby Seamount.
The primary objectives at these sites are to: (1) characterize the in situ properties (stress, permeability, temperature, pressure, physical properties, fluid pressure) of an active low-angle normal fault zone to understand how such faults slip, and (2) determine the vertical motion history of both the down-flexed hanging wall and the unloaded footwall and, thereby, derive the timing and amount of extension prior to spreading initiation.