کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
---|---|---|---|---|
8910189 | 1637484 | 2018 | 27 صفحه PDF | دانلود رایگان |
عنوان انگلیسی مقاله ISI
Zircon grain selection reveals (de)coupled metamictization, radiation damage, and He diffusivity
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کلمات کلیدی
موضوعات مرتبط
مهندسی و علوم پایه
علوم زمین و سیارات
ژئوشیمی و پترولوژی
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چکیده انگلیسی
Broad variability in intrasample effective U concentration (eU) in zircon crystals is required to characterize zircon (U-Th)/He (zircon He) date-eU relationships that resolve thermal histories in ancient rocks. We describe a new protocol for selecting grains for zircon He thermochronometry that leverages visual crystal metamictization, a proxy for radiation damage accumulation, to generate a range in intrasample eU and zircon He date-eU/metamictization trends. Plane polarized light images, eU concentration, and zircon He data from 59 individual grains from six Proterozoic and three Archean North American granitoids reveal a progressive increase in crystal opacity and discoloration that correspond to increasing eU in each sample. Zircon eU ranges from 89 to 1885â¯ppm across the dataset and individual samples have eU variations of 538â¯ppm to 1579â¯ppm. Three Proterozoic samples yield distinct negative zircon He date-eU patterns with individual dates of ~908 to 20â¯Ma. Archean grains collectively define a negative date-eU trend from ~661 to 4â¯Ma. In contrast, three other Proterozoic samples yield uniform ~25â¯Ma zircon He dates over an 1800â¯ppm eU range, despite increasing eU with increasing metamictization. Simple thermal history models that account for coevolution of zircon radiation damage and He diffusion demonstrate visible metamictization and diffusivity are either coupled or decoupled depending on a sample's thermal history. Zircon He date-eU/metamictization pediments develop when variable but high eU grains with variable visual damage and closure temperature close with respect to He at the same time. Uniform dates with progressive increases in eU and visual damage, reflect decoupled He diffusion and visual damage, are associated with rapid cooling, and/or imply some forms of damage in zircon may not fully anneal.
ناشر
Database: Elsevier - ScienceDirect (ساینس دایرکت)
Journal: Chemical Geology - Volume 490, 25 June 2018, Pages 1-12
Journal: Chemical Geology - Volume 490, 25 June 2018, Pages 1-12
نویسندگان
Alexis K. Ault, William R. Guenthner, Amy C. Moser, Gifford H. Miller, Kurt A. Refsnider,