Abstract Cosmogenic argon isotopes are produced in feldspars via nuclear reactions between cosmic rays and Ca and K atoms within the lattice. These cosmogenic isotopes can be used as proxies for K and Ca, much like nuclear reactor-derived 39Ar and 37Ar are used as proxies for K and Ca, respectively, in 40Ar/39Ar geochronology. If Ca and K are uniformly distributed, then the ratio of radiogenic 40Ar (40Ar⁎) to cosmogenic 38Ar or 36Ar (38Arcos or 36Arcos) is proportional to the difference between the radioisotopic and exposure ages, as well as the K/Ca ratio of the degassing phase. Thus cosmogenic, radiogenic, and trapped Ar isotopes, all of which can be measured remotely and are stable over geologic time, are sufficient to generate an isochron-like diagram from which the isotopic composition of the trapped component may be inferred. Such data also provide a means to assess the extent to which the system has remained closed with respect to 40Ar⁎, thereby mitigating otherwise unquantifiable uncertainties that complicate the conventional K–Ar dating method.
Highlights Cosmogenic and radiogenic isotopes can be measured remotely on the surface of Mars. Cosmogenic argon isotopes produced in Martian rocks serve as proxies for K and Ca. One can construct an isochron-like diagram with radiogenic and cosmogenic isotopes. An isochron diagram enables one to estimate the isotopic composition of trapped Ar. It also enables one to identify diffusive loss, improving the accuracy of K–Ar ages.
In situ dating on Mars: A new approach to the K–Ar method utilizing cosmogenic argon
Acta Astronautica ; 94 , 1 ; 222-233
2013-07-28
12 pages
Aufsatz (Zeitschrift)
Elektronische Ressource
Englisch
Mars , Geochronology , Argon , Cosmogenic
In situ dating on Mars: A new approach to the K–Ar method utilizing cosmogenic argon
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