National Geochronological Database sample #15334

Outcrop or artificial surface exposure, Schist

Geographic location
-156.693333, 67.303333
156° 41' 36" W, 67° 18' 12" N
AK
Ambler River 1:250,000 scale map quadrangle
Accurate to within 1 minute (~1 mile)
SCHWATKA MOUNTAINS, SOUTHWESTERN BROOKS RANGE
Source of sample Outcrop or artificial surface exposure
Rock name Schist
Description ACTINOLITE SCHIST
Laboratories University of Alaska
Compiler name Marvin, R.F.
Date compiled 1984 11
Precision of location Accurate to within 1 minute (~1 mile)
Location comment SCHWATKA MOUNTAINS, SOUTHWESTERN BROOKS RANGE
Bibliographic reference Turner, D.L., Forbes, R.B., and Mayfield, C.F., 1978, K-Ar Geochronology Of The Survey Pass, Ambler River, and Eastern Baird Mountains Quadrangles, Southwestern Brooks Range, Alaska: U.S. Geological Survey Open-File No. 78-254, 41p.
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Geologic map unit -156.693333, 67.303333
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K-Ar age determinations

Age estimate 345 ± 17.3Ma
Type of analysis conventional K-Ar
Rock or mineral analyzed actinolite
IMPURE ACTINOLITE
Analytical details
Lab sample ID 73 RR 75-3
Decay constants 4.72E-04, 0.585E-04, 1.19E-04
Radiogenic 40Ar concentration 0.3973
Radiogenic Ar 64 %
Comments REDUCED AGE; ARGON LOST DUE TO CRETACEOUS THERMAL EVENT. THIS AGE ALSO REPORTED BY TURNER, FORBES, AND MAYFIELD, 1978