Potassium-Argon Method of Geochronometry

Research Article| June 01, 1957 POTASSIUM-ARGON METHOD OF GEOCHRONOMETRY DONALD R CARR; DONALD R CARR LAMONT GEOLOGICAL OBSERVATORY, COLUMBIA UNIVERSITY, PALISADES, N. Y. Search for other works by this author on: GSW Google Scholar J. LAURENCE KULP J. LAURENCE KULP LAMONT GEOLOGICAL OBSERVATORY, COLUMBIA UNIVERSITY, PALISADES, N. Y. Search for other works by this author on: GSW Google Scholar Author and Article Information DONALD R CARR LAMONT GEOLOGICAL OBSERVATORY, COLUMBIA UNIVERSITY, PALISADES, N. Y. J. LAURENCE KULP LAMONT GEOLOGICAL OBSERVATORY, COLUMBIA UNIVERSITY, PALISADES, N. Y. Publisher: Geological Society of America Received: 21 May 1956 First Online: 02 Mar 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Copyright © 1957, The Geological Society of America, Inc. Copyright is not claimed on any material prepared by U.S. government employees within the scope of their employment. GSA Bulletin (1957) 68 (6): 763–784. https://doi.org/10.1130/0016-7606(1957)68[763:PMOG]2.0.CO;2 Article history Received: 21 May 1956 First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation DONALD R CARR, J. LAURENCE KULP; POTASSIUM-ARGON METHOD OF GEOCHRONOMETRY. GSA Bulletin 1957;; 68 (6): 763–784. doi: https://doi.org/10.1130/0016-7606(1957)68[763:PMOG]2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract A brief history of the development of the potassium-argon method of geochronometry is presented and the evidence for the decay scheme is reviewed. A survey of the experimental measurements of the β and γ activity of K40 indicates that there is fairly general agreement on a λγ/λβ = 0.12.The isotope dilution technique and equipment employed at the Lamont Geological Observatory for the argon analysis are described. The A40/K40 ratio can be determined with an accuracy of better than ±5 per cent. Radioactive A37 has been used as a tracer to check the yield of the liberation and purification procedure. These experiments indicate that within an experimental error of 2 per cent, all the argon present in a sample is released during fusion; that spike equilibration is achieved, and that no argon is lost during purification.The problem of argon retentivity in various minerals is discussed. For minerals of known age the fraction of argon retained can be calculated. Micas retain about 80–100 per cent of their argon, whereas feldspars vary in retentivity from 40–85 per cent for the samples listed. Much more data are needed to evaluate the possible causes of argon loss.In the Southern Appalachians K-A ages have been determined for the pegmatites and several host rocks. The micas of the Spruce Pine District pegmatites yield ages of 340 ± 15 m.y. in excellent agreement with U-Pb ages for the same pegmatites (350 ± 20 m.y.). The host rocks give uncorrected ages of about 400 m.y. which when corrected for the argon loss from the feldspars increase to at least 600 m.y. This establishes the primary regional metamorphism which produced the Cranberry, Carolina, and Roan gneisses and the Beech granite as being Precambrian rather than Paleozoic.In the Bear Mountain area of New York State the K-A ages corrected for retentivity are about 800 m.y. for the Storm King granite and about 1400 m.y. for the Canada Hill gneiss. This proves that the Storm King could not be Paleozoic and suggests that the New Jersey-New York Highlands are older than the Blue Ridge Province of the Southern Appalachians. The spread in ages is interpreted as evidence for the igneous origin of the Storm King granite. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.