370 
PACIFIC SCIENCE, Vol. XXII, July 1968 
TABLE 1 
Potassium-Argon Ages of Hawaiian Extrusive Rocks 
SAMPLE,* ROCK TYPE 
OR MINERAL, 
AND LOCATION 
K, % 
Ar 40 
(radiogenic), 
cc/gm X 10- 7 
Ar 40 
(air), 
% of Total Ar 
AGE 
X 1 0 6 yrs 
UPPER WAIANAE 
HK-121. Mauna Kuwale rhyodacite 
(average of 11 determinations of 
minerals and whole rock) 
1.32-6.03 
1.32-10.5 
75-89 
2.3 ± 0.4 
HK-119-1. Dike through HK-121 
1.43 
1.71 
49 
3.3 ± 0.2 
HK- 119-2. Dike through HK-121 
1.43 
1.90 
50 
3.0 ± 0.2 
HK-143-1. Feldspar from flow 
overlying HK-121 
0.206 
0.348 
91 
4.3 ± 1.1 
HK-122-3. Flow underlying HK-121 
0.885 
0.810 
88 
2.3 ± 0.5 
HK-122-4. Flow underlying HK-121 
0.885 
1.081 
84 
3.1 ± 0.5 
HK-122-5. Flow underlying HK-121. 
Calcite removed 
0.911 
0.838 
91 
2.3 ± 0.6 
HK-124-1. Whole rock 
1.07 
1.22 
38 
2.9 ± 0.1 
HK-126-1. Feldspar 
0.272 
0.235 
80 
2.2 ± 0.2 
HK-126-2. Whole rock less feldspar 
0.970 
1.019 
37 
2.7 ± 0.1 
HK-132-1. Feldspar 
0.238 
0.207 
65 
2.2 ± 0.1 
HK-132-2. Whole rock 
0.697 
0.717 
42 
2.6 ± 0.1 
B-l. Whole rock 
1.02 
1.12 
47 
2.8 ± 0.1 
MIDDLE WAIANAE 
HK-145-1. Whole rock 
0.512 
0.735 
80 
3.7 ± 0.4 
HK-145-2. Whole rock 
0.512 
0.712 
77 
3.5 ± 0.3 
HK-146-1. Whole rock 
1.11 
1.33 
39 
3.0 ± 0.1 
HK-146-2. Whole rock 
1.11 
1.26 
39 
2.9 ± 0.1 
LOWER WAIANAE 
HK-123-1. Whole rock 
0.441 
2.82 
97 
16.1 ± 13.6 
HK-123-2. Whole rock 
0.441 
1.09 
98 
6.2 ± 6.2 
HK-123-3. Whole rock. Fine 
powder. Zeolite removed 
0.435 
1.94 
93 
11.2 ± 3.9 
HK-142-1. Whole rock 
0.209 
0.360 
83 
4.3 ± 0.6 
HK-142-2. Whole rock 
0.209 
0.409 
82 
4.9 ± 0.6 
HK-142-4. Whole rock. Treated 
with HF 
0.264 
0.332 
83 
3.2 ± 0.4 
HK-144-1. Ewa drill core. 
Whole rock 
0.522 
0.820 
88 
4.0 ± 0.8 
HK- 144-2. Ewa drill core. 
Whole rock 
0.522 
0.722 
90 
3.5 ± 0.8 
B-2. Whole rock 
0.70 
1.49 
45 
5.4 ± 0.3 
SAMPLES FROM OTHER HAWAIIAN SITES 
HK-127-1. Whole rock. Nihoa Island 
0.416 
1.25 
56 
7.5 ± 0.4 
HK-107-1. Whole rock. Necker Island 
1.04 
4.66 
57 
11.3 ± 0.6 
B-3. Whole rock nepheline basalt. 
Moiliili, Oahu 
1.02 
0.35 
88 
0.9 ± 0.5 
B-5. Dike edge. Glass. Koolau 
Volcano, Oahu 
1.52 
1.79 
76 
2.2 ± 0.3 
B-4. Whole rock. Trachyte. 
Puuwaawaa, Hawaii 
4.18 
0.64 
79 
0.4 ± 0.3 
B-5. Whole rock hawaiite. 
Laupahoehoe, Mauna Kea, Hawaii 
1.89 
0.43 
73 
0.6 ± 0.3 
B-6. Phlogopite mica from B-5 
5.50 
6.34 
44 
2.8 ± 0.1 
* Samples prefixed by "B” were analysed at 
Brookhaven National 
Laboratory, New 
York, and previously 
reported as an 
abstract (Naughton and Schaeffer, 1962). 
