in this disturbed zone (Figs. 9 and 15), but this is somewhat specula- 

 tive, particularly in the case of anomaly 13. 



If the pole position of Weissel and Anderson is correct, the rela- 

 tive compressional motion of the Pacific and Caroline Plates should 

 decrease to the north, and the relative motion between the plates could 

 conceivably change to a relative left-lateral motion of the Pacific 

 Plate along a transform boundary. Again there is no evidence at pre- 

 sent to either refute or support this possibility. 



South of 3.5°N, the Caroline-Pacific Plate boundary, while still 

 compressional, apparently changes from overthrusting of the Caroline 

 Plate to underthrusting of the plate along the Mussau Trench, This 

 trench is generally considered to be the site of incipient subduction 

 (Bracey and Andrews, 1974; Bracey, 1975; Kogan, 1976; Weissel and 

 Anderson, 1978). 



Bracey and Andrews (1974) felt that the former Pacific-Philippine 

 plate boundary, marked by the Yap-Palau-Ayu Trough may now be extinct, 

 or may be in the process of becoming inactive. They felt that there has 

 been a relatively recent shift to a Pacific-Caroline Plate margin extend- 

 ing from the Mariana Trench at 12°N/145°E to the southern end of the 

 Mussau Trench. While the nature of the northern portion (6°N-12 N) of 

 the boundary is as yet unclear, I follow their interpretation. 



It is likely that the Manus Trench (at least the eastern part - 

 Fig. 15) marks part of the present-day southern boundary of the 

 Caroline Basin. There is general agreement (Krause, 1972; Malahoff 

 and Bracey, 1974; Connelly, 1976; Taylor, 1979) that there is NW-SE 



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