The Determination of a Series of Ages of Hawaiian Volcanoes 
by the Potassium-Argon Method 1 
John G. Funkhouser , 2 
I. Lynus Barnes , 3 and John J. Naughton 
Geologically speaking, the Hawaiian Islands 
are perhaps the most thoroughly studied group 
of oceanic islands in the world. Because of their 
relative petrological and structural simplicity, 
they constitute an example where an intensive 
application of the techniques of geology and 
geophysics may be expected to yield significant 
results particularly relevant to volcanology. An 
example of a thorough effort of this type was 
reported by McDougall (1964) who measured 
the relative ages of the surface lavas of most 
of the older volcanoes of the islands using the 
potassium-argon method of geochronology. We 
would like to report additional age measure- 
ments obtained by the same method, with a 
concentration of our effort on the Waianae 
Volcano on the island of Oahu. A scattering of 
measurements made on samples from other sites 
also is tabulated. 
METHODS AND RESULTS 
The argon measurement equipment and tech- 
niques developed by the Berkeley group (Evern- 
den and Curtis, 1965) were employed in the 
work. Ultrahigh vacuum methods were neces- 
sary for measurements on these young materials 
of relatively low potassium content. Potassium 
was analyzed by flame photometry. 
The results of the potassium-argon age work 
on Hawaiian extrusive rocks are given in Table 
1. The over-all precision of the ages reported 
herein is estimated to be approximately 11% 
1 Chemistry Department and Hawaii Institute of 
Geophysics. Hawaii Institute of Geophysics Con- 
tribution No. 221. This work was supported by the 
National Science Foundation under grant NSF 
GP-140. Manuscript received September 5, 1967. 
2 Present address: Earth Science Department, State 
University of New York at Stony Brook, Stony 
Brook, New York. 
3 Present address: B28 Physics Building, National 
Bureau of Standards, Washington, D.C. 
(standard deviation). The uncertainty for each 
age is based on the experimental errors and the 
effect of the correction necessary for air argon 
contamination. 
The ages of the different members of the 
Waianae Range are in general agreement with 
those of McDougall (1964). However, this 
investigator reported an age of 8.36 my for a 
biotite fraction separated from the Mauna 
Kuwale rhyodacite. This age appears to be 
abnormally high in view of the present work 
which indicates that Mauna Kuwale is con- 
temporaneous with the upper member of the 
Waianae volcanic series. A possible cause of 
this discordance relating to included excess 
radiogenic argon has been discussed alsewhere 
(Funkhouser, Barnes, and Naughton, 1966). 
DISCUSSION 
The results obtained from HK-123, a vesicu- 
lar olivine basalt classified as Lower Waianae, 
are clearly anomalous. The high degree of air 
argon contamination for this specimen con- 
tributes to the large uncertainty; however, this 
does not fully explain the wide variation in the 
results. Thin-section examination as well as 
microscopic inspection of hand samples and 
granular fractions indicated no abnormal 
mineral components or alteration products. The 
basalt contains a large number of very small 
vesicles which probably contain entrapped air. 
This is substantiated by the lower air argon 
correction for HK-123-3 which was ground to 
100-180 mesh while the other two samples 
were analyzed as 10-16 mesh fractions. Of 
course, this sample could be 7-12 my old, but 
there is no confirmation from geological field 
evidence or other potassium-argon dates. The 
ages obtained for HK-142, a Lower Waianae 
olivine basalt, also show a range greater than 
that predicted from experimental uncertainties 
and the atmospheric argon correction. 
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