PACIFIC SCIENCE, Vol. XV, July 1961 
368 
One of the suggested mechanisms by which 
alkalies may be concentrated is volatile transfer 
— volatile compounds moving upward toward 
points of gas escape, carrying alkalies in solu- 
tion and releasing them because of pressure de- 
crease at and near the top of the magma body. 
Another process is thermodiffusion, by which 
certain substances, including alkalies, migrate 
toward cooling surfaces (Wahl, 1946). Either 
or both of these may well have operated to some 
degree in the Kilauea Iki lava pool. Small 
amounts of gas have oozed from the surface of 
the pool constantly, ever since its formation. 
Likewise, the broad crusted surface of the pool 
exposed directly to the atmosphere and cooled 
by wind and frequent rains provides an ideal 
condition for the operation of thermodiffusion. 
These processes may be bringing about a grad- 
ual enrichment of the upper part of the liquid 
magma in alkalies. Further sampling of the 
congealing lava pool is highly desirable, to de- 
termine whether the trend observed in sample 
10 is a continuing one. 
Whether the divergence of Kilauea Iki sam- 
ple 10 from the general tholeiitic trend offers 
a clue to the origin of the alkalic basalts can- 
not now be asserted. It is noteworthy, however, 
that it is closely similar to the transverse trend 
found by Tomkeieff (1937) in the Paleozoic 
basalts of Scotland. 
CONCLUSIONS 
The foregoing evidence: (1) Indicates the 
existence in Hawaii of completely liquid tholei- 
itic magma undersaturated in silica at least to 
the degree of containing nearly 10 per cent nor- 
mative olivine; (2) confirms the dominance in 
the tholeiitic suite of crystal differentiation in- 
volving primarily the movement of magnesian 
olivine, with small amounts of pyroxene and cal- 
cic plagioclase; ( 3 ) indicates that at least mar- 
ginal members of the alkalic suite can be de- 
rived from undersaturated tholeiitic magma; 
(4) suggests that this can be accomplished by 
crystallization differentiation controlled by the 
separation of pyroxene; but ( 5 ) leaves open the 
possibility of the operation of such other proc- 
esses of differentiation as volatile transfer of 
alkalies and thermodiffusion. 
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