During Leg 180 the record of continental rifting evolving to seafloor spreading in the region of Papua New Guinea was documented (Fig. F1). A roughly north-south transect of 11 holes was drilled across the Woodlark rift basin from the footwall to the downflexed northern margin of the rift. During this leg, the tectonic-sedimentary history and rifting processes were revealed from late Miocene to Holocene time as a backarc basin related to subduction (Shipboard Scientific Party, 1999).
The most significant contribution concerns the modeling of a complete lithospheric extension. Seafloor magnetic anomalies show that most of the rifting occurred during the last 6-8 m.y., starting in an eastward extension of the Papuan Peninsula as a westward-propagating spreading center that opened the Woodlark Basin (Weissel et al., 1982; Taylor et al., 1995; Goodliffe et al., 1997; Goodliffe, 1998).
This chapter addresses the petrography of sandstones and epiclastites from the clastic and volcaniclastic units drilled during Ocean Drilling Program Leg 180 from the northern margin throughout the rift basin sites to the footwall. In particular, investigations of metamorphic, igneous intrusive, and volcanic clasts give insights into the relationships between phases of tectonic uplift, consequent erosion of deep material, and episodes of volcanic activity during the evolution of different sectors of the basin.