The Woodlark Basin (in Papua New Guinea) is a region where seafloor spreading occurs in its eastern part and active continental rifting in its western part. It is characterized by a westward-propagating rift axis whose current spreading tip is located on the eastern flank of Moresby Seamount, a continental crustal block (Fig. F1). The seafloor magnetic anomalies indicate that seafloor spreading started at 6 Ma at the east of the basin. The western Woodlark Basin provides a good opportunity to study active continental rifting. The seismic profiles indicate the presence of an active low-angle normal detachment fault gently dipping (25°-30°) toward the north-northeast and emerging on the northern flank of Moresby Seamount, the Moresby detachment. Seismic profiles also show the presence of normal faults on the southern flank of Moresby Seamount antithetical to the major low-angle normal fault to the north (Shipboard Scientific Party, 1999a).
The main objective of Ocean Drilling Program (ODP) Leg 180 was to study a region of active continental rifting prior to spreading initiation by drilling the active low-angle Moresby detachment and its subsiding sedimentary hanging wall (Taylor, Huchon, Klaus, et al., 1999). A north-south transect was drilled just ahead of the spreading tip in the rift basin of the northern margin above the low-angle normal fault zone and in the footwall fault block of the Moresby Seamount (Fig. F2). Site 1114, located just north of the crest of Moresby Seamount, is the only site that was logged in the footwall block. Seismic reflection data indicate that sediments are separated from basement by a south-southwest-dipping normal fault at this location.
The objective of this paper is to present the results of the structural analysis of the Formation MicroScanner (FMS) electrical images that were recorded in the footwall of the Moresby detachment in Hole 1114A. A companion paper presents a similar analysis in the northern margin of this detachment, which consists of a large down-flexed sedimentary basin with less deformed prerift/synrift sediments (Célérier et al., this volume). We will first recall the main results of the shipboard core analysis, then show the FMS images and how they relate to the core-defined lithologic units, then discuss the method and results of the structural analysis of these electrical images in the context of the Moresby detachment kinematics.