Geologic Implications of Magnetic Surveys — Malahoff and Woollard 
283 
the strike of the Molokai Fracture Zone, the 
island of Molokai probably marks the area of 
intersection of two tectonic trends. Probably the 
older one strikes parallel to the axis of the Ha- 
waiian Ridge, and the other strikes parallel to 
the Molokai Fracture Zone. 
In order to assess quantitatively the nature of 
the magnetic anomalies and their association with 
geologic and tectonic features, it is best to carry 
out those analyses over areas of known geology. 
Therefore, the magnetic field has been analyzed 
on an individual basis for each major island of 
the Hawaiian Ridge. 
General Remarks on Geology of 
the Hawaiian Islands 
The Hawaiian Islands represent a series of 
basaltic shields that developed from the out- 
pourings of lava from a number of primary 
volcanic vents. These, in turn, appear to have 
been located on a major crustal rift zone that 
is now defined by the Hawaiian Ridge extend- 
ing some 2000 km from Kure Island to the 
island of Hawaii. Because volcanism appears 
to have been a progressive phenomenon, with 
the island of Hawaii representing the most 
recent addition to the Ridge, the fracture zone 
appears to be one that is undergoing continuous 
development. An alternate interpretation pro- 
posed by Wilson (1963) is that there was only 
one center of volcanism and that the Ridge de- 
veloped by crustal migration to the northwest 
away from Hawaii. The continuity in strike of 
the Molokai and Murray fracture zones across 
large reaches of the Pacific Ocean and the Ha- 
waiian Ridge, however, tends to discount this 
rather intriguing theory. As indicated earlier, 
the present magnetic study indicates that there 
are major anomalies associated with known frac- 
ture systems, such as the Molokai Fracture Zone, 
and with implied fractures in the crust and 
primary centers of volcanism. In each case, the 
intrusion of rock at depth having a high mag- 
netic susceptibility is indicated. 
