This collision is expressed by a south to north series of deformed 

 Mesozoic-Cenozoic shelf sediments, a central ophiolite belt, and a 

 northern zone of submarine mafic and intermediate rocks. Hamilton 

 (1979) took these to be evidence of obduction of the arc over the older 

 New Guinea landmass. This obduction apparently proceeded from west to 

 east across the area. 



At some later time (Upper Miocene ?) the obduction changed to a 

 southward subduction of the Caroline Basin beneath northern New Guinea, 

 creating volcanism along the northern coast. 



Whether this subduction zone is still active is not certain. 

 Hamilton (1979) shows seismic reflection profiles along the northern 

 margin of New Guinea (east of the profiles shown above) that indicate a 

 trench-like feature extending to the southern limit of Figure 15, or 

 the intersection of the Bismarck transform with the New Guinea mainland. 

 His tectonic map shows an inactive trench extending to the east from 

 this point. 



As pointed out by Bracey (1975) , earthquakes at the southern 

 margin of the Caroline Basin are located mainly on the Island of New 

 Guinea, and are not clearly associated with the New Guinea Trench. 

 There is an earthquake mechanism determination that indicates southward 

 underthrusting beneath the trench north of Vogelkop, as noted earlier, 

 but there is no clear indication that this is the case to the east. 



All indications are that the southwestern Caroline Plate margin is 

 now located in a broad, complex zone of NE-SW horizontal compression 



64 



