WARC DISCOVERIES

Promising new approaches in micro isotopic analysis of minerals that may record the earliest processes on Earth

The ability to perform in situ isotopic measurements on planetary bodies remains important because sample return missions are one to two decades away. However, there will be real limits on the precision of in situ analyses compared to that obtainable using Earth-based instrumentation that will likely remain the gold standard. Using the UW-Madison large-radius ion microprobe, WARC researcher John Valley and collaborators report in American Mineralogist that they have achieved oxygen isotope analysis on sub-micron size spots of zircons, an important advance relative to the 10-30 micron spots that are typically done in large-radius ion microprobe analysis. These new results document that oxygen diffusion in natural zircons is very slow, confirming that the high ¹⁸O/¹⁶O ratios that have been measured in the world’s oldest zircons (4.2 billion years old) do indeed reflect the presence of liquid water on the early Earth rather than alteration by later metamorphism, as has been recently proposed. Future work will extend high-resolution isotopic analysis to many elements, in preparation for the exhaustive analytical efforts that are anticipated for samples that will be returned from Mars.

Citation:
Page, FZ, Ushikubo, T, Kita, NT, Riciputi, LR, and Valley, JW (2007) High-precision oxygen isotope analysis of picogram samples reveals 2 μm gradients and slow diffusion in zircon. American Mineralogist 92:1772-1775. A PDF copy of the paper can be found here.

Posted January 11, 2008