Abstract
We have determined an 40Ar/ 39Ar age spectrum for a single grain of magnetite using laser step-heating. A 300 μm magnetite grain from a Grenville Front gneiss was heated in 14 steps to 1600°C. Excess 40Ar∗ resulted in a saddle-shaped age spectrum with an integrated age of 1962 ± 39 Ma. However, the minimum of the saddle gave an age of 1144 ± 107 Ma, consistent with typical Grenvillian cooling ages of 1100–900 Ma. We have also dated a single grain of biotite from the same hand sample as the magnetite. The spectrum yielded an integrated age of 1261 ± 3.6 Ma. The thermal release patterns of 40Ar∗ and of Ca/K ( 37Ar/ 39Ar) were very different for the magnetite and biotite. Thus 40Ar∗ can be retained in measurable quantities in magnetite. Our results are a first step toward the attempted direct dating of different components of NRM in paleomagnetism.
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
