Jökull - 01.12.1974, Blaðsíða 55

TABLE 1
K/Ar ages on whole rock samples from the Húsafell area
Sample no.
Locality
1 Búrfell
2 Lambá
3 Geitá
4 Ásgil
5 Bæjargil at Giljar
6 Augastadir
7 Búrfell, below
Giljafoss tillite
Rock type Altitude k2o % Rad 40Ar Calculated
a. s. 1. (wt. %) Rad 40Ar (10-5 cm3/g) age (M.y.)
tholeiite 340 m 0.30 4 5 0.00119 0.00095 1.0 ± 0.3 0.8 ± 0.2
tholeiite 340 m 0.22 1.3 2.9 0.00084 0.00154 1.0 ± 0.7 1.8 ± 0.6
tholeiite 280 m 0.22 7 5 0.00141 0.00159 1.7 ± 0.3 1.9 ± 0.3
basaltic andesite 320 m 0.56 4 4 0.00525 0.00580 2.4 ± 0.6 2.6 ± 0.7
basaltic andesite 220 m 0.86 8 7 0.00924 0.00854 2.7 ± 0.3 2.5 ± 0.3
dacite 120 m 1.54 25 22 0.0222 0.0227 3.6 ± 0.14 3.7 ± 0.17
tholeiite 250 m 0.24 4 6 0.00315 0.00342 3.3 ± 0.7 3.6 ± 0.6
The 40K decay constants used for the age calculations are: Xj3 = 4.72 • 1 ()—10 yr-1,
A.e = 0.585 • 10-10 yr-1 and 40K = 1.19 • 10-4 atom percent of natural potassium.
TABLE2
Rate of lava production during the Gauss epoch. Length of time intervals within the
Gauss epoch is after McDougall and Aziz-Ur-Rahman (1972).
Length of interval
between two
Thickness of successive flows of Number
Polarity Length of corresponding assumed 8 m of
event time intevals polarity group average thickness flows
Gauss 3 ...................... 410,000 y 390 m 8,500 y 48
Kaena ......................... 80,000 y 100 m 6,400 y 20
Gauss 2 ....................... 70,000 y 60 m 9,300 y 9
Mammoth ...................... 100,000 y 70 m 11,400 y 8
Gauss 1 ...................... 230,000 y 330 m 5,600 y 50
Gauss epoch .................. 890,000 y 950 m 7,500 y 135
JÖKULL 24. ÁR 53