of the rise, and possibly to the rise crest (Fig. 12) would seem 

 to preclude this possibility. 



Weissel and Anderson (1978) suggested that the Eauripik Rise is 

 the result of excess magmatism along a "leaky" transform fault. I 

 would certainly agree that there is transform faulting associated with 

 the rise as indicated by the 325 km offset of the spreading axes on 

 either side of the rise. 



Vogt and Johnson (1975) considered the effect of a "transform 

 dam" on asthenospheric flow from a ridge (spreading axis) centered 

 mantle plume (Wilson, 1965; Morgan, 1971) located "upstream" from 

 the transform. Partial melts from the mantle plume flow through a pipe- 

 like conduit between the spreading plates at depths of 5 - 75 km. The 

 amount and velocity of the melt depends on the radius and depth of the 

 pipe (lower viscosity melts occur near the top of the pipe) . When the 

 flow encounters a transform fault, partial or total blockage of the 

 flow may ensue. This blockage is due to the crustal age differential 

 across the transform resulting in a concomitant change in lithospheric 

 thickness (Parker and Oldenburg, 1973). Thus the older, thicker litho- 

 sphere abutting the axial pipe retards that part of the partial melt flow 

 occuring above its base. This part of the flow may "pile up" along 

 the transform, resulting in a linear topographic ridge or rise. 



Vogt and Johnson (1975) concluded that for a partial melting zone 

 between 5 and 75 km depth at a spreading center whose half-rate is 

 6 cm/yr, a "downstream" transform with an offset of 325 km (as is the 

 case with the Eauripik Rise) could be expected to block 10 - 100% 



48 



