Mathematics – Logic
Scientific paper
Aug 1956
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1956gecoa..10...60f&link_type=abstract
Geochimica et Cosmochimica Acta, vol. 10, Issue 1-2, pp.60-68
Mathematics
Logic
8
Scientific paper
First results in an extensive programme in potassium-argon dating at Berkeley arc reported. Ultra-high-vacuum techniques have been incorporated in the argon extraction apparatus and in a new mass spectrometer especially designed for these researches. It is found that, because of these improvements, the radiogenic argon in small and young samples can be measured with precision. Analytical data for a group of rocks and mineral separates from the Yellowknife subprovince of the Canadian Shield are presented. Results show that micas retain more argon than feldspars and that orthoclase feldspars are more retentive than plagioclase feldspars. Potassium-argon dates for biotites from the region are consistent and in good agreement with earlier age determinations, suggesting that biotite may retain radiogenic argon quantitatively. A very short time for emplacement of the Yellowknife granite series, ranging from hornblende-biotite diorite to muscovite granite, is inferred. Results given for two unseparated granites and a feldspar phenocryst from the Sierra Nevada batholith confirm earlier lead-alpha activity determinations and an age near 100 m.y. for this intrusion. Data on mica separates from this region are needed, however. Results on a chondrite meteorite specimen of the Forest City Fall, Iowa, confirm to a remarkable degree earlier data on another specimen from another laboratory and thus confirm a potassium-argon age close to 4500 m.y. for these objects. An age determination of 285 m.y. for an upper middle Devonian (Givetian) potash salt from western Canada is thought to be a useful addition to age data on rocks from the palaeontologically controlled portion of the geological time scale and is in agreement with the time scale of .
Folinsbee R. E.
Lipson J.
Reynolds James H.
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