ess continues through geologic time, a V-pattem of fossil spreading 

 centers forms a "propagator wake", as Is Illustrated In Figure 5-8. 

 This same pattern Is found In the Isosynchronous magnetic anomaly pat- 

 tern. Since this model uas proposed, similar processes have been 

 observed on other spreading centers, In particular the Cocos-Nazca 

 spreading center (Searle and Hey, 1983). 



A propagating ridge crest model offers one explanation for the 

 abrupt termination of the Gorda Rise crest shown In Figure 5-7. In 

 order to test this hypothesis, a magnetic anomaly map of the Gorda Rise 

 was constructed and is illustrated In Figure 5-9. The chart Is based on 

 original magnetic anomaly data collected by the U.S. Naval Oceanographlc 

 Office. The V-pattem associated with the "propagator wake" Is evident, 

 extending to the east and northwest from the ridge crest at AZ'M. The 

 direction of the V-pattem Indicates that the ridge crest to the north 

 Is propagating toward the south at the e^ense of the southern portion 

 of the Gorda Rise crest. The geometry of the schematic model by Hey 

 (1977) for the. Juan de Ftica Ridge (Figure 5-8), represents a nearly per- 

 fect analog to the magnetic anomaly pattern of Gorda Rise (Figure 5-9). 

 It would appear that the abrupt termination of the high roughness zone 

 shown In Figure 5-7, Is due to Its association with the tip of a prop- 

 agating rift system. 



Another feature of Interest In the distribution of the a parameters 

 In Figure 5-7 is the existence of east-west trends of selected roughness 

 provinces on the ridge flank. One might have expected roughness prov- 

 inces to align themselves sub-parallel to the ridge strike, perhaps 

 reflecting changes in processes through time being felt along the length 

 of the ridge axis. This is the case with the very rough central valley 



68 



