288 
PACIFIC SCIENCE, VoL XIX, July 1965 
TABLE 1 
Ages of Certain Hawaiian Lavas 
SAMPLES 
AGES 
(in millions 
of years) 
Older rocks (whole rock 
investigation) 
Lowest member dated, Waianae, 
Oahu 
5.4 
Low member, Waianae, Oahu 
(trachyte) * 
3.46** 
Upper member, Waianae, Oahu 
2.8 
Dike rock, Koolau, Oahu 
2.2 
rocks from the Waianae range on Oahu have 
been analyzed for cobalt, nickel, vanadium, and 
zirconium. Results indicate that zirconium may 
be a distinctive trace element between suites, 
and, most interestingly, that when the nickel, 
vanadium, and zirconium contents are plotted 
in a tri-varient diagram, there is a grouping of 
results for rocks of the two types ( tholeiitic and 
alkalic) similar to that noted in the A-F-M dia- 
grams. Thus, it may develop that minor ele- 
ments will prove to be distinctive markers for 
lava types. 
Younger rocks 
Puuwaawaa trachyte, Hawaii 
Laupahoehoe, Mauna Kea, Hawaii 
(whole rock) 
Laupahoehoe, Mauna Kea, Hawaii, 
mica (mineral in Laupahoehoe 
whole rock) 
0.4 
0.6 
2.8 
* Subject of many analyses on whole rock and minerals; 
indications are that minerals give older date. 
** Average of six determinations. 
of the recent results coming from the Hawaii 
Institute of Geophysics. Using these analyses, 
the tholeiitic-alkalic dichotomy is readily recog- 
nized from the alkali content, and Macdonald 
and Katsura (1962) have developed the alkali- 
silica diagram as a quantitative means of dif- 
ferentiating the two types. In this diagram, 
when per cent alkali (K 2 O plus Na 20 ) is 
plotted against per cent silica, the tholeiites 
occur as a well defined group in the lower part 
of the diagram and the alkalic lavas occur in 
the upper section. Standard A-F-M ( Alkali - 
FeO-MgO) diagrams also show a distinctive 
grouping of rocks of the two types. The con- 
clusions reached by Macdonald and Katsura 
(1962, 1964) from studies of the chemical 
composition of the analyzed samples are: (1) 
the primitive lavas that built the Hawaiian vol- 
canoes are tholeiitic basalt; and (2), more 
tentatively, alkalic rocks can be derived from a 
tholeiitic parent. 
A study of certain minor elements in tho- 
leiitic and alkalic suites of Hawaiian lavas is 
being conducted (by G. A. Macdonald, N. J. 
Hubbard, and I. L. Barnes) with analyses being 
made by emission spectroscopy. To date 39 
VOLCANIC GASES 
Volcanic gases supply a probe which enables 
a characterization of magma to be made at depth 
within the earth’s crust, at least to the point 
of separation of gas from the parent lava. Once 
separated, such gases have been found to be a 
system in homogeneous equilibrium in the gas- j! 
eous phase, and quite out of equilibrium with j 1 
the associated rock system. Within error of 
measurement, analyzed samples of gas collected 
at high temperatures have been shown to con- 
form to the composition expected thermody- 
namically for a homogeneous system. It is pos- 
sible, then, to extrapolate the composition of 
gases collected during eruption to discover the 
oxidation condition of the underground magma, 
provided the temperature is known; or, con- 
versely, for a given partial pressure of oxygen 
to find the temperature (Heald, Naughton, and 
Barnes, 1963). For a more complete analysis a 
computer may be used to calculate the compo- 
sitional changes in a homogeneous volcanic gas 
system with expected changes in temperature, 
pressure, oxygen partial pressure, and the ad- 
dition or subtraction of gaseous components 
which might be anticipated from surrounding 
rock (i.e., water vapor) (Heald and Naughton, 
1962 ). 
Using reasonable estimated values of tem- 
perature and pressure, it was concluded from 
data obtained from the best Kilauea samples 
that the primary magmatic gas would have the 
composition shown in Table 2. 
Comparison of this calculated composition 
with the analyzed results from good collections 
made from liquid lava shows that an equilib- 
