National Geochronological Database sample #5253

Outcrop or artificial surface exposure, Hornblendite

Geographic location
-76.170833, 39.729167
76° 10' 15" W, 39° 43' 45" N
Lancaster county, PA
Conowingo Dam 1:24,000 scale map quadrangle
Accurate to within 1 minute (~1 mile)
APPROX. 0.6 MILE NORTH OF PENNSYLVANIA-MARYLAND STATE LINE
Source of sample Outcrop or artificial surface exposure
Rock name Hornblendite
Description PLAGIOCLASE HORNBLENDITE (SLIGHT ALTERATION)
Laboratories Berkeley Geochronology Center
Compiler name Godoy, M.M.
Date compiled 1979 03
Precision of location Accurate to within 1 minute (~1 mile)
Location comment APPROX. 0.6 MILE NORTH OF PENNSYLVANIA-MARYLAND STATE LINE
Bibliographic reference Lapham, D.M., and Bassett, W.A., 1964, K-Ar dating of rocks and tectonic events in the Piedmont of southeastern Pennsylvania: Geological Society of America Bulletin, v. 75, p. 661-668
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Geologic map unit -76.170833, 39.729167
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K-Ar age determinations

Age estimate 460 ± 24Ma
age of metamorphic crystallization
Type of analysis conventional K-Ar
NO ANALYTICAL DATA GIVEN
Rock or mineral analyzed biotite
Analytical details
Lab sample ID 16
Decay constants 4.83E-04, 0.585E-04