subduction zone (Bracey and Andrews, 1974; Bracey, 1975; Mairanerickx, 

 1978; Weissel and Anderson, 1978). Hamilton (1979) objected to this 

 interpretation, mainly on the basis that the features do not look 

 much like present-day trenches. This is true in the case of some of 

 them, although Bracey and Andrews (1974) made a qualitative attempt 

 to explain their present morphology. The compelling evidence that 

 these features are in fact trench remnants is to be found in the mag- 

 netic data. If one accepts the anomaly identifications made earlier, 

 and agrees that there was symmetrical crustal accretion from the ridge 

 axis, then it is clear from Figure 15 that at least 400 km of crust 

 (created during a minimum period from 28 - 36 m.y. B.P.) has vanished 

 at the northern side of the West Caroline Basin. Unless this crust 

 was somehow shoved up over the Caroline Ridge, it is difficult to see 

 where else it could have gone other than down a subduction zone. 



The above arguments also apply in the East Caroline Basin. At 

 least one of the widely spaced seismic profiles (Fig. 7, profile 11) 

 gives clear indications of subduction at the northern side of the basin. 



Seismic reflection profiles across the Sorol Trough (Bracey and 

 Andrews, 1974; Weissel and Anderson, 1978; Fornari and others, 1979) 

 indicate that the narrower eastern end of the trough (east of 143 E) 

 contains about 200 - 300 meters of sediment both in the trough and on 

 surrounding areas. The wider western end of the trough shows a con- 

 siderable increase in topographic complexity. There are indications of 

 .. £edinient-f ree area at the base of the southern escarpment some 30 - 60 

 km wide, with the remaining area to the north containing up to 500 



56 



