HR: 0800h
AN: T41A-0362    [Abstracts]
TI: New Observations on the Complex Interplay Between Normal Faulting and Metamorphic Core Complex Formation at the Rifting-to-Spreading Transition in the Woodlark Basin, Papua New Guinea
AU: * Rahilly, K E
EM: krahilly@email.smith.edu
AF: Department of Geology, Smith College, 7 College Lane, Northampton, MA 01063, United States
AU: Goodliffe, A M
EM: amg@ua.edu
AF: Department of Geological Sciences, University of Alabama, Box 870338, Tuscaloosa, AL 35405, United States
AB: The rifting-to-spreading transition in the Woodlark Basin is tectonically very complex. Both low- and high-angle faults and intense magmatic intrusions co-exist in a small area immediately along strike of a region of active metamorphic core complex exhumation that began at about 4 Ma, when the spreading center was still more than 500 km to the east. Though questions still remain with regard to the mode of formation of the core complexes, it seems that isostatic exhumation of less dense felsic crust through a denser overlying ophiolite complex may play an important role. Six-channel marine seismic reflection profiles with coincident HAWAII-MR1 interferometric bathymetry and sidescan data were collected in 1993 in the vicinity of the core complexes and the rifting-to-spreading transition. Re-processing of this extensive dataset has resulted in the removal of artifacts related to poor airgun tuning and revealed a complicated relationship between core complex exhumation and the normal faults associated with rifting ahead of the spreading tip. Three time sections are used as the primary focus of this study. The area directly offshore of the Prevost Range's northern flank is characterized by large back-tilted fault blocks above north-dipping normal faults. The absence of sediment fill in the half graben implies that these structures are relatively recent. Further north, a major graben is bounded by these faults on the south side and south- dipping normal faults on the north side. Seafloor morphology and the location of earthquake epicenters indicate that this graben is the current focus of rifting in the basin. The offshore continuation of the core complex is imaged directly to the west of the Prevost Range. On the north side of the core complex, a north-dipping low-angle normal fault is imaged that is consistent with previous interpretations that the core complex was exhumed along a north- dipping deep crustal detachment. However, at the surface this detachment surface has been broken up by more recent normal faulting, presenting the possibility that it is no longer active. Further south, the core complex is in the hanging wall of a major north-dipping normal fault. The footwall of the same fault is broken up by north- dipping normal faults that cut the seafloor. An interpretation of this is that the normal fault bounding the north side of the core complex has jumped to the south. Whether this is indeed the surface extension of a deep crustal detachment remains to be seen.
DE: 3025 Marine seismics (0935, 7294)
DE: 3045 Seafloor morphology, geology, and geophysics
DE: 8109 Continental tectonics: extensional (0905)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting