Inside isotopic clocks: distribution of parent and daughter nuclides in geochronometer minerals

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Knowing the distribution of U, Th and radiogenic Pb in chondrules and refractory inclusions is important for accurate interpretation of U-Pb isotopic dates. For example, the distribution of U between primary and secondary minerals can indicate whether the date corresponds to formation or to alteration of a chondrule or a Ca-Al-rich refractory inclusions (CAIs). In the case of dating equilibrated (i.e. metamorphosed) chondrites, we need to know the host mineral of U in order to apply correct diffusion parameters for estimating closure temperatures.

The student will explore and advance the sensitivity limits of modern secondary ionisation mass spectrometry, and will use this technique to measure U, Th and Pb concentrations and isotopic ratios in chondrules, CAIs and their components. Extremely low concentrations of U and Th in chondrites in a low parts per billion range, together with micron-scale heterogeneity of chondrules and CAIs makes this project analytically challenging.

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