کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
---|---|---|---|---|
9746643 | 1492400 | 2005 | 10 صفحه PDF | دانلود رایگان |
عنوان انگلیسی مقاله ISI
Ion microprobe (NanoSIMS 50) Pb-isotope geochronology at <5 μm scale
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کلمات کلیدی
موضوعات مرتبط
مهندسی و علوم پایه
شیمی
شیمی آنالیزی یا شیمی تجزیه
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![عکس صفحه اول مقاله: Ion microprobe (NanoSIMS 50) Pb-isotope geochronology at <5 μm scale Ion microprobe (NanoSIMS 50) Pb-isotope geochronology at <5 μm scale](/preview/png/9746643.png)
چکیده انگلیسی
Techniques have been developed for ion microprobe Pb-isotope dating of minerals at a lateral scale <5 μm using the Cameca NanoSIMS 50. Probe spots 3-5 μm in diameter comprising 16 keV 16Oâ ions were utilized in the analyses by magnetic peak-switching of 204Pb+, 206Pb+, 207Pb+, and 208Pb+ in NIST SRM 981 and 982 Pb metals, and â¼1 Ga uraninite, xenotime, and zirconolite reference materials. The Pb+ mass resolution (M/ÎM at 1% peak height) was adjusted to â¼5000 to ensure the separation of molecular isobars. Under such conditions, the sensitivity for Pb+ in zircon and zirconolite was 3.0-3.5 and â¼10 cps/ppm/nA 16Oâ, respectively, about one-third the sensitivity obtained with large-geometry ion probes. Instrumental mass fractionation for Pb+ was undetectable for SRM Pb metals and zirconolite, but values of up to 1.2% per atomic mass unit (enhancement of lighter isotopes) were recorded for xenotime and uraninite. As a demonstration of the technique, small zirconolite grains from a Cambrian mafic sill were analyzed in situ using a 3 μm diameter probe. A mean 207Pb*/206Pb* age of 504 ± 18 Ma was determined, and is considered an accurate measure of the crystallization age. Small-spot geochronology with the NanoSIMS at the present time is practical mainly for high-U mineral chronometers.
ناشر
Database: Elsevier - ScienceDirect (ساینس دایرکت)
Journal: International Journal of Mass Spectrometry - Volume 244, Issues 2â3, 1 July 2005, Pages 125-134
Journal: International Journal of Mass Spectrometry - Volume 244, Issues 2â3, 1 July 2005, Pages 125-134
نویسندگان
Richard A. Stern, Ian R. Fletcher, Birger Rasmussen, Neal J. McNaughton, Brendan J. Griffin,