PACIFIC SUBMARINE PROVINCES 



52') 



300r 



i 200 



E 

 3 



« 100 - 



4 



5 -loo 





















- 















KILOMETERS 



A 



5 



_ 10^ 



^ 15 



20 25 



30 



35 



40 i\ 



k 45 50 



55 









MAGNETIC 



PROFILE 











4 



WATER 

 - SEDIMENTS^ 







/2.I5 KM/SEC 





VOLCANICS ^^ 



g§{ 



0.015 J 



Ita**^. 5.39 



8 



CRUST 







6 89 " 



12 



L MANTLE 







8 29 •■ 



WATER 

 SEDIMENTS. 



CRUST 



MANTLE 



Fig. 32.17. Interpretation of magnetic profile (A), with flat base of basic igneous rock at 6.3 

 km depth (B), and with flat top at 5 km depth (C). After Mason, 1958. 



profile or continental slope apron. If such, sediment has just about buried 

 all previous existing relief there. 



Menard (1955) thinks that the displacement along the fracture zone 

 took place during Cretaceous or Tertiary time and that the structures 

 causing the magnetic anomalies are older than the fracture zones. Pos- 

 sibly, therefore, the east-west fracture zones and the north-south struc- 

 tures are not related mechanically. Menard, Vacquier, and Mason suggest 

 that parallel valleys were filled or partially filled with basalt and that later 

 sediments were carried out by turbidity currents and by being spread 

 in the remaining depressions still further reduced the relief. The cause 

 of the parallel valleys and the nature of the eruptions is not considered, 

 nor the relation to the other volcanic (?) rocks of the "volcanics" layer. 



More intensive seismic surveys will undoubtedly help in solving the 

 problem. 



HAWAIIAN RIDGE 



The Hawaiian Islands are peaks of a ridge or swell built by volcanic 

 action on the ocean floor. It has a relief from deepest ocean floor to top 

 of peaks of nearly 32,000 feet, is about 150 miles across in the widest part 



Fig. 32.18. Generalized topography around southern end of Hawaiian Ridge showing deep 

 and arch, after Hamilton, 1957. Contours in fathoms. 



